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：狡蟹属（Dissodactylus）的物种通常与其他海洋无脊椎动物形成共生关系。本研究从时间尺度、体型分级分布、性比、以最初两个体型级别的个体定义的补充群体，以及繁殖期等维度，记述了与沙钱海胆（Encope emarginata）共生的豆蟹科（Pinnotheridae）细螯狡蟹（Dissodactylus crinitichelis）的种群结构。样本采集工作于2017年8月至2018年7月间开展，由1名潜水员采用自由潜水方式，在圣保罗州东北海岸乌巴图巴的弗拉门戈海滩潮下带沙质底质中进行，每月采样时长为30分钟。本次研究共分析了337只幼体、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。研究结果显示，几乎所有月份均有补充群体出现。种群性比为1:1.3，雌性个体数量多于雄性。在3月的单次采样中出现了显著的补充事件，共捕获337只幼体。雄性个体的最大头胸甲宽度为6.6mm，雌性个体为7.65mm。首个体型级别的个体占比可观，这表明细螯狡蟹在该区域的种群存在一定程度的空间隔离，需对其开展监测以实现保护。