Artificial habitats and the restoration of degraded marine ecosystems and fisheries

Abstract

Artificial habitats in marine ecosys- tems are employed on a limited basis to restore degraded natural habitats and fisheries, and more extensively for a broader variety of purposes including biological conservation and enhance- ment as well as social and economic development. Included in the aims of human-made habitats classified as artificial reefs are: Aquaculture/ marine ranching; promotion of biodiversity; mit- igation of environmental damage; enhancement of recreational scuba diving; eco-tourism devel- opment; expansion of recreational fishing; arti- sanal and commercial fisheries production; protection of benthic habitats against illegal trawling; and research. Structures often are fab- ricated according to anticipated physical influ- ences or life history requirements of individual species. For example, many of the world’s largest reefs have been deployed as part of a national fisheries program in Japan, where large steel and concrete frameworks have been carefully de- signed to withstand strong ocean currents. In addition, the differing ecological needs of porgy and sea bass for shelter guided the design of the Box Reef in Korea as a device to enhance productivity of marine ranching. The effect of these and other structures on fisheries catch is positive. But caution must be exercised to avoid using reefs simply as fishing devices to heavily exploit species attracted to them. No worldwide database for artificial habitats exists. The chal- lenge to any ecological restoration effort is to define the condition or possibly even the historic baseline to which the system will be restored; in other words, to answer the question: ‘‘Restoration to what?’’ Examples of aquatic ecosystem resto- ration from Hong Kong (fisheries), the Pacific Ocean (kelp beds), Chesapeake Bay (oysters) and the Atlantic Ocean (coral reefs) are discussed. The degree to which these four situations con- sider or can approach a baseline is indicated and compared (e.g., four plants per 100 m2 are pro- posed in one project). Measurement of perfor- mance is a key factor in restoration planning. These situations also are considered for the ecosystem and fishery contexts in which they are conducted. All use ecological data as a basis for physical design of restoration structures. The use of experimental, pilot and modeling practices is indicated. A context for the young field of marine restoration is provided by reviewing major factors in ecosystem degradation, such as high stress on 70% of commercially valuable fishes world- wide. Examples of habitat disruption include an extensive hypoxic/anoxic zone in the Gulf of Mexico and nutrient and contaminant burdens in the North Sea. Principles of ecological restoration are summarized, from planning through to eval- uation. Alternate approaches to facilitate ecolog- ical recovery include land-use and ecosystem management and determining levels of human population, consumption and pollution.