Nematode Biomass Spectra at Two Abyssal Sites in the NE Atlantic with a Contrasting Food Supply

Abstract

Abundance and biomass sizes spectra of nematodes have been investigated at two contrasting abyssal sites in the NE Atlantic. The northern site is situated on the Porcupine Abyssal Plain where there is evidence for a high, seasonal input of organic matter derived from the overlying water column. The southern site is the oligotrophic station of the French EUMELI programme off Mauritania and is char acterized by low primary productivity in the overlying water column and consequently by a lower organic input to the deep-sea floor. Low nematode density and total biomass in the surficial centimetre of the sediment at the EUMELI site (89 ind/l0 cm2, 8.52 pg wwt/lO cm2), in contrast to the PAP site (254 ind/l0 cm2, 54.16 pg wwt/lO cm2), supports a presumed lower food supply to this area. Similary, mean individual nematode body weight is significantly smaller at the oligotrophic EUMELI site (0.0241 pg dwt) compared to the PAP site (0.0511 pg dwt), which supports the hypothesis that mean nematode body size is correlated with food availability. However, differences are much less obvious when comparing geometric mean biomasses and median individual body sizes. The abundance size spectra for the two localities diverge appreciably only in the upper quartile. The differences in mean individual body weights are caused by the relatively greater abundance of larger nematodes at the more eutrophic PAP site.