Many of us are familiar with the food chain, especially that of which we find ourselves a part of, but what about aquatic ecosystems? This week we will take a break from hydrilla and talk a little about “who eats who” and the importance of balance in the aquatic food chain.
So what exactly makes up the aquatic food chain, especially in our local water bodies? While it may seem painfully simple, aquatic food webs are often extremely complex. While the complexity of food webs often varies from lake to lake, there are a few elements in the food web for lakes and reservoirs that begin with simple, single celled organisms all the way up to the apex predator. So let’s work our way from bottom to top:
In the aquatic food chain, everything begins with phytoplankton. Phytoplankton are photosynthetic, plant like organisms that can be found suspended in the water column. Phytoplankton need water, nutrients, and sunlight to actively grow and reproduce. Once adequate amounts of “fuel” are available in sufficient quantities, phytoplankton will begin to rapidly grow and produce an algae bloom. Despite common perceptions, not all algal blooms are bad. On the contrary, algal blooms of most phytoplankton drive aquatic ecosystems. Phytoplankton, along with the aquatic macrophytes (plants), are the primary producers of aquatic habitats.
Next in line are the Microinvertebrates, also called zooplankton. These are extremely small (hence the name “micro”) sized creatures that can exist in large numbers in lake water. These organisms feed on phytoplankton. The more phytoplankton present, the more microinvertebrates we typically see. These organisms are often only visible through the use of a microscope.
Following microinvertebrates are the macroinvertebrates. Macroinvertebrates include what many of you would consider “those little bugs” in and around the water. Macroinvertebrates feed on microinvertebrates but also feed on bacteria and plant material. Some common macorinvertebrates include stoneflies, mayflies, caddislfies, etc.
After macroinvertebrates come the small fish species and juveniles/ fingerlings of large fish species found in lakes. These small fish eat the macroinvertebrates present in the water. These small, planktivorous fish include shad and other baitfish species, bluegill, and other panfish. Juveniles of larger, predatory fish often start their life eating macroinvertebrates and other small prey until they grow to sizes that can adequately take larger prey species like shad.
Last in the aquatic food chain are the piscivorous, or “fish eating” fish. In our local lakes, these include the adult largemouth bass, walleye, striped bass, pickerel, etc. These species are often considered the apex predators of an aquatic ecosystem (except when we catch and eat them of course!)
Balance is the key to a productive aquatic ecosystem. Too few primary producers (phytoplankton, algae and other aquatic plants) and there is not enough food to go up the food chain. Too many primary producers and harmful conditions can occur. For example, dissolved oxygen, an essential ingredient for the survival of almost all aquatic organisms, becomes rapidly depleted as large amount of phytoplankton die, sink to the bottom and decompose. This can result in the death of other members further up the food chain. Next time we will talk in further detail about this delicate balance, and what we can do to ensure that we don’t shift that balance to a tipping point in either direction.
Photo Credit: “The Aquatic Life of Lake Chautauqua” – https://www.cs.fredonia.edu/szocki/projects/spring_09/22/info_insects.html
Web Links For Additional Information:
Best Management Practices
NCSU Hydrilla Page
If you have questions please contact your Aquatic Extension Associate, Brett M. Hartis, at (919)-515-5648 or email at bmhartis@ncsu.edu.