Fifth international conference on marine bioinvasions: Introduction

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 10 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 10. 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 Nino 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