Restoring Reefs

The boat bumps over the waves as we speed across the water, occasionally pausing for the captain to remove the clumps of Sargassum algae strangling the propellers. We reach the dive site, and I instruct my team of student research assistants to ready themselves, helping them with the inevitable last-minute scramble as fins, masks and scientific equipment are put in place. We complete our final checks, spit into our masks to prevent them from fogging underwater, and open the tank valves so the high-pressured air flows to our mouthpieces. There’s a moment of calm as we balance on the edge of the boat before taking a last breath and putting our regulators in our mouths. “Tres, dos, uno…” shouts the captain. Then, we roll backwards off the boat and into the turquoise ocean.

I have done this hundreds of times, yet it never gets old. I squeeze the button to let air out of my BCD (Buoyancy Control Device) and begin to sink. The body of water above me grows, the sun dims, and tranquillity takes hold.

Underwater, I relish the subtle sensations: the sound of my breath slowing, the sight of dappled sunlight shifting with the movement of the sea, the terrestrial noise becoming distant and muffled, and the weight of the water’s resistance to my every action.

We float down through the clear Caribbean water, and laid out beneath us is the Mesoamerican Barrier Reef, the second-largest reef system in the world – which spans 1,000 kilometres from the Yucatan Peninsula of Mexico, down to Belize, Guatemala and the beautiful Bay Islands of Honduras.

There are around 80 species of hard corals in the Caribbean, from rounded brain to castle-like pillar and branching and foliose corals, each one housing their own distinct community of invertebrates, fish and algae. These iconic coral species build the reef by depositing a solid, white calcium carbonate skeleton underneath their vibrantly coloured and intricately-patterned fleshy surfaces.

Along the reef, soft corals, such as sea fans, sway with the water surge; giant red barrel sponges stand tall and filter the seawater; lobsters, crabs and snails eat the organic debris that reaches the ocean floor. In the reef’s crevices, spiny black sea urchins hide until nightfall, when they emerge to graze on algae.

Tropical fish with eye-catching stripes and dots and silvery lines eat seaweed off of the reef whilst being cleaned of parasites by smaller, yellow, pencil-shaped wrasse. Giant, dinosaur-like loggerhead turtles, with barnacles growing on their ancient-looking carapaces, swim by, and I am reminded that every animal, coral, plant and critter on the reef has an important ecological role – no matter how big or small – that keeps the system functioning. It is a delicate balance sensitive to change.

On today’s research dive, we are surveying the abundance and diversity of species on the reef to recognise and identify patterns in the changes we see so that we may better understand how to conserve this elaborate ecosystem.

Despite its thriving appearance, it is evident to us scientists that this reef is on the brink of collapse. Coral reefs the world over are facing many anthropogenic pressures – from climate change to localised human impacts, such as overfishing, pollution and excessive coastal development – that affect the reefs’ complex processes in myriad ways.

To the untrained eye, these reefs may still appear beautiful – with their array of colours, textures and intricacies – but often, the vibrant organisms we see on these dives can overgrow and kill corals, colonising their skeletons. Inedible to the herbivorous fish, these invasive encrusting algae, zooanthids, sponges and other aggressive invertebrates proliferate across vulnerable and degraded reef ecosystems, smothering hundred-year-old corals in a matter of months, or even weeks.

As the reef-building corals and herbivorous fish grow scarce, the reef community becomes less diverse and is, therefore, thrown into a negative feedback loop: as coral larvae struggle to settle on algae-covered substrates, the coral population is unable to rejuvenate. This lack of coral then results in fewer habitats for fish and lower rates of herbivory on the reef, and creates a downward spiral that eventually leads to a breakdown in ecosystem structure and function.

Remarkably, coral reefs provide habitat for around a quarter of all marine organisms, yet they cover less than two percent of the ocean floor. This disparity between the small space they occupy and having the greatest diversity of species of any ecosystem on earth – beyond that of tropical rainforests – makes them fascinating to study.

However, due to limited access and the non-existence of underwater photographic equipment until recent decades, coral reef science suffers from a severe lack of long-term data, as monitoring only really began after scientists noted a decline in the mid to later parts of the last century.

Whilst we know that we have lost an increasing amount of live coral cover since the 1970s when scuba diving became more accessible, there is little empirical data available before then. Because of this, we may be underestimating the true loss that has occurred on coral reefs, and, therefore, it is important for there to be long-term continuous monitoring to provide baselines for the future.

Many marine scientists spend their entire careers measuring the rates of death and decline on coral reefs. But thankfully, I am one of the lucky few involved in proactive conservation and direct intervention of reef ecosystems.

After graduating with a degree in Marine Biology 2013, I travelled to the Mexican Caribbean, where, as a trainee dive instructor diving four times a day, I noticed the rapid deterioration of coral colonies. The decline was, and still is, so drastic that after just a few months of diving at the same site, the damage to the reef structure and changes to coral colonies were clearly visible.

As a dive professional, I became motivated to investigate the threats to coral reefs and endeavoured to conduct research to find solutions.