Biodiversity wanes in New York

Throttling invasive species by TJ Sinnott

Bulwark for the Great Lakes and Hudson River by P Gerrity

Stopping ballast water "stowaways" by D Pughiuc

Biological pollutants in the Great Lakes by EL Mills, KT Holeck

Water quality signatures and the zebra mussel invasion by DA Matthews, SW Effler

Zebra mussel population dynamics: Implications for water quality modeling by CL Lange, DR Opdyke, JC Powers

Bad seeds: an introduction to invasive plants by AD Halpern, CA Boesse, AE Altor

You can help stop the plant invasion

President's message by D Ellis

Executive director's message by P Cerro-Reehil

People and places

NYWEA calendar

Sponsors at 73d Annual Meeting

Spring 2001 — Vol. 31, No. 1


Biological pollutants in the Great Lakes

by Edward L. Mills and Kristen T. Holeck

The freshwater crown jewels of North America, the Laurentian Great Lakes, play a major role in the economies of the eight states (United States) and one province (Canada) that border their shores and are a vital source of biodiversity in North America. Thus, both their ecological and economic well being are important. One of the most damaging effects of humanity on the world's ecosystems, including the Great Lakes, is the introduction of biological pollutants or alien species (Elton 1958; Mooney and Drake 1986; Mills and others 1993a).

Figure 1. Eurasia and the Ponto-Caspian area are major donor regions of biological pollutants to the Great Lakes.

In the United States, over 4500 non-indigenous species have established free-living populations (Office of Technology and Assessment 1993). These species include several thousand plant and insect species and several hundred non-native invertebrates, mollusks, fish, and plant pathogen species. Approximately 15% of these non-indigenous species have caused severe harm to agriculture, industry, human health, and the natural environment (Office of Technology and Assessment 1993). Alien invaders have demonstrated a deleterious affect on native flora and fauna, affecting 49% of the over 2500 imperiled or endangered species documented in the United States (The Nature Conservancy 2000). The prevention and control of these biological pests results in a $138 billion cost to the United States' economy each year (Pimentel and others 2000).

Some of the greatest ecological disasters in the Great Lakes have resulted from biological invasions (Mills and others 1994). The introduction of exotics in the Great Lakes has affected native species and thus compromised the biological integrity of this important freshwater ecosystem. Nearly 10% of the non-native species introduced in the Great Lakes have had a significant effect on ecosystem health, a percentage consistent with findings in the United Kingdom (Williamson and Brown 1986) and the Hudson River of North America (Mills and others 1996). At present, the establishment of alien species continues to pose a threat to the Great Lakes and waters of central New York State.

History, origin, and entry vectors

All the Great Lakes have been invaded by exotic species, and each lake has experienced significant adverse effects from these invaders. Before 1800, exotic species entered the Great Lakes basin through range expansion following retreat of glaciation or transport by aboriginals, but clear records of such movements do not exist (Bailey and Smith 1981). Since the early 1800s, scientists have identified 145 non-indigenous fishes, invertebrates, fish disease pathogens, plants, and algae as established in the Great Lakes basin (Mills and others 1993a; Hall and Mills 2000). Some taxonomic groups such as fish and aquatic plants have been well studied while other groups have not. To date, plants, algae, disease pathogens and parasites account for 60% of new species established in the Great Lakes basin since 1810 followed by invertebrates (22%) and fish (18%) (Leach and others 1998). See table.
Table 1. Number of invasive and introduced species established in Great Lakes by taxonomic group and time
Time Fish Inverte- brates Disease pathogens, parasites Algae Plants Total
1810-1849 1       9 10
1850-1899 6 4     23 33
1900-1949 7 8 1 6 18 40
1950-2000 12 20 2 19 9 62
Total 26 32 3 25 59 145
Percent 18 22 2 17 41 100

From Mills and others 1993 and Leach and others 1998

The native ranges of exotic species present in the Great Lakes today include Europe/Asia (referred to here as Eurasia), Asia (only), the Atlantic coast of North America, the Pacific coast of North America, the southern United States, and the Mississippi River drainage. Most exotic species in the Great Lakes are native to Eurasia (65%) and the Atlantic Coast (16%). The large number of organisms introduced from Eurasia is most likely associated with the early transport of goods by Europeans to the basin, the similar north-temperate climates in both Europe and the Great Lakes region (Mills and others 1994), and recent transoceanic shipping (Figure 1).

The entry and dispersal mechanisms which have acted singly or jointly in the movement of organisms into the Great Lakes basin include unintentional release (shipping traffic, escape from cultivation, aquaculture and aquaria, and accidental releases due to fish stocking and from unused bait), deliberate releases (for example, the deliberate introduction of fish species to enhance fisheries), canals, and disturbance linked to the construction of railroads and highways.

The overall rate of establishment of new exotics in the Great Lakes for the past 40 years has been high (about 1.2 species/yr) and continues to be high. The chronology of exotic species introductions since the 1800s indicates the importance of certain entry vectors. Historically, ships played an important role in the transfer of aquatic organisms, particularly in the late 1800s with the release of aquatic plants and invertebrates in solid ballast materials. The surge in ship-related introduced species in recent time has been associated with ballast water. In April 1959 construction of the St. Lawrence Seaway and hydroelectric facility was completed, and transoceanic ships began to ply the largest freshwater resource in North America (Mills and others 1999). The Great Lakes became vulnerable to invasion by alien species from throughout the world! In fact, more than one-third of the exotic species in the Great Lakes have been introduced in the last 40 years (Mills and others 1993a) (Figure 2).

Figure 2. A time line of Great Lakes introductions (after Mills and others 1993a).

Effects of exotic species on ecosystem health

Exotic species must be recognized as a form of biological pollution. The mechanisms for damage to Great Lakes ecosystems resulting from unplanned species introductions are many, including habitat modifications, competition, predation, associated disease pathogens and parasites, and genetic effects (Krueger and May 1991; Li and Moyle 1993; Leach and others 1998). Competition from alien species such as salmonids, alewife (Alosa pseudoharengus), white perch (Morone americana), Eurasian ruffe (Gymnocephalus cernuus), zebra/quagga mussels (Dreissena polymorpha and D. bugensis), and purple loosestrife (Lythrum salicaria) have been a major factor affecting Great Lakes native species (Leach and others 1998).

Exotic species such as sea lamprey, alewife, white perch, and salmonids adversely affect established predator-prey interactions. The sea lamprey (Figure 3), a parasitic fish, has had a catastrophic effect on native lake trout (Lawrie 1970). In the late 1960s, alewife populations accelerated the collapse of coregonid populations (for example, lake whitefish [Coregonus clupeformis] and bloater [Coregonus hoyi]), and negatively affected yellow perch (Perca flavescens) and other native species (Brandt and others 1987; Smith 1970). Recently, the alewife has become an important prey fish for salmonids, including both introduced pacific salmon (Oncorhynchus sp.) and native salmonids such as lake trout (Stewart and others 1981). However, it has been found that thiamine deficiencies in these salmonid species are correlated with a high rate of consumption of alewife, resulting in high early life mortality of these fish (Fitzsimons and others 1999).

Figure 3. Sea lamprey attached to native lake trout. The cost of sea lamprey control in the Great Lakes exceeds $15 million annually. (Photo courtesy of the Great Lakes Fishery Commission)

The white perch passed through the Erie Canal (Christie 1973; Hurley 1986) and gained access to the Great Lakes where it has had substantial effects on native fish species and community stability (Boileau 1985). The introduction of salmonids, either deliberately to enhance the sport fishery or unintentionally as in the case of pink salmon (Oncorhynchus gorbuscha), has had significant and permanent ecological and genetic effects caused by interbreeding with native fishes. These effects have been predation on native salmonids and other fishes and the introduction of parasites and diseases.

Lastly, zebra mussels (Figure 4) are excellent competitors, known to have displaced entire unionid clam communities in Great Lakes waters (Mackie 1999). Most recently, the Great Lakes ecosystem has been invaded by a European amphipod (Echinogammarus ischnus, recently identified in Lake Erie; Witt and others 1997), the blueback herring (Alosa aestivalis; see Owens and others 1998), and the fishhook water flea (Cercopagis pengoi; MacIsaac and others 1999). Although it is unclear now how the fishhook water flea may alter the Lake Ontario food web, previous studies have shown that suppression of small-bodied zooplankton by Cercopagis could have adverse effects on planktivorous fish (MacIsaac and others 1999). Cercopagis could also increase levels of lipophilic organic compounds in piscivores because of the additional link in the food chain (Makarewicz and others unpublished manuscript).

Figure 4. A plate encrusted with zebra mussels. Zebra mussels can attach to almost anything including plants, boats, rocks, pipes, and each other!

Management strategies and future invasions

The long history and the high rate of biological invasions clearly indicate that the Great Lakes continue to be vulnerable to the establishment of alien species. Consequently, the development of management strategies regarding the prevention and control of introduced species into the Great Lakes must incorporate lessons from the past to develop policies that will reduce the risk of unplanned biological pollutants. Mills and others (1993a) have shown that nearly two-thirds of all non-indigenous species established in the Great Lakes have arrived by means of two vectors: shipping activities (31%) and unintentional releases not associated with shipping (34%).

Ships can be considered "biological islands" (Figure 5) that are capable of sustaining and distributing organisms around the world in their ballast water, sludge in the bottom of ballast tanks, hull fouling, marine sanitation devices, and water on decks, and in anchor lockers (Reeves 1999). Private sector activities associated with unintentional releases include aquaculture, bait, horticulture, and aquarium industries. Since 1960, these two entry mechanisms have been responsible for 98% of all new introductions in the Great Lakes. Mills and others (1993b) suggest that vector management is important to make progress toward preventing unwanted organisms from invading the Great Lakes. Both shipping activities and unintentional introductions in the private sector need to be addressed by policy and lawmakers in the future. Both ballasted ships and those without ballast (but with residual unpumpable sediments in their ballast tanks) have been implicated in the transfer of exotic species from abroad.

Figure 5. Transoceanic shipping in the Great Lakes commenced with the opening of the St. Lawrence Seaway in 1959.

The identification of ship ballast water as a major vector transporting unwanted organisms into the Great Lakes has motivated control efforts (Leach and others 1998). In November of 1990, the U.S. Congress passed the Non-Indigenous Aquatic Species Act, and by May 1993 the first and only ballast water law in the world was adopted. The law required that ships that have operated outside the waters of the U.S. and Canada and that intend to enter the Great Lakes with ballast water must have exchanged that water on the high seas (Mills and others 1994). In the Water Resources Act of 1992, the ballast water exchange requirement was extended to ships entering the Hudson River (which connects the Great Lakes via the Erie Canal). Implementation of these ballast water exchange regulations was an important first step in combating the shipping vector of aquatic introductions.

Limits to effectiveness

Unfortunately, ballast water exchange does not totally eliminate the risk of future invasion (Leach and others 1998). Since the mandatory ballast exchange policy was initiated in 1993, three new species have become established in the Great Lakes (seven since the establishment of Canadian voluntary guidelines), all associated with shipping activities. While ballast exchange is not sufficiently protective, it continues to be the backbone of U.S. legislation and Canadian guidelines, and is similarly being promoted for global application by the International Maritime Organization.

The current regulatory regime has clear flaws that must be addressed immediately to stem this vector of exotic introductions. Present regulations require a ballast water salinity concentration of 30 ppt as a standard to verify that open seas exchange has taken place. It has been found that measuring the salinity of ballast water is not an effective indicator of complete ballast exchange and does not deter the survival of all potential invaders. For example, salinity standards correlate with an 85% exchange of ballast water, leaving a sufficient amount of inoculated water in ballast tanks to infect a recipient ecosystem (Reeves 1999). Additionally, ships leaving foreign ports may already carry biologically contaminated water with a significant salinity concentration, negating the validity of the salinity standard as a true measure of exchange altogether.

While full saline salt water may kill freshwater organisms, it may not kill brackish or estuarine water species. The recent introductions of the amphipod Echinogammarus ischnus and the fishhook water flea Cercopagis pengoi to the Great Lakes illustrate this point. They are native to the Ponto-Caspian region and they are tolerant to a broad range of salinity (MacIsaac and others 1999). Future invaders can also enter the Great Lakes in ships with no ballast on board. Ships that contain sedimented material in the hull can pose a potential threat, as resting spores of foreign freshwater organisms are known to remain viable in these sediments (Hallegraeff and Bolch 1992; Kelly 1993).

The threat of transfer of non-indigenous pathogens via ballast water discharge to the Great Lakes and its negative effect on human and ecosystem health is a topic that also requires further analysis. Previous studies (McCarthy and Khambaty 1994; Whitby 1999) have shown that pathogens such as cholera (Vibrio cholerae) and other various microbes (E. coli serovar 0111, Aeromonas sp.) have been found in ballast water after a trans-oceanic voyage. As currently practiced, the open ocean exchange of ballast water will not prevent the dispersal of exotic pathogens, and additional marine pathogens may be picked up and transferred to freshwater ecosystems (Whitby 1999). Finally, ship ballast exchange also has important safety concerns that must be considered in any practice before it becomes policy.

Possible additional actions

Cooperation is needed among shipping industry representatives and government regulators to establish safe, economical, and environmentally sound resolutions. Although the ideal solution may not be currently available, corrective measures must be made to current ballast water management strategies to decrease the invasive potential of this vector. Strategies such as retrofitting vessels (for example, for top-down flow-through exchange of ballast water) and/or using shore-side biological treatments (for example, thermal, microfiltration, ultraviolet radiation, biocides, and ozone) could be considered in future management plans to reduce ship-related introductions into the Great Lakes. A combination of practical technological solutions to meet an agreed water quality standard, freedom of choice to encourage market competition, and an incentive system can potentially lead regulators to meet the present and future needs of both the environment and industry (Reeves 1999). Because of the importance of ships as a primary vector, it is necessary to continue to evaluate the effectiveness of ballast management practices, identify other possible ship-borne entry vectors, and better understand the extent of potential pathogenic damage to human health and recipient ecosystems.

Aquaculture and aquaria

Commercial uses of exotic species in the aquaculture, bait, and aquaria industries have been found to be the second largest Great Lakes contributor of exotic species in recent history. Although the extent of aquaculture contributions are unclear, an annual 10% growth rate of the industry and the broadening of the number of non-indigenous species raised indicate the need for attention to the industry's potential effect (Patrick 1999).

A better understanding of the species involved, including their escape and establishment potential, may be beneficial in preventing future invasions. A financial incentive for the aquaculture industry to be more involved could also lead to stronger and more consistent regulatory control. Harvesters, dealers, and anglers must all be involved to alleviate the invasive effects of the bait industry. The enforcement of existing regulations and the prohibition of the movement of bait across state, national, provincial, and watershed boundaries will aid in preventing the introduction of exotic species. The education of shareholders involved in the industry to understand their roles in mediating this avenue of threat and the benefits these actions will bring to the ecosystem is also a vital component of solving this problem.

Maintaining biodiversity

Biological pollutants are not only a primary threat to the Great Lakes but also to global biodiversity. It has been determined that 400 of the 958 species listed as threatened or endangered under the Endangered Species Act in the United States are considered to be at risk primarily due to competition with and predation by non-indigenous species (The Nature Conservancy 1996; Wilcove and others 1998). For example, in the Great Lakes region, biodiversity has declined dramatically in the Lake St. Clair-Western Lake Erie region as a once stable and diverse native clam community has been changed to a population of zebra/quagga mussels (Schloesser and Nalepa 1994; Nalepa and others 1986) (Figure 6). Many scientific, economic, and aesthetic incentives are in operation to conserve biodiversity. If this ecosystem attribute is to be sustained as well as utilized by people, it is necessary to understand and mediate the detrimental effect of exotic species on biodiversity.

Figure 6. Extirpation of native clam species resulting from competition by zebra mussels has significantly reduced biodiversity. Dead clamshells covered with zebra mussels are now common.

The problem of biological invaders must be considered a priority under the Great Lakes Water Quality Act whose purpose is "to restore and maintain the chemical, physical, and biological integrity of the waters of the Great Lakes Basin Ecosystem." The invasion of the Great Lakes by exotic species is the best-documented case of its kind in the world, and the harm caused to the system should serve as a warning to other nations with large lakes (Mills and others 1993, 1994; Leach and others 1998). If the establishment of biological pollutants in our waters is not curtailed, our Great Lakes food webs will no longer resemble those of the past but will reflect food webs of other parts of the world. Finally, future policies to prevent unplanned introductions must seriously consider vector management and be broad enough to include not only the Great Lakes basin but the entire North American continent.
Edward L. Mills and Kristen T. Holeck are with the Cornell Biological Field Station, Bridgeport, NY. Corresponding author is Ed Mills. Phone 315-633-9243.

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