Natural capital dynamics in coastal planktonic systems: A biophysical accounting perspective

Understanding the biophysical foundations of coastal systems is essential for sustainable coastal management and rests on the principle of preserving natural capital in at least an intact state. This study applied emergy analysis (expressed in solar emergy joule - sej) to assess the natural capital (NC) and environmental support flows (ENFL) associated with planktonic communities within the three main gulfs (Gaeta, Naples and Salerno) along the coast of the Campania Region (central Tyrrhenian Sea, NW Mediterranean), during two seasonal time-snapshots (autumn 2020 and summer 2021). The results revealed seasonal differences in distinct patterns in system organization and resource dependency. Higher NC stocks (6.26 × 10¹⁰ sej m^-2) and a more complex food web structure were observed in summer 2021, with increased self-organization and decreased reliance on external input. In contrast, autumn 2020 showed lower natural capital stock (NC: 2.39 × 10¹⁰ sej m^-2) and a greater demand for environmental support flows (ENFL: 3.88 × 10¹⁰ sej m^-2 day^-1), driven by increased rainfall and geothermal heat, which emerged as key drivers of ecosystem dynamics. Furthermore, the NC and ENFL were also translated into monetary equivalents (em€), facilitating interpretation in socio-economic contexts without altering the ecological meaning of the analysis. The results highlight the potential of emergy analysis as a decision-support tool for policymakers for the development of environmentally sound coastal zone management practices and policies.