A Hawaiian cleaner wrasse provides its cleaning services to a yellowfin goatfish in a reef community off the Big Island in Hawaii. Cleaner species help rid their hosts of ectoparasites, dead tissue, bacteria and fungi. Studies have shown cleaning to play a vital role in keeping many reef ecosystems healthy. (Photo by Marty Snyderman/Caters News Agency)

Thousands of heavy-duty trucks loaded with coal are lined up for up to 130 kilometres from the Mongolia-China border on a sole road in the Gobi desert, Mongolia, October 29, 2017. The journey can take more than a week. (Photo by Bazarsukh Rentsendorj/Reuters)

(L-R) Recording artists Ally Brooke, Normani Hamilton, Dinah-Jane Hansen, Lauren Jauregui and Camila Cabello of Fifth Harmony attend the 2016 Billboard Music Awards at T-Mobile Arena on May 22, 2016 in Las Vegas, Nevada. (Photo by David Becker/Getty Images)

Visitors at the National Zoo check out a parrotfish made from found waste from the ocean in Washington, DC on May 23, 2016. The artwork can be seen at the National Zoo until September 5th. (Photo by Keith Lane/The Washington Post)

The barren landscapes of the south-western US provided inspiration for photographer David Clapp. He visited Nevada, New Mexico, Utah and Arizona as part of his project on other-worldy locations, with surreal results. Here: An infrared image at dusk of strange clay rock formations in Ah-Shi-Sle-Pah Wilderness in Farmington, New Mexico. (Photo by David Clapp/Barcroft Images)

A rider on horseback competes in the Margalla Festival Tent Pegging Championship in Islamabad, Pakistan, June 5, 2016. Tent pegging is an equestrian sport popular in India and Pakistan, with a history going back to the cavalries of ancient armies. (Photo by Caren Firouz/Reuters)

A female participant of the Bela Negara – “defend the nation” – programme applies camouflage face paint on another participant's face at a training centre in Rumpin, Bogor, West Java, Indonesia June 2, 2016. (Photo by Darren Whiteside/Reuters)

(L-R) Miss Universe 2015 Pia Wurtzbach, Miss USA 2015 Olivia Jordan and Miss Teen USA 2015 Katherine Haik attend the 2016 Miss USA pageant at T-Mobile Arena on June 5, 2016 in Las Vegas, Nevada. (Photo by Ethan Miller/Getty Images)