A pigment analysis of feeding modes of Thelepus extensus (Polychaeta, Terebellidae) in relation to wave exposure at the Iles Kerguelen

Pigment analysis (HPLC and fluorometry) and light microscopy observations o f the gut content of Thelepus extensus (Terebellidae) and surrounding sedim ents were carried out at two hydrodynamically contrasting sites at subantar ctic lies Kerguelen; 1) a sheltered site (Port-Raymond) with a dense popula tion of large-bodied animals, and 2) an exposed site (Port-aux-Francais) wi th a scarce population of smaller individuals. Chlorophyll a derivatives (p haeophorbide a-like) were the most abundant pigments in sediments and polyc haete digestive tracts. The second important group of pigments consisted of five unknown carotenoids of which two were present only in the polychaete digestive tract. Pigments in the muddy sediment at the sheltered site appea red to originate from the grazing activity of the polychaetes, as suggested by the high concentrations of degradation products and the same phaeophorb ides observed both in the sediment and in the gut contents. Material origin ating from the dense Macrocystis pyrifera (Phaeophyceae) and Ulvae (Chrorop hyceae) cover constituted a large part of the polychaetes' diet at this she ltered site, as indicated by macroalgal debris in the gut contents and the presence of violaxanthin in the sediment and lutein/zeaxanthin in both poly chaetes and sediments. The polychaetes seem to adapt their grazing mode to the environmental conditions, preferring suspension feeding in the sheltere d site and deposit feeding at the exposed site. The different morphologies, behaviours and life spans of the two conspecific populations may by linked to the contrasting hydrodynamics of the two sites and to their respective diets.