Science in general, and ecological research in particular, has played an important role in linking the different phases of development of marine protected area (MPA) policy. Early efforts of scientists began by identifying the needs for and potential management roles of MPAs. By doing so, this work not only raised the visibility of MPAs as a potential management tool, but also helped to clarify the specific objectives and goals of MPAs. In turn, the goals and objectives identified for an MPA determine criteria for its design as well as approaches for evaluating its effectiveness in achieving its goals and objectives. Moreover, approaches to evaluating the effectiveness of a MPA are largely influenced by the design of a MPA. And of course evaluation is the underpinning of any kind of hope for adaptive management (i.e. modifying a MPA or network of MPAs in response to the relative effectiveness of different designs). Thus, need, objectives, design and evaluation are all inextricably linked to one another and one role of science has been to illustrate the importance of recognizing these links in consideration of each phase of this process.
Two general goals have been identified for MPAs. The primary goal of MPAs (and no-take marine reserves in particular) is to contribute to the protection and sustainability of biodiversity. A secondary goal, closely related to the conservation goal, is to protect fished species and their habitat, and contribute to the sustainability and perhaps even augmentation of fisheries. Each of these goals considers populations, communities and ecosystems. Examples of how scientists have considered the potential role of MPAs in protecting or enhancing natural systems at each of these levels of ecological organization follow.  |
| Mark Carr |
| Concern for the fate of the black-spotted grouper led in large part to the establishment of a marine protected area at the Kermadec Islands in New Zealand. |
One role that scientists have played is in identifying rare or threatened species and fisheries whose concern for protection resulted in the implementation of MPAs. For example, studies of the black-spotted grouper in New Zealand indicated that this species was particularly vulnerable to over-exploitation. Concern for this species led in large part to a MPA at the Kermadec Islands, the largest marine protected area in New Zealand waters. Persistence of the populations of this species within the MPA suggests that, from a conservation perspective, the MPA seems to have been successful. Science has also played an important role in demonstrating how important species diversity is in maintaining the structure (composition and relative abundance of species) and function (ecological interactions) of an ecosystem. This has highlighted the value of protecting and preserving biodiversity and maintaining the integrity of ecological interactions within a community. When particular species, especially predators high in a food web, are removed, unforeseen effects can cascade throughout the ecosystem.
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| Mark Carr |
| The sea urchin plays an important role in reef habitats in coastal areas of New Zealand and California. |
One example includes the New Zealand snapper, which is an important predator on and limits the number of a purple sea urchin. If the abundance of the sea urchin is not limited, they overgraze subtidal rocky reefs, removing most of the macroalgae (i.e. seaweeds) off the rocky reef. This macroalgae supports a great number of species, including other fishes that use the macroalgae for food and shelter. Indeed, when MPAs in New Zealand were established and the New Zealand snapper increased in abundance within the MPA, the reef community shifted from rocky barrens void of kelp, to a kelp-dominated community. Similar examples can be seen along the coast of California. Along the coastline of central California, sea otters graze heavily on sea urchins and limit their numbers. Otherwise, high densities of sea urchins can overgraze kelp forests and create barrens similar to that described above for the New Zealand example. South of Point Conception, throughout southern California, the sea otter is absent but spiny lobster and a large wrasse called the sheephead both feed on and limit the abundance of sea urchins. Both the fish and lobster are heavily fished throughout the coast of southern California. All three of these species play an important role in determining the condition of the reef habitat. In their presence, these shallow reefs tend to be dominated by lush stands of kelp, which harbor large populations of reef fish and enhance recruitment of some species to those reefs.
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| Mark Carr |
| Another contribution scientists have made is in identifying the value of protecting fish so that they grow large and reproduce. In the early 1990s scientists compared the fecundity and egg production of a 60-centimeter red snapper with that of a 40-centimeter red snapper. Despite the fact that the older, larger fish is only one-third greater in length than the younger fish, this increase in length translates into a twelve-fold increase in biomass. Moreover, the larger fish produces the same number of eggs as 212 of the 40-centimeter fish. This difference emphasizes how the relationship between fecundity (the number of eggs produced by a female) and fish size increases disproportionately as older fish allocate more energy to reproduction while young fish allocate more energy to growth. This means that a larger average size of fish in a population can have profound effects on the reproductive potential of that population and its ability to renew depleted populations. |
Marine protected areas can also be used to resolve one of the most problematic issues we have in fisheries management--trying to distinguish changes in fish populations caused by natural changes in the environment from those created by fishing. Comparing the size and trajectories of populations within and outside MPAs can allow mangers to decouple these two causes of change in populations. In this and many other ways, MPAs should be considered as a management tool to supplement, rather than supplant, traditional fisheries management. It is now widely recognized that MPAs alone are insufficient tools to manage a fishery or conserve an ecosystem without additional management regulations outside the MPA. In particular, it is important to recognize that there are many other anthropogenic (i.e. human-caused) impacts besides fishing in coastal ecosystems. The capacity of a MPA to protect fished populations and their ecosystems is limited without simultaneous protection from pollution, other sources of habitat destruction, and other sources of fish mortality (e.g., mortality of fish larvae entrained in cooling waters of power plants).
Translating MPA objectives into design criteria
Defining the specific objectives of a MPA in turn defines the criteria that will be used in designing that MPA. There are several fundamental criteria regarding MPA design, especially with respect to the conservation of biodiversity.
How big should MPAs be? Most studies addressing this question suggest that MPAs should be large. One reason for this is because the few studies that have examined the relationship between area and species diversity indicate that, as on land, diversity increases with area. Thus, the larger the MPA, the greater the number of species protected. Another reason for a large MPA is that it protects a greater representation of the habitats that an individual uses during its lifetime. Fish often shift among habitat types as they grow because they require different resources (i.e. different kinds of food and habitats for reproduction). If these habitats are not near or within a MPA, fish may not encounter the MPA or must leave the MPA as their resource and habitat needs change. Large MPAs are also critical for species whose larvae disperse only short distances. The bigger the MPA, the more likely larval dispersal will be contained within the MPA allowing these protected populations to be self-replenishing. Recent studies of larval dispersal distances suggest that MPAs on the order of 5 to10 kilometers would encompass the dispersal distances for many species whose larvae disperse relatively short distances.
How many MPAs should there be? There are several reasons why the answer to this question is "many". One reason is because it is unlikely that all representative habitats (and associated species) in a region will be included within any one MPA. Thus, for adequate habitat and biogeographic representation, many MPAs will be necessary. In addition, because most marine species produce offspring that are potentially dispersed great distances (10-100s of km) by currents, few MPAs will be large enough for protected populations to be self-replenishing. Instead, protected populations are reliant on recruitment of young born elsewhere in distant populations. If these parental sources are not, in turn, protected, then replenishment of the protected populations within MPAs can be jeopardized. Networks of MPAs, whose larval production and dispersal not only replenish unprotected populations outside MPAs but also nearby protected populations, are necessary to assure that parental populations will exist to replenish protected populations. Another reason for allocating MPA area across a network of many smaller, broadly distributed MPAs is to broaden the range of populations (and fisheries) outside MPAs that will benefit from recruitment of larvae produced within MPAs. At the same time, this design also reduces the impact on local fisheries that would otherwise be excluded from large areas of fishing grounds.
Where do we locate MPAs? As indicated in preceding sections, they need to be located across representative habitats and biogeographic regions to assure that the diversity of habitats and taxa are protected. Special attention might also be given to areas thought to be diversity hotspots, and critical or rare habitats, or spawning grounds were one or more targeted species congregate. Because it is unclear how different coastal features (e.g., up-current and down-current sides of headlands, embayments) influence the export and import of larvae to protected populations, a mix of these features and oceanographic conditions (e.g., upwelling, currents) should be included across the network. Over time, as the relative effects of these features bare on the value of MPAs, the network could be adjusted to increase its regional effectiveness. Spacing, or the distance between adjacent MPAs, is important with respect to the ability of larvae to disperse from one MPA to the next. Several studies of the dispersal distances of coastal marine species indicate that distances on the order of 10's of kilometers are reasonable.
MPA objectives and design dictate their evaluation
Together, the objectives and design of a MPA determine the variables (and their predicted responses) used to evaluate whether a MPA is actually meeting its objectives. For example, if one purpose of a MPA is to protect the diversity of species in a region, multiple MPAs that include a variety of representative habitats (and species) would be necessary. Ascertaining whether these MPAs were protecting this regional diversity of species would require measuring species diversity protected within this network of MPAs and comparing the level and trajectory of that diversity with similar measures in areas outside MPAs. In addition to the stated objectives of a MPA, three design criteria that determine the design of an evaluation study are (1) the number of MPAs in a network, (2) the timing and duration of sampling, and (3) the spatial and temporal scale of the response variable (e.g., within vs. outside MPAs).
For evaluation, the worst-case scenario is when only one MPA has been established long before a sampling program for evaluation is initiated. In this case, differences between MPA and less-protected areas (LPA) are confounded by all other possible differences between two sites and differences cannot be unequivocally attributed to protection. It will never be clear whether observed differences (MPA versus LPA) also existed before MPA establishment.
If only one MPA is to be evaluated and sampling can be initiated at the proposed MPA site and an independent LPA control site prior to MPA establishment, a Before-After-Control-Impact-Paired (BACIP) sampling design can be used to ascertain the effectiveness of that MPA. LPA control sites at varying distances from the MPA (spatial gradient approach) may be incorporated into this design to examine the spatial scale of MPA effects. If evaluation sampling can be initiated near the time of MPA establishment, trends in the difference between MPA and LPA can be compared to determine if the sites are changing in predicted ways (i.e. increasing density and mean size of individuals within MPAs relative to LPAs).
If multiple MPAs and LPAs can be sampled simultaneously, then broader inferences regarding MPA effectiveness can be made; general MPA effects can be described rather than an effect at a specific MPA. Moreover, MPAs that differ with respect to environmental features, design and management criteria can then be evaluated relative to one another. Such an approach is critical to the adaptive management of MPAs, where future MPAs are designed based on lessons learned from comparisons among reserves.
Implicit in all of these sampling designs is sampling (i.e. monitoring) over time. Because different responses are likely to be manifested at different spatial and temporal scales, understanding the probable scale of a response identifies the appropriate spatial and temporal scale for evaluation sampling.
A piece of 1999 legislation in the state of California, the Marine Life Management Act and the Marine Life Protection Act, propose the development of a system of MPAs for both conservation and fisheries management and their evaluation. Sampling programs for evaluating the effectiveness of existing and proposed MPAs in California consider all of the above-mentioned designs as well as identifying appropriate response variables. As mentioned above, our ability to evaluate the effectiveness of MPAs will depend on (1) our understanding of the scales and rates of those ecological processes (e.g., population growth, larval dispersal, recruitment events) that determine MPA effectiveness and are targeted for evaluation, (2) the design (e.g., number, size, location) of the networks of MPAs proposed, (3) accurate information on the magnitude and distribution of fishing effort and how it responds to MPA establishment, and (4) the quality (i.e. timing, duration, extent) and design of the sampling program developed and conducted for evaluating how well MPAs achieve their proposed goals and objectives.
