James T. Carlton

Exotic Species in the Great Lakes: A History of Biotic Crises and Anthropogenic Introductions

Through literature review, we documented introductions of non-indigenous aquatic flora and fauna into the Great Lakes basin since the early 1800s. We focused on the origin, probable mechanism(s) of introduction, and the date and locality of first discovery of Great Lakes exotic species. The Laurentian Great Lakes have been subject to invasion by exotic species since settlement of the region by Europeans. Since the 1800s, 139 non-indigenous aquatic organisms have become established in the Great Lakes. The bulk of these organisms has been represented by plants (59), fishes (25), algae (24), and mollusks (14). Most species are native to Eurasia (55%) and the Atlantic Coast (13%). As human activity has increased in the Great Lakes watershed, the rate of introduction of exotic species has increased. Almost one-third of the organisms have been introduced in the past 30 years, a surge coinciding with the opening of the St. Lawrence Seaway in 1959. Five categories of entry mechanisms were identified: unintentional releases, ship-related introductions, deliberate releases, entry through or along canals, and movement along railroads and highways. Entry mechanisms were dominated by unintentional releases (29%) and ships (29%). Unintentional releases included escapees from cultivation and aquaculture, bait, aquarium, and other accidental releases. Ship-related introductions included ballast water (63%), solid ballast (31%), and fouling. Introductions via canals represent a small percentage of entries into the Great Lakes. We have identified 13 non-indigenous species (9%) that have substantially influenced the Great Lakes ecosystem, both economically and ecologically. The apparent lack of effects of 91 % of the exotic species in the Great Lakes does not mean that they have had little or no ecological impact. Alterations in community structure may predate modern investigations by decades or centuries, and the effects of many species have simply not been studied. As long as human activities provide the means through which future species can be transported into the Great Lakes basin, the largest freshwater resource in the world will continue to be at risk from the invasion of exotic organisms.

A proposed unified framework for biological invasions

There has been a dramatic growth in research on biological invasions over the past 20 years, but a mature understanding of the field has been hampered because invasion biologists concerned with different taxa and different environments have largely adopted different model frameworks for the invasion process, resulting in a confusing range of concepts, terms and definitions. In this review, we propose a unified framework for biological invasions that reconciles and integrates the key features of the most commonly used invasion frameworks into a single conceptual model that can be applied to all human-mediated invasions. The unified framework combines previous stage-based and barrier models, and provides a terminology and categorisation for populations at different points in the invasion process.

Biological invasions: recommendations for U.S. policy and management.

The Ecological Society of America has evaluated current U.S. national policies and practices on biological invasions in light of current scientific knowledge. Invasions by harmful nonnative species are increasing in number and area affected; the damages to ecosystems, economic activity, and human welfare are accumulating. Without improved strategies based on recent scientific advances and increased investments to counter invasions, harm from invasive species is likely to accelerate. Federal leadership, with the cooperation of state and local governments, is required to increase the effectiveness of prevention of invasions, detect and respond quickly to new potentially harmful invasions, control and slow the spread of existing invasions, and provide a national center to ensure that these efforts are coordinated and cost effective. Specifically, the Ecological Society of America recommends that the federal government take the following six actions: (1) Use new information and practices to better manage commercial and other pathways to reduce the transport and release of potentially harmful species; (2) Adopt more quantitative procedures for risk analysis and apply them to every species proposed for importation into the country; (3) Use new cost-effective diagnostic technologies to increase active surveillance and sharing of information about invasive species so that responses to new invasions can be more rapid and effective; (4) Create new legal authority and provide emergency funding to support rapid responses to emerging invasions; (5) Provide funding and incentives for cost-effective programs to slow the spread of existing invasive species in order to protect still uninvaded ecosystems, social and industrial infrastructure, and human welfare; and (6) Establish a National Center for Invasive Species Management (under the existing National Invasive Species Council) to coordinate and lead improvements in federal, state, and international policies on invasive species. Recent scientific and technical advances provide a sound basis for more cost-effective national responses to invasive species. Greater investments in improved technology and management practices would be more than repaid by reduced damages from current and future invasive species. The Ecological Society of America is committed to assist all levels of government and provide scientific advice to improve all aspects of invasive-species management.

Pattern, process, and prediction in marine invasion ecology

Invasions frequently continue long after dispersal corridors have been well established. Six interrelated processes (changes in donor regions, new donor regions, changes in recipient region, invasion windows, stochastic inoculation events, and dispersal vector changes) are examined to explain this phenomenon. The combination of these processes makes it difficult to forge a list of species from potential donor regions that will never become successful invaders and, by extension, to thus define the characteristics of species that have failed to invade. Predictions relative to which species will invade and when they will invade can be improved by more detailed attention to these six categories of interrelated processes that mediate invasion success.

OVERLAND DISPERSAL OF AQUATIC INVASIVE SPECIES: A RISK ASSESSMENT OF TRANSIENT RECREATIONAL BOATING

Predictions of the geographic spread of introduced species are often limited by a lack of data on their mechanisms of dispersal. We interviewed boaters and inspected boating equipment at public boat launches on Lake St. Clair (Michigan, USA) to assess the potential for the zebra mussel, an invasive bivalve, to be dispersed overland to inland waters by transient recreational boating activities. Several mechanisms associated with recreational boating were found to be capable of transporting either larval or adult life stages. Larvae were found in all forms of water carried by boats (i.e., in live wells, bilges, bait buckets, and engines) but were estimated to be 40–100× more abundant in live wells than other locations. Dilution in receiving waters should, however, greatly reduce the risk of establishing new populations by the introduction of larvae. Contrary to common belief, mussel dispersal from these boat launches did not occur by direct attachment to transient boats. Rather, adult and juvenile mussels were transported primarily on macrophytes entangled on boat trailers and, less frequently, on anchors (5.3% and 0.9% of departing boats, respectively). Combining these data with estimates of survival in air and reported boater destinations, we predict that a maximum of 0.12% of the trailered boats departing these access sites delivered live adult mussels to inland waters solely by transport on entangled macrophytes. While this is a small probability, high levels of vector activity resulted in a prediction of a total of 170 dispersal events to inland waters within the summer season from the primary boat launch studied. Many other potential vectors remain to be assessed, but the dispersal of zebra mussels by trailered boats, particularly by “piggybacking” on macrophytes entangled on the trailers, must be controlled in order to limit further range expansion of the zebra mussel within North America.

Exotic Species and the Integrity of the Great Lakes.

Edward L. Mills is a senior research associate in the Department of Natural Resources, Cornell University Biological Field Station, Bridgeport, NY 13030. Joseph H. Leach is a senior scientist at the Ontario Ministry of Natural Resources, Lake Erie Fisheries Station, Wheatly, Ontario, Canada NOP 2PO. James T. Carlton is a professor of marine sciences and the director of the Maritime Studies Program, Williams College-Mystic Seaport, Mystic, CT 06355, and Carol L. Secor is a graduate student in the Department of Biological Sciences, University of South Carolina, Columbia, SC 29208. Both Mills and Leach have served on a special task force on exotics for the Great Lakes Fishery Commission. Carltons research examines the global movement of exotic species resulting from ship ballast introductions. ?1994 American Institute of Biological Sciences. Cumulative effects of

Biogeography and dispersal of coastal marine organisms: experimental studies on a replica of a 16th-century sailing vessel

Observational and experimental studies were conducted on the dispersal of fouling organisms on a replica of a 16th-century sailing vessel along an 800 km transect from Yaquina Bay, Oregon to San Francisco Bay, California. The vessel sailed between four bays at slow speeds (3.5 to 4 knots), resided in each bay for approximately 30 d, and spent 1 to 3 d in the open ocean travelling between ports. Natural hull fouling and experimental fouling panels placed on the vessel were sampled upon departure and arrival at each port. All common fouling species survived the open sea voyages between the harbors, with largely no ecologically significant changes in abundance nor significant losses in overall diversity detected. In one port the vessel settled upon the harbor floor periodically; several entrained benthic organisms were then transported 390 km to the next port. Slow-moving, fouled sailing vessels of relatively long port residencies may have significantly altered the distributions of marine and estuarine organisms not only globally (leading to the invasions of non-native species) but also along continental margins (leading to the alteration of aboriginal patterns of distribution). Shipping traffic may further play an important role in gene flow between isolated populations of obligate estuarine organisms, particularly those with non-planktonic larvae.

Trends in marine biological invasions at local and regional scales: the Northeast Pacific Ocean as a model system

Introduced species are an increasing agent of global change. Biogeographic comparisons of introduced biotas at regional and global scales can clarify trends in source regions, invasion pathways, sink regions, and survey effort. We identify the Northeast Pacific Ocean (NEP; northern California to British Columbia) as a model system for analyzing patterns of marine invasion success in cool temperate waters. We review literature and field surveys, documenting 123 introduced invertebrate, algal, fish, and vascular plant species in the NEP. Major invasion pathways were shipping (hull fouling, solid and water ballast; 1500s-present) and shellfish (particularly oysters) and finfish imports (commonest from the 1870s to mid-1900s). The cumulative number of successful invasions over time increased at linear, quadratic, and exponential rates for different taxa, pathways, and regions within the NEP. Regional analysis of four major NEP estuaries showed that Puget Sound and the contiguous Straits had the most introduced species, followed by Humboldt Bay, Coos Bay and Willapa Bay. Data on cumulative shipping volumes predicted smaller-scale, but not larger-scale spatial patterns in the number of shipping-mediated invasions. We identify the major challenges in scaling up from regional to global invasion analysis in cool temperate regions. Retrospective analyses for distinct biogeographic regions such as the NEP provide insight into vector dynamics and regional invasibility, and are a necessary foundation for monitoring and managing global change caused by biotic invasions.

Deep Invasion Ecology and the Assembly of Communities in Historical Time

A critical component of – and a limitation on – interpreting community structure is a detailed understanding of the ecological and evolutionary history of the assemblage of species in question. There are thus compelling reasons to understand, and seek to measure, how communities have changed over both evolutionary (geological) and ecological (historical) time. Vast waves of change have swept across the Earth in the past one to two millennia as waves of humans invaded across the planet in sequential episodes of exploration, colonization, and urbanization. As an expected and inexorable result of human activity, alterations in biodiversity have impacted terrestrial, freshwater, and marine communities. These alterations include the addition of species (invasions), the deletion of species (extinctions), and altered population dynamics (such as decreasing or increasing the abundance of a species, or altering genetic structure). In even seemingly “pristine” areas – such as wave-exposed high-energy rocky intertidal shores – it is no longer tenable to assume that communities and ecosystems have remained unaltered, in part because of supply-side impacts – impacts that are the indirect cascades of human activity originating outside of the area in question (e.g., Butman et al. 1995; Chap. 7, Johnston et al.). Three (among a number of) reasons drive the interest to understand the first of these alterations – the role of invasions in historical time:

Invasion pressure to a ballast-flooded estuary and an assessment of inoculant survival

The relationships between invasion pressure, post-transport inoculant survival, and regional susceptibility to invasion are poorly understood. In marine ecosystems, the movement and release of ballast water from ocean-going ships provides a model system by which to examine the interplay among these factors. One of the largest estuaries in North America, the Chesapeake Bay, receives tremendous amounts of foreign ballast water annually and thus should be at high invasion risk. To date, however, few introductions in Chesapeake Bay have been attributed to ballast release. To understand better the dynamics of this invasion process, we (1) characterized and quantified the biota arriving to Chesapeake Bay in foreign ballast water, (2) compared temperatures and salinities of ballast water and harbor water in upper Chesapeake Bay, and (3) tested experimentally survival of organisms collected from ballast water in temperatures and salinities characteristic of the region. From 1993 to 1994, we sampled planktonic and benthic organisms from 60 foreign vessels arriving to Chesapeake Bay. Our data show that the estuary is being inoculated by a diverse assemblage of aquatic organisms from around the world. Furthermore, the short transit time (≤15 d) for most vessels ensured that substantial numbers of larval and post-larval organisms were being deballasted alive. Most of the ballast water discharged into the upper Chesapeake Bay, however, was significantly higher in salinity (>20‰) than that of the receiving harbor. In laboratory tolerance experiments, ballast water organisms perished under such conditions. Thus, a mismatch in physical conditions between donor and receiver regions may explain the dearth of invasions in the upper Bay. It is likely that the lower Chesapeake Bay, which is more saline, remains at higher risk to ballast water invasion. Recognition of such intraregional differences should allow more focused predictions for monitoring and management.