Nutrition of Deposit-Feeding Holothuroids and Echinoids (Echinodermata) from a Shallow Reef Lagoon, Discovery Bay, Jamaica

Abstract

Concentrations of organic carbon and nitrogen, ATP, and total plant pigment (chlorophyll a + phaeophytin) were approximately twice as high i n foregut contents of the deposit-feeding, aspidochirote holothuroids Isostichopus badionotus Selenka, Holothuria rnexicana Ludwig and H. arenicola Forskal, and spatangoid echinoids Meoma ventricosa Lamarck and Plagiobrissus grandis Gmelin than in the adjacent sediments. This suggests that holothuroids and spatangoids selectively ingest nutrient-rich grains, contrary to the conventional view that they show poor chemical discrimination. The availability of the organic food resources did not vary consistently between different grainsize fractions of sediment. This obviates any a priori expectation that discrimination on the basis of grain quality, demonstrated here, will be coupled to discrimination according to grain size, previously shown not to occur in these species. Assimilation efficiency of the ingested carbon averaged 42 %. Plant carbon, calculated from pigment concentrations and probably derived from diatoms, represented a major carbon resource in the available sediments, but only a small proportion of that ingested was apparently assimilated. Meiofauna, a minor component of the available carbon (ca. 1 %), were ingested in lower numbers than those at which they occurred in the sediment, and were not digested or assimilated. Bacterial biomass was not determined, but other studies suggest that its contribution to the sedimentary carbon pool is low. It is likely that at least half of the carbon assimilated by these deposit feeders is of detrital origin. This result, which contrasts with present understanding of the nutrition of deposit feeders, may be indicative of qualitative differences between detritus of coral reefs and that of other shallow, coastal ecosystems.