(MENAFN) Rising ocean temperatures pose a severe threat to Prochlorococcus, microscopic marine organisms responsible for about 5% of the planet’s photosynthesis, with their productivity potentially plummeting by 37% worldwide under extreme climate scenarios.

A new study published Monday in Nature Microbiology reveals these crucial microbes can only endure water temperatures up to 86°F (30°C) before their reproductive capacity collapses sharply—far earlier than scientists had anticipated.

The University of Washington-led research shows Prochlorococcus thrive best in waters between 66°F and 84°F (18.8°C to 28.8°C). However, once temperatures exceed 86°F, their cell division rates drop to roughly one-third of their peak performance.

Climate projections indicate that tropical and subtropical oceans will surpass this critical threshold within the next 75 years.

Under moderate warming conditions, the study predicts a 17% reduction in Prochlorococcus productivity in tropical regions and a 10% decline globally. More severe warming could slash tropical populations by as much as 51%.

“Their burnout temperature is much lower than we thought,” said Francois Ribalet, the study’s lead author, who examined 800 billion cells across nearly 100 research cruises spanning 150,000 miles (241,401 kilometers) over a decade.

Prochlorococcus form the cornerstone of marine food chains, sustaining creatures ranging from tiny plankton to massive whales across over 75% of the ocean’s surface waters.

Despite their minuscule size, these cyanobacteria are a vital nutrient source within marine ecosystems.

“For a long time, scientists thought Prochlorococcus was going to do great in the future, but in the warmest regions, they aren't doing that well, which means that there is going to be less carbon — less food — for the rest of the marine food web,” Ribalet added.

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