Callianassa trilobata (Crustacea: Thalassinidea) influences abundance of meiofauna and biomass, composition, and physiologic state of microbial communities within its burrow

Abstract

Biochemical and traditional methods were used to determine the influence of Caflianassa trilobata on microbiological and meiofaunal communities within its large, hghly consolidated burrow. Sediment was collected from the lining of the shrimp's burrow, the burrow matrix, and ambient, subsurface sediment. The lining and matrix were composed of poorly sorted, fine-grained material compared to sandy ambient sediment. Meiofauna, predominantly nematodes, were most abundant in ambient sediment, not in the burrow as has been found for other species of macrofauna. Concentrations of chlorophyll a were very high in the lining, consistent with the suggestion that C. trilobata lines its burrow walls with seagrass. Analyses of lipids indicated that relative to the matrix and ambient sediment, the lining abounds with proand eukaryotic biomass. Thirty-four phospholipid, ester-linked fatty acids (PLFA) were identified and quantified. Fatty acids were assigned to functional groups of microorganisms to assess spatial variations in the absolute abundance and relative proportions of microbial populations. Dominance of prokaryotes was pronounced in all 3 areas, especially the matrix. The lining was the most aerobic location, but anaerobic microhabitats simultaneously allowed proliferation of sulfate-reducing bacteria, e. g. Desulfobacter. A radial trend was detected in the ratio of bacteria with terminally branched PLFA, typical of Gram-positive organisms, to those with unsaturated PLFA common to Gram-negative bacteria. The ratio increased from lining to matrix to ambient sediment. The ratios of tram to cls isomers of 16:lw7 indicated that prokaryotes in the matrix were starved. Through construction and maintenance of its burrow, C. trilobata determines not only the absolute and relative abundances of microbes in its sedimentary environment, but their physiologic state as well.