Population features of the pea crab Dissodactylus crinitichelis Moreira, 1901 (Decapoda, Brachyura, Pinoteridade) associated with the sand-dollar Encope emarginata (Echinodermata, Echinoidea) in the southeastern Brazilian coast

Abstract Crabs of the Dissodactylus genus are commonly found in symbiosis with other marine invertebrate organisms. This study describes the structure of the population of the Pinnotheridae crab Dissodactylus crinitichelis living in symbiosis with the sand dollar Encope emarginata on a temporal scale and over the size class distribution, sex-ratio, recruitment defined as the specimens of the two first size classes, and breeding period. Specimens were collected in sand bottoms at the infralittoral zone at Flamengo Beach in Ubatuba, in the northeastern coast of São Paulo state, using free diving performed by one diver from August 2017 to July 2018, for 30 minutes per month. 337 juvenile, 51 adult females, and 38 adult males were analyzed, comprising 12 ovigerous females. There was registered recruitment, in almost all months. The sex ratio was 1:1.3, with more females than males in the population. In March, there was a significant recruitment period with 337 juveniles in one sample. The maximum carapace width was 6.6mm in males and 7.65mm in females. The representative number of specimens in the first size class may provide information that D. crinitichelis presents some levels of spatial segregation in the population in this area and should be monitored for preservation.

摘要：Dissodactylus属的豆蟹（Dissodactylus）常与其他海洋无脊椎动物形成共生关系。本研究针对与沙钱（sand dollar）*Encope emarginata*共生的豆蟹科（Pinnotheridae）蟹类*Dissodactylus crinitichelis*，从时间尺度、体长分级分布、性比、以头两个体长级个体定义的种群补充量以及繁殖期等维度，系统记述其种群结构。研究样本于2017年8月至2018年7月间，由一名潜水员在巴西圣保罗州东北海岸乌巴图巴市弗拉门戈海滩的潮下带沙质底栖环境中，通过自由潜水方式采集，每月采样时长为30分钟。本次研究共分析337只幼蟹、51只成年雌性个体与38只成年雄性个体，其中包含12只抱卵雌性。几乎所有月份均记录到种群补充现象。该种群性比为1:1.3，雌性个体数量显著多于雄性。3月的单次采样中出现了显著的种群补充期，共捕获337只幼蟹。雄性个体的最大头胸甲宽度为6.6mm，雌性个体为7.65mm。首个体长分级中占比可观的个体数量表明，该区域的*D. crinitichelis*种群存在一定程度的空间隔离，需对其开展长期监测以实现物种保护。