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.摘要 本研究旨在记录圣卡塔琳娜州北海岸的大型水母（macromedusae）物种，并以2012年1月至2014年10月间手工虾类捕捞副渔获物中采集的标本为基础，估算其种群动态及生化组成的变化。研究采用队列分析（cohort analysis）对优势物种的种群动态进行评估；针对水母伞状体开展生化检测，分析其水分、碳水化合物、蛋白质、脂质、灰分及金属元素的含量。本次调查共发现6种大型水母：四手箱水母（Chiropsalmus quadrumanus）与哈氏箱水母（Tamoya haplonema，隶属于立方水母纲（Cubozoa））、桑巴基铃水母（Olindias sambaquiensis）与大西洋根口水母（Rhacostoma atlanticum，隶属于水螅水母纲（Hydrozoa））、乳海刺水母（Chrysaora lactea）与亮唇鞭棍水母（Lychnorhiza lucerna，隶属于钵水母纲（Scyphozoa））。该区域出现频率最高的典型物种为桑巴基铃水母与大西洋根口水母，二者均表现出显著的年际变化：种群密度最高值出现在2014年秋冬季，这与当年冬季气候较为温和、近岸海水盐度更高密切相关。桑巴基铃水母的体型分级分布显示，其种群存在春夏季与秋冬季两个特征明确的世代。大西洋根口水母则表现出持续繁殖与年际波动特征，其蛋白质含量峰值与秋季的繁殖高峰期相对应。相较而言，立方水母纲物种的有机质与金属元素含量显著高于其他类群。