The speaker shows her mussels at natural history talk, a report of the April 2013 MVFN lecture report by Jim Bendell
At a recent natural history lecture in Almonte, the Mississippi Valley Field Naturalists (MVFN) welcomed ‘malacologist’ Jacqueline Madill, Senior Research Assistant, Zoology, Research and Collections, Canadian Museum of Nature as guest speaker for the MVFN 2012-13 ‘Nature Beneath our Feet’ lectures. Madill’s subject was the important but little-understood or appreciated, ‘Native Fresh-water Mussels of the Ottawa Valley’ and she brought many several favourite specimens to the talk. About one-third of the worlds’ mussel species live in North America, with 55 species in Canada, of which 41 are found in Ontario. Madill reminded us first thing that we should not pick up mussels from the river bottom; each species inhabits only a specific water zone and they have limited locomotion. Not only that but freshwater mussels are considered one of the most endangered group of species in North America, with 67% at risk!
Mussels and Clams belong to the family Mollusca (derived from Latin: soft), a very large group of soft-bodied animals that also includes the Chitons, Tooth Shells, Snails and Slugs, Oysters, and the Nautili, Squids and Octopuses! Look them up and be amazed! In abundance and diversity, they are second only to the Arthropods (which includes Insects), and were among the first creatures on earth. Mussels and clams range in size from barely visible to approximately 20 cm in length. Both are bivalves living in a box of two shells. Think of the Blue Mussels or clam chowder you last ate at the fish restaurant, said Madill. Two limey (mainly calcium carbonate) shells enclose their ‘bivalve’ body in a box that may be opened or closed for passage of water, and protection. This structure reflects the life of a sedentary animal (or couch potato), no head or limbs but a muscular foot that provides anchorage and infrequent locomotion. About the body is a mantle that produces the shell and aids in growth and reproduction. Within the body there are various organs that work as in our own. Most important are the gut and gills that act in feeding, as part of a giant filter.
Madill and others assess Mussel biodiversity and numbers in local lakes and rivers as part of their work. Hinge structure and other features are used for identification and often identification can be made just by the feel of the shell underwater. Mussel species may vary in numbers from zero, to a few, to such an amazing density one cannot walk without treading on a shell. Here they earn the names ‘Heelsplitter’ and ‘Ouch’! Other more ‘happy as a Clam’ individuals are Rainbow, Warty Back and Maple Leaf. Eastern Elliptis is a very common species locally, and others such as a Cylindrical Papershell found in Quebec, had not been seen since the 1830’s.
Why mess with mussels? Well, we must agree that water is fundamental to life. Here in the Ottawa Valley we are well supplied with five major rivers and many smaller streams, and so should have abundant clean water and excellent aquatic life. But if we are to sustain and improve our standard of living we must care for our waters. And the study and care for Mussels and Clams are part of that concern because these little-known animals give many ecological benefits. Perhaps the most significant is their filtering; an individual may ingest and clean 3 liters of water per hour, removing toxic chemicals, excess nutrients, harmful bacteria and viruses, and importantly light blocking matter. They also provide benefit by mixing sediments as they slowly move. They provide food for fish, muskrats, shorebirds and others. Also since some mussels are quite long lived, many living decades, they carry within their tissues a useful record of biological and chemical changes in the environment. As they age annual rings form in the shell as in a tree. According to Madill, some Eastern Pondshells can live 200 years!
But why are Mussels so endangered? At one time, commercial harvest and disruption from log drives reduced their numbers, but these are not ongoing. Now the sermon; sadly, and to our peril, the current plight of bivalves reflects the damage we have done and are doing to water and its inhabitants. Mussels need clean, clear running water relatively high in oxygen and water bodies connected to maintain stable levels and flow, provide nutrients, and permit dispersal of the young. In turn, the density and persistence of these creatures are good indicators of healthy waters. Main disrupters are dams and locks that restrict flow and cause extreme fluctuation in temperature and levels of water. According to Madill, it can take 50-100 years for an area of mussels to be reestablished once it has been disrupted. Mussels are also particularly sensitive to pollutants of many kinds which include fertilizers from lawns and cropland. Many large water bodies and waterways have been made uninhabitable by channeling, loss of near shore habitat, and choking with litter and debris. Another significant threat has been the invasive Zebra Mussel, perhaps the most damaging to our native bivalves, as well as to human infrastructure such as intake pipes. It appeared in the Great Lakes in 1988 on ships from Middle Europe. Of incredible reproductive capacity, one female can produce 30,000 to 1,000,000 larvae annually. Madill noted that Mussels of the Rideau River have suffered a ‘double whammy’ from Zebra Mussels and the rapid and alternating water levels due to the canal locks. In 10 years Zebra Mussels have spread throughout the Great lakes smothering large beds of native bivalves.
Another issue raised by Madill’s was the intriguing connection between the decline of particular Mussel species and the decline of biodiversity in local fish. The explanation is as follows. Mussels and clams live partially buried in sediment with little traveling about, which potentially restricts their distribution. The problem is solved by some Mussel species which produce specialized larvae, called glochidia (from the Greek: pointed or hooked), that are shed in clouds, manage to attach to the gills of a particular species of host fish, and so are transported. They then drop off in new habitat suitable to both fish and Mussel. For example, the female Pocket-Book Mussel extends its mantle, the tip of which is shaped, marked and moves like a small fish. This attracts a desired larger fish for a lift. When the fish ‘takes the bait’ the Mussel ejects a puff of glochidia that attach to the gills, thus obtaining a convenient taxi for its young! Other species mimic a worm to attract a ‘ride’. Check out Youtube.com for videos of some of these creative mussel displays, says Madill.
What can we do to improve the health of our waters and native fresh-water Molluscs? How can we make a Mussel as “happy as Clam?” If you would like further information, please contact our speaker, she welcomes inquiries and can be contacted at the Canadian Nature Museum Research Building in Gatineau or via email . An excellent reference guide to local Mussels is by J. Metcalfe-Smith, A. MacKenzie, I. Carmichael and D. McGoldrick, Photo Field Guide to the Freshwater Mussels of Ontario, 2005, published by the St. Thomas Field Naturalist Club. Other useful references for general information on the zoology and ecology of Mussels and Clams include on-line information on Mussels of Eastern Ontario at pinicola.ca and books by Clarke, A. H. 1981, The Fresh Water Molluscs of Canada. National Museum of Natural Sciences, National Museum of Canada, and T.I. Storer and R. L. Usinger, 1957, General Zoology, McGraw-Hill, Toronto.
Jacqueline Madill (left) spoke about the important but little-understood or appreciated, ‘Native Freshwater Mussels of the Ottawa Valley’ and brought many of her favourite Mollusca specimens to the talk, such as the Eastern Elliptio, a very common freshwater Mussel. Photo Pauline Donaldson