Aquatic food web tied to land: Some fish are made out of maple leaves

January 21, 2011
This shows water sampling on Paul Lake. Credit: Steve Carpenter

A distant relative of shrimp, zooplankton are an important food source for fish and other aquatic animals. Long characterized as algae feeders, a new study published this week in the Proceedings of the National Academy of Sciences reports that nearly a third of zooplankton diets are supported by material that originates on land in lake watersheds.

The study brings scientists one step closer to clarifying the role that watershed inputs play in aquatic food webs. While it has been recognized that animals living at the bottom of lakes and streams rely, in part, on inputs from the land, there has been controversy about whether open water animals, such as zooplankton, consume this material.

Lead author and Cary Institute of Ecosystem Studies limnologist Dr. Jonathan J. Cole comments, "Our work changes the paradigm for how we describe the environment that supports fish. Zooplankton are one of the pillars of the aquatic . And while they do feed on algae, they also rely on materials derived from maple leaves, pine needles, and whatever else comes in from the surrounding watershed."

When algae are scarce, Daphnia will feed on bits of leaves that wash in from the watershed. Credit: Paul Hebert

Using ambient stable isotopes of carbon, hydrogen, and nitrogen, Cole and colleagues traced the diets of three zooplankton species commonly found in freshwater lakes: Daphnia, Holopedium, and Leptodiaptomus. Animal samples were taken from two Wisconsin lakes with distinct profiles—Paul , a small lake with moderate nutrient levels, and Crampton Lake, a larger nutrient-poor lake.

While it has been assumed that the zooplankton feed almost exclusively on algae, biomass analyses revealed a different story. In both lakes, that originated on land made up approximately a third of zooplankton biomass. When edible algae were scarce, zooplankton derived a higher percentage of their diet from terrestrial material.

Once seen as closed ecosystems, research now indicates that lake food chains rely on food resources that originate on land. Credit: Steve Carpenter

Cole notes, "Historically, lake ecosystems have been studied in isolation. Yet we know lakes are connected to their watersheds and organic matter from land enters lakes in the form of run-off or ground water." Adding, "Our study adds to the growing body of evidence that aquatic food webs are subsidized by these inputs."

This is the most recent of several Cary Institute-led studies investigating inputs to aquatic food webs; all of them have resulted in findings that indicate zooplankton feed on land-generated organic matter.

Explore further: Fish food fight: Fish don't eat trees after all, says new study

More information: To access the paper, visit: … 807108.full.pdf+html

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3.7 / 5 (3) Jan 21, 2011
Reductionist ecology is not ecology at all. Nature is a system whose veins and arteries extend even beyond our planet. As Carl Sagan said, we (and everything else on the planet including the planet itself) are stardust. We are the complex result of billions of years of evolution and co-evolution with countless other organisms alive and extinct.
not rated yet Jan 21, 2011
And your point would be that anyone who wants to study anything should study everything at once?

Let's begin with you. Are you prepared to holistically prove your statement that reductionism is useless? Or something?
not rated yet Jan 24, 2011
And your point would be that anyone who wants to study anything should study everything at once?

Let's begin with you. Are you prepared to holistically prove your statement that reductionism is useless? Or something?

My point is that if you want to understand the metaphorical whole picture, you can't look at just one sliver of it. Nature is a system whose many parts interlock at many points. That doesn't mean I need to understand the history of philosophy to have an adequate understanding of botany, but if I did have an understanding of the former my understanding of how we view the latter and how our understanding of the latter has evolved in the context of human history would be broader.

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