Robert E. Hecky Talks About the Nearshore Phosphorus Shunt
Emerging Research Front Commentary, October 2010
Article: The nearshore phosphorus shunt: a consequence of ecosystem engineering by dreissenids in the Laurentian Great Lakes
Authors: Hecky, RE;Smith, REH;Barton,
DR;Guildford, SJ;Taylor, WD;Charlton, MN;Howell, T
Robert E. Hecky talks with ScienceWatch.com and answers a few questions about this month's Emerging Research Front paper in the field of Plant & Animal Science.
Why do you think your paper is highly cited?
Dreissenid mussels, popularly known as zebra mussels, are not native to the North American Great Lakes and became established there—and in many other inland lakes and rivers—during the 1990s after their accidental introduction from Europe, likely in ballast water. Their larvae settle and grow into adults on hard surfaces, and consequently they have had severe direct economic consequences by clogging water intakes as well as fouling vessels and coastal infrastructure.
But their greater and more widespread impact has been on nutrient cycling and light transparency in the nearshore coastal regions, which has led to alteration of the aquatic communities and a redistribution of aquatic productivity in the Great Lakes, often to the detriment of the native flora and fauna. The successful invasion, phenomenal spread and substantial impact of the dreissenids has caused them to become the "poster child" for negative consequences that can result from exotic species invasions.
In this way, their "success" and continuing impact has much to do with the high citation rate for our publication.
Does it describe a new discovery, methodology, or synthesis of knowledge?
"Our paper demonstrates the catastrophic, and to this date, irreversible change that an invasive species can wreak on aquatic ecosystems even at the scale of the largest lakes in the world."
At the time of our publication, there had already been a number of studies that identified both direct and indirect effects of dreissenids on aspects of the aquatic environment, but these studies tended to be focused on a particular interaction or locality. Our publication was, in part, a review of these known impacts; but we also offered a synthesis that scaled up these impacts to define the aggregate impact of the dreissenids in changing the physical and chemical characteristics of the entire nearshore zone of the lakes and suggested the possibility of lake-wide effects.
These aggregated impacts, when considered at the extensive geographic scale at which they were occurring, resulted in the redistribution of mass and energy flows over large areas of the lakes, often with a degradation of the beneficial uses of the nearshore environment. Our contribution was in formalizing these larger-scale impacts, which has resulted in a redirection of research and modeling effort on the Great Lakes to examine these larger-scale effects.
Would you summarize the significance of your paper in layman's terms?
Our paper demonstrates the catastrophic, and to this date, irreversible change that an invasive species can wreak on aquatic ecosystems even at the scale of the largest lakes in the world.
The success of dreissenids has imposed hundreds of millions of dollars of economic costs and these costs are continuing. Billions of dollars have been spent by states, provinces and municipalities to reduce nutrient concentrations in the coastal areas of the Great Lakes since the 1970s, but the mussels have reversed some of the success of those expensive programs.
The take-home message is that we must be more aggressive in preventing the introduction of exotic species into our lakes because the consequences can be extreme for the native biota and costly to our society.
How did you become involved in this research, and how would you describe the particular challenges, setbacks, and successes that you've encountered along the way?
Prior to 1996 I had not worked on the Laurentian Great Lakes or dreissenid mussels, but a professional move to an institute devoted to studying the lakes made me aware of the growing concern about the possible effects of dreissenids. I began a research program to study the productivity of algae growing on the lake bottom which involved SCUBA diving on Lake Erie.
I was immediately impressed with the great numbers of mussels completely covering all hard surfaces. Conversations with SCUBA dive operators led me to appreciate that that there had been a dramatic change in the transparency of coastal waters after the mussel invasion and over quite extensive areas—the joke in the dive community being that the good news was that because of zebra mussels you could see forever underwater, but the bad news was that all you could see was zebra mussels.
"The successful invasion, phenomenal spread and substantial impact of the dreissenids has caused them to become the "poster child" for negative consequences that can result from exotic species invasions. ..."
My research on the algae clearly indicated that algae associated with dreissenid-covered rocks had higher rates of production than without mussels, and this could be shown to be a result of nutrient enrichment by the wastes of the mussels. I began to appreciate that the mussels were causing some rather extensive and fundamental changes to nutrient and radiant energy fluxes in the nearshore. Together with my co-authors, who had a wealth of experience on the Great Lakes, we formulated the nearshore shunt hypothesis introduced in the 2004 publication.
The greatest challenge we faced was overcoming reluctance in our community to accept that the activities of these small organisms could fundamentally redirect energy and mass flows at the scale of an entire Great Lake. The "success" has been that this is now largely accepted across the Great Lakes.
Where do you see your research leading in the future?
I remain interested in how animals, through their activities, can direct, or at least affect, the flows of mass and energy within aquatic ecosystems. I have also moved again; this time onto the shores of Lake Superior, the only one of the Laurentian Great Lakes not affected by the mussels (although some of the harbors are infested with the mussels).
Lake Superior is of interest because of all the lakes it is the only one to retain the native fish community, including some deep water fishes endemic to the Great Lakes (but now absent from the other lakes). These deep water fishes migrate vertically hundreds of meters every night causing a massive migration of their invertebrate prey up near the seasonally warmer surface layer of Lake Superior.
With my colleagues we are examining the thesis that this animal migration is important in moving nutrients upward to maintain productivity of algae living just below the surface layer. This nutrient return from the deep allows the lake to sustain a higher rate of algal productivity than would otherwise be possible, which in turn benefits those deep-dwelling fish.
Do you foresee any social or political implications for your research?
I believe the research on the nearshore shunt has already had substantial implications. The US and Canada are just now in the midst of renegotiating the Great Lakes Water Quality Agreement, and it is a near certainty that nearshore issues will receive much greater attention than the previous agreement. The nearshore shunt hypothesis has contributed to the research and management community having a much greater sensitivity to nearshore issues as well as providing a scientific foundation for that new focus on the nearshore.
More generally, I hope that my research both on the shunt and on Lake Superior will lead to a greater appreciation of the need to protect the biological integrity of the Great Lakes so that the lakes provide the beneficial uses that we expect from them.
Prof. Robert E. Hecky
McKnight Presidential Endowed Professor of Lake Ecology
University of Minnesota Duluth
Biology Department and Large Lakes Observatory
Duluth, MN, USA
KEYWORDS: ZEBRA MUSSEL DREISSENA; HATCHERY BAY; FRESH-WATER; SAGINAW BAY; POLYMORPHA; ERIE; INVASION; SEDIMENT; ONTARIO; GROWTH.