Feeding ecology of two sympatric species of large-sized groupers (Perciformes: Epinephelidae) on Southwestern Atlantic coralline reefs

Red and black groupers are large-bodied opportunistic ambush predators commonly found in Southwestern Atlantic tropical reefs. We investigated the diet of both species in order to detail ontogenetic, spatial and temporal trends, and to assess the extent of overlap in resource use between these two sympatric predators on the Abrolhos Bank, Brazil. Decapods and fishes were the main food items of Epinephelus morio while fishes were the main prey of Mycteroperca bonaci. Both diets were significantly influenced by body size and habitat, but only smaller individuals of E. morio feed almost exclusively on crustaceans. While the two groupers rely on many of the same prey types, coexistence may be facilitated by E. morio feeding more heavily on crustaceans, particularly the blackpoint sculling crab Cronius ruber, while black grouper take comparatively few crustaceans but lots of fish prey. Predators like red and black groupers could trigger indirect effects in the community and influence a large range of ecological processes, such as linkages between top and intermediate predators, and intermediate predators and their resources.(AU)

A garoupa e o badejo-verdadeiro são predadores oportunistas de grande porte, com estratégia de emboscada, comumente encontrados em recifes tropicais do Atlântico Sul. A dieta das duas espécies foi investigada, avaliando influências ontogenéticas, espaciais e temporais, assim como a sobreposição no uso de recursos entre estes dois predadores co-orrentes no Banco dos Abrolhos, Brasil. Decápodes e peixes foram os principais itens alimentares de Epinephelus morio, enquanto que os peixes foram as principais presas de Mycteroperca bonaci. Ambas as dietas foram significativamente influenciadas pelo tamanho corporal e habitat, mas apenas indivíduos menores de E. morio alimentaram-se quase que exclusivamente de crustáceos. Como as duas espécies utilizam muitas presas semelhantes, a coexistencia parece ser facilitada pelo fato de E. morio se alimentar principalmente de crustáceos, particularmente do caranguejo Cronius ruber, enquanto que o badejo-verdadeiro consome relativamente poucos crustáceos e grande quantidade de peixes. Predadores como as espécies estudadas podem causar efeitos indiretos na comunidade e influenciar uma grande variedade de processos ecológicos, como conexões entre predadores de topo e intermediários e predadores intermediários e seus recursos.(AU)

Growth of the silverside Atherinella brasiliensis in a subtropical estuary with some insights concerning the weight-length relationship

ABSTRACT Specimens of Brazilian silverside (Atherinella brasiliensis, n=9672) with a length range of 1.5 to 14.2 cm were captured in the intertidal areas of the Estuarine Complex of Paranaguá, Brazil, between August 2010 and July 2011. The species' weight-length relationship was represented by the equation W=0.00533 L3.136 with a slightly positive allometry (b>3) and could be divided into two growth stanzas: W = W1 + W2; Stanza 1: W1= SW. (0.005239 L3.152); Stanza 2: W2= (1 - SW). (0.000699 L3.913); Switch-Function: SW = [1 + e1.204 (L - 11.66)]-1. The breakpoint between the first and second stanza (11.66 cm) matches published values for the estimated size at first maturity of adult females. Frequency distributions indicate that the species is present in the shallow areas of the Estuarine Complex of Paranaguá during all phases of its ontogenetic development, with the recruitment of juveniles taking place between October and November. Modal displacement was monitored throughout 12 months. The von Bertalanffy growth model and longevity was estimated as follow: asymptotic length (L∞) of 17.5 cm, growth coefficient (K) of 0.89 (year-1) and longevity (A95) of 3.33 years. We present some considerations with regard to the general methodology for adjusting weight-length relationships.