Zooming in on Zooplankton

“What happens when you add one more individual to a population? Does greater variation in a species affect its ability to adapt and change in response to its environment?“

Larry L. Bowman, one of the 2015 YIBS grantees, studies ecological questions like these in the coastal lakes of southern Connecticut. The lakes form what Bowman calls a “model system” for studying the dynamics of evolution as they play out in the field. The alewife, a herring species that usually migrates between salt and freshwater, provides a particularly interesting lens for Bowman to look at how zooplankton populations change through these underwater interactions.

“Anadromous [migratory] populations of alewives used to be present in four of the six lakes I study. Several hundred years ago, thanks to colonists, two of those four lakes had their access to the sea closed off by dams. In two of the lakes the alewives were never present; in another two, they can still be found but obviously they no longer spend time in saltwater, having become landlocked due to dams.  I also study two lakes where alewife populations still migrate annually. These three lake types create vastly different environments for the zooplankton that live in these lakes.  By comparing the zooplankton populations in these lakes we can understand how these microcrustacean species adapt to changing environments.”

Scientists have good reason to be preoccupied with alewives and the species they interact with. In the mid 20th century alewives entered the Great Lakes through the Welland shipping canal. As they proceeded to decimate other fish populations in the ecosystem, pacific salmon were introduced to control them. Meanwhile in Connecticut, where Bowman works, the anadromous alewife’s native habitat is considered threatened and repopulation projects have begun. Knowing how zooplankton populations respond to the reintroduction of once-native fish species will help researchers and conservationists understand how best to repopulate lakes without causing the lake community to become unstable.  

“My research will help us understand how populations of zooplankton could react to their new surroundings.A predator they haven’t seen for hundreds of years is back! For example, how many zooplankters with different phenotypes or genotypes do you need in a lake to have a diverse and adaptable group that could withstand a novel predator? When is the population stable and resilient? This is where we get to the within-species diversity dimension that really lies at the core of my work. Interactions between species in an ecosystem are important of course, as the alewife example shows, but they are affected by the inner dynamics of each population,” says Bowman.

In fact, this study of the six Connecticut lakes is part of a much larger research initiative that is yielding long-term data about evolutionary relationships within the lakes. As a PhD student in the Ecology and Evolutionary Biology program, Larry L. Bowman spent last winter drilling holes through the ice to take measurements and samples from these waters. He has specifically been looking for more information about when populations invest in growth and how they respond to ecosystem stress.

“This is the project that my YIBS funding really helped to advance,” says Bowman. “I was able to purchase a Qubit benchtop fluorometer. It’s small size and mobility allow us to have an advanced piece of technology and measure the ratio of RNA to DNA in an organism while we are in the field. In other words, we can observe whether an organism is investing in growth by making lots of RNA and, using this information, draw conclusions about its reaction to other environmental factors in the ecosystem. We hope to understand how growth rates are related across different trophic levels. This gives us a much more complete picture of how species interact in these environments.”

A complete picture of the lake ecosystem helps scientists and conservationists make informed decisions about how to manage species like alewives in the future. If they are reintroduced to lakes, for example with fish ladders that help them climb upstream from the sea, thorough knowledge of the complex web of interactions going on beneath the surface helps ensure that wide-reaching imbalances like those seen in the Great Lakes are far less likely to occur.

Interview and Article by Agnes B. Walton

Title photo credit: David Post