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 important component. These communities inhabit an environment characterised by a low temperature with only a slight seasonal variation, long periods of winter ice cover, and strong seasonal variations in chlorophyll standing stock, light and water movement. The feeding activity of four species of cheilostome bryozoans, from differing depths, sites and substrata, were monitored in situ at Signy Island, Antarctica. Feeding 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 variation. All four species, however, spent most (and in the case of the massive foliose Arachnopusia inchoata, all) of the study period with a high proportion of their lophophores everted. Two erect flustrid species Alloeflustra tenuis and Nematoflustra flagellata showed similar seasonal patterns but differed systematically in the timing of feeding. The shallow water Inversiula nutrix differed in its high between colony variability and the low mean level of feeding activity. These patterns showed no clear relationship to environmental cues such as ice cover, temperature, chlorophyll concentration or vertical flux. It is clear, however, that these species are adapted to feed at very low cell concentrations, and indicate that the polar winter may be shorter and less harsh for shallow water benthic suspension feeders than previously thought.