Ecologia populacional e reprodutiva de espécies simpátricas de Caprella (Crustacea, Amphipoda) associadas à Sargassum cymosum (Phaeophyta, Fucales)

Abstract

The caprellid amphipods play an important role in coastal ecosystems, they establish a link between producers and higher trophic levels, are sensitive to environmental changes, toxins and pollutants. However, detailed studies of the population and reproductive biology of this group are very scarce. Therefore, this study aimed to assess whether sympatric species of caprellids differ in their population and reproductive ecology that allow their coexistence. Purpose, the population structure and reproduction of sympatric species of Caprella (Caprella danilevskii, C. equilibra and C. scaura) that occur associated with a Sargassum cymosum (Phaeophyta, Fucales ) bed in Lázaro Beach in Ubatuba, São Paulo were analyzed. From October 2010 to February 2012, 25 fronds of S. cymosum were collected monthly and subsequently washed to obtain the caprellids. All individuals were identified, measured and the reproductive parameters of females with intact pouch analyzed. The population density of the three species fluctuated during the seventeen months, reaching peaks in spring and early summer. These changes in density may be related to several factors such as food availability, temperature, algae density and reproductive cycle of the species. The sex ratio was favorable to males. Histograms of size classes of C. danilevskii were grouped into 15 classes and C. equilibra e C. scaura were grouped were grouped into 13 classes. The ovigerous females of C. danilevskii, C. equilibra e C. scaura were present in greater intensity in spring and early summer, characterizing a seasonal reproduction. The fecundity did not differ among species, however egg volume varied significantly between them, being the eggs of C. danilevskii higher (0,010 + 0,007 mm³) compared to eggs of C. equilibra (0,005 + 0,006 mm³) and C . scaura (0,005 + 0,020 mm3). Positive relationship between egg number and size of females was observed only for C. danilevskii (1 a 18 ovos; 5, 94 mm + 0,74), as well as a positive relationship between the egg volume and the size of the female of C. equilibra (0,005 + 0,006 mm³; 4,70 + 0,64). An inverse proportion between total egg volume and average fecundity of females occurred for the three species. Changes in eggs volume may result from changes in the size of females or adaptations used by sympatric species. Therefore, the analysis of the population and reproductive ecology demonstrates that the coexistence of these species is possible by since they use different strategies, such as population peaks alternation; dissimilarities between the size of males and females; and reproductive periods with different durations (temporal separation).