Testing latitudinal patterns of tidepool fish assemblages: local substrate characteristics affect regional-scale trends

We tested the regional-scale latitudinal patterns of occurrence and community structure of rocky tidepool fishes in relation to local environmental factors, particularly substrate characteristics. Data were derived from intensive field observations conducted on 36 shore sites spread across ca. 1,000 km north-south (24A degrees 03'N-32A degrees 45'N) in the south-western Japan. While numbers of families, genera, species and individuals per unit area decreased with latitude, these were dependent on substrate types: sites with non-limestone rock substrates tended to harbour larger numbers than limestone sites at the same latitude. Relative abundances of two dominant families (Blenniidae and Gobiidae) varied among sites with weak latitudinal gradients. Species-specific trends of latitudinal distribution were observed in most of the common intertidal fishes, with over half of the species demonstrating substrate-dependent variation. Species composition was clearly different between the Kyushu Island and the Ryukyus and also between limestone and non-limestone sites. Thus, our results clearly demonstrated that the regional-scale latitudinal trends of tidepool fish assemblages were partially dependent on local environmental characteristics (substrate types). Consideration was given to the influences of the Kuroshio Current and other factors including species interactions that might have helped modify observed latitudinal patterns.