Comparative Feeding-Habits of Polychelid Lobsters in the Western Mediterranean Deep-Sea Communities

Feeding habits of the 2 deep-water species of polychelid lobsters occurring in the Balearic Basin (Western Mediterranean) were examined. Samples were taken with an OTSB-14 bottom trawl from depths between 550 and 2300 m in 1988-89. Polycheles typhlops and Stereomastis sculpta occupy d well-defined trophic niche, between the uppermost level of the bottom sediment and the water layer immediately adjacent to the sea bed. Scavenging plays an important role in feeding. However, ontogenetic changes in the diet were clear in both species. Small individuals based their diet on epibenthic peracarid crustaceans, whereas scavenging and ingestion of inert remains became more important in the adult diet. The trophic habits of the 2 species were rather similar; differences recorded are more consistent with depth-related changes in available prey resources than with changes in the position of the 2 species in the food web. The progressive decrease of abundance of P. typhlops with increasing depth coincided with greatly reduced densities of some of its preferential prey (i.e. Calocaris macandreae, Cirolana borealis or euphausiids) and with a different feeding strategy. S, sculpta shows a more microphagic and passive feeding habit. Feeding activity, quite low in both species, was lower in S. sculpta. All these results suggest that S. sculpta is better adapted to the more oligotrophic conditions found on the lower slope. Competitive trophic interaction may also account for the separate depth distributions of the 2 species. These interactions may be especially important on the deep-sea bottoms in the Mediterranean Sea, where environmental parameters like temperature and salinity are constant,