waders and their estuarine food supplies - Vlaams Instituut voor de ...

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Feeding and prey risk The choice of Nereis to filter feed from the overlying water, to leave the burrow to feed al the surface, or to remain inactive in the burrow, depends on the trade-off between gam of energy and avoidance of predation. Though Nereis is one of the best studied estuarine /oobenthic species, il is still impossible to describe (his decision-making in a quantitative way, although some qualitative predictions can be made. Nereis respond immediately to a change in their food supply il ig. 10), which suggests that they evaluate the current yield from filtering or surface feeding. The food supply in water and on the surface layci is different for worms liv ing in mud and in sand. The surface layer contains more food on a mudflat than on a sandflat (Newell 1979), whereas filler feeding on muddy shores is probably less profitable or even impossible, because Nereis probably meet the same problem as oilier filler feeders, viz.. the relatively low concentration of food particles among all suspended material. More suspension feeding and less deposit feeding can therefore be expected if Nereis living in sand are compared with those in mud. Our field observations indeed suggest that surface feeding is common in mud and absent on sandflats. Filter feeding makes no sense when the food supply in the water is too low. The food supply is maximal in summer and minimal in winter, but this variation is much larger in the water than in the upper surface of Ihc substrate (Colijn 1982. Hummel 1985a), so it is to be expected thai filter feeding disappears during the winter. Goerke (1971) indeed observed little filter feeding in winter, whereas it was very common in summer. Filter feeding is impossible il" no water remains at the surface (Twisk 1986). whereas surface feeding can occur regardless of the stage of the tidal cycle. However, worms exposed to a tidal regime do not feed at the surface during immersion (Vader 1964. this paper), probably to escape the high risk of being taken by fish, shrimps and crabs. Filter feeding is not without danger because predators probably see the burrow entrances or even the water current or fluctuating water level at the entrance to the burrow (Twisk 1986). Moreover, filter-feeding Nereis spend about half their time close to the surface. BURROWING AND FEEDING IN NEREIS 314 viz. during the construction of the mucous net and during the consuinpiion of this nei after irrigation (Harley 1953. Goerke 1966). Surface feeding is the most dangerous feeding technique, however, because the worm is very conspicuous and easy to catch. The likelihood of iis escape from an approaching predator depends on how quickly it can retreat into the lower part of its burrow. The time spent by Nereis at the surface is very limited. Figure 9C shows il was only 0.1 to 0.2% during low water in September and (We during 2 other low water periods, also during late summer. Birds feeding on exposed lidal fiats take more worms from the surface than from burrows ( Zwarts & Esselink 1989), which means that the predation risk during surface feeding must be extremely high compared with a situation in which the worms remain in their burrows. Thus worms obtaining all their food from the surface (e.g. worms in soft mud) are exposed to a greater predaiion risk than worms which solely filter feed (e.g. worms in sand). The low body condilion of worms in mud (Fig. 5) and the reduced growth in mud as compared with sand (Zwarts 1988b) might therefore be the consequences of the counterbalancing of the enhanced predation risk. The feeding rate (energy intake s ') must be very high during surface bouts, compared with the feeding rate during filter feeding. The difference in energy gain between both techniques is even greater if one takes into account that the feeding costs of filtering are high (Kristensen 1981). Nevertheless, surface feeding is. in our view, a supplement to filter feeding, because of the very high predation risk it entails. Worms feed at the surface in 3 circumstances in which filter feeding is unprofitable or impossible: (I) during that phase of a tidal cycle when filter feeding is made impossible by lack of water on the surface (Fig. 11). (2) in winter when the low concentration of food in suspension makes filter feeding unprofitable. (3) on muddy shores where ihe relatively low amount of food in the suspended material makes filtering less profitable. The density of Nereis actually available lo predators ihus depends not only on the depth of their burrows but also on their own choice of feeding methods (Zwarts & Esselink 1989).
Chapter 15 VERSATILITY OF MALE CURLEWS NUMENIUS ARQUATA PREYING UPON NEREIS DIVERSICOLOR: DEPLOYING CONTRASTING CAPTURE MODES DEPENDENT ON PREY AVAILABILITY Leo Zwarts & Peter Esselink published in: Mar. Ecol. Prog. Ser. 56: 255-269 (1989). 315
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WADERS AND THEIR ESTUARINE FOOD SUP
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plia^ohi. WADERS AND THEIR ESTUARI
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Waders and their estuarine food sup
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WADERS AND THEIR ESTUARINE FOOD SUP
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figuren: Dick Visser omslagfoto: Ja
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15 Versatility of male curlews (Num
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That science is making progress, ma
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INTRODUCTION The remnants of brushw
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When hcnlhic bivalves extend llien
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the burrow depths and on the fracti
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INTRODUCTION Ms,i invest 409 of (he
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able lo sw itch 10 oiher prey which
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Long-term, broadly-based research c
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Chapter 1 SEASONAL VARIATION IN BOD
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SEASONAL VARIATION IN BODY WEIGHT O
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Tahle 1 Weight loss ('•- ± SE) m
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i 60 50 40 30 20 10 0 • INFESTED
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240- SEASONAL VARIATION IN BODY WEI
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20 10 0 -10 -20h 2 3 4 5 6 7 8 9 se
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a E 400 - S. plana 35 mm 320 240 16
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Chapter 2 HOW THE FOOD SUPPLY HARVE
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FOOD SUPPLY HARVESTABLE BY WADERS H
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Methods The study sites were situat
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less than that of bivalves, partly
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I Fig. 3). Peak condition was reach
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total biomass since most of those t
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on the basis of the preceding and t
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However, for obvious reasons, we ma
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prey. A decrease in the prey densit
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Tahle 2. The intake rate ol < lyste
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* ' % -. . ; a X - . - * • ^ •
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(Zwarts & Wanink 1989). In quiet we
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general law relating handling time
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nearly twice as much time (0.79 s).
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4 5 6 7 8 9 size class of Corophium
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and annually. Second, the lower siz
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Prey switching Waders feeding on ti
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autumn and spring, and the contrary
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where they switch to surface-living
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Chapter 3 BURYING DEPTH OF THE BENT
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DEPTH AND SIPHON CROPPING IN SCROBI
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I DEPTH AND SIPHON CROPPING IN SCRO
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DEPTH AND SIPHON CROPPING IN SCROBI
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Table 3. Three-Way analysis Of vari
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Chapter 4 SIPHON SIZE AND BURYING D
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15 20 size (mm) Fig. 3. Cerasioderm
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10 size (mm) SIPHON SIZE AND DEPTH
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o, 7 01 5 | * CL 5- SIPHON SIZE AND
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4 Q) Si •a a. 16- 20- A predator:
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prey risk for an animal al a depth
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Table 6. Size al which there is a m
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* ' 1 /-/ "».-^*«C
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face and so expose themselves to a
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surface in die containers was varie
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50 OOF 310.00 I 5.00 ^ 1.00 3=" 0.5
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Tahle 1. Macoma and Scrobicularia.
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siphon would not have to reach the
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known siphon weight and burying dep
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ACCESSIBLE PREY ARE OFTEN IN POOR C
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1 2 3 4 burying depth (cm) Kin. I.
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I—1 • • : : : : ! - ! -|-r 0
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Chapter 7 DOES AN OPTIMALLY FORAGIN
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OPTIMAL FORAGING AND THE FUNCTIONAL
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100 200 300 prey density (n-m-2) Fi
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Table I. Results of five one way an
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Table 2. Results of eight iwo-wav a
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prey density II III Fig. 12. Freque
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PREY SIZE SELECTION AND INTAKE RATE
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Predicted 'passive size selection'
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lig. 2. Larger Mussels are less ava
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Fig. 5. Scrobicularia plana. Size c
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and maiiv are too thick-shelled to
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The measurements of handling time i
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1 2 3 4 5 6 7 probing depth (cm PRE
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valves may vary by a factor of two
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optimal foraging model, the minimum
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their gut is full? Do they reduce t
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PREY PROFITABILITY AND INTAKE RATE
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catchers to take only certain prey
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licult error of estimate arose if p
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Counts of feeding and non-feeding b
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20 30 40 50 shell length (mm) PREY
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Nereis Arenicola tipuia earthwo'm M
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take rate. We might therefore expec
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prey species, using parallel slopes
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5.0 4.0 1-3.0 a & • % * • * •
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time during the feeding period. As
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winter. Similarly, handling time in
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5.0 - f-4.0 S 3.0 in I 20 a 2 a | 1
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situation arrived in the western pa
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• ' • 14 PREY PROFITABILITY AND
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Notes lo appendix: PREY PROFITABILI
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Chapter 10 WHY OYSTERCATCHERS HAEMA
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2 4 6 8 10 time on feeding area (h)
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80- 60- o 80 60- 40- 20- INTAKE RAT
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est of bod\ behind: an estimated 22
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INTAKE RATE AND PROCESSING RATE IN
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Wanink 1993). The energy content of
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(7) Age All studies dealt with adul
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irds over long periods. As an examp
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Discussion There is no difference i
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comparison between the weight of ih
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. 1', L ! •
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Introduction PREDICTING SEASONAL AN
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PREDICTING SEASONAL AND ANNUAL FLUC
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1000 r 1 II" 1 - r^Jan'80 PREDICTIN
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IOO BO 60 40 20 0 PREDICTING SEASON
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Page 260 and 261: PREDICTING SEASONAL AND ANNUAL FLUC
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Page 265 and 266: WHY KNOT TAKE MEDIUM-SIZED MACOMA W
Page 267 and 268: in Zwarts & Esselink 1989). The len
Page 269 and 270: shell length (mm) FIR. 3. Peringia.
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Page 281 and 282: WHY KNOT TAKE MEDIUM-SIZED MACOMA T
Page 283 and 284: Chapter 13 ANNUAL AND SEASONAL VARI
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Page 287 and 288: Two sites (N and M in Fig. 2) were
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Page 293 and 294: July ' Aug ' Sept Fig. 9. Proportio
Page 295 and 296: available. There must, however, be
Page 297 and 298: Chapter 14 SEASONAL TREND IN BURROW
Page 299 and 300: BURROWING AND FEEDING IN NEREIS SEA
Page 301 and 302: Table 2. Results of a 2-way analysi
Page 303 and 304: June 1981 June 1982 is * N.MUD •
Page 305 and 306: 8 10 I 12 JZ 5. -g 1*» •e o i 16
Page 307 and 308: 6 - n=!080 5 • g 4 CP > i 3 CO CD
Page 309: 1985) and Curlew (/wails ,v, Lsseli
Page 314 and 315: Smid! 1951. Muus 1967, Wolff 1973,
Page 316 and 317: 0.6 0.8 1.0 1.2 1.4 1.6 jaw lengih
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Page 324 and 325: VERSATILITY OF CURLEWS FEEDING ON N
Page 326 and 327: total time spent al the surface. Th
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Page 331 and 332: PREY DEPLETION BY OYSTERCATCHER AND
Page 333 and 334: the rule: the observed lower limit
Page 335 and 336: to locate the clams after they had
Page 337 and 338: Curlew, by bury ing some hundreds o
Page 339 and 340: PREY DEPLETION BY OYSTERCATCHER AND
Page 341 and 342: SAMENVATTING 345
Page 343 and 344: Voorgeschiedenis In 1960 verscheen
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Page 349 and 350: kunnen opzuigen. of diep leven en z
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was dan ook dank/ij de inzet van al
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REFERENCES 367
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Allen RL. 1983. Feeding behaviour o
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BreyT. 1989. Der Einfluss physikali
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latie tol chironoiiiiilen en de wai
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huch der Vogel Milteleuropas, Band
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llolmann II. & H. Huerschelmann 196
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l-cndrem D.W. 1984. Flocking, feedi
Page 377 and 378:
Pekkarinen M. 1984. Regeneration of
Page 379 and 380:
lion of Mussels Mytilus edulis hy O
Page 381 and 382:
lulal Dal esiuanes: a comparison of
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