Relative effect of seasonality and body size on the diet of juvenile Lutjanus synagris (Perciformes: Lutjanidae) at a sandy beach in southeastern Brazil

Abstract

The relative effect of seasonality and body size on the diet composition of juvenile Lutjanus synagris was investigated at a sheltered sandy beach (20°18’S; 40°16’W) on the coast of Espí­­rito Santo state, Brazil. Monthly collections were carried out during the daytime from May 2004 to April 2005, using a beach seine. The specimens captured in each season (e.g. cold/dry, May to October 2004; hot/rainy, November 2004 to April 2005) were separated into three total length (TL) classes (â"°¤ 40; 41í 50; â"°¥ 51 mm). The stomach contents of 540 specimens with TL ranging from 22 to 135 mm were analyzed. Among the 13 food items consumed by L. synagris, the most important were Amphipoda (Index of Relative Importance, IRI = 81.2), Isopoda (IRI = 13.8) and Mysidacea (IRI = 4.4). Significant variations in the diet composition were observed between the seasons (PERMANOVA; P < 0.001), but not between the size classes (P = 0.170). There was, however, a significant interaction between these two factors (P<0.001), indicating that the differences between the seasons did not occur in every class. The most important items in the cold/dry and hot/rainy seasons were, respectively, Mysidacea and Amphipoda, for every class. The average length of the preys varied significantly (P<0.05) between the size classes, increasing progressively with the TL of the fishes. Overall, the results indicate a carnivore-opportunist food habit for L. synagris, with significant seasonal changes in the relative importance of the food items.