Disibuição e estrutura da erva marinha Zostera capensis e investigação dos parâmetros físicos e ambientais, em duas área da baía de Maputo

Abstract

The present study was carried out from February to April 1997, in two areas of the Maputo Bay: Baía Su! at Inhaca Island and Praia do Bairro dos Pescadores, north of Maputo City. The study presents aspects on the distribution, structure and dynamics of the seagrass Zostera capensis; investigation of temperature, salinity, hydrodynamics, texture and organic matter of the soil in the intertidal zone of the study areas. The species Zostera capensis, occupied 64.8% of the total area of the South Bay and 64.6% of the total area of the Fishermen's Neighbourhood Beach. The average cover percentage was 22.12% in the South Bay and 25.15% in the Fishermen's District Beach. The average stems density was 461 stems/m2 in the South Bay and 206 stems/m2 at Praia do Bairro dos Pescadores. The average leaf area index was 73.03 m2/m2 in the South Bay and 47.41 m2/m2 in the Fishermen's District Beach. In both study areas, there was a strong correlation between stem density and leaf area index (Southern Bay: p=0.000 and r2 = 0.7086; Fishermen's District Beach: p=0.000 and r2 = 0.7332). Mean above substrate biomass was 2.23 gPS/m2 and 1.91 gPSLC/m2 for South Bay and 0.96 gPS/m and 0.13 gPSLC/m2 for Fishermen's District Beach. The average below substrate biomass was 7.0 gPS/m2 and 5.4 gPSLC/m2 for South Bay and 5.12 gPS/m2 and 1.1 gPSLC/m2 for Praia do Bairro dos Pescadores. The ratio between above and below substrate biomass was 1:2 to 1:13 for PS and 1:2 to 1:35 for PSLC. Mean growth rates were 8.3 mm/stem/day, 0.37 mg/stem/day and 1.57 g/m2/day for the South Bay; and 7.4 mm/stem/day, 0.37 mg/stem/day and 0.074 g/m2/day for the Fishermen's District Beach. The average specific growth rate was 3.5%/day and 5.4%/day for Baia Sul and Praia do Bairro dos Pescadores, respectively. The average leaf life was 38 days and 25 days for the South Bay and Fishermen's Quarter Beach respectively. Soils are formed by an average of 99.8% area; the remaining 0.2% is clay and silt. The organic matter content is low, 0.78% in the South Bay and 0.36% in the Fishermen's District Beach. Water movement (hydrodynamism) was higher in the channels within the Zostera capensis community and lower in the seagrass-free zone. Comparing the lower and upper levels of Z. capensis, hydrodynamism was higher at the lower level (close to the substrate) with 2.39% weight loss/hour in relation to the upper level (in the water column) with 0.26% weight loss/hour. Average temperature and salinity for March was 30.6°C and 35 PPM at South Bay and 31.9°C at Praia do Bairro dos Pescadores, for April temperature and salinity were 28.1°C and 35.3 PPM at South Bay and 29.3°C and 35.2 PPM at Praia do Bairro dos Pescadores. (TRADUÇAO NOSSA)