Latitudinal gradient in the distribution of intertidal barnacles of the Tetraclita species complex in Asian waters

Barnacles are a major space occupier in the intertidal zone and are good model organisms to study the biogeography of intertidal invertebrates. In the present study, we used quantitative transect sampling to study the geographical distribution of the common rocky shore barnacles Tetraclita kuroshioensis, T. squamosa, T. japonica japonica and T. j. formosana at 19 sites covering the 3 large Asian marine ecosystems (Kuroshio Current, East China Sea and South China Sea) from 22° 20' to 35°00'N. Tetraclita spp. showed spatial variations in geographical distribution. Species assemblages of >60% similarity can be grouped into 4 distinct regions. On the Pacific coast of Japan T. j. japonica, T. j. formosana and T. kuroshioensis co-existed at the same tidal level, with T. j. japonica at the highest abundance. In North Taiwan and Okinawa T. kuroshioensis and T. j. formosana were common. In East Taiwan, T. j. formosana was the dominant species and T. kuroshioensis occurred in low abundance. In South China, T. squamosa and T. j. japonica were found, but they occupied different tidal levels. T. j, formosana and T. kuroshioensis were abundant in West Pacific waters, suggesting that their larval pool is associated with the Kuroshio Current. T. squamosa was distributed along the South China coast and it is possible that their larvae were transported mainly by the South China Sea Surface Current. T. j. japonica had high abundance in both Japan and South China, but with very low abundance at the Pacific shores between these 2 locations. There may be a physical and genetic boundary between the northern and southern populations in the Pacific Ocean and further studies of Tetraclita spp. in the Asian region should focus on population genetics. © Inter-Research 2008.