Ingestion rates of 4 small copepod species (Oithona simplex, 0. nana. Acrocalanus inermis and Parvocalanus crassirostris) were investigated in Kaneohe Bay, Hawaii, during a nudsummer increase of the pico-and nanoplankton communities. There was no evidence that adult female copepods fed significantly on picoplankton-sized cells. However, all the species responded behaviorally to variations in the concentration (10 to 110 pg C 1-l) and size spectrum (relative increase of cells > 5 pm) of nanoplankton prey. The copepods generally behaved as opportunistic particle feeders, demonstrating higher consumption rates on the most abundant cells (2-5 pm nanoplankton); however, autotrophs were usually selected over heterotrophs of simdar size. Max~murn ingestion rates were similar for the 2 calanoids and 0. nana (around 120000 cells copepod-' d-') and lower for 0. simplex (around 40000 cells copepod-' d-l), but biomass-specific rates of 0. simplex equaled those of the other species. At the highest nanoplankton concentrations, the ingestion rates of copepods appeared saturated, daily rations ranging from 100% body C d-' for A, rnermis to 260% body C d-l for P crassirostris. The differences between ingestion rates measured as cells per copepod per day and those converted to carbon suggested that ingestion might be held below potential by the cumulahve handLing times of individual prey rather than the physioloqcal constraints of food consumption and digestive processing.

The clearance rates of co-occurring appendicularian species, Oikopleura longicauda and O. fusiformis, in Kaneohe Bay, Hawaii, were investigated to evaluate and compare their roles in a tropical food web. Individual appendicularians were captured in situ and allowed to feed on the natural plankton assemblage for 60 to 180 min. Feeding rate estimates were based on flow-cytometry analyses of cell-density changes for heterotrophic bacteria (Hbact), Synechococcus spp. (Syn) and <13.0 µm autotrophic eukaryotes (Aeuks). Despite morphological differences, O. longicauda and O. fusiformis cleared the largest prey size-fraction at statistically indistinguishable rates. For the 3 prey categories (Hbact, Syn and Aeuks), mean clearance rates (± 95% CI) were 12 ± 7, 27 ± 6 and 34 ± 18 ml individual (ind.)-1 h -1 and 25 ± 12, 26 ± 15 and 38 ± 20 ml ind. , O. fusiformis can remove an almost equivalent amount (> 50%). Nevertheless, the consistently higher abundances of O. longicauda make this species a more significant link between picoplankton production and higher-level consumers (chaetognaths and fishes) in this coastal tropical embayment.