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Deepest known coral reef bleaching discovered, alarming scientists

In a startling discovery that defies previous environmental benchmarks, scientists have unearthed evidence of extensive coral reef bleaching occurring at unprecedented depths in the Indian Ocean.

This finding from the University of Plymouth underscores the escalating crisis of oceanic damage due to climate change, extending far beyond known parameters.

Unexpected coral reef bleaching in the deep

During a significant exploration funded by the Garfield Weston Foundation and the Bertarelli Foundation, the research team encountered widespread coral bleaching over 300 feet (90 meters) below the sea surface. This zone was previously believed to be insulated from the ocean warming crisis.

The unforeseen revelation paints a grim picture, challenging the long-held assumption that deeper waters and their ecological communities are shielded from the thermal threats devastating more shallow marine layers.

Dr. Phil Hosegood, an expert at the forefront of this investigation, expressed profound surprise at these findings. He emphasized the erroneous belief in the immunity of deeper coral colonies to temperature fluctuations. This misconception is now corrected by their observations in the Indian Ocean’s central regions, hinting at a global phenomenon that may be silently unfolding.

Peering into the ocean depths

This disturbing discovery was not instantaneous, but rather the culmination of over a decade of meticulous study in the Indian Ocean. Dedicated scientists finally succeeded by using high-tech oceanographic tools. The use of in situ monitoring, underwater robotics, and high-resolution satellite data has provided a multidimensional understanding of this marine environment’s unique characteristics.

The turning point came during a November 2019 research expedition. During the mission, through live feeds from cameras on remotely operated underwater vehicles, the team witnessed the shocking extent of coral bleaching first-hand. The contrast was stark and alarming. While deeper reefs were suffering, their shallow counterparts showed no immediate signs of distress.

Silent underwater storm

Post-discovery, the investigative team embarked on a rigorous analysis, pooling diverse data sources to piece together the causative factors behind this deep-sea anomaly. A startling revelation was the significant rise in sub-surface sea temperatures, shooting up to 29°C (84°F). This was a direct consequence of the thermocline deepening throughout the equatorial span of the Indian Ocean.

Lead author Clara Diaz pointed to the Indian Ocean Dipole, a regional counterpart to El Niño, as the primary driver of these adverse conditions. She warned that climate change is exacerbating these naturally occurring oceanic events, setting the stage for more frequent deep-sea coral bleaching incidents.

Echoing her concern, Dr. Nicola Foster highlighted the broader implications of their findings, underscoring the vulnerability of mesophotic coral ecosystems — those located in deeper ocean layers between 30 and 150 meters. The projected increase in thermal stress and subsequent coral mortality poses a significant threat to biodiversity and the essential ecological services these deep-sea reefs support.

Fragile recovery and continued vigilance

Subsequent visits to the affected sites in 2020 and 2022 revealed a degree of natural recovery in the coral ecosystems. However, this glimmer of hope does not negate the urgent need for enhanced monitoring and protective measures for these fragile deep-sea environments. The fact that mesophotic corals, once considered potential ecological saviors due to their depth, are also at risk magnifies the crisis.

Addressing the broader global context, Dr. Hosegood emphasized the critical nature of expanding research horizons. With the growing influence of climate change on natural oceanic cycles, understanding the far-reaching impacts across these largely unknown marine ecosystems has become an urgent scientific and environmental priority.

Coral reef bleaching poses global challenge

The deep ocean, Earth’s least explored and understood biome, is revealing its susceptibility to the surface’s environmental crises. The case of the Indian Ocean’s deep-sea corals stands as a testament to this interconnected plight.

With similar under-studied deep-water coral ecosystems globally facing undetected threats, the scientific community is called to action. As researchers push for heightened observation and conservation efforts, this discovery reaffirms the ocean’s integral role in Earth’s health, urging humanity to consider the deep as the next frontier in environmental stewardship.

This full study was published in the journal Nature Communications.

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