Assessment of decadal changes in the tidepool fish assemblage of Danjo Islands in the northern East China Sea

Tidepools are a major component of coastal environments and useful for evaluating the potential impacts of various factors on marine environments. We have investigated the structure of tidepool fish assemblages on the Danjo Islands, an isolated and uninhabited group of islands located in the northern East China Sea in the western Pacific. Standardised quantitative fish sampling and supplementary visual observation in 2017–2018 revealed that tidepool fish assemblages on the Danjo Islands were characterised by the dominance of Blenniidae, and that species composition was clearly distinct from sites in southern Japan (Ryukyu archipelagos and Kyushu region), while all species were non-endemic, i.e. widely distributed and common in southern Japan. Compared to the survey in the 1970s, the species composition of tidepool fishes on the Danjo Islands appeared to have shifted slightly towards the pattern observed in southern regions during the past half century. Given little or no anthropogenic impact on coastal environments of the Islands, the observed changes in the tidepool fish community are likely to result mainly from temporal variations under the prevailing environmental changes.