Welcome to part two of our aquatic macroinvertebrate series. In case you missed it, Part One provided a brief intro to the world of aquatic macroinvertebrates. In this article, we will explore a couple of non-insect invertebrates.
Did you Know that Freshwater Mussels can be Great Anglers?
Adult mussels are not very mobile, so they face a challenge when trying to reproduce: how do they spread their offspring far enough to ensure that both the parents and the offspring get enough resources? By going fishing, of course!
Freshwater mussels attract fish using a part of their body that stays outside their shell and looks just like a fish. When surrounding fish come to investigate these fleshy lures, the mussel will release a plume of microscopic larvae, called glochidia, toward the fish’s face. The fish dart away, coughing and confused, but it’s too late; the larvae have already attached to the fish’s gills, fins, and skin.
The glochidia hang onto the fish for the next few weeks to months, stealing tiny amounts of nutrients from their host, which they use to grow into juvenile mussels. These juveniles can range from the size of a dime to the size of a quarter. When they are ready to leave their host, they break off and settle into the sediment, sometimes hundreds of kilometers away from their parents. Usually, the fish are no worse for wear.
Some mussels rely exclusively on a single species of fish to incubate their larvae. As a result, a decline in fish diversity and abundance can directly cause a decline in freshwater mussels as well. This is a major problem in Ontario, which boasts the highest diversity of freshwater mollusks in Canada. Unfortunately, over 65% of the province’s freshwater mussels are endangered, partly due to losses in host-fish species, as well as habitat loss, pollution, and competition from invasive species like zebra mussels.
If you want to get involved with native mussel conservation, consider downloading the ClamCounter App for iOS or Android. Developed by the Toronto Zoo and Fisheries and Oceans Canada, this handy little app lets you report your freshwater mussel sightings, learn about mussels in your area, and help biologists develop conservation programs.
Horsehair Worms and Zombie Bugs
Horsehair worms are parasitic animals straight out of a horror movie—if you’re an invertebrate, that is. As larvae, horsehair worms are harmless, and simply sit and wait to get eaten by an insect. Generally, each species of horsehair worm parasitizes only one type of insect; for example, one species will only parasitize crickets, while another will only parasitize beetles. If the larval worm is eaten by its correct host species, it can change into its parasitic form. If it is eaten by the wrong host, the worm waits for its current host to be eaten by its correct host, and then changes forms. Talk about patient!
Once the worm is inside its host, things get freaky. It releases chemicals called neurotransmitters that influence the insect’s brain and changes its behavior. One worm species will make crickets stop calling so that they are less likely to be eaten by a predator. This improves the odds that the worm can grow to maturity. Once the horsehair worm has grown enough inside its host, it compels the insect to seek water, and jump to its watery grave. Then, the adult worms will emerge from the insect, wriggling out of a hole in its body, and look for a mate to start the life cycle all over again.
If you’re worried, don’t be! Horsehair worms cannot infect vertebrates, such as mammals, amphibians, and birds. Whew!
Leeches: Sucking Blood for Science
Recently, scientists have been looking to leeches as a potential tool for monitoring biodiversity. Why? Because of what they eat!
There are three main types of leeches: predatory, which hunt other invertebrates, fluid/tissue feeding, which feed on the internal fluid and soft tissues of invertebrates, and blood-feeding, which suck the blood from vertebrates. By identifying the leech species, then analyzing the DNA in its stomach contents, we can determine whether an animal or invertebrate is present in its area, based on whether its DNA was found in the leech’s stomach. This technique is called iDNA, or invertebrate-derived DNA.
Leech iDNA is a relatively new, but promising technique for monitoring aquatic biodiversity in Canada. iDNA lets scientists assess fish, animal, and invertebrate populations without having to harass or kill the species of interest. This is especially important when scientists are looking for rare and elusive species that are difficult to catch.
Additionally, using iDNA will also allow scientists to learn more about leeches, which are extremely understudied in Canada. Everybody wins!
Invasive crayfish and their rise to infamy
While Canada is home to several species of native crayfish, invasive crayfish have become an issue in recent years. In Ontario, the aggressive Rusty Crayfish have contributed to the decline of native crayfish. They feed voraciously on aquatic vegetation, out-competing native crayfish for food, and reducing the amount of spawning and nursery habitat for fish.
At a large adult size of 10 centimeters, it is too big to be eaten by most native fish. Additionally, when faced with a potential predator, Rusty Crayfish will take an attack stance with its big, reddish claws raised above its head—quite the intimidating display for such a little critter! This often scares off any would-be predators, allowing them to colonize new areas with minimal competition.
Once invasive crayfish gain a foothold in a new area, they are almost impossible to eradicate. Thus, it is important that we all help prevent their spread. Learn to identify any invasive species in your area, and never transport crayfish between bodies of water.
If you spot a crayfish that you suspect may be invasive, make sure to take a picture and report it and the location where it was found through this directory. Another helpful tool for finding mapping, and tracking invasive species is EDDMaps.
Thank you for doing your part in preventing aquatic invasive species!
We’ve only scratched the surface of the world of aquatic invertebrates. There are many more types of non-insect invertebrates that we couldn’t cover in this article, like scuds, true worms, and snails. If we missed your favorite, give us a shout on social media and tell us about them!
Hungry for more? Join us in a couple of weeks for our next installment of this series, where we will explore some aquatic insects!
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