Habitat restoration aiming at returning an ecosystem to a pre-impact state of structure and function requires that you know what this state was. Often in deeper marine environments you don't. The technology to get in situ information about the deep-sea ecosystems is recently gained. Before that, the development of the bottom-trawling fisheries to heavier gear able to plow their way through the delicate reef habitats had already destroyed much of the habitats we now can go down and look at by means of unmanned (ROVs) or manned submersibles equipped with strong headlights and video cameras. We will often have to make a "best guess" of the pre-impact state of the system we want to restore.
An ecosystem is built by both abiotic and biotic derived structures, and in cold-water coral reefs the main structure is built by one stony coral species - Lophelia pertusa is the main ecosystem engineer of its habitat. There are other stony corals, but they play in another league than Lophelia. Replanting Lophelia is therefore the number one priority, however, it's a slow growing species and you need an abiotic foundation as a substitute for the dead matrix of coral skeleton that usually is present in a reef, i.e. an artificial reef.
What then is the function of a CWC reef? The coral skeleton matrix act as a hydrodynamic trap of nutritious particles and pelagic larvae, thus concentrating nutrients and settling of marine benthos within the reef. It also provide shelter and foraging grounds to animals higher up in the trophic food web. This is the ecosystem function you want to restore.
The key factors you need to identify are:
- the pre-impact state (from available data and/or a reference site)
- the proper restoration endpoint (guided by the above)
- the local restoration potential or constraints (limited larval pool?)
- the functional groups (in this case Lophelia is the key functional species, but there can be more less obvious ones)
- the key linkages (e.g. food web interactions, symbiotic relationships)
- the essential matters to be cycled within the system
- the natural or human induced disturbance regimes that the restored habitat will need to buffer against
- and, finally, what are the key factors that you need to include in the analysis to assess the success?
This 'restoration ecologist's checklist' is derived from a paper written by Palmer et. al (1997), an excellent paper linking Community Ecological Theory with Restoration Ecology and the possibility of cross-fertilization between the two fields. This paper is my map and compass throughout this PhD project. The examples are from ecological restoration in terrestrial habitats, but the authors have managed to generalize so well that you can apply the thinking in any environment. In fact, you could read it solely to understand the magic of generalization. That is a trick that could get your papers into the highest ranked international journals. After reading it the first time I couldn't really tell whether it had a marine or terrestrial focus. It was applicable to my work, so I assumed that it had some marine examples. Reading it again, however, I realized they're talking beetles and grassland. The closest they get to aquatic environments are examples from wetlands and river regulation. They were nowhere near coral reef restoration.