SANDY BEACH ECOLOGY - A REVIEW

ANTON McLACHLAN (Zoology Department, University of port Elizabeth, P.O. Box 1600, Port Elizabeth 6000, South Africa)

1. INTRODUCTION open to the sea. This does not include Sandy beaches dominate most temperate sand flats in estuaries or closed and tropical coastlines where they lagoons but only open marine beaches. represent both important recreational Nevertheless, such beaches may differ assets and buffer zones against the considerably in their degree of exposure 'ea. In some areas they are very to wave action. On a 20 point exposure roductive and are exploited scale, developed for studies on commercially. However, they have been intertidal fauna (McLachlan, 1980a), regarded as marine deserts by many beaches scoring 11 to 18 are considered biologists and were largely neglected exposed and are characterised by until Remane ‘(1933) began studies on the continuous, often heavy, wave action, coasts of Germany. The work of Pearse the absence of silt, a mobile fauna and et al (1S42) was also pioneering and a high degree of oxygenation of the sand. represented the first qualitative Sheltered beaches (scores 5-10) have attempt to evaluate a whole beach less, often intermittent wave action, system. Since then sandy beach ecology fauna which may construct semi-permanent has advanced considerably, though it has burrows and reduced layers present and always lagged behind other aspects of sometimes close to the surface. coastal marine ecology in the attention Beaches scoring below 5 points on this it has enjoyed. During this period rating scale are not open ocean beaches biological research on beaches has and fall outside the scope of this spread from early taxonomic and review. 'Wright, Short (1S82) have ;alitative studies through quantitative developed a six point scale classifying clogy and physiology of important beaches from dissipative to reflective species towards a more holistic systems extremes based on morphodynamics. approach today. As the sandy beach occupies a dynamic The term sandy beach has been loosely interface position between sea and land, used in the literature to cover a range its boundaries with the adjacent of environments from high energy open terrestrial and marine environments are ocean beaches to extremely sheltered not always clear and the functional estuarine sand flats. For the purposes extent of the beach itself has seldom of this review a sandy beach is been discussed. The sand beach is considered to be a sandy littoral area considered here to be part of a system 322

comprising i) the sand body from the been written on sediments, wave action highest drift line near the dune/beach and relationships between sedimentary boundary out to beyond the break point parameters, beach slope and wave action, of the waves and ii) the moving water considerably less attention has been envelope of the surf zone to the outer focused on the important processes limit of surf circulation cells where relating to water movement in the surf they exist. This dynamic environment, zone. The significance of surf which I call the beach/surf zone circulation cells, rip current systems ecosystem, is of great extent in both etc., has still to be realized in beach tropical and temperate areas. It does ecological studies. not include the dunes typical of many sandy coasts, although dune/beach Biological work to date has concentrated interactions are important. Its on the fauna of the intertidal sand body landward boundary is clearer than its and most other aspects of beach ecology, seaward boundary where, in exposed including the surf zone as a whole, have situations, surf circulation cells, been neglected. The intertidal sand driven by breaking waves, mix with body of open sandy beaches is inshore water. The basic topography and characterized by a mobile substratum and features of this system are illustrated the absence of attached plants. in Fig. 1. Normally the substratum provides two

DUNES BEACH NEARSHORE

STABLE DUNES BACK FORE INNER OUTER ACTIVE DUNES SHORE SHORE TURBULENT ZONE TURBULENT ZONE

^ SECONDARY w DU N ES PRIMARY DUNES

BERM SCARP OUTER LIMIT HIGHEST DRIFT LINE^ 1 INTERTIDAL SURF OF SURF ^ ZO N E ZONE BREAKER CIRCULATION CELLS :HIGH WATER LEVEL

LOW WATER LEVEL BAR TROUGH

FIGURE 1. Profile of a typical sandy beach environment, showing areas referred to in the text.

The physical features of this system habitats suitable for faunal will not be examined here. Besides population. These are i) the raacrofauna other papers in this volume, descript­ habitat consisting of the sand surface ions of physical features of beaches and upper layer of sediment and ii) the important to ecologists may be found in interstitial habitat consisting of the many publications, including Bascom porous system of the sand body. The (1S 6 4 ) , King (1972), Davies (1972 ) and former, particularly on exposed beaches, Inman, Brush (1973). Though much has is a uniform but dynamic and unstable, 323

essentially tv/o dimensional system. The environment. Thus although meiofauna- latter is a more stable and complex macrofauna interactions may occur habitat with clear vertical gradients (Hummon et al., 1976; Reise, 1979) and is essentially a three dimensional these are generally of negligible system (McLachlan, 1977a). It has great significance in terms of energy flow on vertical extent on exposed beaches or exposed sandy beaches. high energy 'windows' where strong hydrodynamic forces introduce oxygen The only review on sand beach ecology as deep into the sediment. Elsewhere its a whole is that of Hedgpeth (1957), base consists of reduced layers although some aspects of beach ecology (Fenchel, Riedl, 1S70). are covered by Eltringham (1971). Both these works are outdated and there is a The macrofauna of sandy beaches and the distinct need for a synthesis of meiofauna (and microfauna) of their information on sandy beaches. The aim interstices comprise two entirely of this review is to outline our separate faunal components with knowledge of the ecology of individual virtually no overlap or exchanges of components of sandy beach biotas and the energy. This is because the meiofauna structure and function of beach are extremely small interstitial forms ecosystems as a whole. It progresses while the macrofauna are several orders through the interstitial fauna and of magnitude larger (McIntyre, 1S 71 ; macrofauna of the sand body, McIntyre, Murison, 1973; McLachlan, phytoplankton, Zooplankton and fishes of 1977a). Schwinghamer (1981) disting­ the surf zone and birds of the beach and uished three biomass peaks in intertidal dune margin to functional aspects within sediments corresponding to bacteria, the framework of energy flow and interstitial meiofauna and macrofauna. nutrient cycling. As sediments become finer below 200 um mean grain size, large burrowing forms 2. THE INTERSTITIAL SYSTEM of meiofauna become increasingly The porous system between the sand important and tend to bridge the size grains generally averages about 40% of gap between macrofauna and meiofauna. the total sediment volume. Most This makes separation into two physical properties of this system are components less marked in finer directly determined by the sediment sediments and facilitates better energy properties which in turn are related to flow between these components. Energy the wave and current regime as well as flow between these components also the geological history of an area. increases because the meiofauna are Grain size, shape and sorting are most concentrated near the surface and important in fixing porosity and macrofauna deposi t feeders increase in permeability which influence drainage. abundance in finer sediments. In Drainage is critical in determining the coarser sediments such intermediate moisture content, oxygen and organic forms are absent, probably because they input and the depth of reduced layers. represent a size range selected against Permeability increases with coarser by the physical forces of the beach substrate and better sorting and 324

drainage also increases on steeper

beaches. The interactions between these SHELTERED BEACH EXPOSED BEACH factors are well documented and covered SAND SURFACE in several papers (Webb, 1958; Hulings, \ ZZK ' Gray, 1971; Crisp, Williams, 1971). «Saisis

The major process involving the interstitial system on open beaches is the filtration of sea water. This water is introduced into the sediment either by flushing by waves and tides in the intertidal (Riedl, 1971; Riedl, Machan,

1972; McLachlan, 1979a) or the pumping -400 0 -400 ÍGXfDATfON]_b-400 0 *400 'fOXIDATtONL , Eh(mV) . ■ , I STATES j En(mV> ; STATES effects of waves in the subtidal (Steel io. iOg] et al., 1970a; Riedl et al., 1S72). In exposed situations filtered volumes may □ Yellow layer » oxygenated sand £ G ray la y e r = RPD zone

average 5-10 m per metre strip of H Black layer = reduced sand intertidal beach per day and be several FIGURE 2. Schematic representation of times on very steep, coarse grained vertical chemical gradients in a beaches. In the subtidal surf zone off sheltered and an exposed beach. (After open beaches wave pumping may filter Fenchel, Riedl, 1970; McLachlan et al., 0.05-5.00m2 m-2^ -^. This flushing 1979a) or pumping concentrates dissolved and particulate organics in the sand. Under moisture content and surface temperature high energy conditions, however, the (Pollock, Hummon, 1971; McLachlan et input of oxygen and the high drainage al., 1977a) while in very sheltered rates maintain this system fully situations it can resu11 m sharp oxygenated and there are no steep changes in chemical gradients, for vertical gradients in oxygen and example pH changes coupled to oxidation states of sulphur or nitrogen temperature changes (Gnaiger et al., (Riedl, MacMahan, 1969; McLachlan et 1978). In sheltered beaches with al., 1979a). Permeability and flushing reduced layers three vertical zones generally decrease with increasing (Fig. 2) may be distinguished, namely shelter until drainage is so poor that clean (oxygenated) sand, a gray (or RPD) the sand is constantly saturated. transition zone and black (reduced) Vertical chemical gradients are then conditions (Fenchel, Riedl, 1970). steep and reduced layers occur close to Horizontal zones may also be distin­ the surface (Fig. 2). guished down the beach from the relatively constant conditions of the The interstitial system is subject to sublittoral to the backshore with large cyclic changes related to tidal and temperature and salinity fluctuations diurnal cycles and the seasons. In high (Salvat, 1964, 1967; Schmidt, 1970; energy beaches this mainly results in Mielke, 1976). On exposed beaches, fluctuations in the water table, pore because of its greater vertical extent 325

and better drainage, the interstitial system lends itself to subdivision into

strata. Pollock, Hummon (1971) CRANES BEACH, MASSACHUSETTS A TYPICAL EAST CAPE BEACH recognized five strata in a coarse ■DRV SAND STRATUM ZONE OF DRY SAND grained (Md = 660 um) Massachusetts MOIST SAND ZONE OF DRYING s

Table 1. Summary of stratification of exposed sandy beaches based on interstitial water content (Modified from Pollock, Hummon 1971; McLachlan, 1980). See also Fig.3.

Moisture Content & Water Degree of 2 one/St r atum Circulation Oxygenation Temperature

Zone of dry sand/ Low, loses capillary water High Highly variable Dry sand stratum

Zone of drying/ Low, loses capillary water High Variable Dry sand stratum

Zone of retention/ Loses gravitational v/ater but High Little variation Moist sand stratum retains capillary water

Zone of resurgence/ Gravitational water from zone Moderate Stable Water table stratum of retention drains through to low here during ebb tide

Zone of saturation/ Permanently saturated, little Low to Very stable Low oxygen stratum water circulation very lov; 326

Large numbers of microscopic organisms cells per gram dry sand and increase occupy the interstices: fungi, algae, with finer sediment and greater surface bacteria, protozoans and metazoans. area (Dale, 1974; Meyer-Reil et al., Amongst the animals, metazoans that pass 1978; Mazure, Branch, 1979). Khiyama, undamaged through a 1mm screen are Makemson (1973) recorded 362 bacterial considered meiofauna and the rest strains in beach sand, many associated microfauna. Individual dry weights are symbiotically with metazoans. Those on 10~^-10~®g for meiofauna, 10-^ sand grains made up 54-78% of the total 7 -lO^^g for protozoans and 10“^ numbers of 10-10 per gram of wet -10^g for bacteria (Fenchel, 1978 ; sand. Wicks (1974) demonstrated the Warwick, pers. comm.) Fungi in sandy presence of Azotobacte r in marine sand beaches are generally concentrated at beaches while Rheinheimer (1977) higher tide levels and have been little isolated 31 strains from beach sand, of studied (Upadhyay et al., 1978). A which the majority showed salinity flora of diatoms or flagellates only optima at 30-50°/oo and were gram develops in sheltered beaches and is negative rods that could decompose absent on very exposed beaches (Steel et proteins, carbohydrates and fats. al., 1970a; Brown, 1971a). This also Andrews et al., (1976) studied microbial appears to be more characteristic of development in a model sandy beach, temperate than tropical beaches (Munro recording greatest abundance near the et al., 1978). In sheltered sands the high and low tide marks. diatom flora may be locally important and, due to mixing by wave action, may Organic carbon and nitrogen in the sand occur to some depth in the sand (Steele, have been found to correlate with Baird, 1968; Mclntrye, 1977; Anderson, bacterial biomass and abundance (Dale, Meadows, 1978). Munro, Brock (1968) 1974; Anderson et al., 1981; Bolter et recorded numerous living bacteria and al., 1981) which can be up to four times diatoms attached to sand grains up to the biomass of the meiofauna 10cm below the sand surface and Round (Meyer-Reil, Faubel, 1980). Munro et (1979) described a diatom assemblage al. (1978) estimated microbial — ? living below the sand surface. Amspoker proauction at lSg'C.m for a temperate _ O (1977) described the intertidal beach and 72gC.m for a tropical distribution of epipsammic diatoms on a beach, the higher latter value due to Californian beach. Where sand is greater water percolation. Mazure, permanently saturated diatoms generally Branch (1979) estimated an average _ 2 occur closer to the surface. Pearse et bacterial biomass of 14.2gm dry al., (1942) recorded Chrysophyta, weight in the sands of Langebaan Chlorophyta, Pyrrophyta and Cyanophyta Lagoon. Dye (1979a) showed that on sandy beaches. disturbance caused greatly increased bacterial activity in beach sand. Bacteria are abundant and important in McLachlan et al., (1979a) recorded O beach sediments, mostly being attached bacterial numbers around 10 per gram to the sand grains (Meadows, Anderson, dry sand down to more than lm in the 1966 , 1 968). Numbers range lO^-lO"^ sediment of an exposed beach. Dye 327

(1980a) was able to show tidal 1977; Fenchel, 1978; Hartwig, 1982). fluctuations in oxygen uptake by beach Small protozoans have also been sand. Maximum uptake coincided with enumerated on exposed beaches in the maximum water percolation through the Eastern Cape (Dye, 1979b; McLachlan et sand and maximum fluctuation occurred at al., 1979a; Dye, 1981). Their numbers 1 3 higher tide levels. Desiccation of the ranged 10-10 per gram dry sand and sand caused a severe drop in oxygen they were found to more than lm depth in uptake or bacterial activity. Dye a well oxygenated beach. Their (1981) also attempted to partition total contribution to total benthic oxygen benthic oxygen uptake on exposed East consumption was significant, accounting Cape beaches and concluded that bacteria for 15-25% of interstitial oxygen uptake. were responsible for most of the oxygen consumption except where there was a Meiofauna have received considerable very rich macrofauna. Meyer-Reil et attention on sandy beaches and several al., (1980) estimated microbial turn­ reviews cover aspects of meiofauna over time of 100h with daily microbial ecology (Delamare-Deboutteville, 1960; carbon production of 43mg.m in Swedmark, 1964; Fenchel, Riedl, 1970; sheltered beaches in the Baltic. They Wieser, 1975; Giere, 1975; Fenchel, concluded that 50% of microphytobenthos 1978). primary production was fixed by micro­ organisms. Koop, Griffiths (1982) found Small metazoans occurring on sandy a high bacterial biomass on an exposed beaches may be either temporary beach receiving high kelp input on the meiofauna, i.e., larval forms of west coast of South Africa, bacteria macrofauna, or permanent meiofauna. As being found to 1.2 m in the sediment. we are mainly dealing with interstitial Koop et al., (1982a, b) estimated that meiofauna here, the temporary component bacteria were responsible for over 90% is generally not of importance on open of carbon utilization of these kelps. beaches. The dominant components of Annual turnover (P/B) of bacteria in sandy beach meiofauna are nematodes and this system was estimated to be 30 times harpacticoid copepods with several other (Koop, Griffiths, 1982; Stenton-Dozey, taxa of variable importance. These Griffiths, 1983). Despite this include turbellarians, oligochaetes, informât ion we still know nothing about ostracods, mystacocarids, gastrotichs, the ecology of individual species of halacarid mites, taraigrades, gnathosto- micro-organisms on sandy beaches. mulids, hydrozoans and bryozoans. There is a wel1 established relationship All groups of protozoans may be present between the relative proportions of in the interstitial system but ciliates nematodes and harpaticoids and grain and foraminiierans have been best size. Nematodes tend to dominate in studied as they are usually relatively finer sediments, harpacticoids in large and quite abundant, especially on coarser sediments and in sediments with sheltered beaches with fine sands mean grain size around 300-350 um they (Swedmark, 1964; Fenchel, Jansson, 1966 ; are about equally important (Gray, 1971; Panikkar, Rajan, 1970; Hartwig, Parker, McLachlan et al., 1981b; Raffaelli, 328

Mason, 1981; Hockin, 1982). Fricke, related to differing tolerances to Fleming (1983) have demonstrated reducing conditions (Fenchel, Riedl, experimentally the neamtode preference 1970). Vertical distribution is for finer sediments. generally shallower in the surf zone than on the beach but high numbers may In sands above 200 um the meiofauna is still occur 10-30 cm into the sediment usually entirely interstitial while (McLachlan et al., 1977b). Dean (1981) below 200 um burrowing forms become looked at the effects of wave action on increasingly important due to pore size meiofauna abundance. restrictions (Wieser, 1959). Inter­ stitial harpacticoids may occur down to Horizontal distribution may take the 160 um (McLachlan et al., 1977b; Moore, form of layers, horizontal zones, 1979a) while nematodes can pursue an bathymetrical steps and geographical interstitial mode of life down to regions (Fenchel, Riedl, 1970). 125-100 um (Wieser, 1959; McIntyre, Horizontal zones of meiofauna Murison, 1973; Fenchel, 1978). In distribution have been described from noncapillary sediments nematodes some beaches, particularly under dominate (Fenchel, 1978). As most open relatively sheltered conditions (Coull, sandy beaches have grain sizes in the 1970; Schmidt, 1972a, b; Harris, range 200-500 um, interstitial nematodes 1972a; Moore, 1979b) where the and harpacticoids are almost always meiofauna is close to the surface and dominant. McIntyre, Murison (197 3) the distribution tends to take on a more considered sands of 230 um to be optimum two-dimensional character (Fig. 4). for the development of interstitial fauna while Gray, Rieger (1971) Seasonality has been documented in suggested that meiofaunal diver sity several cases in temperate areas with increases as sands get finer. In South the meiofauna occur ring in lowe r Africa richest meiofauna occurs in sands abundance and moving deeper into the of 250-350 um (McLachlan et al., 1981b). sediment in winter (Renaud-Debyser, 1963; Harris, 1972b; Schmidt, 1972a, On a vertical basis meiofauna distri­ b, ; Hu lings, 1974 ; Mielke, 1976 ; bution is related to the degree of Faubel, 1976; Nodot, 1976; Feder, drainage and oxygenation of the sediment Paul, 1980). In warmer areas (see Fig. 3 and Table 1). Meiofauna seasonality is less clear (McLachlan, abundance drops off drastically in the 1977b) ana in sublittoral areas it may RPD and reduced layers (Fenchel, Riedl, be more complex (Emberton, 1981). 1970; McLachlan, 1978) and a deep Vertical migrations other than seasonal vertical distribution therefore only have been recorded as response to occurs on exposed beaches where reduced factors such as heavy rains (Bush, layers are absent (Renaud-Debyser, 1966), wave disturbance (Boaden, 1968), 1963; Fenchel, Riedl, 1970; McLachlan tidal factors (Rieger, Ott, 1971; et al., 1979a) (see also Fig. 2). Meineke, Westheide, 1979) and changes in Different species and taxa show well moisture and oxygen over the tidal cycle defined vertical distribution patterns (McLachlan et al., 1977a). 329

(a) SHERTALLAI BEACH, INDIA Arenopontia orientalis ALL Arenopontia acantha ^INTERSTITIAL FORMS g Psammopsyllus operculatus WATÊW.. 10 m TABLE (b) A TYPICAL MANX BEACH 3 EURYHALINE UPPER SHORE SPECIES (ALL INTERSTITIAL) J4WS EUL|TT0RAL SPECIES (1 EPIBENTHIC 2 interstitial) 6 SUBLITTORAL FRINGE SPECIES WATER (EPIBENTHIC) TABLE

SAND GETS FINER

FIGURE 4. Comparison of vertical and horizontal distribution patterns of harpacticola copepods in a well drained, exposed beach ( a ) and a sheltered beach ( b) where distribution patterns tend to be very three-dimensional and rather two- dimensional respectively. (After (a) Munro et al., 1978 and (b) Moore, 1979b). In all cases the copepods are concentrated above the low tide water table. On the sheltered beach interstitial fauna are mostly concentrated high on the shore where some drainage occurs. Nevertheless zonation in this case is still mostly across the shore and not vertically in the sediment.

seasonality are becoming clearer as a feeders, non-selective deposit feeders, result of ecophysiological studies on diatom feeders, carnivores and even responses, preferences and tolerances of filter feeders. Various studies have important meiofaunal species (Jansson, shown aggregation of meiofauna in 1967, 1966a; Wieser et al., 1974 ; response to specific bacterial strains Wieser, 1975; Hartwig et al., 1977; (Gray, Johnson, 1970) or where there are Wieser, Scheimer, 1977). high levels of organics generally or localized small scale concentrations A wide range of food items has been (Lee et al., 1977 ; McLachlan et al., recorded for meiofauna including lS77b; Moore, 1979a; Hogue, Miller, diatoms, bacteria, protozoa, detritus, 19 81’) or concentrations of prey other meiofauna and dissolved organics (Fenchel, 1978). Feeding rates have (Jansson, 1968b; McIntyre, 1969 ; been estimated directly for a copepod Fenchel, 1978; Giere, 1975, 1982). (Rieper, 1978). There have also been Feeding categories include bacterial studies on growth, production and 330

population dynamics of important species supply adequate dissolved and (Pawlak, 19 6 S ; Lasker et al., 1970 ; particulate organic food. Meiofauna are Hall, Hessler, 1971; McLachlan 1977c; generally considered to subsist on the Feller, 1980). Most species have year microfauna which in turn are largely round reproduction with generation times fuelled by dissolved and particulate ranging 1-3 months (McIntyre, 1969 ; organics flushed into the sand (McIntyre Lasker et al., 1970; Giere, 1975; et al., 1970). Measurements of benthic Bartsch, Schmidt, 1979). metabolism have attempted to partition oxygen uptake between these different Over the past decade ecological studies components of the interstitial fauna on sandy beach meiofauna have advanced (Munro et al., 1978; Dye, 1980a; 1981). from the more general surveys of the Rates of mineralisation of organics by sixties. More attention has been paid the interstitial system have also been to the complex of factors composing the measured in experimental sand columns in interstitial system and results have an attempt to understand these processes been better analysed statistically better and estimate nutrient cycling (Gray, Rieger, 1971; Hulings, 1971; (McIntyre et al., 1970; Boucher, Hulings, Gray, 1976; McLachlan, 1978; Chamroux, 1976; McLachlan et al., 1981c). Hogue, Miller, 1981). The basic pattern of meiofaunal response to different Vernberg, Coull (1974) estimated the sediment types is well documented and ratio of metabolic activities of responses to chemical features of the ciliates to meiofauna to macrofauna as interstitial system are clearer. More 1:0.5:2.1 for a sandy sublittoral work is needed on biotic interactions sediment and 1:0.54:0.04 for an exposed including competition, feeding and beach. Dye (1981) partitioned benthic predation. meta bol i siri between microfauna, meiofauna and macrofauna on two exposed beaches in With regard to energetics and benthic the ratios 1:0.23:0.04 and 1:0.27:1.85, metabolism the interstitial system has the latter beach having an exceptionally still largely been regarded as a black rich macrofauna. McLachlan et al., box ana few authors have progressed (1981a) partitioned benthic metabolism beyond the estimation of abundance or on East Cape beaches amongst the biomass. On exposed beaches, and in interstitial fauna and macrofauna as most other sediments, meiofaunal numbers 1:0.4. On a west Cape beach receiving a fluctuate within an order of magnitude high kelp input, biomass ratios of of 106m-2 and dry biomass values macrofauna: meiofauna: bacteria were _ O range 20-4400 mg. m . Some figures 3.5:1:1.5 (Griffiths et al., 1983) while are compared in Table 2. these ratios for productivity were 1:1: 4. 7 . 'Clearly biomass tends to be higher in the intertidal on exposed beaches It may be concluded that our knowledge because the great vertical extent of of the interstitial system of open sandy these systems provides greatest habitat beaches has advanced considerably over availability and high percolation rates the past two uecades. We have a good 331

. e 2. Abundance and dry biomass values for meiofauna recorded from marine sands,

Source Locality Abundance Biomass

Wieser (19 60) Buzzards Bay sublittoral 100 - 6 00 mg.m-2 106.nT2

Coull (1970) Bermuda sublittoral 33 - 259 mg.m-2 106.m-2

McIntyre, Murison (1973) South Africa exposed 279 - 1 092 mg.m-2 intert idai 106.m-2

__ O McLachlan (19 77a, b) South Africa exposed 20 - 3 3 6 0 mg.m ^ intertidal 10G.nT2

McLachlan et al., (1977b) South Africa sublittoral 350 - 1 0 4 5 mg.m-z 10 6.m-2

Fenchel (1378) sublittoral sand 50 - 1 700 mg.m-2 105-106.nr2

McLachlan et al., (1981b) South Africa exposed 400 - 4 000 mg.m-2 intertidal IO6, nr2

Stenoon-Dozey, Griffiths South Africa exposed 1 000 -- 4 4 0 00 mg.m-2 (1983) intertidal 6 7-7 1 0 - 1 0 '.m z

general idea of the distribution patterns of meiofauna and most other patterns of interstitial fauna in interstitial processes in intertidal relation to many features of inter­ sands (e.g. Figs. 3 and 4a). This water stitial climate. However, in this flow is the superparameter controlling respect the excellent work of Riedl and interstitial climate and the distri­ co-workers in describing water flow bution of interstitial fauna in beach through beach sand has not received the sands. Both meiofauna and bacteria attention it deserves. The patterns of therefore tend to concentrate in 'the water input, percolation and pulsing moist sand at and above MTL and below disturbance described by Riedl, Machan the sand surface where there is high (1972) (Fig. 5) add a considerable water input, percolation and aeration, degree of comprehension to distribution minimum stagnation and pulsing currents 332

are not too severe. Under sheltered all organic materials it receives, conditions the aerated strata become whether these be dissolved or much flatter, the interstitial fauna particulate. In this process bacteria concentrates close to the sand surface are most important, with meiofauna and the overall dimensions of the system mostly at the top of the interstitial take on a more two dimensional nature. food chain. There is little exchange with higher trophic levels, especially

MAXIMUM REACH OF STRONG -MHWS on exposed beaches. By the removal and INPUT CURRENTS mineralisation of organic materials and -MTL the release of inorganic nutrients the micro- and meiofauna are responsible for -MLWS the 'purification' of large volumes of sea water flushed through the . -M H W S MAXIMUM AERATION AND interstitial system. INPUT CURRENTS -MTL 3. THE MACROFAUNA While not usually asquantitatively -MLWS important in energy flow as the interstitial fauna, the macrofauna of -MHWS MAXIMUM INPUT AND MINIMUM sandy beaches are often abundant and, in PULSING DISTURBANCE -MTL some cases, attain exceptionally high densities. Their main feature on open -MLWS beaches is the high degree of mobility displayed by all species. These animals -MHWS may vary from a few mm in length to 10cm MAXIMUM PERCOLATION AND MINIMUM PULSING and consequently a variety of methods DISTURBANCE -MTL have been used to sample them. Generally sand is passed through a 0.5mm or 1mm -MLWS screen, though in areas of coarse sand, screens of 2mm or even 4mm have been . -MHWS I MAXIMUM INPUT used. Thus not all workers have sampled MAXIMUM AERATION AND MINIMUM DISTURBANCE the same components of the community. -MTL

-MLWS The macrofauna community consists of those organisms too large to move between the sand grains and generally in FIGURE 5. Diagrammatic representation of the size range lmg-2g dry tissue mass. some important interstitial parameters Such species make up shifting popu­ related to water flow in an intertidal lations in the intertidal and surf zones high energy beach. (After Riedl, Machan, of open beaches. When evaluating them 1972). it is best to consider the population across an intertidal strip of beach as a The interstitial system appears to be whole, this unit contracting and very efficient at mineralising virtually expanding as beach profile changes and 333

tides pass from springs to neaps. Consequently all further discussion of SHELTER EXPOSURE abundance and biomass of macrofauna

populations will consider metre wide CRUSTACEANS strips of beach and not square metres, MOLLUSC unless stated otherwise. All authors should present their results in this way, at the same time stating the width POLYCHAETES of the beach.

The macrofauna of sandy beaches includes FIGURE 6. Responses of the major most major invertebrate taxa although it invertebrate groups to the exposure has long been recognised that molluscs, gradient on sandy beaches. crustaceans and polychaetes are the most important (Rees, 1S39; Watkin, 1942; (Stephen, 1928, 1931, 1932; Rapson, Southward, 1S53; Schuster-Diedricks, 1952, 1954; Holme, 1954; Figueras, 1956; Sourie, 1957; Pichón, 1967 ; 1956; Edgren, 1959; Ansell, 1961; Dexter, 1969, 1972). There is a Wade, 1967; McIntyre, 1970; Smith, / tendency tor crustaceans to be more 1971; Brown, 1971b; Ansell et al., abundant on tropical beaches or more 1972b; Irwin, 1973; de Villiers, exposed beaches and molluscs to be more 1974; McLachlan, Hanekom, 1979; abundant on less exposed and/or McLachlan, Van der Horst, 1979; temperate beaches (McIntyre, 1568, McLachlan et al., 1979b; Leber, 1970; Seed, Lowry, 1973; Dexter, 1981) 1982b). Brown (1982) reviewed work on although there are many exceptions to whelks of the genus Bullia and Ansell this and polychaetes are sometimes more (1983) has covered the genus Donax. abundant than either of these taxa (Brown, 1581; McDermott, 1983). There have been some general accounts of Indeed, Dexter’s (1983) work suggests crustaceans on sandy beaches (McIntyre, that crustaceans dominate the most 1963; Epelde-Aguire, Lopez, 1975; exposed beaches and polychaetes the most Kamihira, 1979) and many studies on sheltered beaches with molluscs reaching individual species or groups. Amphipods maximum abundanc e in intermed i ate have been extensively studied on the situations (Fig. 6). In terms of east coast of the United States (Croker, biomass, however, molluscs are usually 1967a, 1967b, 1568, 1970; Dexter, 1967, most important (Trevallion et al., 1971; Sameoto, 1969a, 1969b; 1970; Dexter, 1974, 1976; Eleftheriou, Bousefield, 1970; Craig, 1973; Croker McIntyre, 1976; McLachlan, 1977a; et al., 1975; Scott, Croker, 1976; Ansell et al., 1972a; Bally, 1981; Holland, Polgar, 1976; Donn, 1980) and Shelton, Robertson, 1981). elsewhere (Williamson, 1951; Barnard, 1963; Fincham, 1971, 1974, 1977; There have been many studies on the Kamihira, 1981). Isopods, both air- and biology and ecology of dominant bivalves water-breathers, have also been widely and gastropods of sandy beaches studied (Fish, 1970; Jones, 1971, 1974, 334

1979; Dexter, lS77a; Klapow, 1972; ranges trom one (Gauld, Buchanan, 1956; Fish, Fish, 1972; Kensley, 1972, 1974; McLachlan et al., 1981b) to 82 (Vohra, Holdich, Brown, 1973; Ferrara, 1974; 1971), this number increasing with Glynn et al., 1975; Johnson, 1976a, decreasing exposure. Bally (1981) 1976b; Chelazzi, Ferrara, 1978; divided beaches into three degrees of Eleftheriou et al., 1980; Holanov, exposure and, based on a literature Hendrickson, 1980). Mysids have been survey of 105 beach studies, listed investigated by Fishelson, Loya (1968), average numbers of species, abundances Brown, Talbot (1972) and Wooldrigde and dry biomass values for these (Table (1981) and cumaceans by Pike, Le Sueur 3). (1958) and Corey (1970). TABLE 3. Summary of mean macrofaunal Hippid crabs have been extensively abundance and dry biomass values based studied. Efford (1976) reveiwed on 105 beach surveys.(After Bally, 1981). distribution in the genus Emerita while ______othe r studies include Alikunhi (1944), High Medium Low Matthews (1955), Thomassin (1969), energy energy energy Efford (1965, 1966, 1972), Dillery, No. spp. 11 17 30 _ 2 Knapp (1970) , Wenner (1977) , Wenner, Abundance m 400 752 1710 Fusaro (1979 ) and Subramoniam (1979 ) . Abundance m -''- 20045 34571 2797867 _2 Ocypodids have also been widely studied Biomass g .m 2. 26 1 .97 6.23 (Crane, 19 41 ; George, Knott, 1965 ; Biomass g .m -"'' 871 170 6 3 Fellows , 197 5; Jones, 19 72; Hill, Sand particle Hunter, 19 7 3 ; Vannini, 197 6; Wolcott, diameter um 310 257 238 19 7 8 ; Mebachi an, 1980c ; Robertson, Pfeiffer, 1981; Robertson, Pheiffer, 1981; Hill, 1982; Wada, 1982; Hails, While diversity and abundance decrease Yaziz, 1982) and Caine (1974) and du with exposure (Angus, 1979; McLachlan Preez (1981) have studied portunids. et al., 1981b) individual size There have also been studies on increases, yielding high biomass values cniaarians (Kastendiek, 1982), even at lower abundances in some cases, echinoderms (Buchanan, 1966; Laurence, Though most classifications of beach Ferber, 1971; Scheibling, 1982; exposure are very subjective, the above Dexter, Ebert, 1975; Dexter, 1977b), trends remain clear. The highest polychaetes (Clark et al., 1962; biomass values come from very exposed Longbottom, 1970; Mock, 1981; Wilson, dissipative beaches, e.g. 6621 g ashfree 1981; Brown, 1982) andinsects (New, dry üiass.m"^ in the East Cape 1968 ; Craig, 1970 ; Orth et al., 1977 ; (McLachlan, 1977a) and 25735g dry mass Stenton-Dozey, Griffiths, 1980; Chelazzi m.-^ in Peru (Penchaszadeh, 1971). et al., 1983). These high biomass values are, without exception, due to filter feeders (Donax, Bally (1-981) summarised the results of Emerita ) . Exposed beaches are thus not all beach macrofauna surveys to 1981. necessarily sparsely inhabited. The number of species found on a beach Species diversity normally increases McIntyre, 1970; Lawrence, Ferber, from high to low tide marks (McLachlan, 19 71; Al heit, 1978 ; Bally, 1981, 1977a) and may decrease again around the McLachlan et al., 1981b; Lopez-Cotelo break point (McGwyyne, 1980) and then et al., 1982) beach slope (McLachlan et increase offshore (Field, 1971; Day et al., 1981b) sand moisture (Hayes, 1977; al., 1971; Christie, 1976). However, Salvat 1964, 1966, 1967; Bally, 1981; on a beach dominated by kelp input, Withers, 1977) food in the surf water maximum macrofauna diversity occurred (Brown, 1964; Rapson, 1954; Wade, around the drift line at the top of the 1968 ; McLusky et al., 1975 ; Ansell et beach (Stenton-Dozey, Griffiths, 1983). al., 1972a; hair, 1978; McLachlan et al., 1981a; Hutchings et al., 1983) and The distribution of macrofauna along the dynamic changes such as due to storms beach is generally patchy, the combined (Scott, I960; Brown, 1971a). Effects of result of movement and sorting by the dredging and beach nourishment have also swash, localized food concentrations or been investigated in the inter- and sub­ biological aggregations of species tidal (Reilly, Bellis, 1978; Turbeville, (Loesch, 1957; Thum, Allen, 1975; Marsh, 1982; Culter, Mahadevan, 1982; Achutankutty, 1976; Moueza, Chessel, Saloman et al., 1982), 'while effects of 1976; Hayes, 1977; Saloman, Naughton, disturbance predation have been assessed 1978; Fusaro, 1980; Brown, 1982). experimentally in a sheltered sand flat Bally (1981) investigated patchiness in by Woodin (1981). Many authors have detail on 'west Cape beaches and showed monitored organic or chlorophyll levels it to be a common occurrence in all in the surf without being able to species at all tide levels, often having demonstrate correlations with fauna! 1 2 proportions of 10 -10 m. This abundance. Undoubtedly, however, suggests that line transect sampling beaches with high biomass must receive strat eg i es may be unreliable, high inputs of particulate organics and particularly if not replicated. Dauer, it is noticeable that on most beaches Simon (1975), however, showed that by where very rich filter feeding pooling the results of a whole line populations occur, phytoplankton blooms transect, error due to patchiness can be have been recorded in the surf (New reduced by 10-15%. Hartnoll (1983) has Zealand - Rapson, 1S54; Washington quantified the species area relationship Lewin et al., 1979a; South Africa on a sheltered sandy beach. He found McLachlan et al., 1981a; South America little increase in diversity as sample Gianuca, 1983). Alternately, rich size increased above 0.25m and populations develop in upwelling suggested that for accurate sampling an regions, probably feeding on 2 aggregate area of 0.5m is adequate. phytoplankton advected shorewards after upwelling cycles (Hutchings et al., Distribution and abundance of organisms 1983). on the beach has been related to many factors. Factors said to influence the Of the physical factors, wave action and macrofauna include sand grain size and/ particle size have generally been or organic content (Longbottom, 1970; considered the most important although 336

20- 4000 Eleftherioui, Nicholson (1975) show that (a) grain size alone can not characterize a beach. As particle size, beach slope I15- -3 0 0 0 I and wave action are closely related, C0 UJ o defining the former two fixes the latter lii -2000 w ' (Davies, 1972; McLachlan, 1980a). w 10- U. McLachlan et al., (1981b) obtained o tr significant correlations between ui m -1000 2 macrofauna species numbers and abundance 2 -D 2 and both grain size and beach slope, but not with wave action estimates for lo '2 0 "aO beaches on the south and east coast of BEACH SLOPE South Africa (Fig. 7). This suggests 20- r 4 0 0 0 that it is not wave action but rather (b) steep slope and coarse sands that limit the fauna. Very exposed beaches (in X 15- -3 00 0 I CO terms of wave height) often have richer UJ o faunas than less exposed beaches where UJ -2000 cO the latter have coarse grains and steep w 10- Ii. slopes. Finer sands result in flatter o cr slopes as does heavier wave action. The OQm Ö- «í- 1000 2 5 flatter the slope of a beach the more ZJ 2 evenly wave energy is dissipated in the u0 surf zone and intertidal and this is the 100 500 1000 crucial factor. Thus a very exposed Md Qum) beach can support a rich macrofa.una if FIGURE 7. The relationships between it is dissipative as opposed to macrofaunal species diversity and abun­ relective (e.g. Maitland beach, dance and the slope (a) and particle McLachlan, 1977a; Copalis beach, Lewin size (b) of beaches in South Africa. et al., 1979a). Indeed, high energy (After McLachlan et al., 1981b). dissipative conditions seem optimal for the development of a high biomass of 1S 7 0, 1971 , 1972; Dexter, 19 78 ; Hill, filter feeders. Hunter, 1979; Shin, 1981, 1982; Kastendiek, 1982). The zone inside the Much less is known of macrofauna ecology break point has been termed the inner below the intertidal. Fauna is turbulent zone and the area outside this generally absent around the break point (out to where wave effects on the bottom but increases in abundance and diversity are negligible) the outer turbulent onshore and offshore in accordance with zone. Biomass values are seldom high. less turbulent conditions, less coarse Masse (1970, 1971) recorded 'number of substrates and higher organic levels 1048 - 10031 m-2 and biomass 2.5-11.7g (Clark, Milne, 1955; Morgans, 1962 ; dry mass m-z at various localities in Barnard, 1963; Field, 1971; Day et the Mediterranean at depths 1,5 - 5m. al., 1971; Christie, 1976; Masse, McIntyre, Eleftheriou (1968) recorded an 337

_2 average dry biomass of 1.3g.m m the the midshore in New Zealand. In South intertidal and 3.7g.m m the Africa Dahl's scheme, with modifi­ subtidal with 62 species on the beach cations, has been found acceptable and 116 off the Scottish shore. The (McLachlan, 1980b; McLachlan et al., poorest zone was just below LWS. 1981b).

Much has been written on intertidal distribution patterns. The earliest WATER BREATHERS BROWN'S serious attempt at providing a zonation ^ SUB SUBLITTORAL TERRESTRIAL MIOLITTORAL scheme for sandy beaches was that of ^ FRINGE FRINGE DAHL'S ZONES RESURGENCE SATURATION Dahl (1952)(Fig.8) . This was very «A d RYING RETENTION SALVAT'S ------■lii------1,1------ZONES similar to an earlier suggestion by

Davenport (1903). Based on the distri­ EHWS : A DRIFT LINE bution of crustaceans in northern temperate and South American beaches he proposed three zones essentially equivalent to the three zones of rocky shores. These zones were: the subterrestrial fringe characterized by ocvpodid crabs in warm areas and ELWS taiitria anphipods in cold areas; the midlittoral zone characterized by FIGURE 8. Diagrammatic representation of cirolanid isopods (although these may be schemes of macrofauna zonation on sandy absent in cold temperate areas); and the beaches. sublittoral fringe with a mixed fauna often characterized by hippid crabs in Salvat (1964, 1966, 1967) described an the tropics and naustorid and other alternate scheme based on physical arr.ph ipods in temperate areas. Dahl's factors. He delineated four zones on zones were thus defined biologically. the beach, based on water saturation (Fig. 8). Pollock, Humon (1971) used Subsequently many authors have tried this system for a Massachusetts beach this scheme with varying results. they were studying, except that they Gauid, Buchanan (1956) found an overlap subdivided the zone of drying and they of talitrids and ocypoaias on west extended their zones into strata African shores and also recorded covering the whole interstitial system Excirolana in this zone. Lower zones (see Table 1 and Fig. 3). Salvat's showed less correspondence. Philip system has been found reliable in (1S72) in India, Vohra (1972) in describingzonation of macrofauna, Singapore and Jaramillo (1978) in Chile particularly isopods (Withers, 1977; found Dahl's scheme useful and Escofet- Bally, 1981). Both these authors et al., (1378) found it fairly suitable admitted, however, that boundaries are for beaches in Brazil, Uruguay and not sharp and that zones grade into each Argentina. Wood (1968), however, found other. Eleftheriou, Jones (1976) circolanids replaced by a sphaeromid on pointed out that differences in inter- 338

tidal distribution between different the larger one in the eulittoral (e.g. areas and species make eurydicid isopods Amphidesma spp. in New Zealand, Rapson, unreliable indicators of zonation as 1952; Donax spp. in India, Ansell et proposed by Dahl. They did not, however, al., 1972b; Donax spp, in the Last attempt to use Salvat's scheme. Cape, McLachlan, 1980b).

Views on zonation of macrofauna on sandy Besides zonation patterns at community beaches are thus highly conflicting, a level, intraspecific zonation has been situation not surprising in a dynamic recorded in several species. This environment with a highly mobile fauna. generally takes the form of zonation of It may safely be said that zonation, in size classes and has been recorded in the classical sense, has never been most taxa typical of open beaches, proved on a sandy beach, i.e. sharp including molluscs and crustaceans boundaries have not been demonstrated. (Alikunhi, 1944; Glynn et al., 1975; Further, individual species show much McLachlan et al., iS79b; Wooldridge, clearer zonation than the fauna as a 1981; Ansell, Lagardere, 1980; Brown, whole. Indeed, Brown (pers. comm.) is 1982; Haley, 1982). This may be due to of the opinion that only two zones are differential sorting of the sizes in the distinguishable on sandy shores - air swash or to active migration to areas breathers in the supralittoral and water differentially suitable to the organism breathers below them. However, two at different life stages. boundaries are clearly and indisputably visible on open beaches, namely the Zonation as the researcher records it drift line and the edge of the saturated is, however, only the distribution of sand where the water table reaches the the psamrnol ittoral fauna at an instant surface. These correspond to Dahl's in time and most species undergo tidal boundaries. However, although the migrations of some sort. Typically this boundary between Salvat's zones of involves a simple movement up and down retention and resurgence are not obvious the beach with the tides allowing the there is considerable evidence that animal to stay in the swash zone where meaningful subdivision of the conditions for feeding are op itmai and midlittoral can be made on many predation minimal. In molluscs this beaches. These zonation schemes are movement involves no endogenous rhythms summarized in Fig. 8. Within these but simply a series of responses to zones most species show subzones and changing physical conditions, most there is often blurring of boundaries. notably the degree of saturation and Isopod species usually exhibit a clear thixotropy of the sand (Mori, 1938 ; zonation near the top of the shore and Turner, Belding, 1957; Ansell, midlittoral (Withers, 1977; Eleftheriou, Trevallion, 1969; Trueman, 1971). In Jones, 1976; Bally, 1981; McLachlan et some molluscs' it may be more complex, al., 1981b; Dexter, 1983). Bivalves, e.g. Donax serra in the Last Cape, where also exhibit zonation, often with two there is not normal tidal migration but species occupying a beach, the smaller rather semilunar movement up and down species in the sublittoral fringe and the shore to occupy a position near mean 339

tide level during springs and near low compress so that at high tide most of tide during neaps (McLachlan et al, the invertebrate population on the beach 1979c). Movements related to periods of may be compressed into a narrow strip storm and calm have also been recorded with considerable overlap between (Leber, 198 2a). species. Further, in addition to normal tidal migration, movement into the In crustaceans these rhythms are subtidal lias been recorded in winter in generally endogenous and more complex. Donax parvula (Leder, 1982b). They have been shown to include entry into the plankton at night (e.g. mysids, Temporal changes in beach macrofauna anphipods and isopods), increased have been recorded both in whole activity during springs as opposed to communities (Sanchez et al., 1982) and neaps, and orientation behaviour (Papi, in individual species populations. The Pardi, 1963; Enright, 1963, 1965, 1972; most orainatic of these are those assoc­ Hammer et al., 1968, 1969; Cubit, 1969 ; iated with the monsoon in India where Fincham, 1970, 1973; Alheit, Naylor, most of the fauna disappears during this 1976; MacQuart-Moulin, 1977; McLachlan period (Ansell et al., 1972a; Dwivedi et et al., 1979c; Marsh, Branch, 1979; al., 1973; McLusky et al., 1975). Hager, Croker, 1980; Fusaro, 1980; Longer term fluctuation spanning several Caramillo et al., 1980; Scapini, years have also been recorded (Rapson, Ugolini, 1981). The advantage of 1954; Coe, 1955; Davis, Von Blaricom, increased activity during springs is 1978). Dramatic changes in the long that it prevents the animals being term may also take the form of occas­ stranded as the tides retreat. ional mass mortalities, e.g. Donax spp. (Orton, 1929; Fitch, 1950; Loesch, 1957; Ansell, Trueman (1973) calculated the Johnston, 1966, 19 68; Grindley, Nel, energy costs of migration in Donax and 1968; de Villiers, 1974) such as related Erne rita and concluded that it was more to poisonous uinoflagellate blooms. profitable for the animals to migrate Seasonal changes have been reported in than to attempt to maintain position. most species studied and for several Tidal migrato ry behaviour has several communi ties. advantages; it allows animals to stay in the zone optimal for feeding, i.e. the In an unstructured and physically edge of the swash zone; it keeps them controlled habitat like a sandy beach, too shallow for many fish predators but most species tend to be unspecialized just immersed enough not to be fully generalists with board niches (Brown, open to birds; it helps to prevent Talbot, 1972; Brown, 1982; McGwynne, animals being stranded on the shore; in 1980; Bally, 1981). Because of this, supralittoral forms, e.g. Tylos, it the physical nature of the environment enables them to move down the beach and the mobility of the fauna, during the low tide to feed on debris. competition amongst the sandy beach fauna is unlikely, though the This migration naturally has marked possibility of exploitation competition effects on zonation and all zones can not be ruled out. Wilson (1981) 340

demonstrated negative interactions in a predators. dense assemblage of deposit feeding polychaetes, but this was in a very As the bulk of the fauna are usually sheltered beach. Trophic groups among filter feeders, the size of beach the macrofauna include scavenger/ populations is probably closely related predators, filter feeders (suspension) to the richness of inshore waters in and, on less exposed shores, deposit particulate organic material (Ansell et feeders. Filter feeders usually al., 1972a; Hutchings et al., 1983). In dominate and consist mostly of some areas large amounts of macrodebris bivalves. The tellinaceans of high may be cast ashore, particularly energy beaches, Donax spp., are, unlike adjacent to kelp beds. In such most other members of the family, situations vast populations of supra­ suspension feeders (Ansell, 1983). littoral scavengers develop (Hayes, Deposit feeding is not common in sandy 1974; Griffiths, Stenton-Dozey, 1981). beach filter feeders, except in very- In other areas carrion input may be sheltered situations. In cases where high, e.g. in the form of cnidarians, the fauna is impoverished, however, such and in such cases midlittoral scavengers as on very coarse, steep beaches, such as Bullia reach high abundance supralittoral scavengers may dominate as (McGwynne, 1980; Brown, 1982). a result of the virtual absence of other species (Gauld, Buchanan, 1956; Dye et Macrofaunal food webs have been given al., 1981; Wooldridge et al., 1981). On for beaches in South America (Koepcke, sheltered beaches deposit feeders, e.g. Koepcke, 1952; Gianuca, 1983), the Cape Arenicola, Callianassa and Scolelepis, Peninsula (Brown, 1964; Griffiths et may be very important or even dominate al., 1983 ) and the East Cape (McLachlan (e.g. Saloman, Naughton, 1978; McDermott, et al., 1981a). The main predators on 1963). the macrofauna as listed by several authors are birds, fishes and crabs The tropic structure of the beach macro­ (Coe, 1955; Loesch, 1957; Masse, 1963; fauna is therefore normally dominated by Wade, 1967; Penshaszadeh, Olivier, mobile filter feeders. Even where other 1975). The former two will be discussed forms may be more abundant, filter later. Crabs, being part of the feeders usually dominate biomass benthos, represent a form of predation (Dexter, 1979; Eleftheriou, McIntyre, resident in the beach/surf system. Du 1976). As there is little or no primary Preez (1981) has made a detailed study of production on the beach, the macrofauna the swimming crab Ovalipes on East Cape is dependent on food imports from beaches and shown it to be an important adjacent systems, i.e. the land and the predator on Donax and Bullia. Several sea (Brown, 1964; Ansell et al., 1972a; other authors mention the importance of McLachlan et al., 1981a; Griffiths et both ghost crabs and swimming crabs as al., 1983). The sea is the most predators on beaches (Loesch, 1957; important and supplies particulates for Koepcke, 1953; Ansell et al., 1972a). filter and deposit feeders and carrion Virnstein (1977) showed the importance and macrodebris for scavengers and of crabs in controlling macrofauna 341

communities by predation in subtidal 4. PHYTOPLANKTON sand in Chesapeake Bay. Naticid Blooms of diatoms in surf zones, gastropods are important predators on persistent or sporadic, now appear to be burrowing bivalves but are not generally a typical feature of many sandy beach found on open ocean beaches. surf zones. Rich surf phytoplankton blooms have been reported from the Besides predation, "natural" mortality Washington coast, U.S.A., (Thayer, 1935 ; can at times be important on sandy Lewin, Norris, 1970), the Gulf coast of beaches. This includes not only mass the U.S.A., (Gunter, 1979; Gunter, mortalities due to poisoning (de Lyles, 1979), New Zealand (Rapson, 1954; Villiers, 1S74) but also being cast Cassie, Cassie, I960; Lewin, Norris, above the shore by storms (Brown, 1971a; 1970), South Africa (McLachlan, Lewin, Penshaszadeh, Olivier, 1575 ; McLachlan 1981) and the east coast of South et al., 1981a). McLachlan, Young (1982) America (Gianuca, 1983). These blooms suggested the importance of upwelling are mostly composed of masses of cells and sudden temperature drops in of one or two species belonging to the retarding mobility as a factor contri­ genera Chaetoce ros, Aster ionella, buting towards this. Ansell et al., Aulacodiscus and Anaulus. (1978) have shown that where the mortality rate is fairly constant, the The blooms described by Gunter (1979) mortality coefficient, longivity and and Gunter, Lyles (1979) are Chaetoceros production are related. Ansell (1983) dominated strips hugging the beaches. lists cases of commercial exploitation Heavy rains leach nutrients from the of Donax where heavy mortality may be land and these, being retained near the caused by man. beach by calm seas, apparently cause the blooms. These blooms take the form of It may be concluded that the distri­ strips 5-6m wide for miles along the bución and diversity of beach macrofauna shore. All the other reported surf zone is largely determined by physical blooms occur as patches of phytoplankton factors, prime among 'which are wave within well developed surf zones. Of action, particle size and beach slope. these, those off the Washington coast Food input probably determines abundance have been most intensively studies and of both scavengers and filter feeders. reviewed by Lewin, Schaefer (1983). The most pronounced feature of macrofauna animals is a high degree of Lewin, Norris (1970) first described the mobility and tidal migrations on exposed similarities between blooms on the beaches. The main rôle of the Washington and New Zealand coasts where macrofauna is to process food imports, Chaetoceros and Asterionella were coming mainly from the surf, and in turn dominant. Lewin, Hruby (1973) described to be consumed by terrestrial and marine the diel periodicity in buoyancy of predators. They are thus in the middle Chaetoceros, this species dispersing at of the food chain. night and rising to the surface during the day. Floating at the surface, they create a stable foam which is then 342

retained in the surf by wave action and Subsequently more attention has been often stranded on the beach. This paid to the ecology and distribution of clearly appears to be a mechanism for the blooms. Jijina, Lewin (in prep, a, retention in the surf zone. Lewin b) described physical features of the (1974) described long term changes in coastal zone in relation to blooms at 13 species composition of the blooms with beaches in Washington and Oregon. Aulacodiscus littorii dominant before Blooms were best developed on long flat 1950 and Chaetoceros armatum dominant beaches while steeper beaches and after 1950. Other studies looked at beaches near rocks has poorer blooms. light utilization (Lewin, Mackas, 1972), Low air and water temperatures were nitrate reductase activity (Collos, associated with increased diatom Lewin, 1974), daily periodicity (Lewin, densities while nutrient concentrations Rao, 1975), C:N ratio (Collos, Lewin, were inversely proportional to 1976), respiration (Robertson, Lewin, densities. They concluded that the type 1976), chemical composition (Lewin et of beach and its physical characteris­ al., 1979a) and the clay coat (Lewin et tics were very important in bloom al., 1980) of the surf diatoms development. Chaetoceros and Aster ionella. McLachlan (1980d) suggested that blooms Lewin et al., (1975) analysed environ­ form where surf circulation cells mental conditions associated with the develop and trap beach generated blooms over two years, finding the nutrients, pointing out that this is diatom populations relatively constant most likely on long beaches of flat over this period. Lewin (1978) slope (i.e. dissipative beaches). evaluated factors controlling the McLachlan, Lewin (1981) described blooms seasonal cycle of nitrate in the surf. of Anaulus bi rostratus from the Last Nitrate concentrations fluctuated widely Cape, South Africa, and showed that the in relation to season, upwelling and blooms were positioned over rip currents phytoplankton growth and ammonium seemed by day. All surf bloom forming species to be an important nitrogen source, show a daytime buoyancy and this results particularly during summer. Lewin et in the collection of diatom cells as a al., (1979b) measured ammonia excretion foam or scum over rip currents. Presum­ by Siliqua and concluded that the razor ably the opposing forces of incoming clam populations of Washington beaches waves and outgoing rip current keep them could regenerate significant amounts of in position. 'while diatom cells may ammonium into the surf zone. Lewin travel all around the surf circulation (1977) summarised knowledge of these cells, the rip current area may act as a blooms, pointing out the interdependence bottle-neck for buoyant material. of the diatoms and the razor clams. Diatoms are the main food of the razor McLachlan, Lewin (1981) also showed that clams while the clams in turn regenerate blooms developed in water not very high inorganic nitrogen which is utilized by in nutrients. Though nutrient concen­ the diatoms. tration is low, supply is constnat as inorganic nutrients are continually 343

draining out of the beach. Nutrients species commonly occur in well developed are generated on the beach both by the surf zones on gently shelving beaches. filtration of water and mineralisation Diurnal buoyancy of the diatoms results of organics by the interstitial fauna in their concentration over rip currents (McLachlan, 1980a, 1982; McLachlan et by day. Nutrients are derived from many al., 1981a) and by excretion of the sources, but the beach is probably most macrofauna (Prosch, McLachlan, 1983). important. inorganic nitrogen generated Both of these sources are important and as ammonium by macrofauna and have been shown to generate significant Zooplankton excretion and as nitrate by amounts of nitrogen on East Cape the interstitial fauna is constantly beaches. Subsequently wind has been draining into the surf and passing shown to be of overriding importance in through rip currents where the blooms controlling short term changes in blooms are situated. In this way the blooms in the surf (Romer, Sloff, pers. comm.). are positioned in a site of steady nutrient supply. Wind has a pronounced Estimates of primary production in surf influence on bloom development by zones off beaches have been made by controlling wave action and surf Cassie, Cassie (1960) and Edwards circulation patterns. We need to know (1973a). The latter obtained figures of more of the interaction between wind, 10495 and 5597 kcal.m-2.y-1 for waves, nutrients and blooms. We also phytoplankton primary production in the need more reports on the sources of shallow off two sheltered Venezuelan primary production in surf zones that do beaches. Estimates of primary not support these diatom blooms. productivity in surf phytoplankton blooms are now under way (Lewin, 5. ZOOPLANKTON Schaefer, 1 983) and we should soon have Studies on surf zone Zooplankton are figures for biomass and production of virtually absent from the literature. these rich algal communities. While several taxonomic papers list species taken off sandy beaches, few Recently Wilce et al., (1982), Wilce, were sampled in the surf zone or include Quinlan (19S3) and Quinlan et al. (1983) ecological notes. Brattegard (1969 and reported on masses of free living subsequent works) described mysids from ball-like algae, Pi jayella, on sand shallow water off the Bahamas including bottoms and in the surf off beaches in some from sandy habitats and similar Nahant bay, Massachusetts. This species accounts are given by Wigley, Burns reached peak biomass in summer and (1971) for the Atlantic coast of the proliferated by fragmentation and re­ U.S.A. and Bacescu (1975) for Tanzania. generation. It's nutrient source is uncertain but nutrient recycling within Bowman (1971) described copepods off the the beach/surf system is considered southeast coast of the U.S.A. and important. recognised a 'coastal association' dominated by one'coastal' and one It may be concluded that rich surf 'estuarine' species. Outside this lay diatom blooms consisting of one or two 'shelf' and 'oceanic' associations 344

dominated by four and seven species outer limit of distribution near the respectively. Sander, Moore (1978) outer limit of rips. He postulated that studied inshore and offshore copepods detrital food in suspension decreases around the Viest Indies as shallow as 10m outside this zone and that zonation was and recorded average numbers of 100- mainly related to the nearshore, — 3 500.m with other groups making up wave-induced circulation patterns. 11-22% of total Zooplankton numbers. Youngbluth (1979) studied Zooplankton Several studies have recently been done

within 1km of the coast of Puerto Rico on surf zone Zooplankton in the Last at about 10m depth. He recorded numbers Cape. In most of this work the use of of 41-7568.m-^ of which 65-84% were large nets has attempted to avoid the copepods. Settled volume biomass values normal loss of large forms such as _ O averaged 0.086ml.m and highest mysids, a problem often not appreciated numbers were recorded at night. by workers using small nets. Cockcroft (1979 ) sampled inside the breakers at Ira Moran (1972) found the benthic mysid, depth, just outside at 3 m and further Gast rosaceus sanctus, to occur in shoals out at 10m off a moderately exposed along the shore in the top 1cm of sand, beach. Greatest biomass occurred just but moving into the top l-2m of water at outside the breakers (although netting night in the Mediterranean. It efficiency was very low in the surf). exhibited a clear zonation offshore. Abundance increased considerably after Fincham (1970), studying amphipods in dark when dry biomass values ranged _ -3 Britain, Macquart-Moulin (1977), 6-980mg.m . Mysids dominated biomass studying two benthic mysids and an (21% at lm, 83% at 3m and 84% at 10m; isopod in the Mediterranean, and mean 63%) with copepods averaging only Wooldridge (1981), studying a benthic 13%. At the lm site the prawn, mysid in the East Cape, found similar Macropetasma africana, was very patterns. Night time planktonic important although poorly sampled. The activity of benthic crustaceans, dominant species overall was the mysid, particularly mysids, amphipods and Mesopodopsi s slabberi. Biomass was isopods, is well known (Alheit, Naylor, distinctly higher than offshore in Algoa 1976) . Bay and about the same as recorded in local estuaries, indicating the general The most detailed account of surf zone richness of Zooplankton in the surf zone. Zooplankton yet published is the work of Clutter (1967) at La Jolla. He studied Subsequently Cockcroft (1983) has made a the nearshore zonation of four benthic detailed study of Macropetasma, which and five pelagic mysids out to 17m depth. occurs in vast shoals in Last Cape surf All species formed schools and occupied zones. Growing up to 7cm in length, clear zones, occurring on or near the this prawn is really a nektonic form. bottom. A large species dominated It exhibits a clear zonation with inside the surf while the most abundant juveniles inshore and adults out as far species,' Metamysidopsis elongata, peaked as 20m depth. They shoal near the where rip currents dispersed and had its bottom by day and disperse at night, 345

being most abundant inside the breakers. 1000.m ^ just behind the breakers and Numbers recorded averaged 21-37.m 10.m-^ further offshore. It even _3 giving a dry biomass of 0.9-1.8g.m reached densities exceeding 15000.m — This species uses the surf zone as a (mainly juveniles, dry biomass _ 3 nursery area and, being an opportunistic 1.02g.m ) behind the breakers at omnivore, it feeds on detritus, times. Other mysid species seldom _ 3 phytoplankton and small crustaceans. totalled more than 10.m . Dry

Shoals tend to move inshore at night and Zooplankton biomass averaged about - 3 to concentrate around phytoplankton 0.25g.m J behind the breakers and _ 3 blooms by day. 0.015g.m offshore, an order of magnitude lower. Romer (pers. comm.) is investigating food chains around surf phytoplankton Mesopodopsis formed vast shoals which blooms, including small and large virtually disappeared by day (presumably Zooplankton. He finds that Zooplankton moving to deeper water) and then became is concentrated around blooms by day but abundant at night. This inshore more dispersed at night, this resulting population consisted largely of in a slight decrease in biomass after juveniles and breeding occurred at sea dark. Crustaceans (Macropetasma, even though large numbers often moved mysids, copepods) account for about 85% into estuaries. This study indicates of biomass and siphonophores, that the inshore area and surf zone has chaetognaths, and others for the a mysid dominated Zooplankton community remainder. Mean total numbers in a of very high biomass. Abundance and bloom during the day are about 2000 biomass in this region are an order of zoopiankters.m-^ with a dry biomass of magnitude higher than offshore and even _ o u.Sg.m . However, higher values, up higher than recorded in most estuaries. _ ^ to 750g.m have oeen recorded m Many authors have probably dense swarms of plankters, particularly underestimated the contribution of the where prawns were abundant. larger and more mobile Zooplankton through using small nets. Wooldridge (1983) studied the Zoo­ plankton of Algoa Bay from just behind Clearly our knowledge of surf zone the breakers to about 4km offshore (20m Zooplankton is abysmal. Few papers go depth) using a net of 1.5m diameter. beyond species lists or counts of While salps, medusae, ctenophores and abundance. While it is difficult to others were often common, crustaceans extrapolate from the small amount of dominated, making up about 80% of hard cata currently available, three biomass. Fifteen species of mysids points seem clear: i) the Zooplankton of accounted for more than 90% of exposed surf zones may be very rich with crustacean biomass, with copepods second high biomass values, ii) large in importance. A single species of crustaceans (e.g. mysids, penaeids) mysid, Mesopodopsis slabberi, was by far dominate the biomass (as they can cope the dominant species, especially close with the turbulence of these areas) but inshore, with average numbers around are difficult to sample, iii) there are 346

clear offshore zonation patterns and recruitment, growth and feeding of diurnal changes in abundance. Much work juveniles in the shallow subtidal off remains to be done in this field, in sandy beaches (Riley, Corlett, 1966; particular relating distribution and Macer, 1967; Edwards, Steele, 1968; abundance to wave induced circulation Lockwood, 1974; Poxton et al., 1982). patterns and available food in the near­ Among these fish, plaice (Pleuronectes shore zone. platessa), dabs (Limandia limandia) and turbot (Scophthalmus maximus) are the 6. FISHES most important. In summer, after Though far better studied than metamorphosis, large numbers move into Zooplankton, we still know comparatively fine sand bays where the water is less little of the ecology of fishes from than 3-5m deep. There they feed on surf zones off open beaches, largely demersal plankton and benthos, including because of the difficulties of sampling mysids and the siphons of Tellina and in these environments. pearse et al., tentacles of polychaetes. Mortality is (1942) list fish caught by seine net off high and the populations of these North Carolina beaches and more juveniles generally decline rapidly extensive reports of fishes in surf through autumn until they move into zones of the United States are given by deeper water again at the onset of Gunter (1958) et al. (1960), McFarland winter. (1963), Schaeffer (1967, 1970), Cupka (1972) and McDermott (1983). Around the In the United States Gunter (1958) coasts of Britain and Europe much sampled surf fish off the Texas coast, attention has been paid to juvenile recording fewer species off open beaches flatfish using beaches as nursery than inside the barrier. Be mostly grounds (Macer, 1967; Edwards, Steele, caught small and juvenile fish which 1968; Edwards et al., 1970; Steele, were most abundant in spring and Edwards, 1970; Steele et al., 1970b; summer. McFarland (19 63) found that Jones, 1973; Gibson, 1973; Thijssen et Zooplankton was the primary food source al., 1974; Lockwood, 1974; Poxton et for the surf fish at Mustang Island, al., 1982). In South Africa Rossouw Texas. Planktivores were the most (1983) has studied elasmobranchs from abundant trophic group and even mullett surf zones with particular emphasis on (Mugil cephalus) and benthic feeders the sandshark Rhinobatos annulatus, took large amounts of Zooplankton at Lasiak (1982, 1983) has made a detailed times. He recorded 47 species with an investigation of surf zone ichthyofauna average of four in winter (biomass communities and Romer, (pers. comm.) has 25.81b/acre) and 16 in summer (biomass investigated food chains around surf 103.21b/acre). High primary production phytoplankton blooms. in the surf, he concluded, was more than sufficiënt to support the fish community. In the cold temperate waters of Britain Moddle, Ross (1981) also recorded and Europe shallow sandy bays are midwater planktivorous fish dominating important as nursery areas for flatfish the surf zone in the northern Gulf of and several authors have studied Mexico. Armitage, Alevizon (1980) 347

recorded the diet of the Florida pompano Edwards (1973b) sampled with a beach (.Trachinotus carolinus ) and found Donax seine net off two Venezuelan beaches and to be an important item. recorded 49 species (31 at one beach and 32 at the other) which he divided into Carlisle et al., (1960) recorded 71 plankton feeders, fish carnivores, species off Californian beaches with an benthos feeders and herbivores (Mug il). average of 284 specimens per beach seine Fish biomass was estimated at 5g.m-^ haul. The surfperch, Amphistichtus dry mass at the unpolluted beach and — 1 argenteus, and the orbina, Mentici r rhus lg.m at at a polluted beach. undulatus, were dominant but flatfish, Plankton feeders and benthos feeders skates, rays and sandsharks (Rhinobatos) were most important. Penchaszadehi were also common. Best catches were (1583) found mysias and other motile taken on the low tide. They made a crustaceans to be the main prey of detailed study of the biology of the fishes off Venezuelan beaches. surfperch including reproduction, growth and feeding and found the mole crab, In Australia Lenanton et al. (1982) Emerita analoga, to be the main item in described the utilization of surf zone the diet. accumulations of macrophytes and their associated amphipods as nursery feeding Schaefer (1970) studied feeding of the areas for 0+ year classes of three fish striped bass, Morone saxatilis, in the species. surf at Long Island. Amphipods and mvsids were the dominant foods though In the Eastern Cape, South Africa, fishes, particularly anchovies, were Rossouw (1983) has studied elasmobranchs also important. During sampling 71 with particular reference to the biology species of fish were recorded. of the sandshark, Rhinobatos annulatus. This species comes into the surf to give McDermott (1983) sampled the fauna of a birth in summer. Juveniles stay in the barrier beach in New Jersey by means of surf but adults move offshore in cores and seine netting. The dominant winter. They feed on mysids, small Donax bent hie organism and main food for the and other benthic prey. Amongst various fish was the polychaet, Scolelepis other elasmobranchs, duckbill rays, squamata, which reached densities up to My1 iobat i s spp., come into very shallow - 7 — 7 40000.m (=50g dry mass.m ) m a water to prey on Donax spp. These, band approximately 20m wide. Of 26 fish together with other large rays are very species only seven were common and one important predators on the benthos. As resident. This species, Menidia menidia, in the case of flatfishes in European the silverside, made up 85% of fish waters, the great success of skates and numbers and 40% of fish mass and rays in these environments is probably Scolelepis formed 70-80% of its diet. due to their flattened shape allowing Leber (1982a) recorded four fish species them to forage in very shallow water, feeding on beach macrofauna, including thus being able to take even the the silverside. Donax and Emerita were macrofauna that undergo tidal migrations. the main prey items. 348

Romer (pers. comm.) is investigating controlled by winds. food chains around surf phytoplankton blooms. He has found that mullett, Liza Lasiak (1982) distinguished six feeding richardsoni, grazed directly on the categories, namely: benthic feeders, phytoplankton and are taken in turn by plankt ivores, cietr itivores , piscivores, larger predatory fishes. The mullett as herbivores and omnivores. Herbivores well as other juvenile fish in the surf owed their occurrence to the presence of also prey extensively on Zooplankton. some rocky reefs near the sampling site at the less exposed beach, and were Lasiak (1S82, 1S83) has made the most virtually absent at the more exposed detailed study to date of surf fish beach. The mullet, Liza richardsoni, communities, seining on two Algoa Bay was the only detritivore, but in beaches over a period of three years. Lasiak's study fed mainly on Zooplankton At the less exposed beach she recorded and may thus be considered a planktivore. 66 species and 29 at the more exposed Her feeding groups may thus be site with teleosts dominating numbers simplified to include, benthic feeders, and elasmobranchs dominâting biomass. planktivores, piscivores and omnivores. Seven common species were resident while At both beaches motile organisms other species were intermediate or (mysids, prawns, fish, cephalopoda and sporadic in occurrence. The community, Zooplankton) dominated the food base and showed no overall seasonal trends but a these foods were taken by all feeding very high degree of short term groups including benthic feeders. variability which seemed to be largely Almost all species employed oppor­ coupled to the effects of wind on the tunistic feeding strategies. Table 4 surf zone as save rai biological summarises the biomass, composition and parameters were closely correlated to food consumption of this surf zone fish wind direction and intensity prior to assemblage. sampling. Studies over 24h showed no clear trends though maximum abundance, We still know very little of surf zone biomass and diversity often tended to ichthyofauna and the danger of sampling occur around twilight. Sampling on in heavy surf will probably keep the consecutive days proved to be very situation that way. To really variable. She concluded that the surf understand resource partitioning and zone fish assemblage was a highly niche structure of surf zone fishes some variable community whose structure and more accurate means of sampling is dynamics were probably dominated by necessary whereby the actual location of abiotic factors while biological fish within uifferent parts of the surf interactions were of secondary can be made. Perhaps SCUBA counts are importance. As most food organisms were the solution. In this way the distri­ highly motile, their availability would bution and feeding of fish in the surf be strongly influenced by surf could be better understood in terms of conditions which in turn are determined spatial partitioning of this zone in by wind effects on the wave regime. three dimensions. However, Zooplankton Hence short term variability is largely as food for fish will be more important 349

Table 4. Biomass, composition and food consumption of fishes in less exposed surf zones in the East Cape. (After Lasiak, 1982).

FISH TOTAL PREY TAKEN Number of Species -1 Feeding group Biomass g.m Amount consumed (dry mass) Dominants Other Species or group g.m ^.y

Benthic feeders 78 Macrobenthos 269 Planktivores 60 Mysids/prawns 657 piscivores 10 Zooplankton 200 Omnivores 10 Fish 672 Total 158 Total 1798

at night and studies not employing after there are few published reports on the dark sampling will miss this. ecology of birds on sandy beaches. Most papers simply record counts of waders Surf zone /fish communities are highly and other birds along sandy shorelines. dynamic assemblages with few resident species. They are variable in space and Fitch (1950) recorded gulls dropping time and short term variations in wind, clams to break them and Brunton (1978 ) controlling surf conditions, are recorded guii predation of toheroa probably a major factor controlling clams. Veitch (1980) recorded dead these communities. Most species show a birds on beaches in Nev.7 Zealand and high degree of opportunism in feeding, similar records have been made in and consequently all feeding types may Belgium (Kuyken, 1978) and Britain predate heavily on Zooplankton and (Cadbury, 1978). Prater, Davies (1978) larger schooling crustaceans w hen they recorded sanderling overwintering on are locally abundant. Planktivores, and British beaches, while Schneider, benthic feeders with opportunistic Harrington (1981) demonstrated depletion planktivore tendencies, are therefore a of benthic prey at a migratory stopover major component of surf zone for shorebirds. Burger et al. (1977) ichthyofauna. Fish are important as compared the utilization of an open energy transformers in surf zones and, beach, a sheltered beach and a salt because they are highly motile, are also marsh by migrating birds. There are important in the export of energy from several reports of birds breeding on or the beach/surf zone system. adjacent to beaches, particularly terns (Fuchs, 1977; Davies, 1981; Randall, 7. BIRDS McLachlan, 1982) and plovers (Summers, VJhile some authors have made brief Hockey, 1980). mention of birds as predators on sandy beach benthos (Koepcke, Koepcke, 1952; In South Africa there are several count Brown, 1964; Leber, 1982; Vader, 1982) records for the western Cape. Pringle, 350

Cooper (1977) conducted counts over 18 amounts of insects blowing onto the months which revealed eight migrant and beach and carrion cast ashore. On kelp seven resident species. Summers et al. dominated beaches on the west coast (1977) recorded higher bird numbers on birds are the main predators and were the west coast than the south coast of estimated to take 40% of herbivore the western Cape, presumably due to standing stock (Griffiths et al., greater food abundance in the former 1983). Hockey et al. (1983) summarised area. They recorded 1267 birds over the rôle of shorebirds on sandy beaches 99,6km of sandy beaches and 8319 birds in South Africa. They found diversity over 120,4km of mixed shores. Twelve and abundance of shorebirds to increase wader species occurred on the beaches with latitude. Birds consumed 10-49% of with sanderling (Calidr is alba), white- macrobenthic production in different fronted sandplovers (Charadrius areas and return significant amounts of marginatus ) and black oystercatchers faeces, feathers and carcases to the (Haematopus moquini ) most important. beach system. Resident species averaged 7,3km-'1 and migrants 15,2km-'1' in summer. Summers, Moran, Fischelson (1971) recorded two Cooper (1977) recorded fewer oyster­ plovers, Charadrius hiaticula and C. catchers on beaches than rocky shores alexandr ius, feeding on the raysid and Summers, Waltner (1979) recorded Gastrosaccus sanctus. They found these mass changes in waders, showing most plovers to hunt at random, regardless of species to be heavier in winter. On the the size of the mysids, preferring areas Natal coast Joubert (1981) made counts where mysids were densest. However, over 10 months, recording 14 species and Schneider (1981) reanalysed their data densities of 39km-'1', with waders to show that C. hiaticula selectively making up only 0,52km-1. Terns takes larger mysids. Schneider (1982) roosted on the beach in relatively high studied the foraging behaviour of numbers. turnstones (Arenaria interpres) feeding on Donax variabilis on a florida beach In the Eastern Cape McLachlan et al. and Pienkowski (1982) described diet and (1980) counted birds on three beaches feeding of two plovers on a sand flat in over 12 months, recording 17 species Northumberland. They fed during day and with average numbers of 18,9km-'1 of night and polychaet worms and crus­ which waders accounted for 47%. They taceans dominated in the diet. estimated bird biomass and also food consumption from standard metabolic Myers et al. (1980) analysed the rates for four dominant species which predation of sanderlings on beach made up 95% of numbers. From this they crustaceans in detailed laboratory estimated that birds were taking 32% of experiments. They showed how several available macrobenthic production from variables affect a sanderling's capture these beaches each year. This was rate. Capture is determined by prey mainly - in the form of sand mussels density, the sampling rate and sampling (Donax spp.), mussel siphons, and efficiency. Sampling rate depends on mysids. Birds also took significant penetrability of the substrate and 351

sampling efficiency depends on prey flow between them. The macrofauna are size, depth and substrate part of a larger food web including penetrability. Prey risk varied Zooplankton, fishes and birds, while the inversely with prey depth, 60% of prey interstitisal fauna constitute their own 10mm or shallower being taken and very food web in the sand (McIntyre, Murison, much less below 10mm. Larger prey were 1973; MeLachlan, 1977a; McLachlan et more vulnerable than smaller prey but al., 1981a). The only links between small prey were never rejected. Prey these two food webs is the common input risk was higher where prey organisms of particulate (and probably dissolved) occurred close together. Capture rate organics to both and the possible could be predicted on the basis of prey washing of micro-organisms from the sand size, density and sand penetrability. (Munro et al., 1978 ) to provide food for For prey it was bestto be small, deep filter feeders. In more sheltered in the substratum and not near other situations, however, deposit feeders and individuals. Prey species had no effect sand swallowers may take in large (Excirolana vs. Emerita). However, this amounts of interstitial fauna. Oliver was all done with dead prey. Most et al., (1982) recorded phoxocephalid feeding was ^done without visual cues amphipods feeding on a variety of foods although sanderling may use visual cues including nematodes and Croker (1967b) at times, e.g. when feeding on beach recorded a haustorid amphipod feeding on wrack insects. Although probe location meiofauna, both cases being in sheltered was random it could also be affected by sands. On a lagoon beach Alheit, the feeding patterns of nearby birds. Scheibel (1982) recorded juvenile demersal fish feeding on harpacticoid Wading birds are important predators on copepods. however, as these exchanges sandy beaches, being efficient croppers are mostly negligible on open beaches I of the macrobenthos during periods of look separately at the macrofauna food low tide. On beaches where high inputs web and interstitial energetics. of macrodebris concentrate macrofauna along the drift line above the reach of 8.2 Macrofauna marine predators, birds may be the most Several authors have mentioned aspects important predators. Even birds that of predation or food chains relating to only roost on the beaches may be sandy beaches (Pearse et al., 1942; important where the faecal deposits of Bonnet, 1946; Koepcke, Koepcke, 1952; large flocks may add significant amounts Hedgpeth, 1957; Brown, 1964; Steele et of nutrients locally. al., 1970b; Philips, 1970; Edwards, 1973a, 1973b; Reilly, Bellis, 1978; Ansell et al., 1978; Reilly, 1979; 8. FOOD WEBS AND ENERGY FLOW McLachlan et al., 1981a; Leber, 1982; Gianuca, 1983). Macrofauna food chains 8.1 Introduction start and end in the sea, with the land The macrofauna and interstitial fauna of playing only a negligible rôle, mainly open sandy beaches form two separate in the form of insects blowing onto the communities with little or no energy beach and land crabs, birds and mammals moving onto the beach to feed. Open herbivorous fishes. Ansell et al., beaches are characterized by the absence (1978) uistinguished two groups of of attached plants (Brown, 1964) and macrofauna, (I) herbivores and primary production by the benthic detritivores and (2) carnivores. microflora is generally negligible. On McLachlan et al., (1981a) separated only a sheltered temperate beach, however, filter feeders and scavengers/predators Steele, Baird (1968) found viable on Last Cape beaches, where deposit diatoms mixed to 20cm depth in the sand feeders were of negligible importance. and primary production low but On kelp dominated beaches Griffiths et measurable. They considered vertical al. (1983) uistinguished herbivores, mixing due to wave action to be the main carnivores and filter feeders. The limiting factor. In the shallow possible food sources and trophic groups subtidai off two Venezuelan beaches, of raacrofauna on sandy beaches are Edwards (1973a) recorded significant listed in Table 5. benthie primary production due to both micro- and macro-algae (2943 and 6500 Zooplankton, which are extremely import­ — 2 —1 kcal.rn y at two beaches) but ant in surf water, although largely these areas are hardly typical of open ingored to date, would fall in cate­ beaches and the latter area wassubject gories (1) and (4). On most sandy to heavy pollution. Primary production beaches food source (1) is by far the in the water column may be very most important, with food sources (3) important, particularly where surf and (4) being next. On sheltered phytoplankton blooms occur. Unfor­ shores, however, particulate detritus tunately primary production figures for and living microflora and fauna may be a surf phytoplankton bloom have yet to of most importance once incorporated in be published. Edwards (1973a) estimated the sediments, and under such conditions primary production in the water column deposit feeders such as Arenicola, off Venezuelan beaches as Call janassa and Scolelepis may be 2 9 3 4mgC.m~2. d_1. abundant.

Different authors have partitioned food While inputs of particulate matter to sources for sandy beaches in a variety beaches have yet to be measured, some cf ways. Brown (19 64) distinguished an estimates are available based ori the erratic supply of macrodebris and a requirements of the macrofauna. In regular supply of particulates while India particulate feeders accounted for Hayes (1974) recognised dissolved and 56141 kj.m 2y 1 and carnivores for microparticulate organics, stranded 4291 kj.m. 2y ^ on Sherfallai beach plankton and large organic masses. and 38765 kj.m-1.y-1 and 235kJ. Edwards (1973a) distinguished three main m y at Cochin beach respec­ pathways by .which energy travels from tively. particulate feeders thus primary foods to fishes; (1) via Zoo­ accounted for 91% of the food plankton to plankton feeding fish, (2) consumption on average (Ansell et al., via benthos to demersal fishes and (3) 1978). In the Last Cape, filter feeding directly from benthic algae to macrofauna were estimated to assimilate Table 5. Food sources and trophic groups of macrofauna on open sandy beaches.

FOOD SOURCE______FEEDING GROUP

1. particulate organics including phytoplankton Filter feeders

2. Deposited detritus, benthic diatoms, interstitial fauna Deposit feeders

3. Stranded debris - plants Scavengers - herbivores - animals - carnivores

4. Other fauna Predators

109421 kJ.m-'i.y-±, 93% of the total and fly larvae (Muir, 1977; Koop, Field, for the beach macrofauna, with 1980, 1981; Stenton-Dozey, Griffiths, scavenger/predators making up the 1980; Griffiths, Stenton-Dozey, 1981; remaining 7% ^(McLachlan et al., 1981a). Koop et al., 1982a; Griffiths et al., This does not include Zooplankton 1983). Biodegradion of macrophytes by organisms which are mainly filter the macrofauna is thus very important. feeders and very abundant. Scavengers are only important where there are large In sheltered localities or where large inputs of debris or where filter feeders amounts of particulate organics are are absent because of unstable physical deposited, deposit feeders may reach conditions or the absence of food (e.g. high biomass values (Eleftheriou, East Coast of South Africa, Dye et al., McIntyre, 1976? McDermott, 1983). On 1981; Wooldridge et al., 1981). most beaches organic content of the sand is very low, e.g. 0,2-0,4mg. g-"'" sand Huge inputs of macrophytes characterize in Scotland and India (Steele, 1976) and beaches adjacent to kelp beds or similar undetectable amounts in the West Cape areas. In southern California Hayes and East Cape (Brown, 1971a; McLachlan, (1974) estimated these inputs to amount 1977a). to 473kg wet (ca.78kg dry) algae m -J'.y-'*' ( Macrocystis ) , while on West Predators on the other benthos include Cape beaches adjacent to kelp beds crabs, starfish and gastropods. These values range around 2000kg wet Ecklonia normally occur in relatively low m'^.y-^ (Koop, Kield, 1980; Koop et abundance, making up 5-10% of biomass. al., 1982a; Stenton-Dozey, Griffiths, As many are supralittoral forms, e.g. 1983; Griffiths et al, 1983). While Ocypode, they may be the only macrofauna Hayes (1974) found Tylos punctatus to where swash conditions are too dynamic consume only 4-5% of the edible kelp for intertidal macrofauna to survive input, estimates for macrofauna (Gauld, Buchanan, 1956; Dye et al., consumption in the West Cape range 9-74%, 1981). They generally take both living this being taken by isopods, amphipods benthic prey and stranded carrion. 354

Energy flows through different species These food chains end in fishes, birds, and trophic efficiencies vary widely. crabs and other invertebrate predators Turnover (P/B) ranges from 0.3 for and man. Very lew studies have Tellina tenui s on a temperate beach estimated the importance of these (Trevallion, 1971) to 10.3 for Donax different predators. in Scotland spiculum on a tropical Indian beach juvenile flatfish are the most import­ (Ansell et al., 1972b). Ansell et al., ant predators, cropping siphons of (1978) found turnover on these tropical bivalves, palps of polychaetes and whole beaches generally ten times higher than prey. Bivalves may then put more energy on cold temperate Scottish beaches. into regeneration of siphons and less in­ Edwards (1973a) recorded average P/B's to reproduction. Trevallion (1971) of 2.8-3.5 for the macrobenthos, estimated that up to 1.3% of total McLachlan et al., (1981a) used P/B's of annual energy expenditure in Tell ina G.5-5.0 for somatic production of tenuis may go into regenerating molluscs and crustaceans, and Koop, siphons. In India crabs were considered Field (1981) estimated the P/B for Ligia the most important predators, with dilatata at 3.75 times per year. fishes and man less important and birds virtually absent (Steele, 1976; Ansell Assimilation efficiencies * et al., 1S78). Edwards (1973a) 100%) vary widely, commonly being very estimated fish to account for 71-89% of low for scavengers/grazers feeding on production at his two beaches, starfish abundant macroalgae, e.g. 64% for Tylos accounting for 13% on one and crabs for (Hayes, 1974), 5.5% for Ligia (Koop, 13% on the other beach. McLachlan et Field, 1981) and 30-50% for Talorchestia al., (1981a) partitioned predation on and fly larvae, (Stenton-Dozey, east Cape Leaches. Birds took 32% of Griffiths, 1980). Koop et al., (1982a) intertidal macrofauna production estimated an overall average (McLachlan et al., 1980), fishes were assimilation efficiency of 22% for estimated to take 55% and benthic invertebrate kelp grazers while Ansell predators (mainly crabs, Ovalipes) 10% et al., (1978) and Edwards (1973a) with man accounting for less than 3%. assumed assimilation efficiencies of 8 0% Du Preez (1981) has subsequently made a for carnivores and 60% for herbivores. detailed investigation of the predation Ansell et al., (1978) estimated of Ovalipes on Donax and Bullia and efficiencies of transfer of energy Lasiak and Rossouw (1983) have studied through the food chain (P/. X 100%) fish predation. On kelp dominated A as 15-16% for herbivores and beaches of the West Cape, however, birds detritivores and 25-30% for carnivores are the major predators (Griffiths et in India while Edwards (1973a) estimated al., 1983). P/c X 100% as 15% for benthos, 17% for demersal fish and 11-15% for other Evaluating our knowledge of sandy beach fish at his unpolluted site. Ecological food chains as a whole is made difficult efficiencies calculated from McLachlan by not only the small number of et al. (1981a) were 9-19% for the quantitative studies, but also the macro-fauna with a mean of 17%. absence of data on Zooplankton. The 355

macrofauna cannot be considered in iso­ To conclude this section on macrofauna lation when describing these food energetics it appears that five main chains. Surf zone Zooplankton beach types can be recognised in terms production, also untimately falling prey of macrofauna energy flow patterns to fishes and being exported from the (Table 7). Information on surf zone system, is probably more important in Zooplankton in different zoogeographic terms of energy flow. In the East Cape regions is unfortunately not available for example, where we have some idea of to allow incorporation into this scheme. surf zone Zooplankton biomass, a It may be expected, however, that as different pattern emerges if larger zoopolankton and macrobenthic filter mobile crustaceans, such as mysids and feeders utilize the same food resources, prawns, are included with Zooplankton their total biomass would be roughly out to 500m from the beach (Table 6). similar in many cases.

Table 6. Summary of approximate f aunal 8.3 Interstitial Fauna dry biomass for an average beach and Less attention has been paid to surf zone in the East Cape. (From interstitial energetics, although as McLachlan, 1S83) early as 1942, Pearse et al., proposed that the interstitial systems of sandy BIOMASS beaches had digestive and incubating CATEGORY g .m-^ functions, the microfauna mineralising organic materials in the sand. Little attempt was made subsequently to Macrobenthos 1500 evaluate or quantify this until quite Zooplankton 1100 recently. This system consists Birds 5 typically of bacteria, protozoans and Fi shes 300 meiofauna constituting their own food web in the sand.

The food chain is centred around filter Dissolved and fine particulate organics feeding benthos and Zooplankton feeding form the base of this food chain, on particulate detritus and phyto- although in sheltered situations the piankton ana being taken in turn by benthic microflora might also play a fishes, birds and crabs. As Zooplankton role. McIntyre et al., (1970) were the turnover is 6-7 times that of the first to demonstrate that interstitial macrofauna, the centre of gravity of the fauna could subsist on oissolved food chain is clearly in the surf and organics. Using two experimental sand not on the beach. McFarland (1963) came columns, they maintained viable micro- to a similar conclusion, showing that and meiofaunal populations in the second plankton was the predominant fish food column on the effluent leaving the first off Texas beaches, greatly exceeding the column. They suggested that bacteria benthos as an available food source. The were the prime utilizers of cissolved surf zones he studied were characterized organics, utilizing these organic mole- by high primary productivity in summer. cules when they adsorb onto sand grains 356

Table 7. Major beach types in terms of macrofauna energetics.

Predominant Food Macrofaunal Dominant Type Latitude Sources Biomass Trophic Group Predators

1. High turnover, Tropical Particulates Low to Filter Invertebrates particulate- moderate Feeders Fishes based food chain

2. Low turnover, temperate Particulates Low to Filter Fishes, Birds particulate- high Feeders Invertebrates based food chain.

3. Macrodebris- temperate Stranded Moderate Scavengers/ Birds based food macrophytes Grazers chain.

4. Sediment-based Temperate Deposited detritus Low to Deposit Birds, Fishes food chains in or microorgan isms and high Feeders Invertebrates sheltered Tropical benthic microflora beaches.

5. Carrion-based Temperate Stranded carrion Low Scavengs food chains in or Predatoi extremely ex- Tropical posed steep beaches.

where they can be digested with extra­ some meiofaunal species may feed cellular enzymes. The meiofauna in turn directly on detritus, microflora or fed mainly on these bacteria, accounting dissolved organics, in a broad sense for approximately 5% of bacterial con­ meiofauna do form the top of the inter­ sumption. stitial food web as most species feed on bacteria, protozoa or other meiofauna Fenchel (1972) considered bacteria the (McIntyre, Murison, 1973; McLachlan et only primary decomposers of particulate al., 1981a). The position of protozoans plant detritus with their decomposition in this system lias been little studied rate limited by oxygen and nutrients. in open beaches; while some forms may Consequently he suggested that higher have a similar trophic status to trophic levels in the interstitial food bacteria, others are even predatory on web are dependant on initial processing meiofauna. However, in a broad sense of plant detritus by bacteria. Although they probably occupy a position inter­ 357

mediate between, and overlapping with, (1977) and Dye (1983). Another approach bacteria and meiofauna in interstitial has been the study of experimental sand food chains. columns in the laboratory.

Three trophic types may be recognised Several authors have maintained within the meiofauna, predators, laboratory sand microcosms for extended herbivores and bacterivores, with only periods (McIntyre et al., 1970; Pugh, the Hydrozoa and Turbellaria exclusively 1976; Boucher, Chamroux, 1976; Chamroux predatory (Tiet jen, 1980 ). Swedmark et al., 1977; Wormald, Stirling, 1979; (1964) however, listed four categories, McLachlan et al., 1981c). A closed predators, diatom and epigrowth feeders, circuit system has been successfully detritus eaters and suspension feeders. maintained for 16 months on soluble Besides direct grazing of meiofauna on amino acids (Boucher, Chamroux, 1976) the microfauna, Tietjen (1980) con­ confirming the utilization of dissolved sidered that meiofauna stimulate organics by microorganisms and their bacterial activity in the interstitial subsequent consumption by the meiofauna. system by (1) mechanical breakdown of However, changes in meiofaunal community detritus, making it more susceptible to structure (decreased diversity) bacterial colonisation, (2) excretion of indicated that the utilization of nutrients for microbial use, (3) soluble organics via bacteria was not secretion of mucous thereby attracting the only trophic path to the meiofauna. bacterial growth and (4) movement In this case bacteria and meiofauna were conveying nutrients and oxygen. estimated to account for 95% and 5% of Assimilation efficiencies x the carbon input respectively, the same 100%) for meiofauna have been estimated proportions as found by McIntyre et al. in the range 6-26% while transfer (1970). TD efficiencies (" / x 100%) were 79-97% for three nematode species There have been few detailed studies of

(Tietjen, 1980). For turnover ( ?/D ) interstitial energy budgets in situ on D a ratio of 10 has been widely used for open beaches. The three cases that meiofauna (Gerlach, 1971). warrant attention concern a comparative study of Scottish and Indian beaches, Because of the difficulty of scale when studies on high energy beaches in the working with the minute inhabitants of Eastern Cape and studies on beaches the interstitial fauna, investigations receiving high kelp inputs in the of interstitial energetics have Western Cape. generally taken the form of 'black box' studies of the system as a whole. This Munro et al. -(1978) made a detailed has commonly been done by measuring comparative investigation of inter­ interstitial or benthic oxygen consump­ stitial ’ dynamics on tropical Indian tion in situ and then attempting to beaches (Md 150-I90um) and Scottish partition this. Benthic oxygen consump­ beaches (Md 250um) using small and large tion measurements have been discussed sand columns and .in situ measurements. and reviewed by Lassere (1976), Pamatmat The tropical beach lacked epipsammic diatoms which were common on the temper­ organic levels were 500-1000 ug c.l 1 ate beach. Dissolved organics were in Scotland and 900-3700 ug.l-1 in estimated to make up 80% of the input on India. However, surf flushing of the the Scottish beach and 39% on the Indian Indian beaches may remove significant beaches. Interstitial community respir­ quantities of bacteria, thus making them ation on the tropical beach (164gC. available to macrofauna filter feeders -2 -1 m .y ) was nine times the winter and decreasing the quantity available to values and twice the summer values for the meiofauna. _ ? the temperate beach (mean = 42gC.m . y -1) with microbial production In the Last Cape the interstitial fauna -_ O2 -1 estimated to be 72 gC.m .y in the consists essentially of meiofauna, former and an annual average of protozoans and bacteria to considerable 15g.C.m 2.y 1 in the latter (using depth in the sand (Dye, 1979a; McLachlan respiration figures based on an assumed et al., 1979a). Dye (1980) showed tidal conversion efficiency of 45% and the fluctuations in benthic oxygen consump­ assumption that the contribution of tion as a result of tidally induced meiofauna was negligible). Meiofauna changes in pore moisture and interstitial biomass was, however, much higher on the water flow, lowest values being recorded Scottish beach (273-523mg. m-2) than when the sand dried out. Dye (1979a) the Indian beach (24-6Omg.m-2)(Table investigated biological oxygen demand in 8). They postulated that more vigorous beach sand, using intact sand cores in flushing of the sand on the tropical the laboratory as these gave higher Indian beach both boosted respiration values than _in situ techniques. He and striped bacteria from the sand showed that disturbance caused a g rains. significant increase in oxygen uptake.

The tropical beach received more In a more detailed study Dye (1981) organics and had a higher interstitial later partitioned this oxygen uptake oxygen consumption rate than the between bacteria, protozoans and Scottish beach as a result of increased meiofauna on two beaches (Table 9). water flow by wave flushing. Surf

Table 8. Biomass, production and respiration of interstitial organisms on Scottish

- 2 — 1 and Indian beaches. (After Munro et al., 1978). All values in gC.m .y .

INDIA SCOTLAND Respiration Production Biomass Respiration Production Biomass

Algae 0 0 7 Microfauna 160 72 31 15 Meiofauna 4 2 0.02 4 2 0.2 359

Table 9. Partitioning of interstitial oxygen uptake on two East Cape beaches. (After Dye, 19 81).

MODERATELY EXPOSED BEACH VERY EXPOSED BEACH Biomass % O^ uptake % Biomass % 0^ uptake %

Meiofauna 75 18 79 21 Protozoa 19 18 17 24 Bacteria 6 64 4 55

In the West Cape very rich interstitial rapidly. The great significance of populations develop on beaches with high these microbes indicates why Hayes kelp inputs. Koop, Griffiths (1982) (1974) recorded such little kelp recorded dry biomass of 241, 200 and 663 breakdown in California where he looked g . m -'*' of macro- meio- and microfauna at only one grazer, Tylos punctatus. respectively. Bacteria were concen­ trated at lower tide levels, probably 8.4 Conclusions subsisting on small particles of broken It may be concluded that intertidal down kelp resulting from feeding and sandy beaches are important in the faeces of macrofauna and meiofauna. processing of organics whether these be Koop et al., (1982a) quantified carbon as DOM, POM or larger animal and plant flow through this system. Bacteria on remains. These foods generally come the stranded fronds were responsible for from the sea and in turn most production much initial degradion. Breakdown of returns there. The interstitial fauna the kelp resulted in high concentrations are always more important than the of leachates (up to 5640 m g C . l -'*') in macrofauna in this mineralisation of the sediment below the kelp. Over 90% organic materials, even where a rich of this was utilized by bacteria after macrofauna occurs (Table 10). seeping through lm of sand and 23-27% of carbon in the kelp was converted to The interstitial system is driven by bacterial carbon. The ratio of increase inputs of soluble and particulate in bacterial biomass to kelp carbon used organics, the main path being via was 58.7%, giving a conversion bacteria attached to sand grains to efficiency of 29.4% if bacterial biomass meiofauna. The intermediate rôle of is 50% carbon (Koop et al., 1982a). protozoans is uncertain. On exposed Much of the faeces of invertebrate beaches there is little exchange between grazers were also converted to bacterial this sytem and the macrofauna although carbon as these grazers have low the importance of microorganisms flushed assimilation efficiencies. The from the sand as food for the macrofauna remaining 73-77% of the kelp was needs further investigation. The mineralised by the microbes quite concentrations of meiofauna flushed from 360

Table IO. Approximate partitioning of total benthic assimilation between macrofauna and interstitial fauna in four geographic areas based on data in Munro et al. (1978) Ansell et al. (1978), McLachlan et al. (lS81a) and Koop, Griffiths, (1982).

ASSIMILATION f k J.m 1.y 1 (%) ]

LOCALITY AND BEACH Macrofauna Interstitial BEACH WIDTH TYPE fauna ( m)

Scotland, temperate 30 000 ( 23 ) 99 000 (77) 6 0

India, tropical 427 000 ( 38) 703 000 (62) 60

East Cape, warm temperate 116 000 ( 37) 236 000 (63) 60

West Cape, temperate 42 000 (3) 1599 000 (97) 63 with high kelp input

the sand of exposed beaches were 9. NUTRIENT CYCLING measured by McLachlan (1977a) and found It has long been speculated that beaches to be negligible. On sheltered beaches may be of importance in recycling a greater size spectrum of organisms may nutrients by mineralising organic occur, filling the gap between inter­ materials comingfrom the sea (Pearse et stitial fauna and larger macrofauna and al., 1942). This is effected by the thereby facilitating energy flow by fauna consuming organic nutrients predation. In such environments deposit including nitrogen anu phosphorous and feeders may also ingest significant then excreting this in inorganic form, quantities of interstitial fauna. e.g. In some areas Inshore food chains in beach environ­ groundwater seepage can, however, also ments are however centred in the surf supply considerable amounts of inorganic zone rather than the intertidal, even nutrient via the beach to the surf zone. where rich intertidal macrofaunas occur. This can take the form of both artesian Our area of least understanding at the aquifers arid general seepage around the moment is these dynamic food chains of area where the permanent water table the surf zone and in particular the role meets the sea. Johannes (1980) found of Zooplankton and larger motile this to be very important in Western crustaceans. Australia where submarine groundwater 361

discharge ranged l-5m.y ^ and con­ nitrogen (Chamroux, 1965; McIntyre et tained up to 380 ug at 1 ^ NO^-N. al., 1970; Pugh, 1976; Boucher, Chamroux, 1976; Cahet, 1976; Wormald, Nutrient regeneration by the macrofauna, Stirling, 1979; Munro et al., 1978; Zooplankton, birds and fishes has been McLachlan et al., 1981c). Generally virtually ignored. Lewin et al., nitrification is the dominant activity (1979b) and Prosch, McLachlan (1983) in beach sand and organic nitrogen is respectively investigated ammonia efficiently mineralised to nitrate. excretion in bivalves of the genera Increasing organic loading tends to Siliqua and Donax on beaches in raise equilibrium levels and it is Washington and the East Cape, South usually only at very high levels that a Africa. In both cases very large beach can not cope and anoxic conditions populations of these bivalves develop and ammonia appear (Oliff et al., 1970; and nutrients regenerated by them could Pugh, 1976). Boucher, Chamroux (1976) be of significance in supplying recorded total mineralisation of amino phytoplankton requirements in the surf acids added to their sand columns while zone. Hayes (1974) found Tylos to Munro et al., (1978) recorded 70% consume only 4-5% of kelp input on mineralisation of natural organics, Californian beaches while Griffiths, mostly in the top 5cm of their columns. Stenton-Dozey (1981) and Koop et al. McLachlan et al. (1981c) found 35% (1982a) estimated that 9-74% of stranded mineralisation of natural organics in kelp was consumed by the macrofauna. 50 cm sand columns and this increased to Not all of this is assimilated, however, 65% when amino acids were added. and low assimilation efficiencies may result in a comparatively small Most of these sand column studies have prop¿rtion of kelp nitrogen being been somewhat artificial as water flow regenerated directly by the macrofauna. has been unrelated to in_ situ flow The contribution of other faunal com­ rates, there has been continuous submer­ ponents must also be important in this gence, and inputs have been constant regard but have yet to be investigated. rather than tidal or pulsing. Except­ ions are Pugh (1976) and McLachlan et Generally the interstitial system of al. (1981c), although even these experi­ sandy beaches has been thought more ments did not incorporate pulsing important in nutrient regeneration than flows. Filtration rates have ranged -2 -1 the macrofauna. Water filters through 25-1000 l.m .d , covering a variety the sand, as a result of tides and waves of flows both intertidal and subtidal. both in the intertidal and the subtidal, and DGM and POM are removed by the McLachlan (1982) followed up earlier interstitial fauna and mineralised. sand column work with a model of water filtration and nutrient regeneration by Several studies of experimental systems sandy beaches. This was based on a of sand columns or model beaches have regression model predicting filtration looked at mineralisation and/or nutrient volume as a function of sand particle regeneration, mostly concentrating on size, beach slope and tide range. 362

Coupled to this was an estimate of the to rocks and subject to larye kelp degree of mineralization of organics in inputs are interesting for comparison. relation to sand particle size and the filtration distance. The average It may therefore be concluded that sandy filtration distance is about 35% of the beaches can mineralize most organics horizontal intertidal distance (Riedl, they receive, the bulk of this being Machan, 1972) and average mineralisation done very efficiently ( 80-100%) by the was estimated to be at least 60-80%. At interstitial fauna. This is a filtration rate of 1041 .m-1.d_1 accompli shed by the process of water and an organic nitrogen level of 0.15mg. filtration through the beach and will be I- '*' this predicted regeneration of greatest where steep beaches and short 0.9g NO -N m-1.d-1. An attempt to period waves result in high filtration estimate total nutrient production by volumes (e.g. in the tropics). Where beaches in the East Cape was made by vast macrofauna populations occur they McLachlan et al. (1981a). They estimated may also contribute significantly to nitrogen excretion by the macrofauna and nutrient regeneration. Zooplankton, interstitial fauna of the beach and surf birds and fishes must also be very zone at 35OgN.m-^.y-"*- and 591gN. important. m ' ^ . y -^ respectively. Thus, even on beaches such as these with very high Most organic nitrogen and phosphorous macrofauna biomass, the interstitial supplied to a beach will rapidly be fauna are more important in nutrient returned to the surf as nitrates, regeneration, accounting for 63%. While ammonia and phosphates. Thereafter the only approximate, the above figures fate of these nutrients will depend on suggest that the mineralising activities physical conditions in the surf zone. of the benthos alone can replenish the Where cellular circulation patterns occur nutrient pool of the surf zone in a there may be a high degree of retention, matter of days or weeks. while on irregular coasts or reflective beaches, exchange with the open sea may Koop et al. (1982b) quantified micro­ be much more rapid. As many surf zones bial regeneration of nitrogen from are characterized by high primary stranded kelp over an eight day cycle. productivity7, utilization of beach In this time the microbes incorporated generated nutrients in the surf zone may 94% of the kelp nitrogen, which normally be very important and is in need of more strands at an average input of attention. Hayes (1974) and Koop et al. 12gN. m -"'-. d-’*'. However, in the long (1982b) consider such nutrients of term the beach can not act as a nitrogen little importance in the surf while sink and this must return to the sea. McLachlan et al. (1981a) suggest that In this case this could supply roughly these nutrients may be sufficient to one quarter of the nitrogen requirements maintain surf phytoplankton blooms on of phytoplankton in the adjacent kelp long open beaches. beds. While hardly typical of open beaches, even on the west coast (Bally, 10. TOWARDS A MORE HOLISTIC APPROACH 1981), these figures for beaches adjacent This review has attempted a functional 363

look at our present knowledge of the Energy flow and nutrient cycling in a ecology of beach/surf zone environments long open beach typical of the Last Cape as a whole, incorporating all aspects of is illustrated in tig. 9. This is a fauna and flora, energy flow and rich system with considerable flows of nutrient cycling. Unfortunately, most energy and nutrients. It includes published studies of beach environments producers (phytoplankton), consumers have not attempted such a holistic (benthos, Zooplankton, fishes) and approach and have tended to investigate decomposers (interstitial fauna). one or more components in isolation. Energy flows within this system appear to be greater than across its In the East Cape research on beach boundaries. However, although exchange environments has been unique in across the dune/beach boundary is attempting a holistic approach towards negligible, exchanges across the outer the quantification of energy flow and boundary of the surf cells remain to be nutrient cycling under the concept of a quantified. The main trophic pathway is beach/surf zone ecosystem. This is from fine organic materials (POM and based on two contentions (McLachlan, phytoplankton) via Zooplankton and 1980c): (1) that the sand body of the filter-feeding macrofauna to fishes. beach together with the water envelope The interstitial fauna is also extremely of the surf zone form an ecosystem where important in mineralising POM and DOM. internal energy flows are greater than The total amount of inorganic nitrogen exchanges across boundaries and (2) that regenerated by the beach and surf zone this system has definable bounds ries, fauna is not yet known, but must be sub­ these being the drift line on the stantial as the macrofauna and inter­ landward margin and the outer limit of stitial fauna alone can regenerate surf circulation cells on the seaward enough to replenish the surf zone margin. The central concept is that the nutrient pool within a few weeks to circulation cells that typify the surf days. Although not indicated in Fig. 9, zones of open beaches (Inman, Brush, wave action probably represents the most 1973) imply a certain measure of important factor controlling this system, integrity of surf zone water and as it is responsible for transporting retention of materials within this water, sediment and biological zone. This is in opposition to the idea materials, driving surf circulation that beaches are purely high energy cells and pumping water through Leach interfaces between sea and land. sand. Clearly, however, this can not apply to pocket beaches, beaches associated with Clearly, not only biological and rocky shores or beaches dropping chemical information is needed to directly into deep water where there is understand beach/surf ecosystems. Water no real -surf zone. The kelp input movement, the- key to all dynamic beaches of the South African west coast, processes occurring here, is the realm for example, function as interfaces of the physical oceanographer. The between adjacent kelp beds and the land. discreteness of surf circulation boundaries and exchanges across them 364

SEA SURF BEACH DUNES

EXPORT OTHER

OTHER BENTHIC + PISCIVO- 1837 OURCE PLANKTON ROUS FISH FEEDING 1000 FISH 4000 4570

SCAVEN BIRDS IMPORT 8337 6500 600 I EXPORT 5120 CARRION 90

ZOO­ PLANKTON OMNIVORE 6000 3000 20000

NSECTS

FILTER FEEDERS HYTOPLANKTO 280 13

89269 \

INTER IMPORT ORGANIC POM 8 STITIAL FAUNA 1890

591 g N NUTRIENT)« POOL U 350 g N

OUTER LIMIT OF SURF DRIFT LINE CIRCULATION CELLS

FIGURE 9. Energy flow (solid lines) and nutrient cycles (broken lines) for a typical East Cape beach, largely after McLachlan et al. (1981a). All values in kJ.m^.y ^ except nutrient values in g inorganic N. need to be quantified. It is therefore ecosystems, and this can only be essential that pnys i cal oceanographers, evaluated in the presence of a detailed biologists and chemists work together. knowledge of the physical and chemical Beaches in different geographic areas envi ronment. need to be studied in this fashion.

Biologists in particular must not only REFERENCES study the intertidal fauna, but must Achutankutty CT (1976) Ecology of venture out into the surf zone. In the sandy beach at Sancoale, Goa: Part 1. dynamics of fine organic materials, Physical factors influencing production of macrofauna, Indian J. mar. Sei. 5, phytoplankton and Zooplankton lies the 91-97. key to a more realistic understanding of Alikunhi KH (1944) The zonal distri­ bution of the mole crab (Emerita the function of sandy beach/surf zone 365

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