Coral reefs, the underwater cities of the ocean, are facing a sneaky threat: microplastics. These tiny plastic particles, less than 5 millimeters in size, are becoming increasingly common in our seas. Scientists wanted to figure out how different amounts of these microplastics affect reef-building corals. They chose two coral species, Stylophora pistillata and Pocillopora verrucosa, and exposed them to varying concentrations of microplastics for 12 weeks.

They looked at how the corals grew, how they calcified (built their stony skeletons), if they had any tissue death (necrosis), and how active their polyps were. They also checked how well the tiny algae living inside the corals (photosymbionts) were doing their job of photosynthesis. The scientists used a mix of six different plastic types to mimic what's found in nature.

The results? Both coral species showed slower growth, more tissue death, less active polyps, and better photosynthesis as the microplastic concentration went up. However, the effects on the coral hosts were straightforward, while the effects on the algae were more complicated. Photosynthesis only improved after hitting a certain level, which differed between species.

Low to moderate microplastic levels didn't cause much harm, but high levels did. This is likely because the more microplastics there are, the more chances corals have to get entangled, which can transfer toxins or pathogens.

The good news is that corals can handle current pollution levels. The bad news is that we need to stop microplastic pollution from getting worse to keep coral reefs healthy.

Plastic Pollution: How Corals Face the Microplastic Challenge

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