1National Research Institute of Aquaculture, Fisheries Research Agency, Yokosuka, Kanagawa 238-0316, 2Aichi Prefectural Fisheries Experimental Station, Minamichita, Aichi 470-3412, 3Soma Branch, Fukushima Prefectural Fisheries Experimental Station, Soma, Fukushima 976-0022, 4Chiba Prefectural Fisheries Experimental Station, Chiba Prefectural Fisheries Research Center, Minamiboso, Chiba 295-0024, 5Department of Marine Ecosystems Dynamics, Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba 277-8564, Japan
A sudden outbreak of a parasitic sea spider Nymphonella tapetis began in a narrow area of Tokyo Bay in 2007, and subsequently occurred in remote areas of Mikawa Bay (Aichi Prefecture) in 2008 and in Matsukawaura (Fukushima Prefecture) in 2009, causing damage to local Manila clam Ruditapes philippinarum fisheries. A partial nucleotide sequence (562 bp) of the mtDNA COI gene was determined for a total of 110 individuals collected from these three localities. Average nucleotide sequence divergence between individuals was low (0.2±0.07%), and three local samples shared the most common haplotype with no significant difference in haplotype frequency between the samples. Since there have been few reports on the occurrence of this species in these areas, it is likely that these local populations share a common source which may be recently derived from introduced Manila clam for stocking. We also determined the nucleotide sequences of the 16S rDNA, 18S rDNA and ITS1 regions of the species. Phylogenetic reconstruction of sea spiders using the 18S rDNA data suggests that N. tapetis is a terminal clade within the genetically and morphologically diverse genus Ascorhynchus, which should probably be split into multiple genera.