As the global climate heats up, so do the ocean waters off Alaska, meaning big changes for marine ecosystems and bad news for some species. Scientists gathered in Anchorage last week for the Alaska Marine Science Symposium at the Hotel Captain Cook reviewed new research probing those changes and what may be ongoing shifts in the marine ecosystem. Here are some of their findings.
Arctic warming is looking like bad news for one of the region’s namesake species – Arctic cod.
The high-fat fish, eaten by seabirds, marine mammals, people and even other fish, is considered a keystone species and crucial to the Arctic ecosystem and its food web.
New research presented last week at the Alaska Marine Science Symposium shows how higher water temperatures harm Arctic cod eggs and larvae and favor lower-latitude, lower-fat fish that have been moving north: Pacific cod and walleye pollock.
The research is by Louise Copeman of Oregon State University and her partners at the National Oceanic and Atmospheric Administration. Their findings are from a program underway at the NOAA Alaska Fisheries Science Center laboratory in Newport, Oregon. Earlier work, which included the first successful spawn and hatch of captive Arctic cod, focused on growth rates of juvenile cod in different water temperatures.
The newer work focused on eggs and larvae, life stages that are generally more sensitive, said Ben Laurel of NOAA, one of the scientists involved in the project. By focusing on eggs and larvae, the scientists were able to examine what could happen in future Arctic spring seasons, he said in an email. Their work on juvenile fish was on summer conditions.
“The questions are essentially the same — how will warming in the Arctic determine the winners and losers of ecologically important fish species?” he said.
The scientists exposed multiple batches of eggs from each species to different temperatures, including those expected under future climate scenarios, Laurel said in an email.
They found that hatch success for Arctic and saffron cod occurred within a relatively narrow water-temperature range – from minus 1 degrees Celsius to 5 degrees Celsius (30 to 41 degrees Fahrenheit), the scientists found. Above freezing, at 3.5 degrees Celsius (38.3 degrees Fahrenheit), hatch success for those two species dropped off noticeably, they found.
But for Pacific cod and pollock — considered “boreal” fish species — there was hatch success at much higher temperatures. For Pacific cod, the upper limit was 8 degrees Celsius (46 degrees Fahrenheit) and for pollock it was 12 degrees Celsius (54 degrees Fahrenheit), according to the results.
Egg incubation for the Arctic species took about twice as long as for the boreal species, according to the results, and the emerging Arctic larvae were 30 percent to 40 percent larger than the boreal larvae. Arctic cod in particular had much higher fat contents in their eggs than the boreal species — about triple the levels in Pacific cod eggs and more than eight times the levels in pollock eggs, according to the results.
It appears that Arctic cod have “unique cold-water adaptations but are much more temperature sensitive to warming than the other species,” Laurel said.
Other recent research has shown how juvenile Arctic cod thrive under the sea ice — leading to concerns about the habitat’s vulnerability at a time when summer and fall sea ice is diminishing.
Bering Sea as warming hot spot
Farther south, the Bering Sea has emerged as a hot spot for warming-water studies — almost literally. Sea-surface temperatures in the Bering reached 14 degrees Celsius last summer (57 degrees Fahrenheit) and were generally 3 degrees Celsius (5 degrees Fahrenheit) warmer than normal, scientists reported.
Warmer conditions that bring earlier sea-ice retreat have some worrying implications for birds, according to one study presented at the symposium.
Forty years of bird population surveys in the southeastern Bering Sea found that in years when ice melts out early, bird diversity suffers, according to a study presented by Martin Renner, a Homer-based biologist.
In general, species with low numbers in normal years are even more scarce in years when ice melted early, Renner said. One example, according to his findings, is the short-tailed albatross, a critically endangered bird that has begun recovering from the brink of extinction and that travels to Alaska waters from breeding sites in Japan.
Lack of rare birds such as short-tailed albatrosses in early-melt years does not mean they are gone from Alaska, Renner said. But it indicates that the southeastern Bering Sea is not attractive to them in those years, he said.
“It looks like they might have to move,” he said.
High-fat euphausiids and copepods — tiny creatures in the food web — were also much less abundant in the years of early ice retreat, the research found. If early melt becomes the norm, that could have some widespread effects, he said.
“It’s looking bad for birds, and it’s looking really bad for the fisheries as well,” he said.
Warming conditions are potentially more hospitable to invasives, and vessel traffic — which may increase as sea ice diminishes — can be a way of introducing non-native species, according to another presentation.
With that threat in mind, a multiagency project is underway to assess and rank invasive species and their risks to the Bering Sea ecosystem, and preliminary results were presented by Jesika Reimer of the University of Alaska Anchorage,
“Of all the species that could potentially knock on the door, who is going to get here?” Reimer said in her presentation.
So far, the team — with members from the U.S. Fish and Wildlife Service and the U.S. Geological Survey as well as UAA — has evaluated 26 possible invasive species, including some that are already in the Bering Sea.
So far, she said, the invasive species that ranks as the most dangerous to the Bering Sea system is the European green crab.
The crab has not been spotted in Alaska waters but has been seen as far north as British Columbia, according to the Alaska Department of Fish and Game.
Another candidate on the risk list is the sea grape, a sea squirt that looks deceptively “like a cute little gummy bear,” Reimer said. It prefers temperatures in the range of 10 to 24 degrees Celsius — and a warmer Bering Sea might become comfortable territory for it.
In all, there are about 160 potential invasives that could move into the Bering Sea, Reimer said.
Warm conditions, algal blooms and chronic exposure
Warmer northern waters are stimulating more algal blooms, some of them emitting toxins that have proved harmful or even deadly to mammals and birds. A study released a year ago showed how algal toxins have been documented for the first time in marine mammals in Alaska’s Arctic waters.
Algal toxins are leading suspects in the deaths of dozens of large whales found floating in the Gulf of Alaska in 2015 and 2016, and they have harmed other marine mammals, including California sea lions seen on beaches in the grip of seizures.
But what happens when animals — or people with shellfish-heavy diets — ingest very low levels of algal toxins over long periods?
There may be a glimmer of hope about potential resilience to the toxins, according to a new study by some of the same scientists that was presented at the symposium by Kathi Lefebvre of NOAA’s Northwest Fisheries Science Center.
A first-of-its-kind experiment found that laboratory mice could recover from the ill effects of harmful algal toxins — as long as exposures were at very low levels.
The study was carried out by members of the Wildlife Algal-Toxin Research and Response Network, a multiagency group that has been monitoring effects of algal toxins in animals from the Arctic Ocean off northern Alaska to the Pacific waters off southern California.
It built off previous work by Peter Cook of Emory University that explored memory loss among sea lions poisoned by algal toxins. He examined food-finding behavior of rescued sea lions being rehabilitated in California.
The experiment on mice used regular and repeated injections of low levels of algal toxins, so low that the test subjects showed “no outward signs of toxicity” — a contrast to the acute exposures that sent marine mammals into seizures or paralysis and sometimes death, Lefebvre said.
The mouse study used a maze test to evaluate the animals’ ability to navigate and memorize exit routes.
Chronic exposure to low levels of toxins did hamper that ability, Lefebvre said.
“The exposed mice just did not learn,” she said.
But after a nine-week recovery period, the mice bounced back and were able to work their way through the maze as well as mice that had never been exposed, she said. There was no sign of brain-cell death for the exposed mice, either, she said.
“So this is not a permanent issue,” she said. While “clinical” levels of toxin exposure cause seizures, brain damage and sometimes death, the damages from sub-clinical exposures are “reversible as long as you don’t slip into that clinical seizure effect,” she said.
Still, even temporary toxin-caused impairments could make marine mammals vulnerable, Lefebvre noted. Questions remain about possibly compromised navigational skills, lowered defenses against predators and reduced ability to avoid collisions with vessels — all issues that would have to be considered in the future.