Exploring Sur Ridge’s coral gardens
One of the most striking features of Sur Ridge is the abundance of corals and sponges on its rocky slopes. Most of the deep seafloor is an endless expanse of mud inhabited by animals living in, on, and just above the sediment. Corals and sponges need hard substrate for attachment, so seamounts, rocky ridges, and submarine canyons are hotspots for these sessile invertebrates. Moreover, these geologic features alter the currents that stream along the deep seafloor. The currents carry plankton and tiny particles of food called “marine snow” (a mix of dead plankton, mucus, poop, and other organic matter). Corals have tiny, tentacled polyps that snatch food from the surrounding seawater, while sponges feed by filtering particles of food from the water. Currents accelerate as they move over Sur Ridge. Faster currents mean a higher flux of food particles moving past hungry corals, sponges, and other animals.
During MBARI’s expeditions to Sur Ridge, we’ve enlisted a suite of different technologies to monitor the coral communities as part of our Deep-Sea Coral and Sponge Observatory (DiSCO) project. MBARI scientists, engineers, and marine operations crew have worked together to develop and deploy these cutting-edge tools to understand the oceanographic conditions, physical habitat, and predator-prey interactions that mold the community of life at Sur Ridge.
Joint expeditions between MBARI and the Monterey Bay National Marine Sanctuary have taken stock of the diversity of corals and sponges at Sur Ridge. We’ve found two dozen different corals here and nearly as many sponges. These come in a dazzling display of shapes and forms—stick-like red rope corals (Swiftia simplex), fanned branched tree corals (Parastenella sp.), funnel-shaped white trumpet sponges (Chonelasma sp.), and rugose stalked ruffled sponges (Farrea truncata). But several more remain unidentified and since the taxonomy of sponges remains in flux, there may be several new or undescribed species at Sur Ridge too.
The “gardens” thriving on the slopes of Sur Ridge offer refuge for countless creatures. The large corals and sponges create complex, three-dimensional structures that provide places for other animals to perch on, hide in, and climb up. A closer look reveals a community of life thriving on the colorful corals and sponges—a pair of arbiter snailfish (Careproctus kamikawai) sit nestled inside a sponge, a long-armed crab (Sternostylus perarmatus) climbs over a coral to nab food swimming overhead, and a basket star (Gorgonocephalus eucnemis) props itself up on a sponge and unfurls its finely branched arms to snag prey drifting with the currents.
The corals growing on Sur Ridge’s rocky ledges can reach over two meters (six feet) in height and grow as big as a king-size mattress. Deep-sea corals grow slowly, gaining mere centimeters in height each year. The corals at Sur Ridge are likely hundreds, if not thousands, of years old. We don’t know much about growth and longevity in sponges, but the massive sponges one to two meters (three to six feet) across may be just as old. The gardens of corals and sponges at Sur Ridge are like the old-growth forests on land.
While conditions at the surface change frequently, the deep sea has remained fairly stable—until now. Ancient deep-sea corals now face a changing ocean and an uncertain future.
Burning fossil fuels releases carbon dioxide and other heat-trapping gases into our atmosphere, causing our planet—and ocean—to warm. The excess carbon dioxide doesn’t just drive climate change, it’s altering the ocean’s chemistry. Ocean chemistry change (or ocean acidification) is turning the ocean more acidic. Deep-sea corals are especially vulnerable to changes in ocean chemistry. They require precise chemical conditions to lay down their skeletons, and as the ocean becomes more acidic, it may be harder for them to grow.
Fisheries also threaten deep-sea corals and sponges. Some types of fishing gear scour the seafloor, indiscriminately dragging along the seafloor and damaging delicate corals and sponges. Because these animals grow so slowly, it may take decades, if not longer, for these communities to recover. Learn more about how our seafood choices affect ocean health from our education and conservation partner, the Monterey Bay Aquarium.
Because deep-sea corals and sponges provide vital habitat for so many other animals at Sur Ridge, MBARI researchers are trying to understand their biology to see how resilient they are against environmental changes and how populations might be able to recover.
While protection remains the surest solution for safeguarding vulnerable coral and sponge communities, it might be insufficient in the face of a rising tide of threats. MBARI researchers embarked on a multi-year study to translocate deep-sea corals as a strategy for repopulating these species after disturbance.
Using MBARI’s ROVs, researchers collected samples from seven of the most common coral species at Sur Ridge—precious coral (Corallium sp.), shaggy bamboo coral (Isidella tentaculum), pink bamboo coral (Keratoisis sp.), black coral (Lillipathes sp.), bubblegum coral (Paragorgia arborea), deep-sea cauliflower coral (Sibogagorgia cauliflora), and red sea fan (Swiftia kofoidi)—and propagated them into multiple, smaller fragments in the lab. Those fragments were anchored in cement pots, returned to Sur Ridge, and monitored over three years.
After three years, about half of the transplanted corals survived. Some species seemed to fare better than others, with transplanted fragments of precious coral (Corallium sp.), black coral (Lillipathes sp.), and red sea fan (Swiftia kofoidi) exhibiting the greatest survivorship after the first year—the period most critical for ensuring long-term success. Further research is needed to understand long-term success of transplanting corals, especially over greater distances, but these preliminary results were a promising indication that repopulation efforts may help speed recovery of damaged coral and sponge communities.