The sunscreen worn by tourists is killing coral reefs. In high enough concentrations, oxybenzone, a UV filtering chemical found in most sunscreens, kills baby coral by altering its DNA. Without the recruitment of new coral, reefs have a difficult time maintaining themselves, which has led to their overall decline. The problem is particularly acute in popular tourist destinations like Hawaii and the Caribbean. The research adds a new dimension to the understanding of sunscreen’s impact on the marine environment.
Prior to this study, researcher Roberto Danovaro and colleagues began examining the impacts of a variety of less-obvious pollutants on marine life, including sunscreen. Working both in the lab and on actual coral reefs, the group exposed isolated pieces of coral to diffuse sunscreen or component chemicals.
The findings were alarming: at both high and low concentrations, sunscreen and most of its component chemicals induced rapid bleaching (death of the zooxanthellae, a symbiotic algae that help coral feed). The chemicals induced genetic changes which allowed viruses, already present in the coral, to move from a slow reproductive cycle inside individual cells (lysogenic) to a lytic cycle. In a lytic cycle, the virus reproduces to the point where it explodes the host cell. Then, the newly released viruses immediately begin infecting new cells, e.g. a spreading infection. The infection soon progresses to the point where there are more viruses than zooxanthellae, leading to the bleaching.
The exposed corals were able to recover if given a break, but Danovaro also made some rough calculations about the scope of the problem. Globally the group estimated that four to six thousand tons of sunscreen were released annually in reef-laden areas. Furthermore, coral isn’t the only thing affected; an earlier study demonstrated how sunscreen also increases the vulnerability of certain plankton. On a local scale, sunscreen might threaten the basic marine food web.
The new study shows how the risk of sunscreen sometimes goes beyond bleaching and can actually kill some coral outright. They are at greatest risk in areas with less water flow, such as in enclosed bays or atolls. Enclosed bays have shallow, calmer water and are especially popular with amateur snorkelers. In well-known areas, the coral are not only exposed to sunscreen by the presence of people, but also don’t receive the necessary freshwater flow needed to flush away the harmful chemicals. Under such circumstances, the corals that do survive never get a chance to recover.