The Washington State Department of Ecology (DOE) along with groups like Washington Audubon armed with incomplete and misleading science will be responsible for the decrease of important estuary species by stopping the control of the invasive burrowing shrimp.
This decision by DOE now prevents the only workable type of control (chemical) of expanding ghost shrimp populations known to be effective. It is felt all conceivable mechanical, biological and chemical methods, which might be utilized to control burrowing shrimp numbers, have been tried without success during the past half century. The attempt has been to maintain those special productive portions of the intertidal to keep them from being converted into biological wastelands by ghost shrimp. These key intertidal areas within given elevations and salinity ranges, if free of burrowing shrimp allow rich benthic algal and invertebrate populations to exist. These also are privately owned shellfish growing areas and are in stark contrast to thousands of similar public intertidal acreages which are now unproductive sandy soupy wastelands made so by ghost shrimp.
DOE knows not what they do — unless their real objective is to drive oyster farming from the marine intertidal in disregard of the consequences such as decreasing the benthic (bottom) fauna and flora and imposing a large hit to the economic impact of Pacific County.
More than 60 years ago, state and federal fisheries biologists, along with shellfish growers, recognized that the destructive bioturbation and hydration by burrowing shrimp could displace nearly all other benthic floral and faunal species that normally occupy or utilize those biologically rich intertidal areas. They found: Buried dead native clams; that young crabs were absent; no shorebirds were feeding; no eelgrass remained; and only ghost shrimp were present deep in the soupy fine sand they create to burrow through. These biologists and those whose who knew the estuary understood the natural resource was being negatively modified by the ghost shrimp.
This seems a fact which escapes those in charge today, even though there are thousands of biologically barren public intertidal acres to serve as examples.
To correct this burrowing shrimp takeover of the intertidal, and after extensive testing of various means to reduce burrowing shrimp numbers in the 1960s, those responsible determined that a pesticide (carbaryl) was the best solution with the lightest and quickest touch to slow down the intertidal takeover by burrowing shrimp. It left the critical sedimentary structure in place and was gone within a few hours or at most days. Return of the normal benthic animals and plants was rapid and within a short time (a few weeks) there was a far more naturally diverse and abundant fauna and flora than prior to treatment. When the benthic food source (phytoplankton-diatoms) exists, it is quickly utilized by those invertebrates who arrive with the tide to forage. In the summer, eelgrass seeds can normally sprout and grow again on oyster beds. This same control sequence has proved itself over the past half century keeping valuable oyster farming areas of the intertidal open for all of the important estuary species while useable for growing of oysters and clams.
Since the mid-1960s the oyster growers have assumed the responsibility and costs to at least control the rate of burrowing shrimp expansion on certain areas of the privately owned tideland. These are often the best oyster growing grounds (termed fattening beds) with the highest abundance and diversity of natural estuary biota (plants and animals). In fact, the oyster shells and clusters on the sediment surface are responsible for enhancing the abundance and diversity of many other species.
At some point the state and federal fisheries biologists or their administrators lost this concern, resulting today in around 10,000 acres of the important intertidal in Willapa Bay with only ghost shrimp. The other normal benthic species have been replaced. That now leaves the privately owned highly productive intertidal that is being used for growing oysters as an important contributor to the diversity of natural plants and animals in the bay.
What is key is that those thousands of once productive, ghost shrimp infested public intertidal acres have lost the capability of supporting the biota necessary to form a food web. Thus, oyster growers today now are owners of a unique portion of lower intertidal that is still viable, with productivity made possible by the careful use of a pesticide over the past 50 years. However, DOE has now set in motion the conditions for the ghost shrimp to take over and eliminate more of the unique fauna and flora.
Without careful repeat treatment of certain areas at an average frequency of every six or so years, we likely will see the continued loss of the estuarial benthic diatoms, then the micro invertebrates dependent upon them, and on up the food web to higher trophic forms, such as birds and fish. With the unstable sediment caused by ghost shrimp, there will be continual loss of eelgrass and other sessile benthic forms plus oysters on the surface which provide attachment and sheltered places. Foraging migrants like our shorebirds will feel the impact when spring tides only uncover barren invertebrate free sand flats. Young fish will find less area to forage and the small first-year Dungeness crabs will find no place to hide from predation.
The “littoral bottom line” for the food web is this: The stable open intertidal sediment surface of Willapa Bay, composed of igneous silicate mineral sands (i.e. the mudflat), is utilized by over 80 species of benthic diatoms (single celled algae), which through photosynthesis are the basis of productivity by their formation of useable carbohydrates and lipids to fuel the food web. Ghost shrimp eliminate this diatom habitat. By not controlling the rapidly increasing population of ghost shrimp abundance and biomass, as the DOE has just decreed, the result will be a steady decrease in abundance of normal estuary fauna and flora. This is not only through destabilizing the sediment by elimination of smaller sand grains, silt, and clay, thus rendering the remaining sand unstable and unusable, but perhaps even worse by decreasing and eliminating the lipid- rich nutrients from diatoms that would naturally create their biofilm on the surface. This last effect, the loss of the biofilm coating, eliminates the basis of the food web originating on the mudflat surface. This is critical to the majority of the nearshore plants and animals.
In short, the DOE, urged on by uninformed activists and politics and then by going against science and the long-term history and success of control, will have to stand accountable for continuing to decrease the abundance and diversity of dozens of important biotic benthic species. The very species that comprise the important basic trophic levels leading up to shorebirds, fish, shellfish and crabs.
Using just one of many feeding sequences, as example, let’s take a favorite sandpiper, the dunlin. Probably over 100,000 dunlin winter over on Willapa Bay and forage for shallow invertebrates to store energy to migrate north to nest. Much of this probably is gained in the spring before migrating when daylight low tides uncover those rich oyster farming areas for foraging. Dunlin are dependent upon lipid rich invertebrate prey they can access on the mudflats at low tide.
One key invertebrate they forage for is a small burrowing amphipod (sand flea cousin) of genus Corophium. This small crustacean makes a tiny lined burrow, about as deep as the dunlin bill, provided the surface sediment is stable. From studies involving invertebrate sampling on oyster beds, the number of individuals is typically over 10,000 Corophium per square meter.
In turn each, Corophium must depend upon scooping in a thousand or more lipid-rich benthic diatoms that it can reach from its burrow entrance (a few millimeters) during each high tide period. Corophium is adapted to actually chew and break up the diatom’s silica shell.
There are over 80 species of benthic intertidal, largely motile, diatoms on the Willapa Bay intertidal that depend upon a stable and nutrient-rich sedimentary surface. These diatoms move within the biofilm they form and build up abundances often over 10 million cells per square meter. Under favorable conditions and with nutrients largely supplied from silicate mineral breakdown, they can divide and double in a few days. It is a huge nutritive biomass that most do not see or realize. They re-suspend into the water column and move along often as a mass with currents as tides rise. Again, from the sedimentary surface comes the source of nutrients and the soluble silica essential for diatoms to form their shell.
Ghost shrimp bioturbation and hydration reduce, then eliminate, the above food chain sequence for Dunlin. This species and other shorebirds don’t forage on those thousands of acres taken over by burrowing ghost shrimp, which shows there is no longer a food source present. Similar examples of the food web could be drawn for dozens of species, such as the foraging of young fish or crabs, or even the direct consumption of benthic diatoms by both native and cultured shellfish.
I have commented on these aspects in more detail and posted them in albums for viewing on Flickr. The latest is ‘Sand to Shorebird’: www.flickr.com/photos/76798465@N00/sets/72157686760839915
I would like to thank the Chinook Observer and its editor for bringing this burrowing shrimp issue up to a headline news and editorial level and to Kathleen Sayce for her edit and review of these comments. It is the hope of many that one day we can again get our resource and regulatory agencies to fully understand the ecological dynamics of the marine nearshore and work constructively on problems such as the serious damage burrowing shrimp are doing to our coastal estuaries and biota.
Richard Wilson, Ph.D., is a long-time oyster grower on Willapa Bay and owner of Bay Center Mariculture Co.