SEASONAL-VARIATION IN THE FEEDING-ACTIVITY OF 4 SPECIES OF ANTARCTIC BRYOZOAN IN RELATION TO ENVIRONMENTAL-FACTORS

Many areas of the Antarctic continental shelf support rich communities of benthic suspension feeders, of which Bryozoa are frequently an imp ortant component. These communities inhabit an environment characteris ed by a low temperature with only a slight seasonal variation, long pe riods of winter ice cover, and strong seasonal variations in chlorophy ll standing stock, light and water movement. The feeding activity of f our species of cheilostome bryozoans, from differing depths, sites and substrata, were monitored in situ at Signy Island, Antarctica. Feedin g activity was recorded photographically, monitoring the same colonies over 2 yr. The patterns of feeding activity differed between the four species, in duration, timing and the degree of between colony variati on. All four species, however, spent most (and in the case of the mass ive foliose Arachnopusia inchoata, all) of the study period with a hig h proportion of their lophophores everted. Two erect flustrid species Alloeflustra tenuis and Nematoflustra flagellata showed similar season al patterns but differed systematically in the timing of feeding. The shallow water Inversiula nutrix differed in its high between colony va riability and the low mean level of feeding activity. These patterns s howed no clear relationship to environmental cues such as ice cover, t emperature, chlorophyll concentration or vertical flux. It is clear, h owever, that these species are adapted to feed at very low cell concen trations, and indicate that the polar winter may be shorter and less h arsh for shallow water benthic suspension feeders than previously thou ght.