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Understanding how human activity impacts zooplankton is essential for managing and protecting lakewater
By Annabelle Fortin-Archambault, PhD Candidate, Aquatic Ecology, Université du Québec à Montréal (UQAM)Beatrix Beisner, Professor, Aquatic ecology, Université du Québec à Montréal (UQAM)Alison Derry, Professeure agrégée, Sciences biologiques, Université du Québec à Montréal (UQAM),
We are researchers at the Université du Québec à Montréal and part of the Groupe de recherche interuniversitaire en limnologie , a network of researchers across Québec who study lake ecosystems. We focus much of our research on zooplankton as they are such central food web players.
Zooplankton are a diverse group of microscopic animals that live in lakes, some large rivers and oceans. They are an essential central link in freshwater food webs and can act as first indicators of any impacts on entire lake ecosystems .
This article is part of our series Our lakes: their secrets and challenges . This summer, The Conversation and La Conversation invite you to take a fascinating dip in our lakes. With magnifying glasses, microscopes and diving goggles, our scientists scrutinize the biodiversity of our lakes and the processes that unfold in them, and tell us about the challenges they face. Don’t miss our articles on these incredibly rich bodies of water!
Dormant eggs
Zooplankton consist of several different groups, of which copepods and cladocerans are the two most studied. As crustaceans, both groups are covered in a hard exoskeleton or carapace made of chitin . Copepods have elongated bodies and can be herbivorous, omnivorous or carnivorous. They have complex life cycles and reproduce sexually .
In contrast, cladocerans are generally more rounded, with bivalve carapaces and are more often herbivorous. They can reproduce both sexually and asexually, and have life cycles that range from days to weeks .
Both copepods and cladocerans can produce dormant eggs — eggs that do not hatch right away — when the environmental conditions are unfavourable, usually in the fall . These eggs hatch later, when environmental conditions are suitable, such as in the spring.
However, many dormant eggs, rather than hatching, are instead buried in lake sediments each year, creating a historical record that can then be used to study how zooplankton populations potentially adapt to human and other disturbances in lakes .
An important food source
Zooplankton can affect lake ecosystems in several ways. In part, this is because of their intermediate food web position between phytoplankton (microscopic algae), which primarily harness energy from the sun to produce food, and predators that depend on zooplankton as prey.
Ongoing research into these stressors, and how zooplankton respond to them, is essential for our ability to understand, predict and mitigate their impacts on freshwater ecosystems.
Pollution has been a major threat to freshwater ecosystems since the beginning of the industrial era . Lakes can be polluted by many different types of contaminants, including pesticides, salt, microplastics and metals. These pollutants come from many different sources, such as agricultural practices, mining and industry and urban waste.
Lake salinization reduces zooplankton abundance and diversity, impairing their functional roles in controlling algal abundance and as a food resource for their predators . This, in turn, reduces the energy and resource transfer by zooplankton, thereby leading to knock-on effects .
Another long-standing threat to freshwater zooplankton is eutrophication — an over-supply of nutrients essential to primary production, primarily phosphorus and nitrogen . In eutrophic lakes, zooplankton communities often shift towards smaller-bodied species that are less rich in phosphorus than larger species that tend to dominate temperate lakes .
This reduces the regulatory role of zooplankton, making them less efficient in controlling algal blooms, which are also strongly favoured by the nutrient additions associated with eutrophication.
The impacts of climate change
Climate warming will also cause a shift towards smaller-bodied and faster-growing zooplankton through both direct effects on metabolic rates and through increased predation by fish, who prefer feeding on larger zooplankton, further decreasing their abundances in lakes .
Because larger zooplankton are more efficient grazers of phytoplankton (algae) and given their role as fish prey , this shift reduces the efficiency of zooplankton in food web transfers in lakes.
The study of freshwater zooplankton and the effects that human actions have on their communities is essential to our understanding of lake functioning in our changing world. Zooplankton research is essential for the effective management of freshwaters because it helps us mitigate, restore or work with the impacts to lakes caused by human activity.
Alison Derry receives funding from the Natural Sciences and Engineering Research Council of Canada and the Fonds de recherche du Québec - nature et technologies.
Annabelle Fortin-Archambault receives funding from the Groupe de recherche interuniversitaire en limnologie (GRIL) and the Natural Sciences and Engineering Council of Canada Discovery grant awarded to Alison Derry.
Beatrix Beisner receives funding from the Natural Sciences and Engineering Research Council of Canada and the Fonds de recherche du Québec - nature et technologies.
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