Flow Cytometry Sheds Light on Deep-Sea Coral Feeding Habits

The Deepwater Horizon disaster in 2010 fouled over 1,000 miles of coastline, causing significant impacts to wildlife and coastal communities. Oil spilled from the wellhead on the seafloor, forming a surface slick over a large area of the continental shelf and slope and damaging deep-sea habitat, while contaminated marine snow fell to the seafloor.

Since 2021, the National Oceanic and Atmospheric Administration and Department of the Interior have engaged in the Mesophotic and Deep Benthic Communities restoration projects, working to restore some of these deep-sea habitats in the Gulf. This summer, Bigelow Laboratory for Ocean Sciences got to play a small part in that effort. Laura Lubelczyk, a research associate with Bigelow Laboratory’s Center for Aquatic Cytometry (CAC), spent 10 days supporting an MDBC expedition.

The research cruise focused on restoring corals that were injured by the spill living in the low-light mesophotic zone, or “twilight zone.” Lubelczyk joined for the first leg of the journey, sailing out of Gulfport, Mississippi, in late June aboard the R/V Point Sur and stopping at several sites along the continental shelf of Florida, Alabama, and Mississippi.

The team focused their sampling around 150 to 600-feet deep. This region is home to unique biological life, including octocorals and black corals that feed on plankton and organic particles drifting through the water (in contrast, many shallow-water species of coral rely on a symbiotic relationship with photosynthetic algae for energy). These corals tend to be slow growing and long-lived, making it harder to recover from disturbances like the oil spill.

The MDBC Coral Propagation Technique Development project has been working to cultivate these enigmatic animals in aquariums and lab environments, with the ultimate goal of transplanting them back into the wild to regenerate their habitats. Because many of these corals live beyond conventional SCUBA diving range, they have to rely on technology like remotely operated vehicles to survey coral communities and retrieve specimens from the seafloor.

Yet, even with these tools, scientists know surprisingly little about their ecology and life history. That’s where CAC’s expertise in flow cytometry comes in.

“To help the corals thrive in the lab setting, we need to better understand what they eat,” Lubelczyk explained. “The goal of bringing us in was to help determine what types and sizes of particles are out there in the water that these corals might actually be feeding on, so they can take better care of them in the lab.”

Flow cytometry is a technique adapted from the biomedical field and first applied to the aquatic sciences at Bigelow Laboratory. Individual cells and minuscule particles are lined up, single file. The instrument measures how each emits and scatters light when passed in front of a laser, which allows researchers to rapidly count and characterize particles in seawater.

The FlowCam, a tool originally developed at Bigelow Laboratory and now produced by Yokogawa Fluid Imaging Technologies, complements those measurements with a focus on larger particles. From a single drop of water, it can produce thousands of magnified images like what one would see under a microscope, of everything from larger plankton to the non-living clumps of organic material that make up marine snow.

“A lot of the areas we were sampling in had so much marine snow and other particles raining down through the water that on the ROV video, it really looked like driving through a snowstorm,” Lubelczyk said — if each snowflake was a potential bite of food.

Lubelczyk collected samples throughout the cruise to analyze back at the CAC this fall, and she ran a FlowCam onboard. The team also undertook some preliminary feeding trials, which they hope to continue and expand in the lab this fall, to get a sense of which particles the corals are actively feeding on. Together, these data will provide a more complete picture of the size, abundance, and kinds of food available to these corals in their natural environment, which will help scientists raise them more effectively in a lab or aquarium.

Of course, flow cytometry was just one component of the expedition, and Lubelczyk said they “squeezed in a lot of different science” over the 10 days at sea.

The interdisciplinary team also featured researchers from the University of Rhode Island, Mote Marine Laboratory, University of North Carolina Wilmington, University of Southern Mississippi, the US Geological Survey, and several teams at NOAA. Some sampled water for environmental DNA. Others collected small pieces of coral for genetic and isotope analysis. Some retrieved artificial structures put in previously to understand what settles on the seafloor and what kinds of materials corals prefer to grow on. The ship even stopped briefly for a survey of a proposed site for the sinking of the SS United States, a retired ocean liner that one Florida county is proposing to decommission and sink to potentially turn it into the world’s largest artificial reef.

Lubelczyk says the experience highlighted the possibilities of flow cytometry and particle imaging as research tools and showcased the analytical expertise the CAC can bring to these interdisciplinary projects.

“In the lab we can control a lot of variables, but we also need to understand what’s actually happening out in the water,” she said. “There’s still so much that’s not known about these coral species and just so many exciting questions to ask.”

This work was supported with a grant from the National Marine Sanctuary Foundation, with funding to restore natural resources injured by the 2010 Deepwater Horizon (DWH) oil spill from the DWH Open Ocean Trustees.

Photo Captions

Photo 1: Corals living in a deep-sea habitat impacted by the Deepwater Horizon spill (Credit: NOAA, National Marine Sanctuary Foundatino, UNCW UVP).

Photo 2: Bigelow Laboratory Research Associate Laura Lubelczyk performs sampling (Credit: Sierra Sarkis/NOAA NCCOS).

Photo 3: Lubelczyk runs the FlowCam aboard the R/V Point Sur (Credit: Sierra Sarkis/NOAA NCCOS).

Photo 4: Coral samples collected for analysis (Credit: Laura Lubelczyk/Bigelow Laboratory).