The marine cladoceran Penilia avirostris and the “microbial loop” of pelagic food webs1

Abstract

We used quantitative microscopy to examine feeding of Penilia avirostris on natural (< 1 pm) and cultured (0.5-2.0 pm) bacterioplankton, autotrophic phytoplankton, heterotrophic microflagellates (2-5 pm), and bacteria-sized (0.2-l .O pm) fluorescent beads. Natural and cultured bacterioplankton were not appreciably ingested, except for extremely high concentrations (>9.0 x lo6 cells ml-l) of clumped cells from bacterial cultures. Bacterivorous microflagellates were ingested. Most species of available natural phytoplankton (chain-forming or large diatoms) and Pseudoisochrysis paradoxa (5-6 pm) were not ingested, but the 4-6-pm diatom Thalassiosira pseudonana and the 1 O-l 2-pm Thalassiosira weiss$?ogiii were. Food choice and feeding rate appeared related to food concentration as well as cell size. Our results contrast with previous reports of bacterivory by P. avirostris and other cladocerans, possibly due to preferential bacterivory on large or aggregated bacteria, elevated bacterial abundance levels in cultures, or failure to recognize heterotrophic microflagellates as an unseen intermediate trophic step in studies with nonmicroscopic techniques.Although P. avirostris does not feed on free-living bacterioplankton, it may be an important component of the "microbial loop" between bacterioplankton and higher consumers because of its predation on bactcrivorous microflagellates.

Relationship between nutrients and plankton biomass in the turbidity maximum zone of the Pearl River Estuary

“…In contrast, phytoplankton density was very low in TMZ and zooplankton had to depend on bacteria and detritus to support their high abundance. Although we lack the grazing experiments to investigate the feeding behavior of zooplankton, there are several studies that described the ingestion of bacteria by the naupliar and juvenile copepodite stages of small copepod species (Bedo et al, 1993;Turner et al, 1988). Moreover, high abundance of bacteria can support high abundances of ciliates and nanoflagellates, which are prey for ominvorous and carnivorous copepods, thus resulting in high abundance of copepods.…”

Seasonal patterns in plankton communities in a pluriannual time series at a coastal Mediterranean site (Gulf of Naples): an attempt to discern recurrences and trends

“…The peaks of Penilia avirostris observed in July-August very often co-occur with peaks of the small suspension-feeding copepod Paracalanus parvus. Due to their remarkable abundance, these two species can have a notable impact on the phytoplankton community, being able to graze on small diatoms, flagellates (Paffenhöfer and Orcutt, 1986;Turner et al, 1988) and heterotrophic dinoflagellates (Suzuki et al, 1999).…”

Aureococcus anophagefferens: Causes and ecological consequences of brown tides in U.S. mid‐Atlantic coastal waters

“…In 1986, when normal conditions prevailed, abundances returned to levels found in previous nonbloom years (Smayda and Fofonoff 1989). Given that some cladocerans preferentially ingest small (2-5 pm) algae comparable in size to brown tide, and not larger or chain-forming diatoms (Turner et al 1988), cladoceran grazing may have been seriously impacted by brown tide. In Narragansett Bay, abundances of meroplanktonic larvae, including polychaetes and bivalves, were also negatively correlated with brown tide concentration and were lower than in nonbloom years (Smayda and Fofonoff 1989).…”