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Marine Ecology Progress Series

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MEPS 250:105-116 (2003)  -  doi:10.3354/meps250105

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

Covadonga Orejas1,*, Josep Maria Gili2, Wolf Arntz1

1Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, 27568 Bremerhaven, Germany
2Institut de Ciències del Mar (CMIMA-CSIC), Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain

ABSTRACT: The diet composition of 2 Antarctic octocorals Primnoisis antarctica and Primnoella sp. from the shelf of the eastern Weddell Sea (Antarctica) has been studied 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 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 x 10-5 mgC polyp-1 d-1 for P. antarctica and 1.34 x 10-4 mgC polyp-1 d-1 for Primnoella sp.). In P. antarctica, the small plankton food covers approximately 49% of the daily energy demand. The ability of these suspension feeders to take 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 communities

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