Hence, to test conclusively whether reserves have a particular ecological effect relative to their original goals, it is necessary to establish monitoring regimes at multiple localities that include surveys before and after reserve establishment. Ideally, species survey methods should be rigorous enough to detect a 10-25% change in biomass, density, or species numbers. In many cases, however, such quantitative rigor is difficult to achieve. For example, in surveys of economically important snails on Kenyan reefs, McClanahan (1995) found that the population increases observed in reserves for seven of nine species of snail were statistically nonsignificant because of the overall low density of snails and high variation among sites.
Monitoring species diversity requires knowledge of the systematics of marine species. Taxonomic expertise is necessary to identify the early life stages of various species to assess changes in recruitment success due to reserves. Although the taxonomy of most fish is well known, there are currently few scientists capable of identifying a large number of invertebrate and algal taxa in marine ecosystems. There are well-illustrated atlases for the larval forms of many temperate fish. However, similar resources are not available for the identification of fish larvae in other regions, specifically at low latitudes, or for the identification of fish eggs. Molecular tools to augment and perhaps automate the identification of species are being developed, but even these depend on a firm taxonomic foundation and require input from specialists. A matter of concern in this regard is the decline in the number of trained taxonomists, due to decreased institutional emphasis on systematics, as noted in a prior report (NRC, 1995).
Many reserves in the United States and around the world have focused on enhancing or preserving commercially valuable species. Consequently, these populations have been the major or exclusive focus of monitoring (e.g., Davis, 1977; Russ and Alcala, 1989; Smith and Berkes, 1991; Keough et al. 1993; Attwood et al., 1997; Jennings and Polunin, 1997). In reserves designed to enhance biodiversity or stabilize populations of exploited or nonexploited species, monitoring programs have generally emphasized the distribution and abundance of species throughout a wide taxonomic range (e.g., Castilla and Durán, 1985; McClanahan, 1989; Cole et al., 1990; Castilla and Varas, 1998).
Monitoring trophic status (e.g., mean trophic level) of aggregated macrofaunal biomass in the community can provide information on the state of community maturity and potential stability. Such ecosystem-wide monitoring has been instrumental in deciphering the dynamics of marine community interactions, with the result that critical linkages among trophic levels have been revealed.