Debate on corals is broad, but too shallow

Corals have a future – we need to go deeper to see it

 In his July 13, 2012 New York Times OpEd "A World Without Coral Reefs", Roger Bradbury asserts that the world's coral reefs are unsalvageable, the delicate ecosystems irreversibly devastated by overfishing, pollution, and ocean acidification. Following its publication, numerous blogs, opinion pieces, and reports from scientists and conservationists alike debated the accuracy and implications of Mr. Bradbury's claims. We at the Marine Conservation Institute noticed, however, that deep sea coral habitats have been conspicuously absent from the discussion. In an attempt to rectify this oversight, our resident deep sea coral expert Sandra Brooke wrote the following response to Mr. Bradbury's article. 

By Sandra Brooke

The Marine Conservation Institute and our coral experts have followed the ongoing discussion on corals in the pages and the DotEarth blog of the New York Times with great interest. The alarming opinion piece by Bradbury (“A World Without Coral Reefs”) and backers like Randy Olson has been met with more reserved opinions by other respected marine conservation leaders, like Carl Safina and John Bruno. But this discussion on corals is missing a vital perspective – that of deep sea coral habitats, not just the more visible shallow reefs that are predominantly found in the tropics.

  

Sea pens, such as these Ptilosarcus gurneyi found in Alaska, grow in
soft sediment, as opposed to the rocky hard-bottom preferred by
most deep-water corals. Photo Credit: P. Malecha, NOAA Fisheries.

 The science on deep sea corals lags far behind shallow tropical corals. But deep sea corals are vital both as habitats and spawning grounds for some fisheries species, and they are globally distributed from the Arctic to the Southern oceans. Some species of deep sea stony corals form complex structures that provide similar – although not identical – ecosystem services as shallow tropical reefs: habitat for abundant and diverse associated fauna, commercial fish breeding grounds, and potential medicines for human use. And while human impacts on deep sea corals are different from shallow corals, they can be equally devastating – especially in the form of destructive fishing practices such as bottom trawling.

Yellow Enallopsammia rostrata stony coral and pink
Candidella imbricata. Photo Credit: "Mountains in the Sea"
scientific party, NOAA, and the Institute for Exploration.

Deep sea corals also show very different tolerance to ocean pH levels and lower aragonite satuarate states than shallow corals. Because CO₂ dissolves more easily in cold water than warm, deep sea corals are already living in lower saturation states than warm corals. Increased acidification may harm the corals’ ability to form the structures that maintain not only their own survival, but that of the marine life depending on them. Calcification takes energy, so increased biological energy needed to form and maintain deep sea coral structures may diminish the corals’ other biological processes, including reproduction. This could lead to deep sea corals slowly diminishing in complexity, scale, and in the biological diversity they support as habitats. We still don’t know the lethal and sublethal tolerances of deep sea stony corals to changing ocean pH levels. Scientists at the Marine Conservation Institute are trying to better forecast the impacts of ocean acidification over time for a variety of coral habitats – particularly the reef-building scleractinians, Lophelia pertusa, and Solenosmilia variabilis – to identify which areas are most resilient to changing ocean conditions, representing the best prospects for conservation. We are also examining OA impacts on soft corals in waters surrounding the Aleutian Islands, one of the most biodiverse deep sea coral sites anywhere in the world.

Christmas Tree Coral (Antipathes dendrochristos) off of
Southern California. Photo Credit: Mark Amend, NMFS SWFSC
Fisheries Ecology Division, NOAA

 While the global picture of corals is gloomy in both the shallow and deep seas, the overall evidence is strong that marine protected areas protect not only corals, but the associated biological diversity that they support – fishes, invertebrates, marine mammals, seabirds, and more. In light of the evidence of coral declines and global overfishing, it is incumbent on policymakers and marine advocates to identify and protect the diverse marine ecosystems that are still biologically productive – by creating large, well-funded and properly-managed MPAs as safety nets for the global ocean ecosystem.