The role of the small planktonic communities in the diet of two Antarctic octocorals (Primnoisis antarctica and Primnoella sp.)

Abstract

The diet composition of 2 Antarctic octocorals, Primnoisis antarctica and Primnoella sp., from the shelf of the eastern Weddell Sea (Antarctica) is studied here for the first time. Although mesozooplankton is very scarce in the diet of these organisms, it seems to be important because of its high carbon content. Feeding experiments showed that components of the seston, including the finer fraction of suspended organic matter (ciliates, dinoflagellates and phytoplankton), are also an important part of the octocoral diet. In P. antarctica, the diatom Fragillariopsis spp. accounted for 77% of the total number of cells captured, followed by dinoflagellates (20%), Nitzschia spp. (2%) and ciliates (1%). In Primnoella sp., dinoflagellates were consumed preferentially (92%), followed by ciliates (6%) and centric diatoms (2%). Biomass consumed, however, was low (1.11 × 10 -5 mg C polyp -1 d -1for P. antarctica and 1.34 × 10 -4 mg C polyp -1 d -1 for Primnoella sp.). In P. antarctica, small plankton food covers approximately 49% of the daily energy demand. The ability of these suspension feeders to capture small cells at lower concentrations may allow them to remain seasonally active for considerably longer periods than previously thought. KEY WORDS: Feeding ecology · Suspension feeders · Antarctic gorgonians · Small-plankton communitiesResale or republication not permitted without written consent of the publisher

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