Infaunal recruitment patterns in soft bottom habitats of the Patos Lagoon estuary, southern Brazil: influence of Chasmagnathus granulata (Brachyura, Grapsidae) disturbance

A comparative study of the infaunal recruitment patterns among disturbed surface sediment mounds around Chasmagnathus granulata Dana, 1851 burrows and undisturbed adjacent sediments was done in two intertidal soft bottom habitats (an upper and a lower mudflat zone) in an estuarine inlet of Patos Lagoon, southern Brazil. The most abundant infaunal organisms were recruits of the polychaete Laeonereis acuta Treadwell, 1923 and of the tanaid Kalliapseudes schubartii Mañé-Garzón, 1949. The densities of these species did not differ significantly between upper and lower mudflat habitats. These species showed lower densities around crab burrows than in adjacent areas, where differences in sediment characteristics were observed as well. The results indicate that C. granulata disturbances may play an important role in regulating the soft bottom benthic community by controlling infaunal recruitment in the estuarine intertidal mudflats of the Patos Lagoon.

Seasonal variability on the structure of sublittoral macrozoobenthic association in the Patos Lagoon estuary, southern Brazil

The aim of this study is to analyze and relate the spatial-temporal variability of macrozoobenthic assemblages to bottom characteristics and salinity fluctuations, in an estuarine shallow water region of Patos Lagoon. Monthly samples, between September 2002 and August 2003, were taken on six sampling stations (distant 90 m). Three biological samples with a 10 cm diameter corer, one sample for sediment analysis, fortnightly bottom topography measurements, and daily data of temperature and salinity were taken from each station. Two biotic and environmental conditions were identified: the first corresponding to spring and summer months, with low macrozoobenthos densities, low values of salinity, small variations in bottom topographic level and weak hydrodynamic activity. A second situation occurred in the months of fall and winter, which showed increased salinity, hydrodynamics and macrobenthos organisms. These results which contrast with previous studies carried out in the area, were attributed to failure in macrozoobenthos recruitments during summer period, especially of the bivalve Erodona mactroides Bosc, 1802 and the tanaid Kalliapseuses schubartii Mañe-Garzón, 1949. This results showed that recruitments of dominant species were influenced by salinity and hydrodynamic conditions.