Benthic foraminiferal assemblages in Explorers Cove, Antarctica: A shallow-water site with deep-sea characteristics

Abstract

During November and December 1993, we sampled foraminiferal populations living at a 25–28m deep site in Explorers Cove, McMurdo Sound, Antarctica, by means of an airlift suction apparatus and sediment coring. Mean standing stocks (stained specimens per 10cm 2) were 8.55±2.60 (all specimens >1mm, 0–10cm layer), 62.1±27.5 (all specimens >500μm, 0–10cm layer), 483 (all specimens >63μm, 0–1cm layer) and 632 (all specimens >28μm, 0–1cm layer). The fauna comprises diverse taxa including both hard-shelled and soft-shelled forms. The coarser fractions (>1mm) are dominated by large agglutinated foraminifera, mainly “spheres” and domes (psammosphaerids, saccamminids, notodendrodiids), but also contain some large calcareous taxa ( Cibicides, Pyrgo). The finer fractions (>500, >63, >28μm) yield numerous soft-bodied monothalamous foraminifera in addition to the more commonly studied calcareous and multilocular agglutinated forms. Many species adopt epifaunal or shallow infaunal (0–1cm layer) microhabitats but a few smaller ones are more deeply infaunal (>1cm). A variety of trophic strategies can be inferred from the limited available evidence. Some abundant large species ( Crithionina spp., Gromia oviformis) may be shallow infaunal or epifaunal deposit feeders, but the most striking feature of the fauna is the conspicuous occurrence of large epifaunal species which appear to be suspension feeders (e.g. Astrammina, Astrorhiza, Notodendrodes, Cibicides). Some of these foraminifera can probably switch trophic mode, for example, from suspension feeding to osmotrophy in response to a fluctuating food supply. The Explorers Cove fauna includes a mix of wide-ranging and endemic species. The main features of the fauna are consistent with environmental similarities (uniformly low temperatures, physical tranquillity, episodic food inputs) between Explorers Cove and deeper water settings. In the Northern Hemisphaere, comparable faunas (i.e. those in which large agglutinated taxa are a conspicuous element) are found in deep sublittoral and fjordic areas (100–1000m), as well as at some bathyal and abyssal localities (down to several thousands of metres) which receive a substantial organic matter input from processes such as upwelling. Foraminifera probably play a major ecological role in these systems, particularly in trophic interactions and organic carbon cycling. Their success may depend on two main attributes. First, they possess extremely efficient food gathering organelles (reticulopodia) and second, they become quiescent when starved but can rapidly increase their metabolic rate when presented with food. Our SCUBA-accessible study site in Explorers Cove provides a unique opportunity to clarify the role that these important protists play in shallow Antarctic waters as well as in more remote deep-water environments.