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4 Q) Si •a a. 16- 20- A predator: Calidris alba prey: Exorolana linguitrons r}r , Excirolana kincaidn y I A 0.0 0 5 1.0 SIPHON SIZE AND DEPTH IN BENTHIC BIVALVES predator: Haematopus oslralegus prey: Scrobicularia plana )0 0.5 1.0 relative prey risk predator: Numenius arquata prey: Mya arenaria Fig. II. Predation risk as a function of burying depth in three different studies: A. Sanderling Calidris alba preying on beach crustaceans (Myers el ul. 1180). B. Ovsicrcaicher Haematopus oslralegus feeding on a benthic bivalve (Wanink .V Zwans 1985) and C Curlew Numenius ariliiatii feeding on benthic bivalve (/.warts A: Wanink 19X41. Prev risk is expressed in relation to the maximal predalion risk of a single size class i set to I); •*• indicates a shallow prey taken bv a Curlew, but not occurring in ihe sampling programme, resulting in an infinitely large prey risk. overlying water while the siphon is just at the surface (Brafield & Newell 1961. Hughes 1969. de Wilde 1975. Earll 1975. Hummel 1985a). Macoma lake deposit al a maximum of 4 lo 6 cm from their burrow (Brafield & Newell 1961. Gilbert 1977) and Scrobicularia up to 10 cm (Thamdrup 1935. Hughes 1969) or even 20 cm (Linke 1939). Both species might be able to double their burying depth by shifting from deposit feeding to filter feeding. Since filter feeding is limited to the immersion period and deposit feeding can occur during immersion as well as during emersion, a vertical movement within a tidal cycle might be expected. as suggested by Yonge 11953). No evidence, however, was found for this in our laboratory (unpublished data) when we measured continuously the burying depth of individual Macoma with the aid of thin nylon threads, which connected the shells with a registration apparatus. It is likely dial the remarkable difference between the summer and winter burying depths oi Macoma and Scrobicularia (Figs. 4 and 5) can be explained by the absence of deposit feeding in winter (Linke 1939, Hughes 1969. Hummel 1985a). Individuals with a 106 similar siphon weight live 2-3 times as deep in winter as in summer (Figs. 7 and 8). The siphon weights in Scrobicularia are about the same in both seasons (Fig. 6D). whereas for Macoma the siphon is 35% heavier during winter than in summer (Fig. 6C). so that most individuals of both species are able to live at greater depths in the non-feeding season (Figs. 4 and 5). The relatively low siphon weight of Macoma during the summer can be attributed lo heavy siphon cropping by fishes, crabs and shrimps (de Vlas 1985). It would be of interest to know to what degree die occurrence of suspension feeding during the summer in Macoma (Hummel 1985a) is caused by the reduction of siphon size. The suspension feeders Mya and Cerastoderma remain at nearly the same depth during the whole year: Cerastoderma burrow to a 20'7< greater depth in winter than in summer (Fig. 3) and in Mya the difference is only 10 to 15* (Figs. 2 and 9). Burying depth as a protection against predation The relationship between burying depth and size can be described with an S-curve (Figs. 2-5). Burying
SIPHON SIZE AND DEPTH IN BENTHIC BIVALVES Tabel 4. Ovcrv iew ol existing know ledge about obsei veil depth .mil si/e selection by different bird species on European tidal flats. Actual measiirenienls on depth selection are rare figures given are derived from bill lengths, which seem to be a good predictor for exploited depth luvcr. although prey jusi vv iilun reach are rarely taken (Fig. 11). Prey species taken by bird species Depth, cm Size, mm Sources s. robicularia plana Haematopus oslralegus Hughes 1970a. Wanink & Zwarts 1985 Mya arenaria Haematopus oslralegus 7 >I7 Numenius arquata It >30 Cerastoderma edule C alidri.s canuliis 3 < 10 Tringa toianus •I < 7 Somateria mollissima 20 Macoma balihica t 'alidri.s alpina 3 3- 7 Tringa totanus •I 8-12 Calidris canutus 3 8-15 limosa lapponica 7-10 8-18 Haematopus oslralegus 7 > 10 depth levels off for all four species when they reach a si/e which equals about 50'-i of their maximum size. The burying depth levels off at 1 to 2 cm in Cerastoderma and at 16 to 18 cm in Mya. It is different for summer and winter in the two deposit feeders: Macoma (2 and 5 cm, respectively) and Scrobicularia (7 and 11 to 12 cm. respectively). \s shown in Fig. 11. a deep burrow guarantees maximal survival and below a certain level predation risk is nil. We will analyse in ibis section whether the observed depth curves level off below which there is no predation ("depth refuge'). Since the depth refuges are determined by the predators which can probe at maximal depths, we will focus our attention on longbilled bird species (Table 4). Invertebrate predators play no part in the predation on bivalves just beyond their depth refuges. Shrimp Crangon crangon. Shore Crab Carcinus maenas. Plaice Pleuronectus platessa and Rounder Plaiichthys flesus select the smaller bivalves present in the upper layer of the substrate. Their si/e seleciion is well doc Zwarts & Wanink 1984 /.w.rris.v wanink 19X4 Ciuss-Custard etal. 1977b Burton 1974 Swennen 1976 Hulscher 1976, Goss-Custard el al. 1977b. Sutherland 1982c Worrall 1984 Goss-Custard 1969. doss-Custard el al. 1977. Blomert & /.wans unpubl. data I'ratei 119?: i. Cioss-Cusiard .••(•/. 1977b. Zwarts & Blomert (1992) Cross -Custard
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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
Page 55 and 56: less than that of bivalves, partly
Page 57 and 58: I Fig. 3). Peak condition was reach
Page 59 and 60: total biomass since most of those t
Page 61 and 62: on the basis of the preceding and t
Page 63 and 64: However, for obvious reasons, we ma
Page 65 and 66: prey. A decrease in the prey densit
Page 67 and 68: Tahle 2. The intake rate ol < lyste
Page 69 and 70: * ' % -. . ; a X - . - * • ^ •
Page 71 and 72: (Zwarts & Wanink 1989). In quiet we
Page 73 and 74: general law relating handling time
Page 75 and 76: nearly twice as much time (0.79 s).
Page 77 and 78: 4 5 6 7 8 9 size class of Corophium
Page 79 and 80: and annually. Second, the lower siz
Page 81 and 82: Prey switching Waders feeding on ti
Page 83 and 84: autumn and spring, and the contrary
Page 85 and 86: where they switch to surface-living
Page 87 and 88: Chapter 3 BURYING DEPTH OF THE BENT
Page 89 and 90: DEPTH AND SIPHON CROPPING IN SCROBI
Page 91 and 92: I DEPTH AND SIPHON CROPPING IN SCRO
Page 93 and 94: DEPTH AND SIPHON CROPPING IN SCROBI
Page 95 and 96: Table 3. Three-Way analysis Of vari
Page 97: Chapter 4 SIPHON SIZE AND BURYING D
Page 100 and 101: 15 20 size (mm) Fig. 3. Cerasioderm
Page 102 and 103: 10 size (mm) SIPHON SIZE AND DEPTH
Page 104 and 105: o, 7 01 5 | * CL 5- SIPHON SIZE AND
Page 108 and 109: prey risk for an animal al a depth
Page 110 and 111: Table 6. Size al which there is a m
Page 112 and 113: * ' 1 /-/ "».-^*«C
Page 114 and 115: face and so expose themselves to a
Page 116 and 117: surface in die containers was varie
Page 118 and 119: 50 OOF 310.00 I 5.00 ^ 1.00 3=" 0.5
Page 120 and 121: Tahle 1. Macoma and Scrobicularia.
Page 122 and 123: siphon would not have to reach the
Page 124 and 125: known siphon weight and burying dep
Page 127 and 128: ACCESSIBLE PREY ARE OFTEN IN POOR C
Page 129 and 130: 1 2 3 4 burying depth (cm) Kin. I.
Page 131 and 132: I—1 • • : : : : ! - ! -|-r 0
Page 133 and 134: Chapter 7 DOES AN OPTIMALLY FORAGIN
Page 135 and 136: OPTIMAL FORAGING AND THE FUNCTIONAL
Page 137 and 138: 100 200 300 prey density (n-m-2) Fi
Page 139 and 140: Table I. Results of five one way an
Page 141 and 142: Table 2. Results of eight iwo-wav a
Page 145 and 146: prey density II III Fig. 12. Freque
Page 149: PREY SIZE SELECTION AND INTAKE RATE
Page 152 and 153: Predicted 'passive size selection'
Page 154 and 155: 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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WHY KNOT TAKE MEDIUM-SIZED MACOMA W
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in Zwarts & Esselink 1989). The len
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shell length (mm) FIR. 3. Peringia.
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fused, specimens larger than this w
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50 100- s s I — f = S. plana, n=2
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area is twice as large as the touch
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10 15 lower size threshold (mm) Fig
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lime (Hughes 1979). This would furt
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WHY KNOT TAKE MEDIUM-SIZED MACOMA T
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Chapter 13 ANNUAL AND SEASONAL VARI
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VARIATION IN FOOD SUPPLY OF KNOT AN
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Two sites (N and M in Fig. 2) were
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20 30 VARIATION IN FOOD SUPPLY OF K
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20 l i r'l ' i •o j^y^T n ^ ' " ^
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July ' Aug ' Sept Fig. 9. Proportio
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available. There must, however, be
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Chapter 14 SEASONAL TREND IN BURROW
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BURROWING AND FEEDING IN NEREIS SEA
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Table 2. Results of a 2-way analysi
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June 1981 June 1982 is * N.MUD •
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8 10 I 12 JZ 5. -g 1*» •e o i 16
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6 - n=!080 5 • g 4 CP > i 3 CO CD
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1985) and Curlew (/wails ,v, Lsseli
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Chapter 15 VERSATILITY OF MALE CURL
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Smid! 1951. Muus 1967, Wolff 1973,
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0.6 0.8 1.0 1.2 1.4 1.6 jaw lengih
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Na oi both Nrieck Fig. 7. Numenius
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6 8 10 12 14 16 18 worm length (cm)
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too (Fig. 11 A). Indeed, the averag
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VERSATILITY OF CURLEWS FEEDING ON N
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total time spent al the surface. Th
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2 4 . • 2.2 • 30 .-.2.0 to Q. 1
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PREY DEPLETION BY OYSTERCATCHER AND
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the rule: the observed lower limit
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to locate the clams after they had
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Curlew, by bury ing some hundreds o
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PREY DEPLETION BY OYSTERCATCHER AND
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SAMENVATTING 345
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Voorgeschiedenis In 1960 verscheen
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maken. Als gebied A een grotere voe
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omdat ze nog vrijwel niets wegen. l
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kunnen opzuigen. of diep leven en z
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van de uitgerekte sifo over het wad
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het toen niet gemakkelijk hebben ge
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doende nonnetjes van 10 tot 15 mm l
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aangevoerde voedsel en de wulp past
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zijn dan twee jaar en wulpen geen s
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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
Page 371 and 372:
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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