Coral bleaching returns to Costa Mar's reefs as heat spreads

At dawn on Thursday, a small research vessel left Puerto Azul's harbour with a team of five divers and two technicians. Their destination was the Boca Negra reef system, thirty kilometres offshore, where the monitoring network's automated sensors had registered water temperatures of 31.2 degrees Celsius—two degrees above the seasonal average for late June.

The Reef Monitoring Network is Costa Mar's most visible conservation institution. For three decades, it has tracked coral health, fish populations, and water chemistry across twelve permanent monitoring stations. The network's latest report, released Monday, marked a shift in that narrative: for the first time since late 2024, bleaching—the stress response by which corals expel their symbiotic algae and turn white—has appeared in significant patches.

The finding arrives as Costa Mar confronts a larger climate paradox. The region's hundred-percent renewable grid and tourism-based economy are built on the assumption of ecological stability. But the ocean that defines the region is warming faster than the Federal Statistical Office's climate models predicted, and the reefs that draw divers and tourists are showing signs of strain.