内湾および干潟における物質循環と生物生産【55】

摘要

The factors of the decrease of flatfish in Harima-nada of Hyogo prefecture are examined. One point is the reclamation which has been done since the mid of 1960'. The reclamation of tidal flat is thought to lead to the disappearance of nursery ground and spawning ground of flatfish. In consequence flatfish has been decreased. Sec-ond point is the oxygen-deficient water which is thought to be set up by the reclamation. It was found that the decrease of flatfish went along with the decrease of short-necked clam in Harima-nada. The catch of flatfish is found to be inversely related to the cumulative areas of the reclamation. The relation between flatfish and clam is thought as follows: The decrease of clam by the reclamation leads to the increase of phytoplankton by the decrease of grazing, which leads to the oxygen-deficient water in the lower layer, and as a result flatfish is decreased.