Fluctuating population density of the goby Lubricogobius exiguus during the breeding season with artificial nests at Oto Beach, Kagoshima, southern Japan

Abstract Cryptobenthic reef fish (CRF), which are benthic reef fish with body lengths of less than 50 mm, generally exhibit life history characteristics, such as a short lifespan, early maturation, high mortality, and microhabitat specialization. In this study, we investigated breeding season and population fluctuation patterns of a gobiid CRF fish Lubricogobius exiguus . At our field study site, the breeding season of L. exiguus extended from April to November. The population densities of L. exiguus fluctuated considerably, starting at low density early in the breeding season, increasing to a peak in the middle of the season, and stabilizing at a medium density by the end of the season. This seasonal pattern was influenced by two peaks in juvenile recruitment, and the adult population increased after these peaks. The fluctuating numbers of juveniles and adults suggest that some individuals may have a short post-settlement lifespan of less than 80 days.