Seasonal variation of the biomass of the marine oligochaete Thalassodrilides cf. briani in Fukuura Bay, Japan and its optimal culture conditions

We studied the environmental remediation of polluted marine sediments using annelids and demonstrated that aquatic annelids had a high potential to lower the concentration of pollutant chemicals. We investigated the seasonal variation of dominancy of a marine oligochaete Thalassodrilides cf. briani(Naididae), which has high tolerance to pollution, in the benthic community in Fukuura Bay, Ehime Prefecture, Japan. In addition, the growth rates of oligochaetes under different temperatures were examined in our laboratory to establish an efficient oligochaete culture system. In the field studies, we investigated annual changes in the abundance and biomass of the oligochaete from 2011 to 2014 in Fukuura Bay. Throughout the investigation period, T. cf. briani dominated more than 60% of the total abundance of benthic communities, except in the winter of 2013 and 2014, and reached 121,400 individuals/m in February 2012. From spring to summer, the average body weight per individual reached a maximum, and the proportion of mature individuals was the highest in summer. These results suggested that new generations of this species occur in summer. In the laboratory experiment, T. cf. briani was cultured at 15, 20, or 25°C , and the growth and maturity rates of individuals with egg sacs were measured. The growth and maturity rates cultured at 15, 20, and 25°C after 30 days were 130% , 138% , and 160% and 1% , 23% , and 71% , respectively. Therefore, we determined that temperatures between 20 and 25°C triggered T. cf. briani maturation, and culture at 25°C was the most effective for inducing maturation.