Beyond 300 feet under the waves off Guam, light fades into a dusky blue. This layer of the ocean, known as the upper twilight zone, remains largely unexplored. It’s not easy for humans to reach—special equipment and training are required.
Recently, a team from the California Academy of Sciences made a significant dive. Their goal? To retrieve monitoring devices embedded in Guam’s reefs for over eight years, gathering data on marine life and ocean temperatures.
During their dives, they encountered a variety of strange marine life, like colorful corals, unique sea slugs, and curious crabs. The temperature readings from these devices hinted at changes in the ocean, possibly connected to climate change.
Diving into this zone is dangerous. Regular equipment isn’t sufficient; divers need special gear that lets them breathe a mix of helium and air to avoid severe decompression sickness, or “the bends.” Luiz Rocha, an ichthyologist from the team, noted that a quick descent to 500 feet could take them six hours to ascend safely, limiting their time to work.
Over eight dives, the team successfully retrieved 13 monitoring devices. These devices serve as artificial reefs, allowing marine organisms to thrive. Rocha describes them as “small underwater hotels” for coral reef dwellers.
Back at the lab, scientists examined the collected samples, discovering around 2,000 specimens, including 100 species not previously documented in the region. Among these were potential new species of fish and crabs. One standout find was a hermit crab that surprisingly uses clam shells instead of the usual snail shells.
Despite these exciting discoveries, concerns loom over the deep reefs. More than half of the species in this area are still unknown, yet they face threats from fishing, pollution, and climate change. Rocha remarked that signs of human impact, like plastic debris, are evident on every dive, even at such depths.
Recent research highlights that plastic pollution seems to increase with depth, especially in the upper twilight zone. There’s also a worrying trend: temperature data suggests that these deep waters are warming, contradicting earlier beliefs that they might be safe from climate change.
The mission in Guam represents the beginning of a larger project to collect data from deep reefs across the Pacific, hoping to better understand and protect these vital ecosystems. The journey has just started, but the findings so far illuminate the delicate balance of life beneath the waves.
For more on the environmental challenges facing our oceans, check out resources from the California Academy of Sciences here.
