Aspectos ecológicos de Halimeda opuntia (L.) J.V. Lamour. (Chlorophyta, Bryopsidales) em trecho recifal da Praia de Pirangi, Rio Grande do Norte

Abstract

The calcareous green algae of the genus Halimeda are recognized as an important component of the coastal ecosystems in the tropical region for their capacity of production of sediments and, consequently, participation on the structuring of the marine landscape. Some species of this genus are abundant in the coastal areas of northeast Brazil, in particular H. opuntia, a species that reportedly grows on hard substrate, as the numerous reefs commonly found on this region. The present work aims to study ecological aspects of this species, such as: percentage cover, biomass, growth rate, primary production and their association with fauna and floras, as a mean to better understand the role of H. opuntia in the marine environments of the western south Atlantic. In this regard, it was chosen an intertidal reef flat, called parrachos de Pirangi, at the municipality of Parnamirim-RN, where this algae is found on relatively high abundances. On this reef, it was established three transects, and the data was collected on those in six campaigns during six different months (second semester of 2009 and first of 2010). The results suggest that the H. opuntia occupies an area of almost 4,500m2 at the recifes de Pirangi, with a biomass distributed in aggregate tufts, reaching 1.6 kg/m2 where those can be found. This population appears to be affected by environmental factors, specially disturbance, light and rain, diminishing its percentage cover when the environment becomes excessively turbulent and having its morphology altered when a high amount of light is available. The estimated oxygen production was between 11.38 and 33.25 mgO2.gDW-1.day-1 and the calcium carbonate (CaCO3) production was calculated as 705.2 g of CaCO3/m2/year. The major components of the associated flora were the algae Gelidiella acerosa, Amphiroa fragilissima and Pterocladiella caerulescens. The associated fauna was mainly dominated by crustaceans, especially Amphipoda, Tanaidacea and Decapoda, followed by polychaetes, gastropods and ophiuroids. This fauna, depending on which group is analyzed, appears to be affected by environmental factors, the population dynamics of the host algae and the associated flora populations.