As a marine ecologist at the University of Tasmania in Hobart, Australia, I make about 150 dives a year, looking for threatened marine species. I focus on animals and plants that go largely unnoticed: small crustaceans and fish species such as gobies and blennies that grow 3 or 4 centimetres long. I’m trying to illuminate the complex interactions between marine species and to understand how human activities disrupt that process.

This photo was taken in February 2018 at Elizabeth and Middleton Reefs in the southern Coral Sea Islands. I was counting species of fishes and invertebrates, and assessing changes since my last visit in 2013. The silver schooling fish behind me are Pseudocaranx georgianus, but I’ve also seen whale sharks, humpback whales, dolphins and sea snakes. I love the sense of peace underwater: all the stresses and problems of the terrestrial world drop away.

The Reef Life Survey Foundation in Hobart, of which I am president, uses trained volunteer scuba divers to do underwater surveys of biodiversity on rocky and coral reefs worldwide. The project will provide an irreplaceable record of underwater life on Earth as it is now. We have data from more than 3,000 sites across 53 nations. The work is extremely important because many changes are happening underwater, out of sight. The Great Barrier Reef and Coral Sea reefs are threatened by coral bleaching associated with climate change, cyclones, outbreaks of crown-of-thorns seastars (Acanthaster planci) and fishing.

This is the best of jobs in terms of seeing fantastic places that no one has been to before, and knowing that you’re recording information needed for dealing with threats to marine biodiversity. But it’s depressing to return to places that were once so beautiful to find that climate change, or sediment or pollution, has largely destroyed them. You can’t help but reflect on the damage we’re doing, and on what a poor state we’re leaving Earth in for future generations.