Restoring Diadema
In February we will be shifting gears, bringing new blog posts from different topics, written by the ISER team. This post differs from other ISER posts, not because it veers off from our core values, but because it is not about farming or gardens. We will be bringing you brief snapshots of the other issues that we are tackling at ISER. This post is written by Dr. Stacey Williams, a member of ISER and a marine biologist, who specializes in coral reef ecology. In this blog post she shares with you her efforts to help restore sea urchin populations on coral reefs off the southwest coast of Puerto Rico.
Last year I received funding to start a pilot project to restore populations of Diadema antillarum or commonly know as black sea urchin. I am very excited about this project because it is the first attempt of this type of project in the field of marine biology and thus a challenge to me as a scientist. You might ask yourself why is this project necessary, who really cares about this animal? Why is this creature valuable other than to poke you with its spines? Prior to the 1980s’ this sea urchin was prolific on the reefs around Puerto Rico and abundant in the entire Caribbean. They were so plentiful on the reefs that snorkelers and divers would intentionally kill them to get some relief from their poking spines. If you have ever been poked yourself with a sea urchin spine, you know the pain! In 1983-84, Diadema populations around the Caribbean were being wiped out by a possible water-borne pathogen. Diadema started to die everywhere, from Panamá to Florida, from hundreds to thousands on a reef to a couple of urchins. This event was reported as the most extensive mass mortality of any marine organism. The death of Diadema was devastating. Diadema is one of the most important herbivores on the reef, it is an organism that eats macroalgae. Corals, the building blocks of a reef, compete with algae for light and space. As a herbivore, this sea urchin kept the population of macroalgae on check. After the mass mortality, populations of macroalgae exploded, smothering and killing corals and other marine organisms. Thirty years later, Diadema populations are still very low, and macroalgae are the dominant organisms on many reefs. Parrotfish (pez de loro) is another important reef herbivore, however their populations are being wiped out by overfishing. So what will happen to reefs when there are no Diadema or parrotfish?
This is where my project comes in to action! The project consists of placing out settlement plates (Astroturf) at a reef in La Parguera, PR to collect Diadema settlers, aka “little urchin babies”. Diadema release their eggs and sperm in the water column, the fertilized egg matures into echinopluteus, a type of zooplankton. These echinopluteus are microscopic and live suspended in the water column. The echinopluteus spends about a month floating in the water, and if not eaten, matures into a small little urchin (0.4 millimeter in size), and settles on a reef of choice. I am collecting the small urchin babies that settle on the plates that I have fixed on lines at the shelf edge in La Parguera. I then transfer these little Diadema into tanks with seawater at the facilities of the Department of Marine Science, UPR-Mayagüez. I had three collection trips to the self-edge and right now about 50 Diadema have survived, are growing, and they are growing fast. The largest urchin is about 4 centimeters in size. However, it looks bigger because of its long spines, which can be 6 to 8 centimeters.
In February, I will be teaming up with scientists from NOAA and Sea Ventures to reintroduce the cultured Diadema on a reef that has recently been restored from a vessel grounding. When coral reefs are impacted by vessel groundings, there is significant damage to the reef structure and coral populations. Emergency restoration, through reattaching broken corals and placing cultured corals, can rebuild lost reef structure and can directly save some of the impacted corals. Full recovery of coral populations takes time since the coral recruitment and growth are slow. We hope placing the Diadema on the reef will help increase coral recruitment and survival rates, and enhance reef recovery by clearing substrate for coral recruitment and reducing competition with algae. As Ira Glass would say: “Please stay with us”.
