If you haven’t already read it, please see our previous blog post about how we prepared for this trip. 

TLDR: We didn’t catch any elkhorn coral spawning during our August 2024 expedition.

It happens. Figuring out a spawning calendar is really hard and takes years of looking. Coral are clever and secretive in ways we don’t fully understand. But even though we didn’t get the result we wanted, we did learn a lot.

Lesson 1: Next year, we start monitoring in July!

We think the elkhorn corals probably spawned in July instead of August this year. We were watching social media from other reefs and no one reported elkhorn spawning after the full moon in August either. One group did catch the spawn two days before the August full moon, which is very odd.

After the prime spawning period ended, we looked at small sample of the elkhorn coral in the microscope. We didn’t see any eggs inside the coral polyps. It takes coral about six to eight months to make their eggs, so if there was nothing inside, it’s more than likely they’d already released them. We feel certain we would have seen evidence of spawning between our night dives and our nets if it had happened during the time we were monitoring for it. So, the eggs seem like they must have been released before we started monitoring.

One more reason we think the coral might have spawned in July is that through our collaboration with the University of Miami, several dozen colonies from Tela were taken to Florida in June, where they are being held in aquaria known as biobanks. They told us those elkhorn colonies spawned in July. Those corals could have spawned early due to the stress of being packed up and flown across the Gulf of Mexico.

But coupled with our empty corals in Tela and no other spawning reports in August, it seems possible the elkhorns–following some cues that we don’t understand–shifted their spawning a month early this year.

Lesson 2: Our net design worked great!

Even the blingy one. Especially the blingy one. Did the boat captains make fun of it and call it a party dress? Yes, they did!

But did the reflections off the sequins scare away any animals and who might be tempted to snack on a net? It’s possible. Each morning for a week, we checked our nets for damage and to make sure they were still secure and not touching any corals. A few days into our deployment, one of our nets had a pretty big (bite-sized?) hole in it – and it wasn’t the blingy one. I now think, in addition to making sewing the nets more fun, bling might be an a useful deterrent.

We fastened the nets to the seafloor using ropes that we tied around rocks on the reef, so we didn’t leave a trace afterwards. The nets floated just above the colony and didn’t touch it even as the waves washed it back and forth. We installed six nets and held back the others for backup. That turned out to be smart because the nets were out for a week and they did need repairs. When all six were positioned above the colonies rocking in time together with the gentle waves, it looked like the boat captains had been right. They did appear to be a party of nets dancing over the reef.

Lesson 3: We Need to Think about the Sediments

Even though we were in the water as long as we could be beginning an hour after sunset and didn’t see the corals spawn, we were still holding out hope that the corals might have just shifted their clock a bit later and spawned after we left. So each morning we went back to the nets to check the collection bottles on top.

The first morning after we deployed them, it was clear the nets had definitely not collected coral eggs, but they had collected something else: sediment. After just 24 hours in the water, the white nets were tinted red with sediment. There was so much that the nets were slightly weighted down and we had to clean them in order to keep the nets from having too much drag in the water’s movement. That became our pattern each morning: we’d go out to clean the sediment off the nets.

One interesting thing to think about was that had the net not been there, much of that sediment would have fallen onto the coral colony. And yet, the coral colonies are healthy and clean from sediment.

It’s well known that corals make a lot of mucus and that mucus collects bacteria and sediment, much like the mucus in our nose collects dust and pollen. But coral can’t blow their noses, so instead they eat the mucus and all that’s caught in it in order to clean themselves. It’s also a source of food.

In Tela, along with minerals. the sediment might have a lot of organic matter that the coral can use to bolster its nutritional intake. With so much sediment in the water, it’s possible that part of Tela’s elkhorn corals’ health has to do with this rain of potentially nutritious sediment.

There’s another interesting idea about these sediments too: shading. When coral bleach, they lose the symbiotic algal partner that lives inside their tissues. Under normal conditions, that algae photosynthesizes, makes sugar, and feeds as much as 90% of the sugar to the coral host. During bleaching, the coral is starved of that important energy source, and can die.

The main reason for bleaching is elevated temperatures, a problem that’s exacerbated in our warmer world. But many scientists who study bleaching believe that there’s another, less-discussed culprit: sunlight. It’s thought that some wavelengths of light, while maybe not sufficient to cause bleaching, exacerbate it.

So, it’s possible that that all these sediments in the water absorb the rays of sun that can exacerbate bleaching. It’s also possible that, much like standing under a tree on a hot day, simply blocking the sun’s radiation has a cooling effect on the reef below.

These ideas are very much on our radar as we try to unravel the mysteries of the Rebel Reef. But for this season, the rainy season has started, and the party is over. All of our nets, stained with sediment, were pulled from the reef, along with all the lessons we learned. But we’ll be back to gather more–and hopefully catch the coral spawn–in July next year!