Estimating the effect of phenotypic flexibility in feeding morphology on cockle growth (Cerastoderma edule) under different environmental conditions
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Dynamic Energy Budget (DEB) models are often used to describe growth in bivalve species. Ingestion rate determines the amount of energy assimilated and therefore the amount of energy allocated to growth, maintenance, and reproduction. Gills and palps are involved in the ingestion of food as their size determines clearance rate and selection efficiency. In bivalves, gills create a water current from which particles are filtered and palps sort these particles into edible and non-edible. Gill and palp sizes are phenotypically flexible and depend on environmental conditions. So far, variation in gill and palp size has not been incorporated in DEB models, even though they could greatly affect the amount of energy assimilated. Therefore, this research aims at linking environmental conditions to variation in gill and palp size in cockles (Cerastoderma edule) and incorporates this into a standard DEB model to estimate growth for cockles that adjusted their feeding apparatus to optimize food intake. Data on variation in feeding morphology has been collected under different conditions in the Dutch Wadden Sea. DEB models were applied to three different sites to compare variation in growth under different environmental conditions with and without flexibility in the feeding morphology. Results indicate that variation in gill size is mostly explained by shell length and exposure time while variation in palp size relates to shell length, median grain size, exposure time and density. Model estimates for cockle growth show a reduced growth under low Chlorophyll a and high Suspended Particulate Matter concentrations. In addition, it is beneficial for cockles to adjust their palp size, as this result in increased growth, while adjusting gill size seem to negatively affect growth. Therefore, it is concluded that flexibility in feeding morphology influences the growth of cockles and should not be ignored when modelling bivalve growth.