The importance of having urchins.

By Alizee Zimmermann, Turks & Caicos Reef Fund

With flickers of iridescent blue, elegant spines of obsidian black, five self-sharpening teeth (yes, you did read that right), and an ample appetite, the long-spined sea urchin (Diadema antillarum) might just be the most interesting creature you didn’t know would fascinate you.

Long-spited sea urchins take their natural place on the seabed.

A deep dive into the world of echinoderms (urchins and sea stars) will send the imaginative mind reeling from images of teeth with individual jaws, limbs that can regenerate whole bodies, and painful pricks on unsuspecting feet when exploring rocky shores and surf zones.  Aristotle’s Lantern (the urchin’s mouth) alone can be a little nightmarish. Truth be told though, the real nightmare would be a reef without them. 

You see, these sunlight-shy herbivores love to roam at night, “grazing the lawns” of an underwater world. Have you ever seen those halos that form around patch reefs along the banks or around coral bommies on your favourite dive sites? Those are the markings of active herbivory. Somewhat territorial and although hungry, not mindless eating-machines, the distance of their nightly travels and the vigor of their appetites can be discerned via these aquatic crop circles. 

A keystone species on our reefs, these surprisingly active “spikey boys” keep substrate, coral skeletons, and rocks clean of algae, a must to create an attractive spot for coral larvae to settle on. Baby corals can travel through the currents for weeks at a time, looking for that perfect spot to land, at which point they become “settlers.” A clean surface without algae is top of the list when perusing real estate options! 

In the mid 1980s there was a massive die-off of D. antillarum throughout the region, covering an area of approximately 3.5 million km² . This loss remains one of the most widespread invertebrate mortality events ever recorded. Over a 13-month period, more than 93% of the population perished.  Beginning in Panama (with unknown origins), the die-off then extended around the Caribbean, Florida, the Flower Garden Banks, and Bermuda. 

A recently dead long-spined sea urchin, notice that the spines have dropped off.

Nearly four decades later, another mortality event is threatening the still-recovering Atlantic and Caribbean populations. According to the Atlantic and Gulf Rapid Reef Assessment (AGRRA) program, “While we do not know what is causing these dispersed die-offs, the speed at which large numbers of sick urchins are now dying on affected reefs resembles the mass mortality event of four decades ago. We worry that a real crisis is developing in the Caribbean, where stony coral tissue loss disease (SCTLD) has already caused widespread coral losses affecting about 34 coral species in 20 countries/territories.” Although regional reports of urchin die-offs seem to have stopped, we have no way of knowing if this current mortality event is over yet. 

Comparing the 1983–84 and 2022 mass mortality events we can see differences in where each began (Panama versus U.S. Virgin Islands) as well as in their primary dispersal mechanisms. The 1980s event spread from Panama by surface currents eventually to virtually everywhere to its north and east in the Greater Caribbean while the 2022 event has greater evidence of possible anthropogenic dispersal, given the scattered new geographic locations that popped up during this past spring.

Another difference is that only Diadema were affected in the 1980s, whereas individuals of other urchin species have also very occasionally died this year, however, this has occurred exceedingly rarely (<1% that we know of) at the same time and place as Diadema. 

With the widespread effects of SCTLD across our reefs, the loss of our urchins would be a huge hurdle and a devastating blow to the hope for recovery. The takeaway from this? Everything is connected and our impact upon the environment as a species is increasingly destructive. 

** WE INTERRUPT THIS ARTICLE FOR A SHAMELESS PLUG ** We Need To Do Better. We Need To Reduce The Pollutants That Are Resulting In The Loss Of So Many Of Our Reef’s Creatures. Everything Happening In The Ocean Is A Direct Result Of Our Collective Actions On Land. Please Support Environmentally Conscious Products, Reconsider Whether You Really NEED That, and Make Choices With The Planet In Mind!!! **

The Atlantic and Gulf Rapid Reef Assessment team have stepped up again and created the Diadema Response Network (DRN) (https://www.agrra.org/sea-urchin-die-off/). Here you can find up-to-date information on what is known, as well as an interactive GIS map of where reports have been submitted. It shows red for those with reported deaths and green for those reporting healthy urchin populations. Submitting reports, especially with photos, to the DRN is highly encouraged. Remember, reports of healthy urchins are just as important for the overall picture as reports of mortality. 

Here in the Turks & Caicos we have been lucky enough so far to have escaped this die-off, but our oceans are connected, and a proactive approach is needed if we are to better prepare ourselves for the possibility of a local die-off. For this, the Turks & Caicos Reef Fund (TCRF) has applied for and been granted a scientific research permit to collect healthy urchins for gene-banking in case of the mortality event’s arrival to the country. TCRF is working to make a holding area for these urchins with consul from around the region and Florida to help create the right environment to keep these animals safe.

This less-than-one-centimeter coral recruit needs a clean surface to settle — created by herbivores such as sea urchins.

In the meantime, TCRF is actively participating in the regional effort to understand what is happening to our beloved turf munchers through both biological and abiotic sampling for Cornell University. Several urchins were collected from pre-determined sites, dissected, and preserved in a fixative before being sent off for microbial analysis at Cornell. The results of these efforts are currently under peer review.

We are working together with the Department of Environment and Coastal Resources (DECR) on a response plan for what happens if/when it arrives to the Turks & Caicos Islands. This involves collecting baseline data on the population densities around the Islands, the capacity for which has recently been increased through survey protocol and identification training conducted with DECR staff. Several days of joint surveys have been conducted to monitor for urchin health and get baseline information on the current Diadema population. We are thankful for the collaborative efforts and hope to continue working with the DECR on this project. 

One thing we’ve learned through urchin husbandry over these past few months at our South Bank Marina facility is that these Spikey Boys have serious personalities. They bully each other when bored or hungry, need a lot of personal space when there’s not a ripping current, and will race each other around the aquarium glass at night for what seems to be no other reason than a need to expel energy or interact. Anyway, philosophical musings aside, I hope that you have a new appreciation for the importance of having urchins.

Please contact al****@tc****.org and en*********@go*.tc to report urchin sightings. Consider donating to our Diadema preservation efforts by visiting our website https://www.tcreef.org/donate.