The UW study took a different approach. Brett and colleagues raised zooplankton in the lab, feeding them a diet of either pure algae, pure land-based carbon, or various mixtures of the two. They found that zooplankton fed a purely land-based diet survived and reproduced but were small and produced relatively few offspring. Zooplankton fed a diet of pure algae were 10 times bigger than their tree-fed twins and produced 20 times more offspring. Zooplankton fed a mixed diet were larger and produced more offspring as the proportion of algae in their diet went up. Even when zooplankton ate almost nothing but land-based carbon, nearly all their lipids came from algae.
"I think we were able to show that the terrestrial source is such low quality that it's inconceivable that it could be nearly as important as what that study suggested," Brett said.
This research was funded by the National Science Foundation. Co-authors are Sami Taipale and Hari Seshan of the UW and Martin Kainz of the Danube University Krems in Austria.
So why did the earlier study suggest that fish were eating land-based food? Brett believes the reason is those researchers discounted the idea of zooplankton migration, the daily movement down to deeper waters during the daytime to hide from predatory fish. Researchers sprinkled tagged food in the upper waters and assumed that any other food source must be land-based.
"The flaw was that there was an alternative source. They could h
|Contact: Hannah Hickey|
University of Washington