Zooplankton Feeding Ecology: Contents of Fecal Pellets of the Cyclopoid Copepods Oncaea venusta, Corycaeus amazonicus, Oithona plumifera, and O. simplex from the Northern Gulf of Mexico

Abstract

Abstract. In situ feeding habits of the cyclopoid copepods Oncaea venusta, Corycaeus amazonicus, Oithona plumifera, and O. simplex were investigated by scanning electron microscope examination of fecal pellets, the contents of which reflected copepod gut contents upon capture. Peilet contents were compared with assemblages of phytoplankton present in surface waters at times of copepod collection. All samples were from the northern Gulf of Mexico. All four copepods fed upon phytoplankton and O. venusta also ingested other crustaceans. Dominant components of fecal pellets generally did not mirror those of available phytoplankton assemblages. In some cases, O. venusta ingested primarily larger‐sized particles even when these were not most abundant, and in other cases it did not ingest large cells even when they were present in bloom concentrations. The presence of small (< 2–5 urn diameter) centric diatoms in O. venusta pellets suggests the possibility of feeding by mechanisms other than suspension or raptorial feeding. Limited observations suggest that C. amazonicus and O. plumifera may feed raptorially on larger particles even when these are not particularly abundant, and that the small O. simplex (< 500 nm total length) feeds mainly upon nanoplankton. It appears that cyclopoid feeding mechanisms are complex, and likely more so than those of many calanoids.

Seasonal variations in biomass, growth rate and production rate of the small cyclopoid copepod Oithona davisae in a temperate eutrophic inlet

“…simplex the population in Fukuyama Harbor. Due to differ- (Turner 1986). Gonzdez & Smetacek (1994) found that ences in the relation of egg development times to tem-0 .…”

“…Although information on their biology and ecology has been accumulated recently (cf. Turner 1986, Uchima 1988, Paffenhofer 1993, Sabatini & Knrboe 1994, Nielsen & Sabatini 1996, Nakamura & Turner 1997, much less is known of their ecological importance, compared to calanoid copepods (cf. Huntley & Lopez 1992).…”

Are taxonomic details of relevance to ecologists? An example from oncaeid microcopepods of the Red Sea

“…Pasternak 1984;Turner 1986;Ohtsuka et al 1996). The substrate-feeding modus of oncaeid copepods enables them to utilize colonial phytoplankton cells (Phaeocystis spp.)…”

“…Arinardi 1990) or ''detritivore'' (Yamaguchi et al 2002). Published data on the food of oncaeids are still restricted to a few larger species feeding in the upper water (surface) layers, such as the epipelagic Oncaea venusta (Turner 1986) or the vertically migrating Triconia conifera (Ohtsuka et al 1996) and O. curvata (Metz 1998), but interspecific differences between oncaeid species, as indicated in a recent study in the Red Sea (Ohtsuka et al 1996), have not been investigated in sufficient detail yet. Virtually nothing is known about the food requirements of the smaller species of less than 0.5 mm in length and of those in the meso-and bathypelagic zones.…”

An assessment of the effects of diatoms on planktonic copepods

“…Other major groups of copepods, such as Oithonida and Poecilostomatoida, do not (Uchima & Hirano 1986 for Oithona davisae) or rarely ingest diatoms (e.g. Turner 1986). …”