Google Earth Image of halos at Heron Island

Watching Google Earth over time could show the effects of predator removal, such as through fishing, nearly anywhere on Earth, according to a study published this week in Scientific Reports.

A Google Earth image survey of the lagoon habitat at Heron Island within Australia’s Great Barrier Reef revealed distinct halo patterns within algal beds surrounding patch reefs. Underwater surveys confirmed that, as predicted, algal canopy height increases with distance from reef edges. This was due to herbivore grazing. In conjunction with behaviour studies, this shows that the actions the herbivores collectively took to avoid predators could be seen from space. Watching this over time provides and amazingly low cost way of monitoring the effects of predators. And indeed of the herbivores.


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Freely-available satellite imagery of the entire Earth’s surface via Google Earth allows examination of landscape features in even the most remote areas, including difficult-to-access habitats within them. But the study has shown that it is possible to remotely observe the landscape-scale footprint of behavioural interactions between predators and prey on shallow coral reefs.

Grazing halos—rings of bare substrate devoid of seaweed—have long been noted surrounding coral patch reefs. Halos have been attributed to fish or urchins, suggesting that they shelter from predators within reefs and take foraging excursions that radiate outwards from this central refuge.

The study concludes that the technique could allow remote monitoring of indirect effects of predator removals (e.g., due to fishing; hunting) and/or reintroductions (e.g., North America’s wolves; India’s cheetahs; African game reserves) anywhere on earth. In nations with limited conservation resources, this technique may prove particularly valuable.

Further Reading:
Landscape of fear visible from space. Elizabeth M. P. Madin, Joshua S. Madin & David J. Booth. Scientific Reports Volume: 1 DOI: doi:10.1038/srep00014