Some Corals Prefer To Eat Microplastics

Since the development of the first synthetic plastic over a century ago (Bakelite debuted in 1907), global plastic production has increased 200-fold. In 2015 alone, over 380 million tons of plastic was produced, and total plastic waste around the world weighs approximately 275 million tons. Nearly 80% of plastic waste in the world's oceans originates from land (as opposed to pollution from ships), with 8 million tonnes coming directly through rivers. Because it is a synthetic product, plastic does not ever fully break down beyond mechanical erosion from waves or degradation from sunlight, leaving small, microscopic bits of plastic ("microplastics") floating in the ocean.

Plastic pollution is especially threatening to the health of coral reefs. Plastics can affect the feeding and cleaning mechanisms of certain stony corals. For cold-water corals, they can create physical barriers for corals that prevent corals from capturing food, thereby slowing their growth rates. Plastic pollution in coral reefs has also been associated with increased rates of disease. And, a new study published earlier this week suggests that some corals can even consume such high volumes of microplastics that the synthetic particles outnumber natural foodstuffs in the corals' guts.

This study focused on the coral Astrangia poculata, which is found in the Atlantic Ocean and Caribbean Sea, and exists in shallow areas from Cape Cod, Massachusetts to the Gulf of Mexico. Unlike their tropical cousins, Astrangia corals do not build reefs nor do they rely on algae to produce the energy they require. The researchers collected the Astrangia from a site near Providence, Rhode Island that is subjected to plastic pollution to determine whether these corals were consuming microplastics (measured as plastic fragments smaller than five millimeters in size).

Ultimately, the scientists found that the Astrangia corals voraciously consume microplastics. The researchers found at least 100 pieces of microplastic in the guts of every wild coral they examined. Additionally, when Astrangia were raised in the lab with the option of consuming plastic microbeads or shrimp eggs (their preferred food item in the wild), the lab-grown corals consumed twice as many microbeads as they did shrimp eggs. Therefore, it seems that the Astrangia corals preferentially uptake plastic over natural food items.

In a different experiment, the researchers soaked the plastic microbeads in ocean water, so that each bead became encased in a thin layer of bacterial scum ("biofilm"). The researchers then injected E. coli bacteria into the biofilm and fed the infected beads to the lab-raised corals. Although the corals ejected the beads within 48 hours, they still became infected with E. coli and died. Thus, microplastics may also serve as disease vectors in the ocean.

There is still much to be learned about how microplastics affects different coral species - but it is clear that these small synthetic fragments have serious implications for corals and their ilk (anemones, which are closely related to corals, were recently found to consume microfibers that are released from laundry).