. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. PREDATION ON BIVALVE VELIGERS 301. Figure 1. (A) D-hinge veliger of the oyster Crassostrea gigas. (B) Trochophore larva of the polynoid Arctonoe viihiia with a vehger of the oyster C. gigas in its gut. (C) Metatrochophore larva of spionid A with a C. gigas veliger in its gut. (D) Trochophore larva of polynoid A with two C. gigas veligers in its gut. A, C, and D are viewed with cross-polarized light. Scale bar = 100 /jm. of seawater. No plankton net was towed: the water was collected in a plastic bag, then immediately concent
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. PREDATION ON BIVALVE VELIGERS 301. Figure 1. (A) D-hinge veliger of the oyster Crassostrea gigas. (B) Trochophore larva of the polynoid Arctonoe viihiia with a vehger of the oyster C. gigas in its gut. (C) Metatrochophore larva of spionid A with a C. gigas veliger in its gut. (D) Trochophore larva of polynoid A with two C. gigas veligers in its gut. A, C, and D are viewed with cross-polarized light. Scale bar = 100 /jm. of seawater. No plankton net was towed: the water was collected in a plastic bag, then immediately concentrated and fixed. This method allowed little time for artifactual predation. The true frequency of encounters between predators and prey in the field may, however, be far greater than estimated by models or from laboratory experiments if natural densities are greater than those recorded by inves- tigators. The effect of plankton patchiness on sampling accuracy has received some attention (Hamner and Carle- ton, 1979; Omori and Hamner. 1982) and could cause underestimation of field densities. Plankton can be highly concentrated in a localized area—for example, through behavior-related aggregation (, Alldredge and Ham- ner, 1980: Ueda et 1983) or the accumulation of plankton in a front (Stommel, 1949: Bray. 1953: George and Edwards. 1973). A net towed through such a patch and then through a sparsely populated region would col- lect a sample with an apparent density lower than the actual density within the front or aggregation. Further- more, bivalve veligers are known to associate with marine snow (Green and Dagg. 1997: Shanks and Walters, 1997), creating localized high larval densities. Larval poly- chaetes can also be strongly associated with marine snow (Shanks and del Carmen. 1997) and, as a result, may encounter potential prey items such as bivalve veligers more frequently. Published observations of predation upon bivalve veligers by larval polychaetes may thus re-
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