1993 Volume 30 Pages 351-359
Although there are many development activities in coastal areas, influence of such activities on ecosystem is not revealed enough. In Ajisu tidal land, wave dissipating concrete blocks were established in front of seawal. The purpose of this study is to estimate the influence of the wave dissipating concrete blocks on ecological environment of Ajisu tidal land, especially on littleneck cram which is the most important resource of fishery afound the area. Ground level, ground water leve1, current velocity, SS and Cl concentration in sea water, particle size distribution of mud, ignition loss of mud, and biomass of littleneck clam were surveyed at 126 grid points in 800m×100m area during 1991 and 1992. The results were combined and put it in cluster analysis. The area in front of the wave dissipating concrete blocks were clusterized in one special cluster. The results are; In normal weather condition, wave dissipating concrete blocks worked positive to clam because they promoted the settlement of juvenile shell and its feed. In abnomal weather condition such as typhoon, wave dissipating concrete blocks worked negative to clam because they scattered sand which accumulated during normal weather period and might caused death of clam by burying them.
