Sediment distribution, enzyme profiles and bacterial activities in the guts of Oneirophanta mutabilis, Psychropotes longicauda and Pseudostichopus sp. - What do they tell us about digestive strategies of abyssal holothurians?

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Sediment distribution, enzyme profiles and bacterial activities in the guts of Oneirophanta mutabilis, Psychropotes longicauda and Pseudostichopus sp. - What do they tell us about digestive strategies of abyssal holothurians?
*David Roberts, * H M Moore, **J Patching, **M Carton

*School of Biology & Biochemistry, The Queen’s University, Belfast BT9 7BL, Northern Ireland.
**Marine Microbiology, Ryan Institute, University College, Galway, Ireland

Gut morphologies can be used to infer the digestive strategies of animals and can be substituted for differences in diet in analyses of resource partitioning (Penry 1993). These premises form the basis for our developing studies into the nutrition of and resource partitioning amongst sympatric abyssal deposit-feeding holothurians. Based on the application of chemical reactor models to digestive strategies in deposit feeders promoted by Penry and Jumars (1987), our previous studies (Moore, Manship & Roberts, 1995) inferred that the gut of Oneirophanta mutabilis may act as a plug-flow reactor whereas the guts of Pseudostichopus sp. and Psychropotes longicauda may show predominantly fore- and hind-gut fermentation respectively.
To further test these ideas, a comparative study of different regions of the guts of the three species was undertaken. The three approaches adopted involved investigation of:
sediment distribution in the gut, to provide quantitative support for previous anatomical interpretations
enzyme profiles in the gut and gut contents, to identify holothurian and possible sedimentary sources of hydrolytic enzymes
bacterial profiles and activities in the gut which might support the concept of fermentation in specific regions of the gut.

Preliminary results indicate clear interspecific differences in sediment partitioning in the gut which supports previous interpretations. Profiles of 19 hydrolytic enzymes determined using API Zym assays ((BioMerieux) were similar for both gut tissues and contents although higher values were recorded for the former. Total bacterial counts and profiles of cell-specific rates of bacterial thymidine incorporation also revealed interpecific diferences but these are more difficult to interpret.

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