Our knowledge of how nonindigenous species influence ecological and evolutionary processes in marine systems is fragmentary in comparison with our understanding of terrestrial and aquatic systems. To characterize the state of our knowledge regarding the ecological and evolutionary consequences of marine invaders, I will highlight examples of studies that have measured the impacts of nonindigenous species on native populations, food webs, and ecosystem processes. I will also discuss examples of studies that have quantified the evolutionary consequences of marine invasions for native and nonnative species. My goal is to emphasize what I believe have been the most productive approaches to the study of ecological and evolutionary consequences of marine invasions and what will be the most fruitful directions for future actions.
Author to Contact: Edwin Grosholz
Department of Environmental Science and Policy
University of California
Davis, CA 95616
T 530-752-9151
F 530-752-3350
Email: tedgrosholz@ucdavis.edu
Key Words: European green crab, ecological impacts, trophic levels
Using long-term data and experiments in both field and laboratory, we quantitatively examine the ecological impacts of the nonindigenous European green crab in a soft-substrate food web in Bodega Harbor, CA, USA. Our results show that significant direct effects of green crab predation--large reductions in green crab prey including bivalve molluscs and crustaceans--have occurred within two years of the invasion. These prey populations have remained at very low abundances for four years since the introduction of the green crab. Also, significant indirect effects of green crab predation--increases in non-prey including polychaetes and tube-building crustaceans--have also occurred within two years of the direct effects. These direct and indirect responses to green crab predation are rapid and are nearly concurrent given the time scale of sampling. However, reductions in invertebrate prey populations have not resulted in changes at the higher trophic level occupied by shorebirds in the Bodega Harbor system. We have found no reductions in the abundances of wintering shorebirds over the four years since the green crab invasion. Therefore, the timing of changes in the abundances of native species, whether directly or indirectly affected by the invading green crab, may be more a function of life-history and recruitment rate than of position in the food web.
Author to Contact: Edwin Grosholz
Department of Environmental Science and Policy
University of California
Davis, CA 95616
T 530-752-9151
F 530-752-3350
Email: tedgrosholz@ucdavis.edu
Key Words: seaweeds, seagrasses, marine lichens, marine algae, estuarine, cryptogenic, dispersal, biogeography, Port Valdez, Alaska
During a recent field and literature survey of marine and estuarine species introductions in Port Valdez, Alaska, a new checklist of the seaweeds, seagrasses and marine lichens of the area was prepared and examined for the presence of nonindigenous species. Although no unequivocal introductions were discovered, over half of the 115 species were found to be widely distributed: 32 occurred circumboreally and 28 had ranges that extended into the southern hemisphere. These widespread species, called "cryptogenic" by James Carlton, Williams College/Mystic Seaport, Mystic, CT because they have hidden origins, are thought to have a high probability of being anthropogenically introduced or misidentified in at least some parts of their range. Many of these taxa do have excellent natural dispersal capabilities. Of the 60 cryptogenic species reported for Port Valdez, 32 are known to survive unattached, and at least 27 have life histories that are ephemeral and frequently reproduce and/or fragment. However, nearly all also occur as fouling organisms on the hulls of ships, and recent studies have shown that the propagules of many can survive the now shorter entrainment times required for transport in ballast water across the North Pacific. It is likely that the broad ranges of these species have been created by both natural and anthropogenic means. Future ecological and taxonomic studies that employ field, molecular and morphological techniques should help to resolve the cryptogenic nature of these species and determine their native vs. introduced status in the areas that they inhabit.
Author to Contact: Gayle Hansen
Hatfield Marine Science Center
2030 S. Marine Science Drive
Newport, OR 97365 USA
T 541-867-0200
F 541-867-0138
Key Words: Rapana venosa, gastropod, Chesapeake
Bay, habitat use, infauna, burrowing, hermit
crab, Clibanarius vittatus
The recent discovery of Veined Rapa Whelks Rapana venosa in the lower Chesapeake Bay has ecological consequences beyond the obvious potential for predation on commercially valuable shellfish prey species (e.g., Crassostrea virginica, Mercenaria mercenaria. In the Black Sea and in their native Sea of Japan, Rapana have been reported primarily from hard bottom habitats. Adult Chesapeake Bay Rapana have been collected from both hard and soft bottom habitat. Laboratory observations indicate that adult Rapana prefer sand bottom and will burrow almost completely into the sand at water temperatures > 20 C (i.e., not overwintering behavior). Burrowing behavior by these large apex predators expands the potential suite of vulnerable prey items to include infaunal shellfish (e.g., Mya arensis, Ensis directus, Cyrtopleura costata. The presence of large (>100 mm) empty Rapana shells in Chesapeake Bay may enhance growth of the local hermit crab Clibanarius vittatus. Recent collections of C. vittatus from the Hampton Roads area indicate that these animals use empty Rapana shells as shelters and are reaching previously unrecorded sizes. The implications of abnormally large crustacean scavengers on Chesapeake Bay benthic epifauna (e.g., oyster spat) are discussed.
Author to contact: Juliana Harding
Department of Fisheries Science
VIMS
P.O. Box 1346
Gloucester Point, VA 23062-1346
Phone: (804) 684-7302
Fax: (804) 684-7045
e-mail: jharding@vims.edu
Key Words: Codium, Membranipora, range expansion, niche shift, predators
Introduced species often undergo stages of expansion in range, niche breadth and the acquisition of predators as established species recognize a new food source. The alga Codium fragile and the bryozoan Membranipora membranacea illustrate these patterns in the Gulf of Maine. Codium became common in several protected areas in the early 1980"s and has continued to expand its distribution in such habitats. More recently, it has expanded to occupy exposed habitats and is now the dominant canopy species to 8m in both former urchin barrens and established form kelp beds in both protected and exposed locations. The saccoglossan Placida dendritica has become an important herbivore on Codium and appears to be causing a reduction in this alga in some protected sites. Membranipora first appeared at the Isles of Shoals in 1987 and has expanded its range throughout the Gulf of Maine, first as an epizooite on kelps and then on a wide diversity of algae, including arborescent, cylindrical algae such as Desmarestia. Over the last five years, the dorid nudibranch Onchidoris muricata has adapted to recognize Membranipora as a food source in the settling larval stage. This annual winter predator on dormant populations of Membranipora has the potential to significantly alter the impact of this competitively dominant encrusting species, particularly in the cooler northeastern portions of the Gulf of Maine. Patterns of expansion of habitat and interaction within the Gulf of Maine are discussed.
Author to Contact: Larry G. Harris
Zoology Department - Spaulding
University of New Hampshire
Durham, NH 03824
T 603-8623897
F 603-862-3784
Email: lharris@christa.unh.edu
Key Words: New Zealand, Tasmania, Spartina, Undaria, eradication, site led control
Two case studies, the saltmarsh cord-grass, Spartina, and the Asian kelp, Undaria, illustrate internal management issues in New Zealand. Spartina, long established in numerous estuaries, dramatically changes estuarine habitat. Undaria, a relatively recent arrival, has become ecologically dominant in several harbours and in some areas has reached the open coast. Coastal shipping and the marine farming industry are rapidly dispersing Undaria throughout New Zealand. Both species are perceived as weeds by conservation agencies, and there have been attempts to eradicate them at sites of high conservation value.
In the case of Spartina, the eradication attempts have been largely successful with no significant reinvasion after ten years. Recent attempts to eradicate Undaria from Stewart Island in southern New Zealand appear to have been less successful, as have attempts to eradicate the plant at a site in neighbouring Tasmania.
Both examples illustrate the need for understanding impacts and invasion mechanisms to provide a good basis for making management decisions, and of the vital need for internal quarantine if site-led control is to be effective. Using both examples, we show how the likely impacts and the success and failure of eradication could be predicted from a knowledge of their biology gained through observation and experimental studies.
Author to Contact: Cameron Hay
Cawthron Institute
Private Bag 2
Nelson
New Zealand
T (64) 3 548 2319
F (64) 3 546 9464
Email: cameron@environment.cawthron.org.nz
Key Words: New Zealand, ballast water, mid ocean exchange, effectiveness, compliance
Research on the ballast water problem in New Zealand since 1995 is briefly described, including the results of a two-year sampling survey of container ships and bulk carriers in the ports of Lyttelton and Nelson. Current research funded by the New Zealand Ministry of Fisheries, jointly involving both the Cawthron Institute in NZ and Battelle in Massachusetts, is looking at methods of measuring the water volumes exchanged by ships in mid-ocean (by reballasting and by dilution) and the efficiency of these exchanges in ridding tanks of unwanted species. The research also includes existing and potential methods that may be used by quarantine agencies to confirm independently that mid ocean exchanges have occurred. Other research by Cawthron, and funded by the Foundation for Research Science and Technology, which investigates the survivorship of species in ballast tanks, particularly on trans-Tasman Sea voyages, is also described.
Author to Contact: Cameron Hay
Cawthron Institute
Private Bag 2
Nelson
New Zealand
T (64) 3 548 2319
F (64) 3 546 9464
Email: cameron@environment.cawthron.org.nz
This paper details the ballast water risk assessment currently being developed by the Centre for Research on Introduced Marine Pests (CRIMP). The risk assessment comprises a series of modules that deal with discrete elements of the introduction cycle (port infection status, vessel infection scenarios, journey survival) up to and including survival in the recipient port environment. Several levels of assessment are catered for within each of the modules, allowing a progressively more accurate assessment with additional data. The risk assessment is species specific and in the first instance will be applied to a target list of marine pests. An assessment based on surrogate taxa, however, may allow an assessment of the wider introduction risk associated with ballast water and sediment discharges. The paper will address the role played by the risk assessment within the Decision Support System being developed by the Australian Quarantine and Inspection Service (AQIS), and will demonstrates its approach and results with reference to the further spread of Asterias amurensis from ports in SE Australia.
Keith R. Hayes
Centre for Research on Introduced Marine Pests
CSIRO Marine Research
GPO Box 1538
Hobart, 7001, Tasmania, Australia.
T (+ 61) 03 62325260
F (+ 61) 03 62325485
Email: Keith.Hayes@marine.csiro.au
Key Words: encrusting community, fouling, invasibility, resistance
The Eltonian concept of a native community-level resistance to the invasion of new species forms the foundations of modern invasion theory. This paradigm has received tacit support from mathematical models and recent work in terrestrial plant communities supports the corollary argument that disturbance surmounts the intrinsic native resistance. An empirical evaluation of invasibility in a marine encrusting community of Coos Bay, Oregon is presented in which a reciprocal community transplant was used to explicitly test these assumptions. Species-rich (marine derived) communities were hypothesised to be less invasible (i.e., more resistant) than species-depauperate (estuarine) communities. In summary, native communities were susceptible to invasion in all instances, but to varying degrees. These differences in invasibility were primarily due to differences in native species cover at the outset of the experiment. These results are then compared with more recent information collected from a series of port surveys from around Australia.
Chad L. Hewitt
Centre for Research on Introduced Marine Pests
CSIRO Marine Research
GPO Box 1538
Hobart, 7001, Tasmania, Australia.
T (+ 61) 03 62325102
F (+ 61) 03 62325485
Email: Chad.Hewitt@marine.csiro.au
Key Words: survey, mechanisms, vectors, invasion rates
Port Phillip Bay (PPB) is a large (1900 km²), temperate embayment in southern Victoria, Australia. Extensive bay-wide surveys of PPB have occurred between 1803 and 1963. In 1995/96 the CSIRO Centre for Research on Introduced Marine Pests (CRIMP) undertook an intensive evaluation of the region with the aims of developing a comprehensive species list of native and introduced fauna and contrasting previous bay-wide assessments with a current field survey in order to detect new incursions and discern alterations to native communities. Two methods were used to meet these aims: a re-evaluation of regional museum collections and published research in PPB to identify and determine the timing of introductions; and field surveys for introduced benthic (infauna, epifauna and encrusting) organisms conducted by CRIMP between September 1995 to March 1996. The historic component of PPB invasions groups into four periods based on the record of first collection: exploration/colonisation; immigration; Gold Rush (1852-1860); and modern mechanisms (including aquaculture). Invasions within PPB appear to be increasing, possibly due an increase in modern shipping traffic and an increase in aquaculture (historically associated with incidental introductions). As expected, the majority of introductions are concentrated around the shipping ports of Geelong and Melbourne. Recent incursions into the region include Undaria pinnatifida, Codium fragile tomentosoides, Asterias amurensis, Schizoporella unicornis and Pyromaia tuberculata. Port Phillip Bay is presented as one of the most invaded marine ecosystems in the southern hemisphere.
Chad L. Hewitt
Centre for Research on Introduced Marine Pests
CSIRO Marine Research
GPO Box 1538
Hobart, 7001, Tasmania, Australia.
T (+ 61) 03 62325102
F (+ 61) 03 62325485
Email: Chad.Hewitt@marine.csiro.au
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