As the seawater temperature rises, the nutritional value of giant kelp decreases.

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As a foundation species, the giant kelp (Macrocystis pyrifera) is essential for the shallow coastal ecosystems in which it grows. When kelp flourishes, so do communities that rely on fast-growing seeds for food and shelter.

Giant kelp has proven to be elastic against some stressors brought by (so far) Climate changeIt is an encouraging development for those interested in the ability of algae to maintain a herd of fish, invertebrates, mammals and birds that rely on algae to survive, such as intense storms and ocean heat waves.However, in a recent study published in the journal Oikos, A researcher at the University of California, Santa Barbara, Giant kelpThe ability to hit temperature can come at the expense of its nutritional value.

“It seems that the quality of nutrition, or the amount of nutrients in the kelp tissue, is changing,” said Heili Roman, the lead author of the study, a biogeochemist at the University of Nevada, Reno, who conducted the study as a doctoral degree. Said. A student in the Department of Ecology, Evolution and Marine Biology at the University of California, Santa Barbara. “We have found that these changes are associated with or correlate with changes in seawater temperature. From a big picture perspective, this is very important as many of them rely on kelp as their primary food source. . “

“This is one of the more hidden effects of ocean warming,” said Kyle Emery, co-author of the study and graduate researcher. “The kelp wasn’t lost in places where the temperature rose significantly, but it’s still nutritious and still remains, but it can’t perform the same function as when the temperature is low.”

These findings on the hidden effects of ocean warming on kelp are derived from long-term data collected at the UCSB Santa Barbara Coastal Long-Term Ecology Study (SBC-LTER) site. Kelp forest Located in the Santa Barbara Channel. Data collected over nearly 20 years have allowed researchers to track patterns of seasonally fluctuating nutrient content and identify key trends.

“In the Santa Barbara Channel, the temperature of seawater and the availability of nutrients are very closely related, which we have known for some time,” said Roman. In general, colder temperatures cause nutrient-rich water to rise from the depths, but warmer months are deficient in nutrients, especially nitrogen, in shallow waters and upper seas.

“Physiologically, kelp plants cannot store nitrogen for more than a few weeks, so whatever is happening around them in the water requires a constant supply of nitrogen to continue to grow and reproduce. So they will react very quickly, “she said.

Researchers who knew this pattern investigated how nutrient content works over the long term as seawater temperature rises. They did so by examining data from monthly primary productivity samplings in the SBCLTER waters.

“As part of that sampling, kelp blades are collected from these sites and returned to the lab before the carbon and nitrogen content is processed,” Emery explained.

According to the paper, in the 19 years covered by SBC LTER, the nitrogen content of giant kelp tissue decreased by 18% and the carbon content increased proportionally.

This apparent reduction in nutritional content is not a good omen for kelp consumers in and around the Santa Barbara Channel. Sea urchin Underwater abalone, intertidal beach hoppers and other invertebrates consume kelp debris that is washed ashore.

“As a result, sea urchins, for example, may go looking for more kelp, in certain places, potentially from kelp forests, if they are only reaping the reefs they are looking for. More food that could shift to sea urchin barren, “Roman said. Animals that eat kelp can consume more energy if they try to eat enough to meet their nutritional requirements.

Emery added that sea urchins have the ability to go looking for more food, but coastal consumers are sticking to what they get.

“If demand increases but kelp does not come in, whether it is undersupply or depopulation, it presents a rather difficult situation for them,” he said.

In both cases, the effects can spread to the rest of the food chain, the researchers said: undernutrition. kelp For example, beach hoppers are small, few, and can probably mean poor health. This reduces the food for the stag beetles that eat them. Underwater, low nutrition of sea urchins and abalone can mean low food for consumers such as fish, red shrimp, sea otters, and humans.

“Our results raise a lot of very interesting open questions and suggest many widespread implications,” Emery said.

After investigating the potential relationship between seawater temperature and nutritional content, researchers are considering expanding the spatial scale of their research.

“The next step is to think about what everything is doing to determine nutritional content, and then how we can predict it in the future,” Roman said.

Biodiversity is the key to the health of the kelp forest

For more information:
Heili E. Lowman et al, rising seawater temperature reduces the nutritional value of giant kelp, Oikos (2021). DOI: 10.1111 / oik.08619

Journal information:

Quote: The nutritional value of giant kelp decreases as the temperature of the sea rises (October 26, 2021). Obtained from on October 26, 2021

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As the seawater temperature rises, the nutritional value of giant kelp decreases.

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