Effects of macrobenthic burrows on infaunal communities in tropical tidal flats

The effects of burrows on the infaunal community in a tropical tidal flat were studied on the northeast coast of Australia. A comparative survey of infauna in burrows versus adjacent sediment was carried out for the burrows of 3 crustaceans (Scopimera inflata, Uca spp., Callianassa australiensis) and a brachiopod (Lingula anatina). More (1.5 to 2.5x) infauna occurred within burrows than in adjacent sediments. Densities of meiobenthic nematodes, copepods and Platyhelminthes were significantly higher within the burrows of Uca spp., C. australiensis and L. anatina. In the latter 2 cases multivariate analyses showed distinct communities in burrows and adjacent sediment, although this was not consistent over time for the brachiopod burrows. No differences in community composition were detected in the cases of Uca spp. and S. inflata. In a field experiment, C. australiensis was excluded from 7 sites, and infaunal abundances and species compositions were followed for 1 yr and compared with control sites. From the very beginning, meiofaunal densities were significantly lower in the exclusion sites, mainly due to reduced densities of nematodes and copepods. The effect of the shrimp exclusion on macrofauna was less pronounced, but after 1 yr total numbers of macrofauna were significantly lower in the exclusions, due to the distribution of amphipods. The results showed that promotive interactions play an important role in structuring tropical tidal flat communities.