the main stresses experienced by the ecosystem. Some of the questions that should be addressed through monitoring include the following: Does the MPA system meet its goals and why or why not? Are there unanticipated consequences? Are the size and location of reserves within the MPA optimal? Monitoring programs provide managers with crucial information for evaluating the current status of protected areas and the efficacy of conservation measures. For researchers, monitoring programs provide valuable data that are needed to identify trends in the health of living resources, trends that reveal fundamental features of how ecosystems function and help scientists distinguish between changes that are the result of human influences and those that are natural environmental fluctuations.
Four categories of information may be included in a monitoring program: (1) structure of marine communities (abundance, age structure, species diversity, and spatial distribution); (2) habitat maintenance or recovery; (3) indicators of water quality or environmental degradation (e.g., pollutants, nutrient levels, siltation); and (4) socioeconomic attributes and impacts. For each category it is important that monitoring programs survey sites representative of the MPA, include replicated and comparable sites with different levels of protection, and employ standardized sampling techniques.
There are two approaches to analyzing the impacts of marine reserves on living resources. In the first approach, changes within the reserve are evaluated temporally such that conditions are documented before the implementation of protections and then compared to conditions following implementation. A limitation of this approach is that environmental variation in the years before and after the establishment of the reserve may obscure trends resulting from protection. For instance, variable recruitment in a fishery due to a change in oceanic conditions may affect, either positively or negatively, the apparent recovery of a stock after closure of an area. In Kenyan reefs, a twofold increase in fish abundance was observed in surveys of both unprotected and protected sites (McClanahan, 1995); hence, the change was independent of the reserve.
In the second approach, changes in the marine reserve are evaluated spatially such that conditions inside the reserve are compared to conditions in a similar area outside. The limitation of this approach is that reserves often encompass unique habitats; hence, there are few situations in which comparison areas accurately represent the features found within the reserve. For example, in the Polunin and Roberts (1993) study of marine reserves in the Caribbean, differences between fished and unfished areas could have been due to differences in habitat. The site chosen for the reserve might have had higher overall fish abundances even before fishing was halted.