Keywords: Climate change, Species and food webs, Algae, Nearshore habitat, Kelp, Salish Sea Currents magazine

Identifying kelp stocks that are tolerant of warmer waters could help the Salish Sea’s iconic underwater forests survive climate change.

Kelp forests, the dense stands of seaweed that provide food and habitat for hundreds of marine species, are in trouble around the world. Kelp forests off the coasts of Australia and California have been especially hard hit, but there’s also increasing evidence that kelp beds are shrinking or disappearing altogether from many spots in the Salish Sea.

Many of these declines have been linked to warming waters. Kelp species prefer cool temperatures, and researchers are worried that the losses could accelerate in the coming years as climate change continues.

One possible solution is to use kelp stocks that can thrive in warmer waters to augment or rebuild struggling kelp forests. “They've been doing things like this with land plants for a long time,” says Sherryl Bisgrove, a plant biologist at Simon Fraser University in Burnaby, British Columbia. “It's really a new strategy in the ocean.”

Still, it’s not unheard of. Scientists have begun transplanting corals or manipulating the algae that live inside them to help coral reefs survive warming waters. Bisgrove’s idea is to establish a bio-bank that would preserve kelp propagules from different locations and with different characteristics, much like a seed bank for land plants.

A kelp bio-bank might be useful not just for responding to climate change, but also to help restore beds that are wiped out due more localized disasters, like an oil spill, Bisgrove says. In that case, restorationists might be able to replant beds with previously collected propagules from local stocks.

Bisgrove is beginning to explore government or other institutional sources of long-term support for such a project. She’s also investigating how to keep kelp propagules viable for long periods. It might be best to store them under cryogenic conditions, like human eggs or sperm in a sperm bank. Or, it might be possible to leverage kelp’s own biology, since the seaweed overwinters in a microscopic, dormant form.

A sorus patch in a blade of kelp (left) and spores at 100x magnification (right). Photo: Brian Allen/PSRF

A sorus patch cleaves from a blade of kelp before releasing spores (left).  Spores at 100x magnification (right). Photo: Brian Allen/PSRF

Then there’s the question of identifying warm-tolerant kelp stocks. Bisgrove and Braeden Schiltroth, a graduate student in her lab, have been analyzing the biology of bull kelp (Nereocystis luetkeana) collected from a site near Stanley Park in Vancouver and another site on the outer coast of Vancouver Island, near Victoria.

On the outer coast, water temperatures are relatively cool. Near Vancouver, the water is warmer.  “In the central Strait of Georgia, the temperatures are approaching those that caused some of the [kelp] die-off in California,” Bisgrove says. Yet stands of bull kelp, the main component of kelp forests in inland waters of the Salish Sea, remain abundant and apparently healthy in the area.

That’s a promising sign that the central Strait of Georgia bull kelp stocks might be adapted for living in warm waters – but it’s circumstantial evidence, Bisgrove cautions. The seaweeds might be thriving because they’re adapted to other local conditions, not (or at least not only) the water temperature. “We can't necessarily assume that if we transplant them to the outer coast and the outer coast warms that they'll do equally well there,” Bisgrove says.

For a more definitive picture of temperature tolerance, Bisgrove and her team are collecting spores – reproductive structures that form on the leaf-like fronds of kelp from late spring through fall – and incubating them at different water temperatures in the lab.

Spores from both sites die when placed in 20 °C (68 °F) water, the researchers have found. At 17 °C (63 °F), most of the Stanley Park spores do just fine, and some Victoria spores make it – although a lot fewer.

At 17 °C, the Stanley Park spores are also better able to manage reactive oxygen species – byproducts of cellular processes that can damage cells – compared to those collected from Victoria. Future experiments will look at the spores’ ability to produce compounds that protect proteins from damage at high temperatures.

On the other hand, preliminary data also suggest that kelp from the Stanley Park site, which is exposed to the highest water temperatures during prime spore-making summer months – produces fewer spores over the course of the whole year than the Victoria plants. But this may not, in the end, affect the size of the population as a whole, Bisgrove says. “To get a really good picture of it is going to take more years” of data, she says.

About the author: Sarah DeWeerdt is a Seattle-based freelance science writer specializing in biology, medicine, and the environment. Her work has appeared in publications including Nature, Conservation, and Nautilus.