Understanding the Salinity Range of the Larvae of an Isopod Endoparasite in an Estuarine Mud Crab Host

Abstract

Salinity is one of the most important environmental factors in estuarine ecosystems as it determines organismal distribution. In the Chesapeake Bay, the white-fingered mud crab, Rhithropanopeus harrisii (Rh), is a host to two castrating endoparasites, a rhizocephalan barnacle, Loxothylacus panopaei (Lp), and an entoniscid isopod, Cancrion sp. While much is known about Lp, there is little information surrounding the newly discovered Cancrion sp. Rh can live in salinities ranging from 0.5-25 ppt, while Lp cannot survive in salinities <10 ppt. Before knowledge of Cancrion sp., it was theorized that Rh could escape castration by moving to salinities <10 ppt; however, recent field data shows that Cancrion sp. exists in these low salinity areas. This research aims to understand the salinity range of the first larval stage of Cancrion sp. Rh were collected from low salinity regions of the Chesapeake Bay. Rh was monitored daily for the release of Cancrion sp. larvae into the water. Upon release, 70 larvae from each brood were equally divided amongst 7 salinities (0.25, 3, 6, 9, 12, 15, and 18 ppt) with 10 replicates/brood in each salinity across a total of 9 broods. Larval mortality was assessed after 2, 4, 8, 12, and 24 hours and every subsequent 24 hours for 7 days. Initial data exploration revealed that larvae have the highest survival rates in 9 ppt and above. This research will elucidate the extent of Rh’s salinity refuge and provide the first natural history understanding of Cancrion sp.