Effects of water temperature, dissolved oxygen concentration and turbidity on population dynamics of larva of Golden Mussel Limnoperna fortunei in reservoirs
Golden mussel Limnoperna fortunei is a freshwater bivalve that adheres to water intake facilities and produces several troubles by growing. Biofouling problems have been expanding recently in Japan, and the planktonic stage is considered to have an important role for their habitat distribution. However, little information has been obtained on the survival, growth, and reproduction of L. fortunei in lakes of Japan. We investigated population dynamics of larval L. fortunei in two reservoirs, Lake Ohshio and Lake Takenuma, which are connected by headrace channel. The L. fortunei larva occurred between late June and late September in the lakes. Larva were initially found on 18 June 2008 when water temperature (WT) was about 17 degree C. No larvae were found in autumn when WT was about 20 degree C in Ohshio lake. The larvae density in Lake Ohshio was more than 10,000 ind./m3 with maximum of 80,000 ind./m3 in summer of 2007 and 2008. The density in Lake Takenuma was much lower and maximum value was near around 200 ind./m3. The larvae were mainly distributed in deep area of the lakes during the day. However, it moved to near surface area with increasing turbidity. The WT and dissolved oxygen concentration (DO) were almost uniform regardless of water depth in Lake Ohshio because of destratification due to continuous aeration. Summer WT and DO in the lake were considered to be kept good for the survival and reproduction of L. fortunei. On the other hand, stratification was found for WT and DO in Lake Takenuma throughout the season. Low WT and DO in summer found in deep area of the lake were not considered to be acceptable for the survival of larva and adults of this species. Thus the population of L. fortunei larva differed extremely even in adjoining two lakes, and WT and DO are considered to be critical factors especially for their reproductions.