The 4 Tiers of Aquatic Ecosystems in Freshwater Lakes

Monday, September 23

By Lilly Center staff

When an organism fits seamlessly into its ecosystem, it is considered to be native. For example, monarch butterflies consume milkweed as caterpillars and then consume nectar and disperse pollen as adults. Shelf mushrooms live on the sides of decaying wood and assist in breaking down the dead tree into energy and nutrients. Opossums eat anything they can easily put in their mouths, especially ticks. All of these species are native to Northern Indiana and are important parts of our ecosystem.

Native: Plants and animals that grow naturally or have lived for a long time in a certain region. Native plants and animals tend to be self-sustaining and already adapted to the region they’re in. For instance, native plants can survive dry and rainy seasons better than non-native plants.

Every native organism has a niche, and every niche exists on a level of the ecosystem. Each level contains an extremely diverse group of organisms, and though we already talked about some of our favorites, and about the food chain as a whole, here are some examples of the four broad levels of a freshwater lake’s aquatic ecosystem.

The Producers

Producers comprise the base of the food chain. They take energy from the sun, or natural chemical processes, and use it to make energy. Many producers, like trees and duckweed, don’t actively move. Some, like cyanobacteria (known as blue-green algae) move up and down but not much more. Sometimes, though, there are producers that are truly mesmerizing to watch. One the Lilly Center team observed recently is called a euglenoid. Its name means it is “like a euglena”. For the 99% of you who aren’t euglenenthusiasts, euglena are microscopic free-swimming organisms that, in this case, use photosynthesis to gain the energy to swim in their graceful spiral motion.

The Little Consumers

There are countless kinds of zooplankton! We’ve decided to talk about an in-office favorite: the rotifer. The best way to envision a rotifer is as an itty-bitty lake Roomba. Rotifers swim around at high speed using their tail (or tails) as a paddle and their mouth as a vacuum, hoovering up algae and tiny protozoa as they go along their busy microscopic lives.

The Big Consumers

Anything that moves and can be seen with the naked eye consumes other organisms, too. This group of consumers is likely the most well-known group, as it contains everything from smallmouth bass to crawfish and even to mussels (but more on them later). Big consumers are often specialized in how and what they eat, with some having large mouths to easily scoop up small fish and others with down-facing jaws used for sucking up meals of algae and invertebrates.

The Decomposers

This group is diverse and pretty hard to find. They do the dirty work of converting feces, dead organisms and other detritus into energy and nutrition for themselves and those that eat them. Although these little creatures often go unnoticed, they are always there, doing the job we’re so glad we don’t have to do.

Every level of a lake’s ecosystem does a unique and important job in protecting and prolonging native species and the habitats they live in. There’s a direct benefit for us, too: When the lakes are healthy, so are property values, family memories, local businesses, farms and more.

But what happens when that system is interrupted by a species that disrupts the natural balance? Cyanobacteria and zebra mussels are two notorious local offenders. More on them later! For now, sign up for the Lilly Center’s monthly e-newsletter to receive relevant, locally sourced lake science news from the research team.