Earth's most prevalent species at risk of disappearing due to climate catastrophe

Prochlorococcus, the smallest and most common photosynthetic organism on Earth, plays a crucial role in marine food chains as it inhabits over 75% of the sunlit ocean surface worldwide. This cyanobacterium, which lives in the upper layers of oceans, makes up almost half of the phytoplankton biomass in nutrient-poor tropical and subtropical waters, producing about one fifth of the oxygen in the Earth's atmosphere.

However, a study published in "Nature Microbiology" suggests that under moderate and high warming scenarios, up to half of the Prochlorococcus population could disappear in tropical oceans by the year 2100. This is due to the organism's reduced genome, which could limit its ability to adapt to rapid warming.

According to the RCP8.5 concentration pathway, average sea temperatures could rise by 3.8 degrees. Under this scenario, regional surface water temperatures could exceed 28 degrees by the end of the century, a temperature at which the reproduction of Prochlorococcus decreases and the division rate of its cells drops sharply.

The division rate of Prochlorococcus cells increases up to a water temperature of about 28 degrees, but this increase is not enough to counteract the decreasing reproduction rate at higher temperatures. This could lead to a significant decline in the Prochlorococcus population, a decline that scientists fear could trigger chain reactions in marine food webs.

The study's limitations include sampling being limited to spatially restricted marine areas and not adequately capturing less common, heat-tolerant variants. Criticisms have also been raised about the measurement method, with Bernhard Fuchs stating that the sampling being limited to the surface layers does not provide information about what's happening in deeper layers.

While the decline of Prochlorococcus could have devastating effects on marine ecosystems, it's not all doom and gloom. The cyanobacterium Synechococcus, also studied by the team, could potentially benefit from climate change and at least partially fill the ecological gap left by Prochlorococcus at higher water temperatures.

It's important to note that the findings of this study are based on computer models and predictions. More research is needed to fully understand the impact of climate change on marine microorganisms and the broader marine ecosystem.

Prochlorococcus cells are approximately 0.5 to 1 micrometer in diameter, making them nearly invisible to the naked eye. Their importance, however, cannot be understated. As we continue to monitor the effects of climate change on our planet, the fate of these microscopic organisms will be a crucial factor to consider.