Kelp continues steady decline in Puget Sound
Scientists are trying to learn how to restore Puget Sound’s diminishing kelp forests in an effort to stave off habitat loss for rockfish and other threatened species. We report on new findings presented at the 2018 Salish Sea Ecosystem Conference in Seattle.
Ever alert to predators, young rockfish swim warily among the stems of bull kelp that reach up from the bottom of Puget Sound. Within the kelp forest lurk many larger fish, such as lingcod, which would quickly gobble up the 2-inch juveniles if given a chance.
Kelp forests, which are becoming rare in Central and South Puget Sound, are not necessarily secure refuges for the tiny rockfish, which feature spiny dorsal fins like their much larger parents. Still, the vegetation provides a safer cover than open water. It also offers the growing fish a rich smorgasbord of food — phytoplankton, krill, copepods, invertebrate eggs and other tiny bite-sized creatures.
“Kelp are the carbon factories of the estuaries,” said Brian Allen, an ecologist with Puget Sound Restoration Fund who is studying methods to encourage isolated kelp to grow and multiply into self-sustaining populations.
Kelp take up nutrients and minerals coming down the rivers, Allen said. With the help of sunlight, kelp can grow into massive vegetative structures, feeding a multitude of species from bacteria to hefty grazers, such as sea urchins. Tiny crustaceans, including buglike amphipods and isopods, grow on the kelp and become prey for many other species, including juvenile salmon and rockfish.
This predator-prey dynamic, played out thousands of times, makes a kelp forest one of the most productive habitats on the planet. That’s why kelp is known as a “foundational species.” It’s also the reason why Puget Sound researchers are growing more concerned about the ongoing disappearance of kelp’s most familiar type, the bull kelp, whose broad green leaves float and sway in the water column near the shore.
“People who grew up in the ’80s remember swimming out to kelp beds off Restoration Point (Bainbridge Island) or off Jefferson Head (near Kingston),” Allen said, noting that kelp beds in those areas are now gone.
Bull kelp disappearing
Based on the observations of boaters and shoreline residents, bull kelp (Nereocystis luetkeana) has disappeared from many locations in Central and South Puget Sound, where it once grew in large patches. The total extent of the loss has not been estimated, because most of the lost patches were never measured for size. But the loss of kelp habitat has been linked to the decline of rockfish and many other species.
For about eight years, Allen has been keeping an eye on a kelp bed just outside Bainbridge Island’s Eagle Harbor. “It has been in steady decline,” he said, “and for the last couple of years there is nothing showing on the surface.”
Allen’s current research, which he presented at April’s Salish Sea Ecosystem Conference, involves identifying enhancement techniques to restore lost kelp beds. It is easy enough to plant kelp and get it growing, he said, but it is more difficult to find ways to sustain and expand kelp beds without ongoing human intervention.
Bull kelp, which resembles long whips with bulbs on the end, is an “annual,” meaning it generally starts from scratch every year. Kelp goes through two stages of life. Fully-grown kelp puts out an enormous number of microscopic spores, each containing a single set of chromosomes — as opposed to two sets of chromosomes found in adults.
If they survive, the spores will settle on the bottom and grow into microscopic gametophytes. Each gametophyte is either a male or a female, still bearing just one set of chromosomes. The male gametophytes produce sperm and the females produce eggs. Pheromones released by females trigger the release of the sperm, which swim over and fertilize eggs on the female gametophytes.
“It is a significant gauntlet they have to run, but they are prolific,” Allen noted.
After fertilization, the egg begins a rapid growth into a full-size kelp, sometimes gaining more than 2 inches per day. From a microscopic organism in the early spring, single bull kelp can grow to 30 or 40 feet tall by midsummer. The kelp uses a holdfast to latch onto a rock or other hard material on the bottom, while gas-filled bulbs keep the upper part afloat. The long stem is called a stipe, and leaflike appendages are known as blades.
Stipe growth is rapid at first, but when the bulb on the end reaches the surface, growth switches to the blades. Boosted by extra sunlight, the blades grow to form a canopy, creating an unsurpassed level of productivity. The ends of the blades continuously slough off, leaving room for more growth and more productivity.
Because bull kelp does not stick around from year to year, changing conditions can lead to success or failure for a single kelp or for an entire kelp forest. For kelp to survive, habitat conditions must be suitable, not only for the full-size kelp but also for the tiny and poorly understood gametophytes.
“I think about the interactions and relationships with habitats and species assemblages,” Allen said. “Populations wax and wane in abundance. Competition and predation affect populations and their distribution.”
Allen entered the world of kelp through the study of sea urchins and abalone, which live in the kelp forests. In Washington, he conducted research at the University of Washington’s Friday Harbor Laboratories in the San Juan Islands.
“I spent years in Friday Harbor studying sea urchins,” he said. “Kelp has been a constant presence, but I haven’t been thinking of it as an imperiled habitat form until recently. I became interested in kelp because of the special things that we know kelp do in the estuary.”
Other researchers studying kelp on the Washington Coast and Strait of Juan de Fuca have reported generally stable populations of bull kelp mixed with another large species called giant kelp. Some declines of both species have been observed in the eastern Strait near Port Townsend.
Potential factors for declines
Warmer temperatures during cyclic periods, such as El Niño, seem to reduce kelp abundance on the coast, but the kelp tend to rebound when cooler temperatures return, according to a recent study.
In other kelp studies, temperature has been found to be a key factor in spore production and survival — a potential bottleneck for the population, which could be increasingly threatened by climate change.
Other factors that might play a role in the long-term survival of kelp forests include:
While some researchers continue to examine those and other potential problems, Allen says he would rather grow bull kelp to see if he can establish a population and coax it to grow on its own. If successful, he will know what the kelp can and cannot tolerate. After all, the reasons that kelp disappeared in the past may or may not be the reasons for the present declines.
“If I were to hazard a guess, I would say it is a multitude of things working in concert,” Allen said.
His current experiments involve out-planting kelp in its various life stages and observing changes during the complex reproductive phase, leading to a new generation of kelp emerging from the bottom of Puget Sound and growing toward the surface.
“The two questions we were asking is which life history stage will produce the best effects, and when is the best time to put them out in the world,” he said.
It turns out that planting in January is soon enough to watch new annuals spring up in late February or early March. Researchers have long suspected that changes in light levels trigger the growth of young kelp. After much observation, Allen suspects that the shift in low tides from nighttime to daytime, which occurs in February, may be the answer.
Allen is still experimenting with planting methods that could be scaled up to a large area, as he begins to consider how he might enhance the substrate to help the young kelp overcome their problems. A likely spot for further experiments are places where kelp has grown before, such as Point Jefferson, he said.
“Is there something in the substrate that has fundamentally changed over time?” he asked. “We could enhance the substrate by getting basalt cobbles (for the kelp to hold onto). We could use different treatments in different sections of the bottom.”
Another big question involves the amount of kelp needed to create a sustainable population. If one introduces 100 kelp outplants, 99 of them might get eaten, Allen said, but introducing 1,000 could produce a different long-term result.
Importance as habitat
Restoring bull kelp could become a major habitat objective to save rockfish from extinction, in the same way that eelgrass restoration is considered important to restoring salmon populations and the herring they prey upon. The 2005 listing of Puget Sound Chinook as a threatened species brought increasing attention to eelgrass, which lives in shallow, sandy substrate.
Kelp, which prefers rocky bottoms, supports not only rockfish but also juvenile salmon and herring as well as many other species, according to studies. Currently, yelloweye rockfish and bocaccio in Puget Sound are listed as “threatened” under the Endangered Species, Act but other species of rockfish also are a concern.
Rockfish are long-lived and slow to reproduce. Experts say it will take considerable time for their recovery, which is why restoring kelp habitat has been declared a high priority. The federal recovery plan, approved in October, says the decline of rockfish may be linked to the decline of kelp beds.
“Given the importance of kelp and the nearshore to juvenile rockfish, we have identified research and conservation of these areas,” the plan states, going on to stress the need to understand where and why kelp has disappeared and to begin prioritizing restoration actions.