Balance of nature: importance of ecosystems (Introduction)

by David Turell @, Wednesday, July 10, 2019, 18:09 (7 days ago) @ David Turell

Another marine system involving sea urchins described:

https://phys.org/news/2019-07-marine-scientists-important-overlooked-role.html

"Sea urchins have gotten a bad rap on the Pacific coast. The spiky sea creatures can mow down entire swaths of kelp forest, leaving behind rocky urchin barrens. 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.

***

"'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. Indeed, only one species, a type of brittle star, ate a significant amount of kelp in the absence of sea urchins.

"'Even then, the brittle stars used much more kelp when the urchins were present," added Yorke.

"Urchins excel in their role of processing kelp for other detritivores. They are remarkably messy eaters, scattering all sorts of bits and pieces as they chow down on giant kelp. What's more, sea urchins digest remarkably little of what they actually eat. Meanwhile, their guts contain a rich assortment of microbes, some of which can pull nitrogen from the seawater itself, enriching the urchin's waste. Some studies have shown that urchin feces can be more nutritious than fresh algae, said Yorke.

"'Essentially, they create a kelp smoothie for the reef," Miller said.

"Yorke agreed and stated that "without the urchins there, it's possible that this kelp would just get washed out of the kelp forest by the current and be unavailable altogether."

***

"'A lot of times urchins are portrayed as grazers," said Yorke, "but that's actually an uncommon condition. Most of the time the urchins are just sedentary detritivores that wait for leaf litter from the kelp to fall and drift past them. They capture this detritus and consume it.

"'Urchins switch from this sedentary behavior to active grazing if drift kelp becomes limited," she explained. This can happen for a number of reasons. If urchins become super-abundant there may not be enough drift kelp to sustain them. Alternatively, oceanographic conditions like El NiƱo can impact kelp productivity.

"In this way, urchins are more like grasshoppers. Under normal conditions, grasshoppers are a healthy part of their ecosystem. But in certain circumstances, some species will swarm, becoming a plague of locusts.

"'Urchins are generally cast as the villain in the kelp forest," said Miller, "but this study shows that they can play an important role as an intermediary in the food web."
"We should not go around and vilify or smash sea urchins before we understand their role in the ecosystem better," he added. "They're not necessarily always the bad guy they're made out to be.'"

Comment: More evidence that the diversity of life is the source of the ecosystems that provide the food energy to support life and these systems supported the long time it took for evolution to occur to this point.


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