Tâmara de Almeida e Silva

Diel and seasonal changes in the macrozooplankton community of a tropical estuary in Northeastern Brazil

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.

Mesozooplankton of an impacted bay in North Eastern Brazil

Mesozooplankton abundance and distribution at Suape Bay, Pernambuco, was studied to assess the impacts caused by the construction of an internal port to increase the capacity of the Suape Port Complex. Zooplankton sampling was done at 3 stations during the dry (November-December/1997) and rainy (April-May/1998) seasons. A plankton net with 300 µm mesh size was used. Wet weight plankton biomass ranged from 44 mg.m-3 to 3,638 mg.m-3. Forty-five macrozooplankton taxa were registered. The most abundant was Copepoda. Among copepods, Acartia lilljeborgi, Parvocalanus crassirostris, Oithona hebes, Corycaeus (C.) speciosus and Temora turbinata were most frequent. Minimum abundance was 9 ind.m-3 and maximum was 2,532 ind.m-3. Average species diversity was 2.55 bits.ind-1. As a whole, Suape Bay has been under severe environmental stress and it seemed reasonable to assume that the recent modifications of the basin have resulted in changes in species composition and trophic structure, with an increase in marine influence.

The plankton from Maracajaú reef ecosystem (Brazil) - offshore coral reefs under multiple human stressors

To evaluate the Maracajau reef ecosystem (Northeastern Brazil), observations, sampling and measurements were performed monthly during spring low tides from February to June 2000, covering the transition from dry to rainy season. In this area, there is an extensive (approximately 10 km x 4 km), but to date poorly investigated, offshore coral reef formation, where a Marine Protected Area was established recently. The reef area presented chlorophyll a concentrations varying from 1.1 mg m to 9.3 mg m, with higher values registered during the rainy season. Average zooplankton biomass values were 117.0 mg m (microzooplankton) and 15.7 mg m (mesozooplankton). A total of 136 phytoplankton taxa were identified. Diatoms were the most abundant and diverse group, with 102 species. Average phytoplankton density was 3,125 10 cells 1. It was identified that there were 61 zooplankton taxa, with copepods showing the highest diversity (23 species) and abundance. Seasonal forcing determined the microand mesozooplankton community structure, rather than the coastal-offshore gradient. In spite of the distance from the coast (5 to 7 km offshore), this area is intensively used by local populations, mainly for artisan fishery and diving tourism. The area is exposed to seasonally varying negative impacts due to freshwater runoff, mangrove degradation and tourism, being also menaced by coastal eutrophication.

Hydrology, plankton, and corals of the Maracajaú reefs (Northeastern Brazil): an ecosystem under severe thermal stress

This study provides baseline information on the hydrological conditions and on the coral and plankton communities at the Maracajau reef ecosystem (Northeastern Brazil). Studies were performed from February to June 2000, covering the transition from dry to rainy season. In this area, there is an offshore coral reef formation, where corals were observed in loco; the water samples were collected to obtain the hydrological and plankton data. Six scleractinian species were identified. Stable isotope analysis on the carbonate fraction of Favia gravida fragments showed that these corals were under severe thermal stress. Chlorophyll-a varied from 1.1 to 9.3 mg m-3, with higher values during the rainy season. Average zooplankton wet weight biomass were 117.0 (microzooplankton) and 15.7 mg m -3(mesozooplankton). A total of 136 Phytoplankton and 61 zooplankton taxa were identified. Seasonal forcing determined the phyto-micro-and mesozooplankton community structure, rather than the coastal-offshore gradient.