FUNCTIONS OF SWIMMING SETAE WITHIN CAPRELLID AMPHIPODS (CRUSTACEA)

¹ Friday Harbor Laboratories, University of Washington, Friday Harbor, Washington 98250

1. All caprellids with swimming setae do not swim, but of those that do, a 9.0% decrease in swimming rate was measured after swimming setae removal. The literature indicates that many caprellids without swimming setae are found in the plankton, and presumably swimming. The importance of swimming setae to the ability to swim is not absolute.

2. Rearing attempts of caprellids with swimming setae showed that some species required periphyton for survival while other species could sustain themselves by filter-feeding. If periphyton was added to the trials, all species survived.

3. Regression analyses indicated two patterns of swimming setal spacing. Linear regressions gave the best fit of cumulative filtering area: setal spacing lines for those species requiring periphyton. Those species surviving only with filterable material were best fit with log regressions.

4. Particle frequency in Puget Sound is constantly descreasing as particle size increases. The log pattern of setal spacing more than doubles the amount of material filtered over the linear pattern.

5. Caprella has 49% of the described species of caprellids; the next most numerous genus has 4%. Swimming setae opened a new feeding niche for caprellids and this led to the species explosion. Other genera with swimming setae are competitively subordinate to Caprella.