giving coral reefs a future

We realize this night is supposed to be one of THE nights. One of our target species, the important reef building Star corals, is expected to spawn between 9.30 and 11 PM. As we enter the water, the reef looks still quiet, but we hear the hungry noises of thousands of crustaceans, waiting for an extra meal.

We approach the reef area where we want to collect eggs and sperm, we see some of the colonies getting ready to release, showing the egg-sperm bundles in the mouth of their polyps. We start to place collection nets over some colonies and wait… Suddenly it starts! Everywhere we see corals releasing patches of orange colored bundles into the water column.

Collection tubes are fixed on the top of the nets to catch egg-sperm bundles on their way to the surface. One by one, these tubes get filled with gametes while we cruise the reef, enjoying this wonder of nature.

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(pictures: Vanessa Cara-Kerr and Ben Mueller)

The night before, we already witnessed another spectacular event. The massive Siderastrea siderea erupted in a major spawning event from 10 till 11 PM. Contrary to Montastraea faveolata, whose egg-sperm bundles drift to the water surface where they fertilize, Siderastrea is a gonochoric species with male and female colonies. The male colonies release dense sperm clouds into the water, covering the reef in mist. Shortly after, the females start releasing their eggs into the murky water and fertilization basically takes place everywhere in the water column. These different strategies might have implications for larval dispersal and the population structure - an interesting question for future research.

Although this species has been randomly observed releasing gametes during previous years, we have never witnessed a real mass spawning event! After a while, the water gets so cloudy and filled with eggs, that we can't even distinguish anymore which colonies release gametes. A very impressive sight, even for our most experienced team members!

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(pictures: Ben Mueller)

For the first time, we have managed to catch gametes and rear larvae from this reef building coral. We have good hopes that we will be able to settle those on artificial substrates in the coming days!

After the third spawning night, we are rearing larvae of the broadcast spawners Montastraea faveolata, M. cavernosa, Colpophyllia natans, Diploria strigosa, Siderastrea siderea, and the spawncasters Dendrogyra cylindrus and Eusmilia fastigiata. We expect that the results will not only contribute better understand the life history of these species, but also to coral reef restoration.

We also collected and reared larvae of Ophioderma rubicundum (Ruby brittle star) and Diadema antillarum (Black sea urchin) for the first time.

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(picture: Skylar Snowden)

Needless to say that the lab is buzzing with activity until early morning hours and that we are all waiting for the fertilization and settlement rates to become more clear in the upcoming days.

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If you see these huge amounts of gametes that are released by corals in mass spawning events, you may think that corals don't need any aid to reproduce successfully.

However even under non-disturbed conditions only very few propagules will be fertilized, survive the planktonic stage, settle on a suitable substrate and develop into a juvenile coral. Due to man-made stressors, natural coral recruitment has decreased by 50 percent in the past thirty years. So it makes sense to help threatened coral species to overcome this most fragile stage in their life history through active coral restoration. Nevertheless, coral reef restoration will only be useful if the ultimate causes for reef degradation are addressed parallel.