Sunscreens Cause Coral Bleaching by Promoting Viral Infections

TLDR

Coral bleaching, the loss of symbiotic zooxanthellae, threatens reef biodiversity and ecosystem services and is linked to temperature spikes, high irradiance, pollution, and bacterial disease. The study aimed to assess how sunscreen ingredients affect hard corals and their symbiotic algae. Researchers applied sunscreen and UV‑filter aliquots to coral branches in field and laboratory settings across multiple oceans and examined zooxanthellae for viral infection using epifluorescence and transmission electron microscopy. Sunscreens, particularly organic UV filters, rapidly and completely bleach hard corals by triggering the lytic viral cycle in latent zooxanthellae infections even at very low concentrations.

Abstract

Coral bleaching (i.e., the release of coral symbiotic zooxanthellae) has negative impacts on biodiversity and functioning of reef ecosystems and their production of goods and services. This increasing world-wide phenomenon is associated with temperature anomalies, high irradiance, pollution, and bacterial diseases. Recently, it has been demonstrated that personal care products, including sunscreens, have an impact on aquatic organisms similar to that of other contaminants.Our goal was to evaluate the potential impact of sunscreen ingredients on hard corals and their symbiotic algae.In situ and laboratory experiments were conducted in several tropical regions (the Atlantic, Indian, and Pacific Oceans, and the Red Sea) by supplementing coral branches with aliquots of sunscreens and common ultraviolet filters contained in sunscreen formula. Zooxanthellae were checked for viral infection by epifluorescence and transmission electron microscopy analyses.Sunscreens cause the rapid and complete bleaching of hard corals, even at extremely low concentrations. The effect of sunscreens is due to organic ultraviolet filters, which are able to induce the lytic viral cycle in symbiotic zooxanthellae with latent infections.We conclude that sunscreens, by promoting viral infection, potentially play an important role in coral bleaching in areas prone to high levels of recreational use by humans.