Abstract
Environmental factors are encoded in shells of marine bivalves in the form of geochemical properties, shell microstructure and shell growth rate. Few studies have investigated how shell growth is affected by habitat conditions in natural populations of the commercial clam Chamelea gallina. Here, skeletal parameters (micro-density and apparent porosity) and growth parameters (bulk density, linear extension and net calcification rates) were investigated in relation to shell sizes and environmental parameters along a latitudinal gradient in the Adriatic Sea (400 km). Net calcification rates increased with increasing solar radiation, sea surface temperature and salinity and decreasing Chlorophyll concentration in immature and mature shells. In immature shells, which are generally more porous than mature shells, enhanced calcification was due to an increase in bulk density, while in mature shells was due to an increase in linear extension rates. The presence of the Po river in the Northern Adriatic Sea was likely the main driver of the fluctuations observed in environmental parameters, especially salinity and Chlorophyll concentration, and seemed to negatively affect the growth of C. gallina.
Highlights
Valuable ecological interactions between organisms and their habitat can be unravelled through studies carried out along latitudinal gradients, where varying environmental pressures can be explored on both biological and evolutionary processes[1]
High porosity influenced bulk density which was lower in small size shells. This suggests that during the first year of life, C. gallina seems to promote porosity, enabling it to keep higher linear extension rates in order to reach the size at sexual maturity
Knowledge of the growth rates allows a proper management of bivalve fisheries and the observations highlight in this study can be used in predictive models to explore the evolution of C. gallina resource exploited during time under extended changes in their habitat conditions, for example seawater temperature, salinity or food
Summary
Valuable ecological interactions between organisms and their habitat can be unravelled through studies carried out along latitudinal gradients, where varying environmental pressures can be explored on both biological and evolutionary processes[1]. Previous studies identified several drivers that influence the shell growth rate of bivalves including temperature[5,6], food supply and quality[7,8], salinity[9], latitude[1] and reproduction[10]. Shell growth occurs as the result of the umbonal-ventral linear extension of the shell per unit time and net calcification rate is the product of shell bulk density (shell mass/volume ratio, including the volume of pores) and linear extension rate. Shell linear extension rates in bivalves decrease through ontogeny[12] and it might be influenced by seasonality or changes in environmental parameters[13]. Since decreasing linear extension rate is usually accompanied by an increasing in shell bulk density, total CaCO3 variations deposited by the organism and linear extension rate may not correlate[13]. Bulk density and non-continuous linear extension over the year, or modifying bulk density and homogeneous linear extension rate
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