When one looks out on the St. Lawrence waterway, they normally see large container ships passing by. However, the traffic below the surface is far greater, as it is teeming with life. Although they constitute a large part of this underwater community, aquatic macroinvertebrates are often overlooked. Despite this, they represent a key link between primary producers and other consumers, breaking down organic matter and making it available for other organisms. Aquatic macroinvertebrates are also greatly affected by watershed conditions, making them ideal bioindicators for pollution and other changes in water conditions.
Aquatic macroinvertebrates form a rather large group of organisms, which includes representatives from multiple phyla, such as arthropods, annelids, and molluscs. The aquatic arthropods, when considering freshwater species, are comprised of multiple orders of insects, spiders, and crustaceans. Insects constitute the most numerous arthropods, and orders such as Odonata (dragonflies and damselflies), Trichoptera (caddisflies), Plecoptera (stoneflies), Coleoptera (beetles), Diptera (flies), Ephemeroptera (mayflies) and Hemiptera (water bugs) are common inhabitants of freshwater bodies (Richardson 2008). Annelids (worms and leeches), though less represented, are also present in freshwater ecosystems. Molluscs are represented in freshwater ecosystems mainly by the gastropod class. Most aquatic gastropods are snails (Kershner, Lodge 1990) and are found near the substrate or on supporting structures like rocks.
Aquatic freshwater invertebrates can live in nearly any freshwater body, with the exception of very highly polluted or deep ground waters bodies (Strayer 2006).
Aquatic macroinvertebrates can be divided into two different groups: benthic and nektonic organisms. Benthic organisms are those organisms that live near the substrate. Leaf litter material and other organic matter that falls to the substrate significantly affect these organisms. Nektonic organisms reside in the water column above the substrate, swimming freely. These organisms are generally more affected by factors such as water current.
Aquatic macroinvertebrates play a crucial role in nutrient cycling, decomposition and translocation of materials (Wallace, Webster 1996). Watson-Ferguson et al. (2006) described five major functional groups of aquatic macroinvertebrates: shredders, collectors, scrapers, piercers, and engulfers. Each occupy a particular niche within an ecosystem. Shedders, like some caddisfly larvae, feed on coarse organic material such as wood and leaf litter and create fine particles, which are readily available for collectors to feed on. Collectors, such as mayfly larvae, are not limited to eating these particles, as they also feed on bacteria and waste from other organisms. Snails and water pennies are scrapers, which are adapted to feed on algae and plant matter attached to substrate. Piercers, such as water scorpions, obtain food by injecting their prey with a digestive enzyme, which turns the internal organs of prey into a consumable liquid. Engulfers, which include dragonfly larvae, feed on other invertebrates, and can even consume small fish. Many insect larvae undergo metamorphosis and leave the water as adults, translocating nutrients to terrestrial ecosystems.
Understanding the habitat preferences of aquatic macroinvertebrates can aid in the preservation and monitoring of aquatic habitats. Their large taxonomic diversity has allowed aquatic macroinvertebrates to adapt to a wide variety of environmental conditions and factors. The type of river habitat being studied can be used to predict the traits of macroinvertebrates within them, as well as the taxonomic composition present. Factors such as pH, elevation, water depth, and substrate type affect how different organisms adapt to their aquatic habitats. For example, in sand and silt substrate, deposit feeders are responsible for detritus, whereas it is done by filter feeders within water bodies containing high amounts of submerged vegetation (Demars et al. 2012).
Dragonfly larvae are an example of aquatic macroinvertebrates that can be used as biological indicators for changes in aquatic habitats. Knowledge concerning these adaptations can provide important information about habitat conditions. For example, dragonfly abundance increases with a higher amount of aquatic plant density. Dragonfly larvae use plants for a number of purposes, such as for the protection of larvae from predators. Additionally, the pH of an aquatic habitat has been shown to affect dragonfly larvae abundance, with more acidic habitats decreasing the amount of dragonflies present (Honkanen et al. 2011). With knowledge about how aquatic factors affect dragonfly abundance, habitats can be monitored for changes in conditions, such as pH, by observing changes in dragonfly populations.
Currently, researchers are investigating the effects of aquatic macroinvertebrates on other species, as well as on their environment. Many are investigating the potential use of predatory invertebrates as biological controls for mosquito populations. This includes studies by Banerjee et al. (2010) and Saha et al. (2012). Downing and Leibold (2010) found that increased macroinvertebrate diversity accelerated the recovery rate of ecosystems following environmental shocks. Additionally, the potential impacts of new nanotechnologies on aquatic ecosystems are being studied. Pokhrel and Dubey (2012) researched the effect of silver nanoparticles on the predator-prey relationship of Daphnia magna and larval dragonflies and found that these nanoparticles reduced the ability of the Daphnia to detect predators.
Though aquatic macroinvertebrates are physically small, they are a major link in the energy exchange from producer to consumer. The biodiversity of aquatic invertebrates within watersheds is an important indicator of the ecosystem’s function. Knowing the types of aquatic invertebrates present in a watershed allows for proper environmental assessments to be made. Benthic organisms are especially important for this, as they reside on the substrate, which is where debris and pollutants often collect. Having a detailed natural history of these species is important for seeing the changes happening in the populations. With these kinds of records, changes in diversity caused by pollutants or litter collection can be correlated more easily. Aquatic macroinvertebrates play important roles within their ecosystems, while also providing valuable data for humans to use.
Banerjee, S., Aditya, G., Saha, N. & Saha, G.K. (2010) An assessment of macroinvertebrate assemblages in mosquito larval habitats-space and diversity relationship. Environmental Monitoring and Assessment, 168, 597-611. DOI: 10.1007/s10661-009-1137-9
Demars, B.O.L., Kemp, J.L., Friberg, N., Usseglio-Polatera, P. & Harper, D.M. (2012). Linking Biotopes to invertebrates in rivers: Biological traits, taxonomic composition and diversity. Ecological Indicators, 23, 301-311. DOI: 10.1016/j.ecolind.2012.04.011
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Saha, N., Aditya, G., Banerjee, S. & Saha, G.K. (2012) Predation potential of odonates on mosquito larvae: Implications for biological control. Biological Control, 63, 1-8. DOI: 10.1016/j.biocontrol.2012.05.004
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Watson-Ferguson, K., Han, C., McGarvey, J., Miller, L. & Izaak Walton League of, A. (2006) A guide to aquatic insects and crustaceans. Stackpole Books, Mechanicsburg, PA.