2021 Volume 87 Issue 1 Pages 11-22
In the last 20 years, the population of the alien hard clam Mercenaria mercenaria in Tokyo Bay, Japan has grown. This alien species is expected to have some impacts on ecosystems, however, there are no reports on the ecosystem engineering effects of the hard clam in Tokyo Bay. In this study, we deployed a field manipulation experiment by using enclosures (including hard clam treatment, manila clam treatment, and control) to evaluate the effects of the hard clam on the physical characteristics of the sediments, microphytobenthos, and benthos communities in a sandy tidal flat. In the hard clam treatment, ORP at a depth of 5 cm and the median grain size of subsurface sediment, and chlorophyll a and pheo-pigment content of all sediment layers were significantly higher than in the other treatments at 4 and 6 weeks after the start of the experiment. However, there was no effect on the density and species composition of benthic diatom, meiobenthos and macrobenthos. These results suggest that the bioturbation of the hard clam has an ecosystem function that increases the permeability of the sediment and the biomass of benthic diatoms in Tokyo Bay.