(In this guest post, one of a series on monitoring and experimentation in the Jefferson Project at Lake George, Matt Schuler, a post-doctoral researcher in the laboratory of project director Rick Relyea, explains how researchers survey macro-invertebrates in Lake George, their importance in the food web, and how this effort fits into the overall strategy of the project. Schuler took the above image of macro-invertebrates as seen under a microscope.)
As a source of clean drinking water, food, and endless recreation, Lake George is a prime example of how freshwater lakes improve our lives. Less obvious is the importance of hundreds of animal species that call Lake George home. Many of these animals are small and easy to miss. They live everywhere from the wave-struck shores of the lake, to the deepest, darkest basins. They even share the soft sandy beaches with thousands of swimmers every year. Commonly referred to as macro-invertebrates, numerous species of insects, worms, clams, and snails live in the soil and on the rocks of Lake George. Some of these animals are so small that they are barely visible, while others are a few inches long.
The majority of the macro-invertebrate species in Lake George have been documented over the last century, thanks to the efforts of scientists at the Rensselaer Darrin Fresh Water Institute. However, there may still be undetected species, and we still have a lot to learn about these often overlooked organisms.
Although they often go unnoticed, many of these animals are essential members of the complex food web in Lake George. Clams and mussels filter algae from the water, helping keep Lake George waters clear and clean. Meanwhile, snails and some insect larvae graze across the rocks, keeping at bay the shaggy green carpet of algae that would otherwise cover many areas of the lake. Many species of insect larvae, amphipods (a type of shrimp), and isopods are essential for recycling nutrients in the lake, and are a major source of food for fish. These macro-invertebrates are also generally sensitive to human disturbances such as pollution, warming of the lake due to climate change, and disturbance from shoreline development and boating.
As part of our work, researchers associated with the Jefferson Project at Lake George are asking questions related to the abundance and distribution of macro-invertebrates in Lake George. We want to understand what environmental factors determine the spatial distribution of macro-invertebrates, the population dynamics of important species, and how humans are affecting their numbers and their distributions in the lake. Given that many of these species are indicators of water quality, monitoring changes in macro-invertebrate populations over time can be the canary in the coalmine for water quality in Lake George.
We are also interested in the few non-native species present in Lake George. Zebra mussels, Chinese mystery snails, and Asian clams are three recent invaders of Lake George. Another snail, the banded mystery snail, quietly moved into the waters of Lake George around a hundred years ago, after moving northward from the mid-Atlantic region. Although the banded mystery snail is considered generally harmless in Lake George, we still don’t know how the other three species affect the pristine waters of Lake George. Additionally, we don’t know if the presence of other non-native species will alter the effects that banded mystery snails have on water quality or change how banded mystery snails affect native snail species.
To understand what species are present in the lake and in the nearby streams, we use a variety of common tools to collect the macro-invertebrates. To measure spatial variation in the species of macro-invertebrates in the lake, we use a Ponar grab-sampler, a tool that looks like the grabber in the claw machine game that you may have played in an arcade. The grab-sampler is dropped to the bottom of the lake, and a spring-loaded mechanism releases the hinge, allowing the researcher in the boat to pull up on the rope, shutting the trap around the soil and macro-invertebrates that live in and on the soil. The trap is then pulled up to the boat, and dumped into large, white trays for sorting. Once the large pieces of vegetation are removed, the researchers pour the sample into a sieve – a small mesh filter – to separate the remaining soil from the snails, clams, amphipods, and insect larvae. In the image below, Rensselaer undergraduates Mike Kaloustian and Alex Brooks sort through a macro-invertebrate sample.
To get a full picture of the macro-invertebrate populations across the 32-mile long lake, we repeat the sampling process in 30 different locations, at a variety of depths. These invertebrate surveys are also used to understand the complex food web at Lake George, assessing what food resources are being consumed by the macro-invertebrates, and what macro-invertebrates are the most important food resources for larger predators like fish.
Over the next few years, researchers working on the Jefferson Project will continue to survey the physics, chemistry, and ecology of Lake George. The macro-invertebrate samples will be coupled with plankton samples and fish samples to create a comprehensive food web model for Lake George. Researchers from different lab groups associated with the Jefferson Project will conduct dozens of experiments to test specific hypotheses about how humans and changes to the environment will affect macro-invertebrates. We will also conduct experiments to investigate how some of the invasive species of Lake George interact, and how they may be affecting the water quality of the lake.
To carry out this work, we have assembled a comprehensive team from a variety of disciplines, and an army of undergraduates working with Jefferson Project researchers. To date, nearly 30 undergraduates have assisted post-docs, graduate students, and faculty with research on the macro-invertebrates living in Lake George. We expect that our work will not only lead to solutions for Lake George, but also prepares future scientists with the tools and global perspective to solve ecological issues in freshwater ecosystems around the world.