Community composition, assemblages and latitudinal pattern of benthic intertidal invertebrates at marshes in the southwestern Atlantic, Argentina.

ALBANO MARIANO J.; OBENAT SANDRA; TOMÁS LUPPI

Mar del Plata

Conferencia; CERF’s Inaugural International Conference of the Americas.; 2012

In the present study we assess if community composition and assemblages of invertebrates varies seasonally in different marshes along a latitudinal gradient of the Argentinean coast. Sampling were conducted in four locations latitudinally separated each other: The Mar Chiquita coastal lagoon 38° 32’ S, 57° 19’ W (MC), Bahía Blanca estuary 38º 45’ S, 62º S, 20’ W (BB), Río Negro estuary 41º 00’ S, 62º 49’ W (RN) and San Antonio Bay 40º 46´ S, 64º 50´ W (SA). Sampling was stratified in three different strata (upper-salt marsh, mid-mudflat and lower-mudflat) in each of these regions during spring 2006, summer and autumn 2007. Seven corers of sediment of 20 cm in diameter (0.03m2) and 20 cm deep were taken at each stratum. Samples were sieved through a mesh of 0.5mm, fixed in formalin 4% and preserved in 70% alcohol. The fauna were separated, identified and counted. Multivariate approaches (PRIMER software) were used to examine invertebrate’s composition in each location. Community composition was defined by the abundance, species richness and diversity (Shannon´s index H). Assemblages were evaluated trough ANOSIM and SIMPER analysis. Mean abundances of Crustaceans, Mollusca and Polychaeta showed highest values in SA, BB and RN respectively. Mean species richness showed highest values in SA (6.4), followed by RN (2.3), BB (2.2) and MC (2.0); meanwhile mean diversity showed the same pattern. ANOSIM showed differences (Global R=0.522; p=0.001) only for SA versus the others 3 sites along the sampling period. SIMPER showed that Nematoda in SA was the taxa that most contribute (45%) in all seasons in each strata; meanwhile at the other marshes the same species, polychaete Laeonereis culveri was the dominant (>65%). Results suggest that community indices diminished from south to north showed latitudinal gradient, in contrast species assemblages don’t show a latitudinal trend.