Feeding activity of bivalves is understood to change in response to a suite of environmental conditions including food quantity and quality. Characterizing inter- and intraindividual variability in the feeding activity of bivalves is important to understand the ecosystem interactions of bivalves. The purpose of this study was to explore intra- and interindividual variability in feeding rates of the blue mussel Mytilus edulis using natural seston. For five days, physiological rates related to feeding (pumping and ingestion) and digestive processes (gut passage time) were measured every 20 minutes, and 24 hours, respectively using natural seawater in a flow-through system. This high temporal resolution of pumping rate measurements permitted the observation of both intra- and interindividual variability of feeding rates. 10 individual mussels were used for the experiment, and interindividual differences were minimized by collecting mussels of the same length (50mm) and standardizing feeding rates to gill area (mm2).
Results indicate both intra- and interindividual variability in feeding rates, with some individuals pumping on average at high rates (~5 Lh-1) and some at low (~1 Lh-1), despite being held in similar conditions. Gut passage time also varied both between individuals, and temporally throughout the experiment. To examine drivers of variability in feeding rates, pumping rate was correlated to food availability (Fluorescence (µgL-1)) using temporal mismatches informed by gut passage time. Results indicate that there is a higher degree of correlation when pumping rates are matched to food availabilities from 10 hours prior, where pumping rate increased with increased fluorescence. 10 hours was also the average gut passage time of M. edulis during the experiment. This finding suggests that digestion may play a role in the variability of feeding activity of bivalves, and that current feeding rates may reflect food availability from some hours prior, although correlation may not imply direct causation. This research contributes to our understanding of intra- and interindividual variability in feeding rates of bivalves and may be informative for in situ measurements of feeding, as well as individual growth models.