Humans have negatively impacted the world’s oceans for centuries, which becomes startlingly evident when studying marine life forms. You have probably seen this already in the form of sad sea turtle photos with plastic soda rings around their neck, or maybe seals getting caught in fishing nets. However, the large, more popular marine animals aren’t the only life forms affected by this human tragedy. In fact even the smallest, slowest sea crawlers have fallen victim to our trash- but the weirdest thing is, some organisms have learned to adapt to it!
Sea urchins, also called Lytechinus variegatus, are a type of echinoderm (a classification of marine invertebrates like sea stars and sea cucumbers) that dwell on the seafloor. Sea urchins are more stationary than seals and sea turtles, but this doesn’t mean they are any less affected by the debris. Instead of swimming into fishing nets like marine mammals do, sea urchins have adapted to utilize the marine debris on the seafloor as part of their covering behavior. Covering behavior is essentially employing random objects to cover the urchin’s body. This behavior is speculated to be a mechanism to camouflage and better escape from predators, or to offer protection against strong UV light. Typically, sea urchins cover themselves with natural material, such as shells, algae or rock, but with the increase in pollution, are shifting to use plastic, glass, and other debris. As featured in a volume of Marine Pollution Bulletin, Francisco Barros and his colleagues examined covering behavior to determine whether there was a sea urchin preference to utilize artificial debris instead of natural material.
To perform the experiment, one free diver searched for 20 isolated sea urchins, and for each organism, measured how large the sea urchin was and approximated the area covered in the debris. After collecting these measurements, the team then measured opacity, and calculated mass and width. They acknowledged that the marine debris was heavier, larger, and more transparent than natural material. After accumulating the data, the team used computer simulations to estimate the covering behavior of other sea urchins.
In the end, Barros and his team determined that sea urchins picked up more artificial debris than natural marine materials, which was a significant discovery and supported their original hypothesis. However, when considering this data, one has to consider the fact that all the artificial debris was larger than the natural material, as well as more transparent. So at this point, you may be thinking “Okay it’s sad, but why does this matter?” Because the trash picked up by sea urchins tends to be more transparent, this could actually negatively affect sea urchins in the long run. Why? For one, covering behavior is presumed to be used in efforts to protect against UV light, but transparent objects do very little to protect the sea urchin from light (see Figure 1). Additionally, if covering behavior is used to hide from predators, the artificial debris is next to pointless for the same reason, as both UV light and predators would be able to penetrate through the transparent objects with ease. These are both claims made rooted in assumptions, but because this phenomenon has such limited knowledge, there would have to be future tests to prove or disprove the negative effects of transparent trash in covering behavior. This research allows us to see the direct impact of human activities on the earth’s ecosystems, and will hopefully inspire future tests to further examine the modification of animal behavior due to pollution.
Barros, Francisco, et al. “Choosing Trash Instead of Nature: Sea Urchin Covering Behavior.” Marine Pollution Bulletin, Pergamon, 25 Apr. 2020, Choosing Trash Instead of Nature: Sea Urchin Covering Behavior
