Fifth international conference on marine bioinvasions
Introduction
MIT Sean Grant College Program
Smithsonian Environmental Research Center
Among the most serious environmental concerns facing the world today are global warming, habitat loss, and ecological changes as a consequence of introduced species. Of these, the threat of introduced species has been probably the most overlooked; in particular, marine bioinvaders have been less well studied and documented than terrestrial and fresh-water invasions, in large part because marine organisms are less accessible and less visible, especially to the public. Over the past couple of decades, however, research on vectors, patterns of distribution, ecological and economic impacts, and evolutionary consequences of non-native marine species has expanded to such a degree that nearly every major conference now devotes a session to introduced species.
In 1999, the First Conference on Marine Bioinvasions was one of the very first major meetings to focus specifically on marine bioinvasions. The papers in the Proceedings from that first conference collectively represented an overview of our understanding of the status of marine bioinvasions research and management at that time. Subsequently, the Conference has been held biennially at locations throughout the USA and in New Zealand. The Fifth International Conference on Marine Bioinvasions was hosted at the Massachusetts Institute of Technology from 21 to 24 May 2007. The Conference was co-sponsored by the National Sea Grant Office, the North Pacific Marine Science Organization (PICES), and the International Council for the Exploration of the Seas (ICES). The papers contained in this volume are a peer-reviewed selection from among those presented at the meeting and represent a range of topics, while also providing state-of-the-art insight into our current understanding of the ecological, economic, and evolutionary impacts of marine bioinvaders.
One of the underrepresented areas in research on introduced marine species is the study of smaller organisms, such as amphipods, bryozoans, hydroids, and phytoplankton, as well as on microbes such as viruses, bacteria, fungi, and protozoa. Our PICES plenary speaker, Janet Lawrence, provided an overview of the role of viruses in influencing phytoplankton populations that, in turn, are the underpinning of marine foodwebs. If we thought that 7000 organisms being carried around the world in ballast water each day (or 2.5 x 106 each year) was an extraordinary number, it is even more impressive that the number of virus-like particles being discharged each year is around 3 x 1022. Viruses are not homogeneously distributed in marine waters, and our present limited understanding of their role in controlling phytoplankton populations, particularly harmful algal blooms, is a rapidly growing area of research.
Another key area of marine bioinvasion research is the study of how invaders can persist over time in advective environments. The ICES plenary speaker, James Byers, addressed this dilemma and discussed how successful species use strategies such as spawning over several seasons or years, having shorter pelagic periods that enhance population growth rates, and possessing prodigious larval production. In developing his theory, Byers looked at life histories and ecological interactions, e.g. competition and how it influences larval retention both upstream and downstream to result in persistence against prevailing downstream currents.
Physical events may also aid in the persistence and spread of marine invaders in certain systems. For example, Sylvia Yamada and Graham Gillespie suggested that the El Niño event of 1997/1998 may have been responsible for moving young green crabs, Carcinus maenas, north along the west coast of the USA. They noted that the prevailing southward currents should have resulted in the disappearance of this crab in the Pacific Northwest, but that local recruitment might be responsible for the population growth that occurred instead.
Several papers examine species distribution, persistence, spread, and ecological impacts of invaders on ecosystems. In particular, Arthur Mathieson and colleagues evaluated the occurrence of introduced macroalgae in New England, using historical and recent floristic studies, rapid assessment surveys, and molecular techniques. Two Asian species, Codium fragile subsp. tomentosoides and Neosiphonia harveyi, have expanded their ranges in New England more broadly than expected, so suggesting the possibility of multiple introductions for these species. Other species have remained cryptic for decades. For example, several species of nori (Porphyra spp.) were only recently described as introduced species after detailed molecular studies were able to provide an adequate level of detection. The impacts of these ubiquitous introduced algae have not been well documented, often because they were not recognized as introduced. Moreover, it is large, historical datasets and voucher specimens, such as the one used in the cited study, that are needed for developing predictive models, risk assessment of impacts, and support for management efforts to prevent and manage non-native species.
The use of habitat models to predict dispersal of established introduced populations depends on adequate data covering large areas. Deborah Reusser and Henry Lee used a non-parametric multiplicative regression (NPMR) to model distributions at a habitat and estuary scale. Using datasets from the west coast and a selected number of species, they determined that geographic variables were the strongest single predictor of probable introductions at the scales of habitat and estuary. This predictive value stems in part from the availability of large datasets covering a range of habitats, and well-known distributions, permitting validation of model outputs using independent datasets.
The next two papers in this issue explore the question of why seemingly similar habitats are impacted differently by invaders. Megan Tyrell and her colleagues evaluated experimentally the effects of grazing by the introduced snail Littorina littorea (common periwinkle) on Spartina alterniflora (smooth cordgrass), noting that areas of stress favoured snail grazing and impacted marsh grass productivity. Jeffery Cordell and his co-workers discuss the probable arrival via ballast water of Asian copepods in the Columbia River system and how they are currently dispersing and likely replacing or causing declines in native populations. They note that some copepod species have moved upstream, whereas others remain in the tidal regions. In both these papers, the role of climate change in altering the spread of native and non-native species and resultant impacts is currently unknown and clearly requires investigation.
Shipping, ballast water, and aquaculture practices are likely causes for new and spreading introductions. In particular, ballast water has been implicated as a vector for phytoplankton. In 1987, New Brunswick initiated a phytoplankton monitoring programme to respond to concerns about the increasing number of red tides. Examining samples from 1995 on, Jennifer Martin and Murielle LeGresley identified 8 new dinoflagellate species, 14 new diatom species, and 5 additional species, while also noting a decline or disappearance of several other species previously recorded. Identifying whether or not these new species are introduced remains challenging, because the data and analyses are not as far advanced for phytoplankton as for other taxonomic groups.
Tunicates, particularly compound ascidians, have been successful invaders in North America. Several papers focus on both compound and solitary tunicates, examining their recruitment and abundance, distribution and dispersion, risk assessment for impacts, and prevention and management options. Didemnum sp. A (soon to be identified formally in the literature) is a compound tunicate that disperses rapidly, grows over many organisms, and prevents settlement in areas where it is established. Linda Auker and Candace Oviatt assess the spread and recruitment of Didemnum in Narragansett Bay, Rhode Island, by surveying locations, monitoring environmental information, noting distances between ports within the bay, and determining the number of vessels entering the area. Temperature and salinity, along with the availability of suitable substrata, play an important role in recruitment of this species. Such basic life-history data are essential to reducing uncertainty in risk assessments and selecting effective management options. Murielle LeGresley and colleagues also surveyed compound and solitary tunicates that have been particularly problematic for aquaculture in Canada. Using collectors deployed at monitoring stations, they documented the distribution and spread of these tunicates, particularly related to salmonid and shellfish growers.
Management options for marine invaders range from comprehensive, agency-based programmes to focused approaches based on vectors and specific activities for eradicating or managing species. Often, management actions are designed to assess the value of an invasion and the cost or benefit to the public. Paulo Nunes and Anil Markandya used several economical value assessment approaches in examining two case studies, including the benefits and costs of a Ballast Detention Centre in Rotterdam, the Netherlands, and the long-term yields of using harvesting systems with lesser to greater impacts on ecosystems (and yield) in the Venice Lagoon.
Risk management assessment for introduced species was another important topic discussed by several participants. Thomas Therriault and Matthias Herborg used expert knowledge of the vase tunicate, Ciona intestinalis, to develop a biological risk assessment. Experts were asked to evaluate the potential for vectors to spread the species, the potential for the species to arrive and become established in a region, and its ecological and evolutionary consequences. Along with requesting that experts assign a risk score, they were also asked to provide an uncertainty rank. In a second paper, Therriault and Herborg used a genetic algorithm for rule-set prediction (GARP), which is an environmental niche model used to predict suitable environments for C. intestinalis on both North American coasts. The models can also be revisited with new information to refine predictive capabilities. Together, the authors' models predict a successful spread potential over a large spatial scale for this species. In another risk assessment paper, Marnie Campbell discussed New Zealand biosecurity approaches to managing introduced species after they had arrived and become established. The agency's risk analysis model, Organism Impact Assessment, uses experts, existing data, and estimated likelihoods of impacts on ecological, cultural, social, and socio-political parameters. Campbell's application of this model to the introduced fresh-water diatom, Didymosphenia germinata, resulted in rejection of an eradication effort, instead focusing agency efforts on an aggressive public awareness programme.
Treatment methods aimed at controlling introduced species are applied in two specific case-studies in this volume. First, Christopher Denny assessed several techniques aimed at eliminating the invasive colonial ascidian, Didemnum vexillum, from seed-mussels in New Zealand. The results of Denny's experiments suggested one particular method, a dilute bleach solution, as a promising technique for eliminating the tunicate without harming the seed-mussels. In the second case-study, Grant Hopkins and Barrie Forrest identified the risks associated with hull-fouling, and the necessity of treating vessels that pose a risk to invasion. The decision to treat or not to treat vessels depended, in part, on the risk posed by doing nothing and the risks associated with the treatment options—two of which are in-water treatments and dry-docking.
In summary, and although not all papers presented at the meeting are published here, the collection of papers offered provides insight into the progression of marine invasion science as a discipline that has continued to enhance understanding of the basic ecological processes related to marine invasions, as well as the evaluation and documentation of their impacts. Experimental research examining such ecological processes has increased over the years along with theoretical studies that lay the foundation for future experimental work. The proliferation of studies on life histories, environmental factors, and biological impacts of invaders on ecosystems is valuable to risk assessments and management options. Along with economic assessments, these studies can become powerful tools for managers and policy-makers alike. Yet, we still have many challenges. Among these is the need to close the gap in our understanding of impacts, prevention, and mitigation of marine invaders, as well as evaluating the role of introduced species in the context of global climate change. Armed with current knowledge, however, we can make predictions, develop risk scenarios, and test hypotheses that should provide managers with greater certainty and more tools for preventing invasions and managing post-invasions.
The Conference proceeded smoothly and successfully thanks to the organizational skills of the Steering Committee and, of course, the quality of the papers presented. We especially thank James Carlton for his advice, our peer reviewers for their excellent assessments of the contributed papers, and Lynne Lenker for administrative assistance. The Conference itself and this publication of the Proceedings were funded in part by the National Oceanic and Atmospheric Administration, grant #NA06OAR4170019, the International Council for the Exploration of the Seas, and the North Pacific Marine Science Organization. Support for student travel from the Woods Hole Oceanographic Marine Policy Center and Biosecurity New Zealand is also gratefully acknowledged.
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