Using Benthic Macroinvertebrates to Determine Water Quality

What are Benthic Macroinvertebrates (BMIs)? animals with no backbones are visible with the naked eye live at the bottom of shallow waterways Benthic means “bottom dweller.” Even though a microscope is not needed to see macroinvertebrates, they can be used for students to see these organisms in much greater detail. The best location to look for BMIs would be riffles. Riffles are shallow areas of fast moving white water. The cobble/gravel bottoms and well-oxygenated water of riffles provide optimal conditions form many BMIs.

Examples of BMIs It’s important to point out that many of these organisms are insect larvae which may look unfamiliar to students. Students may need to study pictures of insect larvae before they try to identify them out in the field. Other macros include mollusks, worms, and crustaceans.

Why Use Macroinvertebrates to Determine Water Quality? important links in the food chain permanent residents of the stream susceptible to any pollutants in the water BMIs are recyclers of nutrients and food for fish. They are relatively sedentary residents of the stream bottom so they are often a pollutant’s captive audience. They can be affected by even subtle levels of degradation. This is a good time to discuss the reason why miners took canaries into the coal mine. Macros are like canaries, they indicate the health of a body of water like canaries indicated the health of the air in a coal mine.

Biologists categorize all forms of life in to various levels of taxonomic groupings. Review those levels with students (kingdom, phylum, class, order, family, genus, and species). The majority of BMIs are in one of three phyla: annelida (leeches and segmented worms), arthropoda crustaceans and insecets), mollusca snails, clams, and mussels). Even though there are thousands of species in each phylum, using the simplified field method of identifying BMIs, students will only need to sort BMIs into major groups (mostly orders). Beyond the major group levels, students will only need to distinguish one individual from another by noticing differences in body parts or overall morphology (body form and structure).

Identifying BMIs Easiest to identify: Snails (class Gastropoda) Clams and Mussels (class Pelecypoda) Snails have one coiled shell. Some snails have sinistral (left-turned) shells with a large shell opening and no operculum (hard covering used to close the shell opening). Other snails have right-turned shells with a concentric operculum. Clams and mussels have a body enclosed within two hinged shells. The picture on the bottom right is that of a zebra mussel which is an invasive species in Missouri. They filter plankton from the surrounding water destroying the food chain in many freshwater habitats.

Characteristics of Worms and Leeches no head No legs No wings No exoskeletons Aquatic worms spend their entire lives in water. The leeches found in the KC area are very small and not a danger to people.

Characteristics of Crustaceans Scud Sowbug Crayfish Exoskeleton Head has 2 compound eyes 2 pairs of antennae 3 pairs of mouth parts Swimmerets on the abdomen Most crustaceans have more than 6 legs, but do not have wings. They shed their exoskeleton (molt) as they grow. Scuds are very similar to freshwater shrimp. Sowbugs are also known as rolly-pollies or isopods. Crayfish are also known as crawdads. Crayfish in the KC area rarely get larger than about 2 inches.

Characteristics of Insects Head has compound eyes, antennae, and mouth parts Thorax has 3 pairs of legs and wings attached Abdomen is the longest region of insect’s body The insect body is segmented and divided into 3 major regions—head, thorax, and abdomen. The head appears to be a single segment but is actually composed of several fused segments. Just below the head, the thorax is composed of 3 distinct segments, with one pair of legs attached to each. If an insect has wings, they are also attached to the thorax. Just below the thorax, the abdomen is usually the longest region of an insect’s body and is composed of several segments. Unfortunately, aquatic insects can be difficult to identify because many are immature forms and thus are not fully developed. While many immature forms do have 6 legs, a distinct thorax and abdomen, and even undeveloped wings, many lack these features, and even appear headless

Aquatic Insect Life Cycle Complete Metamorphosis The change from one form to another is known as metamorphosis. Some insects go through a complex set of changes known as complete metamorphosis. Insects such as flies, beetles, and caddisflies begin their aquatic existence as an egg, laid in the water by the winged adult. The egg develops into a larva. The larva gradually transforms into a pupa. Pupae are generally non-moving and encased, like a cocoon or a butterfly or moth. The pupa undergoes drastic changes in anatomy and physiology, eventually emerging as a winged adult. Other insects, such as dragonflies, stoneflies, and mayflies, undergo a less complex set of changes known as incomplete metamorphosis. These insects begin their lives in streams as an egg which metamorphosis into a larva. The larva metamorphose into a larva. The larva metamorphoses into a winged adult; there is no pupal stage. The larval forms of insects which undergo incomplete metamorphosis are sometimes referred to as nymphs. In general, nymphs resemble their adult counterparts much more than the larval forms of insects which undergo complete metamorphosis.

Categories of Pollution Tolerance Biologists have determined the pollution tolerance of many common BMIs. Usually, in discussions on BMI pollution tolerance, the pollution in question is excess nutrients or sediments, causing low dissolved oxygen conditions. In general, mayflies, stoneflies, and caddisflies have the lowest tolerance to pollution, while midges, aquatic worms, leeches and blackflies have the highest. Beetles, craneflies, and crustaceans tend to be in the middle (“somewhat tolerant”).

Pollution Sensitive macros can only live in clean water Pollution Sensitive macros can only live in clean water. Top row: caddisfly larva, mayfly larva, and dobsonfly larva (also known as a hellgramite). Bottom row: right-sided snail, water penny, stonefly larva, and riffle beetle. Pollution Sensitive

These are macros that can live in clean water or water that contains a moderate level of pollution. Top row: cranefly larva, crayfish, and alderfly larva. Bottom row: scud, fishfly larva, damselfly larva, and dragonfly larva. Somewhat Sensitive

Pollution Tolerant macros can live in clean, moderately polluted, or very polluted water. If these are the only macros found in a body of water, it’s an indication that the water is polluted. Tope row: blackfly larva, left-sided snail, and leeches. Bottom row: aquatic worm and blood midge. Pollution Tolerant