An Ultra-Thin "Sun Shield" On The Sea's Surface Could Protect Our Coral Reefs


Stephen Luntz


Stephen Luntz

Freelance Writer

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

poisonous sunlight

Tropical reefs depend on sunlight but when it gets too hot, the intensity of the sunlight can be lethal for coral, so a layer on the sea's surface that blocks 30 percent of light could be a life-saver. Divedog/Shutterstock

If the world does not act soon, tropical coral reefs could soon be a thing of the past, taking with them a quarter of marine species. In the face of refusal to take global action, scientists have turned to some weird and wonderful stop-gap measures to try to keep a few of our reefs alive. One particularly unlikely-sounding project, to protect reefs with a thin spray of sunscreen, has been found effective in ideal conditions, although it's a long way from demonstrated success on the open seas.

Although coral reefs are also threatened by ocean acidification, nutrient runoff, overfishing, and plastic pollution, the most immediate threat to many reefs is global warming. Most corals can't survive long bouts of hot conditions, instead expelling the photosynthetic algae they need to survive. If these bleaching events last too long, the corals die.


Cooling the reefs by shielding them from sunlight or by drawing cold water up from the depths have been proposed as stop-gap solutions. Besides the logistical challenges of shielding large areas, there are many other problems including the cost of any shield tough enough to last.

The Great Barrier Reef Foundation is promoting an alternative, a biodegradable layer 50,000 times thinner than a human hair that sits on the surface of the ocean. Professor Greg Qiao of the University of Melbourne told IFLScience any reflecting the layer does is unlikely to have a significant cooling effect on the area beneath, but the light itself, particularly at the UV end of the spectrum, harms the coral and works in combination with the high temperatures to induce bleaching.

Using state of the art tanks at the Australian Institute of Marine Sciences facility, Qiao and colleagues have announced this layer can block 30 percent of the light that would otherwise reach the reef. In yet to be published work, coral protected in this way was shown to survive bouts of hot weather, while control corals in tanks exposed to otherwise identical conditions died.

Inevitably, in open water the layer will be dispersed by wind and wave. However, Qiao and the other inventors hope this will not matter as long as it stays in place through the heatwaves when most of the damage is done. Since these are periods of calm, sunny conditions, where there are not enough waves to bring cooler water up from the depths, this looks possible.

The Australian Institute of Marine Science has a set of tanks with water from the ocean controlled to a precise temperature which can be used to test the relative effects of environmental changes, including having 30 percent of the light blocked. Phil Mercurio/Australian Institute of Marine Sciences

The shield is so thin, tiny amounts can cover large areas. Moreover, it is self-dispersing. The atoms it is made of “Like to spread themselves,” Qiao told IFLScience. “To be side by side, one atom thick.”

The idea of shielding reefs evolved from a previous one Qiao was working on with renowned inventor Professor David Solomon, where similar substances would be spread on reservoirs to prevent evaporation. In these cases, Qiao said, the material could be applied to one corner of a water-body 10 hectares (25 acres) in size, and within an hour it would have spread across the entire surface.

In a dry continent like Australia evaporation prevention could prove exceptionally valuable. However, Qiao said the research has encountered unexpected problems. Even on small bodies of water, waves occur, which drag the particles of the layer down into the water. When the water is clean, the particles resurface and resume doing their job, even if some evaporation has occurred in the meantime. However, muddy water prevents resurfacing, requiring frequent reapplication of the protective layer.

The layer's dominant component is calcium carbonate, the very substance from which corals are made, so there should be no environmental drawbacks when particles are removed from the surface, and even the other components are fully biodegradable.


However, “It’s important to note that this is not intended to be a solution that can be applied over the whole 348,000 square kilometers of Great Barrier Reef – that would never be practical,” Anna Marsden of the Great Barrier Reef Foundation said in a statement

Rather they hope that, by applying a shield to the most valuable reefs – whether that value is measured in tourist dollars or biodiversity – as heatwaves begin, a small number can be saved from the approaching marine apocalypse. Then, if the world eventually gets its carbon emissions under control, these reefs could be used to reseed the shallow tropical waters where reefs so recently thrived.


  • tag
  • global warming,

  • coral reefs,

  • sunscreen,

  • coral bleaching,

  • last stand,

  • calcium carbonate