Key Words: ballast water, survivorship, intraoceanic, transoceanic
To develop predictive models of marine invasions, information is
needed concerning which inoculants fail as well as which succeed
and why. The movement of ballast water in commercial ships
is acknowledged as a primary vector for the global transfer of marine
organisms, yet surprisingly little is known about the starting composition
or abundance of the inoculants or patterns of survival during transit.
Data are needed on (1) which taxa start voyages as well as which
finish and (2) how survivorship of the ballast water biota varies
as a function of physical characteristics of the ballast water,
voyage length, and taxa. To this end, we sampled organisms
from the ballast water of coal ships at the start and finish of
both intracoastal (n = 7) and transoceanic (n = 13) voyages.
The domestic vessel took approximately 1.5 d to carry ballast water
from Massachusetts to Chesapeake Bay, while the transoceanic vessel
took approximately 19 d to travel from Israel to Chesapeake Bay.
For both routes, we observed tremendous differences in initial abundances
of major taxa (< 10 to > 10,000 per cubic meter of ballast water)
and substantial mortality during transit. Within each
route, survivorship of different taxa varied both within and between
voyages. Copepods, however, typically showed highest survivorship.
Overall, survivorship was much lower for the transoceanic voyages
(10%) than for the domestic voyages (60%). Mortality
is not likely to have resulted from physiological stress due to
changing salinity or temperature, because these variables remained
relatively
constant throughout the voyages. Instead, other factors such
as starvation, predation, mechanical damage during ballast water
uptake, toxic compounds in the tanks, and encystment may explain
the precipitous decline in numbers.
Author to Contact: L. David Smith
Marine Science Center
Northeastern University
Nahant, MA 01908
T 781-581-7370
F 781-581-6076
Email: ldsmith@lynx.neu.edu
Key Words: phenotypic plasticity, shell thickness, water temperature, Carcinus maenas, Littorina obtusata, Gulf of Maine
Two important goals of invasion ecology are to understand how populations respond to introduced predators and how such responses are modified by environmental conditions over the geographic range of prey. Crab-molluscan predator-prey relationships provide an outstanding system in which to address these questions. Recent transitions in shell form of two intertidal snail species to better defended morphologies have coincided with the invasion of a crab predator (Carcinus maenas) into the Gulf of Maine. Although these adaptive shifts have been attributed to rapid selection by Carcinus, recent experiments have shown that gastropods can alter shell form (e.g., thicken shells) during ontogeny in response to crab effluent. The ability of gastropods to contend with an invading predator over a range of water temperatures, however, is uncertain, because calcium carbonate solubility increases as water temperature decreases. As a consequence, any predator-induced increase in shell thickness could be both physiologically difficult and costly for snails in colder waters. In the Gulf of Maine, water temperatures in the north average 6-8oC colder in spring and summer than those in the south, and previous surveys have shown that northern populations of the smooth periwinkle, Littorina obtusata, are thinner shelled and more vulnerable to crushing than southern populations. To test the influence of water temperature on the degree and cost of a predator-induced phenotypic response, Littorina obtusata individuals collected from a northern (Lubec, Maine) and southern (Manchester, Massachusetts) site were reciprocally transplanted and exposed to two predator treatments (Carcinus effluent, no Carcinus effluent) in field experiments. Regardless of source population or transplant location, snails raised in the presence of Carcinus produced significantly thicker shells than conspecifics raised in the absence of Carcinus. Surprisingly, our data indicate that predator effluent has effects on shell form that are comparable to those resulting from water temperature (geographic) differences. Predator-induced changes were accompanied by trade-offs. Snails raised with Carcinus grew more slowly in terms of shell size and also exhibited significant reductions in tissue mass and tissue growth. Trade-offs were greatest for the northern populations raised in their home site. Thus, while colder water snails maintain the ability to respond to a novel predator, the costs are potentially greater than for warmer water snails. These results will be useful in predicting responses by prey populations to anticipated changes in global climate and community composition. Warming trends evident in the Gulf of Maine and elsewhere will likely expand the species ranges of both prey and predator. This climatalogical phenomenon, in conjunction with increasing rates of biological invasions in marine systems, guarantee that prey populations will be exposed to novel predators.
Author to Contact: L. David Smith
Marine Science Center
Northeastern University
Nahant, MA 01908
T 781-581-7370
F 781-581-6076
Email: ldsmith@lynx.neu.edu
Key Words: New Zealand, ballast water, mid-ocean exchange, hull fouling
Recent trends in marine invasions to New Zealand, especially from Asia are briefly described in relation to changing trade patterns. Since the 1960ís, when emphasis on trade shifted from the United Kingdom to Asia, there has been an associated increase in the proportion of Asiatic species amongst recently discovered invaders. Notable species include the Pacific oyster, the Asian date mussel, Musculista, and the Asian kelp, Undaria.
The likelihood of new invasions from neighbouring Australia and from Asia via ballast water is discussed in terms of geographic proximity and sea trade. Our preliminary studies suggest it is only a matter of time before further well known invaders such as the Northern Pacific seastar and the European green crab arrive in our ports - if they are not already established. While it appears generally accepted that ballast water is the primary mechanism of trans-oceanic dispersal, the role of other mechanisms should not be ignored. Of particular concern are the periodic events when ships, laid up for long periods in foreign harbours, arrive in NZ waters with heavily fouled hulls. If these vessels are cleaned by divers at the wharf-side, or are again laid up for a long period, then new invasions are likely to occur.
At a national level, the problems of internal quarantine to prevent the spread of unwanted species from "infected" harbours and ports are considered, particularly in relation to the practicalities and effectiveness of ballast water exchange in coastal waters.
Author to Contact: Michael Taylor
Cawthron Institute
Private Bag 2
Nelson
New Zealand
T (64) 3 548 2319
F (64) 3 546 9464
Email: michael@environment.cawthron.org.nz
Key words: ecosystem, bivalves, contaminants, food web
The introduction of the Asian clam, Potamocorbula amurensis,
into San Francisco Bay has resulted in changes to the benthic community
structure, food web, and transfer of contaminants within the ecosystem.
The large declines in phytoplankton biomass coincident with the
introduction of P. amurensis is shown to be due to "over-grazing"
by these filter-feeding bivalves. We estimate that the
water column is passed through the northern bay clam populations
in excess of twice a day which leads to an imbalance in phytoplankton
growth rate (doubling less than once per day) and filter-feeder
consumption rate. Other sources of particulate organic carbon
(e.g. detritus, bacteria, and bacteria on particles) may also be
declining due to grazing by P. amurensis. Estimates
of the amount of food consumed by the P. amurensis populations
in northern San Francisco Bay are considerably higher than the amount
of food available from the phytoplankton. Because northern
San Francisco Bay has never had high primary production, it is likely
that detritus and bacteria have always been important food for secondary
producers. It is unknown what percentage of this food source
is consumed by P. amurensis and how this reduction might
affect other levels of the food web. We have begun to see
some food web responses to the reduction in primary producers and
other carbon sources. Populations of the opossum shrimp (Neomysis)
and several zooplankton species, all important food species for
larval and adult fish, have declined coincident with the invasion
of P. amurensis.
The increase in benthic biomass in the northern bay is also changing the flow of contaminants through the ecosystem. Because of the small benthic biomass in the northern bay prior to the arrival of P. amurensis, the food web was dominated by pelagic forms. Although pelagic predators (e.g. mid-water fish, dabbling ducks) may have lost a primary food source, bottom feeding predators (e.g. sturgeon, diving ducks) now have an enhanced food source. However, because P. amurensis has been shown to be a bioaccumulator and biomagnifier of trace elements (e.g. Cd and Se) this shift in the food web may ultimately prove to be detrimental to the bottom feeding predators. Concentrations of some trace elements have begun to accumulate at harmful concentrations in the sturgeon and diving ducks since the appearance of P. amurensis.
Author to Contact: Janet Thompson
U.S. Geological Survey
345 Middlefield Rd. MS496
Menlo Park, CA 94025
T 650-329-4364
F 650-329-4327
Email: jthompso@usgs.gov
Australia has been actively researching and developing management
strategies for invasive marine species since the mid-1980s, following
the discovery by Gustaaf Hallegraeff that the toxic dinoflagellates
whose blooms had both economic and human health implications were
most likely of foreign origin. The effort against exotic marine
species ramped upwards in the mid-1990s with the establishment of
the CSIRO Centre for Research on
Introduced Marine Pests, a permanent Australian Ballast Water Management
Advisory Council (with an associated research body), an Introduced
Marine Pest Program in the federal environment department (Environment
Australia), and initiatives at the university and state levels.
These activities have begun to indicate the real nature and magnitude
of the problem, shifting the discussion from media-driven hyperbole
to that based a bit more on hard information, while also revealing
more clearly the scope for, and constraints on, dealing with exotic
marine pests and their vectors. Australian cultural perceptions
regarding the 'pristine ocean' are part of a suite of social, political,
economic and scientific issues that dictate the direction of current
initiatives and set fuzzy, but very real limits on potential management
options. These are discussed and their implications considered
in the context of where Australian research and management is likely
to go over the next few years in developing practical solutions
to the 'introduced marine pest problem'.
Author to Contact: Ron Thresher
Head, CSIRO Centre for Research on Introduced Marine Pests
CSIRO Marine Laboratory
GPO Box 1538
Hobart, Tasmania 7001
Telephone: 61-03-62-325378
Fax: 61-03-62-325485
E-mail: Thresher@marine.csiro.au
Key Words: Hemigrapsus sanguineus, Carcinus maenas, feeding preferences, gut contents, community structure
The New England rocky intertidal zone has been impacted by several introduced species including the common periwinkle, Littorina littorea, and the green crab, Carcinus maenas. The Asian shore crab, Hemigrapsus sanguineus, is currently established in Massachusetts and is predicted to become established in New Hampshire and Maine. In order to predict the potential impacts of an invasion by H. sanguineus, various aspects of its feeding ecology were examined. An investigation into the algal feeding preferences of H. sanguineus elucidated which algal species are most likely to be negatively affected by herbivory by this crab. H. sanguineus significantly prefers Enteromorpha intestinalis and Fucus vesiculosus in multichoice feeding preference trials, but will consume significant amounts of all species tested when presented in isolation. Gut contents of crabs collected from Massachusetts indicate a primarily herbivorous diet composed of Spartina spp. and algae, with some evidence of omnivory. Feeding preferences of both H. sanguineus and C. maenas on molluscs were assessed to determine potential competitive overlap. Both crab species preferred Mytilus edulis, L. obtusata and L. saxatilis (in descending order) and avoided L. littorea. The pre-invasion community structure of two sites that are likely to be impacted by populations of H. sanguineus was also examined. Quantitative sampling documented the abundance of potential prey (algae, molluscs, barnacles) and potential competitors (C. maenas). Models are presented which illustrate predicted consequences of this crab invasion in New Hampshire.
Contact person: Megan Tyrrell
Zoology Dept.
Spaulding Life Science
University of New Hampshire
Durham, NH 03824
Email: mct@hopper.unh.edu
Key Words: Atlantic salmon, aquaculture, Pacific Northwest, niche competition, steelhead
Farmed salmon is British Columbiaís largest agri-food export product. Approximately 80% of production is Atlantic salmon (Salmo salar), an exotic species on the Pacific coast. Large scale escapes and small scale "leakage" of adults from marine net pens are not uncommon and lead to over 2600 marine and 150 freshwater reports of Atlantic salmon in B.C. waters in 1997 alone. The continuous addition of free ranging adult Atlantic salmon into the coastal environment combined with the weak state of many native Pacific salmon (Oncorhynchus spp.) stocks has been suggested to enhance the likelihood of colonization. We present preliminary results of our work conducted to delineate what, if any, ecological or genetic impacts are associated with aquaculture escapee Atlantic salmon on native Pacific salmon species. We also present evidence that suggests colonization may be occurring on a Vancouver Island river, an event which would mark the first anadromous expansion of the species beyond its native range.
Author to Contact: John P. Volpe
Centre for Environmental Health, Dept. of Biology
University of Victoria
Victoria, British Columbia, CANADA V8W 3N5
T 250 721 7098
F 250 721 7120
Email: jvolpe@uvic.ca
Key Words: ballast water, phytoplankton, biogeography, exotic species, biological invasion, North Carolina
The spread of exotic species is cited repeatedly as one of the greatest threats to marine ecosystems today. One of the chief transport vectors of non-native aquatic organisms is ballast water discharged from ships. The principal objective of this study was to determine the taxonomic composition of viable phytoplankton species in ballast water collected from ships berthed in the Port of Morehead City, North Carolina, USA. During 1997, a ten-liter volume of unfiltered ballast water was collected from each of nine ships. These ships originated from ports in Japan, Spain, Dominican Republic/ Florida, Belgium, Louisiana and North Carolina. Each sample was filter concentrated, and the live phytoplankton organisms were cultured for 21 days with a range of media and light intensities to simulate different receiving waters. Over 150 genera of viable freshwater and marine phytoplankton were identified from the cultures. Additionally, over 450 more live species morphologies were observed (predominantly protists and unidentified microalgae). These results provide evidence that numerous species of both freshwater and marine phytoplankton are not only viable when discharged in the ballast water of ships, but may also establish successfully reproducing populations. The biogeography of marine phytoplankton species is imperfectly understood; many phytoplankton species are considered globally ubiquitous. Yet, some phytoplankton species are known to have limited distributions. It may be possible that earlier ballast water transfers contributed to the current cosmopolitan distribution of some phytoplankton species. In an effort to reduce the probability of future marine biological invasions, further research needs to focus on the present, as well as historical, capacity of ballast water to homogenize the distributions of phytoplankton species globally.
Author to Contact: Heather P. Walton
Nicholas School of the Environment
Duke University Marine Laboratory
135 Duke Marine Lab Road
Beaufort, North Carolina 28516 USA
T 252-504-7530
F 252-504-7648
Key Words: Carcinus maenas, control factors, trapping
In response to the threat to publicly maricultured shellfish posed by the invasive European green crab, Carcinus maenas, in embayments on Marthaís Vineyard, MA, several municipalities conduct trapping programs designed to reduce the abundance of this pest, thereby increasing shellfish survival. The presumed benefits of control of the long established green crabs has led to extensive trapping, although the effectiveness of this trapping remains to be tested. Despite large catches, municipal catch records of C. maenas do not suggest obvious decreases in catch per unit effort and/or changes in population structure. Given this experience, we attempt to determine if, in fact, trapping can be effective and, if so, what is the optimum level of trapping. Within each embayment, the adult C. maenas population appears to be relatively closed, although short-term movements within embayments will affect trapping strategy and success. Multi-year data on C. maenas abundance and population structure will be presented to identify seasonal fluctuations. Additionally, trap-independent snorkel surveys are used to evaluate short-term effects of trapping on C. maenas density. Lastly, we compare trapping success of two trap models. Broadly, given the increased need for control of exotic marine pests, the feasibility of trapping programs such as this need to be assessed.
Author to Contact: William Walton
Smithsonian Environmental Research Center
Box 28
Edgewater, MD 21037 USA
T 410-798-4424 x141
F 301-261-7954
Email: walton@serc.si.edu
Key Words: Porphyra, monitoring, Maine
Intentional introductions of species for the purpose of mariculture balance minimizing ecological impact with maximizing economic gain. Coastal Plantations International is in its 8th year of commercially farming an introduced species of nori, Porphyra yezoensis, in Cobscook Bay, Maine. Permits were granted based on the inability of the alga to complete sexual reproduction while under Gulf of Maine temperature regimes. Surveys are being conducted of the intertidal area surrounding the mariculture sites for P. yezoensis recruitment and survival. A preliminary survey conducted in 1996-97 found some evidence of P. yezoensis recruitment surrounding the Mathews Island farm site during the growing season, but there was no evidence of the plants over-wintering. The current study examines the potential for dispersal and establishment of P. yezoensis in the intertidal zone near CPIís nursery farm site at Huckins Ledge. To examine dispersal potential we conducted transect surveys of Porphyra in the associated intertidal areas. In addition, we deployed artificial substrates consisting of synthetic netting used in the commercial growing of nori to enhance Porphyra settlement. These were constructed radially within a kilometer of the farm site and were exchanged seasonally. Porphyra species are collected from the transects and artificial substrates and identified by microscopic examination and isoenzyme electrophoresis. P. yezoensis has not been positively identified in any transect samples to date at Huckins Ledge, however 5 putative P. yezoensis were identified on the artificial substrates in November, 1997. Four of these potential exotics recruited at a single location, and this site effect is being investigated further by examining water flow patterns. To examine the potential for P. yezoensis to survive the winter, seeded net fragments were placed in the intertidal that same November. The existing plants did not overwinter, did not spread to surrounding netting and plant regeneration was not detected by the following March. Laboratory freezing tolerance experiments are being conducted to compare the overwintering ability of P. yezoensis with that of local species. We currently hypothesize that P. yezoensis can recruit ephemerally during CPIís limited summer/autumn farming season, but that it does not survive through the winter and therefore cannot form a permanent established population.
Author to contact: Katherine Watson
Northeastern University
Marine Science Center
East Point
Nahant, MA 01908
T 781-581-7370
F 781-581-6076
E-mail: kwatson@lynx.dac.neu.edu
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