On the Hunt for Deep-sea Corals
Editors Note: UMaine marine scientist Rhian Waller is currently on an National Geographic and National Science Foundation funded expedition in the fjords around Chile, where she is studying the reproductive ecology of deep-sea corals and links to climate change and fishing pressures. National Geographic is following along with the expedition on its News Watch website. Waller received the grants in order to establish three long-term sites where she will monitor and take coral samples. UMaine diving safety officer Chris Rigaud is accompanying her on the trip.
Scientists have long known that corals are found far beyond shallow, tropical waters. Since the 1800s, researchers on multiyear voyages have collected coral samples from colonies found at much deeper, darker, colder spots in the ocean. In the past two decades, coral has surfaced on trawlers working in more remote fishing grounds in the hunt for an increasingly elusive catch. And that’s when the importance of these invertebrate animals became apparent, and when Rhian Waller began working on her Ph.D. about the reproduction and development of the seldom-seen creatures. Waller’s research now focuses on how environmental factors such as climate change, fishing and oil exploration affect deep-sea coral reproduction, and what effect that altered life cycle could have on the rest of the marine ecosystem. “We’re now beginning to realize that these reefs in the deep sea are very similar to the reefs in shallow water and can be very important to certain fisheries species,” says Waller, a University of Maine assistant research professor in the School of Marine Sciences. “These corals have thousands of associated species that live on and around them so we’re starting to realize they’re important deep-sea ecosystems builders, just like corals in shallow waters.” Earlier this year, Waller received a more than $78,000 RAPID Grant from the National Science Foundation and a $30,000 National Geographic Society award to establish three long-term monitoring sites in Chile where she will sample corals for reproductive ecology studies. Waller also received another $9,000 from UMaine to explore Maine’s coastal areas for deepwater emergent coral habitat sites, and $48,000 from the National Oceanic and Atmospheric Administration (NOAA) to continue a long-time series in Alaska of Red Tree corals. Waller hopes to show through each project the importance of deep-sea coral systems to the rest of the ocean ecosystem. “If we continue to damage these coral habitats, we’re going to damage the fish and invertebrate populations that live around them,” Waller says. “Even though they’re out of sight, out of mind, and many people don’t know they’re there, we have to start to explore and research why these ecosystems are important.”
Waller grew up in England and Riyadh, Saudi Arabia, where she spent weekends snorkeling off coral reefs in the Red Sea or the Arabian Gulf while her parents scuba dived. That experience sparked her fascination with the beautiful, mysterious animals. Corals are marine invertebrates, in the same phylum as jellyfish and anemones, but corals can form a calcium carbonate skeleton. Corals are made up of individual polyps – some just single polyps with skeletons, whereas larger reef-building corals and gorgonian sea fans can be many thousands of genetically identical polyps all living joined together. There are two types of corals. Tropical corals have photosynthetic algae known as zooxanthellae, which require sunlight and warm water to survive, and so found at less than 100 meters depth. Waller studies the other kind of corals, which do not have zooxanthellae and so do not require photosynthesis and survive instead solely on food in the water column. Although they can live in the relatively shallow, cold waters of Alaska, northern Canada, southern Chile and the Antarctic — areas where corals that have zooxanthellae can’t survive because of the temperatures — these corals are most often found in the deep sea — usually more than 500 meters deep, roughly the end of a continental shelf, and below the depths scuba divers can go. Such deep-sea corals have been found to be thousands of years old. The current record holder is a 4,000-year-old coral found off the coast of Hawaii. The depths at which deep-sea corals grow is also one of the reasons so little is known about them. Researchers in the small community of deep-sea coral science typically retrieve and preserve specimens for each other, and fishermen and conservation agencies occasionally hand over samples they find. Most corals are retrieved via manned submersibles, remotely operated underwater robots or human dives, if the depth is shallow enough.
In Southern Chile and Southern Alaska, for example, which both have glacial fjord ecosystems that are too cold for photosynthesis and little competition for food among corals, some corals typically found at deep-sea depths are living much shallower. In Alaska, Waller is working on a species known as the Red Tree coral that is typically found at 500 meters, but recently has been found at less than 10 meters, which means she can scuba dive for samples year-round, rather than using a submersible. Scientists haven’t yet discovered why the deep-sea corals are being found at shallow depths, but they believe it is because the water is colder and darker than tropical waters and competition from photosynthesizing species (such as fast-growing algae) is less, and so it is more like the deep-sea environment than a regular shallow water ecosystem. The deepest dive for corals Waller has made in a submersible was to a depth of 3,600 meters on the New England Seamount chain in 2005. With more research on deep-sea corals, scientists are discovering just how much their presence affects the world around them. One example, Waller says, is deep-sea corals have been found harboring eggs of the Dumbo octopus, a small creature that lives in deep waters about which little is known. As yet, deep-sea corals are the only place those eggs have ever been found. Scientists wonder what else might live or rely on the corals, and what animal next in the food chain might in turn rely on those animals – and how the food chain would be affected if the corals began to disappear. “You can imagine all it takes is one trawler or one piece of garbage to land on the coral and suffocate it, and that’s 4,000 years of growth and 4,000 years before that colony will grow back to support 1,000 different invertebrates which in turn support maybe tens of different species of fish,” Waller says. “Our understanding of deep-sea biology is still very much in its infancy, so there’s a lot we don’t know. But we do know from other systems that you can upset the whole ecosystem by taking just one bottom piece away.”
When Waller began her Ph.D. research at Southampton Oceanography Centre in England, there were no published studies on reproduction in deep-sea corals, even though there are more than 3,000 species living at deep spots in the ocean, compared to around 2,000 species of shallow-water corals. Waller set out to establish some basics about deep-sea coral reproduction, such as determining whether the corals are males, females or hermaphrodites; if they reproduce via broadcast, as the shallow-water corals do; if they brood larvae; have multiple offspring; and what time of year they reproduce. She has also looked at larval processes and has managed to get different corals to spawn in order to closely examine their larvae. For her Ph.D. research, she compared deep-sea regions that faced fisheries damage with corals constantly being turned over and broken, to pristine areas, and found that corals in the areas that were damaged were reproducing in much lower numbers or not at all. Answering questions about how and why this happens at different depths in the ocean is at the crux of Waller’s research. “If there is any kind of stress, reproduction can cease,” she says. “Looking at how these stressors are affecting reproduction, whether populations are sustainable, how reproduction changes in the same species that are living at different depths and how all those things are being changed both by human activity and the general environment, is really where my interest lies.” Waller’s work in Alaska involves reproduction processes of the Red Tree coral in the Alaskan fjords, where the corals form essential habitat in this region for rockfish and crustacean species. In 2010, Waller and NOAA collaborators established a site of 40 corals, which have since been sampled every three months for reproductive analysis. This site has provided the best time-series reproductive data on any deep-water coral species to date. Waller will return in January 2013 to investigate fertilization and larval dynamics in this species and continue the reproductive timeline to assess when and how much this species reproduces, with the goal of providing essential management information.
Researchers are starting to realize that climate change may affect deep-sea corals more than previously believed — perhaps more than it does shallow tropical corals. Although there is no doubt that tropical corals are heat-stressed, Waller says, they can live within temperature swings of up to 15 degrees. But for corals in the deep sea, where the water is much colder, has stable temperatures year-round and is relatively acidic compared to surface waters, a temperature swing of up to 2 degrees in a year could make for a complete change. She has seen deep-sea corals brought up from the Antarctic region that, due to deterioration in the ocean, disintegrate when handled. Corals in Chile’s northern Patagonian fjords are facing pressures from such human activity such as intense salmon farming and logging, which is why there is an urgent need to document and understand the coral systems in this region. Measurements of reproduction will provide information to understand recruitment, recolonization, population connectivity and recovery from damage in this area. In Chile, Waller will launch her research from the Huinay Scientific Field Station and work in the waters of the northern Patagonian fjords, which are influenced by strong tides, large volumes of freshwater runoff, upwelling of deep ocean waters and steep climatic gradients from north to south. Species found in these fjords can more usually be found at depth of up to 3,000 meters, yet in these locations they can now be collected by scuba at just 10 meters. This presents researchers such as Waller with a unique opportunity to form baseline data on ecological and population processes — a sort of window into a deep-sea ecosystem.
Waller’s goals in Maine are to discover, characterize and map areas of gorgonian corals, also known as sea fans or sea whips, along the coast. She intends to register the new locations and depth ranges in the U.S. Geological Survey Cold Water Coral Geographic Database and also hopes to discover a scuba-accessible site from which to launch future studies of deep-sea, cold-water coral ecology and physiology. Her hope is to find spots in the Gulf of Maine – ideally within an easy boat road from UMaine’s Darling Marine Center in Walpole, where she is based – that would give her access. To that end, she has been working with Chris Rigaud, the Darling Center’s diving safety officer, to train for deeper dives in Gulf of Maine waters. Although Waller has seen photographic evidence of Red Tree corals pulled from the area around Monhegan Island, there have been sporadic reports in the last 100 years of deep-sea corals coming up in shallower gulf waters. “Just as in Alaska, we have areas where it is cold all year round, and we have deepwater coming up on the shelf,” she says. “But the oceanographic conditions here are very different from Alaska, so although we might get species that usually live within 1,000 meters or so, they’re probably not going to come up within meters of the surface, like we have seen in other high-latitude areas. We might be able to find them within 50-100 meters, which is within technical diving limits.” More than 60 species of cold-water coral are known in the Gulf of Maine, but little is understood of their biogeography and diversity. However, anecdotal and other information gathered from fishermen indicate the distribution of coral communities may be wider than thought, particularly closer to shore. The same concerns about environmental impacts on deep-sea coral apply in the Gulf of Maine, with one exception. While there are no offshore oil exploration platforms in the gulf, there could soon be offshore wind turbines anchored to the ocean floor there. Anchoring devices could be a boon for deep-sea corals, Waller says, in the same way that disused oil rigs in northern Scotland provide habitat for corals. “I would predict a similar situation with offshore wind platforms, although they’re not going to be placed in rocky areas where we tend to find deep-sea corals,” Waller says. “There is the potential they could form great hard substrate habitat, allowing coral larvae to grow and maybe thrive.”