Designing marine protected area networks in the Dover Strait

Heightening world-wide concern about the Earth’s marine ecosystems is directed towards the problems of habitat degradation, pollution and heavy exploitation of living resources. Whilst protection of biodiversity requires a suite of management strategies, the creation of reserves or restricted access areas is increasingly identified as one of the solutions to problems of intense pressure from exploitative uses. This research utilised a unique marine dataset to explore conservation planning methods and identify priority areas to protect early life stages of marine fish in the Dover Strait. These methods, mainly tested and utilised in terrestrial environments, have the potential to identify efficient and effective networks of marine protected areas (MPAs). The Dover Strait and adjacent waters contain spawning and nursery grounds important to species commercially fished in nearby waters. These habitats are vital for the survival of fish stocks and consequently the fishing industry and local communities. The study area was divided into 4 km2 selection units. Surveyed data of marine ichthyoplankton abundances and environmental variables were mapped. It was found that the ‘hotspot’ approach to identify MPA networks provided a wide range of protection to both ichthyoplankton distribution and abundance, and was consequently considered to be less efficient and reliable than ‘complimentarity’ methods tested using 10%, 20% and 50% conservation targets. Proportional area was found to be more effective than presence / absence data in identifying MPA networks to protect abundance. A ‘summed rarity’ complimentarity algorithm identified 9.7% to 9.9% of the 4 km2 selection units (in three surveys) required to protect 10% of ichthyoplankton distribution. 7.03% to 7.94% of the selection units were required to protect 10% of ichthyoplankton abundance. Two algorithms using ‘irreplaceability’ were found to identify similar networks for proportional abundance targets with similar efficiencies to those identified by the ‘summed rarity' algorithm. A ‘site irreplaceability’ algorithm identified 7.03% to 7.73% of the selection units required to protect 10% of ichthyoplankton abundance and a ‘summed irreplaceability’ algorithm identified 7.03% to 7.62% of the units required for the same target. Several surrogates for ichthyoplankton diversity were tested using three proportional conservation targets and found to protect 36% to 87% of ichthyoplankton elements to the required target. The protection provided by each surrogate varied between ichthyoplankton elements and between sampling surveys. Using a 10% conservation target, ‘seascapes’ protected 44.5% to 67% of the ichthyoplankton elements to the target, ‘commercial species’ protected 81% to 86%, ‘higher taxa’ protected 36% to 75% and ‘assemblages’ protected 42% to 64% of the ichthyoplankton elements to the 10% target. It was found that incorporating measures to force the selection of clustered networks using ‘summed rarity’ produced MPA networks that were well connected. This technique may provide an opportunity to increase persistence of populations with little loss in efficiency. Increased publicity and awareness of softwares to enable the use of these techniques and incorporation of socio-political, economic and biological factors, is necessary to facilitate the wider knowledge, acceptance and use of the approaches advocated in this research, in both marine and terrestrial environments.