Taxonomic Composition and Seasonal Distribution Changes of Pelagic Tunicates in the Waters Off Nuclear Power Plants in Northern Taiwan in Relation to Environmental Conditions

Abstract

Pietro Franco, HongJu Chen, and Jiang Shiou Hwang (2016) The ecological importance of pelagic tunicates and their role in marine ecosystems are receiving increasing attention, especially with respect of their role in the carbon flow through the planktonic food web and their fundamental influence on the microbial food web. Nuclear Power Plants I and II are located in most populated northern Taiwan. Effects of the discharge of the cooling water from nuclear power plants have drawn great attention since 1977. No studies on pelagic tunicates were carried out in the area. Taxonomic composition, distribution, abundance and seasonality of pelagic tunicates belonging to the two taxonomic classes Larvacea and Thaliacea were studied and their relationship with environmental conditions were analyzed from 21 stations in the waters adjacent to 2 nuclear power plants in northern Taiwan. A total of nine species were identified: the appendicularians Oikopleura dioica, O. caphocera, O. rufuscens, O. longicauda, Fritillaria aberrans and the thaliaceans Doliolum denticulatum, Thalia democratica orientalis, Dolioletta gegenbauri and Thetys vagina. There is a strong seasonality in the area. In fact, the highest abundances were measured during the summer season, whereas low abundances prevailed in the rest of the year. No relationship was found between tunicate abundance and surface temperature and salinity, likely due to slight changes of the two environmental parameters of the studied area within each season. The hypothesis regarding a direct effect of the discharged cooling waters on the organisms was consequently discarded. The abundances of larvaceans and thaliaceans were significantly influenced by the concentration of chl-a, among the four seasons as well as within all the stations for each season. There is a strong seasonality in the area concerning the distribution and abundance values of the nine species of pelagic tunicates in the area. The presence of the organisms is more influenced by the availability of food during the four seasons rather than by the effects of the discharged waters from the two nuclear plants. Further research needs to describe inter-annual changes in seasonality of pelagic tunicates in this area.