Water means different things to different people. This year, the conversation around World Water Day is about what water means to you. March 22 marks a day to celebrate water and raise awareness of the global water crisis. The value of water is about much more than its price –
“Water has enormous and complex value for our households, food, culture, health, education, economics and the integrity of our natural environment. If we overlook any of these values, we risk mismanaging this finite, irreplaceable resource.”
Fragility of Freshwater Systems
Currently, water worldwide is under extreme threat from a growing population, increasing demands of agriculture and industry, and the worsening impacts of climate change. One of the effects of these pressures that most of us may see on a daily basis, is the degradation of freshwater systems – including lakes, rivers, ponds and wetlands. The loss of vital freshwater systems is happening at up to 3 times the rate of the loss of forest systems. The fate of freshwater biodiversity, including many species of mammal, fish, bird and macroinvertebrate, currently hangs in the balance, with 27% of freshwater species threatened with extinction.
In order to slow and hopefully halt the speed of freshwater ecosystem and biodiversity loss, agreements including the Convention on Biological Diversity (CBD) and the Sustainable Development Goals (SDGs) are currently in place. One of the SDG’s in particular (SDG6) strives to achieve water and sanitation for all by 2030. For us to achieve these goals and safeguard this critical resource for the benefit of everyone, we need to understand the function of freshwater systems and how current pressures are changing their integrity.
Mighty Macroinvertebrates
Benthic macroinvertebrates, referring to the invertebrates which live in amongst the sediment of freshwater systems, can provide us with a great deal of information regarding water quality in freshwater habitats. Groups of macroinvertebrates, including mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera) and dragonflies and damselflies (Odonata) have different levels of sensitivity to factors such as water pollution and oxygen availability, meaning they are ideal biological indicators of freshwater health.
These groups of species do not only act as health indicators, they also play very important roles in to enable freshwater systems to function and maintain their integrity. Different families of macroinvertebrate have different feeding strategies, meaning they all have important roles in aquatic food chains and nutrient cycling. For example, larvae of sludge worms (Tubificidae) and non-biting midges (Chironomus) speed up the decomposition rate of organic detritus, larvae of finger-net caddisflies (Philopotamidae) are collector-filterers and create silk nets to catch debris and narrow-winged damselfly larvae (Coenagrionidae) are predators that actively stalk and engulf their smaller macroinvertebrate prey.
In STREAM, we target macroinvertebrates to gain and understanding of how healthy watersheds are across Canada, through the presence and absence of key bioindicator groups in benthic DNA samples. In honour of World Water Day, we have selected some bioindicator species to feature in this post which have been commonly found across Canada in samples collected by our partnering community groups.
Mayflies (Ephemeroptera)
Small square-gilled mayfly (Caenidae) larvae can be found in slow-moving or stagnant water, where there is an abundance of silt and loose sediment. They are most often found sprawled on/in the silt or climbing among the plants in aquatic habitats. There are 30 North American species of this family from 4 genera.
Their main feeding styles are collector-gatherer and scraper; they feed by collecting and gathering tiny bits of food or by scraping algae and biofilm from rocks and other substrates in their habitat. From 0 to 10 (0 being least tolerant and 10 being most tolerant), their pollution tolerance score is 6, meaning they can be found in systems which are somewhat compromised in terms of pollution and quality.
Spiny crawler mayfly (Ephemerellidae) larvae are found in lotic-erosional (running-water riffles with coarse sediments) or lotic-depositional (running-water pools and margins with fine sediments) habitats, often among the rooted aquatic plants, moss, root masses, or woody debris. In North America alone there are 80 species of this family from 9 genera.
This family of mayfly has a variety of feeding strategies, differing among species, including collector-gatherers, scrapers, some shredders of detritus or algae, and even one predator. In terms of pollution tolerance, overall this family scores a 2, meaning they tend to be found in low-pollution environments with good water quality.
Stoneflies (Plecoptera)
Common stonefly (Perlidae) larvae are often found clinging to substrate in riffles and other lotic-erosional (running-water riffles with coarse sediments) habitats. They are widespread across Canada (hence the name) and there are roughly 84 North America species and almost 1,000 worldwide.
Young larvae tend to collect and gather small amounts of food until they are large enough to engulf their prey, including caddisflies, midges, and other small invertebrates, meaning this family occupies a large range of feeding styles. From 0 to 10, their pollution tolerance is a 2, which means they tend to be found in low-pollution environments with good water quality.
Giant stonefly (Pteronarcyidae) larvae are usually found in lotic-erosional (running-water riffles with coarse sediments) or lotic-depositional (running-water pools and margins with fine sediments) habitats. They are a widespread family with a total of 9 species found in Canada.
These large stoneflies are mostly shredders, eating mostly algae and decomposing leaf litter. Like most stonefly families across North America, they have a low tolerance to poor environmental conditions, with this family scoring around a 0 on the pollution tolerance scale of 0 to 10. This family is very intolerant of poor water quality and therefore mostly found in healthy, pollution-free systems.
Caddisflies (Trichoptera)
Trumpet-net caddisfly (Polycentropodidae) larvae are usually found in lotic-erosional (running-water riffles with coarse sediments) or lotic-depositional (running-water pools and margins with fine sediments) and lentic-littoral habitats. They live in a silken net that is funnel-shaped, tubular, flattened, or like a spider web.
Larvae of this family either function as collector-filterers or engulfer-predators and there are currently 37 species of this family in Canada. In terms of pollution tolerance, larvae score a 6, meaning they can be found in systems which are somewhat compromised in terms of pollution and quality.
Humpless casemaker caddisfly (Brachycentridae) larvae live in lotic-erosional (running-water riffles with coarse sediments) habitats. This caddisfly lives where the currents are consistently swift and are often found anchored to rocks at the heads of riffles.
This family typically occupy a wide range of feeding types, including grazer-shredders, collector-gatherers or collector-filterers. They are widespread across North America and there are currently 16 species in Canada. Larvae are not very tolerant of pollution (score = 1) and are mostly found in high-quality aquatic environments.
Dragonflies & Damselflies (Odonata)
Narrow-winged damselfly (Coenagrionidae) larvae are mostly found in lentic habitats, except species from the Argia genus, which is usually found in streams among rocks and plants. Nymphs are climbers and stalking predators among plants and roots.
This family is widespread across North America, with 90 species across 15 genera. They are engulfing predators that actively stalk their prey then snatch it up with their labial mask, an arm-like extremity that extends from below the face. In terms of pollution tolerance, they are very tolerant of poor-quality systems, scoring an 8. They can be found within highly degraded habitats with high pollution levels.
Emerald dragonfly (Corduliidae) larvae can be found in varying habitats including streams, as well as lentic habitats such as lakes, ponds, and wetlands. They are sprawlers along the benthos and climbers on plants.
Similar to most other Odonates, they are engulfing predators that actively stalk their prey. This family is fairly widespread, with 7 genera and 50 species in North America. They score a 2 for pollution tolerance, which means unlike other Odonata families, they are indicators of good water quality and low pollution levels.
Summary
Benthic macroinvertebrate larvae can help us understand the value of water based on their individual tolerances to pollution and the functions they perform within freshwater systems. Through monitoring their distribution across Canada in the STREAM project, we can identify watersheds which are health-compromised and inform decision-making to tackle threats to water security.
For more information on World Water Day, visit the official site here.
All invertebrates photos: Learning to See, Seeing to Learn: Freshwater Macroinvertebrates (CC BY-NC-SA 4.0).
By Dr. Chloe Robinson (Postdoc and STREAM project manager)