WHAT ARE AQUATIC MACROINVERTEBRATES?
"Aquatic" means water, "macro" means big (or big enough for us to see without using a microscope), and "invertebrate" means without a backbone, so an aquatic macroinvertebrate is a water bug that we can see with our naked eye.
Some aquatic macroinvertebrates spend their entire lives living in water, although many just live in the water when they are immature. As they reach maturity, larvae metamorphose and leave the water, spending their adult life on land. In many cases, the insects are adults for a very short time. For example, many mayflies live in streams for months to years but last on land for just a few days. During this time they mate and lay their eggs in or near water so the cycle can continue.
The larval and adult forms do not look alike, as can be seen with these dragonfly images above. However, in some ways they're quite similar. For example, dragonfly larvae and adults are both skilled predators.
WHY CARE ABOUT AQUATIC MACROINVERTEBRATES?
Aquatic macroinvertebrates live in many different types of aquatic habitats. Some live in fast moving streams, consuming leaves, twigs, and other plant material that falls into the water. Others live in wider, sunnier rivers or shallow ponds, scraping algae off rocks or on the surfaces of large aquatic plants. Many are predators, or prey upon other macroinvertebrates. Some live within the soft sediments at the bottom of lakes and ponds and others capture food that is drifting along in the current. In all these settings, macroinvertebrates provide an important food source for fish and other predators.
Because different types of macroinvertebrates tolerate different stream conditions and levels of pollution, their presence or absence is used to indicate clean or polluted water. For example, most larvae of caddisflies, mayflies, and stoneflies cannot survive in polluted water so streams with these bugs are assumed to have good water quality. The absence of these organisms in a water body, however, does not necessarily indicate that the water quality is poor. Other natural factors, such as temperature and flow, also come into play.
FACTORS THAT INFLUENCE MACROINVERTEBRATE HEALTH
Seasons- life histories of invertebrates are tied to food availability. For example, macroinvertebrates that eat algae are most abundant in the summer when algae production is at its highest.
Dissolved Oxygen- macroinvertebates breathe oxygen that is dissolved in the water. In the immature stage, many species require high levels of dissolved oxygen in order to survive.
Substrate- what the bottom of the stream is comprised of will affect the types of macroinvertebrates. For example, macroinvertebrates that eat tiny food particles prefer sandy or muddy substrate.
Nutrient enrichment- added nutrients from human sewage, fertilizer or manure can accelerate the growth of algae and other plants. When these plants die, decomposition by microorganisms can use up dissolved oxygen in the water.
pH- Dumping of industrial pollutants and runoff from mining activities can lower pH (making water more acidic). Low pH can weaken shells and exoskeletons and kill macroinvertebrates.
Removal of riparian vegetation- this takes away important food sources and breeding grounds for macroinvertebrates.
Learn more about limiting human impacts: Protect Your Water.
Check out http://macroinvertebrates.org for additional information and cool, interactive photos.
Check out https://leafpacknetwork.org/ for information on a unique macroinvertebrate monitoring technique.