Spatial variations in tidepool fish assemblages related to environmental variables in the Tama River estuary, Japan

Abstract

Spatial variations in fish assemblages in soft-substrata estuarine tidepools（n = 55, 0.6-6.4 m² were investigated on tidal flats 0-4 km from the mouth of the Tama River estuary, central Honshu, Japan in early June 2003. A total of 1,838 individuals, representing 2 families and 11 species, were collected during the study period. All fishes collected were less than 50 mm SL, being mostly gobiid juveniles and adults. Acanthogobius flavimanus was the most abundant species, comprising 52.2% of the total individual number, followed by Pseudogobius masago（24.6%）, Gymnogobius macrognathos（12.7%）, G. breunigii（7.0%）, Mugil cephalus cephalus（1.0%）, Favonigobius gymnauchen（0.9%）, Mugilogobius abei（0.7%）and Eutaeniichthys gilli（0.5%）. Of these, six benthic gobies except for G. breunigii and M. cephalus cephalus occurred at different densities in the lower, middle and upper estuarine areas. The canonical correspondence analysis using densities of abundant species in each tidepool revealed that spatial variations in the fish assemblage structures were largely associated with environmental variables, including mud shrimp-burrow density, median grain size, salinity, height above low tide level, water temperature, pool size and water depth.