Do Artificial Reefs Make Good Homes?
This unit focuses on a research project to determine if a structure designed as an artificial reef and placed into a cove near Whittier, Alaska, will provide habitat for fish. The research follows a public decision-making process which resulted in the placement of the structure as an attempt to mitigate, or reduce, the negative impacts of a development project that eliminated fish habitat in another location. This decision-making process occurs for many types of development activities along the shoreline or in wetlands and is an excellent "real world" example of how science, technology, and society intersect to serve the purpose of conservation. The unit has three investigations with the following intended outcomes.
Investigation 1. Understanding the ecology of high-latitude rocky reefs as the basis for attempting to mimic this ecology in the design of an artificial reef.
The biological community on a rocky reef is an excellent demonstration of the importance of structure as a feature of habitat. Rocky reefs, and hard bottoms in general, provide habitat for a greater diversity of marine life than soft bottoms. There are two main reasons for this increased diversity: 1) rocks provide complex structure in terms of the vertical dimension (lacking in a mud or sand flats) that provides the means for organisms to climb up on to reach higher in the water column, and 2) as the rocks are eroded by the action of water, cracks and holes appear which increase the availability of shelter from the full strength of currents and access by some predators. Different rock types weather in different ways and may provide habitat for different species. Large reefs like those formed as seamounts can alter the flow of currents around the structure and produce upwellings of nutrients.The biological community on the rocky reef includes the many marine organisms that evolved adaptations to attach themselves to the rocky surface and the mobile grazers and predators that feed on them. Encrusting organisms include sponges, hydroids, anemones, worms, bryozoans, and soft and hard corals, many of which are filter or suspension feeders on prey or detritus in the water column. Kelps, one of the most abundant and largest of the seaweeds with strong holdfasts for attachment to the rocky reef, provide additional three-dimensional structure to the community. They provide more attachment sites and shelter for other organisms, as well as food for grazers. Communities of the largest kelps are often referred to forests. Predators such as octopi and sharks concentrate around the reefs. A variety of fish are mobile predators who find food, shelter, and spawning sites on rocky reef habitats at some stage during their lives.
Rocky reef habitats are similar to rocky intertidal habitats but lack the stresses of exposure to air during the tidal cycle. Both types of habitat provide the substrate for a diverse benthic community that lives in or on the bottom of the ocean and pelagic organisms that live in the water column, but tides limit the residence time of pelagic organisms in the intertidal area. More information about food webs in rocky intertidal and subtidal habitats.
Investigation 2. Understanding the nature of the design process for a structure that will mimic both the structure and function of natural habitat and the scientific assessment of its success.
Designing a structure intended to replace or create new marine habitat involves both ecological considerations (will the structure have the same ecological function as a natural rocky reef?) and technological considerations. Placing artificial materials in the ocean involves trade-offs in terms of materials, costs, and potential positive and negative impacts of the materials on the ocean environment. You can provide your students guidance in the "Build Your Own Reef" activity by reviewing the design criteria for artificial reefs that have been developed after many different types of materials were placed or dumped in the Atlantic Ocean and Gulf of Mexico over many years. These include function, compatibility with the marine environment, durability and stability, and availability and cost. Additional guidance is provided in the form of a table that compares how wood, rock, concrete, plastic, tires, vehicles (cars, trucks, military vehicles), fiberglass boats met or failed to meet the criteria
Students will also have the opportunity to learn how scientists treated the placement of artificial reef structures as an experiment to answer the ecological question. The Whittier Artificial Reef project was designed as an experiment to monitor whether or not the area where the artificial structures were placed would provide habitat for the same number and type of fish as a nearby area of natural rocky reef. While this same experiment had shown that artificial reefs were successful in attracting fish in many other places in the world, the experiment had never been tried in cold Alaskan waters. A PowerPoint presentation made by the scientists for the project at the Alaska Marine Science Symposium in 2007 summarizes the scientific process and early results of the experiment.
Investigation 3. Understanding the nature of the decision-making process that led up to the placement of the structures and the broader conservation purpose of the research project.
The outcome of the science question in the experiment is of interest because the artificial reef was intended to be a means to mitigate, or reduce, the loss of fish habitat in another location where fill was placed to extend a gravel loading ramp out into a shallow area of a bay. If the result of the experiment is positive, this technology could provide a conservation tool to offset other losses of fish habitat from development of Alaskan shorelines.
The story about why artificial reefs or other structures may be placed along the shoreline or in the ocean involves a decision-making process focused on the need for an Army Corps of Engineers permit that involves stakeholders, or people who will affected by the decision, in a determination of the potential positive and negative trade-offs of doing so. If negative impacts are anticipated, but the decision to proceed is made, then mitigation is also required occur to offset negative impacts. The National Marine Fisheries Service (NMFS), a division of the National Oceanic and Atmospheric Administration (NOAA) participates in the process specifically to protect marine fish and their habitats.