The other day I introduced our upcoming Aquarius mission, so I thought today I would take a few minutes to introduce the science behind it all. While the opportunity to live underwater and dive nine hours a day seems like reason enough to me, it can get pricey to pull off such an endeavor and “because it’s awesome” typically doesn’t get a project funded. In my previous post I mentioned I’d be studying herbivory and grazing across a depth gradient so I thought I would briefly discuss why it’s important to understand.
I won’t spend much time here arguing why reefs are important; suffice to say, if you don’t appreciate the intrinsic value of a reef, or that ~ 10% of the world’s population depends on them for food, you may appreciate the services they provide, such as tourism, fisheries, coastal protection and natural products, which could be worth as much as $375 billion per year. Despite their various values, coral reefs are in bad shape these days and their prognosis looks bleak. Warming oceans, overfishing, changes in seawater chemistry, and more severe tropical storms are just a few of the factors that have contributed to the loss of as much as a third of world’s coral reefs in just a decade. When these slow-growing corals die on shallow reefs, faster- growing algae quickly take their place. These algae smother and kill the remaining corals, while preventing new coral from settling. The job of preventing this transition from a coral- to algae-covered reef falls to coral reef herbivores such as urchins and parrotfishes, which eat algae and maintain the open space for swimming coral larvae to settle and grow. Unfortunately, due to human impacts the speed at which corals are now dying is so fast that herbivore populations, already decimated by overfishing and disease, are often unable to keep pace with the algae growth.
But there’s still hope for the future. In addition to traditional strategies, such as better management of shallow reefs, deep-water or “mesophotic” coral reefs that grow between 30 m and the depths that light can no longer penetrate, are gaining attention from researchers as naturally protected “source” populations for surrounding areas. Because the deep waters above these reefs can provide a natural buffer from threats such as artisanal fishing, storm damage, and the high-temperatures that trigger coral bleaching, these reefs are naturally protected from many of threats humans have created for shallower reefs. As a result, these deep reefs may act as a sort of self-sufficient Marine Protected Area, where species survive and their offspring eventually repopulate the surrounding shallower reefs. Due to the technical difficulties of working at depth, researchers are only recently beginning to understand the role of these deep coral reefs and the processes important to their continued health. While we know herbivory is important for shallower reefs, declining numbers of herbivores at depth, coupled with slower rates of algae growth, have created uncertainty in how important herbivory is to maintaining the health of deep-water coral reefs. And that’s where our science fits in. Starting on Sunday we will begin documenting herbivore communities, feeding patterns and algae growth to understand the role of herbivores in structuring these important systems.