Estructura de la comunidad de céspedes algales en interacciones con corales masivos en arrecifes del Parque Nacional Natural Tayrona, Caribe colombiano

Algal turfs are currently the most abundant benthic component on most coral reefs. Their wide distribution, functional role and positive responseto factors that stress corals confirm their importance in the functioning of reef ecosystem. It has been shown that species composition, structuraldevelopment and sediment retention influence their capacity to kill and displace adjacent live coral tissue. In this study in two reefs of the Tayrona National Natural Park (Colombian Caribbean), the variation in structure of turfs growing on and in direct interaction with massive live corals was determined,and its structural complexity was related with its sediment retention capacity. For that, the taxonomical composition was determined, and canopy height, cover and density of filaments and algal biomass were quantified for turfs growing on live colonies of four species of corals. The results showed that there are important structural differences between reefs and substratum type. In Granate reef (10-16 m), turfs form discontinuous carpets over crustose algae, and are constituted by articulated calcareous and little corticated algae, and juveniles of frondose algae, mostly of the genus Dictyota. During coastal upwelling, this genus grows profusely forming transient dense algal beds that later detach. In contrast, in Nenguange reef (4-6 m), turfs are perennial, form low, thick and dense carpets, with few crustose algae, and are dominated by filamentous and small corticated algae. It´s suggested that the presence of territories ofdamselfishes (Stegastes spp.) aid controlling the structural complexity of the turfs, and that vegetative propagation is the most frequent growth mechanism. In addition, it was found that the most morphologically complex turfs can retain greater amounts of sediments (silt-clay). This particulate material supports them; they can advance laterally and smother adjacent live coral tissue. This investigation provides the first quantitative data on the structure and amount of retained sediments by algal turfs growing on Colombian reef corals.