IMIS

Vertical distribution patterns of meiobenthos and their relation to the different mangrove vegetations Avicennia, Bruguiera, Ceriops, Rhizophora and Sonneratia have been examined. The vertical distribution pattern in the sediment (to a depth of 20 cm) of density and biomass of the meiofauna, and abiotic factors such as sediment granulometry, nutrients, organic matter were used to explain the observed distribution patterns. A total of 17 taxa has been observed and high densities were encountered: Bruguiera (6707 ind/10 cm2 ), followed by Rhizophora (3998 ind/10cm2 ), Avicennia (3442 ind/10cm2 ), Sonneratia (2889 ind/10cm2 ) and Ceriops (1976 ind/10cm2 ). Nematodes dominated; the remainder was made of copepods, tubellarians, oligochaetes, polychaetes and rotifers. Other taxa were only sporadically observed, partially governed by the sediment. The data indicate high densities still occur at greater depth: 54 ind. At Avicennia 15-20 cm; 759 ind. At Bruguiera 10-15 cm; 380 ind. At Ceriops 15-22.5 cm; 37 ind. At Rhizophora 15-17 cm and 13 ind. At Sonneratia +15 cm. Particle size measurements performed for the five stations show medium sand. The mud levels reached often considerable amounts (up to 8%). Both Kjeldahl-N and total organic matter are generally more concentrated with depth. The nutrient concentrations in the depth intervals, as well as the compared sediments, show great variability. Nematode length increases with increasing depth, although important differences between the stations were observed. Length and density are invertedly related. The data of total biomass differ considerable from one station to another: Ceriops (9.10 -5g) and Sonneratia (19.10 -5g). Besides granulometry, oxygen is the most important factor influencing composition and distribution of the meiofauna.