Interplay among anthropogenic impact, climate change, and internal dynamics in driving nutrient and phytoplankton biomass in the Gulf of Naples

摘要

Due to an ever-increasingdemographic pressure, coastal areas are hotspots ofanthropogenic impact on marine ecosystems. Understanding the extent and natureof these impacts is critical for developing effective conservation and managementstrategies to protect and restore coastal marine ecosystems and the services theyprovide. The Gulf of Naples is a coastal embayment in the Tyrrhenian Sea, WesternMediterranean Sea, which is severely impacted by human activities. Here, we discussthe intertwining of anthropogenic pressures and climate variations in regulatingphytoplankton biomass dynamics in the Gulf and the presence of possible long-termchanges. We analysed three decades of T-S,nutrient, and chlorophyll a data collectedat a fixed station, the LTER-MCsite. Despite some spikes in nutrient concentrations(up to 9.92 mmol m~(?3) for NO_3~?, 13.12 mmol m~(?3) for NH_4~+, 0.75 mmol m~(?3) for PO_4~(3?), and 13.59 mmol m~(?3) for Si(OH)_4), median surface and depth-integratedconcentrationsare relatively low (0.73 mmol m~(?3) and 0.45 mmol m~(?3) for NO_3~?, 0.73 mmol m~(?3) and 0.47 mmol m~(?3) for NH_4~+, 0.07 mmol m~(?3) and 0.04 mmol m~(?3) for PO_4~(3?), 1.61 mmol m~(?3)and 1.44 mmol m~(?3) for Si(OH)_4, respectively). Chlorophyll a concentrations, heretaken as a proxy of phytoplankton biomass, occasionally display high values (up to17.33 mg m~(?3)) and fluctuating highs and lows lasting several months, with an overallmedian value of 1.37 mg m~(?3) at the surface, and 0.55 mg m~(?3) as integrated mean. Thesevalues are nine and three times higher than the offshore concentrations. The planktonfood web at the site is mostly driven by terrestrial inputs. The effect of large-scale–long-termtrends in nutrient inputs (e.g., phosphate load reduction) is comparable tothat of local drivers, also because of the relatively shallow depth (75 m) of the stationand its vicinity to the coastline. Importantly, the physical dynamics, despite the moreclosed morphology of the Gulf with respect to other bays in the Tyrrhenian Sea,efficiently removes excess nutrients and biomass, preventing dystrophic phenomena.