The ghost shrimp’s swelling population is a reminder of the many challenges and environmental costs of managing ecosystems for the benefit of any one species.
Pacific oysters, good. Ghost shrimp, bad.
It’s a skewed ecological equation that sounds frighteningly over-simplistic, and for good reason.
There is a renewed push to apply the dangerous neurotoxin imidacloprid onto areas of Willapa Bay and Grays Harbor oyster beds to kill burrowing shrimp. Lost in this proposal are the reasons why the shrimp’s ecologically important digging skills started posing problems for oyster farmers.
A look at some of the triggers for the shrimp’s swelling population offers a chilling reminder of the many challenges and environmental costs of managing ecosystems for the benefit of any one species.
Fed by both salty Pacific tides and freshwater rivers, many of the region’s shallow estuaries provide perfect natural breeding grounds for oysters, clams, Dungeness crab and, yes, burrowing shrimp.
Evidence suggests these ghost-shrimp populations have been increasing since the 1930s, when Pacific oysters became the dominant local oyster crop, replacing the area’s native, but smaller, Olympia oysters.
The growing demand for oysters encouraged farmers to raise their crop in single layers for quick harvesting. But that process prevented the oysters’ natural inclination to clump into protective reefs and left parts of the bay much more susceptible to intensive ghost-shrimp colonization.
Longtime observers point to evidence that dams limit the natural freshwater flooding of the estuaries, increasing water temperatures and salinity and helping to create conditions favorable to burrowing shrimp overgrowth.
For their part, the shrimp not only play an important role in aerating the mud flats and breaking down organic matter but serve as prey for Dungeness crabs, fish and migrating birds. And it’s likely the decrease in endangered salmon and green sturgeon, which prey on the shrimp, have also helped the shrimp to thrive.
Since the 1960s, the pesticide carbaryl has been used to kill burrowing shrimp. When carbaryl was outlawed in 2012, oyster farmers turned to imidacloprid.
Imidacloprid belongs to the neonicotinoid class of pesticides implicated in the worldwide decline of pollinators. Its use is largely banned in the European Union and is facing a proposed ban in Canada because of its severe impacts to aquatic species.
The Washington Department of Ecology has hosted two hearings on the imidacloprid spraying proposal, including one held earlier this month in Olympia at which I testified. It’s unsettling that even our state scientists, who are accepting comments on the plan through Nov. 1, admit there is much we don’t know about the pesticide’s risks. And what we do know is not reassuring.
The researchers’ assessment states that spraying imidacloprid on oyster beds has “immediate adverse, unavoidable impacts to juvenile worms, crustaceans, and shellfish to the areas treated … and the nearby areas covered by incoming tides …”
And the report acknowledges “significant uncertainty” about the pesticide’s cumulative impacts as well as potential harms to other marine animals.
What we do know is that invertebrates are very good at developing resistance to neonicotinoid pesticides like imidacloprid. And this proposal seeks to spray the pesticide at levels that will only kill 60 to 80 percent of the shrimp in a plot, a scheme that is tailor-made for the quick development of chemical resistance.
After a couple of years of spraying, shrimp that are resistant to imidacloprid will flourish, rendering the pesticide largely ineffective. And we’ll be back on the pesticide treadmill looking for the next toxic solution. Approving use of imidacloprid is an ill-advised Band-Aid that will provide temporary relief.
At worst it will wreak havoc on these ecosystems in ways that are difficult to predict.
And it’s troubling that the environmental-impact statement fails to explore the human-caused reasons for why burrowing shrimp are overgrowing in these regions in the first place.
Instead, we’re here once again focusing on finding a quick fix for the symptom when we should be working to find ecosystem-based solutions that benefit all of our best long-term environmental and economic interests, including those of oyster farmers.
But we can only find those answers if we’re willing to look.