What can the shell tell about the scallop? Using growth trajectories along latitudinal and bathymetric gradients to reconstruct physiological history with DEB theory

The great scallop, Pecten maximus, presents a strong variability of growth and reproductive patterns along its spatial distribution range. Such differences in life history traits result from complex interactions between organisms and environmental conditions that can be apprehended through the study of energy dynamics. As the determination of accurate food proxy can be a limitation for modeling bioenergetic, recent work by Lavaud et al. (accepted, this issue), based on the DEB theory, provided a new approach consisting of using temperature and growth time series to reconstruct the required assimilated energy to support observed growth. In this study we present an application of this method to growth trajectories of the great scallop P. maximus used to elucidate: (1) life history traits patterns and (2) the choice of food availability proxies. The inverted DEB model was used to reconstruct the functional response (f) for different age classes of P. maximus in 10 locations of its spatial distribution range. We especially explored the patterns of reconstructed f along latitudinal and bathymetric gradients. Average reconstructed f as well as its maximum value were found to increase with latitude. The variability of f, although increasing, did not show a significant relationship with the geographical position. Along the bathymetric gradient strong positive relationships were found between the mean f or its variability and depth. Ontogeny had low effect on the reconstructed f. Furthermore, as the inverted DEB model allows the reconstruction of physiological variables and energy fluxes, we explored the potential differences in reserve and maintenance fluxes dynamics from great scallops living in these contrasting environments. For one of the study sites, comparisons of f with field measurements of 11 food indicators (chlorophyll-a from the pelagic/benthic domains, phytoplankton cell counts, etc.) highlighted the complexity of the functional response and the diet of P. maximus. Pelagic or benthic phytoplankton biovolume, diatoms and dinoflagellates counts and chlorophyll-a were found to be the major contributors to the variability of f. Results suggest that although assimilation is best described by a combination of indicators, chlorophyll-a remains a good enough indicator of food availability for great scallops and bivalves in general. •We reconstructed food assimilation from growth in P. maximus using inverted an DEB model.•Ten locations from France to Norway an