ECOLOGY OF MACROALGAL WRACK
ON EXPOSED SANDY BEACHES ECOLOGIA DE LOS ARRIBAZONES DE MACROALGAS EN PLAYAS EXPUESTAS
TESIS DOCTORAL FRANCISCO BARREIRO ROMANO VIGO 2013
Departamento de Ecología y Biología Animal Tesis Doctoral
Ecology of macroalgal wrack on exposed sandy beaches
Ecología de los varamientos de macroalgas en playas arenosas expuestas
Francisco Barreiro Romano
Directores Mariano Lastra Valdor Jesús López Pérez
Vigo 2013
Departamento de Ecoloxía e Bioloxía Animal
Os doutores Mariano Lastra Valdor e Jesús López Pérez, profesores titulares do Departamento de Ecoloxía e Bioloxía Animal da Universidade de Vigo
CERTIFICAN:
Que a presente memoria de doutoramento titulada “Ecology of macroalgal wrack on exposed sandy beaches”, presentada por Francisco Barreiro Romano para optar o grado de Doutor pola Universidade de Vigo, realizouse baixo a nosa dirección no Departamento de Ecoloxía e Bioloxía Animal da Universidade de Vigo, e considerando que cumpre os requisitos necesarios para ser considerada como un traballo de Tese Doutoral, autorizamos a súa presentación ante o Consello do Departamento e a Comisión de Posgrado. E para que así conste, emitimos e asinamos a presente certificación, en Vigo a 09 de Maio do 2013.
Fdo. Mariano Lastra Valdor Fdo. Jesús López Pérez
Edificio de Ciencias Experimentales Campus As Lagoas Marcosende 36310 VIGO
Ecology of macroalgal wrack on exposed sandy beaches
Dissertation presented in fulfillment of the requirements for the degree of Doctor by the University of Vigo
PhD thesis Francisco Barreiro Romano Vigo 2013
TABLE OF CONTENTS
1. CHAPTER I. GENERAL INTRODUCTION 6
1.1. SANDY BEACHES ...... 888 1.2. PHYSICAL CHARACTERIZATION ...... 9 1.2.1. Structural beach components ...... 9 1.2.2. Main influential factors in a beach system ...... 12 1.2.3. Beach morphodynamics ...... 13 1.3. ECOLOGY OF SANDY BEACHES ...... 18 1.3.1. Influence of the physical environment in the beach macrofauna ...... 20 1.3.2. Zonation patterns on sandy beaches ...... 22 1.3.3. Beach connectivity ...... 24 1.4. Wrack ...... 25 1.5. The socio-economic value of sandy beaches ...... 27 1.6. Background of this project ...... 28 1.7. Approach taken in this thesis ...... 30 1.8. Aims of this thesis...... 31 1.9. Literature cited ...... 33
2.CHAPTER II. ANNUAL CYCLE OF WRACK SUPPLY TO SANDY BEACHES: EFFECT OF THE PHYSICAL ENVIRONMENT 40
1. ABSTRACT ...... 42 2.2. INTRODUCTION ...... 43 2.3. MATERIALS AND METHODS ...... 45 2.3.1. Field sampling design ...... 45
2.3.2. Statistical analysis ...... 47 2.4. RESULTS ...... 49 2.4.1. Beach characteristics and wrack deposition ...... 49 2.4.2. Time-scale variability in wrack composition and biomass ...... 50 2.5. DISCUSSION ...... 57 2.6. ACKNOWLEDGEMENTS ...... 60 2.7. LITERATURE CITED ...... 61
3. CHAPTER III. COUPLING BETWEEN MACROALGAL INPUTS AND NUTRIENTS OUTCROP IN EXPOSED BEACHES 64
3.1. ABSTRACT ...... 66 3.2. INTRODUCTION ...... 67 3.3. MATERIALS AND METHODS ...... 69 3.3.1 Field sampling design ...... 69 3.3.2. Nutrient analysis ...... 71 3.3.3. Statistical analysis ...... 72 3.4. RESULTS ...... 73 3.4.1. Beach characteristics ...... 73 3.4.2. Dissolved nutrients and wrack biomass ...... 74
3.4.3. Intertidal pore water (IPW) ...... 75
3.4.4. Surf zone water (SZW) ...... 77 3.5. DISCUSSION ...... 79 3.6. ACKNOWLEDGMENTS ...... 84
3.7. LITERATURE CITED ...... 84
4. CHAPTER IV. THE INFLUENCE OF ALLOCHTHONOUS INPUTS ON THE MACROFAUNAL ASSEMBLAGES IN OCEAN-EXPOSED SANDY BEACHES 90
4.1. Abstract ...... 92 4.2. Introduction ...... 93 4.3. Material and methods ...... 95 4.3.1. Field sampling design ...... 95 4.3.2. Statistical analysis ...... 97 4.4. Results ...... 98 4.4.1. Species richness and total abundance ...... 98 4.4.2. Community composition ...... 101 5. Discussion ...... 104 4.6. ACKNOWLEDGMENTS ...... 109 3.7. LITERATURE CITED ...... 110
5. CHAPTER V. EFFECT OF MECHANICAL GROOMING ON THE MACROFAUNAL COMMUNITY OF EXPOSED SANDY BEACHES 116
5.1. Abstract ...... 118 5.2. Introduction ...... 119 5.3. Material and methods ...... 121 5.3.1. Field sampling design ...... 121 5.3.2. Statistical analysis ...... 123 5.4. Results ...... 124 5.4.1. Number of species and density ...... 124 5.4.2. Community composition ...... 126 5.4.3. Specie-site association ...... 128 5.5. Discussion ...... 130
5.6. Acknowledgements ...... 134 5.7. Literature cited ...... 135
6. CHAPTER VI. General conclusions 140
7. RESUMEN GENERAL 144
7.1. LAS PLAYAS ...... 146
7.2. ECOLOGÍA DE PLAYAS ...... 146
7.3. ANTECEDENTES ...... 147
7.4. ENFOQUE ...... 149
7.5. OBJETIVOS ...... 149
7.6. CAPITULOS ...... 151
7.6.1. Capítulo II. Ciclo anual de algas arribadas en playas expuestas: efecto del ambiente físico...... 151
7.6.2. Capítulo III. Acoplamiento entre los aportes de macroalgas y la liberación de nutrientes en playas expuestas arenosas...... 152
7.6.3. Capítulo IV. Influencia de los aportes alóctonos de materia orgánica en la comunidad macrofaunística de playas arenosas expuestas...... 153
7.6.4. Capítulo V. Efecto de la limpieza mecánica en la comunidad macrofaunística de playas arenosas expuestas...... 154
7.7. CONCLUSIONES ...... 155
8. APPENDIXES 158
APPENDIX B (CHAPTER III) ...... 160 APPENDIX C (CHAPTER IV) ...... 162
CHAPTER I
I. General introduction
GENERAL INTRODUCTION
1.1. SANDY BEACHES
Sandy beaches are deposits of unconsolidated sediment at the sea-land boundary reworked by waves. Beach systems occupy a wide range of environments both at a regional scale, from estuarine mouths or tidal flats to oceanic expose beaches, and at global scale, from the tropical to the Arctic and Antarctic beaches (Fig.1.1). Resulting of this broad spatial extension, beaches cover the 70% of all continental margins (McLachlan & Brown 2006), it is important to define the exact type of environment which each study is dealing with. This work is focused on open ocean beaches, i.e. beaches directly exposed to the wave action. Ocean beaches predominate in tropical and temperate regions (Davies 1980). They are estimated to represent between the 11% and 34 % of the coastline (Short 1999).
A B
C D
Fig. 1.1. Photographs showing different beach types: a tidal flalt in the inner part of the Ría de Arousa (A), a reflective beach in the Atlantic coast (B), a dissipative beach in the Atlantic coast of Galicia (C) and a beach on the Antarctic coast (D).
| 8 CHAPTER I
1.2. PHYSICAL CHARACTERIZATION
1.2.1. Structural beach components
Beaches are commonly defined as “wave-deposited accumulation of sediment between wave base and the limit of wave uprush or swash. The wave base is the seaward limit or depth from which average waves can entrain and transport sediment shoreward” (Short 1999). Thus, beaches are the product of the waves, sediment and substrate and the factors that may alter or affect them. One of the most important is the tidal regime, the periodic rise and fall of the sea surface, which varies on open coasts from a few centimetres to 10 m. Other factors such as temperature, biota, and wind may influence significantly the beach system.
. Waves (specifically surface gravity waves) and the currents they induce constitute the driving forces behind the most process occurring on open sandy beaches (McLachlan & Brown 2006). A wave is generated by the opposite forces exerted on the water surface by the wind and the superficial tension. During this disturbance energy and momentum are transferred to the water mass. Wave action penetrates in the water column to a depth approximately half of the water length (Fig. 1.2). As the deep sea decreases landward, there is a point where the wave touches the sea floor (Short 1999, Masselink & Hughes 2003)(Fig. 1.3).
Fig. 1.2. Diagram of water motion in waves showing the decrease in the diameter of the orbital paths with depth. Modified from Davis & Fitzgerald (2004).
| 9 GENERAL INTRODUCTION
Fig. 1.3. Increasing asymmetry of waves approaching the shoreline. H/L denotes the ratio of wave height to wave length. Modified from Carter (1989).
Fig. 1.4. Features of a high energy beach at mid tide. Modified from Short (1999).
According to the Short (1999) definition, this point is the lower boundary of the beach -the nearshore zone- . Waves start compacting, and the ratio wave height to wave length (H:L) increase. In this zone will begin the transport of material in addition to energy (Fig. 1.3). When the ratio H:L reach 1/7 the wave collapse. This is the breakpoint where starts the surf zone. The last phase of the wave action is where water runs up and down the beach face; this is the swash zone. The highest boundary of the beach is the limit of the swash during spring tide. The zone comprises between the upper limit of the swash and the highest boundary of the beach constitutes the subaerial zone (Fig. 1.4).
| 10 CHAPTER I
. Sand. Beaches received sand from terrestrial origin (from erosion of the land and its transport to the sea) and also from marine provenance (both from sea cliff erosion and from animal skeleton). Therefore, the two main types of sediment material are quartz and carbonate sands. Both materials differed in their density and form, carbonate particles tend to be more irregular. The sediment grain size is considered the most important feature of sand. Particle size can be classified according to the Wentworth scale (in phi units, where ø = -log2diammeter (mm)) although metric units are more commonly used in beach ecology. Both the size as the form of the sand particle determine the sediment porosity, that is the volume of void space in the sand and is usually expressed as a percentage of total volume. Generally the finer sand the greater its porosity. Other important characteristic of the sediment is the permeability, the rate of flow or drainage of water through the sand, which tend increase from fine to coarse sands (McLaclan 2006).
. Substrate. The type and size of a beach depends on the geological nature of the substrate upon which it is established in three major ways (Short 1999):
- Beaches only occur on cross-shore gradients between 0.1° and 0.8°. Below this range subaqueous sand ridges and flats tend to arise while stepper gradients than this range induce offshore sediment transport and shoreline erosion. - The three-dimension morphology of the substrate determines the amount of sediment that can be accommodated between the substrate and the beach surface. - The bed rock or older sedimentary deposits where all beaches are located (the geological inherence) modify the nearshore zone as with reefs or hard surfaces, and thereby influence the shoaling. This modifies the wave height and direction at the shore, and in turn influences the overall beach characteristics controlling the beach length, orientation and curvature.
| 11 GENERAL INTRODUCTION
Fig. 1.5. A typical semi-diurnal tidal record over six weeks showing the Spring- Neap cycle in relation to the phase of the Moon. Modified form Carter (1989).
1.2.2. Main influential factors in a beach system
. The tidal regime. The systematic variations in the relative position of the Earth, Moon and Sun caused periodic rise and fall of oceanic and coastal waters (Fig 1.5). The coastal environments are classified according to the absolute tidal range in: microtidal ranges of less than 2 m, mesotidal ranges between 2 and 4 m, and macrotidal ranges in excess of 4 m (Davies 1964). Although tides are not required for beach formation they contribute substantially to beach morphology. Tides shift the shoreline both horizontally and vertically. In areas of high tide range, the tidal variation in nearshore water depth can also modify breaker wave height by increasing wave shoaling at low tide. At higher tidal ranges the beach width tends to increase (Masselink 1993). Tides also may alter the sediment transport (Short 1999).
. Biota. Marine biota contributes to the production of calcareous material that can be incorporated to beach sediment. Although the sediment proportion of skeletal carbonate material in beaches is globally low, in some tropical and temperate beaches can reach a majority of the sediment (Short 1999). The macroalgae and seagrasses commonly stranded on the upper beach influence the
| 12 CHAPTER I
sediment dynamics and together with the dune vegetation play a important role in the dune maintenance and stabilization (Nordstrom et al. 2012).
. Wind. Wind direction, particularly longshore winds, contributes to nearshore currents and thereby sediment transport. Wind velocity intensifies all its impacts, and even can contribute to subaqueous sediment transport through downwelling and upwelling currents (Short 1999).
. Temperature. The temperature effects are maximized in the low and high latitudes. When seawater falls below -4 °C it freezes leading to the formation sea ice. The presence of ice impedes and finally ceases all wave and swash activity. The subaerial beach surface below 0 °C will freeze, impeding swash percolation and encouraging the accumulation of frozen swash on the beach. Seawater temperatures above 26 °C encourage the take-up of calcium carbonate. This can lead to the precipitation of calcium carbonate in the interstitial pore space, leading to the cementation of the sand grains and the formation of beach calcarenite (also called beach rock) (Short 1999).
1.2.3. Beach morphodynamics
Wright & Thom (1977) introduce this term in the costal literature defining it as: “the mutual adjustment of topography and fluid dynamics involving sediment transport”. On beaches this implies that the surface topography of the beach will adjust to accommodate the fluid motions produce by waves. Therefore, beach morphodynamics involves the mutual interaction of waves with the beach topography, such that the waves modify the topography, which in turn modify the waves.
Given the high interdependence among the structural components of beaches, they are commonly defined according to morphodynamic criterions. Although, at the most elementary level, sandy beaches can be classified in the basis of their overall slope
| 13 GENERAL INTRODUCTION
into steep and gentle gradient beaches. These two types represent two fundamentally morphodynamic process regimes (Fig. 1.6).
On steep beaches, a surf zone is generally absent, an incident waves break directly on the beachface. A significant part of the incoming wave energy is reflected back from the shoreline and hence these beaches are referred to as reflective beaches (Fig. 1.6-A). On gentle-gradient beaches, the surf zone is wide. The majority of the incoming wave energy is dissipated during the wave breaking process and these beaches are known as dissipative beaches (Fig. 1.6-B) (Short 1999, Masselink & Hughes 2003). As a predictive purpose of the beach type, (Wright & Short 1983) use the fall velocity (Gourlay 1968, Dean 1973), also called Dean parameter (Ω), to classify microtidal beaches into reflective, intermediate and dissipative types.
A
B
Fig. 1.6. .A reflective (A) and a dissipative (B) beach types under microtidal conditions. Modified from McLachlan & Brown (2006).
| 14 CHAPTER I
Fig. 1.7. Tidal zonation scheme. Modified by (Short 1999).
1.2.3.1. The interaction of tides with beach morphodynamics
Short (1999) subdivided the beach profile into four regions (nearshore zone, surf zone, swash zone and the aeolian zone) characterized by its typical morphology and hydrodynamic processes (Fig. 1.4). On microtidal beaches, the location and the spatial extent are relatively fixed. On tidal beaches, however, these zones shift both vertically and horizontally with the rise and fall of the tide (Fig. 1.7). Consequently, the equilibrium conditions on the intertidal profile are defined by a mixture different hydrodynamic processes that depend on the specific location and wave, tide and sediment characteristics.
Masselink & Short (1993) proposed a classification model that takes into account the most important environmental constraints of sandy beaches by combining the Dean parameter (Ω) with the relative tidal range parameter (RTR). The RTR indicates the relative importance of swash, surf zone and shoaling wave process in determining profile morphology (Fig. 1.8).
| 15 GENERAL INTRODUCTION
Fig. 1.8. Beach classification model from the prediction of the beach morphology on the basis of the dimensionless fall velocity (Ω) and the relative tidal range (RTR). Modified from Masselink & Hughes (2003).
1.2.3.2. Tidal effect on the water table
The water table is defined as the mean water surface where pore-water pressure is equal to atmospheric pressure (Fig. 1.9). The elevation of the water table within beaches is determined by the hydraulic conditions, including wave run-up, tide range and rainfall and the characteristics of the beach material principally, sediment size, sorting and porosity. Capillary forces can result in a saturated region extending above the water table (Fig. 1.9).
Several processes can cause fluctuations in the water table on beaches (Dominick et al. 1971, Clarke & Eliot 1987, Turner & Nielsen 1997). However the tidal effect is one of the most important (Short 1999). During the falling tide the water table typically decouples from the ocean, resulting in the formation of a seepage face where groundwater outcrops on the beach face (Fig. 1.10). Following the ocean-water table
| 16 CHAPTER I decoupling, the continued motion of the exit point remains independent of the still water level, prior to overtopping by the flooding tide.
Fig. 1.9. Definition of the water table as the surface where the pore pressure is equal to atmospheric pressure. The saturated fringe may extend up to 0.5 m above the water table in fine sand beaches. Modified from Short (1999).
Fig. 1.10. Scheme of the exit point. Distinguishing the upper boundary of the seepage face where the water table coincides with the beach face. The arrows indicate the direction of the water flow within the beach. Modified from Short (1999).
| 17 GENERAL INTRODUCTION
1.3. ECOLOGY OF SANDY BEACHES
Haeckel (1869) defined ecology as “the total relations of the animal to both its organic and inorganic environment”. Since then, this broad definition has been redefined and bounded by several authors (Elton 1927, Andrewartha 1961, Odum 1963) until the clearest and most precise comtemporaneus definition “ecology is the scientific study of the interactions that determine the distribution and abundance of organisms (Krebs 2001). According to this definition, beach ecology tries to understand the critical forces structuring the biological communities and thereby reaching a complete understanding of the beach ecosystem processes.
Comparing with other marine and coastal systems, beach ecology is a relative new discipline (Schlacher et al. 2007). Indeed, before the 1970 scarce ecological studies had been performed on beaches (Pearse et al. 1942, Dahl 1952). The first international symposium of sandy beaches, celebrated in South Africa in 1983, started to create a body of theory in order to drive the ecological research on beaches (McLachlan & Erasmus 1983). Since then, a variety of hypotheses have been developed and several broad principles in beach ecology have been articulated (Schlacher et al. 2007).
Most of the adaptations that characterize beach animals from those of other marine or terrestrial habitats result from the instability of the substratum coupled with heavy wave action (McLachlan & Brown 2006). During the last decades, the ecological research has greatly improved the knowledge of these singular adaptations to the highly dynamic environment where they live, including mobility and burrowing abilities, rhythmicity in their behaviour, complex orientation mechanism and plasticity (Fig. 1.11) (Kensley 1974, Dauer 1983, Brown & Odendaal 1994, Scapini & Buiatti 1995, Dugan et al. 2000b, Pardo & Amaral 2004, Scapini 2006, Lastra et al. 2010)
| 18 CHAPTER I
Fig.1.11. Endogenous rhythms of activity of the semiterrestrial isopod Tylos during a circadian (A) and a tidal (B) cycle, modified from McLachlan & Brown (2006). Scolelepis sp. resting in the gallery (C:1), capturing food (C:2-3-4) and collecting suspended particles (C:4), modified from Pardo & Amaral (2004).
| 19 GENERAL INTRODUCTION
1.3.1. Influence of the physical environment in the beach macrofauna
The composition, diversity and abundance of the macrofaunal communities on beaches are generally thought to be more strongly controlled by physical factors than by the biological interactions (Fig. 1.12) (McArdle & McLachlan 1991, McLachlan & Dorvlo 2005). This scientific framework arises from the following paradigms (McLachlan 2001, Defeo & McLachlan 2005):
- In harsh environments, physical forces are more important in shaping the ecosystem than biological interactions. - The beach morphodynamic models. - The species richness, abundance and biomass increase from microtidal reflective to macrotidal dissipative beaches.
Fig.1.12. Conceptual model relating community parameters and beach state (R=reflective, I=intermediate, D=dissipative, UD=ultradissipative, and TF=tidal flat). Modified from McLachlan & (Brown 2006).
| 20 CHAPTER I
Fig.1.13. Conceptual model of species richness response to beach type. The theoretical framework for sandy beach ecology is shown, including the general Autecological Hypothesis and more specific hypotheses defined for sandy beach intertidal and supralittoral macrofauna. Modified from Defeo & McLachlan (2011).
Several non-exclusive hypotheses have been developed to predict how sandy beaches are structured, as well as how individual species respond to variations in morphodynamics (Fig. 1.13) (Defeo & McLachlan 2005, Defeo & McLachlan 2011):
- The “autoecological hypothesis (AE)” adapted by McLachlan (1990) to sandy beaches states that communities are structured by independent responses of individual species to the physical environment. - The “swash exclusion hypothesis (SEH)” (McLachlan et al. 1993), restricted to the intertidal, predicts a consistent increase of species richness, abundance and biomass from reflective to dissipative beaches. The harsher swash climate toward reflective conditions determines the progressive exclusion of species until, in extreme reflective situations, only remain supratidal forms (Defeo & McLachlan 2005). - The “habitat harshness hypothesis (HHH)” (Defeo & Martnez 2003) postulates that population features (abundance, fecundity, growth and survival) increase from reflective to dissipative beaches. The rationale is that harsh environments
| 21 GENERAL INTRODUCTION
forces organisms to divert more energy toward maintenance and their populations, therefore have lower abundance, mean individual sizes and weights, growth rates, longevity, fecundity, reproductive output and survival. - The “habitat safety hypothesis (HSH)” (Defeo & Gómez 2005) suggests that the combination of narrow swashes and steep slopes makes reflective beaches a more stable and safer environment for supratidal species.
1.3.2. Zonation patterns on sandy beaches
Zonation patterns reflect the restriction of species of particular sections of environmental gradients (Raffaelli 1991). In intertidal systems, one of the most important observations was the “universal features of zonation” on the rocky shore (Stephenson & Stephenson 1949). This zonation pattern recognizes three zones characterized by the same type of organism world-wide.
Several attempts have been made to find universal zonation patterns on sandy beaches (Fig. 1.14). However, two general zonation schemes have been traditionally used. Dahl (1952) introduces a scheme of zonation consisting of three zones based on the crustacean distribution. A higher zone (the subterrestrial fringe) occupied either by talitrid amphipods or ocypodid crabs, an intermediate zone (the middlitoral zone) characterized by cirolanid isopods, and a lower zone (the sublittoral zone) characterized by hippid crabs (Emerita spp.) in the tropics and haustoriid and oedicerotid amphipods in temperate areas. (Salvat 1964, Salvat 1967) proposed an alternative scheme based on physical factors. He defined a drying, retention, resurgence and saturation zones, each one characterized by increasing water content. Both schemes show a high correspondence among zones and they have traditionally been used as referential zonation schemes. However many exceptions have emerged and therefore they cannot be considered as universal its equivalent for rocky shores (Raffaelli 1991).
| 22 CHAPTER I
Brown states that at a global scale, only two zones can be recognized (in McLachlan & Erasmus 1983): a zone of air-breathers above the drift line and a zone of water breathers below that point. However, several studies suggest that the number of recognizable zones depends on the beach type, reflective having fewer zones than dissipative beaches. At the morphodynamic extremes, only the supralitoral zone may be found on very harsh reflective beaches and up to 4 zones are recognized on ultradissipative beaches (Defeo & McLachlan 2005).
Species inhabiting sandy beaches may vary the range of distribution across the intertidal daily and seasonality (Scapini & Buiatti 1995, Scapini 1997, Gambineri et al. 2008, Fanini et al. 2012). Interaction between species can modify also the species distribution. In addition the tidal variations in the water level may affect to all the zonation process. Consequently, the zonation on sandy beaches is an extremely spatial
Fig.1.14. General schemes of macrofauna zonation on sandy beaches. Modified from McLachlan & Brown (2006).
| 23 GENERAL INTRODUCTION
and temporal variable process (Brazeiro & Defeo 1996).
1.3.3. Beach connectivity
Although in ecology is long known that all ecosystems receive considerable quantities of materials outside their boundaries (Elton 1927) only recently the ecological research begun to ask how these flows affect to the recipient ecosystem (Polis et al. 2004).
Beaches are commonly defined as an interface zone between marine and terrestrial systems. They are subjected to an active exchange of materials between the sea and land. McLachlan (1988) identified four main components integrating these fluxes: sand, salt spray, groundwater, and living and dead animals (Fig. 1.15).
The organic exchanges through the beach constitute one of the most important processes for the ecosystem. Beaches are characterized by a low primary productivity
Fig. 1.15. Exchanges of materials between dunes and intertidal beaches. Modified from McLachlan & Brown (2006).
| 24 CHAPTER I and therefore most of the food chain is maintained with allochthonous inputs of organic matter (Table 1.1).
Food type Source Remarks Benthic microflora Beach sand On sheltered beaches Surf diatoms, flagellates Surf water In well developed surf zones Stranded macrophytes The sea Near kelp beds, estuaries, etc. Carrion The sea Particulates The sea Dissolved organics The sea Particularly during strong, Insects The land offsohre winds Litter The land
Table 1.1. Food sources for sandy beaches. Modified from McLachlan & Brown 2006
1.4. WRACK
The term wrack, also called “beach cast” or “drift”, is generally applied to any organic matter stranded on the beach surface. This refers to macroalgae, seagrasses, driftwood, fruits, seeds, and carrion (Colombini & Chelazzi 2003). Given wrack is compose by matter originate in other ecosystems, the standing stock of wrack on the beach depends on the production in the donor ecosystems and the elements implied in their transport. The spatial and temporal variability of the wrack deposits are still poorly understood and they are commonly associated with random events.
Once deposited on the beach surface, the wrack material is a potential resource for the organisms inhabiting sandy beaches both as food and refuge (Ince et al. 2007). For example, talitrids amphipods can process large amounts of stranded macroalgae daily (Lastra et al. 2008). Generally, large deposits of wrack induce a great abundance of
| 25 GENERAL INTRODUCTION
invertebrates associated to them (Dugan et al. 2000a, McLachlan & Brown 2006). This numerically increase may be transferred to higher trophic levels (Dugan et al. 2003, Lewis et al. 2007) and the overall increment in the net organic matter may influence adjacent ecosystems (Polis & Hurd 1996). Wrack may serve to the macroinfauna as shelter from predation and against the environmental conditions such as air temperature and humidity (Colombini & Chelazzi 2003, Jaramillo et al. 2006).
The interaction between the wrack deposits and the macrofauna is a very dynamic process highly variable spatial and temporally (Colombini & Chelazzi 2003). After wrack deposition, the aging on the beach surface induce progressive changes in its physic-chemical properties. Preferences by each type of wrack with specific physic- chemical properties cause complex colonization and succession process (Olabarria et al. 2007, Garrido et al. 2008, Lastra et al. 2008, Rodil et al. 2008).
Wrack decomposition on the beach may be important in the nutrient regeneration (Dugan et al. 2011). Macrofauna may increase the wrack fragmentation and thus accelerate the decomposition processes (Mews et al. 2007, Lastra et al. 2008). Wrack decay involves a rapid breakdown of biomass, resulting in release of nutrients and CO2 (Buchsbaum et al. 1991, Chapin et al. 2002, García-Robledo et al. 2008, Hardison et al. 2010). The released nutrients can be retained in the sediment (where they become available to bacteria and diatoms) or they can be washed from the beach into the surf zone (where they may be taken by phytoplankton) or adjacent coastal zones (where they could be used by macroalgae and/or seagrasses).
Wrack plays an important role in the sediment dynamics. Once deposited, wrack increases the surface roughness and provides a physical obstacle to aeolian transport which promote the sand accumulation (Jackson & Nordstrom 2011). The uppermost wrack line influence the sediment budget of the existing foredune and form the basis of the new foredune crest (Nordstrom et al. 2011, Nordstrom et al. 2012). Consequently,
| 26 CHAPTER I wrack has a notorious role in the beach profile and in the dune formation and stabilization (Nordstrom et al. 2011, Nordstrom et al. 2012).
1.5. THE SOCIO-ECONOMIC VALUE OF SANDY BEACHES
The ecosystem service defines the benefits that people obtain from ecosystem. This concept refers the contribution of nature to a variety of goods (e.g., products obtained from the ecosystem such as resource harvest) and services (e.g., recreational and tourism benefits or ecological regulatory and habitat functions such as water purification, habitat provision and erosion control) (Barbier & Hacker 2011).
Sandy beaches provide a wide range of services such as raw materials, coastal protection, erosion control, dynamic response to sea-level rise, breakdown of organic matter, nutrient mineralization and recycling, water catchment and purification, water storage in dune aquifers, maintenance of wildlife, carbon sequestration, tourism and recreation. However, very few of these services have been properly valued, with the exception of erosion control and recreation activities (Defeo et al. 2009, Barbier & Hacker 2011).
Tourism and other recreational activities related with beaches are one of the most important economical resources for many coastal populations (Klein et al. 2004, Schlacher & Thompson 2012). This has potentiated the increase of the human pressure on sandy beaches in the last decades (Schlacher et al. 2007, Defeo et al. 2009). In this scenario, the beach management traditionally tries to achieve a high aesthetic quality of the beach, i.e. beaches are only considered as a geophysical landscape at expense of the ecological quality of the beach environment (Weslawski et al. 2000, Lercari & Defeo 2003, Gheskiere et al. 2005). Activities to improve the perception of the beach-goers are central in the management plans. Thereby, remove all the wrack present on the beach has become a common practice world-wide (Kirkman & Kendrick 1997, Dugan &
| 27 GENERAL INTRODUCTION
Hubbard 2010, Gilburn 2012, Nordstrom et al. 2012). This activity, carried out with heavy mechanical equipment, consists in the sieving of the sand to take out all the material deposited on the beach surface. This general procedure does not take into account the ecological impact of this anthropogenic activity. Indeed, the effects that they could cause in the ecosystem remain largely unclear (Gilburn 2012).
1.6. BACKGROUND OF THIS PROJECT
This work was carried in Galicia, a region located on the NW coast of the Iberian Peninsula. The Galician coastline extends along 1995 Km of which 278 Km corresponds to sandy beaches. This region is characterized by a transitional climate between the Oceanic and Mediterranen regimes (Mounier 1979b, a). Roughly, it can be describe by the abundant precipitations and the temperate temperatures in winter and summer. According to the “World bioclimatic Clasification” the Galician territory belongs to the temperate macrobioclimate (Rodríguez Guitián & Ramil-rego 2007). The coast is at the northern limit of the Canary upwelling system (Wooster & Bakun 1976) -an oceanographic phenomenon involving persistent upward motion of sea water toward the ocean surface, replacing the surface water which has moved away in a process called divergence-. This process increases the nutrient concentration of the coastal seawater. The effects of the upwelling are amplified by the coastal morphology resulting in high levels of biological productivity (Varela et al. 1984).
Globally the ecological research on sandy beaches is a relatively recent discipline (McLachlan & Brown 2006, Schlacher et al. 2007). As a consequence, in Spain, scarce scientific studies have been published before the nineties (Penas & Gonzalez 1983). Since then, several theses have been performed about different ecological aspects of sandy beaches in Galicia (Incera 2004, Rodríguez Patiño 2004, de la Huz 2008) and in the Iberian Peninsula (Gonçalves 2007, Rodil 2008). From all these researches, a strong
| 28 CHAPTER I scientific baseline has arisen. However, this new knowledge also generated open questions to solve.
Most of the beaches located in the N and NW coast of Spain are classified as intermediated (de la Huz 2008, Rodil 2008). The specific richness on the Galician beaches is higher than in other template zones (de la Huz 2008). The community descriptors, such as number of species, abundance and biomass, tend to increase from reflective to dissipative states in the intertidal. However, the supratidal zone often shows the opposite tend for the same parameters (de la Huz 2008). In the N coast of Spain, community characteristics are affected by several physical factors, i.e, they are not only determined by beach morphodynamics (Rodil 2008). Several studies covering both the N and NW coast demonstrated changes in the community descriptors related with the longitude in which each beach is located. This spatial variability may be caused by an increased in the primary productivity toward the western due to the location of the upwelling (Lastra et al. 2006, Rodil et al. 2012). These results indicate that, in addition of the physical characteristics, factors dependent on coastal processes such as food availability on the water column may affect to the macrofaunal community of sandy beaches.
The biopolymeric carbon concentration may be a useful indicator of the food availability in the sediment. This is related with the beach slope, with steeper beaches showing lower concentration than flatters ones. The same tended was observed with the diversity, density an biomass of the macrofauna (Incera 2004).
In addition of the availability of food in the water column and in the sediment, the availability of wrack deposited on the beach surface may be an important factor controlling the macrofaunal community. This has been demonstrated in the western coast of Portugal studying two beaches with the same morphodynamic characteristics but with differences in the wrack deposits (Gonçalves 2007). Differences in the wrack
| 29 GENERAL INTRODUCTION
composition and size may affect also to the assemblage composition (Olabarria et al. 2007, Rodil et al. 2008).
Analyses of the macrofaunal distribution along the intertidal show two clear zones in accordance with the model propose by Brown (Fig. 1.14). A supratidal and an intertidal zone defined by the drift line and occupied by air-breathers and water breather species respectively (de la Huz 2008, Rodil 2008). In intermediate beaches with gently slope sometimes a third zone can be observed between the resurgence and the retention zone. This zone is characterized by the spionid Scolelpis squamata and isopods of the genus Eurydice (de la Huz 2008). The biological interactions may play an important role in the distribution of the macrofaunal species increasing the complexity of the zonation studies (Incera 2004, Lastra et al. 2010).
1.7. APPROACH TAKEN IN THIS THESIS
Fluxes of organic matter and nutrients through the beach system are processes well documented world-wide. The ecological significance of this energetic transfer is potentiated by the low primary productivity of sandy beaches, and thus the strong dependence of the beach organisms from allochthonous organic inputs. However, the traditional hypothesis that try to explain the macrofaunal community structure and even the beach ecosystem functioning mainly rely in the consideration of the physical control of ecosystem in harsh environments. Therefore, these hypothesis states that from an ecological point of view beaches can be described in terms of the interaction of waves, tides and sediment. Nevertheless, a growing number of exceptions to this general rule have been published in the last years.
Wrack deposits are one of the main organic inputs periodically stranded on the beach surface. In many coastal regions has been reported vast amounts of algae and/or seagrasses washed into shore habitats or conducted to subtidal zones with ecological
| 30 CHAPTER I consequences. On beaches, the macrofauna use this resource as food and refuge. The spatial and temporal wrack distribution as well as its composition may govern the macrofaunal utilization, the decay process, and the release of nutrients. However, despite to the significant ecological and biogeochemical consequences of this subsidy on beaches, the processes and agents involved in the deposition and this role in the macrofaunal community and ecosystem functioning require further investigation.
1.8. AIMS OF THIS THESIS
The overall aim of this thesis was to deepen our understanding of the ecological role of macroalgal wrack in the beach ecosystem. Specifically, the objectives proposed were:
. Established the magnitude and composition of the wrack inputs at different spatio-temporal scales.
o Perform the first characterization of the macroalgal deposits on exposed beaches of the Galician coast. - Quantify the range of biomasses and identify the species stranded on different beach types. - Investigate the presence and the biomass of invasive species. - Compare the results obtained in the wrack assessment of the Galician beaches with data published from other geographical areas.
o Analyse which environmental variables may influence the openness and permeability of beaches to the inputs of macroalgae.
o Investigate the variability that the life cycle of the predominant species of macroalgae could induce in the biomass and composition of wrack.
| 31 GENERAL INTRODUCTION
. Assess the importance of the macroalgal wrack in the release of nutrients from beaches to nearshore systems.
o Analyse the relationship between the wrack magnitude and the spatio- temporal variability in the nutrient concentration in the intertidal water.
o Investigate the influence of wrack in the relation of the different nutrient species in the intertidal water.
o Assess if the nutrient release in the intertidal water affect significantly to the nutrient content in the swash zone.
. Determine the influence of the availability of wrack in the macrofaunal community structure of exposed beaches.
o Investigate if the biomass of wrack affect to the community composition and abundance at different spatio-temporal scales.
o Assess the relative importance of the physical environment and the wrack availability structuring the macrofaunal communities.
o Analyse if the variability in the inputs of algae affect to the stability of the macrofaunal assemblages.
. Investigate the potential impact of the wrack removal on the beach macrofauna. o Quantify the effect of the removal of wrack in the supratidal and low intertidal zones of exposed beaches.
o Evaluate the potential use of macrofaunal species as indicators of the relative health of sandy beaches.
| 32 CHAPTER I
1.9. LITERATURE CITED
Andrewartha H (1961) Introduction to the study of animal populations, Vol. University of Chicago Press, Chicago Barbier E, Hacker S (2011) The value of estuarine and coastal ecosystem services. Ecological Monographs 81:169-193 Brazeiro A, Defeo O (1996) Macroinfauna zonation in microtidal sandy beaches: is it possible to identify patterns in such variable environments? Estuarine, Coastal and Shelf Science Brown A, Odendaal F (1994) The Biology of Oniscid lsopoda of the Genus Tylos. Advances in marine biology 30:89-144 Buchsbaum R, Valiela I, Swain T, Dzierzeski M, Allen S (1991) Available and refractory nitrogen in detritus of coastal vascular plants and macroalgae. Marine ecology progress:131-143 Carter (1989) Costal Environments. An introduction to the physical, ecological and cultural systems of coastlines, Vol. Academic Press, San Diego (USA) Chapin F, Matson P, Mooney H (2002) Principles of terrestrial ecosystem ecology, Vol, New York Clarke DJ, Eliot IG (1987) Groundwater-level changes in a coastal dune, sea-level fluctuations and shoreline movement on a sandy beach. Marine Geology 77:319-326 Colombini I, Chelazzi L (2003) Influence of marine allochthonous input on sandy beach communities. Oceanogr Mar Biol 41:115-159 Dahl E (1952) Some aspects of the ecology and zonation of the fauna on sandy beaches. Oikos:1-27 Dauer D (1983) Functional morphology and feeding behavior of Scolelepis squamata (Polychaeta: Spionidae). Marine Biology 77:279-285 Davies J (1964) A morphogenetic approach to world shorelines. Zeitschrift fur Geomorphologie 8:127-142 Davies J (1980) Geographic variation in coastal development.212 Davis R, Fitzgerald D (2004) Beaches and coasts, Vol. Blackwell Science Ltd, United Kingdom de la Huz R (2008) Ecología de la macrofauna de las playas expuestas de Galicia. In: Dean R (1973) Heuristic models of sand transport in the surf zone. In: Proceedings 1st Australian coastal engineering conference Defeo O, Gómez J (2005) Morphodynamics and habitat safety in sandy beaches: life- history adaptations in a supralittoral amphipod. Marine Ecology Progress Series 293:143-153 Defeo O, Martnez G (2003) The habitat harshness hypothesis revisited: life history of the isopod Excirolana braziliensis in sandy beaches with contrasting
| 33 GENERAL INTRODUCTION
morphodynamics. Journal of the Marine Biological Association of the UK 83:331- 340 Defeo O, McLachlan A (2005) Patterns, processes and regulatory mechanisms in sandy beach macrofauna: a multi-scale analysis. Marine Ecology Progress Series 295:1- 20 Defeo O, McLachlan a (2011) Coupling between macrofauna community structure and beach type: a deconstructive meta-analysis. Marine Ecology Progress Series 433:29-41 Defeo O, McLachlan A, Schoeman DS, Schlacher Ta, Dugan J, Jones A, Lastra M, Scapini F (2009) Threats to sandy beach ecosystems: A review. Estuarine, Coastal and Shelf Science 81:1-12 Dominick TF, Wilkins B, Roberts H (1971) Mathematical Model for Beach Groundwater Fluctuations. Water Resources Research 7:1626-1635 Dugan JE, Hubbard DM (2010) Loss of Coastal Strand Habitat in Southern California: The Role of Beach Grooming. Estuaries and Coasts 33:67-77 Dugan JE, Hubbard DM, Engle JM, Martin DL, Richards DM, Davis GE, Lafferty KD, Ambrose RF Macrofauna communities of exposed sandy beaches on the southern California mainland and Channel Islands. In: Browne (ed). Proc Fifth California islands symposium, outer continental shelf study. Camarillo, CA: Minerals Management Service (99-0038). Dugan JE, Hubbard DM, Lastra M (2000b) Burrowing abilities and swash behavior of three crabs , Emerita analoga Stimpson , Blepharipoda occidentalis Randall , and Lepidopa californica Efford ( Anomura , Hippoidea ), of exposed sandy beaches. Journal of Experimental Marine Biology and Ecology 255:229-245 Dugan JE, Hubbard DM, McCrary MD, Pierson MO (2003) The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of southern California. Estuarine, Coastal and Shelf Science 58:25-40 Dugan JE, Hubbard DM, Page HM, Schimel JP (2011) Marine Macrophyte Wrack Inputs and Dissolved Nutrients in Beach Sands. Estuaries and Coasts 34:839-850 Elton CS (1927) Animal Ecology. In: Jackson Sa (ed), London Fanini L, Gecchele LV, Gambineri S, Bayed A, Coleman CO, Scapini F (2012) Behavioural similarities in different species of sandhoppers inhabiting transient environments. Journal of Experimental Marine Biology and Ecology 420-421:8- 15 Gambineri S, Rossano C, Durier V, Fanini L, Rivault C, Scapini F (2008) Orientation of littoral amphipods in two sandy beaches of Brittany (France) with wide tidal excursions. Chemistry and Ecology 24:129-144 García-Robledo E, Corzo A, García de Lomas J, van Bergeijk S (2008) Biogeochemical effects of macroalgal decomposition on intertidal microbenthos: a microcosm experiment. Marine Ecology Progress Series 356:139-151
| 34 CHAPTER I
Garrido J, Olabarria C, Lastra M (2008) Colonization of wrack by beetles (Insecta, Coleoptera) on a sandy beach of the atlantic coast. Vie et milieu 58:223-232 Gheskiere T, Vincx M, Weslawski J (2005) Meiofauna as descriptor of tourism-induced changes at sandy beaches. Marine Environmental … 60:245-265 Gilburn AS (2012) Mechanical grooming and beach award status are associated with low strandline biodiversity in Scotland. Estuarine, Coastal and Shelf Science:1-8 Gonçalves SC (2007) Macrofaunal key crustaceans in Atlantic and Mediterranean exposed sandy beaches. Does knowledge on key species bio-ecology have a role in assessing global changes? In: Gourlay M Beach and dune erosion tests. In. Haeckel E (1869) Ueber die fossilen Medusen der Jura-Zeit. Zeitschrift fuer Wissenschaftliche Zoologie 19:538-562 Hardison A, Canuel E, Anderson I, Veuger B (2010) Fate of macroalgae in benthic systems: carbon and nitrogen cycling within the microbial community. Marine Ecology Progress Series 414:41-55 Ince R, Hyndes G, Lavery P, Vanderklift M (2007) Marine macrophytes directly enhance abundances of sandy beach fauna through provision of food and habitat. Estuarine, Coastal and Shelf Science 74:77-86 Incera M (2004) Influencia de los factores ambientales sobre la macrofauna y la composición bioquimica del sedimento en intermareales arenosos. In: Jackson NL, Nordstrom KF (2011) Aeolian sediment transport and landforms in managed coastal systems: A review. Aeolian Research 3:181-196 Jaramillo E, De La Huz R, Duarte C, Contreras H (2006) Algal wrack deposits and macroinfaunal arthropods on sandy beaches of the Chilean coast. Revista Chilena de Historia Natural 79:337-351 Kensley B (1974) Aspects of the biology and ecology of the genus Tylos Latreille. Annals of the South African Museum Kirkman H, Kendrick G (1997) Ecological significance and commercial harvesting of drifting and beach-cast macro-algae and seagrasses in Australia: a review. Journal of Applied Phycology 9:311-326 Klein Y, Osleeb J, Viola M (2004) Tourism-generated earnings in the coastal zone: a regional analysis. Journal of Coastal Research 4:1080-1088 Krebs C (2001) Ecology: the experimental analysis of distribution and abundance 5th Ed., Vol. Benjamin Cummings, San Francisco (California) Lastra M, de la Huz R, Sánchez-Mata AG, Rodil IF, Aerts K, Beloso S, López J (2006) Ecology of exposed sandy beaches in northern Spain: Environmental factors controlling macrofauna communities. Journal of Sea Research 55:128-140 Lastra M, Page HM, Dugan JE, Hubbard DM, Rodil IF (2008) Processing of allochthonous macrophyte subsidies by sandy beach consumers: estimates of feeding rates and impacts on food resources. Mar Biol 154:163-174
| 35 GENERAL INTRODUCTION
Lastra M, Schlacher Ta, Olabarria C (2010) Niche segregation in sandy beach animals: an analysis with surface-active peracarid crustaceans on the Atlantic coast of Spain. Marine Biology 157:613-625 Lercari D, Defeo O (2003) Variation of a sandy beach macrobenthic community along a human-induced environmental gradient. Estuarine, Coastal and Shelf Science 58:17-24 Lewis TL, Mews M, Jelinski DE, Zimmer M (2007) Detrital subsidy to the supratidal zone provides feeding habitat for intertidal crabs. Estuaries and Coasts 30:451-458 Masselink G (1993) Simulating the effects of tides on beach morphodynamics. Journal of Coastal Conservation 15:180-197 Masselink G, Hughes MG (2003) Introduction to coastal processes geomorphology, Vol. Inc., Oxford University Press, New York Masselink G, Short AD (1993) The effect of tide rangeon beach morphodynamics. Journal of Coastal Research 9:785-800 McArdle S, McLachlan A (1991) Dynamics of the swash zone and effluent line on sandy beaches. Marine ecology progress series Oldendorf 76:91-99 McLachlan A (1988) Dynamics of an exposed beach/dune coast, Algoa Bay, southeast Africa. Journal of Coastal Research 3:91-95 McLachlan A (1990) Dissipative beaches and macrofauna communities on exposed intertidal sands. Journal of Coastal Research 6:57-71 McLachlan A (2001) Coastal beach ecosystems. In: R L (ed) Encyclopedia of Biodiversity. Academic Press, New York McLachlan A, Brown AC (2006) The ecology of sandy shores, Vol. Elsevier, Amsterdam McLachlan A, Dorvlo A (2005) Global Patterns in Sandy Beach Macrobenthic Communities. Journal of Coastal Research 21:674-687 McLachlan A, Erasmus T (1983) Sandy beaches as ecosystems In: McLachlan AaE, T (ed). Junk, The Hague McLachlan A, Jaramillo E, Donn T, Wessels F (1993) Sandy beach macrofauna communities and their control by the physical environment: a geographical comparison. Journal of Coastal Research 15:27-38 Mews M, Zimmer M, Jelinski D (2007) Species-specific decomposition rates of beach- cast wrack in Barkley Sound, British Columbia, Canada. Marine Ecology Progress Series 328:155-160 Mounier (1979a) La diversité des climats oceániques de la Penínsule Ibérique. La Meteorologie 106:205-227 Mounier (1979b) Les origines du passage du domaine oceánique au domaine méditerranéen dans la Península Ibérique. Mediterranee 36:3-17 Nordstrom KF, Jackson NL, Freestone AL, Korotky KH, Puleo Ja (2012) Effects of beach raking and sand fences on dune dimensions and morphology. Geomorphology 179:106-115
| 36 CHAPTER I
Nordstrom KF, Jackson NL, Kraus NC, Kana TW, Bearce R, Bocamazo LM, Young DR, De Butts Ha (2011) Enhancing geomorphic and biologic functions and values on backshores and dunes of developed shores: a review of opportunities and constraints. Environmental Conservation 38:288-302 Odum E (1963) Ecology, Vol. Holt, Rinehart and Winston, New York Olabarria C, Lastra M, Garrido J (2007) Succession of macrofauna on macroalgal wrack of an exposed sandy beach: Effects of patch size and site. Marine environmental research 63:19-40 Pardo E, Amaral A (2004) Feeding behavior of Scolelepis sp.(Polychaeta: Spionidae). Brazilian Journal of Oceanography 52:75-79 Pearse A, Humm H, Wharton G (1942) Ecology of sand beaches at Beaufort, N.C. Ecological Monographs 12:135-190 Penas E, Gonzalez G (1983) Relationship between benthic infauna and environmental factors in three beaches of the ria de Arosa embayment (Spain) using canonical correlation analysis. Journal of Experimental Marine Biology and Ecology 68:245- 256 Polis G, Power M, Huxel G (2004) Food webs at the landscape level, Vol. The University of Chicago Press, Chicago Polis GA, Hurd SD (1996) Linking marine and terrestrial food webs: allochthonous input from the ocean supports high secondary productivity on small islands and coastal land communities. The American Naturalist 147 Raffaelli D (1991) Zonation schemes on sandy shores" a multivariate approach. J exp mar Biol Ecol 148:241-253 Rodil I, Olabarria C, Lastra M, Lopez J (2008) Differential effects of native and invasive algal wrack on macrofaunal assemblages inhabiting exposed sandy beaches. Journal of Experimental Marine Biology and Ecology 358:1-13 Rodil IF (2008) The ecology of macrofauna in sandy intertidal habitats. In: Rodil IF, Compton TJ, Lastra M (2012) Exploring macroinvertebrate species distributions at regional and local scales across a sandy beach geographic continuum. PloS ONE 7:e39609 Rodríguez Guitián M, Ramil-rego P (2007) Clasificaciones climáticas aplicadas a Galicia : revisión desde una perspectiva biogeográfica. Recursos rurais 1:31-53 Rodríguez Patiño JG (2004) Ecología de la meiofauna en intermareales arenosos. In: Salvat B (1964) Les conditions hydrodynamiques interstitielles des sediments meubles intertidaux et la repartition verticale de la fauna endogenee. CR Acad Sci Paris 259:1576-1579. Salvat B (1967). La macrofauna carcip, ologique endogenee des sediments meubles intertidaux (tanaidaces, isopodes et amphipodes): ethologie, bionomie et cycle biologique. Mere Mus Natl Hist Nat Ser A Vol. 45:1-275.
| 37 GENERAL INTRODUCTION
Scapini F (1997) Variation in Scototaxis and Orientation Adaptation of Talitrus saltator Populations Subjected to Different Ecological Constraints (ec960205). Estuarine Coastal and Shelf:139-146 Scapini F (2006) Keynote papers on sandhopper orientation and navigation. Marine and Freshwater Behaviour and Physiology 39:73-85 Scapini F, Buiatti M (1995) Orientation behaviour and heterozygosity of sandhopper populations in relation to stability of beach environments. Journal of Evolutionary Biology 52:43-52 Schlacher TA, Dugan J, Schoeman DS, Lastra M, Jones A, Scapini F, McLachlan A, Defeo O (2007) Sandy beaches at the brink. Diversity and Distributions 13:556-560 Schlacher Ta, Thompson L (2012) Beach recreation impacts benthic invertebrates on ocean-exposed sandy shores. Biological Conservation 147:123-132 Short AD (1999) Handbook of beach and shoreface morphodynamics.379 Stephenson T, Stephenson A (1949) The universal features of zonation between tide- marks on rocky coasts. The Journal of Ecology 37:289-305 Turner I, Nielsen P (1997) Rapid water table fluctuations within the beach face: Implications for swash zone sediment mobility? Coastal Engineering 32 Varela M, JM F, E P, JM C (1984) Producción primaria de las Rías Baixas de Galicia. Cuad Area Cienc Mar Sem Estud Gal 1:173-182 Weslawski JM, Stanek A, Siewert A, Beer N (2000) The sandhopper (Talitrus saltator, Montagu 1808) on the Polish Baltic coast. Is it a victim of increased tourism? vol. 29, 77–87. Oceanological Studies 29:77-87 Wooster W, Bakun A (1976) The seasonal upwelling cycle along the eastern boundary of the North Atlantic. Journal of marine research 34:131-141 Wright LD, Short AD (1983) Morphodynamics of beaches and surf zones in Australia. In: Komar P (ed) Handbook of Coastal Processes and Erosion. C.R.C. Press, London Wright LD, Thom BG (1977) Coastal depositional landforms: a morphodynamic approach. Progress in Physical Geography 1:412-459
| 38
CHAPTER II
II. Annual cycle of wrack supply to sandy beaches: effect of the physical environment
Barreiro F., Gómez M., Lastra M., López J., de la Huz R. (2011) Marine Ecology Progress series (2011) 433: 65-74
WRACK SUPPLY TO SANDY BEACHES
1. ABSTRACT
Connectivity between ecosystems has been widely recognised as an important issue in ecological studies. Sandy beaches are very dynamic and open ecosystems, mainly supported by allochthonous subsidies of stranded organic matter (mostly macroalgae), also termed wrack supply. The magnitude and composition of algal wrack biomass throughout the annual cycle was assessed for 6 sandy beaches on the Galician coast, NW Spain. The effect of wave action and the topographical features of each beach in the wrack deposition process were investigated. Wrack species composition, biomass and coverage were measured monthly along 6 transects at each beach. Mean dry weight of wrack fluctuated from 14 ± 5.3 to 9189 ± 3594 g m–1 (along transects) between locations. Wrack was predominantly composed of brown algae, which accounted for 70% of the average biomass year round; the dominant species were Cystoseira sp. (30.3 ± 17.4%) and Sargassum muticum (14.2 ± 7.1%). A cyclical pattern in wrack composition, coupled with the life cycle of the predominant macroalgae, was observed. Wrack biomass and species composition were mostly explained by wave height and the ratio of beach length to beach area. Small, wave-sheltered beaches received the largest inputs of wrack, and had the lowest relative contribution of brown algae. These results provide evidence that variability in wrack supply on sandy beaches can be explained through interactions between wave exposure, coastal topography and seasonality.
KEY WORDS: Connectivity · Marine–terrestrial ecotone · NW Spain · Sandy beaches · Spatial subsidy · Wave exposure · Wrack
| 42 CHAPTER II
2.2. INTRODUCTION
Studies focusing on the linkages between habitats have increased in the last few decades, revealing the importance of ecotone zones and connectivity in the analysis of ecosystem functioning. These linkages involve the transfer of resources (e.g. nutrients, detritus and prey) from a ‘donor habitat’ to a ‘recipient habitat’ in a process termed ‘spatial subsidy’ (Polis et al. 1997). In this regard, several authors have shown how allochthonous subsidies of organic matter can greatly affect community structure, productivity and stability in a wide variety of marine and coastal ecosystems (e.g. Vetter 1994, Polis & Hurd 1996, Anderson & Polis 2004, Wernberg et al. 2006, Coupland & McDonald 2008, Crawley et al. 2009, Spiller et al. 2010).
The ocean–land interface occupies approx. 8% of the earth’s surface (Ray & Hayden 1992). Primary production across the coastal ecotone is variable, ranging from 0 to ca. 3500 g m–2 yr–1 dry mass (Polis et al. 2004). Among the several classes of organic matter that have been linked to productivity in coastal environments, 2 are of paramount importance: macroalgae on rocky shores, and seagrasses in sheltered estuarine areas. Values from approx. 300 to 1900 gC m–2 yr–1 have been reported in kelp forest in different geographical areas (Mann 1973, Kirkman 1984, Foster & Schiel 1985). The productivity of seagrasses is com parable, reaching 1500 gC m–2 yr–1 (Mateo et al. 2006). Duarte & Cebrian (1996) estimated that, after being fragmented or detached, macroalgae and seagrasses export approx. 43 and 24%, respectively, of the net primary production to neighbouring ecosystems.
Sandy beaches form a dynamic interface between marine and terrestrial ecosystems. Primary production on wave-exposed beaches is low, with values ranging from approx. 0 to 10 gC m–2 yr–1 (McLachlan & Brown 2006). Allochthonous subsidies support most of the beach food web (Griffiths et al. 1983, McLachlan & Brown 2006), also serving as habitat and refuge for the macrofaunal community (Ince et al. 2007). The
| 43 WRACK SUPPLY TO SANDY BEACHES
amount of allochthonous subsidies on any beach firstly depends first on the production of the adjacent habitats. In many coastal regions, beaches near areas with high production of macroalgae and/or seagrasses receive extensive wrack inputs (e.g. Stenton-Dozey & Griffiths 1983, Hobday 2000, Mateo 2010). Parameters based on the edge-to-interior ratio are commonly used to evaluate habitat openness to such input (Polis & Hurd 1996). Fluxes between ecosystems are assumed to increase at higher edge-to-interior surface ratio because the higher this ratio is, the more edge is exposed to the donor ecosystem (Witman et al. 2004). However, fluxes between ecosystems depend on the permeability of the boundaries (Cadenasso & Pickett 2000, Witman et al. 2004), which, in the case of wrack supply to sandy beaches, means complex interactions among physical factors such as waves, currents, winds, coastal topography, etc. (Polis et al. 2004). Witman et al. (2004) concluded that, at decreasing flow velocities, deposition should be favoured.
Species composition and biomass of wrack inputs vary both spatially and temporally (e.g. Stenton-Dozey & Griffiths 1983, Marsden 1991, Dugan et al. 2003, Orr et al. 2005). Following deposition on the beach as wrack, drift materials are subjected to a variety of processes, including in situ consumption by beach herbivores, microbial degradation, desiccation and export by tides and currents (Griffiths & Stenton-Dozey 1981, Griffiths et al. 1983, Inglis 1989, Je¸drzejczak 2002, Orr et al. 2005, Mews et al. 2006). These processes are dependent on the species composition of the wrack (Orr et al. 2005, Mews et al. 2006). For example, Orr et al. (2005) observed that the more buoyant species stranded on the beach were more likely to be resuspended during the following tide.
In order to understand the ecological implications of wrack subsidies, it is important to gauge both the magnitude and variability of the inputs at different spatiotemporal scales. The primary objective of this study, carried out on the coast of NW Spain, was therefore to evaluate changes of wrack supply on exposed sandy
| 44 CHAPTER II beaches over time and in space (i.e. from beach to beach). We hypothesized that (1) physical characteristics such as beach size, wave height and beach slope affect habitat permeability and thus the magnitude of the inputs; and (2) time scales of variability in wrack supply depend on beach characteristics.
2.3. MATERIALS AND METHODS
2.3.1. Field sampling design
SIx beaches on the NW coast of Spain (Fig. 2.1) were sampled monthly between December 2007 and November 2008: Balieiros (BA), Ladeira (LA), Samil (SA), Toralla (TO), Abra (PA) and America (AM). These beaches encompass an exposure range (McLachlan 1980) from very exposed to sheltered (Table 2.1). Tidal conditions were meso- macrotidal, with spring tides ranging from 3.5 to 4 m.
The following 6 environmental variables were recorded at each site: beach slope, estimated using Emery’s profiling technique (Emery 1961); beach length; beach width, measured as the distance between the base of the dune and the lower swash level; wave height, estimated by measuring 30 breaking waves with graduated poles against the horizon; wave period, measured with a stop watch and calculated as the time interval between breakers; and beach area, calculated as the product of beach length and beach width.
Field sampling was carried out during low spring tides. Samples were collected from the base of the dune to the lowest swash level along 6 transects randomly spaced over a 100 m-long stretch in the centre of each beach. Coverage, specific composition and biomass of wrack were calculated along each transect. Coverage was measured using the line intercept method (Dugan et al. 2003). All wrack present on the sand surface within a 1 m wide strip of beach along each transect was collected to assess specific composition and biomass (Lastra et al. 2008).
| 45 WRACK SUPPLY TO SANDY BEACHES
Wrack species composition of wrack was determined to the lowest taxonomic level possible. Dry weight (wt) of each species was calculated after drying to a constant weight at 60°C. Due to the vast amounts of wrack stranded on PA and TO, 3 subsamples were taken from each transect at these sites to estimate the specific composition of the wrack (Fig. 2.2).
Fig. 1.1. Sampled beaches on the NW coast of the Iberian peninsula: America (AM), Abra (PA), Toralla (TO), Samil (SA), Ladeira (LA) and Balieiros (BA).
Table. 2.1. Physical Beach Intertidal characteristics of Beach length (m) width (m) 1/Slope Exposure rate studied beaches. Exposure index PA 210 60 9.8 11 (Exposed) estimated according AM 2200 110 18.7 12 (Exposed) to the rating system of McLachlan (1980). BA 840 100 10.9 18 (Very Exposed) See Fig. 1 for site LA 5000 130 33.9 13 (Exposed) abbreviations. SA 1640 100 16.9 12 (Exposed) TO 100 60 13.8 10 (Sheltered)
| 46 CHAPTER II
Fig.2.2. Photographs detailing the sampling procedure.
2.3.2. Statistical analysis
2.3.2.1. Beach characteristics and wrack deposition:
The relationship between beach characteristics and wrack composition based on biomass data was investigated using a non-parametric multiple regression test, viz. distance-based multivariate analysis for linear model (DISTLM) (McArdle & Anderson 2001, Clarke & Gorley 2006). First, each environmental factor was analysed separately (ignoring any other factor) to evaluate the potential relationship between wrack composition and biomass (marginal test). Next, the abiotic factors were subjected to a best-selection procedure, where the amount of variability explained by each factor added to the model is conditional upon the factors previously included (sequential test). Both tests were based on the Bray-Curtis dissimilarity index. Data on the 6 transects at each location were averaged per month. The distance-based redundancy analysis (dbRDA) was used to represent the relationship between the multivariate data and the predictor variables. Differences in wrack composition among groups of beaches characterized according to the wave exposure and topographical factors in the dbRDA were tested with analysis of similarities (ANOSIM) (Clarke & Warwick 2001).
To analyse the specific composition of wrack on each beach, a non-metric multidimensional scaling (NMDS) was performed with the monthly relative bio mass of each species per location. Prior to this, data were logtransformed to calculate the Bray-
| 47 WRACK SUPPLY TO SANDY BEACHES
Curtis similarity index. Differences among groups of beaches were tested with ANOSIM. A similarity percentage (SIMPER) analysis was performed to find the species with the highest contribution to the similarity of each group.
2.3.2.2. Time-scale variability in wrack composition and biomass:
The relative biomass of each wrack taxon per month was used to analyse the temporal variability of the wrack composition for all locations together, and for each beach individually. Data were log-transformed to calculate the Bray-Curtis similarity index. The cyclic-RELATE procedure (Clarke & Warwick 2001) was used to assess the monthly variation. This analysis computes the Spearman correlation between the corresponding pair of months in the similarity matrix; each pair of data points is then compared with a model of cyclicity. NMDS ordinations were performed to visualize the monthly relationship in wrack composition. A 2-way PERMANOVA was carried out with the relative biomass of each species; beach (6 levels) and month (12 levels) were fixed factors.
Temporal variability in total wrack biomass among beaches was calculated using a 2-way ANOVA, again with beach (6 levels) and month (12 levels) as fixed factors. A posteriori multiple comparison analyses were performed using Student-Newman-Keul’s (SNK) tests (α = 0.05).
Multivariate analyses were conducted with the package PRIMER v6 (Clarke & Gorley 2006). Univariate analyses were performed with WinGMAV (http:// sydney.edu.au/science/bio/eicc).
| 48 CHAPTER II
2.4. RESULTS
2.4.1. Beach characteristics and wrack deposition
Multiple-regression analysis was performed to assess the extent to which the environmental variables selected affect wrack composition on each beach. Monthly data for species biomass (dry wt), length area ratio (L:A), wave height and 1/slope were included in the calculations (Table 2.2). Wrack biomass and composition were explained by L:A (24.7%, p = 0.001), wave height (23.0%, p = 0.001) and slope (11%, p = 0.001). The sequential test explained 44.3% of the variability.
Beaches were divided into 3 groups, defined on the basis of topographical and wave exposure characteristics in the constrained dbRDA ordination (ANOSIM, global R = 0.61, p = 0.001) (Fig. 2.3). PA and TO were characterized by the highest L:A ratios, low wave height and steep slope; AM, SA and LA were characterized by a low L:A, intermediate wave height and the flattest slope; BA was characterized by a low L:A, the greatest wave height and a steep slope.
Marginal tests Sequential tests Variable Pseudo-F %Var Pseudo-F %Var %Cum L/A 22.96 24.7 22.96 24.7 24.7 H 20.96 23.04 15.91 14.11 38.81 1/Slope 8.92 11.31 6.69 5.48 44.29
Table 2.2. Tests for relationship between wrack composition and selected physical variables using the distance-based multivariate analysis for linear models (DISTLM) (p = 0.001). In marginal tests, each variable is analysed separately. In sequential tests, the amount of each variable added to the model (best procedure) is conditional upon variables previously included. % var = percentage of the multivariate variance explained by variable; % cum = cumulative percentage of variance explained; L:A = ratio of beach length to beach area; H= wave height (m).
| 49 WRACK SUPPLY TO SANDY BEACHES
) ) 40 n n Beach o o i i t t a a i i AM r r 1/Slope a a v v BA l l a a t t 20 LA o o t t f f SA o o TO % % 9 9 . . PA 2 2 1 1 0 , , d d e e t t t t i i f f f f o o L/A H % % -20 9 9 2 2 ( ( 2 2 A A D D R R -40 -40 -20 0 20 40 60 RDA1 (70.1% of fitted, 31.1% of total variation)
Fig. 2.3. Distance-based redundancy analysis (dbRDA) ordination results for fitted model of wrack biomass and composition data (based on Bray- Curtis after log transformation) at each beach throughout the year versus explanatory variables. Beaches are grouped according to the environmental variables and wrack characteristics in: PA-TO, AM-LA-SA and BA. L:A = ratio of beach length to beach area; H = wave height). See Fig. 1 for site abbreviations
2.4.2. Time-scale variability in wrack composition and biomass
The average monthly biomass of wrack varied widely in the beaches studied (Fig. 2.4), ranging (along the transects) from 14 ± 5 to 9189 ± 3594 g m–1 (mean ± SE) of dry wt in BA and PA, respectively. Average annual coverage fluctuated between 0.1 m2 m–1 in BA (equivalent to 0.1% of beach width) and 9.7 m2 m–1 in PA (equivalent to 16% of
| 50 CHAPTER II
Taxonomic division Nº.spp PA TO AM LA SA BA Average Heterokontophycophyta 19 57 (±5.4) 57 (±7.3) 74 (±5.6) 83 (±2.2) 74 (±4.0) 81 (±6.1) 70.9 Rhodophycophyta 16 11 (±3.5) 2.8 (±0.4) 0.3 (±0.2) 0.2 (±0.1) 1 (±0.3) 6.2 (±1.6) 3.5 Chlorophycophyta 3 5 (±1.4) 15 (±3.1) 2.9 (±1.7) 1.8 (±0.5) 7 (±3.1) 1.1 (±0.7) 5.3 Magnoliophyta 2 0.2 ±0.1) 1.1 (±0.2) 0.6 (±0.2) 2 (±1.7) 4 (±1.4) 2.8 (±2.7) 1.8 Remains - 27 (±5.6) 25 (±4.9) 23 (±6.0) 13 (±1.5) 15 (±3.3) 9 (±3.7) 18.5
Table 2.3. Total number of wrack species and mean % biomass ± SE (n = 12) of each taxonomic division at the studied beaches. See Fig. 1 for site abbreviations beach width). A significant correlation was obtained between wrack biomass and coverage throughout the year (R2 = 0.81, p < 0.001).
A total of 38 species of macroalgae, 2 species of seagrasses and 1 specie of Cyanophyta were identified. Brown algae dominated the wrack with 19 species and accounted for 70% of the average annual biomass (Table 2.3). The number of species of red algae (16) was higher than that of green algae (3), although biomass values were more similar (3.5% and 5.3%, respectively). The contribution of seagrasses to total biomass was low. The group classified as ‘remains’ (amounting to 18.5% of the average annual biomass) corresponds to fragmented seaweeds that could not be identified due to their small size or excessively decomposed state. The main drift species, calculated on the basis of the total biomass of the 6 beaches, were Cystoseira spp., (30.3 ± 17.4%), followed by, Sargassum muticum (14.2 ± 7.1%), Saccorhiza polyschides (9.8 ± 8.6%), Fucus spp. (4.9 ± 4.0%), Ulva spp. (3.8± 4.6%), Himanthalia elongata (3.7 ± 6.9%) and Halydris siliquosa (3.3 ± 3.0%); contributions from other species amounted to less than 2%. Specific composition of wrack differed among the groups of beaches (see previous subsection) (ANOSIM, global R = 0.72, p = 0.001; Fig. 2.5). Of species appearing across several groups, Cystoseira spp. was the most abundant. Among beach groups, the largest influence of Cystoseira spp. was observed in the beaches exposed to intermediate wave action (AM, LA and SA); at these sites S. muticum and Fucus spp. also made their greatest contribution. In the more protected locations (PA and TO) a greater number of taxa were found; these beaches were characterized by the largest
| 51 WRACK SUPPLY TO SANDY BEACHES
contribution of S. polyschides and Ulva spp. At the beach with the strongest wave action (BA), the contribution of Zostera spp. and Ulva spp. was lowest, and that of H. elongata relatively high (Table 2.4).
Fig. 2.4. Monthly variability in wrack input among and within the 3 beach groups throughout the year. Lines denote aver- age monthly biomass at each beach. Error bars represent SE. y-axis is log scale
| 52 CHAPTER II
Fig. 2.5. Non-metric multidimensional scaling showing similar- ity of wrack species composition among and within beach groups, elaborated with standarized and log-transformed data. Average similarity across entire study: BA = 50.2% ; AM-LA- SA = 62.5% ; TO-PA = 61.9%. See Fig. 1 for site abbreviations
The monthly specific composition of wrack showed a cyclic correlation throughout the year both for all beaches combined (cyclic RELATE, ρ = 0.798; p = 0.001), and when each one was analyzed separately (cyclic RELATE: BA, ρ = 0.419; p = 0.001; AM, ρ = 0.467; p = 0.001; SA, ρ = 0.315; p = 0.001; LA, ρ = 0.497; p = 0.001; TO, ρ = 0.502; p = 0.001; PA, ρ = 0.702; p = 0.001) (Fig. 2.6).
The contribution of each taxon to the wrack composition shifted throughout the year, but this seasonal variation was different from beach to beach (PERMANOVA beach × month, Pseu do-F55, 360 = 7.03; p < 0.001). Despite the differences between beaches in each group, some trends were observed in the relative biomass of the dominant species (Fig. 2.7). In the more wave-protected locations (PA and TO) Cystoseira spp.
| 53 Table 4. Contribution to similarity (%) of the most abundant species stranded in each beach group. See Fig. 1 for site abbreviations
WRACK SUPPLY TO SANDY BEACHES
Beach group Wrack taxa Table 2.4. PA-TO AM-LA-SA BA Contribution to similarity (%) of the Chlorophycophyta most abundant Codium spp. 4.25 < 1 < 1 species stranded in Ulva spp. 11.44 3.37 < 1 each beach group. See Fig. 1 for site Rhodophycophyta abbreviations. Asparagopsis armata < 1 < 1 4.25 Gelidium spp. < 1 < 1 3.78 Plocamium cartilagineum 1.76 < 1 < 1 Others spp. 3.82 < 1 < 1 Heterokontophycophyta Cystoseira spp. 19.1 46.45 28.31 Dictyota dichotoma 4.86 < 1 < 1 Dictyopteris polypodioides 3.85 < 1 < 1 Fucus spp. 3.16 12.96 11.7 Halidrys siliquosa 7.45 3.21 6.49 Halopteris spp. 1.72 < 1 < 1 Himanthalia elongata < 1 < 1 19.18 Saccorhiza polyschides 17.72 < 1 4.11 Sargassum muticum 9.64 22.72 13.06 Magnoliophyta Zostera spp. 2.2 3.62 < 1 reached the highest values toward September, October and November, Sargassum muticum during April and May and Saccorhiza polyschides in March, August and September; Fucus spp. showed low values throughout the year. In the beaches subjected to intermediate wave action (AM, LA and SA), the lowest relative biomass of Cystoseira spp. was recorded in April, May and June, coinciding with the upper limit of S. muticum; the highest proportion of S. polyschides was observed during January, February (at AM), and September and October (at LA); the input of Fucus spp. was low but consistent from month to month. In the beach affected by the strongest wave environment (BA), the relative biomass of Cystoseira spp. did not follow a clear pattern throughout the year. The highest proportion of S. muticum was recorded in April, the relative biomass of S. polyschides increased from July to September, and the highest
| 54 CHAPTER II value for Fucus spp. was observed in January. Wrack biomass differed among beaches throughout the year (ANOVA beach x month, F55, 360 = 7.78; p < 0.001) (Fig. 2.4).
Wrack biomass was higher every month on beaches with the highest L:A and the lowest wave exposure (PA, TO or both) compared to beaches with more wave exposure, although during January, April and May, such differences were not significant (SNK test). The lowest biomass was measured on the most wave-exposed beach (BA). These differed significantly every month from the most sheltered beaches (PA and TO), but differences in biomass with intermediate L:A (AM, LA and SA) were not significant during June, September, October or November (SNK test). Total biomass was significantly different within each beach throughout the year, although no similar pattern was observed when all locations were considered over time.
Fig. 2.6. Seasonal variability in specific composition calculated for standardized and log-transformed wrack biomass data, (A) with all locations included; and (B) for each beach independently. See Fig. 1 for site abbreviations
| 55 WRACK SUPPLY TO SANDY BEACHES
Fig. 2.7 . Seasonal variability among predominant species found in wrack at each beach. Relative biomass of each species was average m – 1 and per beach. Error bars represent SE (n = 6)
| 56 CHAPTER II
2.5. DISCUSSION
In the present study, which set out to quantify habitat openness and permeability, the life cycle of the predominant species of macroalgae, together with various quantifiable physical features, explained the substantial variability seen in wrack dynamics on sandy beaches.
Variability at a spatial scale (i.e. from location to location) in total wrack biomass was greater than that observed on a temporal scale, with values ranging from 0.2 to 110 kg m–1 among sites and 1 to 51 kg m–1 among months. Stranded biomass was greater on beaches with higher L:A. This ratio assesses the relationship between ‘beach edge’ and ‘beach surface’. The higher it is the more edge is exposed to the donor ecosystem, therefore increasing the transfer of allochthonous materials. (Witman et al. 2004). In islands, for example, the amount of drift is a function of the length of the shoreline (Polis & Hurd 1996). Pocket beaches, or beaches inserted spatially along extensive rocky coasts (such as those in this study), could operate like island ecosystems with regard to volume of input received. Stranding of algae and seagrasses was greater in wave- protected environments than in exposed locations in the present study, which may be explained by a depositional process caused by a reduction in the flow of water that usually occurs around beach headlands (Komar 1998), or in rivers and streams (Witman et al. 2004). Low wave energy on the beach front causes a reduction in flow, which creates more favourable conditions for stranding wrack material.
The wide spatial variability in wrack biomass in this study is consistent with the extremely diverse data published on algae and seagrasses stranded on beaches: in South Africa, 2179 kg m–1 yr–1 (Stenton- Dozey & Griffiths 1983), 1200 to 1800 kg m–1 yr–1 (Koop et al. 1982) and 2920 kg m–1 yr–1 (McLachlan & Mc - Gwynne 1986) have been reported; 1000 to 2000 kg m–1 yr–1 have been reported in islands in the Gulf of California (Polis et al. 1997); 473 kg m–1 yr–1 in southern California, (Hayes 1974); 60 kg m–1 yr–1 in Canada
| 57 WRACK SUPPLY TO SANDY BEACHES
(Wildish 1988); 0.7 kg m–1 yr–1 in Kenya (Ochieng & Erftemeijer 1999); and in Australia, from 360 to 2900 kg m–1 yr–1 for macroalgae and from 900 to 1800 kg m–1 yr–1 for seagrass (Hansen 1984). Besides the inherent geographical variability and the frequency of resuspension and redeposition, which may complicate deposition rate estimates (Orr et al. 2005), we suggest that other factors such as wave exposure or the L:A ratio may help explain this variability.
Temporal variation in wrack biomass is a complex process. Some studies have registered a higher standing crop during winter (Koop & Field 1980, Stenton- Dozey & Griffiths 1983, Ochieng & Erfte meijer 1999), others in summer and autumn (Piriz et al. 2003, Kotwicki et al. 2005, Mateo 2010). We found significant differences in all the beaches over the course of the study. On the low-energy beaches wrack accumulations were higher during late summer (TO) and from summer to autumn (PA), but no clear trend was noted in stronger wave environments. This could indicate a more predictable scenario in the protected locations. We suggest that wrack accumulation on the low- energy beaches could mainly be determined by the life cycle of algae. During late summer and autumn senescence (e.g. Saccorhiza polyschydes), branch decay (e.g. Cystoseira baccata) and increases in biomass of opportunistic drifted species (e.g. Ulva spp.) are common processes in the study area. However, with increasing wave exposure, biomass deposition may be more dynamic and sensitive to other factors, such as strong winds or heavy wave action.
All the primary producers in the surrounding ecosystems can potentially drift ashore. Indeed, large amounts of brown algae and seagrass stranded on beaches have been reported close to kelp forest and seagrass beds (e.g. Stenton-Dozey & Griffiths 1983, Mateo 2010). On the Galician coast, rocky shores are dominated by brown seaweeds (mostly of the orders Laminariales and Fucales; Bárbara et al. 2005) and Zostera beds in sheltered estuarine environments. The number of species of red algae in this area is 4 times higher than that of green algae (Bárbara et al. 2005). Throughout this
| 58 CHAPTER II study, wrack composition was dominated by brown algae, and the ratio between red and green algae on sandy shores was similar to that reported on rocky shores. Clear differences were noted, however, in the species-specific contributions from location to location, a phenomenon that cannot be attributed only to the availability of macroalgae in surrounding ecosystems. For instance, at beaches with intermediate and high exposure to wave action, wrack was dominated by algae with air bladders in their structure (e.g. Cystoseira spp, Sargassum muticum, Fucus spp.), a factor which, by increasing buoyancy, might assist in them drifting ashore. Buoyancy properties have been considered important in the supply of organic matter to sandy beaches (Orr et al. 2005). We suggest that buoyancy properties may be relevant in the stranding wrack episodes in beaches subjected to high-energy wave environments.
The greatest number of stranded species was measured on the more sheltered beaches. On the one hand, a lower-energy environment might facilitate algal deposition on the beach front, and, on the other hand, reduced wave energy on the sheltered rocky shore may promote the occurrence of annual opportunistic algal species (Kraufvelin et al. 2009), which can increase wrack biodiversity. Both effects may explain the larger number of species found in the more protected locations.
The specific composition of wrack showed a cyclical pattern throughout the year. This ongoing compositional change indicates that the wrack-stranding process is linked to the life cycle of algae and seagrasses. This cyclic trend implies that the variable arrival of resources to sandy beaches over a period of months is, to some extent, predictable. Focusing on the algae with the largest biomass supplied to the sampled beaches, viz. Cystoseira spp. and Sargassum muticum, we observed that the biomass contributed by these species to wrack is consistent with their life-cycle traits. These 2 algae have significant differences in their seasonal growth cycles, Cystoseira spp. showing a similar growth rate in summer and winter, and S. muticum showing a slow growth rate in winter, and a faster rate in the spring (Arenas et al. 1995). As the year
| 59 WRACK SUPPLY TO SANDY BEACHES
progresses, these different traits produce dissimilar stocks of macroalgae in the rock habitat, which, once detached by waves and currents, can differentially subsidize sandy beaches over time. A further factor that has been suggested (in the population dynamics of S. muticum) is a ‘self-thinning process’, whereby the population becomes self-limiting as density increases (Harper 1977). The negative biomass–density relationship (as a measure of biomass accumulation-driven mortality) (Arenas & Fernández 2000), could increase the likelihood of occurrence of drifting S. muticum during the months with high growth rates (spring).
Our paper presents the first study on the temporal variability of wrack supply to sandy beaches over a range of environmental conditions. The results provide evidence that variability in such wrack supply can be explained through interactions between wave exposure, coastal topography and season. Differences in the source-community composition as well as differences in the buoyancy of macroalgae and seagrasses may influence wrack composition on beaches with different exposure rates (Orr et al. 2005). We did not quantify other potential factors, such as biomass in the donor areas, wind or currents. Our results provide evidence to support our initial hypothesis that smaller beaches, which have a higher L:A, namely a longer border with the donor ecosystem in relation to beach area, receive larger subsidies per unit surface area.
2.6. ACKNOWLEDGEMENTS
The authors thank L. Soliño, L. García, J. Hernández and I. Rodil for help with field work. Thanks are also due to L. García for valuable comments and C. Villaverde for advice on statistical techniques. We are very grateful to 3 anonymous reviewers for their insightful and constructive comments. This research was supported by the Ministerio de Ciencia y Tecnología (REN2002-03119), Xunta de Galicia- CETMAR (CO-150-07) and the Universidade de Vigo (C505122F64102).
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2.7. LITERATURE CITED
Anderson WB, Polis GA (2004) Allochthonous nutrient and food inputs: consequences for temporal stability. In: Polis GA, Power ME, Huxel GR (eds) Food webs at the landscape level. University of Chicago Press, Chicago, IL, p 82–95 Arenas F, Fernández C (2000) Size structure and dynamics in a population of Sargassum muticum (Phaeophyceae). J Phycol 36:1012–1020 Arenas F, Fernández C, Rico JM, Fernández E, Haya D (1995) Growth and reproductive strategies of Sargassum muticum (Yendo) Fensholt and Cystoseira nodicaulis (Whit.) Roberts. Sci Mar 1:1–8 Bárbara I, Cremades J, Calvo S, López-Rodríguez MC, Dosil J(2005) Checklist of the benthic marine and brackish Galician algae (NW Spain). An Jard Bot Madr 62:69– 100 Cadenasso M, Pickett STA (2000) Linking forest edge structure to edge function: mediation of herbivore damage. J Ecol 88:31–44 Clarke KR, Gorley RN (2006) PRIMER v6: user manual/tutorial. PRIMER-E, Plymouth Clarke KR, Warwick RM (2001) Change in marine communities: an approach to statistical analysis and interpretation. PRIMER-E, Plymouth Coupland G, McDonald J (2008) Extraordinarily high earthworm abundance in deposits of marine macrodetritus along two semi-arid beaches. Mar Ecol Prog Ser 361: 181–189 Crawley KR, Hyndes GA, Vanderklift MA, Revill AT, Nichols PD (2009) Allochthonous brown algae are the primary food source for consumers in a temperate, coastal environment. Mar Ecol Prog Ser 376:33–44 Duarte CM, Cebrian J (1996) The fate of marine autotrophic production. Limnol Oceanogr 41:1758–1766 Dugan JE, Hubbard DM, McCrary MD, Pierson MO (2003) The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of southern California. Estuar Coast Shelf Sci 58(Suppl): 25–40 Emery KO (1961) A simple method of measuring beach profiles. Limnol Oceanogr 6:90– 93 Foster MS, Schiel DR (1985) The ecology of giant kelp forests in California: a community profile. US Fish and Wildlife Service Biol Rep 85, Washington, DC Griffiths CL, Stenton-Dozey JME (1981) The fauna and rate of degradation of stranded kelp. Estuar Coast Shelf Sci 12: 645–653 Griffiths CL, Stenton-Dozey JME, Koop K (1983) Kelp wrack and the flow of energy through a sandy beach ecosystem. In: McLachlan A, Erasmus T (eds) Sandy beaches as ecosystems. Junk, The Hague, p 547–556 Hansen G (1984) Accumulations of macrophyte wrack along sandy beaches in Western Australia: biomass, decomposition rate and significance in supporting nearshore production. PhD dissertation, University of Western Australia
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Harper JL (1977) Population biology of plants. Academic Press, London Hayes WB (1974) Sand beach energetics: importance of the isopod Tylos punctatus. Ecology 55:838–847 Hobday AJ (2000) Abundance and dispersal of drifting kelp Macrocystis pyrifera rafts in the Southern California Bight. Mar Ecol Prog Ser 195:101–116 Ince R, Hyndes GA, Lavery PS, VanderkliftMA (2007) Marine macrophytes directly enhance abundances of sandy beach fauna through provision of food and habitat. Estuar Coast Shelf Sci 74:77–86 Inglis G (1989) The colonisation and degradation of stranded Macrocystis pyrifera (L.) C. Ag. by the macrofauna of a New Zealand sandy beach. J Exp Mar Biol Ecol 125: 203–217 Jedrzejczak MF (2002) Stranded Zostera marina L. vs. wrack fauna community interactions on a Baltic sandy beach (Hel, Poland): a short-term pilot study. Part I. Driftline effects of fragmented detritivory, leaching and decay rates. Oceanologia 44:273–286 Kirkman H (1984) Standing stock and production of Ecklonia radiata (C.Ag.): J. Agardh. J Exp Mar Biol Ecol 76:119–130 Komar PD (1998) Beach processes and sedimentation. Prentice-Hall, Englewood Cliffs, NJ Koop K, Field JG (1980) The influence of food availability on population dynamics of a supralittoral isopod, Ligia dilatata Brandt. J Exp Mar Biol Ecol 48:61–72 Koop K, Newell RC, Lucas MI (1982) Biodegradation and carbon flow based on kelp (Ecklonia maxima) debris in a sandy beach microcosm. Mar Ecol Prog Ser 7:315–326 Kotwicki L, We˛ s8awski JM, Raczynska A, Kupiec A (2005) Deposition of large organic particles (macrodetritus) in a sandy beach system (Puck Bay, Baltic Sea). Oceanologia 47:181–199 Kraufvelin P, Lindholm A, Pedersen MF, Kirkerud LA, Bonsdorff E (2009) Biomass, diversity and production of rocky shore macroalgae at two nutrient enrichment and wave action levels. Mar Biol 157:29–47 Lastra M, Page HM, Dugan JE, Hubbard DM, Rodil IF (2008) Processing of allochthonous macrophyte subsidies by sandy beach consumers: estimates of feeding rates and impacts on food resources. Mar Biol 154:163–174 Mann KH (1973) Seaweeds: their productivity and strategy for growth. Science 182:975–981 Marsden ID (1991) Kelp–sandhopper interactions on a sand beach in New Zealand: I. Drift composition and distribution. J Exp Mar Biol Ecol 152:61–74 Mateo MA (2010) Beach-cast Cymodocea nodosa along the shore of a semienclosed bay: sampling and elements to assess its ecological implications. J Coast Res 26:283–291 Mateo MA, Cebrian J, Dunton K, Mutchler T (2006) Carbon flux in seagrass ecosystems. In: Larkum AWD, Orth RJ, Duarte DM (eds) Seagrasses: biology, ecology and conservation. Springer, Dordrecht, p 159–192 McArdle BH, Anderson MJ (2001) Fitting multivariate models to community data: a comment on distance-based redundancy analysis. Ecology 82:290–297 McLachlan A (1980) The definition of sandy beaches in relation to exposure: a simple rating system. S Afr J Sci 76: 137–138 McLachlan A, Brown AC (2006) The ecology of sandy shores, 2nd edn. Elsevier, Amsterdam McLachlan A, McGwynne L (1986) Do sandy beaches accumulate nitrogen? Mar Ecol Prog Ser 34:191–195 Mews M, Zimmer M, Jelinski DE (2006) Species-specific decomposition rates of beach-cast wrack in Barkley Sound, British Columbia, Canada.Mar Ecol Prog Ser 328: 155–160
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Ochieng CA, Erftemeijer PLA (1999) Accumulation of seagrass beach cast along the Kenyan coast: a quantitative assessment. Aquat Bot 65:221–238 Orr M, Zimmer M, Jelinski DE, Mews M (2005) Wrack deposition on different beach types: spatial and temporal variation in the pattern of subsidy. Ecology 86:1496–1507 Piriz ML, Eyras MC, Rostagno CM (2003) Changes in biomass and botanical composition of beach- cast seaweeds in a disturbed coastal area from Argentine Patagonia. J Appl Phycol 15:67–74 Polis GA, Hurd SD (1996) Linking marine and terrestrial food webs: allochthonous input from the ocean supports high secondary productivity on small islands and coastal land communities. Am Nat 147:396–423 Polis GA, Anderson TW, Holt RD (1997) Toward an integration of landscape and food web ecology. Annu Rev Ecol Syst 28:289–316 Polis GA, Sánchez Piñero F, Stapp P, Anderson WB, Rose MD (2004) Trophic flows from water to land: marine input affects food webs of islands and coastal ecosystems worldwide. In: Polis GA, Power ME, Huxel GR (eds) Food webs at the landscape level. University of Chicago Press, Chicago, IL, p 200–216 Ray GC, Hayden BP (1992) Coastal zone ecotones. In: Hansen AJ, di Castri F (eds) Landscape boundaries: consequences of biotic diversity and ecological flows. Springer-Verlag, New York, NY p 403–420 Spiller DA, Piovia-Scott J, Wright AN, Yang LH, Takimoto G, Schoener TW, Iwata T (2010) Marine subsidies have multiple effects on coastal food webs. Ecology 91:1424–1434 Stenton-Dozey JME, Griffiths CL (1983) The fauna associated with kelp stranded on a sandy beach. In: McLachlan A, Erasmus T (eds) Sandy beaches as ecosystems. Junk, The Hague, p 557–568 Vetter EW (1994) Hotspots of benthic production. Nature 372: 47 Wernberg T, VanderkliftMA, How J, Lavery PS (2006) Export of detached macroalgae from reefs to adjacent seagrass beds. Oecologia 147:692–701 Wildish DJ (1988) Ecology and natural history of aquatic Talitroidea. Can J Zool 66:2340–2359 Witman JD, Ellis JC, Anderson WB (2004) The influence of physical processes, organisms, and permeability on cross-ecosystems fluxes. In: Polis GA, Power ME, Huxel GR (eds) Food webs at the landscape level.
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III. Coupling between macroalgal inputs and nutrients outcrop in exposed beaches
Barreiro F., Gómez M., López J., Lastra M, de la Huz R. (2013) Hydrobiologia 700: 73-84
NUTRIENT OUTCROP FROM EXPOSED BEACHES
3.1. ABSTRACT
Fluxes of nutrients across habitats are of paramount relevance in ecological studies due to the implication in primary production, trophic structure and biodiversity. This study analyses the role of sandy beaches in the processing of organic matter. Three beaches with different macroalgal inputs were sampled throughout the annual cycle. The standing stock of wrack macroalgae on the beach surface and the nutrient concentration in the intertidal pore water (IPW) and in the surf zone water were measured monthly. Mean concentration of dissolved inorganic nitrogen and phosphate in the IPW increased from the low to the very high subsidized beach. Seasonal coupling was observed between the wrack biomass and the nutrient concentration throughout the year. Among the nutrient species, a variable relationship was found between the
+ ¯ NH4 /NOx ratio and the biomass of macroalgae deposited. These results provide evidences of the active role of sandy beaches in the processing of organic matter and in the nutrient cycling, remarking the feedback connectivity between sandy beaches and their neighbour ecosystems.
KEY WORDS: Sandy beaches · Nutrients · Connectivity · Spatial subsidy · Marine- terrestrial ecotone · Wrack · Ecosystem function · Intertidal
| 66 CHAPTER III
3.2. INTRODUCTION
The coastal zone is a dynamic interface between marine and terrestrial ecosystems. The transfer of nutrients and energy through the coastline is a common process (Anderson & Polis 1999, Burnett et al. 2003, Catenazzi & Donnelly 2007, Strayer & Findlay 2010) significantly affecting the functioning of the receiving system (Polis et al. 1997). One of the most studied components in the connectivity between the terrestrial and the aquatic ecosystems is the nutrient supply through pore water discharge. (Moore 1996) estimated that groundwater flux to the coastal water accounts for about 40% of the river-water flux and suggested the importance of this process in the transfer of nutrients to the global ocean. At the ecosystem level, pore water discharge has been recognized as ecologically relevant in salt marshes, estuaries, tidal flats and beaches, as well as in subtidal environments through submarine groundwater discharges (Billerbeck et al. 2006).
Sandy beaches comprise two-thirds of the world’s ice-free coastlines (McLachlan & Brown 2006). Exposed beaches are characterized by filtering large volumes of seawater due to the hydraulic gradients resulting from tides, waves and aquifer recharge (McLachlan & Brown 2006). During this process, the interstitial environment is supplied with dissolved organic matter from the sea (McLachlan & Brown 2006). (Pearse et al. 1942) pointed out the importance of beaches in the processing of organic matter as well as their role as a provider of resources to the ocean. High concentrations of carbon, nitrogen and phosphorous have been measured nearby of stranded algae (Koop & Lucas 1983, McLachlan & Brown 2006), and even the inputs of nitrogen in ocean beaches have been suggested to be cycled rapidly and returned to the sea (McLachlan & Brown 2006). However, biogeochemical studies in the intertidal sediments have been mainly focused on estuarine areas, due to its higher organic content (Boudreau et al. 2001). Recently, it has been reported that the decomposition rates of organic matter in permeable sands can exceed than those of fine sand (Boudreau et al. 2001, Rusch et al.
| 67 NUTRIENT OUTCROP FROM EXPOSED BEACHES
2006), and several studies suggest the relevance of high energy beaches in the processing of the organic matter and in the nutrients cycles (Billerbeck et al. 2006, Avery et al. 2008, Rocha 2008, Anschutz et al. 2009). In addition, beaches are often subjected to freshwater discharges from the outflow of terrestrial aquifers through the intertidal, or just by the runoff. Both processes increase the amount of nutrients supplied to the coastal ecosystems (Page et al. 1995, Horn 2002, Ullman et al. 2003, Hays & Ullman 2007a).
Wrack is a potential source of organic matter to the interstitial space. In many coastal regions, extensive amounts of macroalgae and seagrasses are drifted from neighbour ecosystems to sandy beaches (Stenton-Dozey & Griffiths 1983, Hobday 2000, Dugan et al. 2003, Mateo 2010). Following deposition, all this organic matter starts to be fragmented, decomposed and mineralized by the beach macrofauna, meiofauna and bacteria (Koop et al. 1982, Mews et al. 2007, Coupland & McDonald 2008, Lastra et al. 2008, Urban-Malinga & Burska 2009); the environmental conditions can intensify this process (Harrison 1989). Macroalgae decay involves a rapid breakdown of biomass, resulting in release of nutrients and CO2 (Buchsbaum et al. 1991, Chapin et al. 2002, García-Robledo et al. 2008, Hardison et al. 2010). The conversion of organic matter into inorganic nutrients is considered a key ecosystem service that connects decomposed algal wrack biomass with primary producers and consumers (Catenazzi & Donnelly 2007).
In this study, we examine the spatial and temporal variability of nutrients released to the ocean in three exposed beaches of the NW coast of Spain. Specifically, we investigate the relationship between the wrack magnitude and the concentration of nutrients in intertidal water over a year cycle as an indirect indicator of the biogeochemical role of ocean beaches in the organic matter processing. We hypothesized that there is a spatial and temporal coupling between the nutrients released and the wrack biomass accumulated.
| 68 CHAPTER III
3.3. MATERIALS AND METHODS
3.3.1 Field sampling design
Three beaches differentially subsidized by wrack macroalgae were sampled in the Galician coast (NW Spain) (Fig. 3.1): Balieiros (BA), which receives very low amounts of macroalgae (14 ± 5 g m-1 of dry weight (mean ± SE)); Toralla (TO), with large inputs (1116 ± 464 g m-1 of dry weight); and Abra beach (PA), with very large deposits of stranded algae (9189 ± 3594 g m-1 of dry weight) (Fig 3.2). The three beaches are oceanic with steep slope and medium-to-coarse sand (Table 1). Field sampling was carried out monthly during low spring tides in a year cycle from December 2007 to November 2008. Tidal conditions were mesomacrotidal, with spring tides ranging from 3.5 to 4.
An area of 100-m long stretch in the centre of each beach was selected to quantify the total inputs of wrack. All species of macroalgae stranded along six 1-m transects randomly spaced from the base of the dune to the lowest swash level were collected, identified, ovendried and weighed. Total and species biomass were estimated for each beach as the average of the six transects per sample day. Details of the wrack biomass assessment are given in Chapter 2. To describe the wrack distribution along the beach surface, the percentage of cover was calculated for each 10 m of intertidal width from the base of the dune to the lowest swash level (n = 6) using the line intercept method (Dugan et al. 2003). The intertidal width was standardized to enable comparisons among beaches.
The samples for the nutrient assessment were taken in the same area and at the same time that the wrack biomass estimation was being conducted. To analyze the nutrient concentration in intertidal pore water (IPW), three sample points, randomly spaced over a 100-m long stretch in the centre of each beach, were taken at the upper limit of the water table outcrop. A hole to a depth where pore water filled the bottom of the excavation was made at each sample point. In each hole, interstitial triplicate water
| 69 NUTRIENT OUTCROP FROM EXPOSED BEACHES
Fig. 3.1 Sampled beaches on the NW coast of the Iberian Peninsula. Balieiros (BA), Toralla (TO) and Abra (PA).
Fig. 3.2 Monthly variability of wrack biomass (dry weight) among and within the study beaches throughout the year. Dotted lines denote the average monthly biomass in each beach. Error bars represent standard
| 70 CHAPTER III samples of 150 ml were collected and stored in polypropylene bottles. Once in the lab, samples were filtered to remove any particulate material (with quantitative filter paper of 2-4 µm) and immediately stored at -30 ºC until analysis. Water samples at the surf zone (SZW) were also collected at three points randomly spaced over a 100-m long stretch in the centre of each beach. In each point, three bottles of 150 ml were filled,
+ filtered and stored at -30ºC as in IPW samples. Salinity and concentrations of NH4 ,
3 NO3‾, NO2‾ and PO4 ‾ were determined for each sample and averaged per sample point to minimize the methodological variability (n = 3). SZW samples collected in December, January and February were not included in this study due to technical problems during the storage.
Triplicate sediment samples for granulometry analyses were taken in the same points where IPW was collected. Mean grain size was estimated by dry sieving (Folk 1980) and porosity (vol. %) was calculated by the gravimetric-volumetric technique determining the weight loss of the saturated sediment after drying at 60 ºC until constant weight (Giere et al. 1988). Beach slope was estimated using Emery’s profiling technique (Emery 1961).
3.3.2. Nutrient analysis
The inorganic dissolved nutrient concentrations were quantified by continuous flow analysis (CFA) with a Bran Luebbe Auto-Analyzer AA3. The Berthelot reaction was used to determine the ammonium concentration (absorbance measured at 660 nm); determination of nitrites was carried out by measuring the absorbance at 550 nm after reacting with sulphanilamide and N-1-napthylethyleneidiamine dihydrochloride; Nitrates were converted to nitrites and measured as above. Phosphates were determined with the ammonium molybdate and ascorbic acid reaction, measuring absorbance at 880 nm. These analyses were carried out in the ‘‘Elemental Analysis Unit’’ of the University of Vigo.
| 71 NUTRIENT OUTCROP FROM EXPOSED BEACHES
Fig 3.3. Location of the sampling points for the nutrient content analyses across the beach profile. Surf zone water (SZW) and Intertidal pore water (IPW).
3.3.3. Statistical analysis
The relationships between monthly wrack biomass with phosphate and total dissolved inorganic nitrogen (DIN) concentration in the IPW and SZW were examined using ordinary least square (OLS) regressions. Data of monthly wrack biomass are given
+ in Barreiro et al. (2011). A quantile regression was carried out between the NH4 / NOx‾ ratio and the wrack biomass (NOx‾ denotes the sum of NO2‾ + NO3‾) to explore the potential relationship between the nitrogen stoichiometry and the macroalgal decomposition. This method is suitable when the statistical distribution of ecological data have unequal variation which implies that there is more than a single slope describing the relationship between a response and a predictor variables measured on a subset of these factors (Cade & Noon 2003). Linear regression models for quantiles
+ ranging from 10 to 90% by steps of 10% were used to describe how the NH4 / NOx‾ ratio varied according to the biomass of wrack stranded on the beach surface. The statistical software packages BLOSSOM (Midcontinent Ecological Science Centre, Colorado) was used for the quantile regression analyses.
Differences in the phosphate and DIN concentration in the IPW among beaches throughout the year were tested with an orthogonal two-way ANOVA. Month (with 12
| 72 CHAPTER III levels) and beach (with 3 levels) were fixed factors. In addition, a comparison between phosphate and DIN concentrations among beach zones between March and December was conducted with a three-way orthogonal ANOVA. Month (9 levels), beach (3 levels) and zone (2 levels) were fixed factors. Samples were log-transformed prior to the analysis to meet the assumptions of normality and homogeneity of variances. A posteriori multiple comparisons analyses were performed using Student-Newman-Keuls (SNK) test (a = 0.05).
3.4. RESULTS
3.4.1. Beach characteristics
The mean beach width during the sampling days fluctuated between 45 ± 6 and 75 ± 10 m among beaches. This variability is caused by differences of the low spring tide height through the year and leads to oscillations of the effluent line. Porosity ranged between 41 ± 2 and 44 ± 3% of the total volume of the sediment. The height of the breaking wave in BA (2 ± 1 m) was considerable higher than in PA and TO (0.20 ± 0.05 and 0.18 ± 0.05 m, respectively) resulting in a different exposure rate (McLachlan 1980) among beaches. The mean grain size was higher and more variable throughout the year in PA than in TO and BA (Table 1).
The effluent line was located always below the wrack deposits. The steep slope and the low intertidal width of the studied beaches caused that the water table outcrop were located close to the swash level. The wrack distribution along the beach was very dynamic in PA and TO and scarce in BA. The average wrack coverage in each region of
Beach Maximum Mean Drift Efluent MGS Porosity Exposure Beach length (m) width (m) width (m) line(m) line (m) 1/ Slope (µm) (vol %) rate Balieiros 840 100 75 (±10) 8 (±7) 57 (±7) 10.9 731 (±217) 44 (±3) 18 Toralla 100 60 45 (±6) 6 (±3) 40 (±2) 13.8 711 (±199) 46 (±2) 10 Abra 210 60 51 (±6) 12 (±6) 45 (±5) 9.8 1123 (±672) 41 (±2) 11
Table 3.1. Physical characteristics of studied beaches.
| 73 NUTRIENT OUTCROP FROM EXPOSED BEACHES
Fig. 3.4. Percentages of wrack cover across the width of each beach. To enable comparison among beaches, the beach width was standardized from the base of the dune (1.0) to the lowest swash level (0.0).
the beach was higher in PA than in TO with the exception of the zone closer to the dune (Fig. 3.4).
The average monthly concentration of total DIN in IPW varied between 41 ± 4 (BA) and 105 ± 20 (PA) lM among beaches. In each beach, the lowest concentration of total DIN was measured in the surf zone water (SZW), with values ranging from 35 ± 5 (BA) to 50 ± 7 (PA) lM. The mean concentration of phosphate in IPW fluctuated between 0.7 ± 0.1 (BA) and 2.2 ± 0.6 (PA) lM. As with total DIN, the lowest concentration of phosphate in each beach was found in the SZW (ranging from 0.21 ± 0.1 (BA) to 1.1 ± 0.6 (PA) µM). The salinity was similar among beaches and between sample zones (Table 2).
3.4.2. Dissolved nutrients and wrack biomass
The quantity of wrack spread on each beach throughout the annual cycle had a significant influence on the total DIN and phosphate concentrations of the IPW (Fig. 3.5). This relationship was stronger for total DIN (R2 = 0.41, P < 0.001) than that for phosphate
| 74 CHAPTER III
IPW SZW BALIEIROS TORALLA ABRA BALIEIROS TORALLA ABRA S ‰ 33.9±0.6 33.7±0.5 31.5±0.6 34.9±0.1 33.7±0.5 33.5±0.4 -3 PO4 0.7±0.1 1.6±0.2 2.2±0.6 0.2±0.1 0.4±0.1 1.1±0.6 - NO2 0.7±0.3 1.1±0.4 1.5±0.5 0.3±0.1 0.5±0.1 0.5±0.2 - NO3 14.1±3.2 24.6±2.1 25.6±8.6 7±3.0 10±4.1 6.8±2.9 + NH4 26.8±2.6 31.1±1.3 77.8±22 27.8±2.0 35.2±2.8 43±4.3 TDIN 41.7±4.2 56.9±2.7 105.0±19.7 35.2±4.6 45.8±6.7 50.4±7.3
Table 3.2. Salinity (%) and average monthly concentration of dissolved nutrients (lM) in IPW (±SE, n = 12) and SZW (±SE, n = 9).
(R2 = 0.29, P < 0.001). The relationship between the wrack biomass stranded in each beach and the nutrient concentration measured in the SZW was weaker than in the IPW although also statistically significant (R2 = 0.12, P < 0.001 and R2 = 0.14, P < 0.001 for total DIN and phosphate, respectively).
+ The quantile regression between the NH4 / NOx‾ ratio in the IPW and the wrack biomass show unequal relations for both variables at different portions of the probability distribution. This is evidenced by the significant changes in the slope of the different regression quantiles. While the slopes for the quantiles 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7 were not significantly different of zero, there were a significantly positive slope for the quartiles 0.8 and 0.9. This means that for the upper 20% of the distribution, there was an increasing positive relation between both variables (Fig 3.6; see Table B.1 in Appendix B).
3.4.3. Intertidal pore water (IPW)
At each month throughout the year, the highest dissolved nutrients concentration in IPW was measured in the highly and very highly subsidized beaches (TO and PA). However, there were significant beach x month interaction in each comparison (DIN and
| 75 NUTRIENT OUTCROP FROM EXPOSED BEACHES
PO4, Table B.2 in Appendix B). Total DIN differed significantly among beaches in May, August, September and October (SNK test). In May and September, there were no significant differences between the high (TO) and very high (PA) subsided beaches, while in August and October total DIN concentration was significantly higher in the very high subsidized beach (PA). Notable was the lack of nitrate and nitrite in PA between August and November; during these months, where ammonium was the dominant inorganic nitrogen species (Fig. 3.7). The phosphate concentration during September, October and November was significantly higher in the very highly subsidized beach (PA). During January, March and July, phosphates were significantly lower in the less subsidized beach (BA). There were no significant differences among beaches during the rest of the months (Fig. 3.8).
Fig.3.5. Relationship between the monthly wrack biomass (standing stock) with the total DIN and phosphate concentration in the intertidal (n = 12) and surf water (n = 9) collected during the study. Data has been previously log (x ? 1) transformed. Best fits of each model to data points were obtained from linear regression (±95% CI—dotted lines). Balieiros (BA), Toralla (TO) and Abra (PA).
| 76 CHAPTER III
Fig. 3.6 Relationship ¯ between the NH4+/NOx ratio measured in the IPW and the wrack biomass deposited on the beach throughout the year (n = 36). Solid lines denote the regression quantile estimates between 0.1 and 0.9 (see Table B.1 in Appendix B).
A lesser variability was observed in the comparison within beaches. The nutrient content did not differ throughout the year in BA neither in TO. However, in PA, TDIN was significantly higher in August and phosphate was significantly higher in July, September, October and November.
3.4.4. Surf zone water (SZW)
The nutrient content in the SZW increased from the low to the high subsidy beaches (Table 2). However, comparisons of the concentration of nutrients in the SZW among beaches are more complex as it is indicated by the interaction beach × zone x month (Table B.3 in Appendix B). The SNK shows that in the SZW, TDIN was significantly higher in PA during July and September and in TO during November (Fig. 3.7). The phosphate concentration in the SZW was also significantly higher in PA during July and September, in TO during November, and in PA and TO during March (Fig. 3.8).
| 77 NUTRIENT OUTCROP FROM EXPOSED BEACHES
Fig. 3.7. Monthly values of the species of DIN in IPW throughout the year and in the SZW between March and November. The average monthly concentration of total DIN is denoted by a short-dash line for the IPW and by a dotted line for the SZW. Error bars represent standard errors (n = 3)
Comparisons within beaches show that TDIN did not varied throughout the year in each beach. The phosphate content in PA was significantly higher during September (Fig. 3.8).
3.4.5. IPW versus SZW
Although the average concentration of inorganic dissolved nutrients was lower in the SZW than in the IPW in all the sampled beaches, values differed among and within beaches over time (Table B.3 in Appendix B). Within each beach, the DIN concentration was significantly higher in the IPW than that in the SZW during October in BA; September and October in TO; May, June, August, October and November in PA (Fig. 3.7). The phosphate concentration was significantly higher in the IPW than in the surf during May, July and October in BA; May, June, July, October and November in TO; May, July–August, September and October in PA (Fig. 3.8).
| 78 Fig. 7 Monthly values of the phosphate concentration in IPW throughout the year and in the SZW between March and November. The average monthly phosphate concentration is denoted by a short-dash line for the IPW and by a dotted line for the surf zone water. Error bars represent standard errors (n = 3)
CHAPTER III
Fig. 3.8. Monthly values of the phosphate concentration in IPW throughout the year and in the SZW between March and November. The average monthly phosphate concentration is denoted by a short-dash line for the IPW and by a dotted line for the surf zone water. Error bars represent standard errors (n = 3)
3.5. DISCUSSION
This study shows that the spatial and temporal variability of nutrients released from intertidal sediments in exposed sandy beaches is related with the magnitude of the wrack subsidies that reach the beach. In addition, some evidences of nutrient enrichment in the SZW were detected, suggesting the influence of beach-linked nutrient cycling in the surrounding ecosystems.
The wide spatial and temporal variability observed during the study period, both in total DIN and in phosphate concentration, is in accordance with the complex and dynamic biogeochemical processes that take place in the intertidal environments of sedimentary shores (Jickells & Rae 1997). It is known that among the multiple abiotic
| 79 NUTRIENT OUTCROP FROM EXPOSED BEACHES
factors affecting intertidal areas, runoff events and groundwater discharge have a significant influence in the nutrient recycling (Page et al. 1995, Uchiyama et al. 2000, Hays & Ullman 2007b, Rocha et al. 2009, Waska & Kim 2011). However, at the studied sites, the freshwater influence seems to be low, as the salinity of the pore and SZW throughout the year range from 34.9 ± 0.6 to 31.5 ± 0.6. The higher nutrient concentration in IPW compared with the SZW should be mainly related to mineralization processes carried out on the beach face.
Recent studies have characterized sandy beach sediments as active biogeochemical reactors (Anschutz et al. 2009). It is a known fact that large quantities of particulate and dissolved organic carbon (POC and DOC) in addition to oxygen are introduced from the coastal waters into the interstitial space. This material is mineralized increasing the nutrient content in the interstitial water (McLachlan & Brown 2006). In the beach with scarce wrack deposits (BA), this process may explain the higher average nutrient concentration measured in the IPW in relation to the SZW. While when the inputs of macroalgae are of relevance (TO and PA), the nutrient content may be released from the mineralization of the DOP, POM and/or the wrack deposits. Coastal waters contain between 0.1 and 10 g C m-3 of DOC and similar levels of POC and filtration in intermediated beaches may range between 1 and 12 m-3 m-1 d-1 (McLachlan & Brown 2006). The mean biomass in the high and very high subsidized beaches fluctuated between 1116 ± 464 and 9189 ± 3594 g m-1 of dry mass (in TO and PA, respectively) which has given the high metabolic rates quantified in algal wrack communities (Coupland et al. 2007) may represent a relevant proportion of the organic matter mineralized. In this sense, the significant relationship observed between the wrack biomass and the released nutrients may be indicative of the prominent influence of the stranded wrack in the net mineralization on sandy beaches, thus, outlining the role of these environments as sites of active organic turnover (Boudreau et al. 2001, Ehrenhauss & Huettel 2004, Rocha 2008).
| 80 CHAPTER III
The nutrient content of IPW has been related with the total inputs of organic matter stranded on beaches in different geographical regions (Koop & Lucas 1983, McGwynne et al. 1988, Nedzarek & Rakusa-Suszczewski 2004, Rauch et al. 2008, Anschutz et al. 2009, Swarzenski & Izbicki 2009, Dugan et al. 2011). The highest nutrient concentration obtained in the IPW of the very high subsidized beach (Abra) did not reach the values measured in other geographical areas, such as South Africa and California (Koop & Lucas 1983, McGwynne et al. 1988, Dugan et al. 2011) where kelp forest supply massive amounts of macrophyte wrack to the sandy shores. Higher interstitial water circulation leads to a decrease in nutrient concentration, and, in turn, water fluxes depend on multiple factors such as grain size, beach slope, permeability or the tidal cycle (Yin & Harrison 2000, McLachlan & Brown 2006, Wilson et al. 2008). Thus, beaches with similar release of nutrients could differ in the instantaneous nutrient concentration. In this case, the physical characteristics of the study beaches (high porosity, steep slope and coarse grain size) are indicative of a high water flow. Conversely, geographical and local differences among the coastal waters, both in the organic matter as in the nutrients concentration, may increase the variability of the intertidal nutrients released; in this sense, the Galician coast is situated along the northern boundary of the Canary upwelling system (Wooster et al. 1976), which injects large amounts of nutrients to the coastal zone and sustains a high primary productivity (Alvarez-Salgado et al. 1996, Prego et al. 1999, Figueiras et al. 2002, Bode et al. 2004). These differences in oceanographic conditions of the surrounding coastal waters may complicate comparisons between beaches (Lastra et al. 2006).
Among the different nutrient species dissolved in the IPW and SZW throughout the year, DIN showed a larger range of variation between beaches and sampling zones than phosphate. However, both were significantly related with the amount of wrack stranded on the beach surface, and both showed a significant spatio-temporal variability. The low structural complexity of macroalgae as well as their potentiality to
| 81 NUTRIENT OUTCROP FROM EXPOSED BEACHES
store large quantities of nutrients causes a rapid leaching of organic compounds and inorganic nutrients during the algal decay (Chapman & Craigie 1977, Tenore & Hanson 1980, Williams 1984, Hanisak 1993).Thus, high concentration of nutrients are usually detected below macroalgae patches in beach sediments (Rossi & Underwood 2002, Corzo et al. 2009). Indeed, in several beaches, the highest nutrient content was detected close to the drift line (Swarzenski & Izbicki 2009, Dugan et al. 2011). Nutrients may be used by the microphytobenthos and/or the microbial community, stored in the sediment or diluted in the seawater. This could explain the decrease in the nutrient concentration from IPW to SZW observed in this study. Indeed the swash is a very dynamic zone where intertidal water is actively mixing with seawater. The hydrodynamic conditions of each beach as well as their spatial and temporal variability and weather conditions may complicate the evaluation of the nutrient content from the interstitial zone. However, despite of all these constraints, the average concentration in the SZW increased from low to very high subsidized beaches. In addition, the increase was significantly higher in the beach and month with larger inputs. This could be indicated by the potential influence of wrack decomposition in the neighbouring ecosystems.
Despite to the active role of sandy sediments in the nitrogen cycle, the influential factors regulating nitrification are poorly understood (Strauss & Lamberti
+ 2000, Avery et al. 2008). The observed changes in the NH4 / NOx‾ ratio in this study are indicatives of the variable nitrogen stoichiometry according to the total wrack stranded on the beach surface. Above the quantile 0.8, the regression model shows positive and
+ increasing slopes between the NH4 / NOx‾ ratio and the wrack biomass. This suggests a positive and increasing release of ammonium as well as a negative and decreasing of nitrates and nitrites above this quantile. The variance of the distribution also increased at this point which seems to indicate that the total amount of algae is a limiting factor controlling the release of ammonium, albeit may interact with other variables which
| 82 CHAPTER III were not measured in this study. The ammonium released from macroalgae decomposition may be transformed into NO2‾ and NO3‾ by nitrification or consumed by heterotrophic bacteria and/or benthic microalgae (García-Robledo et al. 2008). However, with large amounts of wrack, oxygen availability could be depleted in deeper layers by limitation in gas transport and/or consumption by associated macro-, meio- and microfauna (Coupland et al. 2007, García-Robledo et al. 2008). Macroalgae decomposition under oxygen limitation results in a predominant releasing of ammonium (Bourguès et al. 1996). Similar results were observed by (Dugan et al. 2011) in beaches with very high wrack subsidies in California.
A rapid loss of phosphate during macrophyte decomposition was also quantified in laboratory experiments (Sassi et al. 1988). In the oxidized surface sediment, a major portion of the organic phosphorous is mineralized, and the released phosphate leads to a balance between the pore water and the sediment absorption (Sundby et al. 1992). In addition, a strong consumption of phosphate by the bacterial community during the initial algae decay has been suggested (García-Robledo et al. 2008). Both processes could explain the low range of phosphate measured over the study period.
The temporal variability in nutrients supply from sandy beaches to coastal waters seems to be coupled with the temporal deposition of macroalgae on the beach surface. Despite the significant differences among and within beaches throughout time, the nutrients releases tended to be higher in the beaches and during the months with the largest algal subsidies. In addition to the total wrack biomass, other temporally variable factors such as temperature, wrack composition or macrofaunal community (not considered in this study), must have a notorious influence in the decomposition and, thus, in the nutrient dynamics (Hanisak 1993, Mews et al. 2007, Rodil et al. 2008). All these factors should be considered in explaining the observed differences in the nutrients outcrop released between months with similar algal inputs.
| 83 NUTRIENT OUTCROP FROM EXPOSED BEACHES
The spatial and temporal coupling found between the wrack biomass and nutrients is indicative of the active role of sandy beaches in organic matter and nutrient cycling. However, this relationship for the different nutrient species versus biomass was not linear, pointing to the complexity of the biogeochemical pathways linked with the wrack processing in sandy sediments. This study provides evidences that sandy beaches act as a donor ecosystem of nutrients to the coastal zone, thus noting the substantial feedback connectivity between high productive macrophyte based environments, such as rocky shores and salt marshes, and low productive neighbouring sandy beaches.
3.6. ACKNOWLEDGMENTS
The authors thank L. Soliño, L. García, J. Hernández and I. Rodil for help with field work. Thanks are also due to E. Cacabelos for valuable comments and advice on statistical techniques. We are very grateful to 2 anonymous reviewers for their insightful and constructive comments. This research was supported by theMinisterio de Ciencia e Innovación (BFU2010-16080), Xunta deGalicia (10PXIB312152PR) and the Universidade de Vigo (C505122F64102).
3.7. LITERATURE CITED
Alvarez-Salgado X, Rosón G, Pérez F, Figueiras F, Pazos Y (1996) Nitrogen cycling in an estuarine upwelling system, the Ría de Arousa (NW Spain). I. Short-time-scale patterns of hydrodynamic and biogeochemical circulation. Marine Ecology Progress Series 135:259-273 Anderson W, Polis G (1999) Nutrient fluxes from water to land: seabirds affect plant nutrient status on Gulf of California islands. Oecologia 118:324-332 Anschutz P, Smith T, Mouret A, Deborde J, Bujan S, Poirier D, Lecroart P (2009) Tidal sands as biogeochemical reactors. Estuarine, Coastal and Shelf Science 84:84-90 Avery GB, Kieber RJ, Taylor KJ (2008) Nitrogen release from surface sand of a high energy beach along the southeastern coast of North Carolina, USA. Biogeochemistry 89:357-365
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Barreiro F, Gómez M, Lastra M, López J, de la Huz R (2011) Annual cycle of wrack supply to sandy beaches: effect of the physical environment. Marine Ecology Progress Series 433:65-74 Billerbeck M, Werner U, Bosselmann K, Walpersdorf E, Huettel M (2006) Nutrient release from an exposed intertidal sand flat. Marine Ecology Progress Series 316:35-51 Bode A, Varela M, Teira E, Fernández E, González N, Varela M (2004) Planktonic carbon and nitrogen cycling off northwest Spain: variations in production of particulate and dissolved organic pools. Aquatic Microbial Ecology 37:95-107 Boudreau B, Huettel M, Forster S, Jahnke RA, McLachlan A, Middelburg JJ, Nielsen P, Sansone F, Taghon G, Van Raaphorst W, Webster I, Weslawski JM, Wiberg P (2001) Permeable marine sediments: overturning an old paradigm. Eos Transactions 82:133-136 Bourguès S, Auby I, Wit R, Labourg PJ (1996) Differential anaerobic decomposition of seagrass (Zostera noltii) and macroalgal (Monostroma obscurum) biomass from Arcachon Bay (France). Hydrobiologia 329:121-131 Buchsbaum R, Valiela I, Swain T, Dzierzeski M, Allen S (1991) Available and refractory nitrogen in detritus of coastal vascular plants and macroalgae. Marine ecology progress:131-143 Burnett W, Bokuniewicz H, Huettel M, Moore W, Taniguchi M (2003) Groundwater and pore water inputs to the coastal zone. Biogeochemistry 66:3-33 Cade BS, Noon BR (2003) A gentle introduction to quantile regression for ecologist. Frontiers in Ecology and Evolution 1:412-420 Catenazzi A, Donnelly M (2007) Role of supratidal invertebrates in the decomposition of beach-cast green algae Ulva sp. Marine Ecology Progress Series 349:33-42 Chapin F, Matson P, Mooney H (2002) Principles of terrestrial ecosystem ecology, Vol, New York Chapman aRO, Craigie JS (1977) Seasonal growth in Laminaria longicruris: Relations with dissolved inorganic nutrients and internal reserves of nitrogen. Marine Biology 40:197-205 Corzo A, van Bergeijk S, García-Robledo E (2009) Effects of green macroalgal blooms on intertidal sediments: net metabolism and carbon and nitrogen contents. Marine Ecology Progress Series 380:81-93 Coupland G, McDonald J (2008) Extraordinarily high earthworm abundance in deposits of marine macrodetritus along two semi-arid beaches. Marine Ecology Progress Series 361:181-189 Coupland GT, Duarte CM, Walker DI (2007) High metabolic rates in beach cast communities. Ecosystems 10:1341-1350 Dugan J, Hubbard DM, McCrary MD, Pierson MO (2003) The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beach of southern California. Estuarine Coastal and Shelf Science 58:25-40
| 85 NUTRIENT OUTCROP FROM EXPOSED BEACHES
Dugan JE, Hubbard DM, Page HM, Schimel JP (2011) Marine Macrophyte Wrack Inputs and Dissolved Nutrients in Beach Sands. Estuaries and Coasts 34:839-850 Ehrenhauss S, Huettel M (2004) Advective transport and decomposition of chain- forming planktonic diatoms in permeable sediments. Journal of Sea Research 52:179-197 Emery K (1961) A simple method of measuring beach profiles. Limnology and Oceanography 6:90-93 Figueiras F, Labarta U, Fernández Reiriz M (2002) Coastal upwelling, primary production and mussel growth in the Rías Baixas of Galicia. Hydrobiologia 484:121-131 Folk R (1980) Petrology of sedimentary rocks, Vol. Hemphill Publishing Company, Austin García-Robledo E, Corzo A, García de Lomas J, van Bergeijk S (2008) Biogeochemical effects of macroalgal decomposition on intertidal microbenthos: a microcosm experiment. Marine Ecology Progress Series 356:139-151 Giere O, Eleftheriou A, Murinson D (1988) Abiotic factors. In: Higgins RP, Thiel H (eds) Introduction to the study of meiofauna. Smithsonian Institution Press, London Hanisak M (1993) Nitrogen release from decomposing seaweeds: species and temperature effects. Journal of applied phycology 5:175-181 Hardison A, Canuel E, Anderson I, Veuger B (2010) Fate of macroalgae in benthic systems: carbon and nitrogen cycling within the microbial community. Marine Ecology Progress Series 414:41-55 Harrison P (1989) Detrital processing in seagrass systems: a review of factors affecting decay rates, remineralization and detritivory. Aquatic Botany 35:263-288 Hays R, Ullman W (2007a) Direct determination of total and fresh groundwater discharge and nutrient loads from a sandy beachface at low tide (Cape Henlopen, Delaware). Limnology and Oceanography 52:240-247 Hays R, Ullman W (2007b) Dissolved nutrient fluxes through a sandy estuarine beachface (Cape Henlopen, Delaware, USA): Contributions from fresh groundwater discharge, seawater recycling, and diagenesis. Estuaries and Coasts 30:710-724 Hobday A (2000) Abundance and dispersal of drifting kelp Macrocystis pyrifera rafts in the Southern California Bight. Marine Ecology Progress Series 195:101-116 Horn D (2002) Beach groundwater dynamics. Geomorphology 48:121-146 Jickells TD, Rae JE (1997) Biogeochemistry of intertidal sediments, Vol, Cambridge Koop K, Lucas M (1983) Carbon flow and nutrient regeneration from the decomposition of macrophyte debris in a sandy beach microcosm In: McLachlan A, Erasmus T (eds) Sandy beaches as ecosystems, Junk, The Hague Koop K, Newell R, Lucas M (1982) Biodegradation and Carbon Flow Based on Kelp(Ecklonia maxima) Debris in a Sandy Beach Microcosm. Marine Ecology Progress Series 7:315-326 Lastra M, de la Huz R, Sánchez-Mata AG, Rodil IF, Aerts K, Beloso S, López J (2006) Ecology of exposed sandy beaches in northern Spain: Environmental factors controlling macrofauna communities. Journal of Sea Research 55:128-140
| 86 CHAPTER III
Lastra M, Page HM, Dugan JE, Hubbard DM, Rodil IF (2008) Processing of allochthonous macrophyte subsidies by sandy beach consumers: estimates of feeding rates and impacts on food resources. Marine Biology 154:163-174 Mateo MA (2010) Beach-Cast Cymodocea nodosa Along the Shore of a Semienclosed Bay: Sampling and Elements to Assess Its Ecological Implications. Journal of Coastal Research 262:283-291 McGwynne L, McLachlan A, Furstenberg J (1988) Wrack breakdown on sandy beaches– its impact on interstitial meiofauna. Marine environmental research 25:213-232 McLachlan A (1980) The definition of sandy beaches in relation to exposure: a simple raring system. South African Journal of Science 76:137-138 McLachlan A, Brown AC (2006) The ecology of sandy shores, Vol. Elsevier, Amsterdam Mews M, Zimmer M, Jelinski D (2007) Species-specific decomposition rates of beach- cast wrack in Barkley Sound, British Columbia, Canada. Marine Ecology Progress Series 328:155-160 Moore WS (1996) Large groundwater inputs to coastal waters revealed by 226Ra enrichments. Nature 380:612-614 Nedzarek A, Rakusa-Suszczewski S (2004) Decomposition of macroalgae and the release of nutrient in Admiralty Bay, King George Island, Antarctica. Polar bioscience:26- 35 Page H, Petty R, Meade D (1995) Influence of watershed runoff on nutrient dynamics in a southern California salt marsh. Estuarine, Coastal and Shelf Science 41:163-180 Pearse A, Humm H, Wharton G (1942) Ecology of sand beaches at Beaufort, N.C. Ecological Monographs 12:135-190 Polis G, Anderson W, Holt R (1997) Toward an integration of landscape and food web ecology: the dynamics of spatially subsidized food webs. Annual Review of Ecology and Systematics 28:289-316 Prego R, Barciela MaDC, Varela M (1999) Nutrient dynamics in the Galician coastal area (Northwestern Iberian Peninsula): Do the Rias Bajas receive more nutrient salts than the Rias Altas? Continental Shelf Research 19:317-334 Rauch M, Denis L, Dauvin J-C (2008) The effects of Phaeocystis globosa bloom on the dynamics of the mineralization processes in intertidal permeable sediment in the Eastern English Channel (Wimereux, France). Marine pollution bulletin 56:1284-1293 Rocha C (2008) Sandy sediments as active biogeochemical reactors: compound cycling in the fast lane. Aquatic Microbial Ecology 53:119-127 Rocha C, Ibanhez J, Leote C (2009) Benthic nitrate biogeochemistry affected by tidal modulation of Submarine Groundwater Discharge (SGD) through a sandy beach face, Ria Formosa, Southwestern Iberia. Marine Chemistry 115:43-58 Rodil I, Olabarria C, Lastra M, López J (2008) Differential effects of native and invasive algal wrack on macrofaunal assemblages inhabiting exposed sandy beaches. Journal of Experimental Marine Biology and Ecology 358:1-13
| 87 NUTRIENT OUTCROP FROM EXPOSED BEACHES
Rossi F, Underwood A (2002) Small-scale disturbance and increased nutrients as influences on intertidal macrobenthic assemblages: experimental burial of wrack in different intertidal. Marine Ecology Progress Series 241:29-39 Rusch A, Huettel M, Wild C, Reimers CE (2006) Benthic oxygen consumption and organic matter turnover in organic-poor, permeable shelf sands. Aquatic Geochemistry 12:1-19 Sassi R, Kutner M, Moura GF (1988) Studies on the decomposition of drift seaweed from the northeast Brazilian coastal reefs. Hydrobiologia 192:187-192 Stenton-Dozey JME, Griffiths CL (1983) The fauna associated with kelp stranded on a sandy beach In: McLachlan A, Erasmus T (eds) Sandy beaches as ecosystems, Junk, The Hague Strauss EA, Lamberti GA (2000) Regulation of nitrification in aquatic sediments by organic carbon. Limnology and Oceanography 45:1854-1859 Strayer DL, Findlay SEG (2010) Ecology of freshwater shore zones. Aquatic Sciences 72:127-163 Sundby B, Gobeil C, Silverberg N, Mucci A (1992) The phosphorus cycle in coastal marine sediments. Limnology and Oceanography 37:1129-1145 Swarzenski PW, Izbicki Ja (2009) Coastal groundwater dynamics off Santa Barbara, California: Combining geochemical tracers, electromagnetic seepmeters, and electrical resistivity. Estuarine, Coastal and Shelf Science 83:77-89 Tenore KR, Hanson RB (1980) Availability of detritus of different types and ages to a polychaete macroconsumer, Capitella capitata. Limnology and Oceanography 25:553-558 Uchiyama Y, Nadaoka K, Rolke P, Adachi K, Yagi H (2000) Submarine groundwater discharge into the sea and associated nutrient transport in a sandy beach. Water Resources Research 36:1467-1479 Ullman W, Chang B, Miller CD, Madsen JA (2003) Groundwater mixing, nutrient diagenesis, and discharges across a sandy beachface, Cape Henlopen, Delaware (USA). Estuarine, Coastal and Shelf Science 57:539-552 Urban-Malinga B, Burska D (2009) The colonization of macroalgal wrack by the meiofauna in the Arctic intertidal. Estuarine, Coastal and Shelf Science 85:666- 670 Waska H, Kim G (2011) Submarine groundwater discharge (SGD) as a main nutrient source for benthic and water-column primary production in a large intertidal environment of the Yellow Sea. Journal of Sea Research 65:103-113 Williams S (1984) Decomposition of the tropical macroalga Caulerpa cupressoides (West) C. Agardh: Field and laboratory studies. Journal of Experimental Marine Biology and Ecology 80:109-124 Wilson AM, Huettel M, Klein S (2008) Grain size and depositional environment as predictors of permeability in coastal marine sands. Estuarine, Coastal and Shelf Science 80:193-199
| 88 CHAPTER III
Wooster W, Bakun A, McLain D (1976) The seasonal upwelling cycle along the eastern boundary of the North Atlantic. J mar Res 34:131-141 Yin K, Harrison P (2000) Influences of flood and ebb tides on nutrient fluxes and chlorophyll on an intertidal flat. Marine Ecology Progress Series 196:75-85
| 89 CHAPTER IV
IV. The influence of allochthonous inputs on the macrofaunal assemblages in ocean-exposed sandy beaches
Barreiro F., Gómez M., López J., Lastra M (Under Review) Estuarine, Coastal and Shelf Science
INFLUENCE OF WRACK ON MACROFAUNAL ASSEMBLAGES
4.1. ABSTRACT
Links between habitats in space and time are a common and multifaceted process in the coastal zone. Exposed beaches are an open ecosystem characterized by a low primary production. Thus, the resident organisms show a strong dependence of allochthonous inputs of organic matter. However, sandy beaches are traditionally considered extreme environments where species are mainly controlled by physical forces. In this study the effect of the magnitude of macroalgae in the community structure (in terms of number of species, density and assemblage composition) was investigate quarterly throughout a year. Four beaches differently subsidized were sampled from the base of the dune to the swash line during spring tides. The number of species collected per beach ranged from 18 to 40 and the mean density from 241 ± 36 to 3975 ±519 (mean ± s.e). Overall, despite to the significant spatial and temporal interactions observed, number of species and density increase from the beaches with low inputs of macroalgae to the large subsidized. The assemblage composition changed significantly through this gradient of organic input. The influence of the wrack magnitude on the community structure were notorious both in the supratidal as in the intertidal zone. However the effect differed across the beach. While in the intertidal there was a shifting in the identity of the species with greater contribution to the community, in the supratidal changes were mainly due to differences in the dominance of the same species. The present study provide evidence of the wrack influence in the macrofaunal structure and composition on exposed sandy beaches stressing the importance of the interconnections between exposed beaches and their neighbouring ecosystems.
Key words Exposed beaches - Connectivity - Spatial subsidy - Community structure - Wrack
| 92 CHAPTER IV
4.2. INTRODUCTION
Cross-habitat fluxes of resources are common processes in a wide range of ecological systems (Polis et al. 2004). These movements of organic matter and nutrients may greatly affect the community of the receptor ecosystem (Polis et al. 1997). The overall influence may be inversely related with its in situ primary productivity (Barrett et al. 2005). One of the areas with greatest allochthonous fluxes is the land-water interface (Polis et al. 1997). Indeed the linkages from land to water have been studied in detail for years (Wallace et al. 1997). However exchanges from water to land are poorly understood and thus their ecological consequences are less known (Vander Zanden & Sanzone 2004). In general, most studies of subsidized systems indicate numerical response in local populations (Polis et al. 1997). Nevertheless the role of subsidies on the species diversity patterns, community structure and temporal stability are poorly understood (Anderson et al. 2008).
Sandy beaches comprise two-thirds of the world’s ice free coastlines (McLachlan & Brown 2006). They are links between marine and terrestrial ecosystem which provide valuables ecological services (Scapini 2003, McLachlan & Brown 2006). However the study of beach ecology has emerged recently as a theory-driven discipline (Schlacher et al. 2007). The increasing human pressure on the coastal habitats at the actual framework of global change, particularly the sea-level rise and the biodiversity lost, make necessary a deeper understanding of the structure and function of beach ecosystems (Loreau et al. 2001, Schlacher et al. 2007, Defeo et al. 2009, Yamanaka et al. 2010, Schierding et al. 2011, Veloso et al. 2011).
Compared with most ecosystems, exposed beaches support little primary production (McLachlan & Brown 2006). Unless other costal habitats, the substratum instability preclude the growth of attach macroalgae and macrhophyte. Therefore,
| 93 INFLUENCE OF WRACK ON MACROFAUNAL ASSEMBLAGES
beach communities are almost entirely dependent of imported food (McLachlan & Brown 2006).
Allochthonous food on sandy beaches comes mainly from the sea. These consist both of dissolved and particulate organic matter, which is retained into the sediment, as animals, macroalgae and macrophytes (also termed wrack), which are stranded on the beach surface (McLachlan & Brown 2006). Large amounts of wrack (mostly macroalgae) have been quantified worldwide (Hayes 1974, Koop et al. 1982, Stenton-Dozey & Griffiths 1983, McLachlan & Mcgwynne 1986, Polis et al. 1997, Ochieng & Erftemeijer 1999, Dugan et al. 2003, Orr et al. 2005, Barreiro et al. 2011) with important effects for the macrofaunal community (Colombini & Chelazzi 2003). However, exposed beaches are traditionally considered extreme environments controlled mainly by physical forces, specifically morphodynamic forces (Defeo & McLachlan 2005, McLachlan & Dorvlo 2005), that is the interaction of waves and tides with the topography (Short 1999). In this sense, the macrofaunal community structure, i.e. species richness, total abundance and biomass, is explained as a direct response of the environmental harshness or the habitat safer (Defeo & McLachlan 2005, Defeo & McLachlan 2011). However, there are increasing evidences of biological influences in the structure of beach communities (Dugan et al. 2004, Defeo & McLachlan 2005, Lastra et al. 2006, Rodil et al. 2006, Duarte et al. 2010, Ortega Cisneros et al. 2011).
Exposed beaches are a suitable environment to investigate the potential effects of the input of resources at different spatial and temporal scales on the community structure and at the same time to assess the strength of the physical control hypothesis. In this study we examine the spatial and temporal variability of the community structure, in terms of species richness and abundance, on four beaches of the NW coast of Spain. Specifically, we hypothesized that (1) among beaches, the total number of species and total abundance increase from low to high subsidy environments producing changes in the assemblage composition; (2) the variations in these community
| 94 CHAPTER IV parameters differ along the intertidal width; and (3) the highest stability in the community, in terms of intra-annual fluctuation in the number of species and individuals, will be reach in the beaches with less variation of inputs throughout the year.
4.3. MATERIAL AND METHODS
4.3.1. Field sampling design
Four beaches differently subsidized by wrack macroalgae were sampled on the Galician coast (NW Spain). Balieiros (BA), which receives very low amounts of macroalgae (14 ± 5 g m-1 of dry weight (mean ± SE); Ladeira (LA), with intermediate inputs (213 ± 61 g m-1); Toralla (TO), with large deposits (1116 ± 464 g m-1); and Abra (PA), with very large deposits of stranded algae (9189 ± 3594 g m-1). Field sampling was carried out during spring tides in a year cycle from December 2007 to November 2008. Tidal conditions were meso-macrotidal, ranging from 3.5 to 4 m in spring tides. The environmental characteristics of these beaches are shown in Table 4.1.
Sampling was carried out over a 100-m long stretch in the center of each beach. To quantify the wrack biomass, samples were collected monthly from the base of the dune to the lowest swash level along six one-meter transects. Coverage (using the line intercept method), specific composition and total biomass were calculated for each transect. Details of the wrack biomass assessment are given in (Barreiro et al. 2011). To
Physicall characteristics Length Width TMG Beach Wrack biomass Exposure rate M.S. 1/Slope (m) (m) (µm ±s.e ) Abra PA Very high 11 (Exposed) Reflective 210 60 9.8 1123 ± 194 Toralla TO High 10 (Sheltered) Reflective 100 60 13.8 711 ± 57 Ladeira LA Medium 13 (Exposed) Disipative 5000 130 33.9 192 ± 3 Balieiros BA Low 18 (Very exposed) Reflective 840 100 10.9 731 ± 62
Table 4.1. Mean biomass of wrack and physical characteristics of the studied beaches. Exposure index estimated according to the rating system of McLachlan 1980.
| 95 INFLUENCE OF WRACK ON MACROFAUNAL ASSEMBLAGES
Fig.4.1. Biomass of wrack (g m-2 of dry weight) stranded across the width of each beach. To enable comparison among beaches, the beach width was standardized from the base of the dune (0) to the lowest swash level (100). Lines denote average biomass at each beach. describe the wrack distribution along the beach surface, the biomass of wrack was estimated for each 10 meters of the intertidal beach using the close correlation obtained (Barreiro et al. 2011) between the wrack biomass and coverage (r2= 0.81, p<0.001). The intertidal beach was standardized to enable comparisons among beaches (Fig. 4.1).
The macrofaunal samples were taken quarterly for a year (specifically in January, April, July and October 2008) in the same area and during the same period that the wrack assessment was being performed (from December 2007 to November 2008). Samples were taken at 5 levels at the shore (hereafter beach levels): 2 intertidal (low and medium) and 3 supratidal (low, medium and high). The beach division was based on
| 96 CHAPTER IV the scheme proposed by (Salvat 1964). Low intertidal (LI) was located in the low swash point during low tide; the medium intertidal level (IM) was placed at the upper part of the resurgence zone; the low supratidal (LS) correspond with the drift line; the high supratidal (HS) was situated at the base of the dune; and the medium supratidal (MS) was determined as an equidistant point between the two previous levels. Six randomly samples were collected at each beach level with a metallic cylinder of 25 cm of diameter penetrating 15 cm deep into the sediment. Samples were sieved through 1mm mesh and preserved in 4% formalin-sea water solution. The individuals were later sorted from the sediment and determined to the lowest taxonomic level possible. Species number and abundance as well as total density (expressed as total number of individuals per square meter) were calculated for each sample.
4.3.2. Statistical analysis
Differences in the species number and density (ind. m2) among beaches and levels throughout the year were tested with orthogonal three-way ANOVAs. Beach (with 4 levels), time (with 4 levels) and beach level (with 5 levels) were fixed factors (n=6). Samples were log-transformed prior to the analysis to meet the assumptions of normality and homogeneity of variances. A posteriori multiple comparisons analyses were performed using Student-Newman-Keuls (SNK) test (α = 0.05).
To analyse the macrofaunistic community structure on each beach, a non-metric multidimensional scaling (nMDS) was performed with the average monthly abundance of each species per beach and level. Prior to this, data were log-transformed to calculate the Bray-Curtis similarity index. Differences among groups of beaches and levels were tested with ANOSIM. To gauge the contribution of individual species to overall dissimilarity in the community structure among beaches and levels (previously grouped) a similarity percentage (SIMPER) analysis was performed.
| 97 INFLUENCE OF WRACK ON MACROFAUNAL ASSEMBLAGES
The spatial and temporal variability of the community assemblages both in the supratidal as in the intertidal were analysing using a three-way permutacional analysis of variance (PERMANOVA). Beach (with 4 levels), Time (with 4 levels) and beach level (3 levels in the supratidal and 2 levels in the intertidal) were fixed factors. The PERMANOVAs were run on Bray-Curtis dissimilarity matrices of species abundance. Data were previously log-transformed.
4.4. RESULTS
4.4.1. Species richness and total abundance
The number of species and the total abundance of the macrofaunal community increased from the low to the high and very high subsidy beaches (Fig. 4.2 and Fig. 4.3). However there were significant spatial and temporal interactions in each comparison (see Table C-1 in Appendix C).
The total number of species per beach collected during the studied period ranged from 18 to 40 (in BA and PA respectively). At each studied month throughout the year, the lowest numbers of species were registered in BA and the highest in PA, while along the beach profile the species number tended to decrease from the swash level to the base of the dune in all beaches (Fig. 4.2). However variations of the number of species at each beach level were not consistent throughout the year (significant interaction Be x Mo x Le). Focusing in the temporal variability at each beach level, the SNK showed that the species number in the supratidal (i.e. SI, SM and SH) in PA and BA did not differ throughout the year, while in the high supratidal (SH) of TO and in each supralitoral level of LA differed significantly. Both intertidal levels (i.e. SZ and RZ) showed a lower number of species during January and/or April with the exception of the medium intertidal (IM) of LA and TO where no differences were registered throughout the year. Comparisons of each level among beaches were variables for each studied
| 98 CHAPTER IV
Fig. 4.2. Number of macrofaunal species collected in each level of each beach throughout the year. Numbers represent the total number of species on the entire beach. Letters denotes significant differences among the beach levels. month. However, except in the medium intertidal (IM) of LA during January, the number of species in PA and TO was higher than in BA and LA for each comparison.
The mean abundance of individuals increased from BA (241± 36) to LA (815±143) and in turn from these to TO and PA (3975±519 and 2502 ± 344 respectively) (Fig. 4.3). However this trend was not spatial and temporally consistent (significant interaction Be x Mo x Le). Despite of all the observed variability among beaches throughout the year, both in the supratidal levels as in the swash zone the total number of individuals tended to be higher in TO and/or PA than in LA and BA. However in the medium intertidal (IM) the total abundance registered in LA was similar to that of TO and even higher than in PA during July. Within each beach the abundance was also variable between levels and months. In PA, except in the low intertidal (LI), the abundance was similar throughout the year at each level. In TO was notable the high
| 99 INFLUENCE OF WRACK ON MACROFAUNAL ASSEMBLAGES
Fig. 4.3. Mean density of macrofauna (ind. m-2) in each beach level throughout the year at each location. Errors bars represent standard error (n=6). Letters denote significant differences across months at each beach level. Significant differences among beaches each month are written on the graph for each beach level. abundance in the drift (SL) during October coinciding with a low abundance in the medium and high supratidal zone (SM and SH). The abundance in LA and BA were also variable at each level throughout the year (Fig. 4.3). Across the beach in PA the abundance was similar in January, April and July. However in October there were a significant higher number of individuals in the swash zone (IL). In TO, during July and October there were lower abundances in the medium and high supratidal (SM and SH) than in the other beach levels. In LA the abundance was similar across the beach in April and October while in January and July a significant higher number of individuals were
| 100 CHAPTER IV observed in the retention zone (IM). Total abundance in BA was more variable across the beach levels each month. In January and October the lowest abundances were registered in the high supratidal zone (SH), in April in the retention zone (IM), and in July the highest number of individuals was observed in the swash zone (IL)
4.4.2. Community composition
The macrofaunal composition differed significantly between the intertidal and supratidal levels across all beaches (ANOSIM, global R=0.94, p< 0.001; Fig. 4.4). A PERMANOVA was conducted for each zone (i.e. intertidal and supratidal) to explore the community abundance and composition during the studied period across the beach. The macrofaunal assemblage varied differently among beaches and levels throughout the year both in the intertidal (significant interaction B x M x L) as in the supratidal zone (significant interaction B x M x L) (see Table C.2 in Appendix C).
In the intertidal, the macrofaunal community in the swash (IL) and in the retention zone (IM) differed significantly among beaches every sampled month. Within each beach every zone also differed throughout the year except in the retention zone (IM) of BA where the community was similar in July, October and January. Generally, the community in the retention zone (IM) was significantly different of the swash zone (IL). Just during April in BA, July in PA and January in TO the community assemblages did not differed among these levels.
In the supralitoral, comparisons of the macrofaunal community for each level among beaches per month showed a lesser variability than in the intertidal levels. The assemblages did not differ significantly: in January, all the supratidal levels of BA and LA; in April, the low and medium supratidal (SL and SM) of LA and TO; in July, the medium part of the supratidal (SM) of LA and TO; in October, the drift zone (SL) of LA and PA, and the medium supratidal zone (SM) of TO and PA. Within each beach the community assemblages were also less variable than in the intertidal. Comparisons of levels at each
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Fig. 4.4.Non-metric multidimensional scaling (nMDS) showing similarity of community composition among and within beach zones, i.e. intertidal (Int) and supratidal (Sup). See table 1 for site abbreviations. beach throughout the year showed that: in BA the low and medium supratidal levels (SL and SM) were similar every month across the year, and between October and January there were not differences in the high supratidal (SH); in LA the drift zone (SL) was similar in January and July and in April and July, the SM zone between January and April and January and July, and the SH between January and July, April and July, April and October, and July and October; in PA the drift zone (SL) was similar only in April and July, the SM zone in April and October while the SH only differed between January and April; in TO all the supratidal levels differed throughout the year.
Comparisons among supratidal levels within beaches during the studied period showed that: in BA all levels were similar each month; in LA only in October the drift
| 102 CHAPTER IV zone (SL) was different; in PA just the drift zone (SL) differed from the other levels in April and October, and the high supratidal zone (SH) during July; and in TO only was different the drift zone (SL) from the other levels in January and October, and the high supratidal (SH) during April.
The SIMPER analysis shows that the number of species contributing to the similarity of each beach in the intertidal zone increased from BA to PA. This trend was
BEACH TAXA BA LA TO PA Amphipods Talitrus saltator 21.9 20.8 31.9 41.4 Deshayesorchestia deshayesii 9 41.8 24.1 Talitridae (juveniles) 10.4 8.7 13.4 Isopods Tylos europaeus 32.5 5.5 16.1 Eurydice affinis 12.4 Lek anesphaera rugicauda 4.2 SUPRATIDAL Cumacea Cumopsis fagei 4.3 Insects Coleoptera 27.2 Diptera 12.6 30.7 7.2
Amphipods Haustorius arenarius 11.1 Pontocrates arenarius 29.8 7.3 2 Isopods Eurydice affinis 19.3 11 7.2 Eurydice pulchra 24.5 Idotea pelagica 2.2 Lek anesphaera rugicauda 4.6 3.6 2.6 Cumacea Cumopsis fagei 12.7 4.9 Mysidacea Gastrosaccus sanctus 11.5 Polychaeta Aonides oxycephala 1.9 24.4 26 INTERTADAL Malacoceros fuliginosus Scolelepis (Scolelepis) squamata 43.4 4 3.8 Scoloplos armiger 2.7 Capitella capitata c.f. 21.6 16.1 Othe rs Oligochaeta 10.7 Nemertea 5.3 2.8 2.6 3.7 Nematoda 22.3 16
Table 4.2 Mean contribution to the similarity (%) of the most abundant species in the supratidal and intertidal in each beach. See Table 1 for site abbreviations.
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not observed in the supralitoral zone where the numbers of taxa with high contribution were substantially similar among beaches (Table 4.2).
In the intertidal: BA was characterized by the isopods Eurydice pulchra (19.3%) and Eurydice affinis (24.5%), the amphipod Pontocrates arenarius (29.8%) and the mysida Gastrosaccus santcus (11.5%). In LA the polychaeta Scolelepis squamata (43.4%), the cumacea Cumopsis fagei and the amphipod Haustorius arenarius (11.1%) reached the highest values. In TO and PA were registered the highest contribution of nematods and polychaetes, mainly Malacoceros fuliginosus and Capitella capitata c.f. Nemerteans, despite of their low abundance, were common and contribute to all beaches.
In the supralitoral: the contribution to the similarity in PA and TO was mainly due to the amphipods Talitridae (78.9% and 82.4%). In BA and LA the Talitridae also had a high influence (32.4% and 29.8%). However, in these beaches the contribution was more partitioned between the macrofaunal taxas. For example, the highest influence of Insects was registered in LA (57.9%) and the isopod Tylos europaeus reached the greatest contribution in BA (32%).
5. DISCUSSION
The present study, which set out to assess the effect of food availability on the macrofaunal community of exposed sandy beaches, shows that the spatial and temporal variability in the species richness, density and assemblage composition are broadly influenced by the magnitude of wrack stranded on the beach surface.
The number of species collected in the four studied beaches (18 to 40 spp.) was slightly higher than the found in a broader assessment on the northern coast of Spain (9 to 31 spp.) where thirty-four beaches were sampled from the drift line to the swash level (Lastra et al. 2006). In this work the entire supralitoral zone was considered (i.e.
| 104 CHAPTER IV from the base of the dune to the drift line). The species restricted to this area, mainly wrack colonizers (Olabarria et al. 2007), together with the prominent seasonal variability of exposed beaches (Gonçalves & Marques 2011) taken into account in this study, may explain the increase in the species richness. A similar number of species (15 to 37 spp.) were registered on the Californian coast, an area which support commonly large deposits of macroalgae (Dugan et al. 2000). Contrary, a lower number of species inhabiting sandy beaches are frequently cited worldwide, for example: in the coast of Oman (19 to 25 spp.; (McLachlan et al. 1998)), in the Chilean coast (4 to 14 spp.; (Jaramillo 1987)) or in Australia (5 to 19 spp. (Hacking 1997)).
Once stranded on the beach, macroalgae create a new habitat with different microclimatic characteristics than the surrounding areas (Colombini & Chelazzi 2003). This increases the spatial heterogeneity and in turn the environmental range available for organisms on the beach. Comparing with the bare sediment, patches of stranded material are environments more protected to the water loss (Olabarria et al. 2007). They may reduce the physical stress, and thus, make the environment suitable for a higher number of species. Indeed, a high number of species inhabiting patches of wrack have been quantified elsewhere (Stenton-Dozey & Griffiths 1983, Dugan et al. 2003, Jaramillo et al. 2006, Ince et al. 2007, Coupland & McDonald 2008, Rodil et al. 2008). The large diversity is commonly attributed to the proliferation of the wrack-associated species in the upper beach (Colombini et al. 2000, Colombini & Chelazzi 2003, Dugan et al. 2003, Ince et al. 2007). Among the studied beaches the species richness increased from the low to the very high wrack subsidized beach (from BA to PA). However, in the beaches with largest inputs of wrack we recorded a greater diversity in the lower beach levels (IL and IM). These results suggest that both in the swash as in the retention zone, wrack represent a habitat which can be colonized by more species than the bare sediment. In these areas wrack could reduce the physical stress of the wave action in the sediment and make the environment suitable to taxa less tolerant to the hydrodynamic strength.
| 105 INFLUENCE OF WRACK ON MACROFAUNAL ASSEMBLAGES
Across the intertidal, all beaches showed a clear increment of species seaward from the base of the dune. The progressive decline to the air-exposure may enable an increase in the number of marine species (McLachlan & Brown 2006). Contrary, a diverse fauna of insects could appear in the upper beach when the magnitude of wrack is abundant (Foote 1995, Hodge & Arthur 1997, Olabarria et al. 2007, Rodil et al. 2008, Yamazaki 2012). This effect was not reflected in the number of species of the high subsidized beaches. We may highlight that the lack of a dune system in the beaches with high wrack inputs (PA and TO) could reduce the presence of terrestrial insects. In addition, the sampling methodology was developed to quantify mainly the resident macroinfauna, and the ability to capture flying insects may be low.
Recently, wrack patches have been characterized as one of the coastal environments with highest density and biomass of mobile invertebrates (Cowles et al. 2009). Considering beaches as a whole system, during the study, density increase from the sites with low macroalgae (BA and LA) to the high subsidized locations (TO and PA). However, despite to the wrack biomass differed in an order of magnitude between TO and PA (Barreiro et al. 2011), the mean density of invertebrates was lower in PA. Dense wrack accumulations may reduce the oxygen exchange (Mcgwynne et al. 1988, Kirkman & Kendrick 1997) and together the high community respiration of these environments (Coupland et al. 2007) could limit the growing of the resident populations.
Wrack deposition may be variable across the intertidal (Orr et al. 2005, Gomez et al. 2013) and thus, also their potential effect on the macrofauna. On the supratidal zone, the macrofaunal density tended to increase from the low to the high wrack subsidized beaches. In the upper beach, wrack-associated species can process extensive quantities of macroalgae daily (Lastra et al. 2008). Whereby, a greater available of food may enhance the development of these populations (Dugan et al. 2003, Jaramillo et al. 2006). Wrack also may provide shelter from predation and reduce the environmental stress (Orth et al. 1984, Crawley et al. 2006, Jaramillo et al. 2006) contributing to this
| 106 CHAPTER IV numerical increment. The abundance in the intertidal was variable between beach levels. In the resurgence zone, the high macrofaunal density of the intermediate subsidized beach (LA) cannot be explained according to the magnitude of macroalgae received. Thus, other inputs of organic matter have to support the community. The organic matter content in the water column may represent an important food source for beach communities (McLachlan & Brown 2006). Indeed, the phytoplankton concentration can influence the abundance of consumers and in turn the macrofaunal structure of exposed beaches (Lastra et al. 2006, Rodil et al. 2006). However in the resurgence zone of BA the macrofaunal density was lower than in LA. The food content in the coastal water may be similar along the study region, given the local scale of this work, but contrary, the residence time of the seawater into the interstitial space should differ depending on the hydrodynamic characteristics of each beach (McLachlan & Brown 2006). Thus, the accumulation of organic matter into the sediment may be favoured in gently-slope beaches and decrease progressively at higher intertidal slopes, which may avoid the accumulation of organic matter (Incera et al. 2003). In the swash zone, the large macrofaunal densities reached on the wrack subsidized beaches (PA and TO) suggest that the community is supported by these inputs of macroalgae.
The multivariate analysis showed clear differences between the supratidal and the intertidal zones in the structure and composition of the macrofaunal assemblages. This result is in accordance with previous zonation studies which identified an aerial and a sub-aerial community on exposed beaches (Jaramillo et al. 1993, McLachlan & Brown 2006, Rodil et al. 2006, Alves & Pezzuto 2009). However, despite to wrack may affect to the species composition (Dugan et al. 2003, Gonçalves & Marques 2011), the potential effect of this input across the beach is less known.
In the supratidal, the community composition was dominated by the same taxa in all beaches. However the contribution of each specie changed in accordance to the biomass of wrack stranded on the beach. Species that can better utilize this resource
| 107 INFLUENCE OF WRACK ON MACROFAUNAL ASSEMBLAGES
may be favored. For example, the talitrid amphipods can be very abundant in upper zone of beaches with large macroalgae deposits (Colombini & Chelazzi 2003, Jaramillo et al. 2006, Duarte et al. 2009).Wrack may also act as a natural vector for the dispersal of supratidal species (Wildish 2012). Due to the stranded material is frequently resuspended and redeposited (Kirkman & Kendrick 1997, Orr et al. 2005), the wrack associated macrofauna may sporadically become transported long distance allowing the dispersal of species with a direct development (Thiel & Gutow 2004, Herkül et al. 2006, Wildish 2012). The arrival of new individuals to beaches could be related with the average amount of wrack deposited. Thus, we suggest that wrack may play an important role in the resilience of the supralitoral zone.
In the intertidal, the community composition was more variable between and within beaches. The species found in the intertidal on this region show complex zonation patterns due to they can appear at different beach levels (Rodil et al. 2006, De La Huz 2008). However, they show ecological preference across the intertidal which may be responsible of a gradient in the distribution of each specie (Jaramillo et al. 1993) and explain the differences in the community within each beach between the swash and resurgence zone. Among beaches, the number of taxa contributing to the community increased at the beaches with larger wrack deposits. An on other hand, there were a shifting in the dominance of the common species. The organic content may be one of the principal causes of faunal change in coastal benthic environments (Pearson & Rosenberg 1978) and can generate spatio-temporal patterns in natural assemblages (Kelaher & Levinton 2003). Previous researches found a high abundance of Malacoceros fuliginosus and Capitella capitata in benthos with deposits rich in detached macroalgae and macrohytes (Pearson & Rosenberg 1978, Thrush 1986) which are consistent with the density of these species measured in the intertidal of beaches with large wrack inputs. Nematodes may also be favoured in heterogeneous environments whit high algal detritus (Riera & Hubas 2003, Gingold et al. 2010). The greater structural
| 108 CHAPTER IV complexity and organic content may also favor the presence of a higher number of taxa (Thrush 1986, Kovalenko et al. 2011). In LA Scolelepis squamata showed the highest contribution. S. squamata feeds on resuspended particles at the sediment-water interface in exposed beaches where can attain high densities (Dauer 1983). This feeding mode may be a disadvantage when there is a large biomass of wrack deposited on the intertidal. In that situation may be outcompeted by the macrodetritivores. In BA the magnitude of wrack was similar than in LA, however S. squamata did not appear. The steep slope and the coarse grain size may exclude this specie (McLachlan & Brown 2006, Rodil et al. 2012). This beach also showed the lowest number of taxa in the intertidal. The physical stress and the food availability may be acting together reducing the suitability of this habitat to a lower number of species.
The seasonal variability in terms of number of species and abundance was complex; however it was notorious that in the supratidal zone of the beach with largest biomass both parameters did not differed throughout the year. This could suggest that in this zone when wrack is not a limited factor the macrofaunistic community is more stable.
Overall, the present study provides evidences of the influence of the wrack deposits in the macrofaunal structure and composition of exposed sandy beaches. Considering that beaches may export the macrofaunal production to higher trophic levels and adjacent habitats ((Dugan et al. 2003, Polis et al. 2004), this study stress the importance of the interconnections and links of sandy beaches with the neighbouring ecosystems.
4.6. ACKNOWLEDGMENTS
The authors thank R. de la Huz, L. Soliño, I. Rodil, J. Hernández and L. García for help with field work.
| 109 INFLUENCE OF WRACK ON MACROFAUNAL ASSEMBLAGES
3.7. LITERATURE CITED
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Duarte C, Jaramillo E, Contreras H, Acuña K, Navarro JM (2009) Importance of macroalgae subsidy on the abundance and population biology of the amphipod Orchestoidea tuberculata (Nicolet) in sandy beaches of south central Chile. Rev Biol Mar Oceanogr 44:691-702 Dugan J, Hubbard DM, Martin DM, Engle JM, Richards DM, Davis GE, Lafferty KD, Ambrose RF Macro-fauna communities of exposed sandy beaches on the Southern California Mainland and Channel Islands. In. Proc Fifth California Islands Symposium, Mineral Management Service Dugan JE, Hubbard DM, McCrary MD, Pierson MO (2003) The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of southern California. Estuar Coast Shelf S 58:25-40 Dugan JE, Jaramillo E, Hubbard DM, Contreras H, Duarte C (2004) Competitive interactions in macroinfaunal animals of exposed sandy beaches. Oecologia 139:630-640 Foote B (1995) Biology of shore flies. Annu Rev Entomol 40:417-442 Gingold R, Mundo-Ocampo M, Holovachov O, Rocha-Olivares A (2010) The role of habitat heterogeneity in structuring the community of intertidal free-living marine nematodes. Mar Biol 157:1741-1753 Gomez M, Barreiro F, Lopez J, Lastra M, de La Huz R (2013) Deposition patterns of algal wrack species on estuarine beaches Aquatic Botany 105:25-33 Gonçalves SC, Marques JC (2011) The effects of season and wrack subsidy on the community functioning of exposed sandy beaches. Estuar Coast Shelf S 95:165- 177 Hacking N (1997) Sandy beach macroinfauna of the Eastern Australia: A Geographical Comparison. The University of New England, Australia Hayes WB (1974) Sand-beach energetics: importance of the isopod Tylos punctatus. Ecology 55:838-847 Herkül K, Kotta J, Kotta I (2006) Distribution and population characteristics of the alien talitrid amphipod Orchestia cavimana in relation to environmental conditions in the Northeastern Baltic Sea. Helgoland Mar Res 60:121-126 Hodge S, Arthur W (1997) Asymmetric interactions between species of seaweed fly. J Anim Ecol 66:743-754 Ince R, Hyndes GA, Lavery PS, Vanderklift MA (2007) Marine macrophytes directly enhance abundances of sandy beach fauna through provision of food and habitat. Estuar Coast Shelf S 74:77-86 Incera M, Cividanes S, Lastra M, López J (2003) Temporal and spatial variability of sedimentary organic matter in sandy beaches on the northwest coast of the Iberian Peninsula. Estuar Coast Shelf S 58:55-61 Jaramillo E (1987) Sandy beach macroinfauna from the Chilean coast: Zonation patterns and zoogeography Vie Milieu 37:165-174
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Jaramillo E, De La Huz R, Duarte C, Contreras H (2006) Algal wrack deposits and macroinfaunal arthropods on sandy beaches of the Chilean coast. Rev Chil Hist Nat 79:337-351 Jaramillo E, McLachlan A, Coetzee P (1993) Intertidal zonation patterns of macroinfauna over a range of exposed sandy beaches in south-central Chile. Mar Ecol Prog Ser 101:105-118 Kelaher B, Levinton J (2003) Variation in detrital enrichment causes spatio-temporal variation in soft-sediment assemblages. Mar Ecol Prog Ser 261:85-97 Kirkman H, Kendrick G (1997) Ecological significance and commercial harvesting of drifting and beach-cast macro-algae and seagrasses in Australia: a review. J Appl Phycol 9:311-326 Koop K, Newell R, Lucas M (1982) Microbial regeneration of nutrients from the decomposition of macrophyte debris on the shore. Mar Ecol Prog Ser 9:91-96 Kovalenko KE, Thomaz SM, Warfe DM (2011) Habitat complexity: approaches and future directions. Hydrobiologia 685:1-17 Lastra M, de la Huz R, Sánchez-Mata AG, Rodil IF, Aerts K, Beloso S, López J (2006) Ecology of exposed sandy beaches in northern Spain: Environmental factors controlling macrofauna communities. J Sea Res 55:128-140 Lastra M, Page HM, Dugan JE, Hubbard DM, Rodil IF (2008) Processing of allochthonous macrophyte subsidies by sandy beach consumers: estimates of feeding rates and impacts on food resources. Mar Biol 154:163-174 Loreau M, Naeem S, Inchausti P, Bengtsson J, Grime JP, Hector A, Hooper DU, Huston Ma, Raffaelli D, Schmid B, Tilman D, Wardle Da (2001) Biodiversity and ecosystem functioning: current knowledge and future challenges. Science 294:804-808 Mcgwynne LE, Mclachlan A, Furstenberg J (1988) Wrack breakdown on sandy beaches- Its impact on interstitial meiofauna. Mar Environ Res 25:213-232 McLachlan A (1980) The definition of sandy beaches in relation to exposure: a simple rating system. S Afr J Sci 76:137-138 McLachlan A, Brown AC (2006) The ecology of sandy shores, Vol. Elsevier, Amsterdam McLachlan A, Dorvlo A (2005) Global Patterns in Sandy Beach Macrobenthic Communities. J Coastal Res 21:674-687 McLachlan A, Fisher M, Al-Habsi HN, Al-Shukairi SS, Al-Habsi AM (1998) Ecology of sandy beaches in Oman. J Coast Conserv 4:181-190 McLachlan A, Mcgwynne LE (1986) Do sandy beaches accumulate nitrogen. Mar Ecol Prog Ser 34:191-195 Ochieng C, Erftemeijer P (1999) Accumulation of seagrass beach cast along the Kenyan coast: a quantitative assessment. Aquat Bot 65:221-238 Olabarria C, Lastra M, Garrido J (2007) Succession of macrofauna on macroalgal wrack of an exposed sandy beach: Effects of patch size and site. Mar Environ Res 63:19- 40
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Orr M, Zimmer M, Jelinski D, Mews M (2005) Wrack deposition on different beach types: spatial and temporal variation in the pattern of subsidy. Ecology 86:1496-1507 Ortega Cisneros K, Smit AJ, Laudien J, Schoeman DS (2011) Complex, dynamic combination of physical, chemical and nutritional variables controls spatio- temporal variation of sandy beach community structure. PloS one 6:e23724 Orth R, Heck K, Montfrans Jv (1984) Faunal communities in seagrass beds: a review of the influence of plant structure and prey characteristics on predator-prey relationships. Estuaries 7:339-350 Pearson T, Rosenberg R (1978) Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanogr Mar Biol 16:229-311 Polis G, Anderson W, Holt R (1997) Toward an integration of landscape and food web ecology: the dynamics of spatially subsidized food webs. Annu Rev Ecol Syst 28:289-316 Polis G, Power M, Huxel G (2004) Food webs at the landscape level, Vol. The University of Chicago Press, Ltd., London Riera P, Hubas C (2003) Trophic ecology of nematodes from various microhabitats of the Roscoff Aber Bay (France): importance of stranded macroalgae evidenced through δ13C and δ15N. Mar Ecol Prog Ser 260:151-159 Rodil IF, Compton TJ, Lastra M (2012) Exploring macroinvertebrate species distributions at regional and local scales across a sandy beach geographic continuum. PloS one 7:e39609 Rodil IF, Lastra M, Sanchez-Mata AG (2006) Community structure and intertidal zonation of the macroinfauna in intermediate sandy beaches in temperate latitudes: North coast of Spain. Estuar Coast Shelf S 67:267-279 Rodil IF, Olabarria C, Lastra M, Lopez J (2008) Differential effects of native and invasive algal wrack on macrofaunal assemblages inhabiting exposed sandy beaches. J Exp Mar Biol Ecol 358:1-13 Salvat B (1964) Les conditions hydrodynamiques interstitielles des sédiment meubles intertidaux et le repartition verticale de la faune endogée, Vol. C. R. Academie Sciences, Paris Scapini F (2003) Beaches—What Future? An integrated approach to the ecology of sand beaches. Estuar Coast Shelf S 58S:1-3 Schierding M, Vahder S, Dau L, Irmler U (2011) Impacts on biodiversity at Baltic Sea beaches. Biodivers Conserv 20:1973-1985 Schlacher TA, Dugan J, Schoeman DS, Lastra M, Jones A, Scapini F, McLachlan A, Defeo O (2007) Sandy beaches at the brink. Divers Distrib 13:556-560 Short AD (1999) Handbook of beach and shoreface morphodynamics, Vol. John Wiley & Sons, New York
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Stenton-Dozey JME, Griffiths CL (1983) The fauna associated with kelp stranded on a sandy beach In: McLachlan A, Erasmus T (eds) Sandy beaches as ecosystems, Junk, The Hague Thiel M, Gutow L (2004) The ecology of rafting in the marine environment. I. The floating substrata. Oceanogr Mar Biol 42:181-264 Thrush S (1986) The sublittoral macrobenthic community structure of an Irish sea-lough: effect of decomposing accumulations of seaweed. J Exp Mar Biol Ecol 96:199- 212 Vander Zanden MJ, Sanzone DM (2004) Food web subsidies at the land-water ecotone. In: Polis G, Power M, Huxel G (eds) Food webs at the landscape level. The University of Chicago Press, Ltd. London Veloso VG, Neves G, de Almeida Capper L (2011) Sensitivity of a cirolanid isopod to human pressure. Ecol Indic 11:782-788 Wallace J, Eggert S, Meyer J, Webster J (1997) Multiple trophic levels of a forest stream linked to terrestrial litter inputs. Science 277:102-104 Wildish D (2012) Long distance dispersal and evolution of talitrids (Crustacea: Amphipoda: Talitridae) in the northeast Atlantic islands. J Nat Hist 46:2329-2348 Yamanaka T, Raffaelli D, White PCL (2010) Physical determinants of intertidal communities on dissipative beaches: Implications of sea-level rise. Estuar Coast Shelf S 88:267-278 Yamazaki K (2012) Seasonal changes in seaweed deposition, seaweed fly abundance, and parasitism at the pupal stage along sandy beaches in central Japan. Entomol Sci 15:28-34
| 114
CHAPTER V
V. Effect of mechanical grooming on the macrofaunal community of exposed sandy beaches
Barreiro F., Gómez M., Lastra M, López J. (Under Review)
Marine Biology
EFFECTS OF THE MECHANICAL BEACH GROOMING
5.1. ABSTRACT
Heavy machinery sieving the superficial layers of sand to clear out all the material deposited on the beach surface -also known as mechanical grooming- has become a common practice in urban beaches worldwide. The consequent removal of stranded macroalgae has major biological influences, although the overall effect at ecosystem level remains unclear. We investigate the effect of beach grooming in the macrofaunal communities of exposed sandy beaches by comparing the spatio-temporal variability of 4 ungroomed and 2 intensively-roomed beaches, under a wide range of macroalgal inputs. Samples were collected seasonally in the supratidal and intertidal zones of each beach over a one-year period. The number of species, total density and the macrofaunal composition differed widely among beaches. The differences between the groomed and ungroomed beaches were larger in the supratidal zone. Along the intertidal, the lowest number of species were observed in the groomed beaches, but also in natural beaches having the harshest physical environment and the lowest inputs of drifted macroalgae. The indicator species analysis (IndVal) was useful to detect the taxanomic characteristics of the ungroomed beaches. Talitrus saltator in the supratidal zone and Nemerteans in the intertidal are proposed as indicative taxa of the ungroomed sites. This work represents the first approach to the study of the ecological consequences of meachanical gooming including the fluctuations of allochthonous inputs at temporal and spatial scales. Results provide evidence of the strong deleterious effect of this common activity on beach ecosystems.
Key words: Sandy beaches - Mechanical cleanning - human impact - macrofauna - recreational eocology - coastal conservation
| 118 CHAPTER V
5.2. INTRODUCTION
The coastal zone has historically been a focal point of human settlements due to the multiple ecological services it provides (Ewel et al. 2001, Strayer & Findlay 2010) Consequently, as a direct result of the human pressure, coastal areas have become one of the most threatened ecosystems worldwide (Lotze et al. 2006). Despite this intense and growing use of beaches (Barbier & Hacker 2011), the role of humans on the alteration of coastal environments is still poorly understood (Worm et al. 2006, Jackson & Nordstrom 2011).
Sandy beaches constitute a transitional zone between terrestrial and marine ecosystems, which comprises two-thirds of the world’s ice-free coastline (McLachlan & Brown 2006). Beaches offer valuable ecological services to society, such as raw materials, coastal protection, erosion control, nutrient recycling, water catchment and purification, maintenance of wildlife, and tourism and recreational use (Schlacher et al. 2007, Defeo et al. 2009, Barbier & Hacker 2011). One of the most conspicuous beach characteristics is its low primary production and a strong dependence on allochthonous subsidies, which provide food and habitat for a large number of species (Pearse et al. 1942, Colombini & Chelazzi 2003).
The recreational use of sandy beaches has increased greatly over the last decades, generating higher income for the economy of coastal communities (Klein et al. 2004). Therefore, in addition to the general threats posed by climate change, biological invasion and sea level rise on coastal ecosystems (Feagin et al. 2005, Jones et al. 2007, Ehrenfeld 2010, Hoegh-Guldberg & Bruno 2010), tourism and recreational activities also represent an increasing global stressor of beach ecosystems (Defeo et al. 2009, Meager et al. 2012, McLachlan et al. 2013).
In this context, mechanical beach grooming has become common practice worldwide (Dugan & Hubbard 2010, Gilburn 2012, Nordstrom et al. 2012). This activity
| 119 EFFECTS OF THE MECHANICAL BEACH GROOMING
consists of the non-selective sieving of the superficial layers of sand by using heavy mechanical equipment. Along with debris deposits, these grooming activities remove habitual, natural organic material, mostly macroalgal wrack, which is stranded on the beach once detached from neighbouring, highly productive rocky shores, sea grass and salt marsh areas. Mechanical grooming reduces the biodiversity of wrack-associated macrofauna (Colombini et al. 2000, Dugan et al. 2003, Gilburn 2012), depleting the transfer of materials and secondary production towards upper trophic levels, including avian consumers (Dugan et al. 2003, Dugan & Hubbard 2010, Meager et al. 2012). The removal of large quantities of algal biomass may also affect the leaching of nutrients to the coastal zone once decay is initiated by physical and biological processes (Dugan et al. 2011, Barreiro et al. 2012).
Owing to the limited number of studies carried out, the overall effect of beach grooming remains yet unclear (Gilburn 2012). The amount of wrack deposited on each beach and its distribution across the tidal range may strongly influence both faunal abundance and community composition (Dugan et al. 2003, Jaramillo et al. 2006, Olabarria et al. 2010, MacMillan & Quijón 2012). These factors should therefore be included when the potential effects of grooming activities on the macrofaunal community are being investigated. A certain number of macrofaunal species have been used as ecological indicators to assess the nature and severity of human impact at temporal and spatial scales (Niemi & McDonald 2004). Benthic invertebrates can be employed as appropriate indicators of the ecosystem integrity, as they react to disturbance at a fine scale (Carignan & Villard 2002). Indeed, they have been used as ecological indicators of human stressors in a wide range of marine ecosystems, including sandy beaches (Fanini et al. 2009, Sarmento & Santos 2011, Veloso et al. 2011).
The grooming activities mainly impact on the supratidal zone. The algal wrack stranded on the upper beach, remains there for several days, weeks or even months (Colombini & Chelazzi 2003, Orr et al. 2005, Gómez et al. 2013). It is thus common to
| 120 CHAPTER V observe wrack lines or patches in different aging states on natural beaches. The aim of the present study was to examine the effect of mechanical grooming on the algal wrack dynamics and the ecological features of exposed sandy beaches. To achieve this, 2 intensively-groomed beaches vs. 4 ungroomed beaches under a wide range of macroalgal inputs were compared throughout the year cycle on the Galician coast, NW Spain. Specifically, we hypothesise that (1) the number of species and total density are lower in the supratidal zone of groomed beaches, which thereby (2) results in differences in assemblage composition. (3) The variability of the community structure in the intertidal zone may be primarily affected by environmental harshness (McLachlan & Brown 2006, Defeo & McLachlan 2011), with a lower impact of beach grooming here than in the supralitoral zone. An additional objective of this study was to evaluate the potential use of macrofaunal indicator species in assessing the relative ecological health of sandy beaches.
5.3. MATERIAL AND METHODS
5.3.1. Field sampling design
Six beaches on the NW coast of Spain (Fig. 5.1) were chosen as follows: 2 beaches receiving intermediate inputs of drifting macroalgae and suffering from intense grooming activities: America (AM) and Samil (SA); 4 ungroomed beaches under a wide range of macroalgae inputs: Balieiros (BA), Ladeira (LA), Toralla (TO) and Abra (PA). Tidal conditions were meso-macrotidal, ranging from 3.5 to 4 m in spring tides. The environmental characteristics of these beaches are shown in Table 5.1. Sampling was performed monthly on a 100-m-long stretch in the centre of each beach. To quantify wrack biomass, samples were collected from the base of the dune to the lowest swash level along six 1-m-wide transects. Coverage (using the line-intercept method), specific composition and total biomass were calculated for each transect. Details of the assessment of wrack biomass are given in (Barreiro et al. 2011).
| 121 EFFECTS OF THE MECHANICAL BEACH GROOMING
Fig. 5.1. Sampled beaches on the NW coast of the Iberian Peninsula. The red circle represent the location of the mechanical groomed beaches: America (AM) and Samil (SA); and the black circle the ungroomed beaches: Abra (PA), Toralla (TO), Ladeira (LA) and Samil (SA).
The macrofaunal communities were sampled seasonally for an entire year (January, April, July and October 2008) during the same period and in the same area where the wrack evaluation was performed (from December 2007 to November 2008). Samples were taken at 5 levels on the shore (hereinafter “beach levels”): 2 intertidal (low and medium) and 3 supratidal (low, medium and high) levels. This beach division was based on the scheme proposed by (Salvat 1964). The low intertidal level (LI) was located at the lowest swash point during low tide; the medium intertidal (MI) was located at the upper part of the water table outcrop; the low supratidal level (LS) corresponds to the drift line; the high supratidal (HS) was situated at the base of the dune; and the medium supratidal (MS) was determined as an equidistant point between the previous two levels. Six random samples were collected from each level with a cylindrical corer of 25 cm diameter which penetrated 15 cm deep in the sediment. Samples were sieved through a 1-mm mesh and preserved in 4% formalin-sea water
| 122 CHAPTER V
Anchura Longitud Wave Beach 1/slope MGS (µm) Exposure rate (m) (m) height (m) AM 110 2200 17.6 ± 1.1 241 ± 39 0.6 ± 0.1 12 (exposed) BA 100 840 10.8 ± 0.6 783 ± 140 2.5 ± 0.6 18 (very exposed) LA 130 5000 34.8 ± 0.3 190 ± 3 1.2 ± 0.1 13 (exposed) SA 100 1640 15.8 ± 0.2 317 ± 118 0.8 ± 0.3 12 (exposed) TO 60 100 11.6 ± 1 764 ± 105 0.2 ± 0 10 (sheltered) PA 60 210 10.1 ± 0.9 1293 ± 420 0.2 ± 0 12 (exposed)
Table 5.1 Environmental characteristic of the studied beaches. Exposure index according to the rating system of McLachlan (1980). The standard error is shown for 1/Slope, MGS and mean wave height. See Fig. 1 for site abbreviations. solution. The specimens were later sorted from the sediment and determined to the lowest taxonomic level possible.
5.3.2. Statistical analysis
Differences in the number of species and density (ind./m-2) among beaches and levels were explored with orthogonal two-way ANOVAs for each beach zone (i.e., intertidal and supratidal). Beach (6 levels) and beach level (3 levels in the supratidal zone and 2 in the intertidal) were fixed factors (n=4). Density data were log-transformed prior to the analysis so as to meet the assumptions of normality and homogeneity of variances. A posteriori multiple comparison analyses were conducted using Student-Newman-Keuls (SNK) test (α = 0.05).
In order to analyse the similarities in community structure and composition among beaches and levels, a hierarchical cluster analysis was performed with the value of abundance of each species per level and beach (n=4). Source data were log-transformed to calculate the Bray-Curtis similarity index. The similarity profile (SIMPROF) analysis was applied to test the statistical significance of each node in the resulting dendrogram (Clarke et al. 2008).
| 123 EFFECTS OF THE MECHANICAL BEACH GROOMING
The assemblage composition in each zone (i.e., intertidal and supratidal) was examined among beaches and levels through a two-way permutational analysis of variance (PERMANOVA). Beach (4 levels) and beach level (3 levels in the supratidal and 2 levels in the intertidal) were fixed factors. PERMANOVAs were run on Bray-Curtis dissimilarity matrices of species abundance. These data were previously log-transformed. A posteriori pairwise comparison tests were implemented with the significant terms.
We explored the association of species with intertidal and supratidal habitats using the indicator species analysis (Dufrêne & Legendre 1997). Given a matrix composed of the species presence-absence data per beach level and sampling event, the Indicator Value index (IndVal) (Dufrêne and Legendre 2009) was calculated for individual sites and site combinations (De Cáceres & Legendre 2009). The significance of the overall association of each species with individual sites or site combinations (i.e., beaches) in each habitat type (i.e., intertidal and supratidal) was evaluated by means of permutation tests (De Cáceres & Legendre 2009). The association index IndVal was also examined with species combination to assess the potential use of multi-species association with groomed and ungroomed habitats (De Cáceres et al. 2012). The species-habitat association analysis was conducted through the ‘multipatt’ function in the ‘indicspecies’ package available in R (De Caceres & Jansen)
5.4. RESULTS
5.4.1. Number of species and density
The variability in the number of species and density along the supratidal and intertidal zones differ among beaches (Fig. 5.2; Table 5.2). The average number of species inhabiting the supralitoral levels ranged from 1.7 ± 0.3 (SA) to 6.2 ± 0.6 (PA) throughout the year. Groomed beaches (i.e., AM and SA) showed a significantly lower number of species than ungroomed beaches (ANOVA, SNK test). The number of species found on
| 124 CHAPTER V each beach was similar among supratidal levels (ANOVA). The mean density of individuals in this zone fluctuated between 37.8 ± 14.9 (SA) and 3171 ± 1721 (TO), with the lowest quantities measured in groomed beaches (ANOVA). Density varied significantly among supratidal levels, reaching the highest values along the drift line on all beaches (ANOVA).
The number of species obtained in the intertidal zone ranged from 5.5 ± 0.8 (SA) to 14.8 ± 1.7 (PA). The lowest numbers of species were found in SA and BA (groomed and ungroomed beach, respectively). Density in the intertidal zone differed significantly among beaches. Density tended to decrease from ungroomed beaches with high wrack inputs (PA and TO) to ungroomed beaches with scarce wrack inputs (BA); however, beaches were not grouped in the post-hoc analysis (SNK test).
Number of species Total density (ind.m²) df MS F P df MS F P Supratidal Level (Le) 2 10.3 2.5 0.093 2 8 5.4 0.007 Beach (Be) 5 42.6 10.3 0.000 5 45.9 30.9 0.000 Le x Be 10 1.8 0.4 0.927 10 0.8 0.6 0.844 Residual 54 4.1 54 1.5 Total 71 71 Intertidal Level (Le) 1 21.3 1.8 0.192 1 2.7 1.7 0.2 Beach (Be) 5 104.7 8.7 0.000 5 9.2 5.9 0.001 Le x Be 5 9.1 0.8 0.589 5 2.2 1.4 0.253 Residual 36 12 36 1.6 Total 47 47
Table 5.2. Results of the two-way ANOVAs comparing the number of species and total density of invertebrates in the intertidal and supratidal zones among beaches (6 levels) and beach levels (3 levels in the supratidal and 2 levels in the intertidal).
| 125 EFFECTS OF THE MECHANICAL BEACH GROOMING
Fig. 5.2. Number of species and total density in the supratidal and intertidal levels of the studied beaches. Low supratidal (LS), medium supratidal (MS), high supratidal (HS), low intertidal (LI) and medium intertidal (MI). See Fig.1 to for site abbreviations.
5.4.2. Community composition
The cluster analysis evidences the expected dissimilarities between the supratidal and the intertidal assemblages (Fig. 5.3). However, species composition and abundance varied significantly among beaches (Permanova). The supratidal species were similar in the mechanically groomed beaches; on the contrary, assemblages differed from each other in ungroomed sites (Permanova; pairwise comparison). Comparisons among levels indicate that the low supratidal zone (drift zone) differed from the medium and high supratidal (Permanova; pairwise). In the intertidal zone, the species composition was similar in beaches with large deposits of wrack (PA and TO) and varied in the rest of the
| 126 CHAPTER V beaches. The assemblage composition also changed between the low and medium intertidal zones in all beaches (Permanova; pairwise).
Fig. 5.3. Dendrogram showing the similarities of species- composition among beach levels, elaborated with the log- transformed data of species abundance. Number denotes beach levels across the beach: low intertidal (1), medium intertidal (2), low supratidal (3), medium supratidal (4) and high supratidal (5). Dashed lines represent no significant divisions (SIMPROF test).
Table 5.3. Results of the two-way permutacional multivariate analysis of variance (PERMANOVA) among beaches (6 levels) and beach levels (3 levels in the supratidal and 2 levels in the intertidal) in the supratidal and intertidal zones.
Supratidal Intertidal df MS Pseudo-F P(perm) df MS Pseudo-F P(perm) Beach 5 16606 7.7 0.001 5 13166 6.9 0.001 Level 2 3941 1.8 0.007 1 3856 2 0.015 BeachxLevel 10 2280 1.1 0.308 5 1975 1 0.399 Res 54 2148 36 1904 Total 71 47
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5.4.3. Specie-site association
The results of the species-site association analysis show that the intertidal zone involves a higher number of associated species than that in the supratidal zone (Table 5.4), which was consistent in both groomed and ungroomed beaches (Table 5.5). In the supratidal zone, using a minimum association value√IndVal=0.8 of as a threshold, the representative species of site combinations were as follows: Tylos europaeus was
Table 5.4. Species-habitat association analysis for site combinations (α = 0.05). See Fig.1 for site abbreviations.
Specie Site IndVal p-value
Lek anesphaera rugicauda BA 0.674 0.001 Eurydice pulchra BA 0.671 0.001 Eurydice affinis BA 0.612 0.002 Pseudorchestoidea brito LA 0.577 0.002 Pontocrates arenarius LA 0.516 0.008 Cumopsis fagei AM+LA+SA 0.668 0.002
SUPRATIDAL Tylos europaeus BA+PA+TO 0.885 0.001 Deshayesorchestia deshayesii LA+PA+TO 0.87 0.001 Talitrus saltator BA+LA+PA+TO 0.91 0.001
Donax spp. AM 0.632 0.014 Aonides oxycephala PA 0.791 0.001 Nereididae TO 0.802 0.001 Scoloplos armiger TO 0.791 0.001 Eocuma dollfusi AM+LA 0.661 0.006 Nematoda PA+TO 0.86 0.001 Capitella capitata c.f. PA+TO 0.839 0.001 Malacoceros fuliginosus PA+TO 0.839 0.001 Oligochaeta PA+TO 0.722 0.002 Lumbrineridae PA+TO 0.707 0.001 INTERTIDAL Eurydice pulchra AM+BA+LA 0.714 0.008 Gastrosaccus sanctus AM+BA+LA 0.709 0.003 Haustorius arenarius AM+LA+SA 0.866 0.001 Nemertea BA+LA+PA+TO 0.813 0.001 Pontocrates arenarius AM+BA+LA+PA+SA 0.895 0.005 Cumopsis fagei AM+BA+LA+PA+SA 0.852 0.013 Scolelepis (Scolelepis) squamata AM+LA+PA+SA+TO 0.925 0.009
| 128 CHAPTER V associated with BA, PA and TO; Deshayesorchestia deshayesii with LA, PA and TO; and Talitrus saltator with the four ungroomed beaches studied (BA, LA, TO and PA). In the intertidal zone, under the same threshold, Capitella capitata, Malacoceros fuliginosus and Nematoda were associated with PA and TO. Only the nemerteans taxa were associated with the intertidal zone of the four ungroomed beaches.
The multi-species association analysis demonstrates that the supralitoral zone of groomed beaches lacks species combination with a significant indicator value; this was contrary to that observed in ungroomed beaches, where a strong association with T. saltator, separately and combined with other taxa, was detected. Haustorius arenarius,
Table 5.5. Species-habitat association analysis. Both components of the IndVal index are shown: A is a measured of the species or species combination specificity to a site and B is the probability of finding the species when the sample belongs to this site.
Beach Zone Status Specie A B sqrtIV
Supratidal Talitrus saltator 0.88 0.94 0.91 Tylos europaeus 0.95 0.81 0.88 T. saltator + Tylos 0.97 0.77 0.87 Deshayesorchestia deshayesii 0.9 0.75 0.82 D. deshayesii + T. saltator 0.95 0.75 0.84 Ungroomed T .saltator + Diptera 0.9 0.75 0.82 Diptera 0.8 0.81 0.8 Diptera + Tylos 1 0.65 0.8 T. saltator + Coleoptera 0.94 0.63 0.77 D .deshayesii + Tylos 0.97 0.6 0.76 Coleoptera 0.82 0.65 0.73 Groomed
Nemertea 0.92 0.72 0.81 Nemertea + Scolelepis squamata Ungroomed 0.9 0.59 0.73 Intertidal P. arenarius + Nemertea 0.95 0.56 0.73
Groomed
| 129 EFFECTS OF THE MECHANICAL BEACH GROOMING
Fig. 5.4. Density of T. saltator and nemerteans in the supratidal and intertidal zone respectively. See Fig. 1 for site abbreviations. separately and combined with other taxa, was significantly associated with groomed intertidal habitats, although with a low indicator value (below 0.6). Nemerteans, separately and combined, were strongly associated with the intertidal zone of ungroomed beaches. In the groomed beaches, however, T. saltator (in the supratidal zone) and Nemerteans (in the intertidal zone) registered densities close to zero and lower than in ungroomed sites. In ungroomed beaches, both taxa increase in density according to the rise in wrack supply (Fig. 5.4).
5.5. DISCUSSION
This study shows the substantial influence of mechanical grooming activities on the macrofaunal community structure of exposed beaches at different spatial scales over a one-year period. These effects were detected after considering the wide variability in the infaunal community of beaches as a consequence of natural differences in the inputs of macroalgae (Barreiro et al., under review). In addition, we propose two taxa as ecological indicators of the cleaning activities.
Mechanical grooming removes all wrack deposited on the upper part of the beach and, subsequently, the ecological role played by this organic input in the ecosystem is lost.
| 130 CHAPTER V
Wrack represents an important resource for invertebrates either as food or refuge (Ince et al. 2007). Our investigation encompassing one year of temporal variability shows that the supratidal zone of groomed beaches supports a lower number of species and density than those found in ungroomed beaches. Similar results were obtained in snapshot studies performed on different geographical areas (Dugan et al. 2003, Gilburn 2012) which is indicative of the consistent effect of grooming activities on the macrofaunal community. The comparative analyses between the two groomed sites and one of the ungroomed beaches receiving scarce wrack inputs (BA), evidence an additive repercussion of wrack removal on the availability of resources, inducing a cascading effect up and down the trophic web, which depletes the number of species and abundance. The use of heavy machinery in the groomed beaches may directly increase the mortality of the macrofauna by trampling and changing the physical characteristics of the sediment (Gheskiere et al. 2006, Dugan & Hubbard 2010). Wrack removal also alters the shoreline sediment dynamics, preventing incipient dunes from forming and reducing the number of habitats for flora and fauna (Dugan & Hubbard 2010, Nordstrom et al. 2012).
The organic matter processed in the supratidal and high intertidal zones, releases nutrients and organic compounds which reach the low intertidal zone through the water table outcrop (Dugan et al. 2011, Barreiro et al. 2012). All these inputs may affect the abundance and composition of microphytobenthos (García-Robledo et al. 2008) and increase productivity, what could be transferred towards higher trophic levels. As a result, wrack removal, albeit performed in the upper part of the beach, could affect the macrofaunal assemblages inhabiting low intertidal zones, and its effects overlap with other paramount factors driving the ecology of sandy shores, such as the harshness of the physical environment (Defeo & McLachlan 2005, McLachlan & Brown 2006, Defeo & McLachlan 2011). In this study, density and species number in the ungroomed beaches tended to increase from the low to the highest wrack-subsidised sites, irrespective of
| 131 EFFECTS OF THE MECHANICAL BEACH GROOMING
the physical environment. This indicated the important role of food subsidies in structuring the intertidal macrofaunal assemblages in low-productive ecosystems, such as sandy beaches. Differences in species richness between the two groomed sites cannot be explained either in terms of their physical characteristics or by the influence of wrack resource, as both beaches have similar morphodynamic features. This result suggests that other factors may be conditioning the species occurrence at groomed beaches. We did not quantify other food resources such as particulate organic matter or phytoplankton concentration, nor other potential anthropogenic impacts which may disturb the macrofaunal community (Lastra et al. 2006, Rodil et al. 2012, Schlacher & Thompson 2012).
The variation in the species richness and density across the intertidal width was similar for groomed and ungroomed beaches. Beaches are highly dynamic systems which support strong environmental gradients from the base of the dune to the lowest swash level (McLachlan & Brown 2006). The drift line divides two major zones inhabited by air- breathing and water-breathing species, which represent the primary structural factor in the macrofaunal zonation (McLachlan & Brown 2006). At every beach, there were not differences in species composition within each tidal zone (intertidal and supratidal) along the year cycle. The abundance of each species, however, differed significantly among levels within each zone. In the supratidal zone, the density of each species decreased from the drift line to the base of the dune. The water content of the sediment may constrain the sensitive species and the population abundance (Jaramillo et al. 2006). Likewise the sediment, algal wrack becomes drier upwards the drift line, thus limiting the presence of species that prefers fresh deposits located at the drift line. Insects can be abundant in these drier areas (Colombini & Chelazzi 2003). Nevertheless, due to the sampling procedure in this study, the flying species might have been underestimated. In the intertidal zone of each beach, we found the same species list and a similar total density both in the swash level and in the water table outcrop, even
| 132 CHAPTER V though the species composition changed between levels, which is caused by differences in the ecological preferences across the intertidal width (Rodil et al. 2006).
Mechanical cleaning completely changed the supratidal community structure of the studied beaches. In the intertidal zones, a homogeneous group of sites, characterised by large deposits of wrack, differed from the other beaches completely, including both groomed and ungroomed locations, which, moreover, differed from each other. This suggests, therefore, that in addition to the physical constraints, wrack availability and human impact are important factors in structuring the beach communities.
The indicator species analysis is a useful tool to study shifts in association patterns (Dufrêne & Legendre 1997) which may reflect the existence of underlying mechanisms structuring the macrofaunal assemblages (Azeria et al. 2009). In this research, some species showed a significant association with a particular site or group of sites, which may reveal the interaction between habitat characteristics and species requirements. In the supralitoral zone, only Talitrus saltator presented a strong association with all the ungroomed beaches. This is a common widespread species specially adapted to a wide range of beach conditions due to its fast population turnover and a relatively high tolerance to disturbance (Williams 1978, Marques et al. 2003, Calosi et al. 2007, Scapini & Ottaviano 2010). Density of T. saltator is related to the availability of food reaching the beach, mainly wrack macroalgae (Marques et al. 2003, Gonçalves & Marques 2011). We suggest that T. saltator density could be used as a proxy of the anthropogenic impact on exposed sandy beaches, especially with regards of grooming disturbance. In this sense, within the same geographical area, density values of T. saltator obtained in ungroomed beaches with scarce wrack subsidies could be used as a threshold to characterise highly impacted beaches. Nemertean taxa were closely associated with the intertidal zone of ungroomed beaches. These taxa are common predators on polychaetes and crustaceans in intertidal habitats, including exposed beaches (Thiel & Kruse 2001, Junoy & Herrera-Bachiller 2006, Herrera-Bachiller et al. 2008). Our results
| 133 EFFECTS OF THE MECHANICAL BEACH GROOMING
showed a clear increase in Nemertean density from moderately to highly subsidised beaches, which could be linked to a greater density of potential preys. Indeed, under suitable conditions, intertidal nemerteans can be locally abundant (Thiel & Kruse 2001). The lower presence of nemerteans in groomed beaches may not only be related to the availability of prey. The intertidal density of invertebrates did not differ significantly between the groomed and some of the ungroomed beaches. Although human use of the studied beaches was not measured, groomed beaches normally attract a higher number of visitors, which may cause greater sediment disturbance and an increasing trampling effect (Moffett et al. 1998, Ugolini et al. 2008, Schlacher & Thompson 2012). Species inhabiting sandy beaches at low densities, also considered as rare species, such as Nemerteans, are usually sensitive to the press or pulse anthropogenic disturbance (Junoy et al. 2005). Thus, we propose the potential use of Nemertean taxa as an indicator of human pressure on the intertidal zone.
Our study suggests that algal subsidies in natural beaches are a primary factor on structuring macrofaunal assemblages, irrespective of the physical environment. The results provide evidence of the strong effect of mechanical grooming on the supratidal community structure. In the intertidal zone of groomed beaches, some evidences of non-natural variations were detected, although our data did not support a direct relationship between the observed changes and the grooming activities. As a final goal, the use of the indicator species analysis is proposed as a suitable tool to find non- random distribution of species in beach ecosystems. These results could be useful for future conservation studies and management plans, confirming the deleterious effect of beach grooming on the ecological characteristics of exposed sandy beaches.
5.6. ACKNOWLEDGEMENTS
The authors thank R. de la Huz, L. Soliño, L. García, J. Hernández, and I. Rodil for help with field work.
| 134 CHAPTER V
5.7. LITERATURE CITED
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Defeo O, McLachlan A, Schoeman DS, Schlacher Ta, Dugan J, Jones A, Lastra M, Scapini F (2009) Threats to sandy beach ecosystems: A review. Estuarine, Coastal and Shelf Science 81:1-12 Dufrêne M, Legendre P (1997) Species assemblages and indicator species: the need for a flexible asymmetrical approach. Ecological monographs 67:345-366 Dugan JE, Hubbard DM (2010) Loss of Coastal Strand Habitat in Southern California: The Role of Beach Grooming. Estuaries and Coasts 33:67-77 Dugan JE, Hubbard DM, McCrary MD, Pierson MO (2003) The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of southern California. Estuarine, Coastal and Shelf Science 58:25-40 Dugan JE, Hubbard DM, Page HM, Schimel JP (2011) Marine Macrophyte Wrack Inputs and Dissolved Nutrients in Beach Sands. Estuaries and Coasts 34:839-850 Ehrenfeld JG (2010) Ecosystem Consequences of Biological Invasions. Annual Review of Ecology, Evolution, and Systematics 41:59-80 Ewel KC, Cressa C, Kneib RT, Lake PS, Levin La, Palmer Ma, Snelgrove P, Wall DH (2001) Managing Critical Transition Zones. Ecosystems 4:452-460 Fanini L, Marchetti GM, Scapini F, Defeo O (2009) Effects of beach nourishment and groynes building on population and community descriptors of mobile arthropodofauna. Ecological Indicators 9:167-178 Feagin Ra, Sherman DJ, Grant WE (2005) Coastal Erosion, Global Sea-Level Rise, and the Loss of Sand Dune Plant Habitats. Frontiers in Ecology and the Environment 3:359-364 García-Robledo E, Corzo A, García de Lomas J, van Bergeijk S (2008) Biogeochemical effects of macroalgal decomposition on intertidal microbenthos: a microcosm experiment. Marine Ecology Progress Series 356:139-151 Gheskiere T, Magda V, Greet P, Steven D (2006) Are strandline meiofaunal assemblages affected by a once-only mechanical beach cleaning? Experimental findings. Marine environmental research 61:245-264 Gilburn AS (2012) Mechanical grooming and beach award status are associated with low strandline biodiversity in Scotland. Estuarine, Coastal and Shelf Science:1-8 Gómez M, Barreiro F, López J, Lastra M, de la Huz R (2013) Deposition patterns of algal wrack species on estuarine beaches. Aquatic Botany 105:25-33 Gonçalves SC, Marques JC (2011) The effects of season and wrack subsidy on the community functioning of exposed sandy beaches. Estuarine, Coastal and Shelf Science 95:165-177 Herrera-Bachiller A, García-Corrales P, Roldán C, Junoy J (2008) The ignored but common nemertine Psammamphiporus elongatus from the Galician beaches (Spain), affected by the Prestige oil spill. Marine Ecology an evoluionary perspective 29:43-50 Hoegh-Guldberg O, Bruno JF (2010) The impact of climate change on the world's marine ecosystems. Science (New York, NY) 328:1523-1528
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Ince R, Hyndes G, Lavery P, Vanderklift M (2007) Marine macrophytes directly enhance abundances of sandy beach fauna through provision of food and habitat. Estuarine, Coastal and Shelf Science 74:77-86 Jackson NL, Nordstrom KF (2011) Aeolian sediment transport and landforms in managed coastal systems: A review. Aeolian Research 3:181-196 Jaramillo E, De La Huz R, Duarte C, Contreras H (2006) Algal wrack deposits and macroinfaunal arthropods on sandy beaches of the Chilean coast. Revista Chilena de Historia Natural 79:337-351 Jones A, Gladstone W, Hacking N (2007) Australian sandy-beach ecosystems and climate change: ecology and management. Australian zoologist 34:190-202 Junoy J, Castellanos C, Viéitez JM, de la Huz MR, Lastra M (2005) The macroinfauna of the Galician sandy beaches (NW Spain) affected by the Prestige oil-spill. Marine pollution bulletin 50:526-536 Junoy J, Herrera-Bachiller A (2006) Los nemertinos del Parque Nacional marítimo- terrestre de las Islas Atlánticas de Galicia. … de investigación en parques …:311- 325 Klein Y, Osleeb J, Viola M (2004) Tourism-generated earnings in the coastal zone: a regional analysis. Journal of Coastal Research 4:1080-1088 Lastra M, de la Huz R, Sánchez-Mata AG, Rodil IF, Aerts K, Beloso S, López J (2006) Ecology of exposed sandy beaches in northern Spain: Environmental factors controlling macrofauna communities. Journal of Sea Research 55:128-140 Lotze HK, Lenihan HS, Bourque BJ, Bradbury RH, Cooke RG, Kay MC, Kidwell SM, Kirby MX, Peterson CH, Jackson JBC (2006) Depletion, degradation, and recovery potential of estuaries and coastal seas. Science (New York, NY) 312:1806-1809 MacMillan MR, Quijón Pa (2012) Wrack patches and their influence on upper-shore macrofaunal abundance in an Atlantic Canada sandy beach system. Journal of Sea Research 72:28-37 Marques J, Gonçalves S, Pardal M, Chelazzi L, Colombini I, Fallaci M, Bouslama MF, El Gtari M, Charfi-Cheikhrouha F, Scapini F (2003) Comparison of Talitrus saltator (Amphipoda, Talitridae) biology, dynamics, and secondary production in Atlantic (Portugal) and Mediterranean (Italy and Tunisia) populations. Estuarine, Coastal and Shelf Science 58:127-148 McLachlan A, Brown AC (2006) The ecology of sandy shores, Vol. Elsevier, Amsterdam McLachlan A, Defeo O, Jaramillo E, Short AD (2013) Sandy beach conservation and recreation: Guidelines for optimising management strategies for multi-purpose use. Ocean & Coastal Management 71:256-268 Meager JJ, Schlacher Ta, Nielsen T (2012) Humans alter habitat selection of birds on ocean-exposed sandy beaches. Diversity and Distributions 18:294-306 Moffett MD, McLachlan A, Winter PED, Ruyck aMC (1998) Impact of trampling on sandy beach macrofauna. Journal of Coastal Conservation 4:87-90
| 137 EFFECTS OF THE MECHANICAL BEACH GROOMING
Niemi GJ, McDonald ME (2004) Application of ecological indicators. Annual Review of Ecology, Evolution, and Systematics 35:89-111 Nordstrom KF, Jackson NL, Freestone AL, Korotky KH, Puleo Ja (2012) Effects of beach raking and sand fences on dune dimensions and morphology. Geomorphology 179:106-115 Olabarria C, Incera M, Garrido J, Rossi F (2010) The effect of wrack composition and diversity on macrofaunal assemblages in intertidal marine sediments. Journal of Experimental Marine Biology and Ecology 396:18-26 Orr M, Zimmer M, Jelinski D, Mews M (2005) Wrack deposition on different beach types: spatial and temporal variation in the pattern of subsidy. Ecology 86:1496-1507 Pearse A, Humm H, Wharton G (1942) Ecology of sand beaches at Beaufort, N.C. Ecological Monographs 12:135-190 Rodil IF, Compton TJ, Lastra M (2012) Exploring macroinvertebrate species distributions at regional and local scales across a sandy beach geographic continuum. PloS ONE 7:e39609 Rodil IF, Lastra M, Sanchez-Mata AG (2006) Community structure and intertidal zonation of the macroinfauna in intermediate sandy beaches in temperate latitudes: North coast of Spain. Estuarine, Coastal and Shelf Science 67:267-279 Salvat (1964) Les conditions hydrodynamiques insterti- tielles des sédiments meubles intertidaux et la répartition verticale de la faune endogée. Academie des Sciences (Paris) Comptes Rendus 259:1576-1579 Sarmento VC, Santos PJP (2011) Trampling on coral reefs: tourism effects on harpacticoid copepods. Coral Reefs 31:135-146 Scapini F, Ottaviano O (2010) The possible use of sandhoppers as bioindicators of environmental stress on sandy beaches. Zool baetica:33-44 Schlacher TA, Dugan J, Schoeman DS, Lastra M, Jones A, Scapini F, McLachlan A, Defeo O (2007) Sandy beaches at the brink. Diversity and Distributions 13:556-560 Schlacher Ta, Thompson L (2012) Beach recreation impacts benthic invertebrates on ocean-exposed sandy shores. Biological Conservation 147:123-132 Strayer DL, Findlay SEG (2010) Ecology of freshwater shore zones. Aquatic Sciences 72:127-163 Thiel M, Kruse I (2001) Status of the Nemertea as predators in marine ecosystems. Hydrobiologia 456:21-32 Ugolini A, Ungherese G, Somigli S, Galanti G, Baroni D, Borghini F, Cipriani N, Nebbiai M, Passaponti M, Focardi S (2008) The amphipod Talitrus saltator as a bioindicator of human trampling on sandy beaches. Marine environmental research 65:349- 357 Veloso VG, Neves G, de Almeida Capper L (2011) Sensitivity of a cirolanid isopod to human pressure. Ecological Indicators 11:782-788 Williams J (1978) The annual pattern of reproduction of Talitrus saltator (Crustacea: Amphipoda: Talitridae). Journal of Zoology:231-244
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Worm B, Barbier EB, Beaumont N, Duffy JE, Folke C, Halpern BS, Jackson JBC, Lotze HK, Micheli F, Palumbi SR, Sala E, Selkoe Ka, Stachowicz JJ, Watson R (2006) Impacts of biodiversity loss on ocean ecosystem services. Science (New York, NY) 314:787-790
| 139 CHAPTER VI
VI. General conclusions
CHAPTER VI
. The deposition of macroalgae on sandy beaches is not a random process. The quantification of the habitat openness and permeability explained largely the variability in the biomass of algae stranded on the studied beaches. The measured of these habitat characteristics may be a useful tool to improve the ecological understanding of the coastal ecosystems, sites where the transfer of matter and nutrients are common phenomenons.
. The specific composition of wrack showed a cyclical pattern. This ongoing compositional change indicates that the wrack-stranding process is linked to the life cycle of the macroalgae. This cyclic trend implies that the variable arrival of resources to sandy beaches over a period of months is, to some extent, predictable.
. The invasive Sargassum muticum was one of the macroalgae with the largest biomass supplied to all beaches. However, its contribution increases at beaches with intermediate and high wave action. The buoyancy properties of this specie may assist it in drift ashore. The potential effects of this recently introduced alga might differ among beaches.
. Beaches act as a donor ecosystem of nutrients to the coastal zone, thus noting the substantial feedback connectivity between high productivity macrophyte based environments, such as rocky shores and salt marshes, and low productive neighbouring sandy beaches.
. The variable relationship between the different nutrient species versus biomass is indicative of the complexity of the biogeochemical pathways linked with the wrack processing in exposed sandy sediments.
. From low to high wrack subsidized beaches the macrofaunal community changed significantly. This shift in the community composition and abundance
| 141 GENERAL CONCLUSIONS
indicates that the availability of macroalgae it is an important factor structuring the macrofaunal communities of exposed beaches.
. The macrofauna resulted differently affected by the inputs of macroalgae in the intertidal and in the supratidal zones. While in the supratidal the most prominent consequence was the significant increase of species density, in the intertidal it was observed a shifting in the community composition from low to high subsidized beaches. This suggests that for the species living at the high part of the beach, wrack may be a limiting resource. Contrarily, in the low intertidal the deposition of wrack could modify the habitat characteristics and enable the occurrence of the species which better exploit this resource.
. Mechanical grooming has a strong deleterious effect on the beach ecosystem. This activity changed completely the supratidal zone of the groomed beaches; it reduced the macrofaunal biodiversity and density drastically. In the intertidal of these beaches some evidence of human impact was also detected. However, in this zone a direct relationship with the mechanical cleaning could not be established.
. The use of indicator species to assess the ecological state of beach ecosystems could be a useful tool in the environmental management of the coastal zone. The grooming effect on the supratidal zone can be measured employing species with a high tolerance to the different and variables natural conditions.
. Overall, this thesis shows the high connectivity of sandy beaches with the neighbor ecosystems. In addition, it is suggested the potential advantages of the ecological studies performed across several ecosystems.
| 142 7. RESUMEN GENERAL
7. Resumen general
RESUMEN GENERAL
7.1. LAS PLAYAS
Las playas son depósitos de sedimentos no consolidados, removidos por las olas, que se forman en el límite marítimo-terrestre. Ocupan un amplio rango de ambientes tanto a escala regional, desde zonas estuáricas o llanuras intermareales a playas oceánicas, como a escala global, desde los trópicos hasta las playas Árticas y Antárticas. Dada esta gran extensión, las playas cubren aproximadamente el 70% de todos los márgenes continentales, es importante definir adecuadamente el tipo de ambiente en el que se realiza la investigación. Este trabajo se centra en el estudio ecológico de playas oceánicas, es decir, playas directamente expuestas a la acción del oleaje.
7.2. ECOLOGÍA DE PLAYAS
La ecología se ocupa del estudio científico de las interacciones que determinan la distribución y abundancia de los organismos. De acuerdo con esta definición, formulada recientemente por Krebs, la ecología de playas intenta entender los mecanismos que estructuran las comunidades biológicas y de este modo alcanzar una completa comprensión del ecosistema.
En comparación a otros sistemas costeros, la ecología de playas es una disciplina relativamente nueva. De hecho, antes de los setenta se publicaron escasos trabajos. A partir de esta fecha surgen numerosas investigaciones que culminarán en el primer simposio de playas celebrado en Sudáfrica en 1983. Desde entonces, la ecología de playas se ha desarrollado notablemente, muestra de ello son algunos principios ecológicos y varias hipótesis generales que han sido articuladas.
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7.3. ANTECEDENTES
Este estudio se llevó a cabo en Galicia, región situada al noroeste de la península ibérica. La costa gallega se extiende a lo largo de 1995 km de los cuales 278 km corresponden a playas arenosas. Debido a su localización, la característica climática más destacada es la transición entre los regímenes oceánicos y mediterráneos. A grandes rasgos puede describirse por la existencia de abundantes precipitaciones y temperaturas templadas en invierno y verano. Entre las condiciones oceanográficas, destaca la influencia de afloramientos de aguas subsuperficiales (Galicia se encuentra al norte del “Canary upwelling system”). Este proceso incrementa la concentración de nutrientes en el litoral posibilitando una alta productividad biológica.
Como consecuencia del tardío comienzo de la ecología de playas, en España, salvo alguna investigación puntual, no existen trabajos con anterioridad a los noventa. Desde entonces, se han llevado a cabo varias tesis doctorales sobre distintos aspectos ecológicos de los intermareales arenosos. De toda esta reciente investigación, se ha forjado un sólido conocimiento científico de estos ecosistemas. Sin embargo, este conocimiento también ha generado nuevas preguntas pendientes de resolver.
La mayor parte de las playas localizadas en el N y NO de la costa española se clasifican como intermedias de acuerdo a sus características morfodinámicas. En playas gallegas, la riqueza específica es mayor que en otras regiones templadas. En el intermareal, los parámetros comúnmente utilizados para describir las comunidades macrofaunísticas, tales como riqueza específica, densidad y biomasa, tienden a aumentar desde estados reflectivos a disipativos. Sin embargo, en la zona supramareal frecuentemente se observa la tendencia contraria. En la costa cántabra se ha comprobado que las comunidades de invertebrados se ven afectadas por múltiples variables abióticas, es decir, dichas comunidades no están solamente influenciadas por factores morfodinámicos. Varios trabajos llevados a cabo en el N y NW de la península
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Iberica detectaron en la dirección Este-Oeste un cambio gradual en los parámetros utilizados para describir las comunidades. Esta variabilidad, posiblemente, esté relacionada con el incremento en la producción primaria hacia el oeste debido a la localización del afloramiento de aguas. Estos resultados previos indican que además de las características físicas otros factores como la disponibilidad de alimento en la columna de agua afecta al funcionamiento de estos ecosistemas intermareales.
Durante las últimas décadas se ha observado que la concentración de carbóno biopolimérico es un buen indicador de la disponibilidad de alimento existente en el sedimento. Su concentración esta inversamente relacionada con la pendiente de la playa. La misma tendencia se ha observado en la diversidad, densidad y biomasa de la macrofauna.
Además del contenido orgánico del sedimento y del existente en la columna de agua, el varamiento de plantas, algas y animales (también denominado wrack) sobre la superficie de la playa debe ser un importante factor que afecte a la macrofauna. Experimentos realizados en los últimos años han demostrado que los invertebrados que habitan en el supramareal se ven influenciados notablemente por la cantidad y composición de los depósitos depositados en la playa.
Las investigaciones sobre la distribución de la macrofauna en playas gallegas muestran dos zonas muy diferenciadas de acuerdo al modelo propuesto por Brown. Una zona supramareal y otra intermareal delimitadas por la línea de arribazón y ocupada por organismos que respiran o en la superficie o sumergidos. En playas intermedias con pendientes suaves algunas veces se detecta una tercera zona caracterizada por el espiónido Scolelepis squamata. En los utlitmos años también se ha demostrado que las interacciones biológicas intraespecíficas e interespecíficas influyen en la distribución de la macrofauna, incrementando por lo tanto la complejidad de los estudios de zonación.
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7.4. ENFOQUE
Los flujos de nutrientes y materia orgánica a través de las playas son procesos que se han documentado bien en todo el mundo. La importancia ecológica de esta transferencia de energía se ve potenciada por la baja productividad primaria de las playas. Sin embargo, las hipótesis tradicionales que intentan explicar la estructura de las comunidades macrofauníticas e incluso el funcionamiento del ecosistema, principalmente se asientan sobre la consideración del control físico de las comunidades en ambientes extremos. De este modo, estas hipótesis afirman que desde un punto de vista ecológico las playas pueden ser descritas únicamente en función de las interacciones entre el sedimento, el oleaje y las mareas. No obstante, un creciente número de excepciones a esta regla general han sido publicadas en los últimos años.
Los arribazones de algas son uno de los principales aportes orgánicos que periódicamente se depositan sobre la superficie de las playas. Se han cuantificado enormes cantidades de algas depositadas en el intermareal de múltiples regiones costeras. Sin embargo, a pesar de las significativas implicaciones ecológicas y biogeoquímicas de estos aportes orgánicos a las playas, los procesos, las características y los vectores implicados en su deposición así como su efecto en la estructura de las comunidades y del funcionamiento del ecosistema se desconocen en gran medida.
7.5. OBJETIVOS
El objetivo general de esta tesis es aumentar el conocimiento científico acerca de la ecología de los arribazones de macroalgas en playas. Concretamente, los objetivos planteados son:
. Establecer la magnitud y composición de los aportes de macroalgas teniendo en cuenta distintas escalas espacio-temporales.
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o Realizar la primera caracterización de los depósitos macroalgales en playas expuestas de Galicia. - Cuantificar el rango de biomasas e identificar las especies varadas en diferentes tipos de playas. - Investigar la presencia y la biomasa de especies invasoras. - Comparar los resultados obtenidos en la evaluación de las macroalgas varadas en playas de la costa atlántica gallega con la información publicada en otras regiones geográficas.
o Analizar que variables ambientales pueden influir en el grado de apertura y en la permeabilidad de las playas a los aportes de macroalgas.
o Investigar la variabilidad que el ciclo de vida de las predominantes especies de macroalgas podría inducir en la composición y biomasa de los varamientos.
. Evaluar la importancia de los arribazones de macroalgas en la liberación de nutrientes desde las playas a los zonas costeras próximas.
o Analizar la relación entre la magnitud de algas varadas y la variabilidad espacio- temporal en la concentración de nutrientes en el agua del intermareal.
o Investigar la influencia de los arribazones en las relaciones entre los diferentes nutrientes en el agua intermareal.
o Evaluar si la liberación de nutrientes a través del agua intersticial afecta significativamente al contenido de nutrientes de la zona de barrido.
. Determinar la influencia de la disponibilidad de algas en la estructura de las comunidades de macrofauna en playas arenosas expuestas.
o Investigar si la biomasa de algas afecta a la composición y abundancia de las comunidades de macrofauna en diferentes escalas espacio-temporales.
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o Evaluar el peso relativo de el ambiente físico y el de la disponibilidad de arribazones como factores estructuradores de la comunidad macrofaunistica.
o Analizar si la variabilidad en los aportes de algas afecta a la estabilidad de las comuindades. . Investigar el potencial impacto de la eliminación de las algas en la macrofuna de playas expuestas.
o Cuantificar el efecto de la eliminación de algas en la zona supramareal y la zona inferior del intermareal en playas expuestas.
o Evaluar el potencial uso de especies de invertebrados como indicadoras del estado ecológico en playas expuestas.
7.6. CAPITULOS
7.6.1. Capítulo II. Ciclo anual de algas arribadas en playas expuestas: efecto del ambiente físico.
La conectividad entre ecosistemas se reconoce como un importante proceso en estudios ecológicos. Las playas expuestas arenosas son ecosistemas abiertos y ampliamente dinámicos, principalmente sustentados por aportes alóctonos de materia orgánica, entre los más importantes se encuentran las macroalgas. La magnitud y composición de la biomasa de algas varadas se evalúo durante un año en seis playas expuestas de la costa gallega. Se investigo el efecto de la acción del oleaje y las características topográficas de cada playa en el varamiento. Mensualmente se midió la composición específica, la biomasa y cobertura de los arribazones a lo largo de seis transectos en cada playa. Los transectos se relizaron desde la base de la duna hasta el nivel inferior de la zona de barrido durante la bajamar de mareas vivas. La media del peso seco de las algas por transecto fluctuó entre 14 ± 5.3 y 9189 ± 3594 g m-1 (± se; n=6) entre las distintas localidades. Los arribazones estaban compuestos
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predominantemente por algas pardas, las cuales representaron el 70% de la media de la biomasa de todo el año. Las especies dominantes fueron Cystoseira spp. (30.3 ± 17.4 %) y Sargassum muticum (14.2 ± 7.1 %). Se observó un patrón cíclico en la composición de los arribazones acoplado con el ciclo de vida de las predominantes macroalagas. La relación entre la longitud y area de la playa (ratio L:A) y la altura de ola fueron las variables que mejor explicaron la biomasa y composición de los arribazones. Las playas pequeñas y protegidas de la acción del oleaje recibieron las mayores aportes de algas y mostraron la menor contribución de algas pardas. Estos resultados indican que la variabilidad en los arribazones de algas en playas expuestas puede ser explicados en función de la interacción entre la exposición al oleaje, la topografía costera y la estacionalidad.
7.6.2. Capítulo III. Acoplamiento entre los aportes de macroalgas y la liberación de nutrientes en playas expuestas arenosas.
Los flujos de nutrientes entre hábitats poseen una enrome relevancia en los estudios ecológicos debido a su implicación en la producción primaria, influencia en la estructura trófica y en la biodiversidad. Este estudio analiza el papel de las playas arenosas en el procesado de la materia orgánica. Se muestrearon tres playas con diferentes aportes de macroalgas a lo largo de un ciclo anual. La biomasa de algas depositada sobre la superficie de la playa y la concentración de nutrientes en el agua intersticial y en la zona de rompiente se midieron mensualmente. La concentración de nitrógeno inorgánico disuelto y fosfato en el agua intersticial aumento de playas con bajo a alto grado de aportes algales. A lo largo del año se observó un acoplamiento estacional entre la biomasa de algas varadas y la concentración de nutrientes. Entre los
+ distintos nutrientes, se detectó una relación variable entre el ratio NH4 /NOx¯ y la biomasa de algas depositada. Estos resultados aportan evidencias del activo papel de las playas arenosas en el procesado de la materia orgánica y en reciclado de nutrientes,
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indicando la retroalimentación en la conectividad entre las playas expuestas y los ecosistemas vecinos.
7.6.3. Capítulo IV. Influencia de los aportes alóctonos de materia orgánica en la comunidad macrofaunística de playas arenosas expuestas.
Las conexiones entre hábitats en la zona litoral son procesos comunes y con múltiples vínculos. Las playas expuestas son ecosistemas abiertos caracterizados por su baja producción primaria. Por tanto, los organismos que habitan este ecosistema muestran una fuerte dependencia de los aportes alóctonos de materia orgánica. A pesar de ello, las playas son consideradas principalmente ambientes extremos donde las especies están primordialmente reguladas por el ambiente físico en el que viven. En este trabajo se investiga el efecto de la disponibilidad de macroalgas sobre la estructura de las comunidades macrofaunísticas (diversidad, densidad y composición) a lo largo de un año. Cuatro playas con diferentes aportes de algas se muestrearon desde la base de la duna hasta la línea de marea durante la bajamar de mareas vivas. El número de especies recogidas en cada playa osciló entre 18 y 40, la densidad media fluctuó entre 241 ± 36 y 3975 ± 519 (se; n=4). A pesar de la significativa interacción tanto espacial como temporal registrada, el número de especies y la densidad aumentaron de playas con escasa cantidad de algas a playas con extensos arribazones. La composición macrofaunística cambió significativamente a lo largo de este gradiente de aporte orgánico. Este cambio fue notorio tanto en la zona supramareal como en el intermareal. Sin embargo el efecto fue distinto en cada zona. Mientras que en la zona intermareal se registró un cambio en la identidad de las especies, en la zona supramareal el principal cambio fue debido a la dominancia de especies, pero de las mismas especies. Este trabajo evidencia la influencia de los arribazones de algas en la estructura y composición de la macrofauna en playas expuesta. Se destaca la importancia de las interconexiones entre las playas y los ecosistemas próximos.
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7.6.4. Capítulo V. Efecto de la limpieza mecánica en la comunidad macrofaunística de playas arenosas expuestas.
El tamizado de las capa de arena superficial, utilizando maquinaria pesada, para retirar todo el material depositado sobre la superficie de la playa se ha convertido en una práctica habitual en las playas urbanas de todo el mundo. La consecuente eliminación de de las macroalgas varadas influye enormemente en la biota, aunque el efecto general a nivel de ecosistema permanece sin aclarar. En este trabajo se investiga el efecto de la limpieza mecánica en la comunidad macrofaunística de playas expuestas arenosas. Para ello se compara la variabilidad espacio-temporal de cuatro playas no sometidas a tareas de limpieza con la de dos playas dónde estás tareas se realizan intensivamente. Las muestras se recogieron estacionalmente en las zonas supramareal e intermareal de cada playa a lo largo de un periodo de un año. El número de especies, la densidad total y la composición de la comunidad difirió ampliamente entre playas. Entre los dos grupos de playas la mayor diferencia se observó en la zona supramareal. En el intermareal, el menor número de especies se registró en una playa sometida a tareas de limpieza, pero también en la playa natural con el mayor estrés físico y la menor cantidad de arribazones de macroalgas. El análisis de especies indicadoras (IndVal) resulto ser una herramienta útil para detectar las características taxonómicas de las playas no sometidas a las tareas de limpieza mecánica. Talitrus saltator en la zona supramareal y los nemertinos en el intermareal son propuestos como taxa indicativos de estas playas no sometidos a limpieza. Este trabajo constituye el primer estudio de las consecuencias ecológicas de la limpieza mecánica que incluye las fluctuaciones de los portes alóctonos de macroalgas a escala especial y temporal. Los resultados proveen evidencias del enorme daño que esta actividad causa al ecosistema.
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7.7. CONCLUSIONES
. El varamiento de macroalgas en playas expuestas no es un proceso aleatorio. La cuantificación de la apertura y la permeabilidad del hábitat explicaron gran parte de la variabilidad de la biomasa de los arribazones. La medición de estas características del hábitat puede ser una herramienta útil para mejorar el conocimiento ecológico de los ecosistemas costeros, sistemas donde la transferencia de nutrientes y materia orgánica son procesos comunes.
. La composición específica de los arribazones mostró un patrón cíclico. Este continuo cambio en la composición indica que el proceso de varamiento de algas está ligado a su ciclo de vida. Esta tendencia cíclica implica que la variable deposición de algas en playas expuestas es en gran medida predecible.
. El alga invasora Sargassum muticum es una de las especies que aporta más biomasa a los arribazones. Sin embargo, su contribución relativa no es homogénea, aumenta en playas con exposición intermedia y alta al oleaje. La gran flotabilidad de esta especie debe aumentar sus probabilidades de varamiento. Por tanto, lo potenciales efectos que este alga, recientemente introducida, pueda ocasionar deben diferir entre los distintos tipos de playas.
. Las playas actúan como ecosistemas “donantes” de nutrientes al litoral. Este proceso remarca la substancial retroalimentación entre los ecosistemas costeros altamente productivos estructurados a partir de macroalgas o fanerógamas marinas y las playas expuestas, caracterizadas por su baja producción primaria.
. La variable relación entre los diferentes nutrientes y la cantidad de macroalgas depositadas en las playas indica las complejas vías biogeoquímicas ligadas con el procesado de la materia orgánica en los sedimentos de las playas expuestas.
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. La comunidad macrofaunística varió significativamente de playas con escasos depósitos de algas a playas con altos aportes. Este cambio en la composición y abundancia de la macrofauna indica que la disponibilidad de macroalgas es un factor estructural de la comunidad de invertebrados en playas expuestas.
. Los aportes de algas afectaron diferentemente a la macrofauna en las zonas supramareal e intermareal. Mientras que en el supramareal la principal consecuencia fue el incremento en la densidad total. En el intermareal, se observo un paulatino reemplazamiento de especies en la comunidad de playas con escaso a alto aporte algal. Estos resultados sugieren que para las especies que viven en la parte alta de la playa los depósitos de algas pueden ser un recurso limitante. Contrariamente, en la zona intermareal los varamientos de algas podrían modificar el hábitat y posibilitar la presencia de especies que mejor explotan este recurso.
. La limpieza mecánica mostro efectos negativos en el ecosistema. Esta actividad cambió completamente la zona supramareal al reducir drásticamente la diversidad y la densidad de la macrofauna. En el intermareal de las playas sometidas a limpieza se observaron variaciones que podrían evidenciar algún impacto humano. Sin embargo, en esta zona no se puede afirmar que exista una relación directa entre las tareas de limpieza y los cambios en la comunidad macrofaunística.
. El uso de especies indicadoras para valorar el estado ecológico de las playas podría ser una herramienta útil en los programas de gestión ambiental del litoral. La limpieza mecánica de la zona supramareal podría medirse utilizando especies con una alta tolerancia a las diferentes y variables condiciones ambientales naturales.
. En conjunto, esta tesis muestra la importancia ecológica de la conectividad de las playas expuestas con sus ecosistemas vecinos. Se sugieren las ventajas de incorporar varios ecosistemas cuando se llevan a cabo estudios ecológicos.
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APPENDIXES
Appendixes
APPENDIXES
APPENDIX B (CHAPTER III)
Table B.1.. Parameters of the quantil regression model. Constant (b0), slope (b1) and P of the null hypothesis H0: b =0 for the selected quantiles.
Quantil b 0 b 1 P 0.1 0.25 0 0.8 0.2 0.28 0.01 0.9 0.3 0.28 0.02 0.9 0.4 0.38 -0.01 0.9 0.5 0.42 -0.02 0.5 0.6 0.52 -0.04 0.4 0.7 0.59 -0.04 0.9 0.8 0.46 0.22 0.04 0.9 0.65 0.34 0.02
Table B.2. Results of two-way ANOVA comparing the total DIN and phosphate concentration of the intertidal pore water among beaches (3 levels) over the year (12 levels).
Dissolved nutrients SS df MS F Total DIN Beach 9.8 2 4.9 29.2 *** Month 9.1 11 0.83 4.9 *** Beach x Month 7.4 22 0.34 2 ** Res 12 72 0.17 Tot 38.4 107 Phosphate Beach 4.2 2 2.13 25 *** Month 8 11 0.73 8.6 *** Beach x Month 6.7 22 0.31 3.6 *** Res 6.1 72 0.08 Tot 25.1 107 *p≤0.05, **p≤0.01, ***p≤0.001
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Table B.3. Results of the three-factor orthogonal ANOVA comparing the total DIN and phosphate concentration of the intertidal pore water among beaches (3 levels) and zones (2 levels) over time (9 levels).
Dissolved nutrients SS df MS F
Total DIN Beach 9.9 2 4.9 40.2 *** Zone 7.8 1 7.8 63.3 *** Month 3.6 8 0.4 3.6 *** Beach x Zone 2.2 2 1.1 8.9 *** Beach x Month 4.3 16 0.3 2.2 ** Zone x Beach 4.1 8 0.5 4.2 *** Beach x Zone x Month 5.7 16 0.4 2.9 *** Res 13.3 108 0.1 Tot 50.7 161 Phosphate Beach 4.8 2 2.4 37.6 *** Zone 10.4 1 10.4 163 ***
Month 8.2 8 1 16.1 *** Beach x Zone 0.3 2 0.1 2.2 Beach x Month 9.6 16 0.6 9.4 *** Zone x Beach 3.9 8 0.5 7.6 *** Beach x Zone x Month 3 16 0.2 3 *** Res 6.9 108 0.1 Tot 47 161 *p≤0.05, **p≤0.01, ***p≤0.001
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APPENDIX C (CHAPTER IV)
C.1. Results of three-way ANOVA comparing the number of species and density at each beach level (5 levels) among beaches (four levels) throughout the year (4 levels).
SS df MS F Number of espcies Beach (Be) 21.2 3 7.1 59.8 *** Month (Mo) 1.6 3 0.5 4.5 ** Level (Le) 27.2 4 6.8 57.6 *** B eXM o 10.5 9 1.2 9.9 *** BeXLe 8.2 12 0.7 5.7 *** MoXLe 11.9 12 1 8.4 *** BeXMoXLe 16.4 36 0.5 3.9 *** RES 47.3 400 0.1 TOT 144.2 479
De nsity Be 601 3 200.3 166.3 *** Mo 36.1 3 12 10 *** Le 238.3 4 59.6 49.5 *** B eXM o 112.8 9 12.5 10.4 *** BeXLe 154.2 12 12.8 10.7 *** MoXLe 167 12 13.9 11.6 *** BeXMoXLe 274.2 36 7.6 6.3 *** RES 481.8 400 1.2 TOT 2065.4 479 *p≤0.05, **p≤0.01, ***p≤0.001
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Table 2. Results of the three-way PERMANOVA run on the Bray- Curtis matrices of species abundance on the supratidal and intertidal levels (3 levels in the supratidal; 2 levels in the intertidal) among beaches (4 levels) throughout the year (4 levels).
Components Permanova of variation df SS MSPseudo-F Estimate Sq.root Intertidal Beach (Be) 3 216230 72078 56 *** 1475 38 Month (Mo) 3 60610 20203 15.7 *** 394 20 Level (Le) 1 14591 14591 11.3 *** 139 12 BexMo 9 102960 11440 8.9 *** 846 29 BexLe 3 25927 8642 6.7 *** 307 18 MoxLe 3 22422 7474 5.8 *** 258 16 BexMoxLe 9 58599 6511 5.1 *** 871 30 Res 160 205790 1286 Total 191 707130
Supratidal Beach (Be) 3 180840 60279 30.9 *** 810 28 Month (Mo) 3 39088 13029 6.7 *** 154 12 Level (Le) 2 13021 6511 3.3 *** 47 7 BexMo 9 75909 8434 4.3 *** 360 19 BexLe 6 28938 4823 2.5 *** 120 11 MoxLe 6 23875 3979 2 *** 84 9 BexMoxLe 18 63536 3530 1.8 *** 263 16 Res 240 468680 1953 Total 287 893880 *p≤0.05, **p≤0.01, ***p≤0.001
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DEPARTAMETNO DE ECOLOXIA E BIOLOXÍA ANIMAL UNIVERDIDADE DE VIGO