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Aquatic Macroinvertebrates

Trichoptera larva

Aquatic macroinvertebrates are organisms visible to the naked eye that do not possess a vertebral column and spend at least a portion of their lives in water. They include insects, bivalves, gastropods, annelids, and crustaceans. Aquatic insect orders include Trichoptera, Ephemeroptera, Odonata, Megaloptera, Plecoptera, Diptera, and Coleoptera. These invertebrates are ubiquitous to freshwater ecosystems around the world and are present in both lotic and lentic ecosystems, living among the rocks and sediment.

Life Histories

Aquatic macroinvertebrates are oviparous, however their life history strategies vary depending on their temporal and spatial distributions. Their reproductive strategies fall along a continuum between semelparous and iteroparous, and involve differences in egg number, egg size, and brood care. Once they hatch, the majority of aquatic macroinvertebrates undergo three main life stages: larva, pupa, and adult. Once some reach the adult stage, they leave the water including dragonflies while others remain their entire lives like the water beetle. The evolution of different life history strategies of aquatic macroinvertebrates has allowed species to take advantage of differences in food supply and allow some to better tolerate extreme environmental conditions.

Feeding

Macroinvertebrates play an important role in aquatic food webs as they are major food sources for higher trophic levels and cycle nutrients. They are food generalists and have therefore been classified into five main groups called functional feeding groups to facilitate the incorporation of their ecological roles into research studies. Their classification into these five groups is based on a combination of their morphological characteristics and behavioral mechanisms of feeding. These groups include shredders, grazers, gatherers, filterers, and predators.

Shredders

Shredders feed on coarse particulate organic matter (CPOM) and fine particulate organic matter (FPOM) from terrestrial litter inputs. Using their mouthparts, they shred organic matter to feed and in doing so, suspend smaller particles into the water column. Examples include species of Ephemeroptera.

Grazers

Grazers utilize rasping mouthparts to scrape biofilm and algae off rocks and vegetation and include Trichoptera. They influence algal biomass in aquatic ecosystems and therefore primary production in aquatic ecosystems.  

Collectors/Gatherers

Odonata larval species

Collectors/gatherers primarily wander the bottom substrate scavenging for deposited FPOM and dead organisms. They play a role in bioturbation and resuspension of organic matter and include Diptera.

Filterers

Filterers remove suspended FPOM from the water column using a variety of filtering mechanisms. They expend less energy searching for food, rather relying on sufficient current velocity and upstream food supply.

Predators

Predators consume animal tissue and therefore have direct top-down effects on the food web. Some predator species include Odonata and Plecoptera which utilize grasping mouthparts to ambush their prey.

The River Continuum Concept proposed by Vannote, predicts the functional distribution of aquatic macroinvertebrates in a stream based on food resources. This concept highlights the importance of freshwater ecosystem inputs to food resources and how this influences aquatic macroinvertebrate communities

Bioindicators

Aquatic macroinvertebrate communities are strongly influenced by their environment, and due to their dependence on their surrounding environment, act as bioindicators for the overall condition of freshwater ecosystems. Species have been classified based on their tolerance to environmental changes, and their assemblages can therefore indicate if an ecosystem is healthy.