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A bioindicator is a species that helps scientists and environmental managers infer the quality of its habitat. Bioindicators can be plants, birds, reptiles, mammals—any species that is sensitive to certain changes or factors in the environment. Commonly, aquatic macroinvertebrates are used as bioindicators for waterways, lakes, wetlands, and coastal environments. Aquatic macroinvertebrates are small animals that live part or all of their lives in water and are big enough to see with the naked eye, though some are incredibly tiny. The presence or absence of certain aquatic macroinvertebrates can indicate the health of an ecosystem, many times even before other measures of ecosystem health show conclusive results. Bioindicators are tolerant or intolerant of contaminants and other alterations to an ecosystem. For example, damselflies (pictured) live in freshwater as juveniles. Damselflies are insects in the order Odonata, along with dragonflies. Damselfly nypmhs are fully aquatic, and they spend most of their lives as aquatic nymphs. Damselflies lay eggs in plant tissue in or near water, and mayfly nymphs have caudal gills to take in dissolved oxygen from water. Damselfly larvae are sensitive to water depth, water movement, and pH, depending on the species. Although many damselfly species are tolerant of various disruptions to their habitats and certain types of pollution, they also have specific requirements to thrive. For example, several damselfly species require emergent vegetation but are tolerant of acid-rich or base-rich environments. Thus, as considered moderately sensitive to pollution, they are common bioindicators for stream and wetland health when surveyed along with other macroinvertebrates and combined with other measures of ecosystem health. Scientists and managers will systematically collect and survey aquatic macroinvertebrates, along with other data, and put all the results together to determine the approximate health of a waterway. Bioindicator species are also important parts of aquatic food webs. They consume detritus, algae, and/or other aquatic macroinvertebrates, redistributing nutrients and keeping other small predators in check. Healthy aquatic habitats are more biodiverse, and sustaining biodiversity is in turn essential to the health of the environment and the quality of human life.

Photo and haiku by: Samantha Oester