Real-time reef data used to be a luxury

Coral reefs live close to their limits. A degree or two of extra heat, held for a few weeks, can tip a healthy reef into a bleaching event, and the corals do not recover on a hasty schedule. What a reef needs in that moment is not a record of what happened. It needs someone watching while it happens, close enough to respond.

For the managers of the reefs, that kind of watching was out of reach. The cheap option, a data logger, stayed silent until you retrieved it weeks later and showed the temperature spike long after the heat event had passed. The real-time option, a large oceanographic buoy, cost more than the teams overseeing the reefs could afford. The sites that most needed monitoring were often the ones no one could watch in time to act.

Aqualink set out to close that gap. The philanthropic organization started in 2020 with a single aim: put real-time monitoring tools in the hands of the people on the front lines of ocean conservation, for free or close to it. The hardware to do that did not yet exist at the price the mission required. So Aqualink helped create it.

Small enough to put on any reef

Working with Sofar Ocean, Aqualink placed a large early order for Spotters with Smart Mooring, helping fund the platform's development.

What made the Spotter the right choice was not its price but what that price unlocked. The Spotter is compact and solar powered, small enough to deploy from a small boat with no research vessel and no crane. Its data comes back in real time over satellite or cellular, so a reef manager sees what is happening now, not weeks later when someone next gets out to the site. And it is modular. Spotter’s Smart Mooring cable supports plug-and-play subsurface sensing at different depths through the water column, so one Spotter can record temperature at the surface and the seafloor at the same time, and measure more parameters as the work grows.

The real-time link is what set the Spotter apart. As Caesar Hjerten, project analyst at Aqualink, puts it, "you can see the real-time aspect of it. And I think that's huge." A logger tells you what happened. A Spotter tells you what is happening, while there is still time to dive the reef, document it, and act.

150 Spotters became a planet-spanning network

The first move was a bold one for a nonprofit. Aqualink gave away 50 Spotters outright, and researchers and reef managers around the world applied to receive one, monitor their local reef, and join a shared global network. After a successful start, a second batch of 100 followed, and what started as a pilot became the largest real-time coral reef monitoring network in the world, with more than 200 Spotters on reefs in nearly every ocean.

The Spotters are only half of it. The other half is Aqualink itself, a free, interactive platform that lets anyone explore what the network is measuring. Open the map and more than 6,000 reef sites appear, each one colored by its current heat stress. Every site carries NOAA satellite sea surface temperature, degree heating weeks, and bleaching alert levels, with wind and wave data pulled through Sofar's API. Where a Spotter sits on the water, the site also shows live, in-situ readings from the reef itself. And reef managers can add their own dive surveys, repeat photography of the same spot on the reef over time, so a site is not just a number but a visual record of the reef changing.

Aqualink's whole philosophy is that this should be open. "Everything we do is open source and free. It's a fully philanthropic project," Caesar says. Managers are encouraged, never required, to make their data public, so a reading taken on one reef becomes useful to a scientist studying another, half a world away.

The invitation extends past Aqualink's own fleet. Any team managing a Spotter can add it to the map, a direct integration that takes about thirty seconds. Doing so puts that reef on the global map for everyone, and it gives the manager the full Aqualink view layered onto their own readings: satellite data, bleaching alerts, wave and wind measurements, and more. Sharing the data and getting more from it are accomplished in the same act.

Watching the heat arrive, and the reef respond

In March 2022, a Spotter caught a marine heatwave as it built over Wellington Reef in the Galapagos. The reef carries unusual weight: a run of El Niño events stripped the islands of sixteen of their seventeen structural coral reefs, and Wellington is the one still standing. Run by the Charles Darwin Foundation, the buoy logged the surface temperature climbing to 3.6°C above the local normal, well past the bleaching threshold, and holding there for about a month. A few years earlier, none of that would have been visible as it happened. This time the team watched the heat arrive in real time.

Detection is only the start. The real value shows up when a reef manager checks that live temperature against what they're seeing on the reef. Off Elbow Beach in Bermuda, one of the most northerly reef systems in the world, Ted Gosling manages two Spotters and returns to the same corals on every dive. In the summer of 2022, his buoys and a satellite both recorded temperatures above the reef's 28.4°C bleaching threshold, and the conditions held there for nearly six weeks. His survey photos tell the rest: corals healthy at the start of August, badly bleached by late September, then recovering after Hurricane Ian passed offshore and pulled cooler water across the reef. He has said the dashboard's real worth is lining up those temperature trends against his own videos and photos.

Pairing live in-situ data with satellite context is where Aqualink earns its place. Put the Spotter's seafloor and surface readings next to satellite observations and the two sometimes disagree by a meaningful margin, which matters when a few tenths of a degree decide whether a reef crosses its bleaching threshold.

The payoff is scientific, too. Off Palos Verdes in California, a team rebuilding rocky reef habitat with more than fifty tons of rock used their Spotter alongside a NOAA tide gauge and found that each tide cycle washes the reef with cool, nutrient-rich water. Capturing that pattern, documented in their first-year project report (Williams et al., 2022), took exactly the continuous, real-time record the Spotter provides.

Beyond temperature

With Spotter established and the network in place, Aqualink is reaching past temperature into the rest of the water column. Recent projects pair Spotters with a Sea-Bird multi-parameter water quality sensor connected through a Bristlemouth Development Kit and reporting in real time, a hydrophone with edge processing that detects passing vessels and marine mammals, and dissolved oxygen sensors bound for reefs in Hawaii and Brazil.

A Spotter Scout, an uncrewed surface vehicle built on the same platform, is arriving next, and the team plans to send it across reefs to map them on a scale no group of divers could match. The aim has not changed since the first Spotters went out: put real-time ocean data in more hands, on more reefs, and keep it open to everyone.

It gives everything in real time. Accurate data from the seafloor to sea surface, wind, and waves. That's the piece that was missing before. - Caesar Hjerten, Project Analyst, Aqualink

Explore Aqualink's platform or learn more about the Spotter platform.

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