(Ahead of World Oceans Day this Saturday, June 8, Cool Green Science is running posts this week looking at the science and issues of marine restoration. Here’s more information on Restoration Week and what the Conservancy is doing to restore marine habitats such as coral reefs, eelgrass, shellfish, and mangroves.)
James Byrne is marine science program manager for The Nature Conservancy’s South Florida and Caribbean programs. To get a clearer picture of the state of coral reef restoration science, I asked him to respond to two questions — what science do we need to accelerate the impact of coral restoration, and what science do we already have that needs to be applied more widely. –Bob Lalasz
What are the critical science gaps for coral restoration? What don’t we know that, if we knew it, could really make a difference for people and nature?
Coral restoration and ecological function: The interaction between coral restoration and ecological function is a critical gap for exploration. Right now, The Nature Conservancy and our restoration partners are looking at the ecological function of a particular marine system and asking at what scale might coral restoration start to alter and improving that function — such as enhancing fisheries.
To this end, we’re testing (in different sites in the Caribbean) how we put out individual corals, with different spacings. This fall, we’ll actually be trying to re-create a reef — what we call “thicket.” A thicket is when individual colonies of the type of corals that we’re working with — the staghorn coral — grow in next to each other and form a really dense area. Studies have shown those thickets actually increase the amount of fish that come into them. Thickets are basically exponentially more efficient as habitat for fish.
So how can we jumpstart this kind of growth through restoration? Can we actually do out-planting that’s designed to create a thicket immediately, instead of putting individual colonies out there and waiting for them to grow up and into these thickets?
Our test is going to be to help plan a 4-meter-by-4-meter area with hundreds of corals and just completely cover the whole area with larger colonies, instead of the smaller individual ones that we normally would out-plant. To quantify function, we’ll be looking at the amount of fish and how quickly they colonize this new design, and then compare that to the amount of fish we’ve found in the existing reef area as well as in our normal out-planting design. We’re looking at a time horizon of a year or two before we can really nail the answer down.
Coral reproduction and genetic diversity: We’re just on the precipice of really understanding reproduction of coral species. We know how long they can live, how robust they are — but our restoration efforts could also help us understand how to enhance the genetic diversity of corals, by tracking all the different genotypes that we have in our coral restoration nurseries and maximizing that diversity when we out-plant.
We need to get a really good handle on the best way to maximize this diversity in order to increase the possibilities that these corals are going to be able to reproduce on their own when they grow up — because that’s one of the problems these species in particular have had. It’s called the Allee effect, where genetically different individuals are too far apart from each other in terms of outplanting distance to actually have successful sexual reproduction.
This is one of the key questions we’re looking at — how to bring these different genetic individuals closer together when we do the outplanting to maximize that diversity and maximize reproductive success. We’ve seen corals that have been out-planted spawn, so we know that they are plantable, but we have yet not documented successful reproductions.
We also need to figure out what the optimal restoration design is with regard to genetics. Whenever you put these corals out, there is competition between genetic types — so what’s that optimal design that gives you the benefits of having lots of these corals in close proximity, increasing fish populations as well as resistance to predators and disease? And where’s that exact line that, when you cross it, you have too many corals of different types next to each other trying to out-compete each other?
We’re probably about 5 years away from really being able to answer these design and diversity questions.
Coral restoration and wave attenuation: We’re also looking in Florida and in the Caribbean at how we can incorporate coral restoration into wave attenuation — looking at how reefs help break up wave energy coming into shore and if restoration can actually enhance that benefit, which is so critical for averting shoreline erosion and blunting storm surge.
What known science isn’t being applied that, if applied, would make a critical difference for these ecosystems?
10 percent coral cover: A paper in Nature Communications published this January (Perry et al 2013) makes the case that, for sites across the Caribbean, 10 percent live coral cover on a reef keeps it in balance — when you have more than that percentage coral cover, most reefs grow, but less than 10 percent means that reefs start eroding and declining.
This threshold of 10 percent live coral cover is a powerful idea that could really help us focus where we should do our restoration work and give us a target number to shoot for. “Live coral cover” is one of the most common indicators measured on reefs — so we have readily available survey data for much of the Caribbean. We could use this to say: “We know this reef has 8 percent live coral cover right now. How many corals do we need to plant out there on that reef to bump it up over that threshold?”
Learning from science on other ecosystems: There are great, long knowledge bases that exist already for forest restoration and restoration for other systems that could benefit coral restoration. For instance, while keeping track of 1,000-2,000 corals in pilot scale nurseries is pretty easy, the Conservancy and its partners now have close to 60,000 corals in nursery right now — and keeping track of all of them is a huge challenge. So we’re looking at how terrestrial nursery operations keep track of their inventory — the methodologies should be fairly transferable.
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