MEPS 453:151-158 (2012)  -  DOI: https://doi.org/10.3354/meps09642

ABSTRACT: The alteration of sediments by bioturbating organisms plays a major role in aquatic ecosystems, from both ecological and evolutionary perspectives. Several studies have highlighted the ability of bioturbators to alter sedimentary biogeochemical processes and community structure, but the potential influence of bioturbators on pelagic species is unexplored in marine ecology. In the present study, we investigated the direct effects of bioturbation by a southern African burrowing sandprawn, Callichirus kraussi, on primary producers (benthic microalgae) and the indirect effects on the growth of a fish (grey mullet Liza richardsonii) that consumes microalgae. A mesocosm experiment was undertaken in which similar-sized L. richardsonii at 2 densities were exposed to 3 increasing densities of C. kraussi. After 3 wk of exposure to the effects of C. kraussi, the fish were weighed and their lengths measured to calculate their physical condition and growth rates. At the termination of the experiment, the microalgal biomass and sediment turnover were measured in each mesocosm. Higher C. kraussi densities resulted in an increase in sediment turnover and caused reductions in microalgal biomass, which in turn led to a reduction of the biomass and lengths of L. richardsonii. Increasing densities of C. kraussi evidently enhance sediment turnover from burrows to the sediment surface, leading to the burial of microalgae and indirect reductions in food availability to L. richardsonii. This reduction in turn leads to metabolic losses and reductions in the growth of this fish species. These results indicate that benthic bioturbators can have strong effects on aquatic ecosystems, especially by modulating energy flow to nektonic species.

KEY WORDS: Bioturbation · Food webs · Marine benthos · Sediment turnover · Benthic-pelagic coupling