Urchins excel in their role of processing kelp for other detritivores. “Even then, the brittle stars used much more kelp when the urchins were present,” added Yorke. Indeed, only one species, a type of brittle star, ate a significant amount of kelp in the absence of sea urchins. “We found that a whole host of detritivores can take advantage of kelp as long as urchins are there to process it for them, whereas otherwise they can’t,” said Miller. After 28 days, the researchers compared the isotope measurements for the specimens after the experiment to baselines they had established beforehand. To label the kelp, the team spiked it with rare forms of carbon and nitrogen by letting the algae photosynthesize in seawater enriched with these isotopes for three days, allowing them to trace the extent to which the tank residents ate the kelp. To test their hypothesis, Yorke set up several tanks with a number of detritivore from several species, along with some labeled kelp. The activity of sloppy sea urchins offered a promising alternative pathway for funneling nutrients from kelp to the ecosystem’s detritivore. But the team’s previous work found that kelp didn’t appear to be nourishing the filter feeders in this way. Scientists have hypothesized that kelp sheds small particles that could be a food source. “We know that kelp affects animals by providing habitat for fish and other species, but does it actually feed any of these animals?” said Bob Miller, a research biologist at the Marine Science Institute and one of the paper's coauthors. Yorke and her colleagues were curious whether anything might be able to retain this food source within the kelp forest. Kelp is also rather unpalatable compared to single-celled phytoplankton.ĭespite its incredible growth rate and availability, giant kelp is not the first choice for many animals, as it is tough to digest. But a significant amount of this material gets transported away from the ecosystem, washing up on beaches, getting swept out to the open ocean or drifting into the deep sea. Giant kelp is highly productive, growing up to 18 inches per day under ideal conditions. Nevertheless, urchins may be crucial to the health of the kelp forest ecosystem. Some groups have even taken to indiscriminately smashing urchins to stem this scourge. Overhunting of the sea otter, one of urchins’ most significant predators, has allowed some urchin populations to clear cut vast tracts of kelp forest, drastically reducing the productivity and biodiversity of sites they’ve munched through. Urchins can have an outsized effect on kelp forests, especially when their predators aren’t around to keep their population in check, Yorke explained. The paper, published in the Proceedings of the Royal Society B, is the first to look at sea urchins’ role as shredders in the kelp forest ecosystem. An article in the New York Times went so far as to call them “cockroaches of the ocean.” But new research suggests that urchins play a more complex role in their ecosystems than previously believed.Ī team led by Christie Yorke, a postdoctoral scholar at UC Santa Barbara’s Marine Science Institute, studied how urchins might function to break up tough kelp into more manageable pieces that can feed other scavengers, also known as detritivores, living on the kelp forest floor. The spiky sea creatures can mow down entire swaths of kelp forest, leaving behind rocky urchin barrens. Sea urchins have gotten a bad rap on the Pacific coast.
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