Benthic communities associated to Thalassia testudinum (Hydrocharitaceae) at three localities of Morrocoy National Park, Venezuela

Abstract

The benthic community associated with the turtlegrass Thalassia testudinum beds was analized at three localities of Morrocoy National Park, Venezuela. The localities were selected according to their exposure to the open sea : A (protected), B (intermediate) and C (exposed). At each locality, a 20 × 20 m area was randomly chosen, delimited and divided into 400 1×1 m quadrats. Inside each, ten randomly selected quadrats/month were sampled during 13 consecutive months. At each site all macroinvertebrates and several physical variables were recorded, as well as leaf and rhizome biomass of T. testudinum. All parameters had a step-wise gradient from A through C: organic matter, carbon nitrogen, oxygen, salinity and temperature gradient was: A>B>C. Percentages of sand, silt and clay showed an inverse gradient; A C>A. The collected fauna was composed of Coelenterata (Anthozoa), Polychaeta, Sipuncula, Mollusca, Crustacea and Echinoderms. The relative abundance of molluscs increased according to Thalassia rhizome biomass: A< B < .01). Principal Component Analysis: for abiotic parameters the first three components account for PCl (clay-sand): 79.1 %, PC2 (C:N ratio): 91.5 % and PC3 (salinity): 95.8 %. For biotic parameters (species) the first three components account for PCI (Potamilla sp.): 96.4 %, PC2 (Lytechinus variegatus)(Lamarck): 98.5 % and PC3 Condylactis gigantea (Weinland, 1860) - Loimia sp.: 99 %. The changes in the faunal composition, distributional patterns and community structure were evident among the studied places. The abundance of benthic organisms associated to T. testudinum depends on local variation of biotic and abiotic features. This interaction influences the community structure as local characteristics in a differential way.