Copepod grazing in a subtropical bay:species-specific responses to a midsummer increase in nanoplankton standing stock

Abstract

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.

Low grazing impact of mesozooplankton on the microbial communities of the Alboran Sea: a possible case of inhibitory effects by the toxic dinoflagellate Gymnodinium catenatum

“…It is difficult to relate these results with other studies because selectivity patterns are highly dependent on the specific communities investigated. Selection for microzooplankton over algae is not a rare feature (Stoecker & Egloff 1987, Gifford & Dagg 1988, Wiadnyana & Rassoulzadegan 1989, although preference for algae over protozoans has also been observed (Williamson et al 1996, Calbet et al 2000a. A similar contradictory situation is found when comparing selectivity for ciliates and dinoflagellates.…”

“…Although both chl a sizefractions were significantly correlated with ingestion, the regression coefficient was higher for > 5 µm chl a. This is not surprising, considering the numerical relevance of copepods in the mesozooplankton community, which are unable to feed efficiently on < 5 µm prey (Hansen et al 1994, Calbet et al 2000a. Better relationships were apparent for ciliates, although the grazing on dinoflagellates seemed to be independent of cell concentration.…”

“…Aggregated bacterioplankton, on the other hand, is a frequent component of the diet of cladocerans, but this is not the case for free-living bacteria (Turner 1988). Copepods are not able to exploit this food source either (Berggreen et al 1988, Calbet et al 2000a). In any case, at least autotrophic bacteria were already considered within chl a < 5 µm estimations in our study.…”

Zooplankton community dynamics in relation to the seasonal cycle and nutrient inputs in an urban tropical estuary in Brazil

“…Parvocalanus crassirostris was important in July and it is very common in most Brazilian estuaries (Matsumura-Tundisi, 1972;Björnberg, 1981), even those that are heavily impacted . Parvocalanus crassirostris feeds significantly on picoplankton and nanoplankton and behaves as an opportunistic particle feeder, showing higher consumption rates upon the most abundant cells (2-5 µm nanoplankton) (Calbet et al, 2000). Generally, it is an abundant species in eutrophic systems, showing its r-strategist behavior.…”

Grazing of two common appendicularians on the natural prey assemblage of a tropical coastal ecosystem

“…Perhaps not surprisingly, given the relative importance of picoplankton in tropical oceans, Oikopleura longicauda and O. fusiformis can clear naturally occurring prey in this size range at rates substantially higher than those of comparably sized appendicularians studied to date (King et al 1980, Alldredge 1981, Bedo et al 1993, Acuña & Kiefer 2000, Broms & Tiselius 2003, López-Urrutia et al 2003, Fernandez et al 2004, and vastly exceeding the rates of co-occurring copepods (Calbet et al 2000). In fact, grazing by O. longicauda can lead to mean picophytoplankton mortality rates comparable to those resulting from protozoan grazing (specifically 2 to 5 µm heterotrophic nanoflagellates) in Kaneohe Bay (Landry et al 1984, Scheinberg 2004.…”