Sandy Beach Macrofauna Communities on the North Shore of Prince Edward Island: the Influence of Coast Type and Macrophyte Wrack

SANDY BEACH MACROFAUNA COMMUNITIES ON THE NORTH SHORE OF PRINCE EDWARD ISLAND: THE INFLUENCE OF COAST TYPE AND MACROPHYTE WRACK

A Thesis

Submitted to the Graduate Faculty

In Partial Fulfilment of the Requirements

for the Degree of Master of Science

Department of Biology

Faculty of Science

University of Prince Edward Island

Mitchell R. MacMillan

Charlottetown, Prince Edward Island

January 2012

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REMOVED ABSTRACT

Sandy beaches on the north shore of Prince Edward Island (PEI) are associated with three main shoreline types: sand dunes, glacial till bluffs and sandstone cliffs. Standard snapshot sampling techniques were used to determine the influence of physical variability of beaches associated with these three shorelines on invertebrate macrofauna communities. There was no significant difference in morphodynamics between sandy beaches associated with the three shoreline types in terms of 1/slope, sediment grain size or the Beach Deposit

Index. However, erosion rates were significantly greater at shorelines associated with till bluffs and sand dunes. Significant differences were also found between macrofauna communities associated with sandstone cliffs and those associated with sand dunes and till bluffs. The former communities were characterized by low densities of the polychaete Scolelepis squamata, and the amphipod

Platorchestia platensis. In contrast, the latter communities were characterized by much higher polychaete densities and by the amphipods Haustorius canadensis and Americorchestia megalophthalma. Significant positive relationships were found between the rate of coastal erosion and macrofauna abundance and species richness. However, there were no significant relationships between the measures of beach morphodynamics and the biological descriptors. The results of this study suggest that macrofauna communities are linked to shoreline type, which show distinctive levels of coastal erosion. Areas experiencing higher levels of erosion and sediment redistribution seem clearly favourable to suspension- feeding macrofauna, including Scolelepis squamata, which comprised over 95% of total macrofauna abundance at these sites. Sandy beaches lack attached plants and therefore macroalgae and seagrasses that become stranded ashore (wrack) represent an important source of food and shelter. The standing crop of wrack and its influences on macrofauna communities were therefore assessed on the three shoreline types. Wrack was primarily composed of two macrophytes: eelgrass (Zostera marina) and a species of rockweed (Fucus serratus). Wrack cover was slightly, although not significantly, greater on beaches associated with sandstone cliffs, which also showed higher patch densities and wrack water contents. At beaches associated with sand dunes, macrofauna abundances were significantly greater in patches of wrack versus nearby bare sediments. In experimental wrack manipulations, significant positive relationships were found between macrofauna abundance and wrack wet mass, dry mass and water content. Macrofauna consistently preferred rockweed over eelgrass, regardless of whether the wrack was fresh or aged. Nutritional quality (in terms of the concentration of proteins, lipids and carbohydrates) and feeding rates by talitrid amphipods were also significantly greater for rockweed than for eelgrass tissues. These results suggest that nutritional quality in addition to a few physical factors contribute significantly to the structure of the supralittoral macrofauna in the study area. Overall, the two studies included here provide baseline macroinvertebrate community information for sandy beaches on the north shore of PEI. Such information is relevant for the management of these coastal ecosystems, and the vertebrate and invertebrate communities that they support. ACKNOWLEDGEMENTS

First and foremost I would like to thank Dr. Pedro Quijon for allowing me the opportunity to study under his supervision at UPEI. His incredible support, guidance and encouragement was invaluable. I am also grateful to my supervisory committee members Dr. Donna Giberson and Dr. Darren Bardati for their insight and feedback throughout the duration of this study, and Dr. Tim

Rawlings, the external examiner at my thesis defence.

I would like to thank Christina Pater, Veronique Dufour, Bradley

MacMillan, Megan Tesch, Kyle Knysh, Tyler Wheeler, Cassandra Mellish,

Jessica Willis and Marianne Parent for their assistance in the lab and/or field. For their guidance in biochemistry techniques, I wish to thank Dr. Bourlaye Fofana,

Dr. Kaushik Ghose, David Main and Guru Selvaraj. I also wish to thank Tim

Barret for his advice regarding statistical analysis. I wish to thank the UPEI

Biology Department for the use of facilities, equipment and vehicles, as well as

Pat Doyle and Gilbert Blatch for technical assistance, and also Parks Canada for access to Prince Edward Island National Park. I would like to thank my fellow lab mates Kevin Sorochan, Tyler Pickering and Melanie Rossong for their support and camaraderie. Finally I would like to thank all my friends and family members for their support and encouragement over the last two years.

I am grateful for the financial support I have received through scholarships at UPEI. This research was supported by a grant from Environment Canada through UPEI’s Climate Change Research Program. Additional support came from a NSERC Discovery grant to Dr. Pedro A. Quijon. TABLE OF CONTENTS

Page No.

Title Page...... i Conditions for the use of the thesis ...... ii Permission to Use Graduate Thesis ...... iii Certification of Thesis Work ...... iv Abstract ...... v Acknowledgements ...... vii Table of Contents ...... viii List of figures...... x List of tables ...... xiii

CHAPTER 1. INTRODUCTION AND OBJECTIVES...... 1 1.1. Introduction ...... 2 1.2. Study objectives ...... 7 1.3. References...... 8

CHAPTER 2. LITERATURE REVIEW...... 11 2.1. Control of sandy beach invertebrate communities by the physical environment ...... 13 2.1.1. Main hypotheses explaining sandy beach species richness ...... 19 2.2. Influence of Wrack on Macrofauna Assemblages ...... 22 2.2.1. Wrack as Habitat for Macrofauna ...... 23 2.2.2. Wrack as a Food Source for Macrofauna ...... 28 2.2.3. Succession of Macrofauna species in Wrack ...... 29 2.3. Main geomorphological features of PEI coasts ...... 31 2.3.1. Sand Dunes ...... 32 2.3.2. Glacial Till ...... 36 2.3.3. Sandstone...... 38 2.4. PEI’s north shore sandy beaches and their geology ...... 41 2.4.1. Cavendish coastal compartment ...... 43 2.4.2. Rustico-Brackley coastal compartment ...... 43 2.4.3. Stanhope-Tracadie-Deroche coastal compartment ...... 45 2.5. References...... 46

CHAPTER 3. A SPATIAL COMPARISON OF SANDY BEACHES IN A VULNERABLE SYSTEM IN THE GULF OF ST. LAWRENCE: SPECIES COMPOSITION, RICHNESS AND ABUNDANCE IN RELATION TO SHORELINE TYPE AND EROSION...... 54 3.1. Abstract ...... 55 3.2. Keywords...... 56 3.3. Introduction ...... 56 3.4. Methods ...... 58 3.4.1. Study area ...... 58 3.4.2. Sampling protocol ...... 59 3.4.3. Data analysis ...... 62 3.5. Results...... 64 3.5.1. Physical properties of the sandy beaches ...... 64 3.5.2. Macrofauna communities ...... 68 3.6. Discussion ...... 76 3.7. Acknowledgements ...... 82 3.8. References...... 82

CHAPTER 4. STRANDED MACROPHYTES AS A PATCHY RESOURCE: WRACK FEATURES INFLUENCE MACROFAUNAL ABUNDANCE IN AN ATLANTIC CANADA SANDY BEACH SYSTEM...... 87 4.1. Abstract ...... 88 4.2. Keywords...... 89 4.3. Introduction ...... 89 4.4. Materials and Methods ...... 93 4.4.1. Study Area and Stranded Macrophyte Survey ...... 93 4.4.2. Field experiment: Stranded seaweed colonization ...... 95 4.4.3. Plant tissue nutrients and amphipod feeding rates ...... 97 4.4.4. Statistical analyses ...... 99 4.5. Results...... 100 4.5.1. Stranded Macrophyte Survey ...... 100 4.5.2. Wrack colonization experiments ...... 103 4.5.3. Nutritional Quality Analysis and amphipod feeding rates ...... 108 4.6. Discussion ...... 112 4.6.1. Macrophyte survey and spatial variation ...... 112 4.6.2. Wrack colonization experiments ...... 116 4.6.3. Nutritional Quality and amphipod feeding rates ...... 118 4.7. Acknowledgements ...... 120 4.8. References...... 121

CHAPTER 5. SUMMARY OF RESULTS AND FUTURE RESEARCH...... 126 5.1. Spatial variation and coastal erosion ...... 127 5.2. Spatial variation and allochthonous wrack input ...... 129 5.3. Future research ...... 131 5.4. References...... 133 X

LIST OF FIGURES

Figure 2.1. Characteristic reflective and dissipative beaches. The mode of transition between states is indicated by the arrows ...... 14

Figure 2.2. A typical sand dune, located at Brackley Beach, Prince Edward Island National Park, Prince Edward Island ...... 33

Figure 2.3. A typical glacial till bluff, located at Dalvay, Prince Edward Island National Park, Prince Edward Island ...... 37

Figure 2.4. A typical sandstone cliff, located at Doyles Cove, Prince Edward Island National Park, Prince Edward Island ...... 40

Figure 3.1 . Approximate location of the sandy beaches sampled along the north shore of Prince Edward Island, southern Gulf of St. Lawrence. 1 .Cavendish west II, 2.Cavendish west I, 3.Cavendish east, 4.Mackenzies Brook, 5.Cape Turner, 6.Doyles Cove west, 7.Doyles cove east, 8.Brackley, 9.Ross Lane, 10.Stanhope east, 11.Stanhope west, 12.Dalvay west II, 13.Dalvay west I, 14.Dalvay east ...... 60

Figure 3.2. Relationships between the mean physical characteristics measured and shoreline type for 14 sandy beaches sampled on the north shore of Prince Edward Island, summer 2009 / 2010. Error bars represent one standard error. Identical letters indicate no significant differences among coast types ...... 67

Figure 3.3. Relationships between beach physical characteristics and erosion rate for 14 sandy beaches sampled on the north shore of Prince Edward Island, summer 2009 / 2010...... 69

Figure 3.4. Relationships between physical characteristics and mean species richness for the macrofauna community of 14 sandy beaches on the north shore of Prince Edward Island, summer 2009 / 2010. Error bars represent the standard error of four replicates ...... 71 Figure 3.5. Relationships between physical characteristics and mean abundance of the macrofauna community of 14 sandy beaches on the north shore of Prince Edward Island, summer 2009 / 2010. Error bars represent the standard error of four replicates ...... 72

Figure 3.6. Relationships between physical characteristics and mean abundance of the dominant polychaete Scolelepis squamata on 14 sandy beaches on the north shore of Prince Edward Island, summer 2009 / 2010. Error bars represent the standard error of four replicates ...... 74

Figure 4.1. Approximate location of the sandy beaches sampled along the north shore of Prince Edward Island, southern Gulf of St. Lawrence. 1.Cavendish, 2.Cape Turner, 3.Doyles Cove, 4.Brackley, 5.Ross Lane, 6.Dalvay west II, 7.Dalvay west I and 8.Dalvay east ...... 94

Figure 4.2. Mean density, cover and water content of wrack from seven sandy beaches on the north shore of PEI. Bar filling relates to type of shoreline: black - sand dunes, light grey - till bluffs and dark grey - sandstone cliffs. BRA: Brackley; ROL: Ross Lane, CAV: Cavendish; DA-I: Dalvay west I; DA- II: Dalvay west II; DOC: Doyles Cove, CAT: Cape Turner. Error bars represent one standard error. Identical letters indicate no significant differences among coast types ...... 102

Figure 4.3. Mean abundance of macrofauna in wrack versus bare sediments. BRA: Brackley; ROL: Ross Lane, CAV: Cavendish; DA-I: Dalvay west I; DA- II: Dalvay west II; DOC: Doyles Cove, CAT: Cape Turner. Identical letters indicate no significant differences between cover. Error bars represent one standard error. No statistical tests were conducted for Doyles Cove and Cape Turner due to the lack of fauna in the bare sediments ...... 104

Figure 4.4. Mean abundance of macrofauna in fresh and dried rockweed and eelgrass patches placed on Dalvay east and Brackley beaches. Error bars represent one standard error. Identical letters indicate no significant differences among treatment. The mean abundance for the control samples (bare sediments) are also presented but were not included in the statistical analyses ...... 107 Figure 4.5. Results of the regression analyses between physical characteristics of the wrack and macrofauna abundance across experimentally manipulated wrack patches ...... 109

Figure 4.6. Mean percentage of dry weight for proteins, lipids and carbohydrates present in the tissues of rockweed and eelgrass from samples collected in Dalvay east and Brackely beach. Identical letters indicate no significant differences among treatments. Error bars represent one standard error...... 111

Figure 4.7. Mean feeding rates by amphipods in laboratory conditions collected at Dalvay east and Brackely beach. Identical letters indicate no significant differences among treatments. Error bars represent one standard error...... 113 XIII

LIST OF TABLES

Table 3.1. Summary of physical characteristics of the 14 sandy beaches sampled on the north shore of PEI. Sorting categories are based on Folk and Ward (1957) ...... 65

Table 3.2. Results of one-way ANOVAs comparing physical features (1/slope, Beach Deposit Index, Erosion rate) among the 14 beaches surveyed. DF: degrees of freedom, MS: Mean Squares. For simplicity, Sum of Squares and F-values have been omitted ...... 66

Table 3.3. Composition of macrofauna communities of 14 sandy beaches sampled on the north shore of Prince Edward Island, summer 2009 / 2010. Brackets denote the following: (P)olychaete, (A)mphipod, (O)ligochaete, (N)emertea...... 70

Table 4.1. Results of one-way ANOVAs comparing wrack features (patch density, cover and water content) among the seven beaches surveyed. One-way ANOVAs comparing the density of macrofauna in wrack versus bare sediments at each of these beaches are also presented (Doyles Cove and Cape Turner were not compared statistically). DF: degrees of freedom, MS: Mean Squares. For simplicity, Sum of Squares and F-values have been omitted ...... 101

Table 4.2. Results of two-way ANOVAs comparing field colonization rates (number of invertebrates) in patches of wrack placed at Dalvay east and Brackley beaches. Wrack species and state refer to seaweed (rockweed vs eelgrass) and age (fresh vs dried), respectively. DF: degrees of freedom, MS: Mean Squares. For simplicity, Sum of Squares and F-values have been omitted ...... 106

Table 4.3. Results of two-way ANOVAs comparing indicators of nutritional value in stranded seaweeds. Site and wrack species refer to location (Dalvay east vs Brackley) and macrophyte (rockweed vs eelgrass), respectively. The results of a t-test comparing amphipod feeding rates upon the same wrack species is also presented. DF: degrees of freedom, MS: Mean Squares. For simplicity, Sum of Squares and F-values have been omitted...... 110 CHAPTER 1:

INTRODUCTION AND OBJECTIVES 2

1.1 Introduction

At first glimpse, sandy beaches appear to lack obvious signs of life.

However, there are at least two distinct faunistic groups associated with these habitats (McLachlan and Brown, 2006): the “water breathers”, primarily suspension-feeding species generally found in the mid and low intertidal zones, and the “air breathers” or herbivore and detritivore species located primarily at the supralittoral and upper intertidal levels. Although these faunistic groups are known to play a key role as food sources for resident and migratory species

(Dugan et al., 2003), two basic aspects of their ecology must be explored before outlining their trophic role at the ecosystem level: their composition and abundance, and the factors that structure them as populations and communities.

This is especially important in areas where general information on composition and the physical factors that influence sandy beach invertebrates have not been documented. This thesis addresses both aspects in an area where sandy beaches are a prominent feature of the coastal habitat: the north shore of Prince

Edward Island (PEI).

The Autecological Hypothesis developed by Noy-Meir (1979) states that in physically controlled environments like sandy beaches, animal populations have little influence on each other, and communities are structured by their individual response to the physical environment. The strong correlations found between purely physical parameters and macrofauna abundance and diversity on exposed sandy beaches worldwide, suggest that this hypothesis is broadly applicable to these systems (McLachlan, 1990). Sandy beaches are classified according to their “morphodynamic state”, which is the result of a combination of factors such as sediment grain size, slope and wave characteristics. At one extreme, dissipative sandy beaches result from an abundant supply of fine sand and high wave energy from breaking waves washing over gentle beach face slopes. These beaches represent the erosional end of the spectrum of beach types (Short and Wright, 1983). At the other extreme, reflective sandy beaches are characterized by steep beach face slopes where lower energy waves break on the beach face and water flows quickly off the beach. These beaches are composed of coarse sediments, and represent the accretional extreme of beach types (Short and Wright, 1983). Between these two extremes, intermediate sandy beaches include an array transitional states are by far the most common

(Short and Wright, 1983).

One of the most supported generalizations in sandy beach ecology is the trend of increasing species richness of invertebrates from reflective (coarse sediment, steep slope) to dissipative (fine sediment, gentle slope) states

(Brazeiro, 2001). The slope, sediment grain size, and a number of indices can be used as indicators of beach state, and therefore predict their suitability as habitat for macrofauna. These characteristics do not affect the macrofauna directly; rather they correlate with the “swash climate” (swash period, speed, turbulence and water movement over the beach face) experienced by the macrofauna

(McArdle and McLachlan, 1991, 1992; McLachlan and Dorvlo, 2005). Swash climates are harshest on steep reflective states and lessen as the slope flattens towards dissipative, more erodible beaches (McLachlan and Dorvlo, 2005). The macrofauna, particularly the fraction of aquatic organisms located in the mid and

low intertidal levels depend on the swash action (the runup and backwash of water on the beach face resulting from waves approaching the shore) for food.

The more dissipative a beach, the wider its surf zone where wave energy is dissipated, resulting in swashes of longer length and period. For these organisms, the longer swashes observed at flat dissipative beaches provide better feeding conditions than the shorter swash periods characteristic of steep reflective beaches, since they are underwater for longer periods of time

(McLachlan, 1990).

A key characteristic of sandy beach morphodynamic states and their associated swash climate is that they are extremely dynamic, and change over time and among sites. Shifts in storm behaviour, for example, will alter the amount and direction of wave energy approaching the shoreline (Slott et al.,

2006), influencing shore profiles (e.g. Matthew et al., 2010; Morton et al., 1994) and their rates of erosion (Pethick, 2001). Therefore the suitability of sandy beaches as habitat for macrofauna changes in response to storms and calm weather, that is, in response to erosion or accretion of sand on the beach

(McLachlan, 2001). The same applies to physical variation among sandy beaches located in different areas or along shorelines: differences in swash climates should result in differences in macrofauna assemblages. The first part of this thesis uses snapshot surveys to compare an array of sandy beaches presumably exposed to variable physical characteristics and erosion levels. The null hypothesis used in this part of the thesis is that: 5

Ho: different physical characteristics have no effect on the community

structure of the macrofauna.

Based on information published elsewhere (e.g. McLachlan and Dorvlo, 2005), it is expected that sandy beaches closer to the erosional extreme (dissipative states) will support increased macrofauna abundances and diversities, as opposed to sandy beaches at the accretional extreme (reflective states).

Spatial variation in physical characteristics also influences other processes on sandy beaches. One such feature is the arrival, stranding and decomposition of macrophyte wrack (Orr et al., 2005). Regardless of which • specific physical factors explain the biomass and distribution of stranded macroalgae and seagrasses, they constitute a valuable resource or subsidy for the organisms found primarily on the upper shoreline. Food webs of different habitats are often linked through the transfer of energy or nutrients from donor to recipient habitats (Polis et al., 1997). The influence of these allochthonous inputs is expected to be greatest where a highly productive system interfaces with and exports materials to a relatively less productive system which functions as a sink

(Barrett et al., 2005). Sandy beaches have low autochthonous production, as all over the world these habitats are characterized by shifting sands devoid of large plants. However, beaches act as sinks for displaced algal material (Jaramillo et al., 2006). Thus, sandy beach ecosystems provide an excellent opportunity to study the influence of allochthonous inputs from marine systems on the resident macrofauna communities. 6

Unlike the macrofauna of the lower levels of the intertidal zone, the supralittoral macrofauna are generally more affected by the availability of wrack

(Koop and Field, 1980) than by swash climate. This is due to the fact that they usually live buried beyond the intertidal areas directly affected by wave action

(Dugan et al., 2003; Jaramillo et al., 2006). Algal wrack deposited on beaches serves two important purposes for upper shore detritus feeders: it represents their main food source (Colombini et al., 2000; Dugan et al., 2003; Rodil et al.,

2008), and acts as a refuge against harsh physical c.onditions by providing shelter from the surrounding environment (Rodil et al., 2008). In temperate regions, supralittoral macrofauna in areas with moderate macrophyte input are often dominated by talitrid amphipods. These amphipods are considered primary colonizers of newly stranded wrack, which in turn attract secondary (predatory) species from terrestrial systems (Colombini et al., 2000).

Because stranded macrophytes on exposed sandy beaches harbour distinctive macrofaunal organisms (primarily talitrid amphipods) generally not found in lower intertidal levels, they are also an important contributor to overall sandy beach community biodiversity. The deposition of wrack on sandy shores is affected by the same factors that promote spatial variation: storms (Ochieng and

Erftemeijer, 1999), wave exposure (Orr et al., 2005), and coastal erosion (Lastra et al., 2008). All these factors play a role on the density and cover characteristics of stranded seaweed patches, creating spatial differences within and between individual sandy beaches. Such variation is relevant considering that macrofaunal organisms are known to respond to the amount and composition of the stranded patches (Ince et al., 2007; Rodil et al., 2008). In order to characterize and quantify these relationships, this section of the thesis uses the following null hypothesis:

Ho: the amount and characteristics of the wrack are uniform among sandy

beaches and have no discernable influence on the upper shore

macrofauna.

Expected results for this particular study include some degree of variation among beach types located on PEI’s north shore, and an influence on the abundance of macrofauna in wrack patches compared to bare sediments. Moreover, characterization of the use of the main seaweed species forming these stranded patches by macrofauna, as well as their nutritional quality should shed light on their relative roles and the preferences exhibited by the macrofauna.

1.2 Study Objectives

The general objective of this thesis is to explore the influence of spatial physical variability and macrophyte wrack on the community structure of the sandy beach macrofauna on the north shore of PEI. Additionally, relationships with macrofauna in relation to physical variables relevant to the region but not necessarily well studied elsewhere, such as shoreline type and erosion rates, will be explored. My specific objectives are as follows:

(1) to explore spatial variability in the physical characteristics of sandy

beaches on the north shore of PEI (beach face slope, mean sediment 8

grain size, Beach Deposit Index, rates of coastal erosion and shoreline

type) and how these variables relate to macrofauna community

descriptors, specifically abundance and species richness.

(2) to assess the influence of stranded seaweed on the composition and

abundance of upper shore macrofauna, and how aspects such as age and

nutritional value of the wrack play a role on the use of these stranded

seaweeds by the macrofauna.

1.3 References

Barrett, K., Anderson, W.B., Wait, D.A., Grismer, L.L., Polis, G.A., Rose, M.D., 2005. Marine subsidies alter the diet and abundance of insular and coastal lizard populations. Oikos 109, 145-153.

Brazeiro, A., 2001. Relationship between species richness and morphodynamics in sandy beaches: what are the underlying factors? Mar. Ecol. Prog. Ser. 224, 35-44.

Colombini, I., Aloia, A., Fallaci, M., Pezzoli, G., Chelazzi, L., 2000. Temporal and spatial use of stranded wrack by the macrofauna of a tropical sandy beach. Mar. Biol. 136, 351-541.

Dugan, J.E., Hubbard, D.M., McCrary, M.D., Pierson, M.O., 2003. The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of southern California. Estuar. Coast. Shelf Sci. 58s, 25-40.

Ince, R., Hyndes, G.A., Lavery, P.S., Vanderklift, M.A., 2007. Marine macrophytes directly enhance abundances of sandy beach fauna through provision of food and habitat. Estuar. Coast. Shelf Sci. 74, 77-86.

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. 9

Koop, K., Field, F.J., 1980. The influence of food availability on population dynamics of a supralittoral isopod, Ligia dilatata (Brandt). J. Exp. Mar. Biol. Ecol. 48, 61-72.

Lastra, M., Page, H.M., Dugan, J.E., Hubbard, D.M., Rodil, I.F., 2008. Processing of allochthonous macrophyte subsidies by sandy beach consumers: estimates of feeding rates and impacts on food resources. Mar. Biol. 154, 163-174.

Matthew, S., Davidson-Arnott, R.G.D., Ollerhead, J., 2010. Evolution of a beach- dune system following a catastrophic storm overwash event: Greenwich Dunes, Prince Edward Island, 1936-2005. Can. J. Earth. Sci. 47, 273-290.

McArdle, S.B., McLachlan, A., 1991. Dynamics of the swash zone and effluent line on sandy beaches. Mar. Ecol. Prog. Ser. 76, 91-99.

McArdle, S.B., McLachlan, A., 1992. Sandy beach ecology: swash features relevant to the macrofauna. J. Coast. Res. 8, 398-407.

McLachlan, A., 1990. Dissipative beaches and macrofaunal communities on exposed intertidal sands. J. Coast. Res. 6, 57-71.

McLachlan, A., 2001. Coastal beach ecosystems, in: Lewin, R. (Ed.), Encyclopedia of Biodiversity. Academic Press, New York, pp. 741-751.

McLachlan, A., Brown, A.C., 2006. The Ecology of Sandy Shores, second ed. Academic Press, New York.

McLachlan, A., Dorvlo, A., 2005. Global patterns in sandy beach macrobenthic communities. J. Coast. Res. 21, 674-687.

Morton, R.A., Paine, J.G., Gibeaut, J.C., 1994. Stages and durations of post storm beach recovery, southeastern Texas coast, U.S.A. J. Coast. Res. 10, 884-908.

Noy-Meir, I., 1979. Structure and function of desert ecosystems. Isr. J. Bot. 28, 1- 19.

Ochieng, C.A., Erftemeijer, P.L.A., 1999. Accumulation of seagrass beach cast along the Kenyan coast: a quantitative assessment. Aquat. Bot. 65, 221- 238.

Orr, M., Zimmer, M., Jelinski, D.E., Mews, M., 2005. Wrack deposition on different beach types: spatial and temporal variation in the pattern of subsidy. Ecology 86, 1496-1507. 10

Pethick, J., 2001. Coastal management and sea-level rise. Catena 42, 307-322.

Polis, G.A., Anderson, W.B., Holt, R.D., 1997. Toward an integration of landscape and food web ecology: the dynamics of spatially subsidized food webs. Annu. Rev. Ecol. Syst. 28, 289-316.

Rodil, I.F., 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.

Short, A.D., Wright, L.D., 1983. Physical variability of sandy beaches, in: McLachlan, A., Erasmus, T. (Eds.), Sandy Beaches as Ecosystems. Dr. W. Junk Publishers, The Hague, pp. 133-144.

Slott, J.M., Murray, A.B., Ashton, A.D., Crowley, T.J., 2006. Coastline responses to changing storm patterns. Geophys. Res. Lett. 33, L18404.

t CHAPTER 2:

LITERATURE REVIEW Exposed sandy beaches are amongst the harshest aquatic ecosystems on earth, so much so that they have been compared to marine deserts (McLachlan,

1983). As in desert ecosystems, interactions among populations are less important in structuring communities than species responding independently to the physical environment (McLachlan, 1990). If this perception is correct, then community attributes should correlate closely with one or more of the physical parameters that characterize sandy beaches (McLachlan and Dorvlo, 2005).

Sandy beach systems are also the depositary of natural (stranded seaweeds) and anthropogenic (waste) stranded material (e.g. Marsden, 1991a).

Both are expected to play a role on the structure of sandy beach communities, particularly at the upper levels of the intertidal. It is in these levels where invertebrate communities are less dependent on the dynamics of waves and currents, and more sensitive to the habitat and conditions in the supralittoral zone

(e.g. de la Huz and Lastra, 2008; Dugan et al., 2003; Jaramillo et al., 2006).

This literature review focuses on three main themes. First, I review the literature available on the physical factors that control sandy beach communities and how are they classified worldwide. Second, I review what is known about the influence of stranded seaweeds on the communities associated with the upper tidal levels. Lastly, I provide a brief overview of the main geomorphological features of Prince Edward Island (PEI) sandy beaches, and describe the main characteristics of the sandy beach systems located on the north shore of PEI. 13

2.1 Control of sandy beach invertebrate communities by the physical environment

Sandy beaches are dynamic in both space and time, are apparently featureless, consisting primarily of §and and water. They can be defined in terms of wave climate, sand particle size, and tide range (McLachlan et al., 1993).

Indeed, these three variables have been traditionally combined to produce a range of beach morphodynamic types (Defeo and McLachlan, 2005; see also below).

On a global scale, exposed sandy beaches may be divided into three broad categories based on their morphodynamics: reflective, intermediate and dissipative sandy beaches (Short and Wright, 1983). Reflective beaches are characterized by coarse sand, low wave energy and often small tide ranges

(Short and Wright, 1983). They have steep faces and no surf zones, therefore waves move unbroken to the shore where they collapse or surge up the beach face (Fig. 2.1). Because waves break at the base of the beach face they must expend all their remaining energy in the swash zone. Much of the energy goes into the wave uprush and strong backwash, which is reflected back out to sea as a reflected wave (Short, 1999). As a result, reflective beaches have short, frequent swashes (McArdle and McLachlan, 1991). At the other extreme of this range, dissipative beaches are associated with fine sands, heavy wave action and often larger tide ranges (Short and Wright, 1983). Waves break over a broad outer surf zone, dissipating most of their energy. This dissipated wave energy coupled with the fine sand produces a flat beach face slope (Short, 1999; Fig. Figure 2.1. Figure Accretion transition between states is indicated by the arrows. the by indicated is states between transition Characteristic reflective and dissipative beaches. The mode of of mode The beaches. dissipative and reflective Characteristic Swash zone Swash Swash zone Swash Dissipative Reflective

_ _

----- Erosion 14 2.1). The gentle slopes of dissipative beaches result in longer swashes (in terms

of period and distance; Mcardle and McLachlan, 1991, 1992). Between these two

extremes, intermediate beaches have fine to medium sands, moderate to heavy

wave action and a range of tide types. They also have intermediate slopes and

surf zones characterized by bars, channels and rip currents (Short and Wright,

1983; McLachlan and Brown, 2006). Dissipative beaches represent the high

energy end of the beach spectrum, the state to which all beaches head during

periods of high waves and resulting beach erosion (Short, 1999). Beach erosion

widens the surf zone by moving sand from the beach and inner surf zone, and

depositing it in the outer surf zone. This process causes waves to break further

seaward thereby lowering wave height and energy at the shore, and providing a wider surf zone for energy dissipation (Short, 1999). In regions where very large

tides occur, this classification becomes more complex, as macrotidal beaches

have reflective upper shores and dissipative lower shores (Wright et al., 1982).

The changes in drainage, water retention, and other beach face processes that

occur in this spectrum of beach types exert a strong influence on beach faunal

zonation, abundance, and diversity (McLachlan, 1990).

The earliest quantitative demonstration of a biological-physical relationship

in sandy beach literature was a series of correlations of species richness and abundance with sand particle size and beach face slope for a range of microtidal

South African sandy beaches (McLachlan et al., 1981). These authors demonstrated that species richness, density, and total abundance of macrofauna

(invertebrates >500 pm) all increased from steep beaches of coarse sandy sediments towards flatter beaches of finer sands. From these correlations they were able to predict that steep reflective beaches would support an impoverished fauna (0-5 species, <100 individuals • m'1), whereas flat dissipative beaches would support the richest faunas (14-20 species, >1000 individualsnrf1). The standardized measurement individuals • nrf1 is a measure employed to avoid biased results as a consequence of changing beach profile or width during rough and calm conditions (Brazeiro and Defeo, 1996), resulting in dramatic contraction/expansions of the across-shore distribution of macrofauna (Defeo and Rueda, 2002).

A subsequent study by McLachlan (1990) included macrofaunal responses to morphodynamics states from sites in North America, South Africa and Western Australia. This broad array of sandy beaches revealed three major trends across the reflective-dissipative gradient. First, there was an increase in intertidal macrofaunal species richness with decreasing slope, decreasing sediment particle size, or increased dimensionless fall velocity (an index of beach type incorporating measures of wave energy and sand mobility; McLachlan and

Brown, 2006). Second, there was a logarithmic increase in total abundance with an increase in beach width. And third, there was a logarithmic increase in total biomass toward the dissipative beach state (McLachlan et al., 1993). Subsequent work over an even wider range of beach types and geographical regions confirmed this trend and related it to beach morphodynamic types (Brazeiro,

1999; Defeo et al., 1992; Jaramillo and McLachlan, 1993; McLachlan et al., 1996,

1998). In general, macrotidal dissipative beaches supported communities of greater richness, abundance, and biomass than microtidal reflective beaches.

McLachlan et al. (1993) concluded that species richness, abundance, and

biomass respond to changes in beach type in a remarkably consistent manner, although the variation in abundance and biomass was less predictable than the variation in species richness. The results of that study implied that primary

physical control was of overriding importance for beach communities and that zoogeographic considerations were secondary. The robust correlations found between purely physical parameters and faunal abundances suggest that the

hypothesis originally proposed by McLachlan (1990) suggesting that sandy beach communities were primarily physically controlled (the “Autecological

Hypothesis”) was generally applicable to these systems.

McLachlan and Dorvlo (2005) then analyzed data from an even greater number of sites: 161 quantitative sandy beach transect surveys from ten countries (South Africa, Australia, United States, Chile, Oman, Brazil, Uruguay,

New Zealand, Madagascar and Belgium). Once again, significant correlations were found between species richness and mean sand particle size, beach face slope (log(1/slope), tidal range (log(maximum tidal range)) and a series of beach state indices. Significant correlations were also found between abundance

(log(abundance)) and mean sand particle size, beach face slope (log(1 /slope)), tide range (log(maximum tidal range)), wave height and a series of beach state indices. Based on this new set of results, McLachlan and Dorvlo (2005) concluded that species richness was a conservative trait of sandy beach macrobenthic communities, increasing predictably from microtidal reflective toward macrotidal dissipative beaches. At the same spatial scale, the response of abundance and biomass to changes in physical factors was similar to, but more variable than, the response of species richness. Both biological variables correlated the best with log (1/beach face slope).

Sandy beach macrofaunal communities experience and respond to three suites of physical factors: the sediment texture and movement, the swash climate, and the exposure/moisture gradient on the beach face (McLachlan and

Brown, 2006). The first suite of factors (sediment texture and movement) is associated with features such as particle size, sorting, fluidity and accretion and erosion dynamics. Because beach sands at the level of the swash zone (lower intertidal) are generally well sorted, the most important feature of the sand is its mean particle size. As sand particle size decreases, porosity (water holding capacity) increases and permeability (the rate of water flow through the sediment) decreases, resulting in increased nutrient concentrations (McLachlan and Turner, 1994). Sediment grain size also strongly influences the burrowing efficiency of macrofauna (e.g. Alexander et al., 1993), with coarse sand making burrowing difficult or impossible for invertebrates (Mclachlan, 2001). The second suite of factors or “swash climate”, is associated with features such as the period, speed and turbulence of wave and tide driven water movement over the beach face (swash) that is experienced by macrofaunal organisms. These features are closely related to the beach morphodynamic state, with frequent harsh swashes on reflective beaches and less frequent benign swashes on dissipative beaches

(McArdle and McLachlan, 1991, 1992). Since macrofaunal organisms living in the 19 intertidal zone of exposed sandy beaches do not inhabit permanent burrows, all macrofauna interact with the swash at some point (McArdle and McLachlan,

1992). It can be argued that most species are to some extent dependent on the swash in order to move, feed, burrow and reproduce. Thus these species are directly affected by, and adapted to the swash climate (McArdle and McLachlan,

1992). The third suite of factors relates to the gradient of moisture within the intertidal zone. Water retention decreases dramatically from dissipative to reflective conditions, and creates opportunities for species with different desiccation tolerances to inhabit different levels on the shore (McLachlan and

Brown, 2006).

2.1.1 Main hypotheses explaining sandy beach species richness

At large (global) scales, the species richness of sandy beaches seems to be controlled by two processes: An ecological process whereby harsh environmental conditions (in terms of sediment, swash and exposure characteristics) allow fewer species to establish populations on reflective than in dissipative beaches; and an evolutionary process that has led to greater species

pools in the tropics than in temperate zones (Soares, 2003). Several hypotheses

have been proposed to explain these large-scale patterns, all to some extent

related to the Autecological Hypothesis proposed by McLachlan (1990).

The Swash Exclusion Hypothesis (McLachlan et al., 1993) proposed that sand particle size, wave energy, and beach slope were the ultimate factors affecting macrofauna through their combined effects on beach face climate. However, it was not the beach state or type itself that was important for the fauna, but the swash climate associated with it. These authors refined an earlier

“Swash Control Hypothesis” (McLachlan, 1990) to the Swash Exclusion

Hypothesis, by suggesting that swash climate associated with dissipative beaches is sufficiently accommodating and varied to enable virtually all macrofauna species encountered on exposed beaches to maintain viable populations. As beach type changes through intermediate states to reflective conditions, increasingly inhospitable swash climates exclude more and more species until only supralittoral forms such as talitrid amphipods (Crustacea) which live above the swash zone can remain.

The Multi-causal Environmental Severity Hypothesis (Brazeiro, 2001) states that changes in swash climate co-vary with changes in grain size and erosion-accretion dynamics. Given that there are cause-effect pathways between biological processes and swash frequency and velocity, grain size and erosion- accretion dynamics, these three environmental factors are capable of affecting the distribution of species along a morphodynamic gradient. This author suggested that the reduction of species towards the reflective extreme was caused by increasing environmental severity generated by the sum of the independent effects of these three variables.

The Habitat Harshness Hypothesis (Defeo et al., 2001, 2003) also considers the harshness of the swash environment, and proposes that at the reflective end of the spectrum, the harsh physical conditions force the macrofauna to divert more energy toward maintenance and less to reproduction. 21

Ultimately, the fecundity of these invertebrates is potentially lower and their population become more vulnerable to events of mortality from where they cannot recover. Because of its nature, this hypothesis is more applicable at the population than at the community level.

The Swash and Sand Control Hypothesis (McLachlan, 2001) refined earlier hypotheses by also including a mechanism for the reduction in species.

He observed that reflective beaches have harsh swash climates in that they have high turbulence, short swash periods, and rapid swash drainage resulting in lower, more seaward effluent lines. The effluent line separates sands saturated with water from those that are unsaturated in the intertidal zone, above which macrofauna experience difficulty burrowing in (McArdle and McLachlan, 1991).

For example, coarse sand appears to exclude small or delicate faunistic forms by crushing and abrasion, and consequently, most species experience decreasing burrowing efficiency in coarse rather than fine sands. Thus harsh swash climates and coarse sand associated with reflective beaches appear to exclude many species.

Finally, the Hypothesis of Macroscale Physical Control (McLachlan and

Dorvlo, 2005) attempts to combine the two levels of factors responsible for global patterns in sandy beach community species richness outlined previously. Primary control is by a) tide range, which defines the dimensions of the intertidal habitat and the number of species/niches that can be accommodated; and b) latitude, which influences the size of the species pool available to colonize a beach.

Secondary control is by a) harsh swash climates, and b) coarse sand and 22

sediment instability observed towards reflective beaches that result in the

exclusion of species. According to this hypothesis, the primary factors determine

the maximum number of species that could occur under ideal conditions on a

dissipative beach in a particular region. Meanwhile, the secondary factors limit

how many of these species are actually able to establish populations across the

range of beach types by excluding the less well-adapted species to the harsher

conditions developed towards reflective beach states.

All of the above hypotheses imply that post-settlement processes prevent

species that are less robust/well adapted to the harshness of the physical

environment (i.e. swash climate, coarse sand) from developing large populations

on reflective beaches. It does seem clear that on the large scale and toward the

reflective extreme that physical control is overriding. In contrast, towards

dissipative conditions and on finer scales the more benign environment and

greater densities of organisms may allow biological interactions to become

relatively more important (McLachlan and Brown, 2006).

2.2 Influence of Wrack on Macrofauna Assemblages

In general, sandy beach primary consumers include two main groups. The first is located at within the intertidal zone and is directly affected by the swash

climate described above, and includes suspension feeders such as polychaetes,

hippid crabs (Crustacea) and bivalves (Mollusca) that feed on phytoplankton and

associated particulate organic material. The second group is located at or near the high tide level, where it is not as exposed to the effects of waves as the first 23 group and includes herbivores/detritivores such as crustaceans (talitrid amphipods and isopods) and insects which consume macrophytes and other stranded materials (Dugan et al., 2003). This section focuses on the influence of

macrophyte wrack on the second group.

2.2.1 Wrack as Habitat for Macro fauna

One of the most notable features of exposed sandy beaches is the relative

lack of in situ primary production (Duarte et al., 2010; Dugan et al., 2003;

Jaramillo et al., 2006; McLachlan and Brown, 2006). Except where sand dunes transition into the supralittoral zone of the beach face, there are no attached

plants found on sandy beaches. This is because beach sediments are too

abrasive and mobile for macrophytes or dense benthic diatom communities to

establish (Griffiths et al., 1983). With so little in situ primary production,

macrofaunal invertebrates must rely on allochthonous inputs (those entering from

outside the system) from other adjacent marine ecosystems as one of their main feeding resources. These inputs are generally represented by phytoplankton and

drifting marine macrophytes such as macroalgae and seagrasses (Adin and

Riera, 2003; Dugan et al., 2003). Thus, the structure of sandy beach macrofauna

communities are not only related to oceanographic processes such as upwelling

and currents that deliver nutrients and transport phytoplankton onshore, they are

also related to the production and input of nearshore macroalgae and seagrass

beds (Dugan et al., 2003). 24

Beach wrack, the plant and animal litter cast ashore by waves and tides, is

a highly variable habitat providing food and shelter for both aquatic and terrestrial

animals (Behbehani and Croker, 1982). Wrack is known to be highly transient, with material moving daily between the shallow subtidal (surf zone) and the

beach in some locations, or persisting for relatively long periods in others

(Kirkman and Kendrick, 1997). Even in areas which receive little wave action

such as estuaries, storm surges and spring flood tides are able to transport wrack onto the upper beach levels (Behbehani and Croker, 1982). Turnover rates

may relate to spring tides, as reported by Stenton-Dozey and Griffiths (1983) where total replacement of wrack occurred over a 14 day cycle, or be more rapid,

occurring in as little as eight days (Koop and Field, 1980; Koop et al., 1982).

Changes in prevailing weather conditions (e.g. wind direction casting different

materials ashore) not only affects deposition of wrack, but also its composition

(Colombini et al., 2000). These can also relate to season: Stenton-Dozey and

Griffiths (1983) found maximal kelp deposition occurred during the winter when

large offshore swells uproot whole plants and drive them ashore.

The fauna of beach wrack generally changes in response to location of the wrack on the beach, beach morphology, season, climate and vegetation cover

(Colombini and Chelazzi, 2003). On the west coast of South Africa, Stenton-

Dozey and Griffiths (1983) recorded 35 macrofaunal taxa in stranded wrack

comprising crustaceans (amphipods, isopods), molluscs (bivalves, gastropods)

and insects (flies (Diptera) and beetles (Coleoptera)). Talitrid amphipods are an

important component of macrofaunal assemblages inhabiting wrack (Behbehani 25 and Croker, 1982; Griffiths et al., 1983). They are responsible for most of the

primary consumption of surface material (e.g. Griffiths et al., 1983) and function as key detritivores (Griffiths and Stenton-Dozey, 1981; Inglis, 1989; Marsden,

1991a).

All of these groups that are well represented in wrack communities (e.g.

crustaceans such as isopods, molluscs and insects, especially flies and beetles),

have been reported to show seasonal peaks in abundance (Stenton-Dozey and

Griffiths, 1983). For example, isopod abundances may decline during the winter

months if the swash climate becomes inhospitable due to heavy wave action,

and dipteran flies show increases in abundance during the summer and autumn

coinciding with breeding periods (Stenton-Dozey and Griffiths, 1983). Colombini

et al. (1998, 2000) found that staphylinid beetles adopted different spatial

strategies according to season, and were more abundant in the wet season than

during the dry season in wrack deposits. However, Stenton-Dozey and Griffiths

(1983) found that the overall abundance of Coleoptera throughout the year was

erratic with no discernable seasonal patterns. They attributed this to the fact that they are not permanent residents of the intertidal, and instead, they migrate

seaward from the sand dunes.

Spatial patterns have also been shown to vary on shorter temporal scales.

For example Colombini et al. (2000) found that macrofauna showed pronounced

spatial differences in response to their use of wrack during semi-lunar cycles.

The talitrid amphipod Talorchestia martensii and the dipteran flies moved toward

seaward wrack during neap tides and toward landward wrack during spring tides. This was not the case for all macrofauna, however, as these migrations were not observed in gastropods (snails) and staphylinid beetles. Stenton-Dozey and

Griffiths (1983) reported that isopod species were restricted to wrack near the water’s edge, where they feed on organic matter and prey on small animals such as amphipods. furthermore, Colombini et al. (1998) demonstrated that species with nocturnal or diurnal surface regimes demonstrated extended activity into the following day or night. Therefore, wrack deposits may represent not only the diurnal resting grounds for nocturnal species, but also a microhabitat where activity continues in the absence of large predators and unfavourable climatic conditions.

Anthropogenic disturbances which affect wrack deposition can also affect beach fauna. For example, wrack, trash and debris are often removed from popular public sandy beaches (grooming; McLachlan and Brown, 2006;

Colombini and Chelazzi, 2003). Dugan et al. (2003) investigated the effects of beach grooming on the macrofauna and found that the abundance of wrack- associated fauna was significantly lower on groomed than un-groomed beaches.

Species richness also varied significantly among groomed and un-groomed beaches with low and high standing crops of wrack. Fewer than three wrack- associated species occurred on groomed beaches, while un-groomed beaches had from 6-13 species depending on the level of wrack cover. The depressed species richness in groomed beaches was particularly evident in the coleopterans (beetles) and the amphipod crustaceans. Their main finding was that the mean species richness and abundance of wrack-associated macrofauna, specifically talitrid amphipods and flies (primarily larvae and pupae), were both positively correlated with wrack cover. Other authors have also reported increased abundance of macrofauna with macrophyte cover or volume (Ince et al., 2007; Jaramillo et al., 2006; Rodil et al., 2008; Stenton-Dozey and Griffiths et al., 1983). In addition to increased abundances, Behbehani and Croker (1982) found increased seasonal growth and reproductive development in Platorchestia platensis with higher availability of wrack.

The spatial distribution of the wrack debris along the beach profile is a relevant feature because the higher the seaweed is located on the beach, the longer it is presumably present on the intertidal zone (Rodil et al., 2008), where it is prone to desiccation and can be reworked either physically by wind or waves, or biologically through detritivores and decomposers (Ince et al., 2007). Some wrack-associated macrofauna on sandy beaches have been shown to have preferences for wrack in various states of decomposition. For example, Jaramillo et al. (2006) analyzed the population abundances of three wrack associated macrofaunal species on the Chilean coast associated with fresh macroalgae at low tide levels, and older dried algae deposited further up the shore. The mean population abundances of the talitrid amphipod Orchestoidea tuberculata were significantly higher in the lower band of fresher wrack as compared to the upper aged band at all beaches except one. In contrast, the tenebrionid beetle

Phalerisidea maculata was significantly more abundant in the wrack located on the upper beach levels, while the isopod Tylos spinulosus did not show a preference for either upper and lower levels of wrack (Jaramillo et al., 2006). 28

2.2.2 Wrack as a Food Source for Macrofauna

Algal wrack promotes increased population abundances of sandy beach macrofauna by providing a source of food and/or a refuge from harsh environmental conditions and/or predation (Colombini et al., 2000; Ince et al.,

2007; Inglis 1989; Rodil et al., 2008). Population abundances of a variety of consumers can be potentially determined by food availability (e.g. Polis and

Hurd, 1996), especially in habitats where food sources are patchy or limited, such as the allochthonous sources on sandy beaches. Marine algae which makes up the majority of beach wrack, vary greatly in nutritional quality (Duarte et al., 2010), which also influences feeding preferences. For example, Adin and

Riera (2003) investigated food sources of the talitrid amphipod Talitrus saltator by stable isotope analysis and showed that they preferentially used certain species of macroalgae as a food source. Another talitrid amphipod, O. tuberculata, preferentially consumed Durvillaea antarctica over Lessonia nigrescens and Macrocystis pyrifera when given the choice of the three species

(Duarte et al,, 2010). The preferred species was found to have significantly greater protein and carbohydrate contents than the other two species (Duarte et al., 2010). Other studies have shown similar trends, with amphipods preferentially consuming algae containing higher quantities of protein (Cruz-

Rivera and Hay, 2000; Jimenez et al., 1996) or carbohydrates and chlorophyll a

(Rodil etal., 2008).

These feeding preferences may drive the species patterns found in wrack.

Several authors have found differences in macrofaunal communities in response to differences in the species that comprise wrack beds (e.g. Colombini et al.,

2000; Rodil et al., 2008), as well as the size of these wrack beds (Olabarria et al.,

2007; Rodil et al., 2008). In addition to food considerations, the composition and level of compactness of the algal wrack beds provide different microclimatic conditions within the patches which influence the colonization and exploitation of the wrack by macrofauna (Colombini et al., 2000). Morphological differences among seaweeds cause variability in habitat quality, including the quality of the wrack as a shelter from predation (e.g. Colombini et al., 2000; Rodil et al., 2008;

Vandendriessche et al., 2006). Therefore, the presence of different species may relate to a variety of factors. Some species like O. tuberculata may be more influenced by nutritional quality than algal structural traits (Duarte et al., 2010).

These amphipods preferred D. antarctica regardless of whether it was fresh, or it had all of its structural characteristics removed by grinding it into a fine powder.

This was not the case for the remaining two species of macrophytes tested.

Although they were consumed at rates significantly less than that of D. antartica,

L. nigrescens were consumed at a greater rate than M. pyrifera when fresh, while this trend was reversed after removal of structural traits (Duarte et al., 2010).

Thus structural and nutritional traits play varying roles in different taxa, so species patterns rely on complex interplay of all of these factors.

2.2.3 Succession of Macrofauna species in Wrack

Another factor that contributes to the complexity of wrack communities is that ephemeral patches of wrack and carrion are generally characterized by a successional change in species composition. This is due to the fact that different groups of organisms associate with wrack at different stages of decomposition or age (Colombini and Chelazzi, 2003). Analyses of the succession of species in the colonization of wrack have shown that not all the invertebrate species invade the wrack at the same time (Colombini et al., 2000). This suggests a different use of the wrack according to species’ metabolic and trophic needs, and the appearance or disappearance of species due to microclimatic changes related to the position of the wrack on the beach (Colombini et al., 2000). A number of authors have reported amphipod crustaceans as the primary colonizers of wrack

(Colombini et al., 2000; Griffiths and Stenton-Dozey, 1981; Inglis, 1989;

Jedrzejczak, 2002), although some authors have reported that many wrack- associated species, and not necessarily just amphipods, are rapid colonizers of wrack (Olabarria et al., 2007; Rodil et al., 2008).

Species colonize wrack based on a combination of feeding and habitat requirements, and these can change depending on the amount of time that the wrack has been present. Amphipods prefer moist, fresh wrack as a food source because these invertebrates are more susceptible to desiccation (Marsden,

1991b). This is likely the case for the larvae of flies (Diptera; Griffiths and

Stenton-Dozey, 1981) and crustacean isopods as well (Colombini et al., 2000). In contrast, beetles (Coleoptera) prefer older wrack deposits (Griffiths and Stenton-

Dozey, 1981). Herbivorous beetles, such as those in the families Tenebrionidae,

Hydrophilidae, Curculionidae and Scarabaeidae, invade wrack once it has dried out while stranded on the shore (Colombini and Chelazzi, 2003). Predaceous 31

beetles in the families Staphylinidae, Histeridae and Carabidae also form a large component of the wrack fauna and usually follow the establishment of their prey which include amphipods and insects, notably the larvae of dipterans (flies;

Colombini and Chelazzi, 2003, Colombini et al., 2000; Griffiths and Stenton-

Dozey, 1981).

Meiofaunal assemblages consisting of animals usually less than 1 mm in size, play an important part in the colonization of very old wrack (Jedrzejczak,

2002; Inglis, 1989). This is probably related to the fact that the older material is more readily available to microbial decomposers on which meiofauna feed, and does not require macrofauna to break the material into smaller pieces to assist decay (Jedrzejczak, 2002). Microorganisms are thus likely to be of primary importance in the breakdown of seaweeds in the supralittoral zone of sandy beaches (Jedrzejczak, 2002).

2.3 Main geomorphological features of PEI coasts

The sandy beaches of Prince Edward Island (PEI) are associated with three predominant shoreline types featuring sand dunes, glacial till bluffs, and sandstone cliffs. Sand dunes are accumulations of sediment resulting from

Aeolian (wind-driven) processes. Till bluffs on PEI are reddish-brown sediments containing clay, sand, stones and boulders, all of which are derived from glacial redeposition of material derived from underlying bedrock. Finally, sandstone bedrock deposits are composed of very fine to very coarse sand-sized minerals that form prominent cliffs along the coastline. Although these dunes, bluffs or cliffs are not generally exposed to the action of waves and currents, they are related to the dynamics of the entire sandy beach ecosystem. Sediment eroded from dunes, bluffs and cliffs may be incorporated into the intertidal zone, and sediments from the intertidal zone may become incorporated into dunes. The resulting shoreline position and shape may either protect or contribute to beach erosion. The paragraphs below describe in detail these three main geological configurations.

2.3.1 Sand Dunes

Coastal sand dunes characteristically develop landward of most sandy beaches as a result of aeolian sediment transport by onshore winds (Fig. 2.2;

Davidson-Arnott and Law, 1990). To move sand from the beach to the dunes, wind speed must exceed a threshold velocity for the particular size of sand available. If the sand is damp or if the grains must move up a slope, the wind velocities required for sediment transport are greatly increased. The foreshore of the beach may act as a source of sand if it dries between tidal cycles. This is especially true in areas where there are diurnal tides (as opposed to semidiurnal or mixed semidurinal tides), allowing a greater amount of time for the foreshore to dry between inundations (Morang et al., 2002).

The pattern of dune development in the absence of any anthropogenic influence involves the formation of dome dunes, oval or circular mounds of sand, followed by gradual development of parabolic dunes (curved sand ridges with the concave portion facing the beach; Catto et al., 2002). This type of dune often 33

Figure 2.2. A typical sand dune, located at Brackley Beach, Prince Edward Island National Park, Prince Edward Island.

0 34 forms downwind of pools or damp areas (Morang et al., 2002).Two factors operating at the regional scale indirectly influence the development and character of the coastal dunes of the region: rising sea level and climate. In Atlantic

Canada, rising sea level has resulted in relatively rapid landward migration of beaches and spits as well as their associated sand dunes, facilitated by the late onset of spring and slow growth of dune stabilizing vegetation until mid-June

(McCann, 1990).

Most PEI coastal dunes are simple foredunes oriented parallel to the shoreline (Nutt and McCann, 1990) which serve as storm buffers (Morang et al.,

2002), and they are common along the north shore of PEI. Exceptions occur where the shoreline is subject to severe anthropogenic disturbance (such as large numbers of people traversing the dunes) or recent coastal erosion (Catto et al., 2002) from wind-driven waves, wave run-up and overwash (Gribbin, 1990). In the most severely disturbed sites, such as Cavendish, Stanhope and Cabot Head

Provincial Park, these two factors have combined to erode and degrade the foredunes extensively. For example, individual coastal foredunes exceeded 20 m in height before recent anthropogenic disturbance (Catto et al, 2002).

Sand dunes on PEI are derived from local sources. On the north shore, the sands consist mainly of well rounded, spherical grains of quartz, often with a residual red coating. They are derived almost entirely from the erosion and breakdown of the underlying sandstone bedrock (Gribbin, 1990), creating small particles that are driven by onshore winds, and adhere onto moist and snow- covered surfaces (Catto et al,, 2002). Generally most of the sediment transported 35

landward from the backshore is trapped initially by vegetation colonizing the area

just beyond the limit of wave action, leading to the development of an incipient

foredune parallel to the shoreline. Exceptions to this occur where vegetation is

sparse because of limited moisture, or where sediment supply is so large as to

prevent the establishment of vegetation (Davidson-Arnott and Law, 1990).

Shifting and blowing sand creates a difficult environment for plant

establishment, so dune plants must have specific adaptations to survive in these

environments. American beach grass (Ammophila breviligulata) is the most

common dune plant in the region (Matthew et al., 2010), and the first colonizer

where incipient foredunes are developing (Nutt and McCann, 1990). The plants

extend rhizomes to spread rapidly to help stabilize the surface of the dune, then

grow vertically as they are buried by sand, allowing plants to keep pace with

sand deposition on the dune. The leaves of the plant also help trap wind-blown

sand on the dune, facilitating dune growth (Morang et al., 2002).

Dunes vary over time, based on vegetation patterns and sediment

transport. With continued sediment supply, the foredune grows in height and

width, and on accreting shorelines (seaward growth of beach by accumulation of

sediment), a sequence of transverse dunes may form (Davidson-Arnott and Law,

1990). Transverse dunes are asymmetrical ridges with steep lee and gentle

upwind slopes oriented perpendicular or oblique to the dominant winds (Morang

et al., 2002). Over the short term (weeks or months), the rates of foredune

growth are dependent on the volume of sand transport from the beach, the wind

climate, and the sediment characteristics. Such characteristics include grain size,

/ 36

mineralogy, moisture content, salt crusting, and indirectly, beach width which can

influence the threshold of sediment motion and sand transport (Davidson-Arnott

and Law, 1990). Since dunes form from onshore winds transporting beach sand,

sediment supply to the dune involves a loss to the beach deposits. Therefore,

over the long term (years to decades) for foredunes to grow, sand must continue

to be deposited on the beach. Otherwise, a negative feedback cycle will be

initiated through narrowing of the beach and erosion of the dune by wave actions

(Psuty, 1988).

2.3.2 Glacial Till

Prince Edward Island was completely covered with ice only fifteen

thousand years ago (Crowl and Frankel, 1970). Sediments of glacial origin,

known collectively as glacial till, are found in central PEI. Their distribution, along

with abrasion features on the bedrock and deposition of erratic boulders, confirm

the former presence of a glacier (Crowl and Frankel, 1970). The bedrock strata Of

PEI are generally covered by glacial till ranging from several centimetres to

several meters thick. Over much of PEI the drift thickness is not more than 3-4.5

m (Fig. 2.3) but along the north coast, 7.5-9 m of till are readily visible (Crowl and

Frankel, 1970).

The deposits left by the ice include dense tills made up of clay and sand that were mainly derived from the underlying bedrock as the glacier slowly ground its way across the Island. These deposits include loose textured sandy tills resulting from the melting of the debris-laden glacier ice (Prest, 1973). The 37

Figure 2.3. A typical glacial till bluff, located at Dalvay, Prince Edward Island National Park, Prince Edward Island. 38 sediment composition of PEI tills range from clay to silt and sand with a variable stone content. Despite variations in composition (i.e. proportions of sand, clay and silt), they are all related to common Wisconsin glaciations (Prest, 1973).

Typical sand-rich or clay-rich till exhibit the following characteristics. Upon impact, the dry material of sandy till either collapses or breaks into small chips which have little or no cohesive strength. When this till is wet, its plasticity is low such that banks cut in it (bluffs) tend to slump readily. However, with certain grain size mixtures they may retain their form. In contrast, clay till breaks with blocky fractures when dry and these have a much greater cohesive strength. Claystone fragments may be locally abundant and very plastic when wet so that banks cut in it tend to retain a steep face. However, with certain grain size mixtures they slump readily (Crowl and Frankel, 1970). Till types at either extreme, i.e. those dominated by clay or those dominated by sand, are readily distinguishable.

However, the intermediate types are not because their characteristics seem to depend on the amount of silt grains replacing either sand or clay-size materials, and these also vary greatly with changes in moisture content (Crowl and Frankel,

1970).

2.3.3 Sandstone

Bedrock layers of PEI are relatively soft and are made up of (in order of abundance) freshwater sandstone, mudstone and conglomerate (sedimentary rocks, consisting of rounded fragments cemented together) laid down during the

Late Pennsylvanian and Early Permian (300 to 250 million years ago). Some of the Permian strata may be as young as 225 million years old, younger than most of those found in Nova Scotia and New Brunswick (Prest, 1973). Three major intervals have been identified from the Island and the Maritime provinces. The first (earliest) two sequences are widely exposed in parts of New Brunswick and

Nova Scotia. The third upper sequence consist of redbeds which are exposed throughout PEI and extend beyond the coastal regions of the Island beneath the

Gulf of St. Lawrence and parts of the Northumberland Strait (Fig. 2.4; van de

Poll, 1989).The upper red conglomerate-sandstone interval consists of layers of mainly red, fine- to very fine-grained sandstone and mudstone.

The bedrock sediments come from material carried by streams originating in ancient highlands of what are now New Brunswick and Nova Scotia (Prest,

1973), and deposited as a delta at the river mouth located at the present day PEI and Gulf of St. Lawrence. As the streams slowed, the mineral grains were deposited in their channels and on the adjoining flood plains. The ever increasing load of sediment depressed the low regions while the highlands to the west and south continued to rise, and several thousand feet of sediments accumulated.

Oxidizing conditions and aerobic bacteria destroyed the carbonaceous material and formed the oxide of iron that gives the sediments their characteristic red- brown color (Prest, 1973).

Sandstone dominates the PEI bedrock, making up about 60% of the surface area (van de Poll, 1983). It ranges in grain size from very fine to very coarse, and its color depends on the grain size. It varies from pale orange (fine to very fine sandstone) to dark purplish-red (medium to very coarse sandstone) and Figure 2.4. A typical sandstone cliff, located at Doyles Cove, Prince Edward Island National Park, Prince Edward Island. 41 local insertions of grey, grayish-red, or greenish-grey sandstone occur where the iron matrix is in the reduced rather than oxidized form (van de Poll, 1983).

2.4 PEI’s north shore sandy beaches and their geology

Prince Edward Island is approximately 230 km long and 6.5-50 km wide, and its surface rises to a maximum of 127 m above sea level (van de Poll, 1983).

There are approximately 1,260 km of coastline along PEI (Owens and Bowen,

1977), and according to Shaw et al. (1998a,b) PEI has among the most sensitive coastlines to sea-level rise in Canada. Factors contributing to this vulnerability include the predominance of soft (friable) sandstone bedrock, a dynamic sandy shore which is locally sediment-starved (loses more sediment than it accumulates), and an indented shoreline with extensive salt marsh areas. The terrain behind the dunes is also low in relief so there is significant flooding potential, and high rates of shoreline retreat and coastal submergence have been documented (Shaw et al., 1998a). Parts of the north shore of PEI were rated especially sensitive to sea level rise because this coast is exposed to the wave action of the open Gulf of St. Lawrence, where potential wave-generating fetches of several hundred kilometers occur, depending on wind direction and ice cover

(Shaw et al., 1998b).

The development of the coast of northern PEI is controlled by a combination of longshore currents and sediment movement, aeolian activity, sea level rise, and human action (Catto et al., 2002). This entire shoreline system depends upon having a large supply of sand to replace what is being eroded and 42 transported laterally along the shoreline. The north shore has a relatively uniform geology, with sandstone and minor mudstone and conglomerate (van de Poll,

1983) and a variable cover of sandy glacial till or glacial outwash deposits

(sediments deposited by glacial meltwater; Prest, 1973). These easily eroded deposits provide a moderately abundant source of sand to the coastal system.

The beach and nearshore sediments are predominately fine to medium sands

(Owens and Bowen, 1977), but lag gravel (gravel resulting from the removal of fine sediment by wind or wave action) is also present in the vicinity of rock cliffs.

Gravel is also present in minor quantities elsewhere on the shoreface near headlands and in most of the nearshore bar troughs (Forbes, 1987). Another prominent feature of this coastal system is a series of extensive sandy barriers with well developed coastal dunes that appear on the seaward margin of numerous bays and estuaries (Forbes and Manson, 2002).

Investigations within the last decade suggest the existence of distinctive coastal cells, regions separated by headlands experiencing variable longshore or shore-normal sediment exchange, along the western, northern, and eastern coasts of the Island (Shaw et al. 2000, modified by Forbes and Manson, 2002).

These authors subdivided the central portion of PEI’s north shore into six distinct and largely independent compartments. Three of these compartments harbour the sandy beaches sampled in this thesis and are therefore described here in detail. In general, high sandstone cliffs occupy part of the coast, most prominently in the vicinity of Orby Head between Cavendish and Rustico Bay

(Forbes and Manson, 2002). The central-eastern sections of the coast consist of 43 sand dunes as well as lower cliffs cut into glacial till deposits, sometimes resting on sandstone, and typically bounded by a narrow gravelly beach (Forbes and

Manson, 2002).

2.4.1 Cavendish coastal compartment

This segment of the coast forms the slight embayment between Cape

Tryon on the west and Orby head on the east (Fig. 2.5a), a distance of about 15 km. The spit at Cavendish beach extends as an almost linear barrier approximately 5 km westward across the bay to Cavendish Inlet at the western shore. The barrier is typically 200 to 300 m wide with a very discontinuous dune line broken by numerous channels cut into the dunes by storms. This long beach is associated with a system of multiple nearshore bars (Forbes and Manson,

2002). Cavendish Beach extends eastward in front of a low wetland near the east side of New London Bay. High dunes in this area have a very irregular crest, reflecting in part the many years of heavy pedestrian traffic across the dunes to the beach. At the east end of Cavendish where the backshore terrain rises out of the valley, the beach gives way to sandstone cliffs with a variable cover of glacial sediment. Under northeasterly storm conditions, sand and gravel derived from wave erosion of those cliffs is transported westward (Forbes and Manson, 2002).

'*•

2.4.2 Rustico-Brackley coastal compartment

This part of the coast occupies a pronounced embayment between Orby

Head on the west and Cape Stanhope on the east (Fig. 2.5b), encompassing 44

Gulf of St. Lawrence

NW Atlantic

i5?W 61 °W

Cape Tryon

Orby Head

Covehead | Gape ~North A < Robinson's Point \ I Stanhope Rustico A Island Deroche Brackley i / Ross Lane Blooming New London Beach A i / . . BaV / Dalvay Point

Rustico Bay — j Tracadie Stanhope Bay 7.5 15. lane - kilometers

Figure 2.5. The three coastal cells a)Cavendish, b)Rustico-Brackley and c)Stanhope-Tracadie-Deroche housing the sandy beaches sampled in this study. Figure modified from Forbes and Manson (2002). 45 nearly 15 km of shoreline. The shore in this area is characterized by extensive sandy beaches and barriers, and foredunes up to 15 m high (Forbes and

Manson, 2002). Sections with sandstone cliffs are also present in this component. Glacial till deposits are exposed along Robinson’s Island and Cape

Stanhope, and locally at the base of dunes as well (Forbes and Manson, 2002).

The underlying glacial deposits extend seaward as a lag gravel shoal (sandbar comprised of gravel, resulting from the removal of fine sediments by wind and wave action; Forbes and Manson, 2002).

The Brackley region has almost continuous thin deposits of sand (<1 m thick) on the shoreface and inner shelf in areas underlain by former river valleys with sand and mud infill (Forbes and Manson, 2002). The largest volumes of sand are stored in the coastal dunes and in flood-delta deposits at North Rustico and Covehead (Forbes and Manson, 2002). Brackley beach forms a long reach of unbroken beach and dunes extending approximately 6.6 km from the low headland at the Robinson’s Island causeway to Covehead. The beach is fronted by multiple nearshore bars and backed by dunes that vary from long, linear, shore-parallel foredune ridges with crest elevations of up to 7- 8 m, to highly dissected, residual dunes of up to 12 m high (Forbes and Manson, 2002).

2.4.3 Stanhope-Tracadie-Deroche coastal compartment

This more subtle embayment extends from Cape Stanhope in the west to

Point Deroche in the east (Fig. 2.5c). It is erosiohal in places, notably at Cape

Stanhope and where low cliffs are cut into glacial tills at and west of Stanhope 46

Lane, at Dalvay, and at Point Deroche (Forbes, 1987). The beach, while nearly continuous, narrows and typically has more gravel in areas fronting erosional cliffs. Except in areas of cliff backshore, the beach throughout this compartment is sandy, typically 50-100 m in width, and fronted by multiple nearshore bars

(Boczar-Karakiewicz et al., 1995; Forbes and Manson, 2002). The number of bars is generally higher in the middle of the compartment (i.e. Stanhope lane to east Tracadie Bay), where sand is more abundant, and less at the western and eastern ends near Cape Stanhope and Point Deroche, where shoreface sand is sparse. Typically three to four bars are present, however abrupt changes in bar number and position occur in places, reflecting alongshore variation in the nearshore morphodynamic status (Wijnberg and Kroon, 2002; Wijnberg and

Terwindt, 1995).

The beach throughout this compartment is backed by a single, narrow, sharp-crested foredune ridge in places (e.g. west of Ross Lane, east of Stanhope

Lane, parts of Point Deroche), with typical crest elevations of approximately 7-9 m, and more complex multiple dune ridges up to 11 m at Blooming Point. While the extent of white spruce growth on these dunes suggests considerable age and stability, some parts sustained significant wave trimming, blowouts, and landward migration of sand during the middle part of the 20th century (Simmons, 1982).

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CHAPTER 3:

A SPATIAL COMPARISON OF SANDY BEACHES IN A VULNERABLE SYSTEM IN THE GULF OF ST. LAWRENCE: SPECIES COMPOSITION, RICHNESS AND ABUNDANCE IN RELATION TO SHORELINE TYPE AND EROSION 55

MacMillan, M.R., Quijon, P.A., Submitted. A spatial comparison of Sandy beaches in a vulnerable system in the Gulf of St. Lawrence: species composition, richness and abundance in relation to shoreline type and erosion. Ecological Indicators.

3.1 Abstract

Sandy beaches associated with sand dunes, till bluffs and sandstone cliffs constitute the most prominent feature of Prince Edward Island’s north shore. The entire area is vulnerable to sea-level rise and storm-related erosion, and constitutes a model for the study of sandy beach macrofauna in relation to physical variation. This study used snapshot surveys to document the species composition, diversity and abundance of macrofauna communities at 14 sandy beaches, and explored their relationship with shoreline type, erosion rates, slope, sediment grain size and the Beach Deposit Index (BDI). At each beach, 20 samples (0.03 m2) were collected from replicated transects across the intertidal zone in order to characterize the macrofauna, and additional samples and measurements were taken to characterize physical descriptors. The lower intertidal of all sandy beaches was numerically dominated by the spionid polychaete Scolelepis squamata while the upper intertidal was characterized by the amphipods Americorchestia megalophthalma and Haustorius canadensis on beaches associated with sand dunes and till bluffs, and by Platorchestia platensis on beaches associated with sandstone cliffs. Average species richness was low and abundances were highly variable among beaches and shoreline types. Regression analyses identified positive relationships between erosion rate and species richness and abundance, but failed to detect any significant 56 relationship between faunistic variables and the other physical variables.

Similarity analyses indicated that beaches associated with sandstone cliffs, which coincidentally exhibited the lowest rates of coastal erosion, sustained communities significantly different from those collected from beaches associated with till bluffs and sand dunes. This exploratory study represents a first step towards the potential use of sandy beach invertebrates as indicators of weather related phenomena affecting sandy beaches.

3.2 Keywords

Sandy beaches; Shoreline erosion; Macrofauna; Biological indicators; Snapshot survey; Gulf of St. Lawrence

3.3 Introduction

Sandy beaches are characterized by the interactions of the wave energy they experience, their tidal regimes and the nature of the sand available for sorting and transport by tides and waves (McLachlan, 2001). Sandy beaches can be classified into three basic morphodynamic states: dissipative, intermediate and reflective. Dissipative beaches are at the erosional end of the spectrum, and result from a combination of high wave energy dissipating over a wide surf zone, an abundance of fine sands, and are characterized by gentle beach face slopes

(Short and Wright, 1983). Reflective beaches are at the accretionary end of the spectrum, and result from a combination of low energy waves reflecting off of a narrow beach. This type of beach is characterized by coarse sands and steep 57 beach face slopes (Short and Wright, 1983). Between these two extremes, intermediate beach types represent a transition from dissipative to reflective states, and exhibit intermediate physical characteristics (Short and Wright, 1983).

Sandy beach invertebrate communities are primarily structured by the environmental conditions they experience. The autecological hypothesis (Noy-

Meir, 1979) states that in physically controlled environments, animal populations

have little influence on each other, and communities are structured by species

responding independently to the physical environment rather than to biological

interactions. McLachlan (1990) provided initial evidence supporting the application of this hypothesis to an array of sandy beaches, suggesting that the swash climate controlled macrofaunal community structure. More supporting evidence came from a subsequent study by McLachlan and Dorvlo (2005) who

compiled published data from 161 quantitative sandy beach transect surveys from tropical, subtropical, warm temperate and cold temperate regions. That study identified global patterns of community structure in which species richness and abundance increased from narrow reflective to broad dissipative systems.

Since sandy beach macrofauna communities are structured by their

physical environment, changes to beaches as a result of erosion from weather

related phenomena are expected to result in changes to macrofauna communities. For instance, sea-level rise is believed to be responsible for long term beach erosion on United States east coast barrier beaches (Zhang et al.,

2004). Additionally, shifts in storm behaviour (i.e. frequency, intensity) alter the amount and direction of wave energy approaching the shoreline (Slott et al., 58

2006) and influence coastal erosion rates (Pethick, 2001). Sandy beaches are not locked into single morphodynamic states, and respond to changes in wave energy by moving toward dissipative states during storms, and towards reflective conditions during calm weather. During this process, sand erodes or accretes on the beach face as wave height changes (McLachlan, 2001). Similar differences can be expected at the spatial scale, where physical variation among sites is expected to be reflected in infaunal communities.

The objective of this study was to document the composition, diversity and abundance of sandy beach macrofaunal communities on the north shore of

Prince Edward Island (PEI) in relation to a number of physical characteristics.

PEI sandy beaches are associated with three predominant shoreline types: sand dunes, till bluffs and sandstone cliffs. Given the apparent visual discrepancy between these three shoreline types it is hypothesized that sandy beaches associated with them will differ in their physical characteristics, and therefore exhibit differences in their macrofauna communities.

3.4 Methods

3.4.1 Study area

The north shore of PEI is part of a major estuarine system, the southern

Gulf of St. Lawrence. Surface water salinity shows little spatial fluctuation along the study area during the summer months (June 29.53 ± 1.07%o, July 28.29 ±

1.42%o, and August 28.11 ± 0.76%o; Petrie et al., 1996). The region has a cool temperate maritime climate and mean tide range of 0.7 m (Forbes et al., 2004). 59

The coast is dominated by wave-generated processes, exposed to waves from a

direction between northwest and east (Owens and Bowen, 1977). Fourteen

sandy beaches along the north shore of Prince Edward Island, all within Prince

Edward Island National Park (PEINP) were selected for sampling during the

summer seasons of 2009-2010 (see Fig. 3.1 for approximate locations). These

beaches were associated with three distinctive shoreline types: sandstone cliffs

(Doyles Cove east, Doyles Cove west, MacKenzie’s Brook, Cape Turner), till

bluffs (Davlay west I, Dalvay west II, Stanhope east, Stanhope west) and sand

dune deposits (Brackley, Cavendish east, Cavendish west I, Cavendish west II,

Ross lane, Dalvay east). These sites were sampled on the following dates:

Brackley (July 15, 2009), Cavendish east (July 16, 2009), Ross lane and Dalvay

east (July 20, 2009), Doyles Cove east and McKenzie’s Brook (July 21, 2009),

Doyles Cove west and Cape Turner (July 22, 2009), Dalvay west I (July 29,

2009), Stanhope east (July 31, 2009), Stanhope west (August 3, 2009),

Cavendish west I (June 22, 2010), Dalvay west II (June 23, 2010), Cavendish

west II (July 5, 2010).

3.4.2 Sampling protocol

Snapshot surveys, a one-time sampling of each site with values for each

beach regarded as a single point in space and time, are considered the standard

for spatial comparisons of sandy beaches, and were utilized in this study.

Sampling was conducted during a narrow time frame over the summer. Each site was sampled during spring low tides, with 1-2 beaches sampled per day. 60

Gulf of St. Lawrence

45° N - -

NW A tlantic

"65?W 61 °W

OSand dune •Sandstone cliff •T ill bluff

* 1 12 13

kilometers

Figure 3.1. Approximate location of the sandy beaches sampled along the north shore of Prince Edvyard Island, southern Gulf of St. Lawrence. 1.Cavendish west II, 2.Cavendish west I, 3.Cavendish east, 4.Mackenzies Brook, 5.Cape Turner, 6.Doyles Cove west, 7.Doyles cove east, 8.Brackley, 9.Ross Lane, 10-Stanhope east, 11.Stanhope west, 12.Dalvay west II, 13.Dalvay west I, 14. Dalvay east. 61

For characterizing macrofauna communities, four transects spaced two

meters apart extending from the drift line (high tide level) to the lower limit of the swash zone (low tide level) were sampled at each beach. Along each transect, a

0.03 m2 PVC core was used to collect sediment up to a depth of approximately

25 cm at five equally spaced levels from high tide to low tide levels. The sediment samples collected were sieved through a 1 mm mesh screen, and the

macrofauna retained were stained with Rose Bengal solution to facilitate sorting, and stored in 70% ethanol. Macrofauna were identified to the lowest possible taxonomic level using the key by Bousfield (1973) and Bromley and Bleakney

(1984), and counted in order to determine abundance and taxa richness.

Physical characteristics of each beach were determined with the following

protocols. Approximately 250 mL of surface sediment was collected to a depth of

5 cm at each level of the first transect for grain size analysis (n=5 per beach).

Sediment samples were wet-sieved through a nested series of mesh sizes (i.e.

1000, 500, 250 and 125 pm) then dried and weighed. The mean sediment grain size as well as sorting was calculated using the logarithmic Folk and Ward (1957) graphical measures in GRADISTAT 4.0 (Blott and Pye, 2001). Beach face slope was measured in an area that was undisturbed during sampling, immediately adjacent to one of the sampled transects. This was done using graduated rods and the horizon (Emery, 1961) in two meter increments from the drift line to the swash zone. The Beach Deposit Index (BDI) was then calculated according to

BDI = (—)■(—) (1) Vtanb J \M z J ' ’ 62 where tan B is the average intertidal beach slope, a is the median grain size of the sand particle size classification scale (1.03125 mm) and Mz is the average intertidal sand grain size in mm (Soares, 2003). This index is lowest for beaches with steep slopes and coarser sands, and increases with flat slopes and finer sands in a gradient resembling that of the transition from reflective to dissipative beaches.

The erosion rate for each sandy beach was estimated from the measurements recorded at the nearest erosion monitoring site within PEINP. The distance between sampled beaches and erosion monitoring sites ranged from 0-

2 km. These sites were part of a suite of sites established by the PEI Department of the Environment in 1985 to measure coastal erosion. They were monitored sporadically through to 1996, and until the monitoring program was acquired by

Parks Canada in 2002. The amount of shoreline eroded at each site was determined by measuring the distance from a reference point on a cliff, bluff or dune edge/scarp to survey pins installed at each site. The rate of erosion (m • yr'1) was determined by dividing the total distance eroded from the coast by the number of years the site was sampled (Hawkins, 2008).

3.4.3 Data analysis

Physical characteristics (1/slope, sediment grain size, erosion rate) and the BDI were compared among beaches associated with the three shoreline types using one-way Analysis of Variance (ANOVA). Pairwise multiple comparisons were made using the Holm-Sidak method when significant 63 differences were found between shoreline types. Sediment grain size was not normally distributed nor could it be normalized by transformation, so differences between shoreline types were assessed using Kruskal-Wallis one-way ANOVA on ranks. The relationship between physical descriptors of beach state (1/slope, sediment grain size and the BDI) and erosion rate were also explored using linear regression analyses.

Relationships between faunistic and physical variables were explored using linear regression analysis. Preliminary analyses were also conducted with non-linear regressions, and although in a few cases the r2 values were slightly higher, they did not change the outcome or the overall interpretation of the regressions. Therefore, for consistency, only linear regressions are presented.

Data on species composition and abundance per transect (all five samples combined for each transect; cf. Brazeiro, 2001) were used as single replicates to characterize each sandy beach (n=4 per beach). Mean species richness and abundance per sandy beach, as well as abundance of the dominant species

(Scolelepis squamata) were logio(x + 1) transformed when necessary in order to meet assumptions of normality and homoscedasticity for the regression model.

Similarity among communities associated with the three shoreline types was also assessed. Transects were used as replicates for non-metric multidimensional scaling ordinations (MDS) based on the Bray-Curtis similarity index (de la Huz and Lastra, 2008; PRIMER Version 6.1.13) to interpret differences among communities. A measurement of goodness-of-fit of the MDS ordination was given by the stress value, where a low stress factor (< 0.2) was 64 considered an ordination with no serious prospect of a misleading interpretation

(Clarke and Warwick, 1994). Three transects which had no macrofauna, all from sandy beaches associated with sandstone cliffs, were excluded from the similarity analysis. The contribution of rare species (against a single highly abundant species) was accounted for by applying a logio (x + 1) transformation before data were analyzed. Pairwise multiple comparisons using Analysis of

Similarity (ANOSIM; Clarke, 1993) were used in order to test the null hypothesis of no difference among infaunal assemblages from beaches associated with the three different shoreline types. SIMPER analysis was subsequently used to identify the species that contributed the most to the differences between communities associated with each shoreline type.

3.5 Results

3.5.1 Physical properties of the sandy beaches

The physical characteristics of the 14 sandy beaches surveyed exhibited substantial variation. The inverse of beach face slope ranged from 10 to 53 and the BDI ranged from a low of 28 on the steepest beaches to 246 (Table 3.1).

Values for both variables were slightly greater on beaches associated with sand dunes, but the differences were borderline or not significant (one-way ANOVA; p=0.055 and p=0.153 respectively; Table 3.2, Fig. 3.2a,b). Mean sediment grain size ranged from fine to medium sands and sorting varied from well sorted to poorly sorted (Table 3.1), but there was no difference between shoreline types

(Kruskal-Wallis; p=0.997; Fig. 3.2c). Erosion rates, however, were significantly 65

Table 3.1. Summary of physical characteristics of the 14 sandy beaches sampled on the north shore of PEI. Sorting categories are based on Folk and Ward (1957).

Mean Shoreline Mean erosion sediment Site Location (N,W) 1/Slope BDI Sediment sorting type rate (m ■ yr'1) grain size (0) Doyles Cove East 46.47479,-63.30448 Sandstone 24 135 0.20 2.47 Well Sorted Doyles Cove West 46.47603, -63.30550 Sandstone 28 147 0.20 2.36 Moderately Well Sorted MacKenzies Brook 46.49664, -63.34588 Sandstone 11 28 0.17 1.35 Poorly Sorted Cape Turner 46.484737,-63.311872 Sandstone 26 114 0.16 2.07 Moderately Sorted Dalvay west I 46.41736, -63.07385 Till 21 113 0.94 2.41 Well Sorted Dalvay west II 46.418518, -63.085419 Till 21 107 0.81 2.33 Moderately Well Sorted Stanhope East 46.422928, -63.108484 Till 16 82 1.10 2.32 Moderately Well Sorted Stanhope West 46.423553, -63.111156 Till 10 28 1.10 1.47 Poorly Sorted Brackley 46.430635,-63.202985 Dune 40 216 0.41 2.37 Moderately Well Sorted Cavendish east 46.499377,-63.392177 Dune 53 184 0.36 1.74 Moderately Well Sorted Cavendish west I 46.50103,-63.40291 Dune 29 100 0.59 1.74 Well Sorted Cavendish west II 46.50216, -63.41856 Dune 12 49 0.61 1.98 Moderately Well Sorted Ross Lane 46.42580, -63.12159 Dune 31 171 0.99 2.41 Moderately Well Sorted Dalvay East 46.41690, -63.07039 Dune 44 246 0.94 2.44 Well Sorted 66

Table 3.2. Results of one-way ANOVAs comparing physical features (1/slope, Beach Deposit Index, erosion rate) among the 14 beaches surveyed. DF: degrees of freedom, MS: Mean Squares. For simplicity, Sum of Squares and F-values have been omitted.

Comparison Dependent variable Source of Variation DF MS P Beach 1/Slope Between Groups 2 444.601 0.055 Characteristics Error 11 116.439

BDI Between Groups 2 8179.579 0.153 Error 11 3654.760

Erosion rate Between Groups 2 0.650 <0.001 Error 11 0.0368 67

60 300 a) b) 50 250 « 40 200 f 30 a g 150 a ^ 20 100

10 50 0 JL 0 A § 3.0 c) a> ~ 1.2 d) y 2.5 > • 1.0 2.0 c: 1.5 as 0 .6 a> u . I 1.0 a> .1CO 0.4 ” 0.5 2 0.2 (0 LLi £ o.o 0.0 Sandstone Till Dune Sandstone Till Dune Shoreline type Shoreline type Figure 3.2. Relationships between the mean physical characteristics measured and shoreline type for 14 sandy beaches sampled on the north shore of Prince Edward Island, summer 2009 / 2010. Error bars represent one standard error. Identical letters indicate no significant differences among coast types. 68 lower on sandstone shorelines than sand dune and till shorelines (one-way

ANOVA; p=0.006 and p<0.001 respectively; Table 3.2), which also differed significantly (p=0.020; Fig. 3.2d). There were no significant relationships between erosion rate and the three physical descriptors (Regression analysis; Fig. 3.3):

1/slope (p=0.543), sediment grain size (p=0.576) and BDI (p=0.850).

3.5.2 Macro fauna communities

Macrofauna species richness was poor, ranging from 0 to 5 species per transect. Abundance was highly variable, ranging between 0 and 830 individuals per transect. The most abundant species was the spionid polychaete Scolelepis squamata, which dominated sediments near the low tide level and represented approximately 95% of the total abundance (Table 3.3). The next most abundant species were all amphipods, two of which are characteristic of beaches associated with till bluffs and sand dunes, Haustorius canadensis and

Americorchestia megalophthalma which represented 1.49% and 0.50% of total abundance respectively. A third amphipod species, Platorchestia platensis, was characteristic of beaches associated with sandstone cliffs and represented

0.75% of the total abundance (Table 3.3).

Regression analysis revealed a significant relationship between macrofauna and erosion rates, but not other measured physical characteristics or the BDI. Species richness and abundance both increased as erosion rate increased (Regression analysis; p<0.001 and p=0.006, r2=0.721 and r2=0.485 respectively; Figs. 3.4a & 3.5a). However, there were no significant relationships 69

60 50

(U 40

| 30

^ 20 10 0 2.6 2.4 g 2.2

n 2.0 g 1.8 ro O 1-6 1.4 1.2 300 250 200

g 1go 100 50

0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Erosion rate (m • yr~1)

Figure 3.3. Relationships between beach physical characteristics and erosion rate for 14 sandy beaches sampled on the north shore of Prince Edward Island, summer 2009 / 2010. 70

CD .§ CD 5. -cs .c o t o 3 .c o .CO . o CO CD 3 c o c o D) 5> co .§ c c c d G 3 CD O s £ c § ■§5 & S CO co e CD CD 3 CD .CD •2 fo 3 9 - 5C C a I 5 3 CD CO c o C r .CD & « cd §• O CO CD "CD CD CD 1 Site co _Q. S CD CD o Doyles Cove 5 0 55 1 0 0 0 0 0 0 0 0 0 0 CD east Doyles Cove 2 0 0 0 0 0 0 .1 0 1 0 0 0 0 west Mackenzies 3 0 0 0 0 0 1 0 3 0 0 0 0 0 Sandston Brook Cape Turner 115 0 5 0 0 0 0 0 0 2 1 0 0 0 Dalvay 1,102 3 0 3 1 1 0 0 0 0 2 0 0 0 west I Dalvay 968 5 0 2 0 6 0 1 0 0 0 1 0 0 west II Stanhope 126 3 0 50000000001 east Stanhope 874 2 0 6 ' 1 0 9 3 0 0 0 0 0 0 west Brackley 392 23 0 1 0 0 0 0 1 0 0 0 0 0 Cavendish 135 0 0 2 0 0 0 0 0 0 0 0 0 0 east

CD Cavendish c 714 44 0 0 0 0 0 0 0 0 0 0 0 0 3 west I Q Cavendish 167 0 0 6 0 0 0 0 1 0 0 0 0 0 west II Ross Lane 638 0 0 9 8 4 0 0 0 0 0 0 1 0 Dalvay east 2,445 39 0 5 4 2 0 0 0 0 0 0 0 0 71

1 y=0.302 + 0.331 x r2=0.721, p<0.001 0 0.2 0.4 0.6 0.8 0 10 20 30 4 0 50 60 Mean Erosion Rate (m y r 1) 1/Slope 5 5 in in in in a) CD c 4 c 4 XLo XLO 0C 3 a: 3 (!) in 5? 0 0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 0 50 100 150 200 250 30( Mean Sediment Grain Size (-0) BDI

Figure 3.4. Relationships between physical characteristics and mean species richness for the macrofauna community of 14 sandy beaches on the north shore of Prince Edward Island, summer 2009 / 2010. Error bars represent the standard error of four replicates. Figure 3.5. Relationships between physical characteristics and mean abundance abundance mean and characteristics physical between Relationships 3.5. Figure

Log(Mean Abundance + 1) Log(Mean Abundance + 1) 0.0 0.5 3.0 3.0 0.0 2.0 standard error of four replicates. of four error standard of shore north onthe beaches 14sandy of community macrofauna the of Prince Edward Island, summer 2009 / 2010. Error bars represent the the represent bars Error 2010. / 2009 summer Island, Edward Prince . 02 . 06 . 1.0 0.8 0.6 0.4 0.2 0.0 . 14 . 18 . 22 . 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 enSdmn ri ie( BDI ) (0 Size Grain Sediment Mean enEoinRt m y') 1/Slope • yr'^) (m Rate Erosion Mean ^045 p=0.006 1^=0.485, 1.414x + y=0.797 1.2 1.5 j j T3 a)600 2.5 + ro 2.0 400 800 200 3.0 0.0 1.0 0 0 0 0 10 0 20 300 250 200 150 100 50 10 20 040 30 060 50 72 between mean species richness and the beach face slope, sediment grain size or BDI (Regression analysis; Fig. 3.4b,c,d): 1/slope (p=0.714), sediment grain size (p=0.373) and BDI (p=0.817), or between those variables and abundance

(Fig. 3.5b,c,d): 1/slope (p=0.432), sediment grain size (p=0.550) and BDI

(p=0.148). The mean abundance of S. squamata also increased with erosion rate

(Regression analysis; p=0.004, r2=0.504; Fig. 3.6a). However, there were no significant relationships between the abundance of this species and the physical characteristics described or BDI (Fig. 3.6b,c,d): 1/slope (p=0.429), sediment grain size (p=0.761) and BDI (p=0.412).

Macrofauna communities differed significantly between some shoreline types, but not others. Based on species composition and abundance, no significant differences were observed between communities from beaches associated with till bluffs and sand dunes (ANOSIM; p=0.127). However, communities on beaches associated with sandstone cliffs were significantly different from the other two (p<0.001 in both pairwise comparisons; Fig. 3.7).

This distinction among communities matched an arbitrary categorization of beaches based on their rates of coastal erosion: shorelines experiencing relatively low rates of erosion (0.16-0.20 m/year, beaches associated with sandstone cliffs) and shorelines experiencing relatively high levels of erosion

(0.36-1.1 m/year, beaches associated with till bluffs and sand dunes; Fig. 3.2d).

SIMPER analysis revealed that average similarity values were much lower between samples associated with sandstone beaches (18.64%) than in those associated with till and dune beaches (69.43% and 66.06%, respectively). The Figure 3.6. Relationships between physical characteristics and mean abundance abundance mean and characteristics physical between Relationships 3.6. Figure Log(Mean S. squamata Log(Mean S. squamata Abundance + 1) Abundance + 1) 2.0 3.0 0.5 2.0 0.0 0.5 1.0 the north shore of Prince Edward Island, summer 2009 / 2010. Error bars Error 2010. / 2009 summer Island, Edward Prince of shore north the of the dominant polychaete polychaete dominant the of represent the standard error of four replicates. four of error standard the represent . 02 . 06 . 10 1.2 1.0 0.8 0.6 0.4 0.2 0.0 . 14 . 18 . 22 . 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 enSdmn ri ie() BDI (0) Size Grain Sediment Mean enEoinRt m r1 1/Slope yr"1) (m Rate Erosion Mean y=0.549 + 1.643x 1.643x + y=0.549 ^054 p=0.004 1^=0.504, Scolelepis squamata Scolelepis d ra cd 0.5 < S d to cd r- '5 to o (1) ' O 9 o> 1.0 S ' c

2.52.53.0 2.0 2.5 0.0 3.03.0 0 2

0 0 50 020 10 on 14 sandy beaches on beaches 14sandy on 0 10 0 20 300 250 200 150 100 04 060 50 40 30 74 75

Figure 3.7. Multidimensional scaling plot illustrating macrofauna community similarity among sandy beaches associated with sandstone cliffs (black symbols), till bluffs (gray) and sand dunes (white). The oval surrounding samples from beaches associated with till bluffs and sand dunes is based on ANOSIM results and indicates that community structure in these samples were not significantly different. 76 most important species driving similarity among samples in the three shoreline types was S. squamata, followed by Platorchestia platensis (sandstone beaches), Americorchestia megalophthalma (till beaches) and Haustorius canadensis (sand dune beaches).

3.6 Discussion

Worldwide, the diversity and abundance of macrofauna on sandy beaches increases predictably from reflective to dissipative states (Defeo and Mclachlan,

2005). Although such trends have been primarily reported in exposed oceanic beaches, it has recently been demonstrated to be applicable to some beaches associated with estuarine systems (e.g. Lercari and Defeo, 2006). Sandy beaches on the north shore of PEI are embedded within a large estuarine system

(Forbes et al., 2004), and despite their poor complement of species, they were expected to follow a similar reflective-dissipative pattern in abundance and diversity. Surprisingly, no significant relationships were detected between infauna and the physical variables most closely related to reflective-dissipative gradients

(slope and grain size) or the Beach Deposit Index. Instead, consistently significant relationships were found between macrofauna and the rates of coastal erosion: as erosion rates increased, the abundance and diversity of the macrofauna did as well. Among other factors, this relationship can be explained by the supply of nutrients to the suspension-feeding organisms dominating this system. 77

Food sources for sandy beach macrofauna include planktonic surf and epipsammic diatoms, particulate and dissolved organic matter, detritus and carrion (McLachlan and Brown, 2006). The main driving force maintaining sandy beaches is wave energy which transports energy and matter (including suspended food) into, within, and out of sandy beach ecosystems (McLachlan et al., 1981). Menn (2002) reported that highly dynamic beaches, such as those studied here, are affected by high levels of erosion, filter large volumes of seawater and result in high fluxes of particulate organic matter through the beach. Suspension feeders like Scolelepis squamata, by far the numerically dominant species in this system, feed directly on these suspended particulates.

Although this polychaete is a facultative suspension / deposit feeder, Dauer

(1983) demonstrated that even in the absence of currents, deposit feeding is rare in this species. Most commonly (near 95% of the time), when exposed to currents of 5 cm • s'1 or higher this species fed on suspended or re-suspended particles (Dauer 1983). The second most abundant species in this study was the haustoriid amphipod Haustorius canadensis. Haustoriid amphipods are also suspension feeders (Bousfield, 1970; Crocker, 1967; Ivesterand Coull, 1975).

Hudon (1983) reported the amphipod Calliopius laeviusculus was an efficient and selective consumer of re-suspended particulates. Furthermore, although amphipods of the genus Gammarus are considered omnivores, Hudon (1983) observed that the rapid beating of the pleopods necessary for respiration by

Gammarus oceanicus created currents bringing suspended and re-suspended food particles to the mouth. Thus by their very nature, amphipods appear to be 78 well suited to feeding on suspended particulates despite their functional feeding preferences. Since sandy beaches, particularly those exposed to erosion, are not nutrient sinks (McLachlan and McGwynne, 1986), conditions are not favourable for deposit feeder species (Snelgrove and Butman, 1994), which indeed were virtually absent from the surveys.

Previous studies have reported that active swimmers such as S. squamata and the amphipod H. canadensis are predominant on sandy beaches severely affected by wave action (Eleftheriou and Nicholson, 1975; Menn, 2002).

This is consistent with the results of this study, particularly in the case of S. squamata. Although found on all sites, this polychaete was much more abundant on beaches associated with sand dunes and till bluffs which experienced significantly greater rates of erosion than sandstone cliffs. Similarly, H. canadensis was not found on the relatively stable sandy beaches associated with sandstone cliffs, where this species was replaced by the amphipod Platorchestia platensis, aprimary beach colonizer (Bousfield, 1973). A series of other studies have investigated the effects of erosion on beach invertebrates (e.g. Beentjes et al., 2006; Jaramillo et al., 1987; Menn, 2002; Walker et al., 2008). However, this is the first time sandy beach community assemblages have been investigated across a spatial gradient that include three distinctive shoreline types. Erosion levels were considerably lower in sandy beaches associated with sandstone cliffs. This likely implies lower levels of sediment and nutrient re-suspension that limit or reduce the amount of food available to suspension-feeding organisms, by far, the best represented in these communities. Surprisingly, the observed increase in abundance and diversity with rate of

erosion does not appear to be the result of a change in beach state toward

dissipative conditions. Although coastal geomorphology, erosion rates and beach

dynamics are interrelated (Bray and Hooke, 1997), no significant relationships were detected between the rate of coastal erosion and any of the physical characteristics studied here (slope, sediment grain size) or the BDI. Furthermore,

no significant relationships were found between macrofauna abundance or diversity and those physical descriptors. The inverse of beach face slope generally ranges from 10 to 100 for a gradient between reflective and dissipative beaches (McLachlan and Brown, 2006). However, in this study the range was

narrower (10-53) indicating that the beaches sampled fall within a reflective-

intermediate range. Thus, the lack of significant relationships between macrofauna and physical characteristics may be attributed at least in part to the rather homogeneous morphodynamics of the beaches on the north shore of PEI.

Since the increase in species richness with erosion rate appears to be unrelated to beach morphodynamics, the increase may be due to a greater number of predators feeding on the abundant prey species at the eroding sites. For example, Nephtys bucera is known to feed on the polychaete Scolelepis squamata (McDermott, 1987), and nemerteans are known to feed on amphipods and polychaetes (McDermott, 1998; Thiel and Kruse, 2001).

Given the temporal constraints of this survey (a single spatial comparison applicable to summer conditions) it is impossible to infer whether these results are applicable to other seasonal conditions. However, the spatial scope of the comparisons conducted (~40 km of shoreline) is large enough to be relevant for coastal management. Therefore, the results of the regressions conducted provide meaningful information despite the fact that their predictive level is only modest. Further analyses on broader temporal scales are clearly required in order to determine the robustness of these relationships in light of seasonality and inter-annual variation. The results of this study also have implications for the further study and monitoring of sandy beaches. Indeed, the most common and abundant species reported here may be suitable as an indicator species for assessing beach conditions over time (Walker et al., 2008).

One reason that erosion fates may not have related well to physical characteristics was that the erosion monitoring sites used in this study were established to monitor park infrastructure and not necessarily beach conditions.

Forbes and Manson (2002) noted that sand dune shorelines on the north shore of PEI were highly mobile and may rapidly retreat and subsequently heal, while cliff shorelines retreat relatively slowly but persistently (Forbes and Manson,

2002). Given that these shorelines appear to have “characteristic” dynamics of erosion, the differences in erosion rates are assumed to be meaningful and representative of each sandy beach. Regardless, differences in erosion levels recorded over a period of only 10 years should be taken cautiously, as they may not necessarily represent long-term or future trends at a given site (Dolan et al.,

1991).

There are other factors not considered in this study that may also play a meaningful role in the spatial variation of the macrofauna. For example, Dugan et al. (2003) found that species richness, abundance and biomass of macrofauna were not well predicted by any physical characteristic of the sandy beaches of the southern California coast. These authors found that overall species richness and abundance were instead correlated with standing crop of macrophyte wrack.

Talitrid amphipods such as Americorchestia megalophthalma and Platorchestia platensis found in this study are strongly influenced by wrack inputs and may indeed contribute to the variability of macrofauna communities (see Chapter 4).

The macrofauna plays a role of upmost importance in sandy-beach food chains. They consume primary food sources and in turn serve as prey for mid- and top-level predators (McLachlan and Brown, 2006). A known predator of sandy beach invertebrates on the north shore of PEI is the Piping Plover

(Charadrius melodus), a species that has been listed as “endangered” in Canada and the United States (Burger, 1994). Its reliance on sandy beach invertebrates as a main source of food, adds relevance to studies like this that aim to document spatial variation of the plover’s food sources during the time this species nests and feeds in the region. Aiming to predict plover’s food availability in scenarios of sea level rise and increased erosion levels seems the natural follow up to this study. Additionally, being able to predict macrofauna community response to these and other physical and biological factors has relevance for the management and conservation of biodiversity on sandy beaches (McLachlan and

Dorvlo, 2005). 82

3.7 Acknowledgements

Thanks to Veronique Dufour, Christina Pater, Bradley MacMillan, Jessica Willis,

Megan Tesch and Marianne Parent for their assistance with field work. I would also like to thank Dr. Pedro Quijon, Dr. Donna Giberson and Dr. Darren Bardati for reviewing this chapter. Thanks also to Parks Canada for access to PEINP and their collaboration during the selection of study sites. This research was supported by a grant from Environment Canada through funding to UPEI’s climate change research program.

3.8 References

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Bousfield, E.L., 1973. Shallow-Water Gammaridean Amphipoda of New England. Comstock Publishing Associates, London.

Bray, M.J., Hooke, J.M., 1997. Prediction of soft-cliff retreat with accelerating sea-level rise. J. Coast. Res. 13, 453-467.

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Bromley, J.E., Bleakney, J.S., 1985. Keys to the fauna and flora of Minas Basin. National Research Council of Canada, Halifax. 83

Burger, J., 1994. The effect of human disturbance on foraging behavior and habitat use in Piping Plover (Charadrius melodus). Estuaries 17, 695-701.

Clarke, K.R., 1993. Non-metric multivariate analysis of changes in community structure. Aust. J. Ecol. 73, 117-143.

Clarke, K.R., Warwick, R.M., 1994. Change in Marine Communities: an Approach to Statistical Analysis and Interpretation. Natural Environmental Research Council, United Kingdom.

Crocker, R.A., 1967. Niche diversity in five sympatric species of intertidal amphipods (Crustacea: Haustoriidae). Ecol. Monogr. 37, 173-200.

Dauer, D.M., 1983. Functional morphology and feeding behavior of Scolelepis squamata (Polychaeta: Spionidae) Mar. Biol. 77, 279-285.

Defeo, O., McLachlan, A., 2005. Patterns, processes and regulatory mechanisms in sandy beach macrofauna: a multi-scale analysis. Mar. Ecol. Prog. Ser. 295, 1-20. de la Huz, R., Lastra, M., 2008. Effects of morphodynamic state on macrofauna community of exposed sandy beaches on Galician coast (NW Spain). Mar. Ecol. 29, 150-159.

Dolan, R., Fenster, M.S., Holme, S.J., 1991. Temporal analysis of shoreline recession and accretion. J. Coast. Res. 7, 723-744.

Eleftheriou, A., Nicholson, M.D., 1975. The effects of exposure on beach fauna. Cah. Bio. Mar. 16, 695-710.

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Folk, R.L., Ward, W.C., 1957. Brazos River bar: a study in the significance of grain size parameters. J. Sediment. Petrol. 27, 3-32.

Forbes, D.L., Parkes, G.S., Manson, G.K., Ketch, L.A., 2004. Storms and shoreline retreat in the southern Gulf of St. Lawrence. Mar. Geol. 210, 169- 204. 84

Hawkins, R., 2008. Coastal Erosion Monitoring Protocol. Prince Edward Island National Park Ecological Integrity Monitoring and Reporting Program, Charlottetown.

Hudon, C., 1983. Selection of unicellular algae by the littoral amphipods Gammarus oceanicus and Calliopius laeviusculus (Crustacea). Mar. Biol. 78, 59-67.

Ivester, M.S., Coull, B.C., 1975. Comparative study of ultrastructural morphology of some mouthparts of four haustoriid amphipods. Can. J. Zool. 53, 408- 417.

Jaramillo, E., Croker, R.A., Hatfield, E.B., 1987. Long-term structure, disturbance, and recolonization of macrofauna in a New Hampshire sand beach. Can. J. Zool. 65, 3024-3031.

Lercari, D., Defeo, O., 2006. Large-scale diversity and abundance trends in sandy beach macrofauna along full gradients of salinity and morphodynamics. Estuar. Coast. Shelf Sci. 68, 27-35.

Menn, I., 2002. Beach morphology and food web structure: comparison of an eroding and an accreting sandy shore in the North Sea. Helgol. Mar. Res. 56, 177-189.

McDermott, J.J., 1987. The distribution and food habits of Nephtys bucera Ehlers, 1868, (Polychaeta: Nephtyidae) in the surf zone of a sandy beach. Proc. Biol. Soc. Wash. 100, 21-27.

McDermott, J.J., 1998. Observations on feeding in a South African suctorial hoplonemertean, Nipponnemertes sp. (Family Cratenemertidae). Hydrobiologia 356, 251-256.

McLachlan, A., 1990. Dissipative beaches and macrofaunal communities on exposed intertidal sands. J. Coast. Res. 6, 57-71.

McLachlan, A., 2001. Coastal beach ecosystems, in: Lewin, R. (Ed.), Encyclopedia of Biodiversity. Academic Press, New York, pp. 741-751.

McLachlan, A., Brown, A.C., 2006. The Ecology of Sandy Shores, second ed. Academic Press, New York. 85

McLachlan, A., Dorvlo, A., 2005. Global patterns in sandy beach macrobenthic communities. J. Coast. Res. 21, 674-687.

McLachlan, A., McGwynne, L., 1986. Do sandy beaches accumulate nitrogen? Mar. Ecol. Prog. Ser. 34, 191-195.

McLachlan, A., Wooldridge, T., Dye, A.H., 1981. The ecology of sandy beaches in southern Africa. S. Afr. J. Zool. 16, 219-231.

Noy-Meir, I., 1979. Structure and function of desert ecosystems. Isr. J. of Bot. 28, 1-19.

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Pethick, J., 2001. Coastal management and sea-level rise. Catena 42, 307-322.

Petrie, B., Drinkwater, K., Sandstrom, A., Pettipas, R., Gregory, D., Gilbert, D., Sekhon, P., 1996. Temperature, Salinity and Sigma-t Atlas for the Gulf of St. Lawrence. Bedford Institute of Oceanography, Dartmouth.

Short, A., D., Wright, L.D., 1983. Physical variability of sandy beaches, in: McLachlan, A., Erasmus, T. (Eds.), Sandy Beaches as Ecosystems. Dr. W. Junk Publishers, The Hague, pp. 133-144.

Slott, J.M., Murray, A.B., Ashton, A.D., Crowley, T.J., 2006. Coastline responses to changing storm patterns. Geophys. Res. Lett. 33, L18404.

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Soares, A.G., 2003. Sandy Beach Morphodynamics and Macrobenthic Communities in Temperate, Subtropical and Tropical Regions - A Macroecological Approach. Ph.D thesis, University of Port Elizabeth, South Africa.

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Walker, S.J., Schlacher, T.A., Thompson, L.M.C., 2008. Habitat modification in a dynamic environment: the influence of a small artificial groyne on macrofaunal assemblages of a sandy beach. Estuar. Coast. Shelf Sci. 79, 24-34. 86

Zhang, K., Douglas, B., Leatherman, S.P., 2004. Global warming and coastal erosion. Climatic Change 64, 41-58. 87

CHAPTER 4:

STRANDED MACROPHYTES AS A PATCHY RESOURCE: WRACK FEATURES INFLUENCE MACROFAUNAL ABUNDANCE IN AN ATLANTIC CANADA SANDY BEACH SYSTEM 88

MacMillan, M.R., Quijon, P.A., Submitted. Stranded macrophytes as a patchy resource: wrack features influence macrofaunal abundance in an Atlantic Canada sandy beach system. Journal of Sea Research.

4.1 Abstract

Patches of stranded macrophytes (wrack) are a distinctive feature of sandy beaches worldwide and a potential food subsidy for their resident communities. Despite their relevance, the spatial variation of wrack and its potential influence on upper shore beach organisms remain poorly understood.

Wrack and macrofauna were surveyed on seven sandy beaches associated with sand dunes, till bluffs and sandstone cliffs along the north shore of Prince

Edward Island, Atlantic Canada. Wrack patch density, cover, and water content were measured, and the associated macrofauna were compared to the communities inhabiting nearby bare sediments. The survey found among-site spatial differences in wrack characteristics and identified rockweeds (Fucus serratus) and eelgrass (Zostera marina) as the main macrophyte species in the area. Macrofaunal abundances were higher in wrack than in bare sediments but this varied among locations. A field manipulation was conducted at two sandy beaches to measure macrofauna colonization on patches of fresh and aged rockweed and eelgrass. Regardless of macrophyte age, macrofaunal organisms preferentially colonized sediments associated with rockweeds. In addition, calculations across treatments detected positive relationships between macrofaunal abundance and wet mass, dry mass and water content of the wrack patches, regardless of macrophyte species or state. Macrophyte preferences 89 were further explored by comparing the nutritional value of the plant tissues and assessing macrofauna feeding rates under laboratory conditions. Rockweed tissues had consistently higher protein, lipid and carbohydrate contents than eelgrass and were affected by higher invertebrate consumption rates. Overall, these results suggest that spatial variation and wrack features and species composition play key roles on the structure of the supralittoral macrofauna.

4.2 Keywords

Sandy beaches; Allochthonous material; Macrofauna; Eelgrass (Zostera marina)]

Rockweed (Fucus serratus); Gulf of St. Lawrence

4.3 Introduction

Sandy beaches around the world are characterized by intertidal zones of unconsolidated shifting sands devoid of large primary producers (Jaramillo et al.,

2006; Ince et al., 2007). For these habitats, most food availability is allochthonous and limited to phytoplankton cells and other particulates transported onshore (McLachlan and Brown, 2006) and the input of nearshore macroalgae and seagrasses (macrophytes; Dugan et al., 2003). The accumulation of patches of stranded macrophytes or “wrack” represents a key food subsidy for resident invertebrate communities, particularly those living at the upper levels of the intertidal zone (Griffiths et al., 1983; Inglis, 1989; McLachlan and Brown, 2006; Lastra et al. 2008). Wrack is expected to influence these communities, and several authors have reported increased abundances of 90 macrofauna with wrack cover, volume or standing stock (Behbehani and Croker,

1982; Dugan et al., 2003; Ince et al., 2007; Jaramillo et al., 2006; Rodil et al.,

2008; Stenton-Dozey and Griffiths, 1983). Wrack also affects the zonation of macrofauna. For example, some macrofaunal species such as the talitrid amphipod Talorchestia martensii closely follow the movements of wrack as its position on the beach changes during the semi-lunar cycle (Colombini et al.,

2000).

Marine invertebrates living in the supralittoral zone live buried in the sand beyond the intertidal zone, and therefore are minimally affected by intertidal swash conditions (Koop and Field, 1980; Jaramillo et al., 2006). In temperate regions, the supralittoral fauna in sandy beaches with moderate macrophyte input are often dominated by talitrid amphipods (Colombini et al., 2000; Griffiths and Stenton-Dozey, 1981; Inglis, 1989; J^drzejczak, 2002). These organisms are considered primary colonizers of newly stranded wrack (Behbehani and Croker,

1982; Colombini et al., 2000; Griffiths and Stenton-Dozey, 1981; Inglis, 1989;

Marsden, 1991; Stenton-Dozey and Griffiths, 1983), which subsequently attract and sustain secondary (predatory) species (Colombini et al., 2000; Dugan et al.,

2003; Griffiths and Stenton-Dozey, 1981; Ince et al., 2007; J^drzejczak, 2002).

Since macrophytes have different physical and nutritive properties (Lastra et al.,

2008), the colonization of wrack by amphipods is expected to relate to its composition and the amount of time the patches have been stranded over the beach. Wrack deposits may undergo severe dehydration as they age or become covered by windblown sand (Ince et al., 2007; Rodil et al., 2008). Both processes

/ 91 contribute to their decomposition (Ince et al., 2007) and remineralization by

bacteria (Kirkman and Kendrick, 1997).

Wrack species composition and biomass change spatially and temporally

(Dugan et al., 2003; Lastra et al., 2008; Marsden, 1991; Orr et al., 2005; Stenton-

Dozey and Griffiths, 1983) in response to local hydrological processes (Ince et

al., 2007) or larger-scale processes, such as sea-level change and the dynamics

of shoreline erosion (Lastra et al., 2008). Additionally, species of stranded

seaweeds are not uniformly used by colonizing invertebrates (Rodil et al., 2008).

Therefore, changes in composition of the standing crop of wrack may influence

invertebrate communities. For example, Lastra et al. (2008) found that

amphipods of the genera Megalorchestia and Talitrus rapidly consumed brown

algae of the genera Macrocystis and Saccorhiza, respectively, but only

consumed negligible amounts of the seagrass Phyllospadix. The causes for

these differences are diverse. Seaweeds may vary in physical structure (levels of

branching, toughness), nutritional quality and/or quantity, palatability, and

decomposition rates while stranded on the beach face (Duarte et al., 2010;

Dugan et al., 2003; Rodil et al., 2008; Rossi and Underwood, 2002; Stenton-

Dozey and Griffiths, 1983). Few studies so far have attempted to describe the

spatial variation of stranded seaweeds and their individual influence on sandy

beach invertebrates, despite the importance of wrack as food and habitat

Several species of seagrasses and rockweeds dominate the wrack on

eastern North American shorelines and each possess different characteristics that affect their use by invertebrates. Seagrasses possess structural 92 polysaccharides and a low proportion of available nitrogen, limiting its value as a food source (Inglis, 1989). Meanwhile, rockweeds are high in nitrogen content and other soluble substances (Inglis, 1989) but contain secondary metabolites that may deter herbivory and decrease herbivore assimilation efficiency and growth (Boettcher and Target, 1993; Denton and Chapman, 1991; Pennings et al., 2000). Both types of macrophytes are common in the supralittoral wrack on the sandy beaches on the north shore of Prince Edward Island (PEI), but their composition and abundance is expected to vary with shoreline type. For example, sandy beaches in this region are associated with sand dunes, till bluffs and sandstone cliffs, one of which (sandstone cliffs) erode at a much slower rate

(cf. Forbes and Manson, 2002; Flawkins, 2008, see also Chapter 3). Given that little is known about the influence of wrack on the upper shore macrofauna of beaches here and elsewhere, this shoreline system offers a unique opportunity to address this knowledge gap. The goal of this study was to assess the role of macrophyte wrack on the abundance of the supralittoral macrofauna using a combination of exploratory and experimental approaches. Specifically, this study reports (1) a snapshot survey of the standing crop of wrack in seven representative sandy beaches and compares macrofaunal numbers in wrack and bare sediments; (2) a field experiment assessing the colonization on the two most common species of stranded seaweeds; and (3) a comparison of the nutritional quality of those two seaweed species and their corresponding rates of consumption by invertebrates in a laboratory setting. 93

4.4 Materials and Methods

4.4.1 Stranded Macrophyte Survey

% Seven sandy beaches located on the north shore of Prince Edward Island were sampled during summer 2010: Brackley (July 8), Ross Lane (July 8),

Dalvay west I (July 12), Dalvay west II (July 12), Cavendish (July 26), Doyles

Cove (July 13) and Cape Turner (July 13; Fig. 4.1). The sandy beaches at

Brackley, Cavendish and Ross Lane are backed by sand dunes, Dalvay west I and II are backed by till bluffs, and Doyles Cove and Cape Turner are backed by sandstone cliffs. A table of random numbers was used to select the location of samples along the driftline associated with the last high tide in order to prevent bias from unintentional selection of areas with high or low macrophyte accumulation. At each site, the percent cover of macrophytes was visually estimated to the nearest five persent using 1 x 4 m quadrats placed along the driftline. The quadrat was then subdivided in four 1 m2 subunits and the number of distinct macrophyte patches (ranging from individual fronds to large clumps consisting of multiple plants) within each subunit was counted. The mean of the four values were used as an individual replicate, and considered an estimator of seaweed patch density (n=6 per beach).

A 20 cm diameter PVC core was then used to collect invertebrates from a

randomly chosen seaweed patch within each quadrat (n=6 per beach). The core was inserted into the patch to a depth of approximately 20 cm in order to collect both the seaweed at the surface and the sediment underneath. The wrack sample was carefully examined within the core to collect invertebrates in 94

Gulf of St. Lawrence 4 7 ° N ' “

4 5 ° N - -

NW Atlantic

l65?W 6 1 °W

OSand dune •Sandstone cliff •T ill bluff

kilometers

laboratory. The sediments were then sieved on site through a 1 mm mesh

screen. The macrofauna retained on the screen were stored in ethanol until subsequent sorting and identification. An additional core sample was taken

approximately 1 m away from each quadrat (n=6 per beach) in order to

characterize invertebrates associated with bare sediments. In the laboratory,

macrophyte samples were carefully re-inspected for the presence of macrofauna that may have been missed in the field, and then weighed, dried in an oven at

60°C to a constant mass (48 h) and re-weighed to determine water content.

Macrofauna were identified and counted; the majority of the invertebrates

collected were amphipods belonging to Americorchestia megalophthalma and

Americorchestia longicornis (>95%). Due to the difficulty in differentiating

between the juveniles of these two species, these amphipods were quantified as

Americorchestia sp.

4.4.2 Field experiment: Stranded seaweed colonization

Zostera marina (hereafter eelgrass) and Fucus serratus (hereafter

rockweed) were the most common species of stranded macrophytes (see

results) and were therefore chosen to conduct a short-term wrack colonization experiment. Freshly detached eelgrass and rockweed were harvested from a

nearby shallow subtidal shoreline, spread outdoors on a uniform surface and left to dry in direct sunlight for one week to simulate the aging process that takes place in the upper intertidal. The day prior to the implementation of the 96 experiment, a second batch of fresh eelgrass and rockweed were harvested and stored overnight. On August 10, 2010 at Dalvay east beach and August 18, 2010 at Brackley beach (Fig. 4.1), bundles of approximately 0.031 m2 of fresh and dried eelgrass and rockweed were prepared and deployed to simulate natural

patches of stranded seaweeds consisting of fresh and dried eelgrass and fresh and dried rockweed. Four treatments were randomly assigned among the

patches. The bundles (patches) were spaced 2-3 m apart along the drift line of

both beaches. Metal hooks approximately 25 cm in length were pushed into the sediment to anchor these patches to the shore, and other naturally stranded

macrophytes were carefully removed to avoid interference with the experimental

patches. A total of five and seven replicates per treatment were deployed at

Dalvay east and Brackley, respectively.

After six days of deployment, 20 cm diameter cores were used to collect

patches and sediments underneath using the procedure described above. The

seaweed patches were placed in sealed plastic bags, taken to the laboratory, weighed, dried at 60°C in an oven and re-weighed to determine water content.

Due to the loss of some samples due to wave action, the number of replicates

per treatment at the end of the experiments ranged from 4-5 at Dalvay east and

3-7 at Brackley. At each site, 10 additional core samples were taken from bare

sediments located approximately 1 m away from the artificial patches, and

processed using the protocol described above. 97

4.4.3 Plant tissue nutrients and amphipod feeding rates

Macrophytes were collected from the driftline of two sandy beaches,

Dalvay east and Brackley, for processing to determine if there were differences in the nutritional quality of eelgrass and rockweed. Approximately 15 g samples of each species (n=3 per species per beach) were randomly collected to estimate the concentration of proteins, lipids and carbohydrates in their tissues. These samples were stored at -80°C, dried at 60°C until a constant mass (~16 h) and ground to a fine powder with a mortar and pestle in liquid nitrogen. Protein content was estimated using a method adapted from Wong and Cheung (2001).

The powdered material for each sample was mixed with a solution of 100 mM

Tris HCI pH 8.0 and 100 mM NaOH and agitated with a wrist-action shaker for two hours at 4°C before being centrifuged at 10,000xg and 4°C for 20 minutes to obtain the supernatant. Then 100 mM NaOH and 0.5% 2-mercaptoethanol was added to the pellet and the samples were agitated with a wrist action shaker for one hour at 4°C and again centrifuged at 10,000xg and 4°C for 20 minutes. The supernatants were combined and the protein was precipitated from the solution by adding an equal volume of acetone containing 0.07% DTT. The samples were then mixed by vortexing and incubated at -20°C overnight. Afterwards, the samples were centrifuged at 10,000xg and 4°C for 5 minutes, and the supernatant discarded. The pellet was dried under a nitrogen stream and the protein was then dissolved in a solution of 100 mM Tris pH 8.8, 100 mM NaCI and 0.2% SDS. The protein concentration was determined using the bicinchoninic acid method (BCA) from Pierce (BCA Protein Assay Kit) using bovine albumin serum as a standard and measuring absorbance at 562 nm. Lipid content was estimated from a separate sample of powdered material using an

ASE® 150 Accelerated Solvent Extractor. The lipids were extracted from the macrophyte powder with hexane 190 and the extracted solution was then concentrated using a rotary evaporator. The lipid content was then determined gravimetrically. Finally, carbohydrates were extracted from the macrophyte powder following Sadasivam and Manickam (1996) and the carbohydrate content was determined using D-(+)-glucose as a standard and measuring absorbance at

490 nm (Dubois et al., 1956).

Amphipod feeding rates were estimated in the laboratory following the methodology described by Duarte et al. (2010). Approximately 2-3 g of fresh macrophytes (eelgrass or rockweed, separately) were weighed and placed in two-compartment plastic containers (12 x 20 x 5 cm) with a modified top (the top had a large window covered with a 1 mm mesh to allow gas exchange while preventing amphipod escape). Each of these containers was then placed within larger 50 x 70 x 15 cm plastic containers with 2-3 cm of wet sand at the bottom to keep relatively constant humidity levels. At the beginning of the experiment, five adult-size amphipods, starved for 48 h to standardize hunger levels, were placed within one of the compartments of each plastic container and kept there for 24 h.

At the end of that period, the amphipods from each container were carefully removed and the macrophytes re-weighed to estimate amount of tissue consumed per amphipod and per day (n=10 per species). The macrophytes in 99 the second compartment were also weighed in order to calibrate and control for weight loss due to desiccation (Duarte et al., 2010).

4.4.4 Statistical analyses

Data from the survey characterizing wrack and macrofauna, seaweed percent cover, patch density and water content were compared among sites

(beaches) using one-way Analysis of Variance (ANOVA). Percent cover and patch density were square-root transformed in order to meet assumptions of normality and homoscedasticity. When significant differences were found, pairwise multiple comparisons were made using the Holm-Sidak method.

Comparisons of macrofauna abundance between wrack samples and bare sediments were done on fourth-root transformed data using a two-way ANOVA that assessed the influence of site (seven sandy beaches) and cover (wrack versus bare sediments). A significant site x cover interaction was found (p=0.007; i.e. these results cannot be properly interpreted because invertebrate abundance did not vary consistently between the two treatments across different sites), so t- tests were used to compare macrofauna abundance between macrophyte wrack and bare sediment on a site by site basis using log-io (x + 1) transformed data when necessary to meet assumptions of normality and homoscedasticity.

Macrofauna abundances from the field experiment were logio (x + 1) transformed and compared using a two-way ANOVA with species (eelgrass versus rockweed) and age (fresh versus aged) as factors. Additionally, abundances from wrack samples were compared with bare sediments using a 100 one-way ANOVA. Linear regression analyses between macrofaunal abundance and wrack patches’ wet mass, dry mass and water content were performed in

Sigmaplot 11.0 (build 11.2.0.5). Macrofauna abundances as well as physical variables were square-root transformed when necessary in order to meet assumptions of normality and homoscedasticity.

The concentrations of proteins, lipids and carbohydrates measured in eelgrass and rockweed tissues were compared using a two-way ANOVA with site

(Brackley versus Dalvay east) and species (eelgrass versus rockweedj as factors. Protein and lipid contents were logio transformed to meet normality and equal variance requirements. Differences in amphipod feeding rates upon eelgrass and rockweed were assessed using t-tests.

4.5 Results

4.5.1 Stranded Macrophyte Survey

The macrophyte wrack was composed primarily of eelgrass (Zostera marina) and a species of rockweed (Fucus serratus). Other species that were less frequently collected (<5%) included Irish moss (Chondrus crispus), sea lettuce (Ulva lactuca) and one or more species of the genus Laminaria. Mean wrack cover ranged between 0 and 23.8% and was slightly higher (one-way

ANOVA; p=0.062; Table 4.1) at the two beaches associated with sandstone cliffs

(Doyles Cove and Cape Turner; Fig. 4.2). Mean patch density ranged from 0.25 to 15.5 patches per m2 and mean water content ranged between 6.9 and 90.6%

(Fig. 4.2) and in both cases, the differences among sandy beaches were 101

Dependent Source of Comparison DF MS P variable Variation Wrack features Patch density Between Groups 6 5.189 0.001 Error 35 1.105

Patch cover Between Groups 6 2.223 0.062 Error 35 0.993

Water content Between Groups 6 3171.6 <0.001 Error 35 200.2

Wrack vs bare Density Brackley 1 sands Between Groups 1.808 0.003 Error 10 0.123

Density Ross 1 Lane Between Groups 1.622 0.026 Error 10 0.236

Density 1 Cavendish Between Groups 0.807 0.01 Error 10 0.081

Density Dalvay I Between Groups 1 0.172 0.191 Error 10 0.088

Density Dalvay II Between Groups 1 0.083 0.721 Error 10 0.617 102

Sandstone Sand Dunes Till Bluffs Cliffs

U) c a> ab TD ab ■ a a sz o -I—• r 3” ! P n (0 Q. ■■I i i ■I

(D > o o sz a o T (0 T CL a . I. I. ■I

i r BRA ROL CAV DA-I DA-II DOC CAT

significant (one-way ANOVA; p=0.001 and p<0.001 respectively; Table 4.1). In

both cases, the highest values were measured at beaches associated with

sandstone cliffs; Cape Turner and Doyles Cove.

The macrofauna was numerically dominated by the amphipod

Americorchestia sp. (97.6%). Only three other species, two amphipods Calliopius

laeviusculus (0.6%), Haustorius canadensis (1.5%) and one polychaete

Scolelepis squamata (0.3%), made up the remainder of invertebrate abundance.

In general, macrofauna abundances were higher in samples associated with stranded macrophyte wrack than bare sediments. At the three sandy beaches

associated with dunes, Brackley, Ross Lane and Cavendish, the differences

between wrack-covered and bare sediments were significant (t-test; p=0.003,

p=0.026 and p=0.010, respectively; Table 4.1, Fig. 4.3). At the two sandy

beaches associated with till bluffs, Dalvay west I and II, the differences between wrack and bare sediments were not significant (t-test; p=0.191 and p=0.721

respectively; Table 4.1, Fig. 4.3). In sandy beaches associated with sandstone

cliffs, macrofauna were collected exclusively from samples associated with wrack. Due to the absence of fauna in bare sediments, no statistical tests were applied for Doyles Cove and Cape Turner.

4.5.2 Wrack colonization experiments

At Dalvay east, the mean macrofauna abundance in fresh and dried

rockweed patches was 10.2 and 10.0 individuals per core, respectively. In comparison, mean abundance in fresh and dried eelgrass patches only reached 104

Sand dunes

Till Bliffs

Sandstone cliffs

Bare sediments

DA-I

CAV CAT

6.2 and 2.75 individuals per core. Differences among treatments were significant

between seaweed species (two-way ANOVA; p=0.012), but not between ages

(two-way ANOVA; p=0.784). There was no significant interaction between

species and age (two-way ANOVA; p=0.237; Table 4.2, Fig. 4.4) indicating that the abundance patterns varied consistently between species of different ages.

The majority of the macrofauna were talitrid amphipods, with A.

megalophthalma and A. longicornis making up 86% and 4% of the abundance,

respectively. Insects of the beetle family Histeridae accounted for 2.7%, while

beetles in the Hydrophilidae and Curlionidae, and Formicidae (ants) and Diptera

(flies) each had a lone representative (0.67% each). Combined, unidentified

insect larvae accounted for 4.7% of the total abundance. Control samples

collected from bare sediments had a mean abundance of 0.6 individuals per core

(Fig. 4.4).

Similar results were gathered from the experiment conducted at Brackley

beach. The mean macrofauna abundance in fresh and dried rockweed patches was 7.3 and 5.1 individuals per core respectively, compared to 2.5 and 1.8

individuals per core, respectively in fresh and dried eelgrass. Americorchestia

megalophthalma comprised 53.1% of the total abundance, followed by the beetle families Histeridae (35.8%), Hydrophilidae (9.9%) and Curculionidae (1.2%).

Control samples, collected from bare sediments had a mean abundance of 0.4

individuals per core (Fig. 4.4). There were significant differences in abundance

between macrophyte species (two-way ANOVA; p=0.013), but not between ages

(two-way ANOVA; p=0.245). There was no significant interaction between these 106

Dependent Source of Comparison DF MS P variable Variation Wrack colonization Density Dalvay Wrack species 1 0.651 0.012 Wrack state 1 0.00616 0.784 Species x state 1 0.121 0.237 Error 14 0.0791

Density Brackley Wrack species 1 0.591 0.013 Wrack state 1 0.112 0.245 Species x state 1 0.0278 0.556 Error 16 0.0766 107

Rockweed Eelgrass

Dalvay

a> o o TJ JZ

0 O c CD TJ Brackley C 3 jQ < C CD 0

Fresh Dried Fresh Dried Bare sediments

Figure 4.4. Mean abundance of macrofauna in fresh and dried rockweed and eelgrass patches placed on Dalvay east and Brackley beaches. Error bars represent one standard error. Identical letters indicate no significant differences among treatment. The mean abundance for the control samples (bare sediments) are also presented but were not included in the statistical analyses. 108 two factors (two-way ANOVA; p=0.556; Table 4.2, Fig. 4.4) indicating that the abundance patterns varied consistently between species of different ages.

Figure 4.5 shows the relationship between macrofauna abundance and wet seaweed mass, dry seaweed mass, and water content for all the experimental patches combined (across treatments). At Dalvay east, there were significant positive relationships between macrofauna abundance and each of the seaweed parameters measured: wet mass (p<0.001, 1^=0.556), dry mass

(p<0.001, 1^=0.550), and water content (p=0.029, 1^=0.265; Fig. 4.5). Similar relationships between macrofauna abundance and seaweed features were obtained at Brackley: wet mass (p<0.001,1^=0.506), dry mass (p=0.015

1^=0.231), and water content (p<0.001, ^=0.62; Fig. 4.5).

4.5.3 Nutritional Quality Analysis and amphipod feeding rates

Similar trends were observed in the indicators of nutritional quality investigated and amphipod feeding rates. The mean amount of proteins measured for the rockweed was 20.6% and 10.43% dry weight at Brackley and

Dalvay east, respectively. For eelgrass, the mean amount of proteins measured was 0.58% and 0.31% dry weight at Brackley and Dalvay east, respectively.

There were significant differences between species (two-way ANOVA; p<0.001) but not between sites (two-way ANOVA; p=0.089). There was no significant interaction between site and species (two-way ANOVA; p=0.574; Table 4.3, Fig.

4.6) indicating that the concentration of protein varied consistently between species at both sites. The mean amount of lipids measured for the rockweed was r Figure 4.5. Figure Sqrt(Abundance) (Individuals / Core) of the wrack and macrofauna abundance across experimentally experimentally across abundance macrofauna and wrack of the manipulated wrack patches. wrack manipulated 4 6 0 2 3 5 2 4 0 6 3 5 1 1

y = = y = .8 + 101x 0 .1 0 + 1.787 = y 029 2 .0 0 = p <.0 as ^ p<0.001 2= 265 • ‘ • 5 6 .2 0 r2= r2 = 679 0.0296X + 9 7 .6 0 = y p<0.001 • = = 0 0 0 0 0 120 100 80 60 40 20 Results of the regression analyses between physical characteristics characteristics physical between analyses regression of the Results tm 662 + 0.0341X + 2 6 .6 0 550 5 .5 0 556 5 .5 0 0 0 0 80 60 40 20 • • 1 1 20 15 10 5 W ater content (g) content ater W ^ • la East alvav D tmas (g) ass m et W r mas (g) ass m Dry • —

• 100 140 50 0 0 0 0 0 120 100 80 60 40 20 0 25 2 03 "2 ro w CO C ro w If 3 T c T3 ■C > O" TJ « 3 W C c ' 2 — ! 4 0 2 3 b 1 0 20 40 60 80 100 120 140 160 180 200 180 160 140 120 100 80 60 40 20 0 \y * " • • —**" •• y = = y 015 1 .0 0 = p r2 p<0.001 0 2 .6 0 r2 = 0. + . 6X 36 5 0.0 + 8 0 .7 0 = y p<0.001 2= 506 0 .5 0 r2 = 1. + 0.0992X + 9 4 .8 1 = •• = = 5 7 9 8 7 6 5 4 • .3 +0. x 6 5 .2 0 + 0.231 • —— • • 286 8 .2 0 r( r s (g)) ass m Dry qrt( S _ W ater content (g) content ater W -— - -- tmas (g) ass m et W - • •

Brackley - ---

, —

—■ — •

10 109 110

Table 4.3. Results of two-way ANOVAs comparing indicators of nutritional value in stranded seaweeds. Site and wrack species refer to location (Dalvay east vs Brackley) and macrophyte species (rockweed vs eelgrass), respectively. The results of a t-test comparing amphipod feeding rates upon the same wrack species is also presented. DF: degrees of freedom, MS: Mean Squares. For simplicity, Sum of Squares and F-values have been omitted.

Dependent Source of Comparison DF MS P variable Variation Rockweed vs Protein Site 1 0.283 0.089 eelgrass Wrack species 1 6.778 <0.001 Site x species 1 0.0259 0.574 Error 8 0.0754

Lipids Site 1 0.0698 0.124 Wrack species 1 2.029 <0.001 Site x species 1 0.0116 0.504 Error 8 0.0236

Carbohydrates Site 1 1.69 0.538 Wrack species 1 317.7 <0.001 Site x species 1 2.566 0.451 Error 8 4.088

Rockweed vs Feeding rates 1 eelgrass Wrack species 0.00327 0.035 Error 18 0.00063 Ill

25 Rockweed

£ 20 Eelgrass ai P 15

5 0 i

4 -

1 -

Brackley Dalvay

Figure 4.6. Mean percentage of dry weight for proteins, lipids and carbohydrates present in the tissues of rockweeds and eelgrass from samples collected in Dalvay east and Brackely beach. Identical letters indicate no significant differences among treatments. Error bars represent one standard error. 112

3.03% and 3.77% dry weight at Brackley and Dalvay east respectively, compared to only 0.44% and 0.66% dry weight for eelgrass at Brackley and Dalvay east, respectively. There were significant differences between species (two-way

ANOVA; p<0.001) but not between sites (two-way ANOVA; p=0.124). There was no significant interaction between site and species (two-way ANOVA; p=0.504;

Table 4.3, Fig. 4.6) indicating that the concentration of lipids varied consistently between species at both sites. The mean amount of carbohydrates measured for the rockweed was 15.7% and 17.4% dry weight at Brackley and Dalvay east respectively compared to 6.31% and 6.14% dry weight at Brackley and Dalvay east, respectively. There were significant differences between species (two-way

ANOVA; p<0.001) but not between sites (two-way ANOVA; p=0.538). There was no significant interaction between site and species (two-way ANOVA; p=0.451;

Table 4.3, Fig. 4.6) indicating that the concentration of carbohydrates varied consistently between species at both sites. Amphipod feeding rates mirrored the nutritional patterns observed for the macrophyte species: Amphipods consumed on average 13.39 mg rockweed/amphipod/day, and 8.27 mg eelgrass/amphipod/ day. There was a significant difference in feeding rates between macrophytes (t- test; p=0.035; Table 4.3, Fig. 4.7).

4.6. Discussion

4.6.1 Macrophyte survey and spatial variation

The re-suspension and re-deposition of wrack is a typical feature of dynamic systems like sandy beaches (Kirkman and Kendrick, 1997; Ochieng and Figure 4.7. Mean feeding rates by amphipods in laboratory conditions collected collected conditions laboratory in amphipods by rates Meanfeeding 4.7. Figure differences among treatments. Error bars represent one standard error. standard one represent bars Error treatments. among differences at Dalvay east and Brackely beach. Identical letters indicate no significant significant no indicate letters Identical beach. Brackely and east Dalvay at Feeding Rate CD CD 20 oked Eelgrass Rockweed 113 Erftemeijer, 1999). The input of wrack is highly variable and depends on factors such as tides and wave exposure (Orr et al., 2005; Ince et al., 2007), wind

(Colombini and Chelazzi, 2003), storms uprooting or breaking algal holdfasts

(Griffiths and Stenton-Dozey, 1981; McLachlan and Brown, 2006; Milligan and

DeWreede, 2000; Tolley and Christian, 1999), erosion levels (Lastra et al., 2008), and even beach substratum characteristics (Orr et al., 2005). Likely, the same

processes operate on the north shore of Prince Edward Island. In this system, spatial differences in wave exposure and shoreline erosion are likely to create differences in the amount of stranded seaweed that is being retained above the

intertidal area. A parallel study found that Doyles Cove and Cape Turner, both sites associated with sandstone cliffs, were considerably less exposed to erosion than beaches associated with sand dunes and till bluffs (Chapter 3, this thesis), and these sites had the highest amounts of wrack. Lower erosion and sand abrasion slow down decomposition and increase wrack residency time

(Colombini and Chelazzi, 2003), and may explain the relatively high density, cover and water content measured in the wrack of Doyles Cove and Cape

Turner.

Surprisingly, however, the invertebrates did not show the same pattern among beach types as the quantity and cover of wrack. There was considerable variation in the level of utilization of the wrack by the macrofauna. Similar to studies elsewhere (e.g. Behbehani and Croker, 1982; Dugan et al., 2003; Ince et al., 2007; Jaramillo et al., 2006; Rodil et al., 2008; Stenton-Dozey and Griffiths,

1983), the number of invertebrates colonizing wrack on dune-associated sandy beaches was consistently and significantly greater than samples from bare

sediments. Interestingly, this was not the case in sandy beaches associated with till bluffs, which are fairly similar in terms of physical features and macrofaunal

communities (Chapter 3, this thesis). Therefore the pattern of enhanced

communities underneath wrack patches is not as general as the published

literature suggests. At Doyles Cove and Cape Turner, two sites associated with

sandstone cliffs experiencing low rates of erosion (Chapter 3, this thesis),

invertebrates were scarce in bare sand and restricted to sediments associated with wrack. Although statistics could not be applied, this further demonstrates the

importance of wrack to sandy beach communities. Since communities

associated with these sites are less diverse and abundant than sites experiencing higher rates of erosion (Chapter 3, this thesis), local availability of

invertebrates for colonization of wrack may be as important as physical variables to explain spatial differences in wrack utilization.

As a consequence of harboring increased macrofaunal abundances, wrack is also important for vertebrate predators. Dugan et al. (2003) found the mean abundance of two species of shorebirds, the Black-bellied Plover (Pluvialis squatarola) and the Western Snowy Plover (Charadrius alexandrinus nivosus) were positively correlated with stranding crop of macrophyte wrack and the abundance of wrack-associated macrofauna. In the Atlantic Maritimes, it has been demonstrated that an endangered species, Piping Plover (Charadrius melodus), exploit wrack stranded on sandy beaches (Majka and Shaffer, 2008).

These authors found representatives of five families of herbivorous and 116 predaceous Coleoptera were consumed by Piping Plover, and other authors have reported amphipods and flies (Shaffer and Laporte, 1994) as well as polychaetes (Staine and Burger, 1994) in plover diets.

4.6.2 Wrack colonization experiments

Upper shore invertebrates rely on wrack as a food source or refuge against harsh physical conditions (Jaramillo et al., 2006; Olabarria et al., 2007), however, predicting the feeding preferences or traits that influence preferences of marine herbivores is difficult (Pennings et al., 2000). The results of the colonization experiments between the two most common species of stranded macrophytes show that rockweeds were colonized by the highest densities of invertebrates, regardless of age and location. Research elsewhere has reported that the age of wrack does affect colonization, showing strong associations between macrofauna and fresh wrack (Jaramillo et al., 2006; Marsden, 1991), while also reporting only weak associations with aged wrack. The lack of a relationship between macrofauna abundance with the age of wrack in this study could be due to the breakdown rates of the two dominant macrophyte species.

For example, Buchsbaum et al. (1991) found that detritus of a related rockweed,

Fucus vesiculosis, typically loses its mass at a much lower rate than other macrophytes. If F. serratus also exhibits slow breakdown rates, it could help explain why this species was consistently preferred by the macrofauna of this beach system since a high quality food resource would be available for a longer period. In contrast, the colonization of eelgrass was considerably more variable 117 between locations and wrack states. Eelgrass tissues are in general less nutritive than brown algae tissues (Inglis, 1989; this study) and decompose faster. Both aspects likely made eelgrass wrack considerably less valuable as a source of food for macrofauna.

Another factor affecting the colonization of wrack by invertebrates is the physical structure of the habitat. Stranded macrophytes can differ in shape and level of compactness (Colombini et al., 2000), and these differences can translate into distinct microclimates for the macrofauna (Marsden, 1991;

Olabarria et al., 2007). Due to its physical structure and humidity retention, patches of rockweed likely provide a more hospitable environment than eelgrass patches. This is consistent with the higher macrofaunal abundances detected in rockweed in comparison to eelgrass patches of about the same size, though not consistent with the pattern for lowest abundance on the sandstone cliff shorelines that had the highest water content. Desiccation of macrophyte tissues not only affects their water content, it also accelerates the release of cell contents by leaching. This release contributes to the decomposition of the plant and its loss of organic matter (Newell et al., 1986; Ochieng and Erftemeijer, 1999; Rodil et al., 2008), ultimately altering the nutritive value of the wrack. Wrack patch size and water retention are closely related, and given their importance (Olabarria et al., 2007), a series of regressions explored the relationships between these variables and macrofaunal abundance. In spite the rather narrow range of variation in the wrack properties, this study found significant positive relationships between macrofaunal abundances and patch’s water content, dry and wet 118 weight. These results suggest that physical features do play a role in the utilization of wrack by the macrofauna (Inglis, 1989), though factors such as availability of colonizing invertebrates can also be a factor. Virtually no insects were found in the survey of naturally stranded wrack at the most recent high tide levels. However, in the colonization of artificially stranded wrack patches at

Dalvay east and Brackley, insects composed 10 and 47% of the total macrofauna respectively. This suggests that naturally stranded macrophytes on the north shore of PEI do not have long enough residence times for the development of

Diptera larvae which are consumed by predaceous Coleoptera (Colombini and

Chelazzi, 2003), and to dry to a level suitable for herbivorous Coleoptera

(Colombini et al., 2000). However, this is likely not the case for wrack stranded further up the shore during the highest high tides.

4.6.3 Nutritional Quality and amphipod feeding rates

This study also explored whether the differences in colonization rates between rockweed and eelgrass patches may have been related to their nutritive values. Rockweed tissues exhibited significantly greater quantities of proteins, lipids and carbohydrates than eelgrass tissues. Such strong differences provide evidence to suggest that colonization rates may be driven primarily (but not exclusively) by nutritional differences between these two macrophytes.

Preference for rockweed has been widely reported, and to our knowledge, only one study so far (Pennings et al., 2000) has found a complete lack of preference for species of Fucus sp. based on a study of two fairly unrelated upper level 119

invertebrates, the amphipod Traskorchestia traskiana and the isopod Ligia pallasii. All the other existing evidence is consistent with the results of this study and indicates preferential use of brown algae, including Fucus sp. by talitrid amphipods. For example, Adin and Riera (2003) found that rockweeds of the genus Fucus (primarily F. serratus) were preferentially used as a food source by

Talitrus saltator, while the use of eelgrass was negligible or null. Similarly, Lastra et al. (2008) found that brown macroalgae of the genera Macrocystis and

Saccorhiza were heavily consumed by amphipods of the genera Megalorchestia

and Talitrus, respectively. Other macrophytes offered to these invertebrates,

including a seagrass of the genus Phyllospadix, were barely consumed (Lastra et

al., 2008).

Optimal foraging theory suggests that, in general, higher quality foods

enhance fitness and should be selectively eaten when available (Cruz-Rivera

and Hay, 2000; Stephens and Krebs, 1986; Wakefield and Murray, 1998). This

appears to be the case for the supralittoral macrofauna on the north shore of PEI.

The results of an experiment comparing feeding rates on standard amounts of

rockweed and eelgrass were also consistent with the nutritional value of their

tissues: amphipods consumed significantly more (>50%) rockweed than eelgrass

tissues. Although all consumers must choose among prey of different nutritional

value, these choices are particularly critical for herbivores and detritivores: they

rely on food sources that are critically low in protein content compared to what they require to produce animal biomass (Cruz-Rivera and Hay, 2000; Mattson,

1980). Understanding the relationship between nutrition and the feeding 120 preferences of marine herbivores can be challenging (Pennings et al., 2000) since the nutritive value of macrophytes is linked to a wide range of factors,

including but not limited to, seaweed’s level of decomposition, blade toughness, and palatability (Pennings and Paul, 1992; Pennings et al., 1998). Although this study did not address preference directly; focusing on measurements of consumption levels (Duarte et al., 2010), and did not address potential differences in nutritional quality among the structures within a plant (Duarte et al.,

2011), the differences in nutrition and feeding rates between rockweed and eelgrass provide a convincing explanation for the differences in colonization rates observed in the field. However, understanding the contribution of food in the context of among-site spatial variation, and its synergy with physical variability

requires further exploratory and experimental studies.

4.7 Acknowledgements

Thanks to Christina Pater, Megan Tesch, Veronique Dufour, Tyler Wheeler and

Cassandra Mellish for their assistance in the field, Dr. Bourlaye Fofana, Dr.

Kaushik Ghose, David Main and Guru Selvaraj for their assistance in determining

nutritional values, and Kyle Knysh for his assistance during invertebrate

identification. I would also like to thank Dr. Pedro Quijon, Dr. Donna Giberson and Dr. Darren Bardati for reviewing this chapter. Personnel of Parks Canada granted access and collaborated during site selection and preliminary sampling

in the PEI National Park. This research was supported by a grant from 121

Environment Canada through UPEI’s Climate Change Research Program.

Additional support came from a NSERC Discovery grant to P.A. Quijon.

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SUMMARY OF RESULTS AND FUTURE RESEARCH 127

Sandy beach macrofauna play an important role in coastal food webs.

Primary consumers including suspension feeders utilize phytoplankton and associated particulate organic matter, and herbivores consume drift macrophytes and other stranded material. Secondary consumers such as crabs and some beetles prey upon consumers of both types of primary consumers, and eventually fall prey to vertebrate predators such as shorebirds and fish (Dugan et al., 2003). Changes in the availability and input of phytoplankton or macrophyte wrack could shift energy flow to consumers and therefore prey availability to higher trophic levels (Dugan et al., 2003).

5.1. Spatial variation and coastal erosion

On oceanic sandy beaches, the diversity and abundance of macrofauna changes predictably with the variation in beach morphodynamics, typically increasing in numbers and diversity from reflective to dissipative states (de la

Huzand Lastra, 2008; Lercari and Defeo, 2006; McLachlan, 1990; McLachlan and Dorvlo, 2005; McLachlan et al., 1981). The first part of this thesis shows that this is not the case for the study area. Surveys of the intertidal zone of 14 sandy beaches yielded 7,961 individuals belonging to 13 different species, but their diversity and abundance did not reflect a reflective-dissipative pattern of variation: No significant regressions were found between biological descriptors and the physical characteristics frequently used to describe the physical conditions on sandy beaches such as slope and grain size (McLachlan and 128

Dorvlo, 2005), though the beaches in this study did not cover the full range of beach types.

However, the macrofauna communities did change spatially among shoreline types; beaches associated with sandstone cliffs exhibited communities consisting of the talitrid amphipod Platorchestia platensis and relatively low densities of Scolelepis squamata. In contrast, beaches associated with sand dunes and till bluffs exhibited communities consisting of the talitrid

Americorchestia megalophthalma or the haustoriid amphipod Haustorius canadensis, and much higher densities of Scolelepis squamata. These differences seemed related, among other factors, to the distinctive levels of coastal erosion experienced by each of these shoreline types. Significant positive correlations were found between the rate of coastal erosion and macrofauna species richness and abundance. The first part of this thesis concludes that the rate of erosion is indicative of exposure to wave action and therefore food availability for a fauna composed primarily of suspension.-feeding organisms.

Prince Edward Island (PEI) is embedded within the Gulf of St. Lawrence estuary system, and although the system is exposed to wave generating fetches of hundreds of kilometers (Shaw et al., 1998), it does not necessarily behave like oceanic sandy beaches do. Unfortunately, relatively little research has been conducted on these habitats in the Canadian Maritimes so it is impossible to predict if other sandy beaches associated with large estuarine systems will follow the same patterns (e.g. Lercari and Defeo, 2006). To the author’s knowledge, the 129

present study represents the first known survey of the sandy beach macrofauna

communities on the north shore of PEI and in the Maritimes region, providing a

baseline reference for future studies.

With the exception of erosion levels, it is still unclear what factors structure

sandy beach communities on PEI and elsewhere in the region. The precise role

of shoreline type, for example, is both unknown and intriguing. Shoreline type is

generally not considered an important component in sandy beach studies, so it is

rarely reported. The interpretation offered in this thesis links shoreline types and

erosion levels with food availability for suspension feeders. In the absence of

clear relationships between macrofauna and the other physical variables studied

(grain size, slope and the BDI), more studies at other sandy beaches with more

diverse communities (dominated or not by suspension feeders) will be very

useful. These studies will clarify whether erosion and food availability are the

main structural factors, as suggested here, or whether there are other causal factors that were not accounted for.

5.2. Spatial variation and allochthonous wrack input

If erosion levels and food availability for suspension feeders play a role in the structure of intertidal communities, they are unlikely to be relevant for

supralittoral macrofaunal organisms. The second part of this thesis shows that the differences between number of organisms associated with wrack and bare sediments were prominent in sandy beaches associated with sand dunes, but 130 irrelevant for similar sandy beaches associate with till bluffs. The scarce literature available suggests that supralittoral zones associated with dune formations represent a more gradual transition from terrestrial to marine systems, allowing for migration and intermixing of fauna associated with more terrestrial habitats

(particularly insects; McLachlan and Brown, 2006). In contrast, supralittoral zones associated with till bluffs and sandstone cliffs represent an abrupt change between terrestrial and marine systems, with little potential for immigration of terrestrial organisms.

Sandy beaches around the world are devoid of attached plants (Jaramillo et al., 2006), so the input and accumulation of wrack at or behind the high tide level is expected to play a more substantive role than erosion or other physical variables for supralittoral organisms living there. Seven sandy beaches associated with the three predominant shoreline types previously described were surveyed and spatial differences recorded. Wrack stranded on beaches associated with sandstone cliffs seemed to accumulate in larger volumes.

However, at beaches associated with dunes, the macrofauna showed a more clear reliance on sediments associated with stranded macrophytes.

Rockweeds and eelgrasses are common macrophytes of the waters of the

North Atlantic (e.g. Adin and Riera, 2003; Behbehani and Croker, 1982;

Buchsbaum et al., 1991; Robertson and Mann, 1980). Not surprisingly, the two most abundant species of macrophytes making up the wrack on the north shore of PEI during this study were rockweed (Fucus serratus) and eelgrass (Zostera 131 marina). Unfortunately, the lack of information from similar surveys in other areas of the region makes it impossible to determine if these species are the dominant component of the wrack at larger spatial scales. The results of this study also indicate that these macrophytes were not utilized equally by the macrofauna.

Experimental manipulation of wrack patches indicated that macrofaunal organisms were associated preferentially with rockweed, regardless of whether the patches were fresh or dried/aged. Significant correlations were found between macrofauna abundance and the main physical features of these patches. Further evidence on the nutritional value of the two wrack species, revealed that the nutritive value of their tissues may explain the differences in rates of colonization. This was subsequently supported by the significantly higher consumption rates of this species’ tissues by talitrid amphipods in laboratory feeding trials.

5.3. Future Research

Sandy beaches harbour distinct macrofauna communities that are not found in any other habitat. It is clear that shoreline type plays a role in the structuring of macrofauna communities in sandy beaches on the north shore of

PEI, but not necessarily in a clear and predictable way. Future research efforts should take advantage of the baseline information provided in this thesis but should also be well aware of its limitations in scope and depth. For understanding large-scale patterns, intensive long-term sampling in a few areas would be meaningless unless it is complemented with snapshot surveys covering a wide range of conditions (McLachlan and Dorvlo, 2005; Figs.

3.1, 4.1). Snapshot surveys were the methodology adopted for this study: a

number of sites with varying degrees of erosion and shoreline types were sampled. It is well known that sandy beach macrofauna exhibit seasonality; although the sampling conducted here was meant to be representative of summer conditions, it is recommended that future studies on PEI sandy beaches focus on temporal scales. Since the beaches on the north shore of PEI undergo seasonal erosion-accretion cycles, it would be interesting to investigate the short and long-term responses of macrofauna communities to winter erosion.

The wrack characteristics reported in this study are representative of the summer standing stock at the time of sampling, and are not necessarily representative of long-term trends. It is recommended that seasonal inputs of macrophyte wrack be estimated and investigated, preferably on beaches associated with sand dunes. These sandy beaches harboured the highest numbers of wrack-associated macrofauna, and so are the sites where the macrofauna makes a more intensive use of these ephemeral resources.

Additionally, although rockweed and eelgrass are the most common components of the wrack, other species present in lower frequency (e.g. Irish moss, Chondrus crispus; sea lettuce, Ulva lactuca; Laminaria sp.), should be further studied as potential food and refuge sources. Furthermore, it is recommended that future studies investigate the feeding rates of adult and juvenile species of amphipods 133

on these macrophytes in an effort to determine if the age of these dominant

supralittoral fauna affects their rates of macrophyte consumption.

5.4. References

Behbehani, M.I., Croker, R.A., 1982. Ecology of beach wrack in northern New England with special reference to Orchestia platensis. Estuar. Coast. Shelf Sci. 15, 611-620.

Buchsbaum, R., Valiela, I., Swain, T., Dzierzeski, M., Allen, S., 1991. Available and refractory nitrogen in detritus of coastal vascular plants and macroalgae. Mar. Ecol. Prog. Ser. 72, 131-143. de la Huz, R., Lastra, M., 2008. Effects of morphodynamic state on macrofauna community of exposed sandy beaches on Galician coast (NW Spain). Mar. Ecol. 29, 150-159.

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.

Lercari, D., Defeo, O., 2006. Large-scale diversity and abundance trends in sandy beach macrofauna along full gradients of salinity and morphodynamics. Estuar. Coast. Shelf Sci. 68, 27-35.

McLachlan, A., Brown, A.C., 2006. The Ecology of Sandy Shores, second ed. Academic Press, New York. 134

McLachlan, A., 1990. Dissipative beaches and macrofauna communities on exposed intertidal sands. J. Coast. Res. 6, 57-71.

McLachlan, A., Dorvlo, A., 2005. Global patterns in sandy beach macrobenthic communities. J. Coast. Res. 21, 674-687.

McLachlan, A., Wooldridge, T., Dye, A.H., 1981. The ecology of sandy beaches in southern Africa. S. Afr. J. Zool. 16, 219-231.

Robertson, A.I., Mann, K.H., 1980. The role of isopods and amphipods in the initial fragmentation of eelgrass detritus in Nova Scotia, Canada. Mar. Biol. 59, 63-69.

Shaw, J., Taylor, R.B., Solomon, S., Christian, H.A., Forbes, D.L., 1998b. Potential impacts of global sea-level rise on Canadian coasts. Can. Geogr. 42, 365-379.