Aquaculture disturbance impacts the diet but not ecological linkages of a ubiquitous predatory fish
Estuaries and Coasts
By: Kathleen C. McPeek, P. Sean McDonald, and Glenn VanBlaricom
https://doi.org/10.1007/s12237-014-9909-z
Abstract
Aquaculture operations are a frequent and prominent cause of anthropogenic disturbance to marine and estuarine communities and may alter species composition and abundance. However, little is known about how such disturbances affect trophic linkages or ecosystem functions. In Puget Sound, Washington, aquaculture of the Pacific geoduck clam (Panopea generosa) is increasing and involves placing nets and polyvinyl chloride (PVC) tubes in intertidal areas to protect juvenile geoducks from predators. Initial studies of the structured phase of the farming cycle have documented limited impacts on the abundance of some species. To examine the effect of geoduck aquaculture on ecological linkages, the trophic relationships of a local ubiquitous consumer, Pacific staghorn sculpin (Leptocottus armatus), to its invertebrate prey were compared between geoduck aquaculture sites and nearby reference areas with no aquaculture. Mark-recapture data indicated that sculpin exhibit local site fidelity to cultured and reference areas. The stomach contents of sculpin and stable isotope signatures of sculpin and their prey were examined to study the trophic ecology of cultured and reference areas. Results showed that the structured phase of geoduck aquaculture initiated some changes to staghorn sculpin ecology, as reflected in sculpin diet through stomach content analysis. However, carbon and nitrogen stable isotopes revealed that the general food web function of sculpin remained unchanged. The source of carbon at the base of the food web and the trophic position of sculpin were not impacted by geoduck aquaculture. The study has important implications for geoduck aquaculture management and will inform regulatory decisions related to shellfish aquaculture policy.
Critique 3
This critique needs to be taken in context, that it is, the study’s use by the shellfish industry to state that “geoduck farming does not have a significant environmental impact when properly managed.”
As for the science, this is a well performed study studying the effect of a commercial geoduck operation on only a single species, the Pacific Staghorn Sculpin. They didn’t find any major impact on the fish, other than that its diet was a bit different. Why did they choose this fish? Because it is common and easy to study. What is its importance relative to other species in the ecosystem? Not stated other than that it is a “generalist.” They did not present any arguments that the Sculpin represents a sentinel species (one whose well-being might forecast that of the whole ecosystem). It is not always the most common species that has the most important effect in an ecosystem.
What they do say is this: “It is important to note that the present study is based on data from one prevalent member of the fish community with a generalized diet. Nearshore fishes may experience more dramatic impacts compared to staghorn sculpin, depending on how primary prey respond to changes in habitat complexity.” In other words, we don’t know anything about any of the other fishes from this study. As far as I know, there has been no attempt to study any of the other fish.
The paper goes on to say, similar to others reviewed here: “the results cannot be extrapolated to forecast the impacts of geoduck aquaculture operations in close proximity or repeated farming activities in the same location.” In other words, these are limited results in space and time. We don’t know what will happen if you keep running the farm in this spot, or if you put another one nearby.
I do take issue with the authors over their concluding statement: “Despite the aforementioned limitations, the present study and concurrent work by McDonald et al. and VanBlaricom et al. provide data to better balance economic interests with those of maintaining natural ecosystems and are critical for geoduck aquaculture management.” They don’t bother to explain their logic in coming to such a bold conclusion. Those mentioned studies were reviewed in critiques 1 and 2; these three limited papers taken together do provide a few interesting data points concerning commercial geoduck aquaculture. They do not even approach a serious attempt to establish commercial geoduck farming as having no significant environmental impact.
IMO, the authors’ statement is absurd, untrue, and self-serving. In simple terms, it encourages the shellfish industry to misuse this science to further their own business and financial interests.
Ron Smith