Habitat partitioning, habits and convergence among coastal nektonic fish species from the São Sebastião Channel, southeastern Brazil

Abstract

Based on a fish survey and preliminary underwater observations, 17 "morphotypes" were identified that characterize the morphological diversity found within 27 nektonic fish species sampled at São Sebastião Channel. Such "morphotypes" were studied using an ecomorphological approach, with the intention to investigate similarities and differences in shape and habits. Underwater field observations were also performed, to verify if the lifestyle of these species, such as vertical occupation of the water column and the habitat use, are in accordance with their distribution in the morphospace. The results, complemented with data from scientific literature on the taxonomy and phylogenies of these species, allowed discussing some of the typical cases of convergent and divergent evolution. Some of the ecomorphological clusters had no phylogenetic support although this is probably due to the environmental conditions in which theirs members have evolved. The body shape and fins positions of a fish clearly influence its ecological performance and habitat use, corroborating the ecomorphological hypothesis on the intimate link between phenotype and ecology.Com base em um levantamento ictiofaunístico realizado com diversos métodos de captura e em observações subaquáticas preliminares foram selecionados 17 "morfótipos" representativos da diversidade morfológica apresentada dentre 27 espécies de peixes nectônicos amostradas no Canal de São Sebastião. Tais "morfótipos" foram estudados por meio de uma abordagem ecomorfológica com o intuito de investigar semelhanças e diferenças quanto às suas formas e hábitos. Observações diretas no ambiente também foram realizadas para verificar se o modo de vida dessas espécies, assim como a ocupação vertical da coluna d'água e o uso do habitat, condizem com suas distribuições pelo espaço morfológico. Os resultados obtidos, complementados com dados da literatura científica sobre taxonomia e relações de parentesco evolutivo dessas espécies, permitiram discutir alguns típicos casos de convergência e divergência evolutiva. Alguns agrupamentos ecomorfológicos não tiveram qualquer suporte filogenético tendo sido resultantes, provavelmente, das condições ambientais na qual seus membros evoluíram. A forma do corpo e a posição das nadadeiras de um peixe claramente influenciam seu desempenho ecológico e o uso do habitat, corroborando a hipótese ecomorfológica sobre a estreita relação entre fenótipo e ecologia. Introduction"Strong relationships between basic form and ecological function in fishes allow the comparative study of ecological relationships using morphological features" (Winemiller, 1992). Morphology has been used as a predictor of the wayof-life (see Karr & James, 1975;; the ecomorphological hypothesis is based on the idea that the morphological attributes of each species should reflect its ecology and, thus, can be used as indicative of its habits and adaptations to different habitats ( Van der Klaauw, 1948;Keast & Webb, 1966;Winemiller, 1991Winemiller, , 1992. The central focus of an ecomorp...

The structure of rocky reef fish assemblages across a nearshore to coastal islands' gradient in Southeastern Brazil

“…Most of these benthic fishes have elongate, cylinder and/or depressed bodies with disruptive coloration and more sedentary habits, while the nektobenthic fishes are more conspicuous, generally presenting laterally compressed and higher bodies, with better maneuverability due to body, caudal peduncle and fin designs, which are also associated with fins shapes and positions. Such fishes are capable to explore all of the tridimensional complexity of reef habitats (see Gibran, 2004Gibran, , 2007Gibran, , 2010 and are generally more widespread among the different habitats than the benthic species. For instance, the abundant small sized benthic blennioids and gobioids, both carnivores and herbivores/ detritivores characterize the shallow, warm and turbulent tops, being rare or absent in the deeper and colder habitats.…”

“…These fishes frequently co-occur in reef communities, with several specific mechanisms enabling the long-term coexistence of these potential competitors (Schmitt & Coyer, 1982). Detailed studies involving such closely-related species can clarify their ecomorphological relationships and shifts in resource use in order to minimize interspecific competition (see Schoener, 1974;Gibran, 2010). The two small-sized serranids, S. flaviventris and S. baldwini, occur largely in the deeper habitats of the rocky reefs, where boulders and rubble accumulate increasing structural complexity.…”

“…In the 2 m radius only individuals with total length (TL) or disk width (DW) < 10 cm were counted, while in the 4 m radius only individuals > 10 cm TL or DW were counted. Only benthic and nektobenthic fishes were considered (see Gibran, 2004Gibran, , 2007Gibran, , 2010). An acrylic graduated rule was used to estimate individual sizes, and the cylinder base diameter was depicted by five white floats connected by 15 cm nylon lines to lead sinkers, forming an imaginary "+" in the cylinder base.…”

“…Specimen collections and video/ photo records were performed to confirm or facilitate fish identification (see Gibran & Castro, 1999;Gibran, 2007Gibran, , 2010.…”

Ecomorphological patterns of the fishes inhabiting the tide pools of the Amazonian Coastal Zone, Brazil

“…Oliveira et al (2010) have demonstrated a high degree of correlation between morphological characteristics and the exploitation of the resources available in the environment, whereas others have found a weak relationship between the two variables (e.g., Clifton & Motta, 1998;Casatti & Castro, 2006). Some studies, such as that of Gibran (2010), who analyzed nektonic coastal species in southeastern Brazil, have emphasized the need to consider the differential effects of phylogenetic and historic factors in the structuring of fish communities. This is because the characteristics presented by a species may be intrinsic to its evolutive lineage, rather than reflecting morphological adaptations to its environment.…”