Effects of summer mesoscale hydrographic features on epipelagic siphonophore assemblages in the surrounding waters of Taiwan, western North Pacific Ocean

This is the first attempt to examine the relationship between the spatial distribution of siphonophores and mesoscale hydrographic features in the waters around Taiwan in summer. A total of 59 species of siphonophores, consisting of 12 Physonectae and 47 Calycophorae, were identified from our samples. The most abundant species were Lensia subtiloides (49.7 % of the total collection by number), Diphyes chamissonis (12.1 %), Chelophyes appendiculata (9.3 %), C. contorta (8.1 %), and Bassia bassensis (5.2 %). Two clear assemblages were associated with shelf waters (influenced by the South China Sea Surface Current) and oceanic waters (influenced by the Kuroshio Current), respectively. The shelf water assemblage was characterized by low diversity and high abundance of L. subtiloides , whereas the oceanic assemblage showed greater diversity and was dominated by C. appendiculata , C. contorta , and B. bassensis . We discovered strong correlations between temperature and zooplankton and siphonophore abundances, suggesting that temperature and prey concentration are important in determining the spatial distribution of siphonophores. In addition, lower abundance and higher species diversity of siphonophores were observed after the passage of typhoons. This study provides basic knowledge on the distributional patterns of siphonophores, which is essential information to further understand the ecological roles played by siphonophores and their responses to the hydrological conditions in the waters surrounding Taiwan.