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what are aquatic macroinvertebrates?
Aquatic macroinvertebrates are visible organisms with no backbone that spend all or most of their life in water. You can find them in rivers, streams, lakes, ponds, pools and even puddles! Some are very good at swimming while others prefer to crawl around on rocks or burrow into fine substrate. Next time you find yourself beside a creek or pond, turn over some rocks and see if you can spot some aquatic macroinvertebrates!
Caddisflies in cases attached to a river rock!
Why are they important?
Aquatic macroinvertebrates are a necessary part of a healthy ecosystem. Within the food web, they serve as the primary processors of organic material while also being food for larger organisms such as fish and other predatory macroinvertebrates.
The diagram below shows some examples of specialized mouthparts for each feeding group. Predators have strong, sharp mandibles for catching and eating other invertebrates. Scrapers are more suited for eating algae off of rocks. Shredders break down large organic matter into smaller pieces for the collectors and filterers. Collectors consume the fine organic matter that falls to the bottom of the stream while filterers consume the fine organic matter that floats within the water column.
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Certain aquatic macroinvertebrates also are good indicators of water quality because they require specific environmental conditions. The three important ones are the mayflies, stoneflies and caddisflies (the EPTs). They need cold, clean, and well-oxygenated water to survive. Their low tolerance of pollution (e.g. sewage, heavy metals, pesticides) and other stressors (e.g. low oxygen, warm temperatures, invasive species) means that if they are present then it's a good indication that the stream is likely healthy.
Mayfly
(Order: Ephemeroptera)
Stonefly
(Order: Plecoptera)
Caddisfly
(Order: Trichoptera)
the 5 c's of a healthy river
Cold
Clean
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Clear
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Complex
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Connected
Life Cycles
Most aquatic invertebrates will live the majority of their life time in the water and only emerge as terrestrial adults. There are two types of life cycles that an invertebrate will go through as it grows, complete and incomplete metamorphosis.
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Complete metamorphosis has 4 distinct phases in which the organism does not resemble its previous form.
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1. Eggs are deposited in the water and hatch into larvae.
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2. Larvae eat and eat and eat until they grow enough begin their transformation.
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3. Pupae enclose themselves in cases, sacs, or their outer skin hardens into a protective shell. Inside they develop into their adult form.
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4. Adults emerge from their cases and fly off to mate and lay more eggs.
Examples are caddisflies, midges, and crane flies.
Incomplete metamorphosis has three phases.​
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1. Eggs are deposited in the water and hatch into nymphs.
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2. Nymphs eat and grow but periodically shed their rigid exoskeleton during their molting phases so they can grow some more. Molting occurs repeatedly during this stage of development. Wing pads develop gradually with each molt.
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3. Adults emerge after the last molt, dry their wings and fly off to mate and lay more eggs.
Examples are mayflies, stoneflies, and dragonflies.
Anatomy
Anterior
Refers to the head end of the body/structure.
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Lateral
Refers to the side of the body/structure.
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Posterior
Refers to the tail end of the body/structure.
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Dorsal
Refers to the upper or top part of the body/structure.
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Ventral
Refers to the lower or bottom part of the body/structure.
Head
Usually capsule-like and contains the feeding apparatus of the organism.
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Thorax
Composed three segments (pronotum, mesonotum and metanotum) and the location of the legs or leg-like appendages.
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Abdomen
Composed of several segments (often 8-11).
Antennae
A pair of slender movable sensory organs located on the head.
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Mandibles
A pair of appendages near the mouth used to grab, cut and chomp.
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Tarsal claws
Claws located at the end of the leg.
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Cerci
Appendages located on posterior end of some insects.