Scott Brown

by Scott Brown

MWA e-Newsletter Editor

First observed in the waters of Lake Huron in the late fall of 1984, aquatic biologists suspect that exotic invasive spiny water flea (scientific name: Bythotrephes longimanus) entered the Laurentian Great Lakes region via the ballast water discharge of a commercial freighter that had entered the freshwater inundated North American continent after navigating from Europe. A native of the Ponto-Caspian Sea region of Eastern Europe and western Asia, the predatory zooplankton species commonly referred to as spiny water flea likely spread via currents, inter-lake ballast water transfers, and recreational boaters to Lake Ontario by September of 1985, to Lake Erie by October of 1985, to Lake Michigan by September of 1986, and to Lake Superior by August of 1987.

Characterized by a distinctive black eye spot, a single long spiny tail, and an opaque body that ranges from one quarter (.635 cm) to five eights (1.59 cm) of an inch in overall length, spiny water flea are capable of explosive rates of population growth due their inordinate capacity to reproduce asexually by cloning themselves in relatively warm waters that are present in late spring and summer, and by reproducing sexually in the cold waters of late fall by producing and fertilizing eggs that are capable of remaining viable for long periods of time due to their inherent resistance to freezing and drying.

The presence of exotic aquatic invasive spiny water flea represents a ‘clear and present’ danger to the freshwater ecosystems that they invade due to the fact that they make their living by aggressively preying upon often abundant and highly beneficial native zooplankton species such as Daphnia that serve as the primary food source for juvenile fish, and that help achieve and sustain clear water in most of our lakes by grazing upon unicellular green algae phytoplankton species that are generically referred to as diatoms. Aquatic biologists fear that declines in the abundance of Daphnia and other native zooplankton species that are heavily preyed upon by spiny water fleas will significantly alter the food web of the Great Lakes, and therefore reduce the number of young phytoplankton eating fish that are capable of surviving their highly vulnerable first year of life. Researchers have also observed that some valuable Great Lakes species such as chinook salmon, walleye, white bass, alewife, yellow perch, white perch, and lake whitefish often consume spiny water flea. It is not currently known, however, how nutritional the exotic spiny water flea is for fish, given the significant portion of the species overall biomass that is comprised of exoskeleton, and the namesake long spiny tail that are known to possess little or no value nutritional value.

The substantial threat posed to invaded freshwater ecosystems is amplified by the fact that spiny water flea deploy a highly effective survival strategy that allows them to avoid being preyed upon by migrating into deeper, cooler, light deprived waters during the day, and by returning to the upper layers of the water column to feed at night under the cover of darkness. The capacity of spiny water flea to disrupt the aquatic food webs that help sustain a myriad of fish species is also enhanced by the fact that many of the fish that inhabit our inland lakes such as bluegill and red eared sunfish are incapable of eating the highly invasive exotic zooplankton species due to their long spiny tails.

The telltale existence of the highly invasive exotic zooplankton species within a particular lake is usually initially detected by sport fisherman whose fishing rod eyelets become clogged with spiny water fleas, or downrigger cables that become inundated with the black eyed, spiny species.

In addition to becoming aware of the fact that this highly invasive exotic zooplankton species continues to spread from lake to lake in the Great Lakes region, recreational boaters and sport fisherman can help prevent the species from entering your favorite lake by remembering to ‘Clean – Drain – Dry’ before transporting their boat and trailer to a new lake.

To learn more about the Michigan State University Extension Clean Boats, Clean Waters program click here 

Story and Photos by Scott Brown
MWA Board Member

Evoking expressions of surprise and delight, the initial experience of observing an only sporadically occurring swarm of ancient undulating freshwater jellyfish gracefully propelling themselves through the late summer warm waters of one of our wonderful inland lakes always seems to be a joyful one. Commonly referred to as “peach blossom fish” in their native China, words such as exotic, elegant, fascinating, graceful, and mysterious are often used by authors to aptly describe the ethereal freshwater jellyfish species known as Craspedacusta sowerbii that occasionally appears in the inland lakes and ponds of the Laurentian Great Lakes region.

A native of China’s Upper Yangtze River basin, the exponentially increasing pace of international trade that has occurred over the course of the past century has inadvertently led to the fact that C. sowerbii has now been observed on every continent on earth except Antarctica, and has become the most widely distributed freshwater jellyfish on earth. C. sowerbii and the nineteen other species of freshwater jellyfish are classified as hydrozoans, a class of small colonial or solitary predatory animals that are related to sea anemones and corals. Catalogued in England by naturalists in the 1880’s, C. sowerbii was first observed in Michigan waters in the 1930’s. C. sowerbii belongs to the Cnidaria, a diverse phylum of hydrozoans that contains over 11,000 marine and freshwater species whose exotic physical appearance is primarily defined by an umbrella-like radial symmetry.

Representing an extremely delicate and highly elastic gelatinous creature that is intolerant of intense wave action and fast-moving waters, the freshwater jellyfish species known as C. sowerbii that inhabits the waters of our inland lakes is most often observed floating or gracefully swimming near the surface in ponds, reservoirs, quarries, the slow-moving backwaters of rivers, and quiet wind-sheltered areas of inland lakes. Lacking a brain, heart, respiratory system, skeleton, and even blood, the relatively simple, delicate anatomy of C. sowerbii is comprised of a translucent bell-shaped outer layer known as the epidermis; a middle layer consisting of a thick, highly elastic, grayish-blue in color gelatinous substance that is referred to as the mesoglea; and, representing a simple digestive system that acts as both a stomach and intestine with just one opening that serves as both mouth and anus, an inner layer that is referred to as the gastrodermis which includes a crude stomach-like structure that is referred to as the manubrium. Circulation of nutrients within the ancient organism is facilitated by the existence of four radial canals that originate along the edges of the manubrium.

Freshwater jellyfish are known to possess a sense of smell, are able to detect light, and are capable of sensing and responding to near-by stimuli such as motion due to the existence of an elementary network of nerve cells that are widely distributed throughout their gelatinous body. The rim of their translucent bell-shaped epidermis is adorned with up to 400 relatively long tentacles that each possess thousands specialized cells called cnidocytes that are deployed by the organism to capture and pass prey consisting of tiny zooplankton to the opening of their gastrodermis. Drifting in the water column with its tentacles fully extended, jellyfish waits for suitable prey such as a tiny daphnia to come into contact with a tentacle. Once contact is made, nematocyst cells within the tentacle fire into the prey, injecting a tiny quantity of a powerful toxin that acts to paralyzes the animal, with the tentacle then acting to secure the prey by wrapping itself around the immobilized animal. It is important to note that stings by small freshwater jellyfish such as C. sowerbii produce only minor pain and often go unnoticed by swimmers due the miniscule amount of toxin that is injected as a result of contact with a tentacle. Mature C. sowerbii are capable of growing to a diameter of approximately three quarters of an inch, responding to the detection of stimuli such as near-by motion, however, the highly elastic gelatinous species is capable of instantaneously expanding its translucent epidermis to three times its normal diameter.

Beginning life as a tiny polyp attached to aquatic vegetation, rocks, or coarse woody debris, C. sowerbii and other species within the Cnidaria phylum possess a complex life cycle that allows them to expeditiously take advantage of the return of environmental conditions that are favorable to their survival and sustainability. In rare populations of C. sowerbii that possess both female and male individuals, the species is capable of achieving sustainability by alternating with each generation between reproducing sexually, with free floating sperm cells fertilizing eggs, and reproducing asexually by cloning themselves. Freshwater jellyfish are dimorphic, depending upon conditions, such as water temperature, the amount of light penetrating the surface, and/or food availability, freshwater jellyfish such as C. sowerbii are known to alternate between a polyp phase, a larval phase, and a relatively brief life in late summer as a sexually mature free-swimming male or female hydro-medusa. Freshwater jellyfish such as C. sowerbii are known to spend much more time in existence as microscopic podocysts, frustules (larvae produced asexually by budding), planulae (larvae produced sexually by mature male and female hydromedusae), or as sessile polyps that attach themselves to stable submerged surfaces such as coarse woody debris and rocks. It is important to note that the vast majority of C. sowerbii colonies are comprised of all-male or all-female individuals, therefore rendering the species almost completely dependent upon asexual reproductive processes for long-term survival.

Intolerant of the cold-water temperatures that are present in northern temperate waters in late fall, winter, spring, and early summer, the most abundant colonies of mature hydro-medusa phase C. sowerbii are observed as late summer water temperatures reach their maximum in August and September. Most often observed floating or swimming near the surface on bright sunny days, the mature hydro-medusa phase of C. sowerbii comes to an end with the gradual emergence of cold-water temperatures. During the winter months when northern temperate water bodies are frozen over, C. sowerbii contracts and enters a long period of dormancy as resting bodies called podocysts. Once environmental conditions become favorable, they again enter the polyp phase that with the gradual emergence of warm water that occurs in late summer or early fall leads to the formation of a mature hydro-medusa.

Michigan has been awarded $5 million in grants from the non-profit National Fish and Wildlife Foundation that will be dedicated to funding removal of several dams and culverts that are the primary cause of long-term declines in many migrating native fish species due to fragmentation of critical river, stream, and creek habitat located in northern Michigan. The grant will enable local projects whose primary aim will be to restore the natural pathways and aquatic habitat that many native fish species ultimately depend upon during their life cycles for migration back and forth between the Great Lakes, for spawning, for foraging, and for protection against predation. The river and stream aquatic habitat restoration projects are also expected to benefit at risk populations of eastern massasauga rattlesnake, pickerel frog, and several species of increasingly rare freshwater mussels.

The Michigan Department of Natural Resources will manage the grant-funded projects in collaboration with local conservation groups and Indigenous tribes with an intended goal of reconnecting nearly 200 upstream miles of rivers and streams situated in fourteen Michigan counties. Rivers, streams, and creeks where the grant money will fund aquatic habitat connectivity restoration efforts include:

• Twin Lakes Creek in Cheboygan County
• AuSable River in Crawford County
• Carr Creek, Dana Lake, and Little Bay de Noc in Delta County
• Wycamp Creek in Emmet County
• Two Mile Creek in Gogebic County
• Boardman/Ottaway River in Grand Traverse County
• North Branch Cole Creek in Lake County
• Spring Creek in Luce County
• McAlpine Creek in Mackinac County
• Silver Lead Creek in Marquette County
• Little Muskegon River and Buckhorn Creek in Mecosta County
• Stony Creek in Oceana County
• East Branch Big Creek and AuSable River in Oscoda County
• Hayden Creek in Van Buren County

In addition to the project leadership role of the Michigan Department of Natural Resources, several groups including the Conservation Resource Alliance of Traverse City, Huron Pines in Gaylord, Little Traverse Bay Bands of Odawa Indians, Michigan Trout Unlimited, Muskegon River Watershed Assembly, Superior Watershed Partnership and Land Conservancy in Marquette, and the U.S. Forest Service are each also expected to make significant contributions to the overall success of the National Fish and Wildlife Foundation grant funded aquatic habitat restoration initiative.

A leading contributor to the fact that many native fish populations in the United States have suffered severe declines over the course of the past one hundred years, more than two million dams, culverts, and other barriers that act to prevent certain species of native fish from migrating upstream to spawn are present in the United States. The long-term effects of the many physical barriers that prevent life sustaining fish migration is best exemplified by the fact that Atlantic salmon, once present in abundance in every river north of the Hudson River, a coldwater species that seeks to spawn and raise their young in rivers, then migrates back to the ocean to feed, grow, and then again attempts to return upstream to spawn, is now a threatened species.

Michigan’s Once Diverse and Extraordinarily Abundant Mussel
Populations Now in Severe Decline or Extinct

by Scott Brown

Snuffbox, pimpleback, white catspaw, elk toe, slipper shell, Wabash pig toe, fat mucket, deertoe, three ridge, maple leaf, and three horned warty back represent just a small sample of the hundreds of unique common names that humans have assigned over the course of the past two hundred fifty years to members of two indigenous families of freshwater mussels that inhabit North American waters. In spite of their only vaguely descriptive and sometimes amusing common names, aquatic ecologists who have observed the “flamboyant” reproductive strategies and studied the unique life cycles of freshwater mussels have suggested that the venerable creatures of the substrate represent one of our planet’s most fascinating and grossly under-appreciated animals.

The vast majority of the freshwater mussels that are indigenous to North American rivers, streams, and lakes are members of the diverse Order Unionoida, and includes two hundred eighty-six species within fifty-eight genera of the Family Unionidae, and five species representing two genera within the Family Margaritiferidae. Even though approximately one thousand freshwater mussel species within the Order Unionoida inhabit freshwater ecosystems distributed across the planet, North American rivers, streams, and lakes situated east of the Rocky Mountains continue to support at least one third of the species within the diverse Order, and therefore host the greatest diversity of freshwater mussels on earth. It is also important to note that freshwater ecosystems distributed throughout Canada and the United States, including many located within the Laurentian Great Lakes region, and especially Lake Michigan, also currently host massive infestations of two highly invasive non-native species of freshwater mussels within the Dreissena genera of the Family Dreissenidae: Dreissena rostriformis bugensis – quagga mussels; and Dreissena polymorpha – zebra mussels. Moreover, North American fresh and brackish water ecosystems also host two increasingly widespread exotic invasive mollusks within the Corbicula genera of the Family Cyrenidae: Corbicula Corbicula fluminea – Asian clams; and Corbicula largillierti – freshwater clams.

Ranging in size from three to twenty-five centimeters (1.18 – 9.84 inches), native adult freshwater mussels within the Families Unionidae and Margaritiferidae possess calcareous exoskeletons that consist of two distinctive hinged shells that are referred to as valves that provide both structure and protection to an otherwise highly vulnerable gelatinous body. A highly variable set of characteristics that include size, shape, thickness, texture, color, and pattern forming special features such as ridges, rays, chevrons, bumps, and warts that often adorn the distinctive shells of freshwater mussels serve to enable the ability of aquatic ecologists to reliably identify each species in the field. Freshwater mollusks possess a delicate soft tissue body that consists of a mouth, a relatively large stomach, a kidney, an intestine, an in-current siphon, an ex-current siphon, large filamentous gills that enable the extraction of oxygen, a foot that allows the unique creature to slowly move short distances, and remain anchored to substrates even in the presence of strong currents, and ligaments that permit the organism to open and close its surrounding shells. Comprised of neurons and glial cells that are supported by a network of connective tissue, Unionid mussels also possess a rudimentary sensory system that allows the sightless creatures to sense motion induced by nearby fish or potential predators. Representing the longest living invertebrates on earth, freshwater mussels living in optimal habitat are capable of achieving lifespans that often exceed fifty years.

The extraordinary reproductive cycle of Unionid freshwater mussels begins as sperm originating from the mantle cavity of a male mussel is ejected through their ex-current aperture, and is taken via the surrounding water column (hopefully) into a nearby female’s mantle cavity through their in-current aperture. Eggs that become fertilized move from the gonads of the female to their gills where they ripen and gradually metamorphosize into first larval stage mussels referred to as glochidia. Ranging in size from 0.05 to 0.5 millimeters, to those observing the tiny organisms through a microscope, depending upon species, mature glochidia are triangular, oblong, or circular in shape, and appear as miniature bi-valve mussels. Characterized by the presence of sensory hairs on their mantle, and either a larval thread or hook-like structure that protrudes from their partially open shell, the next stage of the reproductive cycle of freshwater mussels begins when up to one million mature glochidia are expelled by the female, and a tiny fraction of those become attached to the gills, skin, or fins of a fish that serves as parasitic host. Freshwater mussel populations located in the Laurentian Great Lakes region often rely upon smallmouth bass or walleye to serve as hosts for glochidia. Upon attachment to a compatible host fish the mature glochidia forms a protective cyst that acts as a parasite while extracting critical growth nutrients that support continued growth and development of the now fast maturing glochidia. Following a period that depending upon species ranges from ten to thirty days, the now juvenile mussel falls off their parasitic host, and enters the third and final stage of development that occurs within the substrates of the host freshwater ecosystem. Lasting from one to eight years, freshwater mussels in the juvenile stage of life complete their internal development, achieve exponential shell growth, and reach sexual maturity. It is important to note that the vast majority (99.999%) of glochidia ultimately fail to become attached to a host fish, and, due to the fact they are not yet capable of living independently in the substrates, die within hours of being expelled from their parent female mussel.

Representing an extraordinary strategy that has evolved in order to enhance an otherwise extremely low glochidia survival rate, species within the Lampsilis genera of the Family Unionidae have evolved the unique ability to deploy their mantle in a manner that bears extraordinary resemblance to the appearance of a small fish. Replete with natural looking markings and false eyes, the realistic decoy moves in the current and serves to attract the attention of fish in the area. Potential host fish that approach and attempt to prey upon the decoy are abruptly doused with a dense cloud comprised of hundreds of thousands of glochidia in the hope that a few of the tiny organisms will succeed in establishing a life sustaining parasitic relationship while attached to the gills, skin, or fins of a fish whose immune system has evolved to accommodate the presence of mature glochidia. Aquatic ecologists familiar with the reproductive processes of freshwater mussels recognize that the unique relationship that exists with fish that are capable of providing support to larval stage reproductive propagules represents an extraordinarily innovative strategy that has evolved in order to provide the sessile creatures with the capacity to successfully colonize upstream habitats. The very fact that at least small populations of approximately one thousand freshwater mussel species within the diverse Order Unionoida continue to be observed in rivers, streams, and inland lakes distributed across the planet serves as a de facto indication of the existence of aquatic habitat that is capable of supporting the ecologically sensitive creatures.

The incredible size, abundance, and diversity of populations of native freshwater mussel that were often present well over a century ago in many North American rivers strongly suggests that optimal habit for members of the Family Unionidae and Family Margaritiferidae is primarily found in large northern temperate rivers whose sensitive aquatic ecosystems are protected from the negative influences of their surrounding watersheds by forests, marshes, wetlands, and densely vegetated riparian corridors. The capacity of large northern temperate rivers to support abundant freshwater mussel communities is ultimately contingent upon the existence of relatively high quality aquatic ecosystems whose continuously flowing pollution and sediment free waters are capable of supporting much higher dissolved oxygen content in contrast to the still waters of inland lakes and ponds, for example, and healthy, moderately productive littoral zones that are capable of providing filter feeding mollusk communities with an abundance of the phytoplankton, diatoms, and other tiny organisms that they depend upon for sustenance. Moreover, due to their glacial origins, the waters of many large northern temperate rivers are also capable of providing the abundant calcium carbonate concentrations that freshwater animals such as mollusks and snails rely upon for the development of their protective shells. Northern temperate rivers that have maintained their capacity to support abundant freshwater mussel populations are also characterized by host fish friendly benthic habitat such as woody debris, boulders, and stones, as well as by natural shorelines, and near shore shallow areas featuring abundant emergent aquatic plants that provide optimal habitat for juvenile host fish. It is important to note, however, that certain members of the Family Unionidae and Family Margaritiferidae exist only in northern temperate inland lakes, streams, and small rivers characterized by slow moving or still waters. The freshwater mussel known as lake floater (Pyganodon lacustris), for example, is primaily observed inhabiting substrates that are situated in wind and wave protected coves and bays of inland lakes. Given the fact that native mollusks are capable of living for periods of up to fifty years, the existence of abundant and diverse freshwater mussel communities accompanied by large quantities of the abandoned shells of previous generations serves as a reliable bio-indicator of the long-term existence of habit conditions that were ultimately capable of supporting the ecologically sensitive bell weather species.

Native freshwater mussels are powerful ecosystem engineers that are capable of rendering highly beneficial ecological services that contribute to achieving and sustaining healthy, diverse aquatic ecosystems. First and foremost, freshwater mussels are highly efficient filter feeders that are perhaps best known for their extraordinary collective capacity to transform turbid, light deprived waters into relatively clear waters by removing algae, bacteria, suspended particulate, and organic matter, allowing life sustaining sunlight to penetrate deeper into the water column, and enabling highly beneficial submerged aquatic plants to colonize larger, deeper areas of the ecosystem. The propensity of freshwater mussels to filter out and utilize suspended algae, inorganic particulate, and organic matter also enables the capacity of the unique substrate-borne creatures to effectively sequester phosphorus, nitrogen, and carbon that would otherwise be available to fuel exponential growth of light attenuating phytoplankton. Freshwater mussels also contribute to sustaining a host of other ecosystem-friendly creatures by converting filtered materials into important sources of food that would otherwise be unavailable for consumption by the myriad of fish, crayfish, amphibians, reptiles, birds, and mammals that often forage within aquatic ecosystems. Diverse in size and shape, the durable abandoned shells of freshwater mussels that have completed their life cycles also provide protective physical spaces that serve as optimal benthic habitat for aquatic insects, and nesting sites for small fish.

Once abundant freshwater mussel communities are also known to have made significant contributions to sustaining North America’s indigenous tribes in centuries past, and in particular the mound-building tribes of the Midwest who placed a high value on the shells of the substrate-borne creatures that were efficiently utilized for making tools, jewelry, and pottery, and upon their meat that was considered an important source of protein rich food. In sharp contrast to the responsible and ultimately sustainable manner in which North American indigenous tribes utilized freshwater mussels to support their culture for many centuries, large scale commercial exploitation of the extraordinarily abundant populations of freshwater mussel that once existed in many of North America’s large rivers, and particularly the Illinois, Columbia, and Ohio Rivers, did not begin until the late 19^th century. Recognized by textile entrepreneurs of the time for the considerable economic value of their pearly, durable shells that were turned into the tens of millions of buttons of various sizes that were in demand by a flourishing garment industry, freshwater mussels were removed en masse from the ecologically sensitive substrates of rivers distributed across North America between 1890 and 1950 in order to support the two hundred button factories that were in operation during the period. Large scale, grossly unsustainable exploitation of freshwater mussel populations in North America lasted for well over half a century, and ended only in response to the advent of plastic that than become a cheaper, and much more readily available source of durable material for manufacturing buttons in the early 1950’s.

Coupled with the historically significant fact that extraordinarily diverse and abundant native freshwater mussel communities that inhabited many large North American rivers were being exploited for their valuable shells at an unsustainable rate, the rampant pace of industrialization that was also occurring on much of the continent within the late 19^th and early 20^th centuries was driving equally unsustainable rates of deforestation that ultimately caused the permanent loss, and/or severe degradation of freshwater habitat that was capable of supporting the ecologically sensitive species such as freshwater mussels has also been caused by the fact that many large rivers have been extensively dredged to allow their once relatively shallow channels to accommodate large commercial cargo vessels that are now deployed to transport coal, iron ore, and other heavy industrial commodities. Not surprisingly, large North American rivers such as the Ohio and Illinois are now widely recognized as the most extensively polluted rivers in the world.

The extent of the loss of freshwater habitat that was once capable of supporting abundant and diverse freshwater mussel communities in North America is best measured by the fact that up until the early decades of the 20^th century the substrates of many large rivers such as the Ohio, Columbia, Illinois, and the Wabash “were paved with mussels.”  Loss of freshwater habitat that is capable of supporting abundant freshwater mussel populations has unfortunately continued at a steady pace for well over one hundred years. For this reason, readers should not be surprised to learn that nearly three-quarters of North America’s once extraordinarily abundant native freshwater mussel species are now classified as endangered, threatened, species of special concern, or, as in the case of as many as thirty-eight ecologically sensitive species, have now passed into extinction.