POLYCHAETE-SEDIMENT RELATIONSHIPS AND DISTRIBUTION AT SUBTIDAL DEPTHS NEARBY PATOS LAGOON MOUTH, RIO GRANDE, RS, BRAZIL.
Camargo, M.G.* & Borzone, C.A. *
CENTRO DE ESTUDOS DO MAR
Av. Beira-mar S/N, Pontal do Paraná - Pontal do Sul - PR
CEP-83255-000 BRAZIL
The coastal region adjacent to the mouth of the Patos Lagoon is composed of an exposed sandy beach, directly influenced by fine sediments discharged by the estuary. Due to hydrodynamic processes, most of this sediment is deposited south of the estuary. This is a region which presents, in shallower areas, mixed sediments as a result of its proximity to the surf zone, and finer, well-sorted sediments in deeper waters. The northern portion experiences, on the other hand, continuously decreasing sediment mixing rates and coarser grains. The region is, therefore, suitable for studies dealing with the animal-sediment interactions. This study aimed to compare polychaete abundance and biomass in both sites, as well as distributional patterns and temporal variations. Two transects perpendicular to the shoreline were defined ¾ one established 10 km south, and the other 6 km north of the Patos Lagoon mouth. Five stations were defined in each transect, at 0.5, 0.75, 1.0, 1.5 and 2.0 nautical miles from the shore. The depths ranged from 2 to 13 m. Sampling was carried out with a 40X15 cm rectangular dredge with 1 mm mesh, at least once per season during one year. The statistical treatment of data included Uni- and bi-factorial ANalysis Of VAriance (ANOVA), Cluster Analysis, non-metric MultiDimensional Scaling (n-MDS), Analysis of Similarities (ANOSIM). A total of 30 species were identified. The most abundant were Sthenelais limicola (16.9 %), Parandalia americana (16.1 %), Kinbergonuphis difficilis (10.5 %) and Nephtys simoni (10.3 %). The highest polychaete abundance and biomass were found during the winter, while the lowest were found in the spring. Despite the high variability among samples, seasonality patterns were not found for most species. The northern transect presented a much higher abundance and biomass than its southern counterpart. Multivariate analysis indicated a closed relation between faunal composition and sediment characteristics, defined by two main groups ¾ one containing all northern stations and those southern stations with coarser sediments; the other including only the southern stations with finer grains.