Blackfin Seabass Utilize Small Estuarine Lagoons as Nurseries: Implications From Juvenile Sampling at Habitat and Seascape Scales

Estuarine lagoons provide nursery habitats for marine fishes; however, small lagoons (< 1 km²) have been overlooked. To evaluate the nursery function of small estuarine lagoons (SELs) for temperate marine fish, this study used seining on the coast of the northwestern Pacific (Kyushu, temperate Japan) during the juvenile seasons (winter and spring) to perform juvenile sampling at two scales and an abundance/size comparison of blackfin seabass (Lateolabrax latus). As a preliminary survey, habitat-scale (inside vs. outside lagoon habitats) sampling was attempted in two SELs during February and April. Subsequently, seascape-scale sampling was undertaken during the juvenile season (January–May). The seascape consisted of two types of estuaries (lagoons and rivers) and sandy beaches (embayed and exposed). A preliminary survey showed no clear difference in abundance among the habitats, but significantly larger juveniles were observed inside than outside the two SELs. In the seascape survey, peak juvenile abundance during the first half of the study period was concentrated in habitats other than the lagoon estuary, whereas no peak was recorded during the second half. Moreover, the lagoon estuary was significantly larger than the marine habitats, and the monthly occurrence of juveniles was continuous in the lagoon estuary but intermittent in the riverine estuary. These results imply that seabass juveniles utilize the SEL habitat as they grow, highlighting the potential nursery function of estuarine lagoons for marine fish, even at a small scale.