Our first day at sea was packed with activity as we arrived at Sur Ridge, a seamount known for its thriving communities of deep-sea corals and sponges. Although deep-sea corals are as diverse as their shallow-water relatives, we still know little about the factors that shape their distribution, abundance, and survival. On this expedition, we have the opportunity to study these organisms in remarkable detail, combining observations, experiments, and long-term monitoring with technology developed at MBARI.

Upon our arrival, we first deployed a mooring that will stay on the seafloor for a year. A heavy anchor tethers the oceanographic mooring to the seafloor and a series of floats at the top keep it suspended above the bottom. A profiler instrument with a package of sensors that will continuously measure temperature and oxygen will slowly crawl up and down the mooring line, providing a better understanding of environmental variability at the seamount.

Then, we launched the Benthic Respirometer System (BRS), which allows us to measure oxygen consumption by organisms, an estimate of metabolism and biological activity. Battling strong bottom currents, the remotely operated vehicle (ROV) Doc Ricketts dove down to the location where the BRS settled on the seafloor and then placed small branches of deep-sea bamboo coral colonies into the instrument’s eight respiration chambers. Over the coming days, the corals will remain inside the chambers, where they will be exposed to seawater across a range of oxygen concentrations. Once the experiment is complete, we will retrieve the BRS and analyze the data to quantify coral oxygen consumption and metabolic rates. The results will help us understand how deep-water corals may respond to changing ocean oxygen levels.

This first ROV dive also provided an opportunity to investigate one of the biggest knowledge gaps in deep-sea coral biology: reproduction. Scientists have documented the reproductive biology of less than seven percent of known deep-sea coral species. During the dive, we observed coral polyps holding what we believe are developing eggs. We collected species that will help us understand if this is true, and patterns of fertilization and fecundity in deep-sea corals.

The dive also supported ongoing efforts to understand the biodiversity found in rocky seafloor habitats. We collected rock samples for Postdoctoral Fellow Olívia Soares Pereira, whose research investigates how the diversity and abundance of small invertebrate communities are influenced by environmental conditions and habitat type. The team sampled rocks at Sur Ridge’s summit, slope, and southern flank during previous R/V David Packard and R/V Rachel Carson expeditions. By gathering new samples from the northern, deeper end of the seamount, this expedition expands both the geographic coverage and environmental range of the dataset.

Together, these experiments, observations, and collections are helping build a more complete picture of deep-sea coral ecosystems, from the physiology and reproduction of individual corals to the environmental processes that shape entire communities. By combining these different approaches, the team hopes to better understand how these ecosystems may respond to increasing temperatures and declining oxygen levels in the deep ocean.