Abstract
Blue mussels, Mytilus edulis , form dense beds of both commercial and ecological importance, and many attempts have been made to determine their filtration rate. The total time in which mussels actually utilise their filtration capacity in nature varies greatly, making in situ methods for filtration rate measurements relevant. Further, it is being debated to what extend filtration rates measured in the laboratory using cultivated algal cells may apply for mussels in nature. In the present study, we have used an open-top chamber setup in order to allow repeated in situ filtration rate measurements of M. edulis using ambient natural phytoplankton and free-living bacteria. We found that the in situ measured filtration rates are comparable to filtration rates obtained in laboratory studies using different methods and controlled diets of cultivated algal cells. Further, we found that the retention efficiency of free-living bacteria was between 22.2% and 29.9%, in good agreement with values from laboratory studies. Our findings support the assumption that mussels in nature tend to use their filtration capacity when the phytoplankton concentration is above a certain lower trigger level.
Highlights
We have used an open-top chamber setup in order to allow repeated in situ filtration rate measurements of M. edulis using ambient natural phytoplankton and free-living bacteria
We found that the in situ measured filtration rates are comparable to filtration rates obtained in laboratory studies using different methods and controlled diets of cultivated algal cells
Laboratory observations of valve gap responses of mussels to absence or presence of added cultivated algal cells to the ambient water have revealed that they close their valves below a lower chlorophyll a (Chl a) trigger concentration of about 0.9 [6] to 0.5 μg Chl a l−1 [7]
Summary
Laboratory observations of valve gap responses of mussels to absence or presence of added cultivated algal cells to the ambient water have revealed that they close their valves below a lower chlorophyll a (Chl a) trigger concentration of about 0.9 [6] to 0.5 μg Chl a l−1 [7]. With algal concentrations between the lower and upper trigger concentrations, mussels tend to filter the ambient water at a maximum rate. Because mussels are often living in dense beds, the ambient Chl a may frequently be strongly reduced [10] [11] [12] [13] [14] and likewise, during winter periods with no primary production [15] [16] [17]. The total time in which mussels utilise their filtration capacity in nature may vary greatly, making in situ methods for filtration rate measurements relevant
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