Interannual Variation of Subtidal Fish Assemblages in Wakasa Bay, Sea of Japan, Revealed By 12 Years of Bi-Monthly Underwater Visual Census

A bi-monthly underwater visual census has been conducted in a temperate rocky reef habitat in Japan since January 2002. My previous paper revealed that fish assemblages from years 2002 to 2006 included more of southern species compared to those found in a survey conducted from 1970 to 1972. The present paper tests following hypotheses: 1) warm water species has increased for the recent 12 years, ii) interannual fluctuation of recruitment is dependent on the pelagic larval duration (PLD) in each species. A total of 95 fish species were recorded in this survey period, during which bottom water temperature ranged from 9.8 to 29.6 °C. Both species richness and fish abundance were high in summer and low in winter. Bottom water temperature gradually increased in this period coinciding with the increase of southern species. Interannual fluctuation was not necessarily dependent on the PLD. For example, jack mackerel with a long PLD and two species of goby with a short PLD had a low level of interannual fluctuation, whereas the recruitment of red sea bream with a medium PLD highly fluctuated in abundance.