CONSERVATION STATUS AND TRAJECTORIES OF CHANGE IN MARINE COASTAL ECOSYSTEMS

Marine environments play a central role for the planet, yet an understanding of how climate change is affecting marine ecosystems has been poorly developed. There is now growing evidence that human activities are driving rapid changes from local to global scale. In last decades, the rates of change is accelerating and may exceed the potential tolerance of many organisms to adapt. Ecological systems and marine organisms have evolved under different regimes of stress and disturbances both of natural and anthropic origin and intrinsically connected. No ecosystem is unaffected and marine coastal habitats are particularly sensitive due to the convergence of multiple stressors. The present work attempts to investigate how variable patterns of stress and disturbance influence the change in marine ecosystems, looking at two iconic coastal habitats: seagrass beds and coral reefs. Effects due to the anthropogenic pressure and a severe storm are here investigated as stress and disturbance respectively, on the endemic Mediterranean seagrass Posidonia oceanica. Thermal anomalies causing repeated coral bleaching events are considered as disturbances on Maldivian coral reefs, while the reduced pH environment that is created at shallow hydrothermal vents of North Sulawesi (Indonesia) is seen as a stress simulating climate and human impact on benthic habitats. The study of change in coastal ecosystems has been carried out by means of several approaches including the comparison with long-time series, the use of indicators able to return a value of ecological status, retrospective analyses and modelling. The present work confirms the complexity of the interactions between stresses and disturbances, different in scale and intensity, operating on a same ecosystem. The increase in seawater temperature starting from the 1980-90s can be identified as a common driver of change in both seagrass meadows and coral reefs ecosystems. In P. oceanica meadows of the Ligurian Sea, anthropic pressures remain the primary causes of impact, although, high intensity, pulse disturbances demonstrated that a single event is able to cause the same loss resulting from hundreds of years of chronic stress. Benthic habitats in close proximity to hydrothermal vents at tropical latitudes seem not negatively affected by the reduced pH as a chronic stress, while, in Maldivian coral reefs, the ability to cope with thermal disturbances seems to be dependent on coral genera. Benthic ecosystems could develop a certain adjustment capacity to chronic stress to the detriment of an enhanced sensitivity towards disturbances but this is of concerns regarding the predicted increase of high intensity disturbances due to climate change. Moreover, chronic stress and disturbances invariably co-occur, so it becomes difficult to assess which may be the proximate cause of ecosystem change. Data on benthic communities suggest that marine habitats are experiencing phase-shifts toward alternative and unknown states. Consequently, future marine habitats will likely lose their original features acquiring a new different shape. Continuing studies and long-term series of data will remain the most effective tool to validate these predictions and evaluate temporal patterns.