Masami Hamaguchi, Tomoyuki Kasuya, Hirofumi Hinata, Keita Furukawa
Bulletin of the Plankton Society of Japan 51 120 - 125 2004年08月
The majority of the benthos are pelagic in their larval stages. The short-necked clam, Ruditapes philippinarum, which is widely distributed on sandy tidal flats across Japan and is a commercially important shellfish, has a planktonic larval stage, which lasts 2 to 3 weeks after hatching. In this stage, most clam larvae are able to disperse over wide areas with the currents and then settle on new habitats on other shores. In the case of Tokyo Bay, reclamation of the tidal flats and shallows has brought a marked decrease in the harvest of the clam. To recover the clam populations on the shores of Tokyo Bay, the creation of suitable habitats for the clam and the preservation of their environment are very important. We also need to understand how local populations of the clam are maintained through wide dispersal ranges over tidal flats during the larval stages. In this paper, we show the dynamics of larval dispersal of the clam in Tokyo Bay introducing the results of field plankton surveys conducted by the National Institute for Land and Infrastructure Management Ministry of Land and the National Research Institute of Fisheries and Environment of Inland Sea in 2001. The spatial distribution of the larval abundance of the clam was investigated at 65 stations along the entire range of Tokyo Bay on August 2, 6, 10 and October 15, 19, 23, in 2001. Identification of the larvae of the clam was performed using the monoclonal antibody technique. A large number of small D-shaped larvae were found shortly after hatching in the sea waters around the Banzu, Futtu, and Sanmaizu-Haneda in August and the Sanbanze, Sanmaizu-Haneda, and Kanazawa areas in October indicating that spawning populations in these areas probably contributed greatly to the larval supply in the bay. Moreover, the smallest size larvae also occurred abundantly around the Yokohama and Chiba port areas, suggesting that these port regions may play an important role in the transport of larvae into Tokyo Bay.