Journal of Coastal Research, Special Issue 56, 2009 Journal of Coastal Research SI 56 376 – 380 ICS2009 (Proceedings) Portugal ISSN 0749-0258 Short-term Temporal Fluctuation of Very-nearshore Larval Fish Assemblages at the Arrábida Marine Park (Portugal) R. Borges†‡, J.Vaz†, E.A. Serrão† and E.J.Gonçalves‡ †CCMAR, Centre Marine Sciences University 8005-139 Faro Portugal rborges@ispa.pt a24292@ualg.pt eserrao@ualg.pt ‡ Eco-Ethology Research Unit, Instituto Superior Psicologia Aplicada, R. Jardim Tabaco, 34 1149-041 Lisboa Portugal emanuel@ispa.pt ABSTRACT BORGES, R., VAZ, J., SERRÃO, E.A. and GONÇALVES, E.J., 2009. Short-term temporal fluctuation of very- nearshore larval fish assemblages at the Arrábida Marine Park (Portugal). Journal of Coastal Research, SI 56 (Proceedings of the 10th International Coastal Symposium), 376 – 380. Lisbon, Portugal, ISSN 0749-0258 Understanding processes affecting fish recruitment and population connectivity is of major importance to the management of Marine Protected Areas. Fluctuations in recruitment of coastal fishes can be affected by processes occurring during the early life stages such as the dispersal and availability of larvae. In nearshore temperate environments, there is a lack of knowledge about the patterns of larval supply or biophysical interactions that may influence recruitment variability in these populations. With the objectives of investigating within season (Spring-Summer period) fluctuations that may affect recruitment, and of understanding patterns of larval retention close to the reefs, we used a plankton net attached to an underwater scooter to investigate weekly variation in the composition of fish larval assemblages, larval density and diversity and ontogenetic patterns of occurrence of fish larvae in the extreme nearshore environment of the Arrábida Marine Park (Portugal). The results from multivariate analysis (PERMANOVA and SIMPER) have showed a lower number of species dominating the assemblage, and significant differences in the abundance between species, when compared to previous studies. The presence of larvae in several developmental stages indicates some degree of retention. These findings are important to the management of the Marine Park. ADDITIONAL INDEX WORDS: Larval fish assemblages, Larval retention, Temporal variation INTRODUCTION The best design and distribution of Marine Protected Areas (MPA’s) requires a deep knowledge of the connectivity patterns between local populations of marine organisms, and particularly of the patterns of supply of new individuals to these populations (LEIS, 2003). Many coastal fish species that live associated to demersal habitats (like reefs) have limited dispersal in the adult phase but have pelagic early life history stages that allow for dispersal from the natal populations and for connection between different populations. Given this potential for large dispersal, marine populations are traditionally considered as open (KRITZER and SALE 2006). However, recent evidence, mainly for coral reef species (see reviews by SWEARER et al., 2002, and LEIS, 2006; COWEN et al., 2006, ALMANY et al., 2007, GERLACH et al., 2007), has shown that self-recruitment can, for some species, be higher than previously expected, as fish larvae may be retained close to the natal reefs and thus recruit locally. Some studies indicate that biophysical interactions can strongly influence the position of larvae in the water column contributing to retention close to the shore and increasing self-recruitment, showing that marine populations can vary from entirely closed to fully open (SPONAUGLE et al., 2002). These interactions between complex larval behavior and physical factors depend on local conditions and on early life history traits which are highly variable among species (SPONAUGLE et al., 2002; LEIS, 2006). Although some evidence of retention also exists for temperate rocky reefs (review by HICKFORD and SCHIEL, 2003; BORGES et al., 2007a; CARRERAS- CARBONELL, 2007), further investigation is needed to understand differences between coastal species in their patterns of dispersal or retention. In addition to spatial variability in larval abundance patterns, temporal fluctuations of larval availability often occur, affecting the supply of new individuals to local populations in different years. These fluctuations can be caused by several factors, and can occur at different scales, from circadian to interannual, and these should be considered when trying to understand which factors affect replenishment and population dynamics, as ecological patterns can be misunderstood if the proper scale is not considered (GRAY, 1996). Processes occurring at a scale of minutes or meters can, in fact, strongly influence larval dispersal (LARGIER 2003). The Arrábida Marine Park is an excellent model for the study of ecological processes structuring nearshore communities. This Marine Park was designated in 1998, but has only been implemented very recently (the management plan was approved in 2005). Some studies previous to the implementation of the Marine Park have shown that there is a highly diverse larval fish assemblage (BELDADE et al., 2006, BORGES et al., 2007a,b) which reflects the high diversity of the adult assemblage (HENRIQUES et al., 1999). These studies also showed that small-scale patterns in the vertical distribution of larvae could contribute to retention close to the reefs, for some species. In spite of these studies on the composition and temporal and spatial dynamics of local larval assemblages, patterns of temporal occurrence of these larval fish assemblages and patterns of