Sediment distribution, hydrolytic enzyme profiles and bacterial activitiesin the guts of Oneirophanta mutabilis, Psychropotes longicauda and Pseudostichopus villosus: what do they tell us about digestive strategies of abyssal holothurians?

This paper describes inter-specific differences in the distribution of sedi ment in the gut compartments and in the enzyme and bacterial profiles along the gut of abyssal holothurian species - Oneirophanta mutabilis, Psychropo tes longicauda and Pseudostichopus villosus sampled from a eutrophic site i n the NE Atlantic at different times of the year. Proportions of sediments, relative to total gut contents, in the pharynx, oesophagus, anterior and p osterior intestine differed significantly in all the inter-species comparis ons, but not between inter-seasonal comparisons. Significant differences we re also found between the relative proportions of sediments in both the rec tum and cloaca of Psychropotes longicauda and Oneirophanta mutabilis. Ninet een enzymes were identified in either gut-tissue or gut-content samples of the holothurians studied. Concentrations of the enzymes in gut tissues and their contents were highly correlated. Greater concentrations of the enzyme s were found in the gut tissues suggesting that they are the main source of the enzymes. The suites of enzymes recorded were broadly similar in each o f the species sampled collected regardless of the time of the year, and the y were similar to those described previously for shallow-water holothurians . Significant inter-specific differences in the gut tissue concentrations o f some of the glycosidases suggest dietary differences. For example, Psychr opotes longicauda and Pseudostichopus villosus contain higher levels of chi tobiase than Oneirophanta mutabilis. There were no seasonal changes in bact erial activity profiles along the guts of O. mutabilis and Pseudostichopus villosus. In both these species bacterial activity and abundance declined b etween the pharynx/oesophagus and anterior intestine, but then increased al ong the gut and became greatest in the rectum/cloaca. Although the data set s were more limited for Psychropotes longicauda, bacterial activity increas ed from the anterior to the posterior intestine but then declined slightly to the rectum/cloaca. These changes in bacterial activity and densities pro bably reflect changes in the microbial environment along the guts of abyssa l holothurians. Such changes suggest that there is potential for microbial breakdown of a broader range of substrates than could be otherwise tie achi eved by the holothurian itself. However, the present study found no evidenc e for sedimentary (microbial) Sources or hydrolytic enzymes. (C) 2001 Elsev ier Science Ltd. All rights reserved.