Monitoring Thermal Stress

Over the past few weeks, the West-Indian Ocean has experienced a period of elevated water temperatures. In Diani, our dive computers showed temperatures hitting the 30ºC mark, which is a known thermal threshold for many coral species.

While most of our coral nursery site remains stable, this heat has confronted our team with the devastating impact of thermal stress on our newly outplanted colonies. During our recent dives, we noted that approximately 10-15% of the 500+ colonies outplanted in the first quarter have bleached and died. This loss was observed primarily among the Acropora species, which are known to be particularly sensitive to sudden temperature spikes.

Interestingly, our observations at a depth of 7-8 meters highlight the varying levels of resilience across different Acropora species. While some coral colonies attached to our metal cages have succumbed to the heat, the neighboring cages with Pocillopora colonies are currently surviving and appear healthy. This confirms that while some species are more vulnerable to heat, others are slightly better equipped to handle these temporary fluctuations.

There is reason for cautious optimism as we move to the end of this month. The Kenyan rainy season has begun, bringing consistent rainfall and cloud cover to the coast. We expect these conditions to gradually cool the surface waters, bringing the ocean temperature back below the stress threshold and allowing the remaining colonies to recover and stabilize.

Our Reef Rangers are continuing their regular maintenance dives to monitor the health of the remaining outplants as long as the weather conditions permit. Our focus remains on cleaning and maintenance by keeping the nurseries free of algae to ensure the corals have the best chance to thrive, and ensuring the additional anchors added earlier this month are holding firm as the seasonal rains and winds increase. By documenting how our corals responds to these thermal events, we aim to be better prepared to build a more resilient reef ecosystem for the future.