A thermodynamic approach to the study of beach ecosystems

An ecological thermodynamic analysis of different beaches in the North-Western Mediterranean Sea has been performed by detecting the spatial and temporal variations of exergy and specific exergy. The calculation of these indicators has been performed for the microbenthic loop that represents a major sub-system within the beach food chain. In all the considered beaches exergy and specific exergy increases are related to increase in sediment depth showing a preferential migration of the complex and mobile organisms through the sediment column by reaching more protected and stable substratum. Along the emerged-submerged gradient both indicators showed that the greatest quantity and complexity of organisms was always detected in the swash zone station confirming the importance of the swash zone as a transitional area between land and sea characterized by high diversity and complexity of the trophic network. The temporal variations of exergy and specific exergy showed that in the tourist exploited beaches decrease in complexity of the trophic network is detectable during the summer period when the anthropic pressure is the greatest ever. Exergy and specific exergy resulted good indicators of beach ecosystem health displaying good sensibility for spatial and temporal variations and for increases in external pressure as the tourist or more generally anthropic disturbances.