Spatial and temporal variations of the benthic macrofauna in different habitats of a lagoon
of the northern coastal system of Rio Grande do Sul State, Brazil
CENZANO1, C.S.S. & WÜRDIG1, N.L.
1 Benthic Invertebrate Laboratory I – Department of Zoology – Institute of Biosciences – IB, Universidade Federal do Rio Grande do Sul – UFRGS. Av. Bento Gonçalves, 9500 - Bloco IV - Prédio 43435 - Sala 204 – CEP 91501-970, Porto Alegre, RS.
e-mail: csscenzano@yahoo.com.br and wurdignl@vortex.ufrgs.br
ABSTRACT: The present work analyses the structure of macrobenthic community in three areas of Itapeva Lagoon, northern coast of Rio Grande do Sul. In each study area, deltaic margin of Três Forquilhas River, central area and east margin, three sample units have been established, 500 meter equidistant, towards NE-SW fetch. Collects have been done during Summer and Winter of 2000 and Summer of 2001, with an Ekman-Birge type sampler, having an area of 225 cm2. More abundant taxons at deltaic margin were Naidinae and Chironomidae (Polypedilum sp. and Cryptochironomus sp.); Tubificinae at the central area, Veneroida, Chaoboridae (Chaobors (Chaoborus) sp.) and Chironomidae (Coelotanypus sp. and Cladotanytarsus sp.) as well as Hidrobiidae at east margin (Heleo charruana and P. ribeirenses). The richness of families varied between 9 and 15, diversity varied between 1.22 and 2.05 and the equitability between 0.48 and 0.8. Variance analysis indicated that for values of families richness, total number of individuals and equitability, habitat has been a major factor in the community. Diversity values, however, varied in function of time. Highest values of correlation (Spearman) were found between macroinvertebrates densities and fine sand, sediments deposition form (Passega’s classification) and hydrodynamics (sand/silt+clay relation); between equitability and organic matter, selection and silt percentage and diversity and asymmetry. Spatial variation of macrobenthos suffered the influence of textural variables of sediment and aquatic vegetation, which have build different substrates, thus supplying shelter and food resource. On the other hand, temporal variation is likely to have been favored by water lamina depth and hydrodynamics.
Key-words: Macroinvertebrates, habitats, spatial and temporal variations, coastal lagoon, Rio Grande do Sul.