Macromedusae of Southern Brazil: temporal variation, population structure and biochemical composition

Abstract

The objectives of this study were to record the macromedusae species on the north coast of Santa Catarina, and to estimate their population dynamics and variations in their biochemical composition, based on the specimens obtained in the by-catch of artisanal shrimp fishing between January 2012 and October 2014. Cohort analysis was performed to evaluate the population dynamic of the most frequent species. Biochemical analyses of the umbrellas were conducted on their water, carbohydrate, protein, lipid, ash and metals contents. Six species of macromedusae were found: Chiropsalmus quadrumanus and Tamoya haplonema (Cubozoa); Olindias sambaquiensis and Rhacostoma atlanticum (Hydrozoa), and Chrysaora lactea and Lychnorhiza lucerna (Scyphozoa). The species with the highest occurrence, and typical of the region, were Olindias sambaquiensis and Rhacostoma atlanticum. These species showed high inter-year variability, the highest densities being observed between autumn and winter 2014, associated with a less severe winter and coastal water with higher salinity. The distribution of size classes of O. sambaquiensis suggests two well-defined cohorts in spring/summer and in autumn/winter. R. atlanticum showed continuous reproduction and inter-year variation but a high value for protein content related to the reproductive peak in autumn. However, the Cubozoa species showed higher organic matter and metal content than the other classes.