Alwin Hylkema

My name is Alwin Hylkema. I work for the University of Applied Science Van Hall Larenstein and also for Wageningen University, and I’ve worked on Saba since 2019.

Sea urchins are very important grazers — they eat the algae on the reef, which allows new corals to settle and survive. In the 1980s, there was a huge die-off that killed 99% of the long-spined sea urchins — the Diadema sea urchins. And more recently, in 2022, there was another die-off that affected most of the sea urchin populations in the Eastern Caribbean. So that also impacted Saba and a lot of islands around us.

We’ve been able to develop multiple intervention methods that proved successful on a small scale. One of them is that we add small structures on the reef, and sea urchin larvae can actually settle on those structures and survive. We can also culture them from gametes. So we start with adult animals and we have a method that makes them release their gametes, then we capture those and culture the larvae on a shaker table for two months before they settle.

Previous methods used aeration — so, pumping in air — and were sometimes successful, sometimes not successful. One of the things we found out is that the air bubbles actually damage the larvae. So we developed a new method by culturing them on shaker tables, which constantly rotate the culture vessel without using any aeration. So now the larvae stay healthy.

But there are a lot of reefs here on Saba, and especially in the Caribbean, so now we need to upscale our technology to actually make a measurable impact on the reef. The shaker table method that I just described can raise around 1,000 larvae per shaker table. But a lot of them don't come through metamorphosis, and then there's post-settlement mortality, so from that we end up with 200 sea urchins that we put on the reef. So we don't want to culture 1,000 larvae — we want a culture like 10,000 or even 100,000 larvae.

Another step we're doing right now is figuring out mortality on the reefs themselves — like which reefs should we restock them? How deep? What predators should not be there to give the urchins a good chance? We also look at shelter availability. The Saba Conservation Foundation is a very important partner in this work. Sea Saba also helps us, and we work together with the public entity. There are a lot of different partners involved. Feel free to come by anytime and you can see it yourself! (We’re next to the Saba Conservation Foundation.)

I think the very special thing about Saba is that everything is so close to the sea because it's so steep. So for example, my house is 500 meters above sea level, but probably 100 meters away from the sea as the crow flies. That's how close things are. And you also see that in the habitat change — in the water and above water — if you drive from here at the harbor to Mount Scenery, you see at least three different ecosystems slowly change into each other. That's very special.