The effects of selected environmental variables on filtration rate of Mytilopsis leucophaeata and evaluation of its potential role in the purification of mariculture effluent

Abstract

Platform mussels, Mytilopsis leucophaeata from Galveston, TX were exposed to various levels of salinity, temperature, dissolved oxygen and suspended solid concentrations to ascertain effects on filtration rate. Filtration rate was determined by turbidity reduction of suspensions over three hours. Sepia ink (0.15 + 0.034 []m) was the primary indicator for turbidity reduction. Mussels were exposed to four types of suspended particles (Sepia ink, colloidal carbon, Nannochloropsis and shrimp mariculture effluent) at various concentrations to evaluate their potential as possible biofiltration organisms. Filtration rate was measured at eight salinity levels (2 to 35 ppt). The highest individual mussel filtration rate (IMFR) was between 20 and 25 ppt. Filtration was measured at seven temperature levels (5 to 34⁰C). IMFR was highest at 20⁰C. Filtration was measured at nine dissolved oxygen levels (1 to 9 mg/l). IMFR was highest at 3 mg/l but much lower at concentrations between 4 and 9 mg/l. IMFR in colloidal carbon (Aquadag[TM]) was highest at 125 nephelometric turbidity units (NTU) but decreased rapidly at higher concentrations indicating gill saturation and/or possible shell valve closure. Mussels exposed to various concentrations of Sepia ink showed relatively constant IMFR with the highest at 200 NTU. Mussels in Nannochloropsis suspensions showed highest IMFR at125 NTU, similar to Aquadag[TM] experiments but gill saturation occurred at concentrations exceeding 200 NTU. Mussels in mariculture effluent decreased turbidity, however, particle settlement due to gravity was high. Salinity tolerances for M. leucophaeata correspond well to temperate mariculture salinities. M. leucophaeata showed strong thermal adaptation capabilities which correspond well to temperate mariculture fluctuations. M. leucophaeata may reduce phytoplankton levels reducing daily D.O. fluctuations. Aquadag[TM] is a good indicator of mussel feeding on microplankton and nannoplankton while Sepia ink is a good indicator of mussel feeding on picoplankton. Nannochloropsis is a good indicator of mussel feeding on nannoplankton between 1 to 3 []m. Because of heavy particle settlement due to gravity, effluent filtration designs utilizing settling tanks are suggested. Polyculture with mussel rafts is suggested for developing countries.