Larval ecology of an ascidian tropical population in a Mediterranean enclosed ecosystem

The larval ecology of a population of the tropical tunicate Ecteinascidia t urbinata was studied in a semi-enclosed lagoon on the island of Formentera (Mediterranean Sea). Due to the lagoon's isolation and processes of extinct ion/regeneration of the population, research was carried out to evaluate so me aspects of the species' ecology which permit it to survive in this habit at. Settlement and recruitment were found to be intimately related to the p eriod of sexual reproduction, and determined by the local production of lar vae. In this sense, the population's spawning potential (larvae m(-2)) matc hed a perfect linear relationship (R-2 = 0.9496, p < 0.05) with the settlem ent and recruitment registered on experimental settlement surfaces. Of the larvae produced by the population 29% settled locally, contributing to the consolidation of populations already established. Only 1.3% of the larval p roduction theoretically calculated developed into colonies at a local level . To determine how Settlement site might contribute to the colonies' surviv al and thus to population distribution, zooids were transplanted from an ap propriate zone to a stressful zone, which showed that there is a risk of in appropriate habitat selection for settlement. The behaviour of the larvae ( philopatry) and gregarious settlement in unpredictable environments (spatio -temporally variable) seems advantageous to prevent advection to inappropri ate sites. E. turbinata ensures local recruitment and renewal of the establ ished population, but it seems that there is partial dispersal of larvae be yond the parent population. The study shows that there is sufficient recrui tment from within the population to maintain it and the timing of larval pr oduction and recruitment strongly suggest that recruits are from the popula tion itself.