The State of the Mediterranean Marine and Coastal Environment

Cumulative and Concurrent Impacts

None of the factors affecting the Mediterranean Sea and its coasts, along with its inhabitants, exist in isolation. Different pressures act over time and in unison to affect the resilience of ecosystems and their ability to deliver ecosystem services. Increasing and multiple uses of ocean space increase the chances that certain threats will cause more impact when occurring simultaneously than the addi- tive effect of individual pressures. Thus, nutrient over-enrichment can cause eutrophication more quickly when occurring in waters warmed by climate change, for example; introduced species can become more quickly invasive in ecosystems where food webs have been altered by fishing. The combined effect of nutrient over- enrichment, over-fishing of certain functional groups like grazing fishes, and climate change can act together to cause imbalances in nearshore ecosystems and loss of ecosystem services. Threats that work synergistically to cause even greater impact than individual threats acting alone should thus be monitored. Nonetheless, understanding cumulative impacts – multiple im- pacts occurring through time – is notoriously difficult, especially in the absence of a monitoring regime that efficiently tracks pres- sures and their impacts. In the absence of such research regimes, as is the case in the Mediterranean, modelling helps us under- stand the impacts of multiple threats acting simultaneously. The National Center for Ecological Analysis and Synthesis (NCE- AS) has undertaken modelling to perform comprehensive spatial analysis and mapping of human pressures throughout the Medi- terranean Basin. This work builds on a previous global analysis of cumulative human impacts (Halpern et al. 2008), including additional information to better reflect the specific pressures and ecosystems of the Mediterranean Sea and coasts. A total of

Sources of environmental impact on the Mediterranean Sea

Average impact score

1.4

Climatic stressor Fishing Development and transport Pollution

PH decrease

1.2

STT increase

UV increase

Demersal shing, high bycatch Trawling and dredging Shipping

1.0

Demersal shing, low bycatch Hypoxia Non-indigenous species Inorganic pollution

0.8

Pelagic sheries, high bycatch Pelagic sheries, low bycatch Fertilizers Coastal population Pesticides

0.6

0.4

Artisanal shing Oil spills Oil rigs

0.2

0.0

Sources: National Center for Ecological Analysis and Synthesis, Mediterranean Cumulative Impacts Model.

Mediterranean cumulative impact model

Cumulative impact

Low Medium Medium/high

Very High High

Sources: adapted from a map by National Center for Ecological Analysis and Synthesis, Mediterranean Cumulative Impacts Model, online database, accessed in December 2011.

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STATE OF THE MEDITERRANEAN MARINE AND COASTAL ENVIRONMENT