Sensitivity of a benthic, metazoan, biomass size spectrum to differences in sediment granulometry

Abstract

Benthic biomass size spectra of meiofauna and macrofauna (BBSS) were examined at 4 sites in the Asko area, on the Swedish coast of the northern Baltic Sea proper. The sites ranged in median sediment grain size from a coarse sand (680 pm) to mud (c63 pm). Previous empirical work and theory suggests that BBSS are bimodal where sediment granulometry permits the existence of both fauna that live interstitially and those that burrow; each biomass mode reflects constraints on organism body size for each activity. Two hypotheses based on this theory are tested here: (1) BBSS are bimodal in sediments which support both an interstitial and burrowing fauna and (2) the biomass trough between modes of the spectrum changes consistently with sediment grain size. None of the BBSS from any of the sites were bimodal; thus, the first hypothesis was rejected. Shapes of spectra varied somewhat among sites but showed no consistent difference related to sediment granulometry; thus, the second hypothesis was rejected. To further test these hypotheses, spectra were conf~ned to infauna by removing the surface sediment layer (0 to 1 cm), thereby removing epibenthic fauna. Both hypotheses were once again rejected when the spectra consisted of only infauna.