Editor’s note: Last December, a scientific team began the rocky 36-hour boat journey from Puntarenas, Costa Rica, to one of the world’s best dive sites: Cocos Island National Park.

In a project developed jointly with the University of Costa Rica, 18 scientists specializing in diverse fields of marine biology made the trip as part of an ongoing effort to evaluate the health of the underwater ecosystems surrounding the island, a World Heritage Site that Conservation International (CI) has supported for 12 years.

Over the next week and a half, the team would log 310 dives — the equivalent of one diver spending more than 10 straight days underwater. Here are some highlights from the busy expedition.

A tiger shark investigates a net filled with bait on a recent scientific expedition to Cocos Island off the coast of Costa Rica. By documenting which species are attracted to it and how they interact with it, scientists are learning more about predator numbers and behavior around the island. (© Mario Espinoza/University of Costa Rica)

Research goals

Our main objective was to assess the status of pelagic fish stocks — the species that spend most of their time far from coasts and the seafloor. Monitoring the health of the reefs surrounding the island was also a priority. CI and the University of Costa Rica created a baseline years ago; since then scientists have been assessing changes that have occurred in this natural laboratory and exploring the influence of different factors, such as El Niño, illegal fishing, climate change or the implementation of better protection measures within the park’s waters.

But our scientists weren’t just comparing the past with the present. They were also implementing new research experiments never before conducted in Cocos Island’s waters.

‘ARMS,’ urchins and algae

The researchers installed autonomous reef monitoring structures (known as ARMS) at different points on the reef to take an inventory of marine life that collects on them over one year. The data will then be compared with other sites around the world. They also collected water samples to analyze their chemical composition. These data will create a baseline against which to compare the acidification of the island’s waters in the years to come.

Other researchers conducted the first analysis of sea urchin ecology in the Cocos Island region. The urchins serve important functions within the reef ecosystem, so assessing their populations and determining the extent to which they serve as a food source for other organisms is fundamental for understanding the health of the island’s reefs.

Part of the seabed is covered by a thin layer of algae, the composition of which we still do not know. A UCR student on his first visit to Cocos collected samples that will give us a first look at this unique component of a complex ecosystem.

University of Costa Rica diver Celeste Sanchez surveys coral cover using a quadrant near Cocos Island, Costa Rica. (© Conservation International/photo by Edgardo Ochoa)

Diver holding a tagged sea urchin for an experiment on sea urchin predators near Cocos Island, Costa Rica. The scientists collected different sized urchins and tied them in front of a camera trap in order to observe which organisms would prey on them. (© Conservation International/photo by Edgardo Ochoa)

The secret lives of sharks

As Dr. Mario Espinoza of UCR has spent 10 years studying sharks, visiting a place known as the “island of sharks” for the first time was a big moment for him — and an important place to document what predators are doing when divers aren’t around.

Espinoza placed five baited underwater camera stations on the seabed at various points around Cocos Island. A sixth hung off the stern of the boat, waiting for predators near the surface.

The operation of these instruments is simple: a net filled with bait is attached to the end of a PVC arm. A camera then documents which species are attracted to it and how they interact with it. Espinoza learned this technique working on Australia’s Great Barrier Reef, where these data helped create a picture of predator numbers there over a 10-year period.

On the first day of our expedition, the pelagic trap (the one floating behind the ship) returned to the ship very damaged. The next day, three of the depth traps returned without bait … and missing an arm. The crew and the scientists gathered on the boat to watch the videos. We saw snappers, whitetip, silvertip and blacktip sharks, Galápagos sharks, trigger fish, even rays investigating the net. But we were thrilled when the “star” of the show made an appearance: a huge tiger shark. Now the damage to the traps made more sense. Still, Espinoza was surprised. In all his years working with sharks, this was the first time that his research instruments have suffered damage like this.

Espinoza is not only interested in identifying the species that appear in the videos, but also the interaction they have with the bait and the effect that some species may have on other animals. In the case of the tiger shark, the hierarchy is clear: as soon as he approaches the bait, the prize belongs to him. No other fish was visible when the tiger furiously attacked the trap. Back on land, special software will use this video to provide more data on factors including species abundance and interaction.

Not always smooth sailing

About halfway through our expedition, a storm formed on the horizon. This threat forced us to make a decision familiar to all marine scientists: should we leave, or see if the weather clears up? We decided to delay diving until conditions improved, after which we were able to continue with our work. Later in the week, this would not be the case; we were forced to cancel several dives due to poor weather.

Doing science in the ocean is a privilege, and it’s not easy. In places where the current is strong, you descend by clinging to a line attached to a buoy. The currents, visibility and other conditions can change multiple times a day, demanding vigilance from even the most experienced diver. Cocos Island is one of the best dive sites in the world, but not all divers are up to the challenge.

CI’s Monika Naranjo González uses a line to fight strong currents as she descends into the waters of Cocos Island, Costa Rica. (© Conservation International/photo by Edgardo Ochoa)

Back to the lab

“Each hour of diving produces about seven days of lab work once we get ashore,” CI Marine Safety Officer Edgardo Ochoa estimated. That means the work is just beginning. The experts returned to land with suitcases full of samples waiting to be processed as part of the endless effort to better understand one of the most productive ecosystems on the planet: coral reefs.

The Cocos Island expedition team. The expedition was conducted by Conservation International and the University of Costa Rica. (© Conservation International/photo by Marco Quesada)

Data collected on previous expeditions to Cocos Island and elsewhere in Costa Rica have been used to support numerous policies, including: the creation of two marine protected areas and the expansion of another one; the drafting of a national coral reef protection decree (currently in the final stages of approval); the banning of shrimp trawl fisheries in the country; and presently, the installation of an enforcement radar system in Cocos and a process to evaluate a potential increase in Cocos Island’s no-take zones, which would make more of the island’s waters off-limits to fishing.

The new data collected on this expedition will not only strengthen the case for increased protections of these waters, it will also expand our knowledge of how to do it.

Mónika Naranjo González is a communications consultant for CI Costa Rica.

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