Published in Pacifica Tribune March 8, 2020
Like New England’s lobsters, savory Dungeness crabs are San Francisco and the northwest’s iconic seafood. While fisheries around the world have declined from overexploitation, Dungeness crabs have been sustainable despite intensive harvesting over the past 40 years. Their resilience partly relies on mature females producing 1 to 2 million eggs each year. Thus, harvesting females commercially is illegal.
Unfortunately, few eggs survive to adulthood. Besides being preyed upon, early life stages (larvae) must survive being swept out to the open ocean and then return a few months later to shallow near-shore waters. The more larvae that survive that trip, the greater their abundance. But if the winds and currents prevent the larvae’s return, populations could crash as they did in the 1950s.
The successful return of Dungeness larvae largely depends on the strength and timing of upwelling currents. When eggs hatch, larvae rise to the surface and are then blown offshore. If larvae float into the California Current, they’re carried southward and further offshore. But below the California Current is the Undercurrent, transporting warmer waters northward. Northward currents also strengthen during winter. By migrating daily between contrasting surface and deeper waters, larvae minimize being swept too far away. Then beginning around April, a strengthening California Current creates upwelling currents that carry larvae back towards the coast while larvae remaining in the open ocean die.
Upwelling currents also promote plankton blooms by bringing essential nutrients back into sunlit surface waters. Upwelling enables the entire marine food web to flourish. Larvae that settle in regions bathed by upwelling water, benefit from 10 times more food than elsewhere. Upwelling also increases the abundance of sardines and anchovies, but that causes a problem for crab fishermen.
Humpback whales feeding on anchovies are attracted to Dungeness fishing grounds. Recovering from past exploitation, larger whale populations are more likely to encounter crab trap buoy lines and deadly whale entanglements increased. So commercial crab fishermen agreed to further restrict fishing season to minimize overlap with feeding whales. Promising technological solutions to eliminate buoy lines are a work in progress.
In 2015, beneficial upwelling also enabled a bloom in plankton species producing domoic acid. Passing up the food chain, high doses of domoic acid cause neurological damage to birds and mammals. Detecting high domoic acid levels in crabs, public health agencies shut down the 2015 Dungeness season until the danger passed. That was economically devastating for fishermen. Hoping to recoup their losses the Pacific Coast Federation of Fishermen’s Associations blamed climate change and sued 30 oil companies. But they are unlikely to win their lawsuit.
Outbreaks of domoic acid poisoning correlate with upwelling and natural ocean oscillations. The northward currents can bring additional domoic-acid-producing species into Dungeness habitat. Then with seasonal upwelling, their numbers explode. In 1961, a similar plankton bloom disoriented seabirds. Monterrey newspapers reported birds flying into buildings and people, inspiring Alfred Hitchcock to produce his iconic horror film “The Birds”.
Unfortunately, bad science also promotes media horror stories such as CNN’s headlines, “The Pacific Ocean is so Acidic that it's Dissolving Dungeness.” But in truth, ocean pH is far above 7.0; oceans are alkaline, not acidic.
Still NOAA’s West Coast Ocean Acidification program seeks worrisome examples of “acidification” and it was their researchers who prompted those horrific headlines. They found Dungeness larvae in off-shore waters (with a slightly higher pH) had smoother inner shells, versus larvae in near-shore waters (with a slightly lower pH) that had shells with patchy dissolution. The dissolution was invisible to the eye. Researchers had to remove the shells’ outer protective layer and examine the inner shell with scanning electron microscopes and various x-ray technologies to find microscopic “changes”. And despite a correlation with lower pH, the measured pH should not have caused any dissolution.
Dungeness larvae reaching near-shore waters are transported by the naturally low-pH upwelling currents. That upwelled water is derived from the Undercurrent, which is fed by waters originating in the deep Pacific Ocean. Those deep waters had not been exposed to our atmosphere for hundreds to thousands of years. Suggesting low-pH upwelled waters are worsened by “atmospheric carbon dioxide” was a false narrative. The lower pH and high nutrients are produced by hundreds of years of decaying organic matter.
When Dungeness larvae return to near-shore waters, they settle to the ocean floor and soon molt into their first juvenile shells. Larvae absorb minerals from their old shell to recycle into their new shell. That causes patches of dissolution. The researchers’ data from one near-shore location was discarded because pre-molt dissolution had clearly started as expected. Still and oddly, researchers blamed that observed pre-molt, but slightly less dissolution, on “ocean acidification” prompting endless media horror stories. What is never told is Dungeness larvae remaining offshore do not molt into juveniles, so would not be undergoing pre-molt dissolution. And despite their smoother shells, larvae remaining in offshore waters die.
Misleading science from researchers who are blinkered by their advocacy for an “ocean acidification crisis” is problematic. We need objective science, not “dissolving Dungeness” fear mongering.
Jim Steele is director emeritus of the Sierra Nevada Field Campus, SFSU and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism.