Impacts of MPAs on the Ecosystem

skateIn the second part of his paper, James discuses that although MPAs are being increasingly used as management measure to protect various habitats and species around the UK and are generally seen as a good thing, is there a need for the added caveat, especially in the case of elasmobranchs, of what differences are they going to cause to both the local and wider marine ecosystem?

Sharks skates and rays are all members of the elasmobranchs family. Many elasmobranchs occupy higher trophic levels in ecosystems, that is to say, they are the top level predators in the system and as such can be seen as regulators.

MPAs are already being used to protect elasmobranchs in the UK and, by definition, the purpose of an MPA is to protect and ultimately increase the numbers of target species in that area. But what will be the impact of increased numbers of top level predators within these sites and the surrounding region?

In other areas it has been shown that the removal of top level elasmobranchs has severe impacts on lower trophic levels as the numbers of mid level predators increases which can in turn decimate numbers of low trophic level species which in at least one case has directly resulted in the closure of a commercial fishery due to severe depletion of the focal species through over predation. This demonstrates the complexity of predator levels within ecosystems and how changes at one levels can filter through to all species within that ecosystem.

Due to this, it is reasonable to assume that increased numbers of apex predators, resulting from the protection offered by an MPA, will also have a pronounced impact on the local ecosystem which would have knock on effects throughout the local and, in a species with high migration potential, the wider area.

In MPAs that are designed to protect elasmobranchs, this will (or hopefully will if the MPA is doing its job) increase the number of predators in the area. This would have an immediate impact on other predatory species abundance as they are subjected to increased predation and experience increased resource competition. This could, however, results in a more natural state ecosystem with good balance between different trophic levels of the ecosystem after an initial imbalance of different level predators. The main issue is that, we cannot predict the exact changes that the system will go through.

This highlights the importance of continued monitoring of MPAs, not just of the species of conservation interest, but also of other species within the area to assess what impacts they are having on the local ecosystem. MPAs have been carefully designated based on a solid base of research and knowledge from multi-stakeholder groups – a positive collaboration of people who have a genuine interest in the marine environment.

The designation of an MPA should not be seen as an end goal, but rather a first step in the conservation of the marine environment and those who have worked so hard to ensure that appropriate MPAs are designated should continue to work and enthuse others about the on-going monitoring.

Protection of any sort in the marine environment should be seen as a positive move forward yet on-going research in these areas is necessary to ensure they are doing what they are intended to and to monitor how they change our oceans.

James was the first Shark Project Officer for SSACN, his main research interests are the spatial ecology of elasmobranchs and Marine Protected Areas and is currently undertaking a project aimed at developing knowledge on the fisheries-relevant ecology of sharks and rays in the Tumbes and Piura regions of Peru.

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