355 6 Energy Flow, Food Webs, and Material Cycling CONTENTS 6.1 Introduction 356 6.2 Food Sources 356 6.2.1 Hard Shores 356 6.2.2 Soft Shores 358 6.3 Energy Budgets for Individual Species 360 6.3.1 Introduction 360 6.3.2 Suspension-Feeding Bivalves 361 6.3.3 Scope for Growth 365 6.3.4 Carnivorous Molluscs 366 6.3.5 Grazing Molluscs 367 6.3.6 Deposit-Feeding Molluscs 371 6.3.7 Fishes 373 6.4 Optimal Foraging 374 6.4.1 Introduction 374 6.4.2 Optimal Diets 374 6.4.3 Optimal Patch Use 376 6.5 Secondary Production 377 6.5.1 Macrofauna 377 6.5.2 Micro- and Meiofauna 377 6.5.3 A Comparison of the Macrofaunal and Meiofaunal Standing Stock and Production Across a Rocky Shore 378 6.5.4 Relative Contributions of the Benthic Macrofauna, Permanent and Temporary Meiofauna, and Mobile Epifauna to Soft Shore Secondary Production 379 6.6 P:B Ratios and Production Efficiency 380 6.7 Relative Contribution of Soft Shore Benthic Infauna to Secondary Production 381 6.8 Community Metabolism 385 6.9 Trophic Structure and Food Webs 389 6.9.1 Introduction 389 6.9.2 Hard Shores 389 6.9.2.1 Coastal Water–Rocky Shore Interactions 389 6.9.2.2 Hard Shore Ecosystem Models 390 6.9.2.2.1 Northeastern Atlantic shores 390 6.9.2.2.2 South African littoral and sublittoral ecosystems 390 6.9.3 Soft Shores 395 6.9.3.1 Exposed Beaches 395 6.9.3.1.1 Examples of macroscopic food webs 395 6.9.3.1.2 Energy flow in beach and surf-zone ecosystems 398 6.9.3.1.3 The sandy beaches of the Eastern Cape, South Africa 399 6.9.3.2 Tidal Flats 400 6.9.3.3 Beach Wrack Communities 401 6.9.3.4 Estuarine and Coastal Soft Shore Food Webs 403 6.10 Carbon Flow Models 406 6.10.1 A Salt Marsh Ecosystem in Georgia 406 6.10.2 Barataria Bay Marsh-Estuarine Ecosystem 407 6.10.3 Upper Waitemata Harbour Carbon Flow Model 407 6.10.4 Interstitial Communities 410 © 2001 by CRC Press LLC 356 The Ecology of Seashores 6.11 Stable Isotopes and Food Web Analysis 412 6.12 Top-down and Bottom-up Control of Trophic Structure 421 6.12.1 Introduction 421 6.12.2 Top-down and Bottom-up Community Regulation on Rocky Shores 422 6.12.3 Trophic Cascades 423 6.1 INTRODUCTION In this chapter we shall first look at food sources in the intertidal zone. Then we shall examine energy budgets for intertidal animals, leading to a discussion of the trophic structure and food webs of intertidal ecosystems, on both soft and hard shores. Early models of these processes in the coastal zone assumed linear food chains of the Lindeman (1942) type, consisting of phytoplankton, zooplankton, benthos, and fish (Clarke, 1946; Riley, 1963). The compartments of such models were equated with trophic levels and ecolog- ical efficiency transfers were used to evaluate energy flux. Ryther (1969) attempted to show how fish production was limited by the number of transfers of energy from one trophic level to another. Steele (1974) developed a com- partmental bifurcated model with one pathway involving phytoplankton, zooplankton herbivores, zooplankton car- nivores, and pelagic fish; and the other pathway involving fecal pellets, bacteria, benthic meiofauna, benthic macro- fauna, epibenthos, and demersal fishes. This model pointed out two unknown factors: first the efficiency of the bacteria in breaking down organic matter, and second the trophic link between the meiofauna and the macrofauna. In a landmark paper, Pomeroy (1979) presented a com- partmental model of energy flow through a continental shelf ecosystem postulating the potential for substantial energy flow through dissolved organic matter (DOM), detritus (POM), and microorganisms to terminal consumers. This model was further developed by Pace et al. (1984). Both of these models have previously been discussed in Chapter 3. These models involved the abandonment of the classical idea of trophic levels and replaced it with the concept of food webs as anastomosing structures that defy classifica- tion into trophic levels. Pomeroy demonstrated that it was possible for energy to flow either through the grazer, or alternate pathways, to support all major trophic groups at a reasonable level and to maintain fish production at about the levels commonly seen. As discussed earlier, benthic microalgal production, organic detritus, dissolved organic matter, the microbial community, and the meiofauna play more important roles than had been previously thought. 6.2 FOOD SOURCES 6.2.1 H ARD SHORES The food resources available on hard shores can be sub- divided into the categories listed in Table 6.1. The princi- pal in situ primary producers are the benthic microalgae growing on the rock surfaces, barnacle tests, molluscan shells and other hard surfaces, and on the attached mac- roalgae. The contribution of the benthic microalgae depends on the availability of suitable surfaces for their growth and the level on the shore. At certain times the sporelings of the attached macroalgae are an important component of the microalgal films. The production of the benthic microalgae is highly variable, depending on the species composition (which varies geographically), the intertidal level on the shore, and competition. Microalgal films are grazed by gastropod molluscs (especially lim- pets, top shells, and chitons), and some fish species. The attached macroalgae are consumed directly by a variety of molluscs (limpets, top shells, chitons, abalones), sea urchins, crustaceans (especially isopods and amphipods), and fishes. Many algal species are highly productive, e.g., on an exposed rocky shore on the West coast of South Africa, Gibbons and Griffiths (1986) recorded a maximum algal standing crop of 403 g m –2 . Many epifaunal crusta- ceans are adapted to feed on particular parts or tissues of algal species. However, some macroalgae have developed chemical defense mechanisms to limit grazing. Bustamante et al. (1995) have documented in situ production of coastal phytoplankton, epithithic microflora (chlorophyll a production cm –2 month –1 ) (Figure 6.1) and the standing stock of the different functional groups of macroalgae around the South African coast (Figure 6.2). A well-documented productivity gradient exists in the pelagic ecosystem around southern Africa, due to the exist- ence of strong upwelling on the west coast and its virtual absence on the east coast (e.g., Shanon, 1985; Branch and Branch, 1981; Moloney, 1992) (see Figure 2.12). In a review of the published productivity data for the Benguela and Agulhas ecosystems, Branch and Branch (1981) dem- onstrated the existence of this gradient for water lying inshore of the 200 m isobath. The northwestern coast is highly productive, supporting chlorophyll biomass up to 16.43 mg chlorophyll a m –3 , whereas intermediate concen- trations (about 5.0 mg chlorophyll a m –3 occur off the south- western and southern coasts. Off the southeastern coast, chlorophyll concentrations are an order of magnitude lower than the northwestern coast (<2.0 mg chlorophyll a m –3 ). Primary production of the intertidal epilithic microal- gae showed a similar pattern to that of the phytoplankton (Figure 6.1) and was correlated with nutrient availability. The dominance patterns of the different functional groups of macroalgae changed around the coast (Figure 6.2), with © 2001 by CRC Press LLC Energy Flow, Food Webs, and Material Cycling 357 TABLE 6.1 Food Sources on Hard Shores Food Type Source Consumers Remarks Benthic microalgae Microalgal films on rocks, mollusc shells, etc. Microfauna Meiofauna Gastropod molluscs, fish Principally limpets Phytoplankton The sea Filter feeders Principally bivalves and barnacles Water column bacteria The sea Filter feeders Water column particulate organic matter The sea Filter feeders and detritovores Bivalves, amphipods, and other crustaceans Water column dissolved organic matter The sea Detritus Intertidal rocks, sea grass beds Detrital consumers Water column micro-zooplankton The sea Filter feeders Attached macroalgae Intertidal rocks Crustaceans, and molluscs Principally amphipods, gastropods, and sea urchins Intertidal sea grasses Intertidal rocks Meiofauna Intertidal rocks, macroalgae Meiofauna, invertebrate consumers, fish Macrofaunal invertebrates Intertidal rocks Invertebrate and vertebrate consumers FIGURE 6.1 Seasonal epilithic chlorophyll a production month –1 in the three biogeographic provinces around South Africa. (Redrawn from Bustamante, R.H., Branch, G.M., Eckhout, S., Robertson, B., Zoutendyk, R., Schleyer, M., Dye, A., Hanekon, N., Keats, D., Jurd, M., and McQuaid, C., Oecologia (Berlin), 102, 193, 1995. With permission.) FIGURE 6.2 Macroalgal standing stocks around South African shores. Bars represent the mean (SD) dry biomass for each of the three functional groups of algae. (Redrawn from Bustamante, R.H., Branch, G.M., Eckhout, S., Robertson, B., Zoutendyk, R., Dye, A., Hanekon, N., Keats, D., Jurd, M., and McQuaid, C., Oecologia (Berlin), 102, 194, 1995. With permission.) © 2001 by CRC Press LLC 358 The Ecology of Seashores foliose algae prevalent on the West coast and coralline algae on the East coast. However, overall macroalgal standing stocks did not reflect the productivity gradient, which was equally high on the East and West coasts, and low in the South. A specific algal food resource that is of importance to some herbivores are the small epiphytic algae growing on other algae and on hard substrates such as the shells of molluscs such as limpets. Filter feeders feed on the water column bacteria, phytoplankton, detritus, and the micro- zooplankton, especially the protozoans. Particulate organic matter (POM), or detritus, is derived from the water column, or the in situ breakdown of algae and the dead bodies of animals, as well as the feces of the invertebrate secondary consumers. POM in the water col- umn is derived from a variety of sources (see Section 3.8.2.1), especially macroalgae, submerged macrophytes, and zooplankton fecal production. Dissolved organic mat- ter, again, is derived from a variety of sources (see Section 3.8.2.1) and is utilized primarily by bacteria both within the water column and in the microbial film on the rock surface, molluscan shells, barnacle tests, and the macroalgae. There is a wide range of predators on rocky shores including gastropod molluscs, seastars, many crustaceans, fishes, and shore birds. 6.2.2 SOFT SHORES Since sand beaches lack macrophytes (seed plants and macroalgae) below the drift line, the basis of the food web is in situ microalgal production or food inputs from the sea or the land. The food inputs can be divided into the categories shown Table 6.2. The principal primary pro- ducers on sand beaches are the epipsammic diatoms attached to the sand grains. Their contribution is greatest on sheltered and fine sand flats. Recorded values range from 0 to 50 g C m –2 (Steele and Baird, 1968). On very exposed beaches, production is practically zero while on those exposed to wave action, values are less than 10 g C m –2 (Brown and McLachlan, 1990). This food resource is consumed by the meiofauna and deposit feeders, e.g., polychaetes and callianassid shrimps. Surf-zone primary production is highly variable. Where surf-zone diatom accumulations occur, production rates may be very high, on the order of 200 to 500 g C m –3 yr –1 , with instantaneous rates of between 5 and 10 g C m –3 hr –1 (Lewin and Schaefer, 1983; Campbell, 1987; Brown and McLachlan, 1990) (see Section 3.5.5.5). Where such accumulations (patches) are absent, primary production rates in the surf zone are much lower in the range of 20 to 200 g C m –3 yr –1 (Brown and McLachlan, 1990). On the Eastern Cape, South Africa, the surf diatoms produced 120 kg C m –1 yr –1 within the surf zone (250 m), while mixed phytoplankton in the water column, mainly autotrophic flagellates, produced 110 kg C m –1 yr –1 in the rip-head zone (250 m) (McLachlan, 1983; Campbell, 1987). This surf phytoplankton is an important food resource for benthic and planktonic filter feeders and some fishes, especially where it is concentrated into foam (Romer and McLachlan, 1986). Particulate organic matter, or detritus, (POM), gener- ally has a higher biomass than the microalgae and it constitutes a relatively constant food resource. It is derived from the breakdown of plants and animals, “sloppy” feeding, and the aggregation of DOM. In Eastern Cape waters, South Africa, values of between 1 and 5 g TABLE 6.2 Soft Shore Food Sources Food Type Source Consumers Remarks Benthic microflora Sediments Microfauna, meiofauna, and deposit feeders More abundant on sheltered beaches Phytoplankton Coastal water Filter feeders Surf diatoms Surf water Filter feeders In well-developed surf zones Stranded macrophytes (sea grasses, macroalgae) The sea Detrital feeders Near kelp beds, rocky coasts, and sea grass beds Detritus (particulate organic matter) The sea Detrital feeders filter feeders Dissolved organic matter The sea Insects The land Particularly during offshore winds Meiofauna Sediments Other meiofauna, macrofauna Macrofaunal invertebrates Sediments Invertebrate and higher consumers Bacteria The sea and the sediments Microfauna, meiofauna, and macrofauna Microzooplankton The sea Filter feeders Carrion The sea Fish, crabs, and birds © 2001 by CRC Press LLC Energy Flow, Food Webs, and Material Cycling 359 C m –3 have been recorded (McLachlan and Bate 1984; Talbot and Bate, 1988d). Talbot and Bate (1988d) mea- sured detrital standing mass along Sundays River Beach, South Africa, and found that it was consistently high in the surf zone (averaging 3.5 kg per running meter of beach, m –1 ), exceeding values recorded in the immediate offshore zone by a factor of four and comprising 91% of the total POC (Figure 6.3). In contrast, in the inner surf zone, nearly 50% of the POC was composed of the surf diatom Anaulus birostratus. In most parts of the world, sand beaches receive large inputs of drift algae from offshore kelp beds or nearby rocky coasts, (Brown et al., 1989). Studies of the input of drift algae to sand beaches have been carried out in a diverse range of localities, e.g., in California (Zobell, 1959), South Africa (Koop and Field, 1981; Griffiths and Stenton-Dozey, 1981; Stenton-Dozey and Griffiths, 1983; Griffiths et al., 1983), New England (Behbehani and Croker, 1982), Aus- tralia (Lenanton et al., 1982: Robertson and Hansen, 1981), and New Zealand (Inglis, 1989; Marsden, 1991a,b). Sten- FIGURE 6.3 A. Morphology of sandy beach at Sundays River Beach, South Africa, showing the various zones sampled for detrital C concentrations. B. Shore normal distribution of detrital C concentrations on four sampling occasions. Each value is the mean of at least 20 replicates. Inset ordinate axis represents detrital standing mass m –1 of each zone (thereby taking dimensions of the various zones into account). Zones are: (1) inner surf; (2) trough; (3) outer breaker; (4) rip-head; (5) nearshore; and 6) offshore. (Redrawn from Talbot, M.M.B. and Bate, G.C., J. Exp. Mar. Biol. Ecol., 121, 257 and 259, 1988d. With permission.) © 2001 by CRC Press LLC 360 The Ecology of Seashores ton-Dozey and Griffiths (1983) estimated the seasonal and annual biomass of macroalgae deposited on a 300 m sandy beach at Kommetjie, South Africa. Highest deposition val- ues occurred in autumn and winter and lowest values in summer. The mean standing stock of kelps on the beach was 25.07 kg m –1 . Using a residence time of 14 days, Griffiths and Stenton-Dozey (1981) estimated a total dep- osition rate of 2,179 kg wet mass m –1 yr –1 , equivalent to 4.07 × 10 6 kJ deposited per running meter of beach each year. The food webs associated with such algal drifts will be discussed in Section 6.9.3.3. Carrion, usually of marine origin, is a highly erratic food supply. Jellyfish, siphonophores, bivalve molluscs, seabirds, cetaceans, and other animals are cast up on beaches at various times. Sometimes after storms that dis- turb sublittoral sediments, burrowing species such as poly- chaetes, holothurians, and echiuroids can be deposited in large quantities (Knox, 1957). In the absence of other major inputs, or on beaches adjacent to seal or seabird colonies, carrion inputs may be seasonally significant, but generally are of minor importance. McGwynne (1980), for beaches on the Eastern Cape, South Africa, estimated an annual input of carrion of about 120 g C m –1 yr –1 . Dissolved organic matter in the water column may be concentrated by wave action into a rich yellow foam, which accumulates in the surf or on the beach. It has been shown that such foam is utilized by the bivalve Donax serra. However, it is principally used by the water column and sediment bacteria. Two organic land sources, insects and plant litter, though usually not found in significant concentrations, are often found on beaches and in the surf waters. 6.3 ENERGY BUDGETS FOR INDIVIDUAL SPECIES 6.3.1 I NTRODUCTION The sequence of food transformations by an individual or species population can be represented by a schematic flow diagram as depicted in Figure 6.4 (Petrusewicz, 1967; Petrusewicz and Macfadyen, 1970). Ingested food may be assimilated, egested, excreted, respired, and ultimately forms new biomass. Energy budgets of an individual organism or popula- tion relate the intake of food energy and its subsequent FIGURE 6.4 Schematic diagram of energy flow through an animal or species population. MR = total material removed by the population; NU material removed but not used (not consumed); C = consumption; FU = rejecta; U = excreta; A = assimilation; D = digested energy (materials); P = production; P g = production due to body growth; P r = production due to respiration; R = respiration (cost of maintenance); B = changes in biomass (standing crop) of the individual or population; and E = elimination. After Petrusewicz (1967) and Petrusewicz and Macfadyen (1970). © 2001 by CRC Press LLC Energy Flow, Food Webs, and Material Cycling 361 utilization according to the well-known balanced energy Grodzinsky et al., 1975). C = P + (R + F + U) where C = consumption (or intake) (energy content of the food absorbed), P = production (energy utilization in growth or gamete production), R = respiration (energy loss through metabolism), F = feces (energy loss through feces egested), U = urine (energy loss through dissolved organic matter, including urine), and expressed in units of energy (calories or joules). Odum (1983) presented a diagram of the main energy sources and flows for a typical population of consumer units in which the influence of additional energy sources (such as recruitment and environmental parameters) were included. Stephenson (1981) adapted this diagram to conform with the terminology of the International Biological Programme (Petrusewicz and Macfadyen, 1970) (Figure 6.5). 6.3.2 S USPENSION -F EEDING B IVALVES Stephenson (1981) developed an energy budget for a filter- feeding bivalve, the cockle Austrovenus stutchburyi in the Avon-Heathcote Estuary, New Zealand (Figure 6.6). This estuary is a small (8 km 2 ), bar-built estuary with a drainage basin of approximately 200 km 2 ), drained by two rivers entering the estuary. The cockle is the dominant mac- robenthic species in the estuary. Densities range up to over 3,000 m –2 with a biomass (total ash free) dry weight of up to 1,200 g m –2 . The flow diagram for the energy budget of an individual A. stutchburyi depicted in Figure 6.7. For an Austrovenus population, inputs from food intake and recruitment result in standing crop through growth, repro- duction, egestion, respiration, and mortality. This is the net organic production of the population. The concept of production, as usually understood, refers to the amount of biomass produced over a given time period and is assumed to be a measure of the food energy potentially contributed to the succeeding stages of the food chain (Macfadyen, 1963). However, the methods of specific measurement and expression of “net produc- tion” in the literature are numerous. Petrusewicz and Mac- fadyen (1970) list five different definitions “each of them characterizing different ecological views of the concept in question.” In its most general sense, “net production” may be considered to be organic matter available to be utilized by the next stage in the food chain, divided by the time taken for the organic matter to be produced. FIGURE 6.5 Diagram of the major sources and flows for a typical population of consumer units. After E.P. Odum (1983). © 2001 by CRC Press LLC equation of Winberg (1956) (see also Ricker, 1968 and 362 The Ecology of Seashores Figure 6.8 summarizes the major compartments and paths of energy flow in the Avon-Heathcote Estuary cockle population (Stephenson, 1981). Stephenson estimated the spatial distribution of “net production” of A. stutchburyi by applying a previously established length-age relation- ship to the mean shell length to estimate age at 200 sample sites. Net production (g ash-free dry wgt m –2 yr –1 ) was estimated for each site as: The maximum net production value was about 15 g ash- free dry wgt m –2 yr –1 . Net production estimated in this manner represents only accumulated organic matter and omits the part of production that has gone into mortality, elimination, and reproduction. This is similar to the concept of “yield” of Petrusewicz and Macfadyen (1970). On this basis the total winter organic biomass of cockles in the Avon-Heathcote Estuary (8 km –2 ) was estimated at being between 8.2 × 10 4 and 1.7 × 10 6 kg (ash-free dry wgt), or 1.62 × 10 6 to 3.4 × 10 10 kJ yr –1 . Stephenson (1981) has also modeled the yearly flow of energy through the A. stutchburyi population. Austro- venus, which have very short siphons, filter organic matter from the layer of water immediately above the sediment surface. This water layer will contain suspended organic matter (microalgae and detritus) of terrestrial, marine, and estuarine origin. Major inputs are the input from the City of Christchurch sewage treatment oxidation ponds, the two rivers entering the estuary, in situ microalgal produc- tion (phytoplankton and suspended sediment microal- gae), and sea phytoplankton production brought into the estuary on incoming tides (Stephenson and Lyon, 1982). This organic matter is filtered from the overlying water and processed by Austrovenus, which passes sediment, nutrients, organic matter, and mucus to the surface sedi- ments as feces and pseudofeces. The assimilated organic matter is passed on to the predators (especially oyster- catchers, fish, and whelks), or upon death to scavengers and decomposers. For a second example of a filter-feeding bivalve, we shall consider Macoma balthica, a lamellibranch mollusc (Tellinidae) that colonizes intertidal and subtidal zones in different climatic regions of the Northern Hemisphere. Its distribution extends from San Francisco Bay (Nichols and Thompson, 1982) to Hudson Bay (Green, 1973) in North America and from the Gironde estuary, France, (Bachelet, 1980) to the White Sea and other parts of northern Russia (Beukema and Meehan, 1985). Individuals of this species are interoparous. Reproduction is indirect and longevity ranges from 5 to 50 years, depending on geographic loca- tion. Food is acquired by suspension and/or detrital feed- ing (Hummel, 1985a,b; Olafsson, 1986). Hummel (1985b) calculated seasonal and annual bud- gets for a tidal flat population of Macoma balthica in the western part of the Dutch Wadden Sea. The budget was calculated as C = P + R + G + F, where C = consumption, P = somatic production, R = respiration, G = gonad output, and F = feces (including excreta, U). Values for the energy budget were obtained by summing monthly values (Table 6.3). In Table 6.3 these values are compared to those obtained for three other tellinid bivalves. The energy bud- FIGURE 6.6 Schematic diagram of the functional components of an energy budget for the New Zealand cockle Austrovenus stutchburyi. (After Stephenson, R.L., Ph.D. thesis, Zoology Department, University of Cantaerbury, Christchurch, New Zealand, 1981. With permission.) Accumulated organic biomass Mean age of the population © 2001 by CRC Press LLC Energy Flow, Food Webs, and Material Cycling 363 get for Macoma as shown in Table 6.3 can be calculated in two ways: (1) when absorption (assimilation) is calcu- lated from A = P + G + R, a value for absorption (A) of 71.7 kJ m –2 is obtained; and (2) when the absorption value is calculated independently from total consumption multi- plied by the absorption efficiency, it amounts to 107.4 kJ m –2 . The former value is close to the values for absorbed chlorophyll a related food (71.4 kJ m –2 ). This close fit suggests that the energy utilized by Macoma is primarily chlorophyll a related food. Thus, the main food of Macoma on the Wadden Sea tidal flat consists of microal- gae, “fresh” algal detritus, and closely associated micro- organisms. Various investigations have established that the preferred food items of Macoma appear to be diatoms, bacteria, and protozoa (Fenchel, 1972). Stable carbon iso- tope measurements at Pecks Cove, Bay of Funday, indi- cated that Macoma were feeding either on diatoms or fresh Spartina detritus and its associated microorganisms (Schwinghamer et al., 1983). Excretion (U) is thought to be quantitatively of little importance. Based on data for other bivalves, e.g., Mytilus edulis (12%) (Bayne and Wid- dows, 1978) and Mytilus chilensis (3%) (Navarro and Winter, 1982), it was estimated to be maximally 8 kJ m –2 . Based on the annual value of 71.7 kJ m –2 for the absorbed food, only 28% of the consumed (ingested) food (257.7 kJ m –2 ) was assimilated. This low assimilation may have been due to a large inert component (C – Cc) with little or no nutritional value in contrast to the chlorophyll amounted to 28% of the assimilated chlorophyll a related food. The values for consumption (C), absorption (A), production (P + G), and respiration (R) for Macoma are all within the range of those found for other tellinid bivalves listed in Table 6.3. Table 6.4 compares average biomass, production, and P:B ratios for Macoma balthica for entire estuaries of FIGURE 6.7 Major components and paths of energy flow relating to the cockle Austrovenus stutchburyi in the Avon-Heathcote Estuary, New Zealand. (After Stephenson, R.L., Ph.D. thesis. Zoology Department, University of Canterbury, Christchurch, New Zealand, 1981. With permission.) © 2001 by CRC Press LLC a related food (Cc) (Figure 6.9). The production (P + G) 364 The Ecology of Seashores FIGURE 6.8 Yearly model of energy flow through the cockle Austrovenus stutchburyi in the Avon-Heathcote Estuary, New Zealand. (After Stephenson, R.L., Ph.D. thesis, Zoology Department, University of Canterbury, Christchurch, New Zealand, 1981. With permission.) TABLE 6.3 Annual Values for Populations of Tellinid Bivalve Consumption (C: kJ m –2 ), Absorption Efficiency (A/C), Absorption (A; kJ m –2 ), Gonad Output (G; kJ m –2 ), Respiration (R; kJ m –2 ), Growth (K 1 ) and Net Growth Efficiency (K 2 ), Number (n; m –2 ), and Biomass (B; kJ m –2 ) C A/C A P G R K 1 K 2 n B Macoma balthica a 257.7 0.35–0.56 107.4 12.6 7.8 (87.0) 0.80 0.19 60 48.1 Western Wadden Sea b (0.28) (71.7) 12.6 7.8 51.3 0.08 0.28 60 48.1 Hummel (1985b) Scrobicularia plana c 3,565.7 (0.71) (2,514.0) 251.4 268.2 1994.4 0.15 0.21 150 855.6 North Wales d 436.6 (0.69) (302.1) 55.7 17.6 228.8 0.17 0.24 55 81.3 Hughes (1970) Tellina fabula e (148.8) 63.2 4.8 80.8 0.46 987 39.2 German Bight f (216.5) 51.1 25.9 139.5 0.36 980 83.4 Salzweldel (1980) Tellina tenius 1966 (186.9) 27.6 2.7 156.6 0.16 111 74.9 N.W. Scotland 1967 (84.4) 4.3 7.1 73.0 0.14 59 59.7 Trevallion (1971) 1968 (111.9) 14.7 17.4 79.8 0.29 47 56.6 Note: Values in parentheses are not directly estimated but calculated from, e.g., A = P + G + R or R = A – P – G. Data for Macoma are calculated for a population of an average 60 1+ year-old individuals. Explanation: a. A is calculated from results given by Hummel (1985a) (Table 6.1) and R = A – P – G. b. R is calculated from results given by De Wilde (1975), and A = R + P + G. c. Low level. d. High level. e. Tellina ground. f. Fine sand center. © 2001 by CRC Press LLC [...]... In muddy areas, their contribution was smaller, 0.3% of the total production of 88 g C m–2 yr–1, or 0.24 g C m–2 yr–1 Fenchel (1 969 ) separately considered the numbers of ciliates (microfauna), meiofauna, and macrofauna in three different soft-bottom habitats In terms of numbers, the meiofauna outnumbered the macrofauna by factors of 10 to 100 (Table 6. 16) However, in terms of biomass, the situation was... that the meiobenthos share in the consumption and production of food was 15% that of the macrobenthos which had more than 97% of the total benthic biomass In a later review, Gerlach (1978) revised these estimates on the basis of more recent data and concluded that the meiofaunal biomass was about 10% of the macrofaunal biomass, but that the production of the meiofauna and the deposit-feeding macrofauna... P:B 2 56 ( 76. 2%) 10 ( 16. 1%) 26 — — — 26 (7.7%) 6 (9.7%) 4.3 (9.7%) 54 ( 16. 1%) 46 (13.7%) 1.2 3 36 62 5.4 English Channela Lynher Estuary 34 1 34 1,7 16 99 17 245 26 8.4 66 54 1.2 1, 961 180 9.12 Bay of Fundayc Pecks Cove 147–1,474 ( 16 66 %)d 0.05–5 (1–9%) 292 573 24 24 147 (7– 16% ) 12 (22–24%) 12 14 (1–3%) 29 (25–28%) 2.1 8 96 1 223 50–55 17.9–44.5 Anker (1977) Warwick et al (1979) Schwinghamer et al (19 86) ... the cochlear zone due the the grazing pressure of the limpets The distribution patterns of the macrofaunal groups across the shore is depicted in Figure 6. 17 In winter, the largest component of the macrofaunal biomass comprised the filter-feeding barnacle Tetraclita serrata, which attained 75 g m–2 in the middle balanoid zone; but as a result of late recruitment and high mortality of this species, the. .. Cerastoderma edule 6. 5.2 MICRO- AND MEIOFAUNA Estimates of the production of micro- and meiofauna are usually made by multiplying the standing crop by turnover times, which have been determined from studies of the life 378 The Ecology of Seashores FIGURE 6. 15 Transect of the rocky shore site studied by Gibbons and Griffiths at Dalebrook, South Africa, showing the zonation patterns of the biota Zones are... production (U = 8,229 kJ m–1 yr–1) of inorganic nitrogen as ammonium is utilized by the surf-zone diatoms Within the beach/surf-zone system, fishes are therefore (1) the major predators on the macrofauna; (2) important transformers of carbon and nitro- 374 The Ecology of Seashores gen; and (3) agents for the transfer of materials across the nearshore boundary 6. 4 OPTIMAL FORAGING 6. 4.1 INTRODUCTION Consumers,... Lawton (1970) The total annual production of the meiofauna, dominated by small polychaetes, nematodes, and copepods, was 20.17 g C m–2 yr–1, nearly four times as much as the macrofaunal production of 5. 46 g C m–2 yr–1 Warwick et al calculated that 16% of the meiofaunal production was consumed by the sediment macrofauna, leaving 16. 83 g C m–2 yr–1, or three times the production of the macrofauna, available... Benthic soft-bottom population energetics have been extensively studied, but the number of groups of organisms involved — bacteria, benthic microalgae, fungi, protozoa and other microorganisms, meiofauna, 3 86 The Ecology of Seashores FIGURE 6. 20 Simplified model of the partitioning of production of an intertidal mussel bed, showing storage and turnover compartments and their availability to predators The. .. biomass, and rate of respiration of the meiofauna in the Lynher River estuary Using various assumptions and literature values, they calculated that the meiofauna produced 14.7 g C m–2 yr–1 and that the P:B ratio for the meiofauna was 11.1; with the small annelids included, it was 7.7 There is agreement from other studies (McIntyre, 1 969 ; Gerlach, 1971) that the P:B ratio for the meiofauna is about 10.0... appear to be the rule 6. 7 RELATIVE CONTRIBUTIONS OF SOFT SHORE BENTHIC INFAUNA TO SECONDARY PRODUCTION There are very few studies in which all the components of the benthic community have been considered together when arriving at estimates of benthic secondary production This would involve the simultaneous measurement 382 The Ecology of Seashores FIGURE 6. 19 Schematic representation of the annual consumption . Introduction 360 6. 3.2 Suspension-Feeding Bivalves 361 6. 3.3 Scope for Growth 365 6. 3.4 Carnivorous Molluscs 366 6. 3.5 Grazing Molluscs 367 6. 3 .6 Deposit-Feeding Molluscs 371 6. 3.7 Fishes 373 6. 4 Optimal. 374 6. 4.1 Introduction 374 6. 4.2 Optimal Diets 374 6. 4.3 Optimal Patch Use 3 76 6.5 Secondary Production 377 6. 5.1 Macrofauna 377 6. 5.2 Micro- and Meiofauna 377 6. 5.3 A Comparison of the Macrofaunal. Press LLC equation of Winberg (19 56) (see also Ricker, 1 968 and 362 The Ecology of Seashores Figure 6. 8 summarizes the major compartments and paths of energy flow in the Avon-Heathcote Estuary