National Oceanic and Atmospheric Administration/Department of Commerce

A view of Monterey Bay National Marine Sanctuary, a marine protected area off the shore of California.

Although there are varying definitions of marine protected areas--and the terms "marine reserves" and "marine protected areas" can sometimes be used interchangeably--let me provide a general definition for our purposes: any areas of the coastal zone or open ocean that confer some level of protection for the purpose of managing resources or protecting vulnerable or threatened habitats and species. There is special interest in "no-take marine reserves," in which all extractive activities are prohibited.

I'd like to provide a historical perspective of MPAs, because the issues that have emerged in the interest of establishing reserves are actually quite longstanding. As early as the fourteenth century there are references in which concerns about the ecosystem effects of harvesting on marine systems have been voiced and even implemented in legislation. In the fourteenth century there was a petition put before the Commons in Britain to ban a certain type of dredge thought to damage sensitive habitats. We would recognize the rationale for this ban today as one designed to preserve ecosystem structure and integrity in these kinds of systems. This shows that the issues we are dealing with today are nothing new.

Similarly, in the fifteenth century trawling was banned in Flanders--again with a very clear ecological rationale for banning this particular type of fishing gear. Different types of trawling were banned again throughout the sixteenth and seventeenth centuries in different areas. Trawling was made a capital offense in France. This makes it quite clear that there was a general and longstanding concern in these areas on the potential impacts of fishing gear on marine ecosystems.

f general concern was a view expressed by a number of important and influential scientists, such as Thomas Huxley. This view stated that the resources of the sea were essentially inexhaustible and in fact virtually nothing that humans could do would really severely impact these systems. Huxley, to be fair, did qualify his remarks to the harvesting methods of his day and was quite clear to say that he was dealing specifically with coastal fisheries. But nonetheless, this sort of view really set the stage for a general perspective, based largely on scientific interest and input that in fact the seas were inexhaustible so there was no serious reason for concern. So there is a tension between general concerns that have been raised about impacts of fishing, either on ecosystems or on the fish populations themselves, and a more general view that Huxley and others presented.

There were also other scientists at this same time who disputed Huxley's conclusions--and in fact this dispute led to a decade-long experiment starting in 1885 in Scotland, where open and closed areas were implemented in the Firth of Forth in St. Andrews Bay with the idea of testing the impacts of fishing on these systems. The final conclusion of that study was that there were serious impacts of harvesting on these systems and that protection was required.

As mentioned, preserving vulnerable areas for fisheries purposes by closing them to fishing has taken place since the Middle Ages. The general idea has been to preserve certain areas that are thought to be vulnerable, particularly either the spawning grounds or nursery areas. The role of dispersal at the larval stage of marine species and through their various migrations at various stages of maturity are key issues in terms of conservation and fisheries management measures. But these aspects are still the greatest source of uncertainty, particularly the egg and larval dispersal component. However, there have been a lot of important advances and tools, ranging from genetics to geochemistry to marking studies that can help us resolve these kinds of issues.

The no-take marine reserve or the marine protected area concept in general is really one that builds on and extends traditional closure strategies in marine fisheries management. But it has a much broader set of objectives and provides more inclusive protection for populations, communities and habitats. Closed areas designed for fishery management purposes traditionally had a much more limited set of objectives, so one of the important things that has come about with current discussions on the utility of marine reserves is this broader ecosystem point of view.

Potential benefits of marine reserves
What are some of the potential benefits of marine reserves? They can potentially increase the abundance of biomass within the reserve, increase the average size of animals and increase the reproductive output by having animals attain larger size. There's the potential to enhance yield in adjacent grounds. There is quite convincing evidence that within closed areas abundance and biomass have increased, as have average size, within the reserve boundaries. Enhanced yield has been demonstrated in some systems. There's a lot of important work going on that looks at the impacts on reproductive output. It is an area that we need to look at much more intensively as we evaluate the utility of marine reserves to meet fishery management goals.

the potential for increases in species diversity and increases in community stability. By lessening the impact on trophic structures, potentially we could increase the overall community stability, enhance habitat quality, create or enhance non-extractive uses such as ecotourism, reduce user conflicts and create areas with intrinsic value and provide baseline systems for scientific study. These are quite important potential benefits of reserves. When we're evaluating reserves, we really need to keep in mind the whole suite of fishery-related potential benefits and the more general benefits that would come about with the use of reserves beyond immediate fishery management goals.

Studying reserves
What we're generally interested in understanding in these reserves is how they might operate overall in terms of both the population dynamics of the systems under study and also of the impacts on the fishery.

If we're harvesting a sink population (a net importer of migrants or dispersal products), one of the important features of a reserve is that it can confer a tremendous amount of resilience to the overall system. If there is a larval subsidy being supplied to the sink area, the upper curve would show where there's a larval subsidy from a closed to an open area. Notice that as the fishing mortality increases, some level of yield can still be maintained because the subsidies coming in from the closed areas are not impacted and the lower curve would show what would happen if there were no such reserve in an area.

Conversely, if we were unfortunate enough to be harvesting the source population rather than the sink population then in fact we're reducing the overall resilience of the system. The upper curve would show the baseline case where an area is not in fact providing any subsidy to an adjacent area. The lower curve would show what happens when we harvest an area that is supplying some of its reproductive output into an adjacent area. The overall resilience in yield is much lower. The population would collapse at a lower level of fishing intensity. Therefore, it's quite important that we understand the source-sink dynamics in such a system and be sure we are thinking about harvesting sink rather than source areas.