Recolonization of the Himerometra robustipinna (Himerometridae, Crinoidea) by macrosymbionts: an in situ experiment

Abstract

It is generally considered that symbiotic organisms colonize their hosts during their early stages of development. The main goals of the present study were to assess whether post-settled (juvenile and adult) symbionts were able to colonize comatulid crinoids, and whether a hosts’ spatial distribution may influence the colonization pattern through a series of field recolonization experiments. Three series of experiments on recolonization of the comatulid crinoid Himerometra robustipinna were conducted in the Nhatrang Bay, South-China Sea, Vietnam. Ten species of macrosymbiont, 1 polychaetes, 1 gastropods, 1galatheids, 1 ophiurids, and 6 shrimps were found to be associated with H. robustipinna host in the controls and in the 3 experimental series. We found that symbionts rapidly colonized depopulated crinoids in all the experimental series. The prevalence was lower in the experimental series than in the controls butthe abundance, species richness were not significantly different. The presence of post-settled juveniles and adults in experimental series indicated migration from neighboring hosts. Dispersal strategies of symbionts varied: some of them such as the polychaete Paradyte crinoidicola, the gastropod Annulobalcis vinarius, and the galatheid Allogalathea elegans were rapid colonizers. The shrimps Periclimenes commensalis, Pontoniopsis comanthi, and ophiuroid Gymnolophus obscura demonstrated low colonization rate. The 1 and 2 experimental series showed that there was movement of symbionts in dense hosts’ aggregations or over short distances. Unexpectedly, the infestation characteristics of crinoids in the spatially isolated site (series 3) didn’t differ from that of crinoids from aggregations (series 1 and 2), which indicates that long distance (tens meters) migrations of crinoid symbionts also occurs.