Protecting marine coastal habitats cost-effectively

Prioritising actions to protect seagrass meadows


KEY MESSAGES:
  • Seagrass meadows provide important ecosystem services but are under threat
  • Prioritisations based on cost-effectiveness are more efficient than prioritisations based on habitat maps or threat maps alone

Posidonia oceanica seagrass meadows in the Mediterranean Sea. (a) Healthy meadow in the study region, (b) meadow impacted by fish farming, (c) meadow impacted by anchoring, and (d) meadow impacted by trawling. (Photos by Yiannis Issaris/www.yissaris.com).

Posidonia oceanica seagrass meadows in the Mediterranean Sea. (a) Healthy meadow in the study region, (b) meadow impacted by fish farming, (c) meadow impacted by anchoring, and (d) meadow impacted by trawling. (Photos by Yiannis Issaris/www.yissaris.com).

Marine coastal habitats, such as seagrass meadows, provide valuable ecosystem services including food provision, carbon sequestration, and coastal protection. But coastal areas are also the focus of human settlement. They concentrate many human activities, both land-based (eg, coastal development) and ocean-based (eg, fishing). Therefore, conserving coastal habitats requires actions that abate multiple threats.

Environmental agencies charged with conserving coastal habitats must decide which threats to act on and where to take actions to abate those threats within their region. To achieve the greatest benefits for conservation, agencies should take the actions that are predicted to conserve the desired amount of habitat for the least cost.

A first step towards that direction is to categorise threats as ‘stoppable’ (eg, fishing) or ‘unstoppable’ (eg, climate change) based on how easily a threat can be abated within a particular time period (eg, 20 years). This will enable environmental agencies to realistically prioritise actions for conservation under a specific budget or conservation target (eg, protecting 30% of the habitat distribution).

An important next step is to combine data on the distribution of habitats and threats, with information on the cost and expected benefits of conservation actions which are easier to manage within the particular time period. Such an approach will lead to cost-effective solutions. On the other hand, prioritisation of actions based on habitat maps and/or threat maps alone can lead to less effective and/or more expensive solutions.

Our study demonstrated this approach for seagrass meadows.

It selected the most cost-effective actions to abate stoppable threats (trawling and anchoring), while avoiding areas affected by threats that are more difficult to manage, such as coastal development. The relative improvement in cost achieved by using the proposed approach was examined by comparing with other common prioritisation criteria that do not consider cost, including choosing sites based on threat level or habitat cover alone.

The establishment of anti-trawling reefs (in the study region in the Mediterranean) was found to be the most cost-effective action to achieve the European Union conservation target for the protection of seagrass (Posidonia oceanica) meadows.

Figure 1: Comparison of the cost of achieving 65% seagrass conservation for three prioritisation criteria: 1) cost-effectiveness, 2) seagrass cover, 3) level of threat. The relative cost of each scenario is expressed as a proportion of the cost associated to the costeffectiveness criterion.

Figure 1: Comparison of the cost of achieving 65% seagrass conservation for three prioritisation criteria: 1) cost-effectiveness, 2) seagrass cover, 3) level of threat. The relative cost of each scenario is expressed as a proportion of the cost associated to the cost-effectiveness criterion.


More info: Sylvaine Giakoumi sylvaine.giakoumi1@gmail.com

References

Giakoumi S, CJ Brown, S Katsanevakis, MI Saunders & Possingham HP (2015). Using threat maps for cost-effective prioritization of actions to conserve coastal habitats. Marine Policy 61: 95-102.

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