Boletim do Museu Paraense Emílio Goeldi. Ciências Naturais (Dec 2006)
Macrobenthos from unvegetated intertidal areas in the Caeté river estuary in Bragança, Pará
Abstract
The macrobenthic community structure was studied in inter-tidal, non-vegetated areas of the Caeté river estuary, Pará, Brazil, during the dry season of 2003. Four samples were collected at four stations on the downstream direction (P1 to P4) using a corer (0.008 m2 and 20 cm long). Samples were sieved through a 0,3 mm mesh and the organisms preserved in a 5% formaline saline solution stained with Bengal rose. At each station, sediment samples were collected and salinity and water temperature recorded. A total of 105,500 individuals were collected, divided in 17 taxa comprising the fphyla: Nemertea, Arthropoda and Annelida. Polychaeta dominated the assemblages (11 taxa and 87.25% of the individuals). The most abundant taxa were Mediomastuscalifornienses, Nephtys Huviatilisand Oligochaeta (Tubificidae). Density and richness values varied from 2625 ind.m-2 and 3 taxa at station P1 to 96625 ind.m-2 among 16 taxa at station P4. Cluster analysis seperated three groups (50% similarity): Group 1, including samples from stations P3 and P4, was characterized by a relatively high salinity (22.6 to 26.5) and a fine sand substrate. This group, dominated by Sigambra grubii, was the richest (13 taxa), most diverse (χH´ = 1.18) and abundant (χ= 12220 ind.m-2); Group 2, including samples from station P1, was characterized by a salinity of 5,1 and a silt-sandy substrate. This group presented the lowest richness (3 taxa), diversity (χH´ = 0.67) and abundance (χ= 665 ind.m-2) values, and was dominated by the species Namalicastysabiuma; and Group 3, including samples from station P2, was characterized by a salinity of 3.6 and a silt-sandy substrate. N. abiuma was the most abundant species of this group that was characterized by intermediate richness (5 taxa), abundance (χ= 2010 ind.m-2) and diversity (χH´ = 0.71) values. Thus, it is concluded that in the inter-tidal area of the non-vegetated Caeté river the species number is low; Annelida is the most abundant group; the species composition reflects the estuary salinity gradient; and richness, diversity and abundance increase from the upper to the lower estuary.
