The nutritional quality, or the amount of nutrients in the kelp tissue seems to be changing. From a big-picture standpoint, that's pretty important because there are a lot of things that rely on kelp as the primary food source. — Heili Lowman, a biogeochemist with the University of Nevada, Reno
The nutritional quality, or the amount of nutrients in the kelp tissue seems to be changing. From a big-picture standpoint, that's pretty important because there are a lot of things that rely on kelp as the primary food source. — Heili Lowman, a biogeochemist with the University of Nevada, Reno

We haven't necessarily lost kelp in places that have had these big temperature increases, but the kelp there has declined in terms of its nutritional content. So although it's still there, it's not able to provide the same function as when temperatures are lower. — graduate student researcher Kyle Emery
We haven't necessarily lost kelp in places that have had these big temperature increases, but the kelp there has declined in terms of its nutritional content. So although it's still there, it's not able to provide the same function as when temperatures are lower. — graduate student researcher Kyle Emery

The nutritional value of giant kelp decreases as sea temperatures increase
As a foundational species, giant kelp (Macrocystis pyrifera) is vital to the ecosystem of the temperate, shallow, nearshore waters where it grows. When the kelp flourishes, so do the communities that rely on the fast-growing species for food and shelter.

Giant kelp has proven resilient (so far) to some stressors brought on by climate change, including severe storms and ocean heatwaves -- an encouraging development for those interested in the alga's ability to maintain the legions of fish, invertebrates, mammals and birds that depend on it for their survival. But in a recent study published in the journal Oikos, UC Santa Barbara researchers reveal that giant kelp's ability to take a temperature hit may come at the cost of its nutritional value.

"The nutritional quality, or the amount of nutrients in the kelp tissue seems to be changing," said the study's lead author Heili Lowman, a biogeochemist with the University of Nevada, Reno, who conducted this research as a Ph.D. student in the Department of Ecology, Evolution and Marine Biology at UC Santa Barbara. "We found that those changes were associated or correlated with changing seawater temperatures. From a big-picture standpoint, that's pretty important because there are a lot of things that rely on kelp as the primary food source."

"I guess you could call it one of the more hidden effects of ocean warming," said study co-author and graduate student researcher Kyle Emery. "We haven't necessarily lost kelp in places that have had these big temperature increases, but the kelp there has declined in terms of its nutritional content. So although it's still there, it's not able to provide the same function as when temperatures are lower."


... "Physiologically, kelp plants can't store nitrogen for longer than a couple weeks, so whatever's happening around them in the water they're going to respond to very quickly because they need a constant supply of nitrogen to grow, and to continue to reproduce," she said.

... Over the 19-year period covered by the SBC LTER, according to the paper, nitrogen content of the giant kelp tissue declined by 18%, with a proportional increase in carbon content, according to the paper.

This apparent decline in nutritional content does not bode well for the consumers of kelp in and around the Santa Barbara Channel, which include sea urchins and abalone in the water, and intertidal beach hoppers and other invertebrates that consume the kelp wrack that washes up on the shore.

"As a result, urchins, for example, might go in search of a lot more kelp and that could cause a shift in certain places, potentially from a kelp forest to an urchin barren, if they're just mowing down the reef looking for more food," Lowman said. Animals that feed on kelp might also expend more energy trying to eat enough to fulfill their nutritional requirements.
Read the full article: https://www.sciencedaily.com/releases/2021/10/211026153343.htm