Limiting abuse: marine protected areas, a limited solution

Designation of marine protected areas (MPAs) is increasing as humans seek t o combat overexploitation of marine resources and preserve the integrity of the ocean's unique biodiversity. Ar present there are over 1300 MPAs. The primary legal responsibility for the designation of MPAs falls to individua l countries, but protection of the marine environment at large scales is al so critical because ocean circulation does not honor legal boundaries and o ften exceeds the influence of any one nation or group of nations. There are many reasons for establishing MPAs; the papers we surveyed principally ref erred to scientific, economic, cultural, and ethical factors. Two approache s predominated: fisheries management and habitat protection. Although the m ajor threat to terrestrial systems is habitat loss, the major threats to th e world's oceans are fisheries overexploitation, coastal development, and c hemical and biological pollution. MPAs may provide conservation of formerly exploited species as well as benefits to the fishery through leakage of 's urplus' adults (spillover) and larvae (larval replenishment) across reserve boundaries. Higher order effects, such as changes in species richness or c hanges in community structure and function, have only been superficially ex plored. Because many MPAs are along coastlines, within shipping lanes, and near human centers of activity, the chance of chemical and biological pollu tion is high. Use of MPAs to combat development and pollution is not approp riate, because MPAs do not have functional boundaries. The ocean is a livin g matrix carrying organisms as well as particles and therefore even relativ ely environmentally sensitive uses of coastal ecosystems can degrade ecosys tem structure and function via increasing service demands (e.g. nutrient an d toxics transformation) and visitation. Whether an MPA is effective is a f unction of the initial objectives, the level of enforcement, and its design . Single reserves need to be large and networked to accommodate bio-physica l patterns of larval dispersal and recruitment. Some authors have suggested that reserve size needs to be extremely large - 50-90% of total habitat - to hedge against the uncertainties of overexploitation. On a local scale, m arine protected areas can be effective conservation tools. On a global scal e, MPAs can only be effective if they are substantively representative of a ll biogeographic zones, single reserves are networked within biogeographic zones, and the total amount of area reserved per zone is 20% or greater. Th e current size and placement of protected areas falls far short of comprehe nsive or even adequate conservation objectives. (C) 1999 Elsevier Science B .V. All rights reserved.