Orion McCarthy in Maui with members of the coral reef ecology lab at Scripps

Another Year, Another Maui Trip!

Scripps Oceanography students monitor long-term changes in coral reef health

Aloha! Our lab just got back from our annual fieldwork trip to Maui, and we have a lot to report!

Members of Jennifer Smith's coral reef ecology lab at Scripps Institution of Oceanography have been visiting Maui for more than a decade to monitor coral reefs along the island's western coast. We return to the same sites year after year and take thousands of pictures of each reef. When we return to the lab, we can stitch these photos into a 3D model using an imaging technique called Structure from Motion. These models allow us to visualize change on the reef over time: coral growth, storm damage, species turnover, and more.

animation showing reef over time

As with previous trips, we were fortunate enough to work with the amazing crew at Ultimate Whale Watch and Snorkel, who chartered us to 15+ sites off the coast. We were also able to work with the Hawaii Division of Aquatic Resources to provide hands-on training in Structure from Motion monitoring methods. After surveying a mock “coral reef” at Kahekili Beach Park, divers got to practice using the cameras to survey the reef at Kahekili and got the hang of it quickly.

In addition to photographing the reef, we also collected tissue samples from branching Porites corals at three of our long-term monitoring sites. These corals form dense thickets that can stretch as far as the eye can see. We don’t currently know if these thickets are made up of multiple individuals or if they constitute a single coral colony that spread via fragmentation. Our samples, paired with the 3D reef models, will allow us to determine the amount of genetic variability within these coral thickets and better understand what constitutes an “individual” coral.

Smith Lab manager Sam Clements holds a syringe containing coral tissue

This year, our team from UC San Diego’s Scripps Oceanography was joined by collaborators from San Jose State University (Anna Rothstein, of former Scripps postdoctoral researcher Maya deVries’ lab) and the Monterey Bay Aquarium Research Institute (Scripps alumnus Yui Takeshita’s lab). With a GoPro and selfie stick in hand, Anna probed the cracks and crevices in the reef, spooking a few fish and moray eels in the process. Her research focuses on comparing the abundance of different coral and algae species between the exposed reef and the more sheltered reef crevices. While Anna focused on reef crevices, Yui’s work focused on deploying the Benthic Ecosystem and Acidification Measurement System (BEAMS), an instrument that measures the rate of reef metabolism, to quantify short-term changes in temperature, pH, and salinity at our monitoring site at Kahekili.   

Anna Rothstein probes a reef crevice using a GoPro
San Jose State University student Anna Rothstein probes a reef crevice using a GoPro

Overall, the reefs looked healthy, with little noticeable change from our last monitoring trip in 2021. Maui’s reefs are currently recovering from sequential marine heat waves that caused coral bleaching in 2015 and 2019. We saw very little bleaching on this trip, and saw promising signs of coral regrowth since 2019. We unfortunately did see high densities of crown of thorns starfish (COTS for short) at several of our sites, including inside the marine protected area at Molokini crater. COTS are voracious coral predators, and while they exist naturally on reefs at low levels, they can cause severe declines in coral cover at high densities. The uptick in COTS that we noticed should be monitored going forward to determine what factors might be driving the apparent increase in COTS abundance at our sites.

During our dry day, we were able to visit the Maui Ocean Center to check out the exhibit featuring the island of Kaho‘olawe. The history of Kaho‘olawe is one of tragedy and rebirth: once home to a community of native Hawaiians and a unique ecosystem, the island was ravaged by decades of war, the arrival of European settlers, and munitions testing by the U.S. military. There is now an effort to restore native vegetation to prevent erosion and protect the nearshore reef ecosystems on the island. We were fortunate enough to survey reef sites at Kaho‘olawe in 2017, 2019, and 2021, and several 3D reef models from those expeditions were on display in the exhibit! It was rewarding to see our efforts utilized in an exhibit about environmental restoration and cultural heritage.

We were treated to a few surprises during our field work, including a rare opportunity to dive along the exposed exterior of Molokini crater. The edge of the crater is a sheer cliff that continues from above the surface down hundreds of meters into the abyss. With 100+ foot visibility, we felt like birds flying through an underwater analogue of the Grand Canyon. As we drifted along the edge of the drop-off, we checked out various species of fish, corals, sponges and echinoderms. It was amazing how different the reef was inside and outside the crater, despite being located mere hundreds of meters apart. That observation serves as a reminder how important oceanographic conditions are in terms of shaping the structure of coral reefs and other marine ecosystems. 

Our other lucky surprise came during our last day of field work. As we retrieved the BEAMS sensor from Kahekili, a pod of spinner dolphins swam by. Dozens upon dozens of curious cetaceans streamed by like the flow of cars on a busy street during rush hour, turning a routine sensor retrieval into a once-in-a-lifetime dive.

In this line of work, any dive has the potential to become a special memory. I will hold onto those special memories from this trip, and can’t wait to return next year!

Orion McCarthy is a fifth-year PhD candidate studying coral reef ecology and conservation in marine biologist Jennifer Smith’s lab.


About Scripps Oceanography

Scripps Institution of Oceanography at the University of California San Diego is one of the world’s most important centers for global earth science research and education. In its second century of discovery, Scripps scientists work to understand and protect the planet, and investigate our oceans, Earth, and atmosphere to find solutions to our greatest environmental challenges. Scripps offers unparalleled education and training for the next generation of scientific and environmental leaders through its undergraduate, master’s and doctoral programs. The institution also operates a fleet of four oceanographic research vessels, and is home to Birch Aquarium at Scripps, the public exploration center that welcomes 500,000 visitors each year.

About UC San Diego

At the University of California San Diego, we embrace a culture of exploration and experimentation. Established in 1960, UC San Diego has been shaped by exceptional scholars who aren’t afraid to look deeper, challenge expectations and redefine conventional wisdom. As one of the top 15 research universities in the world, we are driving innovation and change to advance society, propel economic growth and make our world a better place. Learn more at ucsd.edu.

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