Different Oceanographic Regimes in the Vicinity of the Antarctic Peninsula Reflected in Benthic Nematode Communities

Abstract

Marine free-living nematode communities were studied at similar depths (~500 m) at two sides of the Antarctic Peninsula, characterised by different environmental and oceanographic conditions. At the Weddell Sea side, benthic communities are influenced by cold deep-water formation and seasonal sea-ice conditions, whereas the Drake Passage side experiences milder oceanic conditions and strong dynamics of the Antarctic Circumpolar Current. This resulted in different surface primary productivity, which contrasted with observed benthic pigment patterns and varied according to the area studied: chlorophyll a concentrations (as a proxy for primary production) were high in the Weddell Sea sediments, but low in the surface waters above; this pattern was reversed in the Drake Passage. Differences between areas were largely mirrored by the nematode communities: nematode densities peaked in Weddell stations and showed deeper vertical occurrence in the sediment, associated with deeper penetration of chlorophyll a and indicative of a strong bentho-pelagic coupling. Generic composition showed some similarities across both areas, though differences in the relative contribution of certain genera were noted, together with distinct community shifts with depth in the sediment at all locations.

Fig 1. (a) Location of the four sampling stations (W-120 and W-163 east of the Antarctic Peninsula; DP-243 and DP-250 west in Drake Passage); map adapted from Alfred Wegener Institute bathymetry group; (b) + (c) Surface chl a concentrations (in mg m^-3) at the respective sampling times for both sites.

Graphs are based on MODIS Aqua data (NASA) of the sea surface on 8-day averages during the period of sampling and produced with the Giovanni online data system, developed and maintained by the NASA GES DISC.

Fig 2. Vertical distribution of pigments and nematodes.

Average CPE values (μg g^-1; dots) and nematode densities (ind 10 cm^-2, bars) with their respective standard error in the sediment for all four stations (n = 3).

Fig 3. PCA plot of environmental data.

Each symbol corresponds to a centimetre layer of a different replicate in Weddell Sea or Drake Passage and represents the environmental setting for that sample.

Fig 4. Visualisation of pairwise comparisons of the PERMANOVA interaction ‘station × layer’.

Graph plots similarities of nematode assemblages between the different stations according to depth in the sediment.

Fig 5. Vertical profiles of relative genus abundances for each station.

Only genera with an abundance >4% in one of the layers were included, all others were grouped as “rest”. Where possible, we used the same colours for the same genera in all different plots.

Fig 6. Box plots of the different diversity indices for the different stations.

Boxes display median, first and third quartiles, minimum and maximum.