Mesozooplankton studies were carried out at the Barra das Jangadas estuarine system, Pernambuco, Brazil (8º14'36"S, 34º56'28"W), to assess its community structure. Samples were collected with a plankton net (300 µm mesh size) during the dry (January, 2001) and rainy (July, 2001) seasons, with three hour intervals between each sampling, both in spring and neap tides. Thirty seven mesozooplankton taxa were identified, from which Copepoda were particularly abundant, including the species Pseudodiaptomus acutus (F. Dahl, 1894), Peudodiaptomus richardi (F. Dahl, 1894), Acartia lilljeborgi (Giesbrecht, 1892), Parvocalanus crassirostris (Dahl, 1894), Oithona hebes (Santos, 1973), and Notodiaptomus cearensis Wright, 1936. Total density varied from 69.34 to 8568.34 org.m-3 in the dry season and from 261.98 to 10224.83 org.m-3 in the rainy season. Meroplanktonic crustaceans (brachyuran zoeae) were very frequent and numerically abundant, playing an important role in the pelagic food web. Species diversity varied from 0.44 to 3.13 bits.ind-1 (dry season) and from 0.66 to 2.92 bits.ind-1 (rainy season). Low diversities were caused by the dominance of brachyuran zoeae. Cluster analysis revealed two groups, the first formed by marine euryhaline species and the second by true estuarine species.
Estuary; Northeastern Brazil; zooplankton
