Changes in distribution and abundance of juvenile fishes in intertidal soft sediment areas dominated by the burrowing crab Chasmagnathus granulatus

Abstract

Intertidal estuarine areas located between southern Brazil and the northern Argentinean Patagonia are characterised by extended beds of the burrowing crab Chasmagnathus granulatus. Their activity leads to profound changes in the structure, quality and dynamics of sediments, which affect the entire benthic community and create a patchy distribution of resources for other species. In this study, the differences in habitat use by juvenile fishes above soft sediments inhabited by C. granulatus were evaluated. Adjacent areas with (‘crab beds’) and without crab burrows in intertidal mudflats of the Mar Chiquita Coastal Lagoon (37°32'S, 57°19'W) were sampled seasonally from 2000 to 2002. There were more fish species in crab-bed areas. Abundances of benthivorous and planktivorous fishes were also higher in crab beds during flood tide; however, during ebb tide, planktivorous fishes were more abundant outside crab-bed areas, whereas benthivores did not vary between areas. The present study demonstrated that species composition and abundance of juvenile fishes can be affected by the presence of bioturbator species such as C. granulatus.