Macrobenthic communities of Tróia sand beaches (Setúbal, Portugal):sample size and community structure vs. environmental factors

Tese de mestrado, Biologia (Biologia e Gestão de Recursos Marinhos), 2007, Universidade de Lisboa, Faculdade de CiênciasCoastal environments have always constituted places of attraction for mankind for a number of reasons. Tróia peninsula corresponds to one of those coastal environments, which was acquired in 1998 by a private group Sonae, with the intention to develop a new tourist project Troiaresort. In this project it is foreseen a casino, a fivestar hotel, hotel apartments, tourist apartments, a marina, golf course, a new ferry harbor and several service areas. In the scope of the ongoing environmental monitoring program, the present study had two objectives: 1) determine the minimum sample size (number of replicates) having in consideration the ratio effort/information of the sampling; 2) determine the patterns (distribution and structure) of the benthic communities in relation to the environmental parameters which vary along the peninsula. The morpho-sedimentary environment analysis was part of both objectives of this work, and results revealed an environmental gradient, from the marine margin (exposed marine environment) to the estuarine margin (sheltered estuarine environment). Benthic macrofauna analysis showed a gradient of increasing number of individuals, species richness and diversity from upper intertidal (SL) to lower intertidal (IL) and from the marine margin (Exposed) to the estuarine margin (Sheltered). To achieve the first objective of this work, in each level and transect, several approaches were tested to determine the minimum sample size. In general, the different approaches ix used, suggest minimum sample sizes between 5 (0.0825 m2) and 12 (0.198 m2) replicates, with this value still below a minimum sampling size in most of the cases. The second objective of this work was achieved through a Canonical Correspondence Analysis (CCA). The structure of the sand beach intertidal communities studied showed the definition of four communities and a clear dominance of the spatial patterns over the seasonal ones. The most important environmental factors were beach slope, organic matter and calcium carbonate contents, which appear to have an important role in defining the structure of macrobenthic communitie