ECOLOGICAL EFFECTS OF THE HARVEST PHASE OF GEODUCK (PANOPEA GENEROSA
GOULD, 1850) AQUACULTURE ON INFAUNAL COMMUNITIES IN SOUTHERN PUGET
SOUND, WASHINGTON
Journal of Shellfish Research, Vol. 34, No. 1, 171–187, 2015
GLENN R. VANBLARICOM, 1,2 * JENNIFER L. ECCLES, 2 JULIAN D. OLDEN 2 AND
P. SEAN MCDONALD 2,3
1U.S. Geological Survey, Washington Cooperative Fish and Wildlife Research Unit, School of Aquatic
and Fishery Sciences, College of the Environment, University of Washington, Mailstop 355020, Seattle,
WA 98195-5020; 2School of Aquatic and Fishery Sciences, College of the Environment, University of
Washington, Mailstop 355020, Seattle, WA 98195-5020; 3Program on the Environment, College of the
Environment, University of Washington, Mailstop 355679, Seattle, WA 98195-5679
ABSTRACT Intertidal aquaculture for geoducks (Panopea generosa Gould, 1850) is expanding in southern Puget Sound, Washington, where gently sloping sandy beaches are used for field culture. Geoduck aquaculture contributes significantly to the regional economy, but has become controversial because of a range of unresolved questions involving potential biological impacts on marine ecosystems. From 2008 through 2012, the authors used a ‘‘before–after-control-impact’’ experimental design, emphasizing spatial scales comparable with those used by geoduck culturists to evaluate the effects of harvesting market-ready geoducks on associated benthic infaunal communities. Infauna were sampled at three different study locations in southern Puget Sound at monthly intervals before, during, and after harvests of clams, and along extralimital transects extending away from the edges of cultured plots to assess the effects of harvest activities in adjacent uncultured habitat. Using multivariate statistical approaches, strong seasonal and spatial signals in patterns of abundance were found, but there was scant evidence of effects on the community structure associated with geoduck harvest disturbances within cultured plots. Likewise, no indications of significant ‘‘spillover’’ effects of harvest on uncultured habitat adjacent to cultured plots were noted. Complementary univariate approaches
revealed little evidence of harvest effects on infaunal biodiversity and indications of modest effects on populations of individual infaunal taxa. Of 10 common taxa analyzed, only three showed evidence of reduced densities, although minor, after harvests whereas the remaining seven taxa indicated either neutral responses to harvest disturbances or increased abundance either during or in the months after harvest events. It is suggested that a relatively active natural disturbance regime, including both small-scale and large-scale events that occur with comparable intensity but more frequently than geoduck harvest events in cultured plots, has facilitated assemblage-level infaunal resistance and resilience to harvest disturbances.
KEY WORDS: aquaculture, benthic, disturbance, extralimital, geoduck, infauna, intertidal, Panopea generosa, Puget Sound,
spillover
Critique
As in all scientific papers, the reader is encouraged to evaluate the entire article, which can be found here.
This study was published in 2015, based on data collected between 2008 and 2012. It seeks to determine whether there is a significant effect of a commercial geoduck operation on benthic (in the beach) organisms by comparing samples before, during, and after the harvest phase. Samples were obtained from three sites which were so different that the data from each of these sites had to be evaluated separately. “Such an approach had the unavoidable effect of reducing statistical power for detection of significant differences.” Nevertheless, the data was analyzed using multivariate and univariate methods, the latter described this way: “Some components of our data failed to meet underlying assumptions on which ANOVA (ed. a method of statistical analysis using one variable) methods are based.”
So, what about that data? In this study 50 taxa (species) were identified in samples. They chose to evaluate the 10 most abundant ones, citing reasons for inclusion based on behavior in the ecosystem for only one of those species. So, only 20% of the identified species were evaluated other than a gross measurement by weight. If you alsso recognize that the exhaustive science literature review attached to GARP included data suggesting that a typical sand/gravel beach should contain 165 species, this is miniscule. Please see my discussion about the problem of this approach in critique 1. There is no discussion of the importance or lack thereof for the other 40 species. Their final conclusion was that there was no significant effect of the geoduck aquaculture project, but along the way they state “Of the 10 most frequently sampled infaunal taxa, only 3 indicated evidence of reduction in abundance persisting as long as four months after conclusion of harvest activities.” The math is pretty easy here. 30% of the most common species show reduction in numbers, in their view not significant? But rest assured, the three did not “approach local extinction.”
So, the conclusion is that there wasn’t much effect, but there are also many disclaimers. They point out that, it was hard to find good sites to study, that the sites were relatively isolated and being used for geoduck for the first time, and that patchy harvest could significantly affect the data. Also, that the long-term effects were unknown. “The data may not provide sufficient basis for unequivocal extrapolation when a given plot is exposed to a long series of successive geoduck aquaculture cycles. Likewise, it may not be appropriate to extend the findings of the current study to cases when a number of separate plots are adjacent to one another, and encompass significantly larger surface area than any single plot.” In other words, they can’t really say what might happen in practice.
The authors conclude with “resolution of the questions of larger special spatial and temporal scales will be a major challenge for geoduck farmers as they continue production on existing plots and expand into new areas, and will be an important research goal in the interest of informed management policies by natural resource agencies.”
There has been no attempt that I am aware of to reproduce or further evaluate these findings with follow-up studies as of January 2024, particularly with the regard to the potential cumulative effects of geoduck aquaculture.
This, like the scientific paper in critique 1, is not a landmark study, and I think that it does not have the power to guide major policy decisions. It honestly attempts to draw conclusions based on limited data, and appropriately disclaims the results. It is a gross mischaracterization by the shellfish industry to say: “These studies demonstrate that, similar to other forms of shellfish aquaculture, geoduck farming does not have significant environmental impacts when properly managed.” Quote Diani Taylor E in a letter to the Thurston County Planning Commission 25 November 2020.
Ron Smith