*Editor's Note: Curious about insects that live in our lakes and streams? Here, our Outreach Assistants answer a few frequently-asked questions about benthic macro-invertebrates - the "backbone" of our aquatic habitats! AND SAVE THE DATE!!! This Saturday, August 5th, we will be at DUTCH CREEK with .... BMIs!!!
Q: What is a Benthic Macroinvertebrate?
A: Benthic macroinvertebrates (BMIs) are little creepy crawlies found in our streams and lakes. The word benthic relates to organisms found in the beds of our rivers and lakes. A macroinvertebrate is an organism that lacks a spine but is still visible to the naked eye. These creatures are seen in all different shapes and colours, from dragonflies to worms to mayflies to snails. Many benthic invertebrates, such as stoneflies and dragonflies, are aquatic during the juvenile stages of their life cycle (as nymphs and larvae), but emerge from the water and fly in the air as adults. Other invertebrates, such as snails and some worms, will remain aquatic throughout their entire life cycle.
Q: What's their role in the ecosystem?
A: Benthic macroinvertebrates act as ‘behind the scenes’ workers in lakes and streams. They’re not usually the first thing you see or think of when you look at a body of water, but they function as the backbone of the ecosystem.
These organisms do the literal dirty work for our watershed: stirring up rocks and sediment and increasing nutrient cycling, which helps to support a diversity of organisms.
Some macroinvertebrates are herbivores, shredding and eating plants, or scraping algae off of rocks. Some collect food (e.g. plankton, feces, decaying organisms) from stream bottoms, while still others are predators that prey on smaller live organisms. Despite their small size, they play a large part in the food chain and provide a food source for larger critters and fish. For example, our native Westslope Cutthroat Trout eats mainly invertebrates throughout its lifetime.
Q: What can they tell us about water quality?
A: These macroinvertebrates are used in science as bioindicators. Bioindicators are organisms whose presence or abundance reflect the health of the ecosystem. Benthic macroinvertebrates are abundant, relatively easy to sample, and many of these organisms have very specific requirements for factors such as water temperature, dissolved oxygen, and nutrients in the water. For example, stonefly, mayfly, and caddisfly nymphs can only live in the most pristine conditions with high oxygen and cold temperatures, while leeches, blood worms, and spider mites can tolerate warmer water with lower oxygen.
Bioindicators are organisms whose presence or abundance reflect the health of the ecosystem. Benthic Macroinvertebrates are abundant and relatively easy to sample, and different species tolerate different levels of water quality, making them ideal bioindicators.
Our Outreach team collects BMI to use as part of our public education programs called Point Duties (we always return them to their homes afterwards!).
The benthic macroinvertebrates we’ve collected from the Oldman River generally show colder water and higher oxygen content in the headwaters, while the BMI collected further downstream tended to be more tolerant of warmer conditions. This change is strongly related to the widening and warming of the river.
Q: Are lakes different from streams?
A: Standing (or “lentic”) water, like shallow lakes and ponds, will often read as lower quality (warmer temperatures and lower dissolved oxygen) than moving (“lotic”) water, like creeks and rivers. The reason for this can usually be boiled down to the fact that standing water tends to warm up, and oxygen dissolves more readily in colder, moving water. More tolerant invertebrates such as snails and leeches are better able to survive in warmer, less-oxygenated lentic water bodies compared to their more sensitive counterparts.
Lotic systems also tend to fluctuate more than lentic systems, as the water is flowing and mixing nutrients, water levels are changing, and sediment is being eroded and transported downstream. Read more about lentic vs. lotic systems here.
When assessing water quality, it is important to consider these differences, and not to limit monitoring to a single factor like bioindicators - BMI are just one component of a suite of biological, chemical, and physical data that should be collected.
Q: Are benthic macroinvertebrates dangerous?
A: They don’t bite, if that’s what you’re worried about (leeches aside!). It’s perfectly safe to swim, boat, and fish in water with benthic macroinvertebrates - in fact, their presence lets you know the water is clean and healthy.
While BMIs as a whole play an important role in our aquatic ecosystems, some species do pose a risk to our watershed. Invasive species such as Zebra and Quagga mussels could easily be accidentally introduced to waterways in Alberta and would choke out native species and ruin ecosystems. This is why it’s critically important to Clean, Drain, and Dry your watercraft and gear.
(Read on! There's more story below ....)
Q: Great! Where can I learn more?
A: Every Saturday this summer, our Outreach Assistants set up an interactive, educational display called a “Point Duty,” which teaches people about the connection between BMIs and water quality. We harvest benthic macroinvertebrates from the nearby water source, allowing you to see them up close, and give you more information for all your many questions.
This Saturday, August 5, we’ll be in Dutch Creek. To see where we will be in the following weeks, follow us on Twitter or Facebook.