By Andrew L. Rypel, Miranda Bell Tilcock, and Christine A. Parisek
One of our favorite aspects of teaching is (occasionally) being able to really surprise a student. Many of the fun nature facts folks pick up nowadays come from TV, YouTube, social media, and other media outlets. But these outlets have an inherent bias: they focus on the charismatic species. That is, the species that are big, fluffy, and widely adored. Yet there are so many fascinating species and ecology in the lesser appreciated taxonomic groups (not to mention, focusing on charismatic species leads to inequitable conservation – Rypel et al. 2021). And often, learning about these overlooked species can really blow the mind! Today, we’d like to introduce you all to the fascinating reproductive behavior of freshwater mussels.
Freshwater mussels are fascinating creatures and are spectacularly underhyped. Their ecology and conservation status has been communicated previously on this blog. These animals are long-lived (up to 100 years old or more, Haag and Rypel 2011), are filter feeders, and are widely regarded as sentinels of outstanding water quality in freshwater ecosystems (Vaughn 2018). Some estimate that a single adult mussel can filter ~15 gallons of water per day! Mussels are also highly endangered; 73% of freshwater mussel species in North America are at risk of extinction (Williams et al. 1993). Causes for their decline are multifold, but include severe declines in water quality, fragmentation of rivers by dams, invasive species, overharvest from the pearl and button industries (Fig. 2), and climate change. A final, somewhat mussel-specific cause for their decline can also be the loss of their host fishes.
Wait… did you say “host fishes”?! Yes indeed. Almost all species of freshwater mussels (unlike marine mussels) require fish hosts as juveniles. The glochidia (= baby mussels) attach primarily to the gills, but also the fins and skins of fishes. Here, they live off the blood of the fish host until large enough to fall off, hopefully into optimal habitat where they can become a big old mussel (Fig. 3). But, how then do the baby mussels actually get on the fishes? This is where the (al)lure of the mussel is perhaps most charming.
Many mussels have essentially evolved fishing lures (mantle lures) to attract fish hosts to the mussel (Fig. 1). A potential host fish will approach the lure, and if displayed convincingly enough, may ultimately bite the lure. But instead of getting a nutritious morsel of food, the fish instead gets a magazine of glochidia ejected into its face and mouth. The relationship these young mussels have with their host fish causes the fish some irritation but is not intended to harm the fish, as their main goal is to use the host fish for transport and dispersal (That’s one enterprising way to catch a Lyft!). Because certain species of mussels have evolved to use only certain species of fish, the mantle lures can be exceptionally specific, ornate, and tricky. Other mussel species are generalists, meaning they can use many species as hosts (including even some invertebrates). Below are a few examples of mantle lures in action, but we can also testify that YouTubing “mussel mantle lure” is a simple and effective way to waste a bit of time if you are so inclined.
The connectivity between freshwater mussels and fishes also means something for our ecosystems and their conservation. Put simply, freshwater mussel communities and freshwater fish communities are connected and literally feed off one another. In at least one case (Freshwater Drum, Aplodinotus grunniens), the fish can serve as a generalist host for at least a dozen or more mussel species in a single river. But drum also directly consume adult mussels as prey. In this way, drum literally farm their own food. Thus, the decline of mussels spells bad news for fishes, and vice versa. If native fishes decline, then there are no more hosts for the mussels.
The interestingness and diversity in nature brings joy to these authors’ lives, and hopefully also to yours. Over the years, we have introduced many students and community members to the wild reproductive behaviors of freshwater mussels. Only a handful are aware of this biology. This motivated us to write this blog and share it with all of you. It also gives us pause for how we are so rapidly modifying our ecosystems and losing species. Are we even aware of what we are losing? The more we study nature and ecosystems, the more it seems as though we are largely unaware of what’s being erased. This is sad for our planet, our species, and future generations that might not grow up ever encountering a legitimate, healthy mussel bed, or perhaps even a healthy river. But it’s also never too late to turn it around. To do this we will need broader awareness concerning the plight of all species, including the non-charismatic ones, along with the determination and patience to adequately protect them.
“The more clearly we can focus our attention on the wonders and realities of the universe about us, the less taste we shall have for destruction.” ~Rachel Carson, Silent Spring
Andrew L. Rypel is a professor of Wildlife, Fish & Conservation Biology and Director of the Center for Watershed Sciences at the University of California, Davis. Miranda Bell Tilcock is an Assistant Specialist at the Center for Watershed Sciences. Christine Parisek is a Ph.D. candidate in the Graduate Group in Ecology at UC Davis and a science communications fellow at the Center for Watershed Sciences.
Howard, J.K., J.L. Furnish, J.B. Box, and S. Jepsen. 2015. The decline of native freshwater mussels (Bivalvia: Unionidae) in California as determined from historical and current surveys. California Fish and Game 101: 8-23.
Haag, W.R., and A.L. Rypel. 2011. Growth and longevity in freshwater mussels: evolutionary and conservation implications. Biological Reviews 86: 225-247.
Hewitt, T.L., A.E. Hoponski, and D.O. Foighil. 2021. Evolution of diverse host infection mechanisms delineates an adaptive radiation of lampsiline freshwater mussels centered on their larval ecology. PeerJ 9:e12287.
Lawrence, A.J., and A.L. Rypel. 2023. Will more wildfire and precipitation extremes mussel-out California’s freshwater streams? https://californiawaterblog.com/2023/02/26/will-more-wildfire-and-precipitation-extremes-mussel-out-californias-freshwater-streams/
Maine, A., C. Arango, and C. O’Brien. Host Fish Associations of the California Floater (Anodonta californiensis) in the Yakima River Basin, Washington. Northwest Science 90: 290-300.
Murphy, G. 1942. Relationship of the fresh-water mussel to trout in the Truckee River. California Fish and Game 28: 89-102.
Rypel, A.L. 2008. Field observations on the nocturnal mantle flap lure of Lampsilis teres. The American Malacological Bulletin 24: 97-100.
Rypel, A.L. 2020. Losing mussel mass – the silent extinction of freshwater mussels.https://californiawaterblog.com/2022/10/09/losing-mussel-mass-the-silent-extinction-of-freshwater-mussels/
Rypel, A.L., P. Saffarinia, C.C. Vaughn, L. Nesper, K. O’Reilly, C.A. Parisek, M.L. Miller, P.B. Moyle, N.A. Fangue, M. Bell-Tilcock, D. Ayers, and S.R. David. 2021. Goodbye to “rough fish”: paradigm shift in the conservation of native fishes. Fisheries 46: 605-616 .
Rypel, A.L. 2022. Being patient and persistent with nature. https://californiawaterblog.com/2022/10/16/being-patient-and-persistent-with-nature/
Vaughn, C.C. 2018. Ecosystem services provided by freshwater mussels. Hydrobiologia 810: 15-27.
Williams, J.D. M.L. Warren, K.S. Cummings, J.L. Harris, and R.J. Neves. 1993. Conservation Status of Freshwater Mussels of the United States and Canada. Fisheries 18: 6-22.
America’s freshwater mussels are going extinct — Here’s why that sucks https://blogs.scientificamerican.com/extinction-countdown/americas-freshwater-mussels-are-going-extinct-heres-why-that-sucks/
The strange, savage life of a freshwater mussel https://www.vox.com/down-to-earth/2022/10/27/23424362/freshwater-mussels-fish-lure-extinction
California floater mussel take fish for an epic joyride https://video.kqed.org/video/california-floater-mussels-take-fish-for-an-epic-joyride-iqmps1/
Xerces Society: about freshwater mussels https://xerces.org/endangered-species/freshwater-mussels/about
True facts: mussels that catch fish