Munch! – A Look into Aquatic Food Webs, Insect Larvae, and Bioaccumulation

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Despite having sampled aquatic insect larvae prior to this class, I had forgotten just how much I enjoy doing so. There is something so fun about kicking at rocks, scooping up netfuls of insects, digging through the collection, and taking out everything that moves. I honestly think I could do it for hours. Unfortunately, too much collection in the long-term would result in some major impacts on the health of aquatic ecosystems. Not only are many aquatic insect larvae important to their food web, but they are also important indicators of water quality in aquatic systems. The aquatic food web starts as all food webs do, with primary producers. 

An aquatic food web
Photo credit: bio.libretext.org

Algae, rooted aquatic plants, and phytoplankton control this trophic level, bringing energy into a usable form for the rest of the ecosystem. These producers are then eaten by primary consumers like aquatic insect larvae, zooplankton, and small fish. Larger fish, amphibians, predaceous insect larvae, and some birds, are the secondary consumers of this system, then these too are eaten by tertiary consumers like birds, even larger fish, turtles, racoons, and bears. Depending on the specific ecosystem, some or all of these species can be present. Unfortunately, many aquatic food webs are threatened by the presence of pollution. One of the most vulnerable groups of aquatic biota are the insect larvae. Many organisms needing pristine conditions for life, these small larvae have become a common way to monitor water quality. Ephemeroptera, Plecoptera, and Trichoptera (EPT) specifically, have become the standard for this field. 

Ephemeroptera, Plecoptera, and Trichoptera
Photo credit: researchgate.net

Each order hosts a large diversity of species, many of which are more sensitive to pollution than most. As a result, the number of different species present of EPT, and how sensitive to pollution the species present are, each give a certain measure of water quality for an aquatic system. Depending on the type of pollution, this use of indicator species can be especially relevant. Processes like the bioaccumulation and biomagnification of toxins in food webs fall into this category. Bioaccumulation is the buildup of compounds in the tissues of an individual organism over time. Typically, this involves compounds that are soluble in fat and have no easy mechanism for removal by the body. Biomagnification, then, is the process of compounds increasing in quantity going up the food chain. Typically, the same compounds that are bioaccumulated can be biomagnified. This occurs because the same way compounds that bioaccumulate in the prey cannot be removed through waste, the compounds that bioaccumulate in the predator as they get absorbed from the prey cannot be removed through waste. Unfortunately, the compounds that do this most commonly are ones which are toxic at higher levels. This issue first came to the attention of the public when it was realized that DDT, a commonly used pesticide, was causing the thinning of bald eagle and other bird eggshells, resulting in the deaths of lots of young. Since then, it has been discovered that there are a large variety of chemicals that can be bioaccumulated and/or biomagnified, particularly in aquatic systems. Some of these include heavy metals, pesticides, and certain pharmaceuticals. This is where finding out the quality of water from a biotic perspective is particularly important. The use of EPT species to see how compounds are affecting the livability of a system is very important. There are a variety of studies looking at the bioaccumulation of these chemicals in aquatic insect larvae, as well as some looking at what the biomagnification of these may entail. With such sensitivity, these larvae have become stars in the show. With all the ways they are being studied, maybe it’s good they’re really fun to catch.

Sources: 

Harada, Takanori, et al. “Toxicity and Carcinogenicity of Dichlorodiphenyltrichloroethane (DDT).” Toxicological Research, 31 Jan. 2016, www.ncbi.nlm.nih.gov/pmc/articles/PMC4780236/#:~:text=DDT%20has%20been%20suggested%20to,populations%20(1%2C2).

Katagi, Toshiyuki, and Hitoshi Tanaka. “Metabolism, Bioaccumulation, and Toxicity of Pesticides in Aquatic Insect Larvae.” Journal of Pesticide Science, 20 May 2016, www.ncbi.nlm.nih.gov/pmc/articles/PMC6140630/#:~:text=2.-,Bioconcentration%20and%20bioaccumulation,both%20are%20involved%20in%20bioaccumulation.

“NMDGF - New Mexico Department of Game & Fish.” Freshwater Aquatic Ecosystems , www.wildlife.state.nm.us/download/education/conservation/non-correlated-curriculum/plans-with-presentations/Freshwater-Ecosystems-Food-Chain.pdf. Accessed 2 June 2023. 

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