When we think about the coral reef conservation efforts, hardly, if ever, does the humble sea cucumber cross our minds. However, it turns out that these slimy, faceless creatures—or rather their waste—play an important role in maintaining the health and biogeochemical cycles of the reef.
Scientists believe that by consuming sediment and then excreting it as waste, sea cucumbers aerate the sediment which makes it a healthier place for other sea creatures to live, such as small crabs and mollusks. The process also releases nitrogen that is trapped within the sediment, which is helpful for corals and algae that rely on this element.
Sea cucumber excrement also helps protect coral reefs against ocean acidification, one of the negative side effects of climate change. Because of the increased acidity of the ocean, calcium carbonate, which is what coral skeletons are made of, is becoming scarce. Sea cucumber excrement not only releases nitrogen but also increases the availability of calcium carbonate in their surrounding environment.
So, we know that sea cucumber waste has important functions for coral reef health, but previously, scientists have struggled with assessing just how significant sea cucumber excrement is because it’s quite difficult to assess how big the sea cucumber population is in a given area.
Fortunately, an Australian research team from Macquarie University was able to use drone surveys, satellite imagery, and observations of individual sea cucumbers to come to a reasonable estimate of the number of sea cucumbers in the Heron Island Reef, and of course, how much poop they generate, giving us a more accurate understanding of how beneficial these little animals actually are.
Through these methods, the team was able to estimate that there were more than three million sea cucumbers on the specific reef flats. They were also able to determine that, on average, each sea cucumber produces approximately 38 grams of waste in 24 hours. This means that on a single reef, sea cucumbers produce more than the weight of five Eiffel Towers in excrement each year.
Because we now know the extent of the vital role sea cucumbers play in the health of marine ecosystems, we can put systems in place to ensure that they are not over-harvested. Over 70 countries currently harvest sea cucumbers, but thanks to drone surveillance techniques like the ones employed in this study, it will be easier to keep tabs on their numbers and assess their population numbers as well as those of other exploited shallow-water reef species.