All about Aquatic Macroinvertebrates

Aquatic + Macro + Invertebrate = Aquatic Macroinvertebrate

Aquatic is another word for water. The macroinvertebrates we will be looking at are ones that spend some or all of their lives in waterways.
Macro means big enough to see with your eyes (some of them are difficult to identify without a microscope, however).
Invertebrates are animals without backbones. Some can be soft and squishy, some have a hard shell on their body and others live in specially constructed mobile homes!

These water dwelling, spineless creatures are called aquatic macroinvertebrates.

What’s so cool about macroinvertebrates?
Macroinvertebrates are a diverse group of animals, ranging from insects and crustaceans to molluscs and worms. They have been around for about 500 million years and some were even living in our waterways before the dinosaurs! Can you imagine seeing a dragonfly with a wing span over one metre? Well, pre-historic dragonflies were the largest spineless creatures ever to have lived. Thankfully they have dropped in size.

Our modern day macroinvertebrates are no less amazing however! Many look strange and fascinating. They live weird lives and can have disgusting habits. Some breathe through their bottoms, some stab each other with piercing mouthparts, while others make their home out of a piece of grass! They can be one eyed, ten legged or swim upside down!

Macroinvertebrates are the most common critters to be found anywhere there’s water. You’ll find them in creeks, wetlands, drains, dams and sometimes even in your swimming pool! Fish, frogs and birds depend on these spineless creatures for food.

The Life cycle of a macroinvertebrate
Aquatic macroinvertebrates live and grow in interesting ways, with most beginning life as an egg. When hatching from the egg, different macroinvertebrates may grow in different ways.

Some hatch into nymphs, which are miniature versions of the adult. As they grow in size their skin grows with them, and they do not change in their structure or appearance from baby to adult eg. worms and snails. Some, such as yabbies, have hard outer skins (exoskeletons) that need to be shed so that they can get bigger.

Other macroinvertebrates hatch into larvae which look absolutely nothing like their parents! They must undergo one or two stages of metamorphosis before eventually reaching their adult form eg. dragonflies, mosquitoes.

What’s for dinner?
Macroinvertebrates fit into one or more of these feeding groups, depending on what they eat and how they feed: Detritivores, Herbivores, Carnivores.

Detritivores - these munch on dead plants and animals found at the bottom of waterways.

There are two main groups: Filter feeders and collectors. • Filter feeders feed on organic matter found in the water such as algae, leaves and tiny invertebrates. They include some midge larvae and some fly larvae. • Collectors take up small particles of organic matter from the sediment. They rely on microorganisms to break up larger plant material on the streambed. They include yabbies and worms.

	Herbivores – these prefer to eat living plants and algae. The two main groups are scrapers and shredders.
	• Scrapers, like snails and mayfly larvae, scrape algal growth off surfaces such as rocks, plants and logs. • Shredders break up larger items in the water such as leaves and bark, which they turn into edible food. They include some caddisfly larvae.

	Carnivores - eat other animals smaller than themselves. They are known as predators.
	• Predators reside at the top of the macroinvertebrate food chain (what animals eat, which animals eat other animals), and include dragonflies and damselflies.

Why are we interested in macroinvertebrates anyway?
The abundance and diversity of aquatic macroinvertebrates can tell us how healthy or polluted a waterway is.

Different aquatic macroinvertebrates have different tolerance levels to water pollution. Some water critters are sensitive to pollution, which means if the waterway was to become polluted they will die or move elsewhere. Other critters are tolerant to pollution, meaning they can survive in polluted water.

Macroinvertebrates also require suitable habitat for food, shelter and protection. Suitable habitat includes a good selection of rocks, logs, silt and plants in and along the edge of the waterway.

So by sampling a waterway for macroinvertebrates and identifying what’s there you will get a good indication of water quality and habitat condition.