Respiration and ingestion rates of the filter-feeding bivalve Musculista senhousia: implications for water-quality control

To evaluate the effect of filter-feeding bivalves on water quality, batch and flow type measurements were recorded to estimate the respiration and ingestion rates of Musculista senhousia, which predominates the macrobenthos of Lake Nakaumi, Japan. The results for the respiration rate experiments had a low stable rate at about 15 mg O2 day−1 DFW g−1 (where DFW means dry flesh weight) at low temperatures (between 5°C and 10°C) that increased at middle and high temperatures (from 10°C to 30°C), reaching a maximum rate of about 200 mg O2 day−1 DFW g−1 at 30°C. The dependence of respiration rate on temperature is significant, especially between 10°C and 15°C (Q10=6.9). The vertical 2-BOX numerical model showed that continuous stratification of the water column must be averted if M. senhousia are to survive. Ingestion rate of particulate matter also increased with temperature between 10°C and 20°C. Ingestion rates at 30°C, after being incubated for more than 1 day, were almost the same as ingestion rates at 20°C. Filtration rates were calculated from concentrations of chlorophyll a (Chl.a), particulate total phosphorus (PTP) and particulate total nitrogen (PTN). Obvious differences were observed between the filtration rate calculated from the Chl.a concentration compared to those from PTP and PTN. This may imply that M. senhousia selectively ingested a particular species of phytoplankton. The horizontal 2-BOX model showed a relationship between the Chl.a concentration in L. Nakaumi and the water exchange rate. The ingestion potential of organic matter by M. senhousia is greater than those of the nutrient loads in the field and has less risk of depleting dissolved oxygen (DO) in the bottom layer. If, therefore, the phosphorus and nitrogen supply to M. senhousia increased, and adult M. senhousia are collected and removed efficiently, water quality in L. Nakaumi would improve.