Epifaunal and shallow infaunal foraminiferal communities at three abyssal NE Atlantic sites subject to differing phytodetritus input regimes

Multiple corer samples (0-1 cm sediment layer and overlying phytodetritus) obtained at three northeast Atlantic sites were analysed for Rose Bengal stained benthic foraminifera (> 63 mu m). Strong phytodetrital pulses have been documented at the northern site on the Porcupine Abyssal Plain (PAP; 48 degrees 50'N, 16 degrees 30'W) but not at the southers sites on the Madeira Abyssal Plain (MAP; 31 degrees N, 20 degrees W) and Cape Verde Abyssal Plain (CVAP; 21 degrees N, 31 degrees W). Foraminiferal densities reflected surface primary productivity estimates fairly closely, being higher at the PAP (mean: 800 per 25.5 cm(2) sample area = 314 per 10 cm(2)) than at the southern sites (mean: 502 per sample = 197 per 10 cm(2)). In part, this difference was attributable to the presence of a substantial phytodetrital deposit in two of the PAP samples. The phytodetrital aggregates provided organically-enriched microenvironments exploited by dense foraminiferal populations, which accounted for up to 22.4% of the entire foraminiferal fauna. They were of low diversity with a few dominant species (notably the rotaliid Epistominella exigua), a population structure typical of organically enriched systems. Most of the phytodetrital species were much less common in the sediments. The total (i.e. sediment + phytodetritus) populations were highly diverse (123-167 species); but southern site populations were somewhat more diverse than PAP populations, and the two PAP phytodetritus-rich cores had higher dominance values than other samples. Total species assemblages were broadly similar. However, in addition to the phytodetritus-dwelling species, some species of Reophax, Leptohalysis, Lagenammina and ''Hyperammina'' were more abundant at the PAP site, perhaps benefiting from degraded phytodetritus or from the associated bacterial populations. A few species, e.g. Subreophax aduncus and Lagenammina tubulata, were more abundant at the southern sites. Copyright (C) 1996 Elsevier Science Ltd