Managing multiple stressors to enhance the resilience in threatened marine habitats

Background/Question/Methods

Coastal systems are threatened by multiple anthropogenic activities, such as urban development, organic and inorganic pollution and over-exploitation of resources. Nonetheless, current management activities are still almost exclusively developed in an impact-by-impact framework. We present results from experimental work aiming at understanding the drivers of loss and recovery pathways of degraded systems, following experimental manipulations mimicking management actions geared towards recovery. We experimented with fucoid, canopy-forming algae on Mediterranean coasts, in light of their ecological relevance, their sensitivity to a variety of human impacts, and their declared conservation priority. This habitat is retracting particularly in urban areas, and is being replaced by turf-forming algae and invasive species, with major consequences for associated communities. We used a combination of historical data, quantitative in situ observations of natural recruitment patterns and field experimental work to describe habitat loss of these systems along the coastline of the North Adriatic sea, and identify potential underlying drivers. We also tested through laboratory experiments the effectiveness of alternative management options of potentially interacting cumulative stressors (nutrients and sediment loads) in enhancing the resilience of these systems to projected increase in sea surface temperature

Results/Conclusions

We found that recent declines of forests of canopy-forming algae were prepared by a long history of degradation and fragmentation of these systems, driven by an increasing cumulative impact from natural- and human-induced habitat instability, deterioration of water quality and increased storminess. We also found that at such advanced stage of ecosystem degradation, management of individual stressors would not be sufficient to reverse the loss. However, the combined management of nutrients and sediments would increase significantly the resilience of canopy-forming algae to projected future increase in sea surface temperature. These results highlight the potential risk for failure of separate policies for anthropogenic impacts, and stress the need for a more holistic approach to the management of cumulative multiple stressors in the coastal zone