. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HYDRA FEEDING 297 Prey Interception Nemotocyst Discharge Inhibited (?) Capture \ Ingestion Rate Increases Ingestion. Ingestion Inhibited Digestion Egestion FIGURE 5. Generalized model of feeding showing effects of ingested prey on feeding. —» indicates a stimulatory effect and-O indicates an inhibitory effect. As evident from Figure 4, at high prey densities H. viridis is capable of multiple captures, and an increase in the rate at which it ingests captured prey enables H. viridis to increase the number of prey consumed duri
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HYDRA FEEDING 297 Prey Interception Nemotocyst Discharge Inhibited (?) Capture \ Ingestion Rate Increases Ingestion. Ingestion Inhibited Digestion Egestion FIGURE 5. Generalized model of feeding showing effects of ingested prey on feeding. —» indicates a stimulatory effect and-O indicates an inhibitory effect. As evident from Figure 4, at high prey densities H. viridis is capable of multiple captures, and an increase in the rate at which it ingests captured prey enables H. viridis to increase the number of prey consumed during a single capture-ingestion- digestion sequence. The response of H. viridis to prey at different densities indicates that it is best suited to feeding on densely distributed prey. The enhanced ingestion rates reported here were observed at prey densities of 4,000 Artemia-l l, while crustacean den- sities in lakes are usually in the range of 5-50-I"1 (Wetzel, 1975). Denser con- centrations, however, do occur and may be a regular feature of aquatic environ- ments. In a study of a dense Hydra population in Toolik Lake, Alaska, Cuker and Mozley (1981) captured up to 14,000 Bosmina per day in m2 emergence traps. They report that the Bosmina were found in dense swarms and cite one example of B. longirositis swarms of up to 27,000 •!"'. Swarming has also been observed in Heterocope septentrionalis (Herbert, et al., 1980) and is frequently observed in marine zooplankton which concentrate at the bottom during the day (Alldredge and King, 1977). As predicted, in the presence of plankton swarms Hydra are effective predators. Cuker and Mozley (1981) regularly found Hydra with 5-7 prey per gut and report one case of a Hydra with 23 carapaces in its gut. (The species Cuker and Mozley [1981] studies is much larger than H. viridis, which can hold only 5-7 Anemia in its gut.) At low prey densities the simple gut and the feeding sequence exhibited by Hydra reduce their cap
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
