Infestations of shell-boring polychaetes – including those in the genus Polydora – are responsible for substantial losses to commercial oyster industries worldwide. These polychaetes burrow into the shells of bivalves and cause unsightly blisters that release detritus, mud, and fecal material, fouling oyster meats. Even when blisters remain intact, they compromise the aesthetic presentation of oyster meats on the shell (Figure 1) and reduce an oyster’s value for canning or smoking. We recently documented these worms in Washington State Pacific oysters (Crassostrea gigas) for the very first time, and with support from the Western Regional Aquaculture Center (WRAC, NIFA, USDA), we are leading an effort to map the distribution of these worms across the Pacific Northwest and to offer growers options for avoiding and treating infestations on their farms.
Oyster industries around the globe have experienced economic losses due to mud worm infection. Oyster farm losses due to Polydora infestation have been recognized since the 1940s along the US east coast. As a non-native nuisance species, widespread expansion of Polydora caused the collapse of oyster aquaculture on Oahu, Hawaii. In New South Wales, introduction of Polydora in translocated oysters was responsible for the historical disappearance of once-extensive subtidal oyster beds in the 1860s. Polydora have been described as “the greatest obstacle to intensive oyster culture” in Australia.
Our goal is to help the Pacific Northwest avoid the fate of these other regions. We will accomplish this by:
- Mapping the current distribution of Polydora spp. at commercial oyster farms across the US Pacific Northwest (Alaska, Washington, Oregon, and northern California).
- Identifying the environmental factors that predict high infestation rates.
- Identifying the most effective intervention that growers can use to reduce transmission and mitigate the negative impacts of infection on product value.
We sampled Pacific oysters (Crassostrea gigas; n = 4158) from 35 shellfish farms over four seasons (two winters and two summers) in four states (northern California (CA), Oregon (OR), Washington (WA), and Alaska (AK)) to document the prevalence of shell-boring polychaetes. We extracted worms from infested oysters and used mitochondrial (CO1, n = 139) and nuclear (18S rRNA, n = 224) markers to determine species identities. To identify the environmental correlates that were associated with infestation, we pooled environmental data from seven monitoring stations in Washington. We assessed whether seawater surface temperature (SST), salinity, and pH were associated with shell-boring polychaete infestation. Our sampling confirmed the presence of Polydora websteri in the study region, in addition to four other species of shell-boring polychaetes and seven unidentified haplotypes. The mean prevalences across all shell-boring polychaete species ranged from 23 to 45% across seasons between states (Figure 2). In general, prevalence was higher in the winter and among oysters cultured on the bottom versus in tumbled bags, but these results varied across states. We also found greater infestation by shell-boring polychaetes at less acidified sites (pH = 8–8.2; Figure 3). This work is the most comprehensive dataset to characterize shell-boring polychaetes along the US West Coast, providing an important baseline of prevalence, species distribution, and environmental associations. You can read the full results from this research in Martinelli et al. 2023.
Treatments for shell-boring polychaetes have been tested in other world regions, and we wanted to determine whether these treatments would work for infested Pacific oysters raised in Washington State. We collaborated with local shellfish growers to develop three treatments that could be practically deployed on Washington State oyster farms: drying, a freshwater dip plus drying, and drying with refrigeration. We quantified the extent to which each treatment killed worms, affected oyster physiology, and killed oysters. Experiments were conducted in fall and spring to evaluate seasonal differences. Our results showed that drying and using a freshwater dip plus drying for two days are both highly effective (>95%) at killing worms without negatively impacting oyster survival (4% mortality in the drying treatment in the spring, 0% mortality in all other treatment–season combinations; Figure 4). Use of these treatments on affected farms may help to mitigate the potential effects of shell-boring polychaetes on oyster product value, thus avoiding economic losses. You can read the full results from this research in Martinelli et al. 2022.
Shellfish aquaculture is a low-input, sustainable means of seafood production that augments the supply of locally produced, nutritious food. We sought to address the needs of the Pacific Northwest’s aquaculture sector by assessing the scale of this threat and exploring options for reducing the barrier it presents to oyster aquaculture development. Through our industry advisory group (the Healthy Oysters Steering Committee), we ensured a coordinated and complementary exchange of information and ideas across our public–private partnership, including information on effective treatments for shell-boring polychaete infestation and tools for on-farm identification and quantification of worm burden. Our project provided oyster farmers with tools to prevent an emerging nuisance species from reducing oyster production and profitability in the Pacific Northwest.