Life Underwater

Newfoundland & Labrador is Blessed with an Abundance of Freshwater Habitats

A collage of Aquatic Macroinvertebrates (Fig. 1)

Text & Photos by Mardon Erbland

September 2023

More Than Fish

If you were asked to name something that lives in Newfoundland and Labrador's ponds, how would you answer? Perhaps, "fish". Perhaps "trout". Whatever your response, it's almost guaranteed that you wouldn't say, "amphipods". Nor are you likely to mention copepods, or ostracods, or planarians, or insect larvae, or a host of other tiny animals that make their home in Newfoundland and Labrador's waters. Collectively these organisms are known as "aquatic macroinvertebrates".

Aquatic macroinvertebrates are important members of the earth's ecosystem. Even so, they often go unnoticed because of their small size.

The "aquatic" portion of their name means they live in freshwater. "Macro" means they are large enough to be seen without a microscope (generally greater than 0.5 mm in length.) "Invertebrate" means they lack a spine. Aquatic macroinvertebrates exist in vast numbers, in a wide variety of freshwater habitats, including rivers, streams, brooks, ponds, lakes, bog holes, wetlands, swamps, drainage ditches, vernal pools, and even in abandoned containers that collect rainwater.

The image above (see Fig. 1) is a photographic collage of 14 different types of aquatic macroinvertebrates found in waters on the northeast portion of Newfoundland's Avalon Peninsula. As you look through the images, be aware that all the photos were taken while the animals were alive and swimming underwater.

Everyone 'Hates' Mosquitoes

Mosquito Larva (Fig. 2a)    &    Mosquito Pupa (Fig. 2b)

Mosquito larvae are the most disliked aquatic macroinvertebrate, and for good reasons. Adult female mosquitoes suck human blood. Many species spread disease. According to the Centers for Disease Control, mosquitoes are the world's deadliest animal. One of those deadly species is Aedes japonicas. It was reported as having been seen in the St. John's area as early as 2013.

The life cycle of mosquitoes begins with eggs. These are usually laid in water, but not always. They then progress through several growth stages via a process called metamorphosis. The larval stage (Fig. 2a) and pupal stage (Fig. 2b) are spent entirely in water.

Mosquito larvae hang vertically in the water while breathing and use the respiratory siphon on their tail to take in oxygen. Mosquito pupae breath through the respiratory trumpets (antennae like structures) on their head. Using photos alone, it's difficult to distinguish the pupal stage of mosquitoes from the pupal stage of non-biting midges. The shape of the respiratory trumpets can be one clue. The larvae of most mosquito species prefer quite water. Many prefer habitats such as a bucket filled with rainwater. The same goes for mosquito pupae. The adult stage is the land-based pest that we love to hate.

The red organism on the pupa's tail (Fig. 2b) is a water mite (more on that later).

Beetles Like Water Too

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(Fig. 3a)   Predaceous Diving Beetle   (Fig. 3b)                  

Beetles are often thought of as land-based animals. It is true that many types of beetles spend their entire life on land. It's also true that some beetles like their watery lives better than being on land. Predaceous Diving Beetles are one such animal.

Predaceous Diving Beetles have a life cycle that is somewhat different than mosquitoes. Females lay their eggs into underwater plants. The eggs hatch and become larvae (Fig, 3b). When the larva is ready to pupate, it moves on to land. Once the pupa turns into an adult (Fig. 3a) the beetle goes back into the water.

Amphipod Species Complex & Toxicity Tests

Amphipods

Hyalella wellborni (Fig. 4a)     Crangonyx sp. (Fig. 4b)

Freshwater amphipods are one of the most ubiquitous macroinvertebrates to be found in the freshwater habitats on the Northeast Avalon. Within this area, Hyalella azteca is the 'species' most often encountered. But this 'species' is actually a species complex. A species complex is when many different species get lumped together and referred to by a single species name, such as H. azteca. It is likely that some species within the H. azteca species complex have yet to be described and named. In 2015, David Soucek, et. al. described two new species within the H. azteca complex. These new species are H. wellborni and H. spinicaud.

In 2023, A.G. Cannizzaro used DNA sequencing to identify an amphipod collected by this article's author. The sample came from a drainage ditch in Logy Bay. Subsequent molecular phylogenetic analysis showed the sample to be the species H. wellborni (Fig. 4a). This appears to be the first confirmation of H. wellborni on the island of Newfoundland.

Amphipods are often used to perform toxicity tests on water samples. Amphipods belonging to the species complex H. azteca are commonly used for these tests. One approach is to collect H. azteca samples in the wild and use them to culture new individuals in the laboratory. The cultured individuals are exposed to different water samples and their growth rate, and/or mortality rate, is monitored. This information is then used to determine the level of toxicity in the test material. Newfoundland has a connection to this process via Avalon Laboratories in St. John's. The company's web site lists "Amphipod Mortality" testing as one of their environmental monitoring programs for sediment samples.

Other species of freshwater amphipods are also present in Newfoundland and Labrador. According to a 1968 report by D.H. Steele, the second most prevalent genus of Newfoundland freshwater amphipods (next to Hyalella) appears to be Cragonyx (Fig. 4b).

Copepods are Abundant, Fast, and Strong

(Fig. 5a)            Cyclopoid Copepods             (Fig. 5b)

Copepods are one of several tiny macroinvertebrates that are referred to as zooplankton. Freshwater and saltwater copepods, when counted together, have been said to represent the most numerous multi-celled organism on earth.

Copepods are also fast. This makes them difficult to photograph while alive. One estimate is that they can travel 90 meters in an hour. That is proportionally the human equivalent of walking at a rate of 81km/hr. And when it comes to strength compared to its size, Science Daily has described copepods as the "world's strongest animal".

The cyclopoid copepods found on the Northeast Avalon come in a wide variety of colours. When females produce eggs, many species of copepods place the eggs into sacs attached to the rear of the female's body. (Figs. 5a & 5b) They then remain there until they hatch.

Cyclopoid copepods have a single eye, often red in colour. It's located in the centre of their head. That eye is how they got the name "cyclopoid copepods". In Greek mythology, there were three brothers known as "cyclopes" (the singular form is "cyclops"). Each cyclops had one eye in the center of his forehead. Hence the single-eyed copepods got the name "cyclopoid".

Not All Worms Are Round

Planarian (Fig. 6)

Planarians are aquatic flatworms. They swim freely in the water and are not parasitic. Planarians have one remarkable capability. If a planarian is cut in half, it will regenerate a completely new organism from each half.

According to Britannica Online, planarians range in length from about 3mm to 300mm. The freshwater planarian shown in Fig. 6 is 5mm long. Most live in freshwater although both saltwater and land-based species exist.

According to Susan Bergeron and Betty Miller at Plymouth State University, "If a flatworm is starved it is capable of shrinking to hatching size and when fed it has the ability to grow back to original size."

The term, "Planarian" can be a bit confusing. "Planarian" is not a scientific name, so it's used for multiple types of flatworms. Most frequently it's used to describe flatworms in the Order Tricladida, but not always.

Fleas That Like Water

Anomopods (Water Fleas)

Eurycercus longirostris (Fig. 7a)    Ophryoxus gracilis (Fig. 7b)

Did you know that the pond where you or your friends go swimming is probably filled with fleas? Well, at least "sort of" filled with fleas. "Water Flea" is the name commonly given to water dwelling Anomopods. But anomopods are not actually fleas. They are crustaceans.

Water fleas eat mostly microscopic organic material. They propel themselves through the water by moving their relatively large antennae. When they coexist with fish, water fleas serve as food for the fish. Water fleas are easily found in a variety of Newfoundland and Labrador's aquatic habitats.

According to Ian Gardiner, citing Bekker et al, 2012, the species Eurycercus longirostris (Fig. 7a) "is found in water bodies of different types, and displays a wide range of temperature preferences."

According to Ian Gardiner and the eFauna BC website, a Newfoundland voucher specimen of Ophryoxus gracilis (Fig. 7b) was obtained in Terra Nova National Park on 1997-Sep-17 and photographed in 2017 by Ian Gardiner.

Mites Not Spiders

(Fig. 8a)              Water Mites             (Fig. 8b)

Water mites are arachnids but not spiders. Scientifically speaking, they belong to the infraorder Hydrachnidia. They are generally colourful. Bright red water mites are common, but they also come in various shades of orange or reddish-orange. Green or blueish-green legs are also common.

Water mites have one pair of double eyes. The double eyes can be easily seen in Fig. 8a. This gives the impression that they have 4 eyes instead of 2 double eyes. They also have eight legs that are lightly covered with setae (a.k.a. spines). These are just barely visible in Fig. 8a & Fig. 8b.

Some water mites are parasitic on mosquitoes. A red water mite can be seen attached to the mosquito pupa in Fig. 2b.

The water mites shown in Figures 8a and 8b are both under 2mm in length. They rarely get larger than 3mm.

Most water mites live close to the bottom of their aquatic habitat.

Water mites do not have lungs or gills. They breath by absorbing oxygen from the water directly through the surface of their bodies. This allows them to live in hypoxic water that wouldn't have enough dissolved oxygen to support some of the other aquatic macroinvertebrates.

Ostracods: Tiny But Important

(Fig. 9a) Ostracods (Fig. 9b)

The freshwater ostracods commonly found in Newfoundland are only about 1mm in length. The body of an ostracod is protected inside a 2-part shell. The shells are hinged together on the back edge. This is somewhat like a mussel or a clam, but ostracods are tiny in comparison to those organisms. The ostracod antennae are used for swimming.

Even though freshwater ostracods are common, the majority of ostracods live in saltwater, and a few live on land.

According to a freshwater invertebrate database managed by Daniel L. Graf at the University of Wisconsin, Stevens Point, Wisconsin, North America is home (or presumed home) to 353 named species of freshwater ostracods, 85 genera, and 13 families.

According to Andrea Schneider, et. al., freshwater ostracods have existed since the early Palaeozoic era (about 500 million years ago.) Dr. Schneider et. al. further write that this long survival period has resulted in one of the most complete fossil records of any extant arthropod group. That long fossil record, in turn, makes freshwater ostracods one of the most interesting indicators for studying climate and environmental change over time.

Marsh Fly Larva

Sepedon fuscipennis larva (Fig. 10)

Marsh flies are sometimes called snail-killing flies. That's because they feed primarily on snails and snail eggs. Marsh flies are sometimes used for the biological control of terrestrial gastropods. Marsh flies are in the Family Sciomyzidae. The larvae usually live in marshes and along the edges of ponds. Occasionally they are found in streams. According to S. Schorno et. al. in the Canadian Journal of Arthropod Identification, "adults fly quite low, slowly and for short distances".

Worms That Are Not Worms

(Fig. 11a)        Chironomid Midge Larva        (Fig. 11b)

"Bloodworm" is a term generally applied to red coloured chiromid midge larvae (Figs. 11a & 11b). Less often it is used to describe red segmented worms. Despite the name, chironomid bloodworms are not worms at all. They are the bottom dwelling larval stage of non-biting midges. Chironomids live in many aquatic habitats throughout the Northeast Avalon.

Adult chironomids (which do not bite) look somewhat like small mosquitoes.

The term "bloodworm" originates from the larva's bright red colour. The colouring is caused by the presence of hemoglobin in their bodily fluids. The hemoglobin allows them to survive in water where a low oxygen content would be unsuitable for other aquatic macroinvertebrates.

Chironomid bloodworms are a popular food for feeding fish in freshwater aquariums. Bloodworms can be purchased for this purpose in live or frozen form.

Aquatic Snails - Check the Antennae

(Fig. 12a)         Pond Snails, Bladder Snails, and Allies        (Fig. 12b)

Air breathing aquatic snails (sometimes called basommatophorans) have 2 antennae (Fig. 12a). Land-based snails have 4 antennae. Air breathing aquatic snails have 2 eyes located at the base of the antennae (Fig. 12a). Terrestrial snails have eyes located at the tips of their antennae.

Aquatic snails are common in a variety of Newfoundland and Labrador's aquatic habitats.

Nymphs, Naiads & Larvae

     Mayfly naiad (Fig. 13a)          Damselfly naiad (Fig. 13b)

Naiads, nymphs, and larvae are all juvenile forms of arthropods. In that sense, they are all the same thing. But at a more precise scientific level they are each unique.

The name depends on the exact nature of the process by which the arthropod ages. That process is known as metamorphosis. It involves a transition in appearance and behaviour. Depending on the type of arthropod, the stages can vary, and each stage has a different name. Some of the names include egg, larva, pupa, nymph, naiad, adult, and instar.

The choice between naiad, nymph, and larva depends on two things: (1) if one of the juvenile stages is a pupa, and (2) if a juvenile stage is aquatic. If an insect has two juvenile stages, then one is known as a larva and the other as a pupa.  If an insect goes through an aquatic larval stage but no pupal stage, then that larva is called a naiad. If an insect has a terrestrial larval stage and no pupal stage, then that larva is called a nymph.

Over their lifetime, many arthropods (especially insects) go through a series of progressive molts. A molt is when an arthropod sheds its exoskeleton. The period between two successive molts is called an instar. Only a few arthropods continue to molt as adults. Both Mayfly naiads (Fig. 13a) and Damselfly naiads (Fig. 13b) go through multiple instars. The number of instars depends on the species. It can be less than a dozen, or up to several dozen.

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Author's Message

I'm an amateur naturalist with no formal training in biology. As a hobby, I began photographing arthropods in 2006 and aquatic macroinvertebrates in 2014. It's a fun activity but I'm not good at identifying the organisms that I photograph. For ID's, I rely heavily on community-based identifications from people on BugGuide.net, iNaturalist.org, and recently, on DNA Barcodes.

I also like to learn about the various animals that I photograph and share this information with others. While I've tried to be factual with the material presented in this article, there's no guarantees. I'm not a trained expert in macroinvertebrates.

My latest interest is in DNA Barcoding and molecular phylogenetics. I like the concept of using DNA to identify macroinvertebrates and study the evolutionary relationships between various taxa. I've found that it can be a complicated but fun topic.

Thanks for reading, Mardon

Email: erbland@outlook.com