Use of a wide spectrum of particle food by suspension-feeders: adaptation to low phytoplankton availability?

TATIÁN M, SAHADE R, FUENTES V AND MERCURI G.

Curitiba, Brasil

Simposio; IX SCAR Biology Symposium; 2005

SCAR

Benthic suspension-feeders mainly filter phytoplankton, playing an important role in the coupling between pelagic and benthic systems. Despite heavy sedimentation and low phytoplankton production in Potter Cove (King George Island), suspension-feeders reach a high biomass, while some taxa (particularly ascidians) show one of the highest species richness reported in coastal Antarctic areas. Since several years, ascidians were selected to develop a series of trophic studies in order to know the composition and the origin of food for the benthic community year-round. Analyses of gut contents revealed the presence of organic material which decreased along the gut, suggesting its assimilation by ascidians. Microscopic composition showed a scarce amount of microalgae, while particles previously degraded (macroalgal detritus and fecal pellets) were the bulk of these contents. Experiments using dehydrated and poundered macroalgae as a food source revealed that ascidians were able to filter and assimilate this material, even in different concentration and range size. Macroalgal detritus carried by currents, probably enriched with elements from the bacterial community, may constitute the principal source of food year-round. Due to this “trophic plasticity”, suspension-feeders widely develop at Potter Cove, where other disturbances, (i.e, ice-berg scour), are not strong as in other close areas.