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 m 23), and the lowest at the station farthest offshore (82 ind m 23). 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 m 23), (ii) a mix of neritic and oceanic species and (iii) coastal neritic group. Species diversity was high (mean 3.14 + 0.42 bits ind 21) 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.

ABSTRACT

ABSTRACT. Studies were carried out to assess the macrozooplankton small-scale temporal and spatial variability at three stations in three hours intervals, during 24 hours in July 1996 (rainy season) and December 1996 (dry season). A plankton net 300µm mesh size was hauled at surface during three minutes. Water samples for salinity, temperature, dissolved oxygen and pH were taken simultaneously with the zooplankton samples. Sixty-five macrozooplankton taxa were registered. Copepoda constituted the most common taxon and comprised 58% of the total zooplankton counts. Brachyuran zoeae, cirripedian larvae, Larvacea (Oikopleura dioica Fol, 1872), and Gastropoda veligers were abundant at some tidal cycles, mainly during the night. Species diversity average was 2.0 bits . ind -1 . The mean density ranged from 23 ind . m -3 to 5,201 ind . m -3 . The rainy season presented greater numerical abundance. A regular temporal zooplankton cycle was not observed. Instead, there was a large stochastic variation between samples.

This study was carried out to assess the diversity and the abundance of the reef zooplankton in the Maracajaú reefs. Samples were collected with two plankton nets (65 and 300 micrometers mesh size, each) from February to June/2000 at three stations in a transect perpendicular to coast. Plankton biomass in the 65 µm fraction varied from 45.19 mg.m -3 to 316.45 mg.m . In the 300 µm fraction biomass varied from 9.33 mg.m -3 to 43.16 mg.m -3 . Zooplankton presented 61 taxa. Copepods were the most diverse taxa with 23 species. Euterpina acutifrons, Oithona oswaldocruzi, Oithona hebes, Oithona sp., Parvocalanus crassirostris, Acartia lilljeborgi, Bivalvia and Gastropoda larvae, Trilocularina sp., Balanus sp. larvae, Spirillina sp., Polychaeta larvae, Brachyura (zoea) and Oikopleura longicauda occurred in more than 75% of the samples. The zooplankton followed a seasonal pattern, with the highest numbers occurring during the rainy season (February). A high density of microzooplankton was found which varied from 1,917 ind.m and a maximum of 1,617 ind.m -3 . Species diversity was intermediate (~2 bits.ind -1 ) and eveness relatively high (~0.78). Samples could be joined into 3 groups, mainly influenced by rainfall. Species similarity presented 5 groups: oceanic, neritic, a mixture of neritic and oceanic, reef and estuarine. Our data suggest a dynamic relationship between the zooplankton communities characteristic of inshore water trapped by the coastal boundary layer and more offshore plankton communities.

-