Latitudinal Gradients of Species Richness in Marine Benthos: Insights From Japan's Tidal Flat Areas

Abstract

Studies on latitudinal diversity gradients (LDG) in Japan are restricted by either a relatively small number of sampling sites or are limited to a specific taxon. This study examined the LDG in marine benthos across 171 stations along the tidal flats of Japan spanning a latitudinal range from 24° N to 45° N. Published datasets of macrobenthic communities were obtained to determine the multi-scale variability of marine macrobenthos in 1106 census plots from Hokkaido to Okinawa. A total of 1271 taxa were identified. Mollusca was the dominant taxonomic group in our datasets with 36% of the total composition, followed by Malacostraca (28%), Annelida (20%), and other groups (16%). Gamma diversity was highly variable (2–132 species), with a station in Hokkaido having the lowest species and a station in Kyushu having the highest regional diversity. Decreasing trends were observed in all major taxonomic groups as they plotted against latitude. The analysis of species richness across the latitudinal gradient revealed a general decline in diversity from low to high latitudes, consistent with the expected LDG pattern. However, an unexpected peak in species diversity was also observed in mid-latitude regions (32° N–34° N), particularly in the Kyushu region, possibly due to its extensive tidal flats and its historical connectivity to the Eurasian Continent. Our findings provide new insights into the geographical patterns of macrobenthic diversity along Japanese coasts.