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| Deep-Sea Shock: Coral Bleaching Strikes Mesophotic Reefs in Earth's Depths |
Deep under the Indian Ocean, a startling revelation has come to light. Research from the University of Plymouth in the UK has uncovered the deepest evidence of coral reef bleaching ever recorded, occurring in the Mesophotic Coral Ecosystem (MCE) nearly 90 meters beneath the ocean's surface.
Dr. Phil Hosegood and his team made this groundbreaking discovery, challenging previous assumptions about the resilience of deep corals to ocean warming. These MCEs, residing between 30 and 140 meters in tropical and subtropical waters, have long been considered immune to bleaching due to their cooler and relatively stable environment.
The damage is not caused by insufficient light, as there is a limited trickle of sunlight reaching these depths. Rather, it's the rising water temperatures that are responsible for coral bleaching. The researchers attribute the coral damage to a 30 percent increase in sea temperature, driven by the Indian Ocean dipole. This rise in temperature is believed to have harmed up to 80 percent of the reefs in certain seabed regions.
The lead author of the study, Clara Diaz, explains, "What we have recorded categorically demonstrates that this bleaching was caused by a deepening of the thermocline. This is down to the regional equivalent of an El Nino, and due to climate change these cycles of variability are becoming amplified. Bleaching in the deeper ocean here and elsewhere will likely become more regular."
The research team stumbled upon this revelation during a research cruise in November 2019. Using remote-operated underwater vehicles equipped with cameras, they were able to monitor the health of the reef in real time. It was evident from the transmitted live images that something was amiss, especially with deeper reefs. Surprisingly, shallower water reefs did not exhibit the same bleaching issues at that time.
Although surface temperatures remained relatively stable, the temperatures beneath the ocean's surface had surged from 22°C to 29°C. A follow-up investigation in 2020 and 2022 revealed that substantial parts of the coral had managed to recover.
Dr. Nicola Foster, one of the researchers, underscores the critical importance of these findings: "Our results demonstrate the vulnerability of mesophotic coral ecosystems to thermal stress and provide new evidence of the impact that climate change is having on every part of our ocean. Increased bleaching of mesophotic corals will ultimately lead to coral mortality and a reduction in the structural complexity of these reefs. This will likely result in a loss of biodiversity and a reduction in the critical ecosystem services that these reefs provide to our planet."
This shocking discovery emphasizes the urgent need to address climate change and protect the fragile ecosystems that lie beneath the ocean's surface.
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