Diversity and distribution of the mesozooplankton in the tropical Southwestern Atlantic.

Abstract

Mesozooplankton species distribution and abundance were studied in the tropical Southwestern Atlantic, in neritic and oceanic regions off the state of Rio Grande do Norte, northeastern Brazil (38 to 68 S and 32830’ to 35830’ W). Samples were collected with a 120 mm mesh net towed horizontally at 40 stations along five transects in June 1986. A total of 151 taxa were identified. Copepoda (93 species) numerically dominated (78%) the community. The highest zooplankton abundance was recorded at a coastal station (1098 ind m23), and the lowest at the station farthest offshore (82 ind m23). The low abundance of zooplankton corresponded to oligotrophic water masses, and differences in abundance were locally affected by topographic upwelling. Three groups were distinguished: (i) oceanic with very low total abundance (,15 ind m23), (ii) a mix of neritic and oceanic species and (iii) coastal neritic group. Species diversity was high (mean 3.14+0.42 bits ind21) and increased with the ecological stability of the area. The local oceanographic conditions, with a strong connection between the oligotrophic oceanic water masses and the enriched coastal water, are of paramount importance to the local food chain and patterns of zooplankton diversity.