Spiny Water Flea  (Bythotrephes cederstroemi)

DESCRIPTION

The Spiny Water Flea is one of the recent newcomers to the Great Lakes. The Spiny Water Flea is not an insect at all, but a tiny crustacean, distantly related to shrimp, lobster, and crayfish. It is a small creature, about 1/2 inch long, that is planktonic, meaning it must drift with water currents if it is to move long distances. Its long, barbed tail spine, which gives the animal its common name, makes up over half the length of the body and often catches on fishing lines and downrigger cable. This species is a native of Great Britain and northern Europe, east to the Caspian Sea.

Spiny Water Fleas also reproduce rapidly. During warm summer conditions each female can produce up to 10 offspring every two weeks. As temperatures drop in the fall, eggs are produced that can lie dormant all winter. 

Spiny Water Flea is active in waters it inhabits from late spring until late autumn. As water temperature warms in the spring, individuals hatch from "resting" eggs that have overwintered on the lake bottom. Life span varies from several days to a few weeks. Throughout much of the spring, summer, and autumn, the population is composed mostly of females. These females produce eggs that remain unfertilized and are carried in the mother's brood pouch until they develop into female offspring that are genetically identical to the mother. This cycle of asexual reproduction, requiring no fertilization, continues as long as the water temperature is neither too hot nor too cold, and food is abundant.

During times of stress, such as low water temperatures in late autumn, both males and females are produced asexually. The presence of males allows sexual reproduction to occur. Fertilized resting eggs develop a thick coating, which allows them to withstand extreme conditions, such as very low or high water temperatures. These eggs are released by the mother and fall to the lake bottom where they remain until conditions are again favorable. The adult Spiny Water Flea dies following reproduction. Resting eggs protected by a coating allow the species to persist in the lakes through harsh environmental conditions such as Great Lakes winters.

(Sources: 1 Great Lakes Information Network, http://www.great-lakes.net/envt/flora-fauna/invasive/spinyflea.html, 2. Ohio Sea Grant, http://www.sg.ohio-state.edu/PDFS/PUBLICATIONS/FS/FS-049.PDF)

IMPACTS

The appearance of the Spiny Water Flea in the Great Lakes has scientists at universities and government laboratories, including The Ohio State University's F.T. Stone Laboratory, studying the impact of this invader on other organisms in the Great Lakes.

No one is really sure what effect Spiny Water Fleas will have on the ecosystems of the Great Lakes region. But resource managers are worried, because the animals may compete directly with young perch and other small fish for food, such as "Daphnia" zooplankton. 

Research conducted by Dr. E.D. Mordukhai-Boltovskaia of the USSR Academy of Science determined that Spiny Water Flea is a planktivore, feeding on smaller planktonic animals. Bythotrephes seizes prey with long arm-like antennae and hold them in place with its legs. One Spiny Water Flea may consume as many as 20 prey organisms in a day.

Research conducted by the University of Michigan found that the appearance of Spiny Water Fleas in Lake Michigan coincided with dramatic declines in the abundance of Daphnia. In addition, a native species related to Bythotrephes, the predator Leptodora (lep-to-DOR-a), also declined. It was  concluded that feeding of Bythotrephes on Daphnia had reduced the abundance of the prey organism and that this reduction had left less food available to Leptodora, resulting in decreased numbers of this native crustacean. In addition, it was hypothesized that declines in the abundance of fishes may result because Daphnia and other small plankton also serve as food for young fish. 

Because Spiny Water Fleas eat zooplankton like Daphnia, they compete directly with small fish that also need to eat zooplankton. Research shows that perch aren't growing like they should and some young can't survive because of the lack of food. A decrease in small fish populations could also take away a food source for larger sport fish in Lake Michigan, and the other Great Lakes.

High numbers would not pose a problem if Spiny Water Fleas were heavily consumed by predators. But its sharp long tail spine makes it extremely hard for small fish to eat, leaving only some large fish to feed on them.  Rae Barnhisel of Michigan Technological University found that young yellow perch cough up Bythotrephes, probably because the long tail spine prevents the fish from swallowing its prey. The young perch learn very quickly to avoid eating spiny water fleas. From this information, one can conclude that ability to consume Bythotrephes depends on the size of the fish.  As a result of this selective feeding, spiny water flea populations remain high while populations of plankton, which they eat, have declined. 

Later research conflicted with this interpretation, leaving scientists unsure as to whether Bythotrephes really has altered food abundance in the Great Lakes. However, it is clear that this invader has the potential to affect the food webs of the Great Lakes. Examination of stomach contents has revealed that adult yellow perch, walleye, and salmon consume Bythotrephes, which is rather large and conspicuous compared to other planktonic species. Experiments have determined that hungry yellow perch are likely to spot Bythotrephes before they spot Leptodora, which are similar-sized but transparent. Spiny Water Fleas are also easily captured because they are slow swimmers; however, nothing is known about the nutritional value of Bythotrephes.

Much of the impact of the spiny water flea on Great Lakes ecosystems will depend on its interactions with other species. If Bythotrephes turns out to be a preferred food of perch and other fishes, its invasion of the Great Lakes may have a beneficial impact on fish populations. If it is unsuitable as a fish food, and competition with Bythotrephes lessens numbers of preferred food organisms, the amount of food available to fish may decrease. This may have dire consequences for fish populations. As with many of our inadvertent species introduction "experiments," it may take years to discover how the presence of this European immigrant will affect the Great Lakes ecosystem.

(Sources: 1. Minnesota Sea Grant, http://www.dnr.state.mn.us/ecological_services/exotics/fg_flea.html; 2. Great Lakes Information Network, http://www.great-lakes.net/envt/flora-fauna/invasive/spinyflea.html; 3. Ohio Sea Grant, Fact Sheet 049, http://www.sg.ohio-state.edu/PDFS/PUBLICATIONS/FS/FS-049.PDF)

The most likely means of introduction of the Spiny Water Flea is that it was imported in the ballast water of a trans-oceanic freighters. Spiny Water Flea eggs and adults may wind up unseen in bilge water, bait buckets, and livewells. Also, fishing lines and downriggers will often be coated with both eggs and adults. 

Dr. Gary Sprules and others at the University of Toronto have hypothesized that Bythotrephes was carried to North America in the ballast water of freighters from European ports, especially the port of St. Petersburg, Russia. These freighters carry grain to Europe but return empty to North America. To stabilize the empty freighters, large amounts of water are carried in ballast. Small planktonic organisms, and even fish, are pumped in with the ballast water and may survive the ocean voyage. When ships take on cargo in North America, the ballast water and the organisms in it are discharged. Normally, oceangoing ships take on salt water as ballast (and salt water animals), so a freshwater organism such as Bythotrephes would not be in the ballast water. However, in the spring, St. Petersburg becomes a freshwater port due to runoff from snow melt, and freshwater animals may be taken into the ballast tanks. Thus, spring may provide conditions that enable Bythotrephes and other freshwater organisms to be transported.  Once ships reach North America, the water is discharged and the organisms are released into the waters here, in the Great Lakes. 

(Sources: 1. Minnesota Sea Grant, http://www.dnr.state.mn.us/ecological_services/exotics/fg_flea.html; 2. Great Lakes Information Network, http://www.great-lakes.net/envt/flora-fauna/invasive/spinyflea.html; 3. Ohio Sea Grant, Fact Sheet 049, http://www.sg.ohio-state.edu/PDFS/PUBLICATIONS/FS/FS-049.PDF)

Ballast Water Control
Spiny Water Fleas could be controlled if fish could eat large quantities of them, however, their sharp spine can only be swallowed by larger fish. Smaller fish can't swallow them and can have problems getting a spiny water flea free-meal. Because the fleas don't have many predators, their populations grow rapidly as they continue to eat up much of the zooplankton.

Legislation of the dumping of ballast water remains as the only plausible means of controlling the Spiny Water Flea. For example, the state of Michigan and the Canadian Parliament have introduced legislation that would require ships to sterilize ballast water before discharging into their water.

Michigan Senator Ken Sikkema’s Senate Bill 955 would require ships to sterilize ballast, obtain a permit before dumping ballast in Michigan waters and mandate that the state develops an inspection program.

Canada’s federal bill C-389 would require open-ocean ballast water exchange before entering any Canadian waters.

While both initiatives take the positive and needed step of placing restrictions on the discharge of ballast water, they also contain serious flaws because they don’t go far enough (the Canadian bill), or rely on polluting chemical sterilization when there are nontoxic alternatives (the Michigan legislation).

Bill C-389 requires that every ship entering Canadian waters, completely exchange its ballast water with fresh sea water at a point at sea beyond a prescribed distance from the coast. The bill would be applicable to all Canadian waters, including the Great Lakes.

Bill C-389 is similar to U.S. regulations under the National Invasive Species Act (NISA), which requires ocean-going ships entering U.S. waters to exchange their ballast water in an open ocean area more than 200 nautical miles from any shore in waters more than 2,000 meters in depth. NISA provides an exception for ships that have reason to believe that complying with the regulation would endanger the ship.

Chemical Control
Chlorine would likely be the chemical control agent if this legislation were enacted. Chlorine has a high acute toxicity to aquatic life, with concentrations as low as 0.29 parts per million killing trout and 0.71 to 0.82 ppm killing sunfish.

Chlorination byproducts—"chlorinated hydrocarbons"—cause a wide range of reproductive, developmental, and behavioral dysfunctions, including miscarriages and birth defects. Chlorination byproducts formed by the reaction with organic material have been associated with cancer in animals and humans.  Therefore, the International Joint Commission has called for a phase out of the production and use of chlorine and chlorine-containing compounds.

The problem of exotics is so pressing that immediate efforts are needed. Fortunately, chemical control is neither the only nor the best option. Instead, some environmental groups and decision makers are calling on the governments to require:

All ships, including NOBOB ships, to undergo complete open ocean ballast exchange

All ships, including NOBOB, to undergo frequent open ocean ballast tank flushes and exchanges

The U.S. Coast Guard to perform audits to ensure that NOBOB ships are individually checked for ballast and have undergone open ocean tank flushes and that BOB ships are individually checked for open water ballast exchange

All ships to carry full documentation of ballast tank maintenance

All newly built ships be retrofitted with, or designed to include, equipment to sterilize ballast water using one of several available non chemical technologies

(Sources: 1. Great Lakes United Newsletter, http://www.glu.org/publications/14_3/14_3_11.htm; 2. Great Lakes Information Network, http://www.great-lakes.net/envt/flora-faunflea.html).

New Water Flea Invades Southern Lake Michigan: Illinois-Indiana Sea Grant
    http://ag.ansc.purdue.edu/il-in-sg/calendar/newsg/october_26.htm
This site gives information on another type of water flea that has made its way into the waters of the Great Lakes.

Other Aquatic Invaders: Spiny Water Flea: U.S. Fish & Wildlife Service
   http://www.fws.gov/r3pao/alpena/otherans.htm
This site provides information on many of the exotics that threaten the Great Lakes region including major species, and other aquatic invaders, such as spiny water flea. 

Minnesota waters infested with spiny water flea: Minnesota Office of the Revisor of Statules
    http://www.revisor.leg.state.mn.us/arule/6216/0350.html
This site provides a complete list of all the waters that are currently infested with the spiny water flea in Minnesota.  Other waters invaded by other exotic species are also listed.

Spiny Water Flea in the Great Lakes Region: Great Lakes Information Network 
    http://www.great-lakes.net/envt/flora-fauna/invasive/spinyflea.html
This site provides brief information on the description, impacts, and origin of the spiny water flea.

United States Coast Guard
    http://www.uscg.mil/hq/g-m/mso/mso4/ansgal.html
This site provides an aquatic nuisance species photo gallery.

Help Stop the Alien Invasion!
    http://www.dnr.state.wi.us/org/caer/ce/eek/critter/insect/waterflea.htm
This site provides information to help teach people about these invaders, and their impacts.

The Detroit News: State Battles to Save Lakes From Aquatic Hitchhikers
    http://detnews.com/2000/metro/0002/15/02150128.htm
This site addresses the issue of ballast water, and provides excellent pictures and descriptions of how exotic species are carried in ballast water.