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Fouling around: vessel sea-chests as a vector for the introduction and spread of aquatic invasive species


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Sea-chests, recesses built into the hull of a vessel, have been recently identified as hotspots for fouling organisms. In this study, we examined the types and abundances of taxa found in sea-chests of commercial vessels, and investigated whether vessel specifications and voyage histories influenced the nature and extent of sea-chest fouling. Eighty-two sea-chests were sampled from 39 commercial vessels while in dry dock on the West or East Coast of Canada. Overall, 80% of the vessels showed evidence of sea-chest fouling, and 46% harboured at least one non-indigenous species. In total, 299 unique taxa were recorded, including a number of non-indigenous and cryptogenic organisms that collectively made up 20.5% and 14.4% of the taxa sampled from West and East Coast vessels, respectively. Additional results suggested that in-service period (i.e., duration since last sea-chest cleaning) and vessel origin (i.e., domestic versus international) may, in part, determine the nature and extent of sea-chest fouling. By contrast, vessel size and port duration were unable to explain taxonomic richness or abundance of fouling organisms in sea-chests. Taken together, these findings highlight the role of sea-chests as an important vector responsible for the introduction and spread of a variety of taxa, including aquatic invasive species, but also suggest that the factors that influence sea-chest fouling in commercial vessels are complex. Further research, aimed at better understanding the determinants of sea-chest fouling and the efficacy of anti-fouling systems, would help further refine management strategies and reduce the risks associated with sea-chest fouling.
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Management of Biological Invasions (2014) Volume 5, Issue 1: 21–30
© 2014 The Author(s). Journal compilation © 2014 REABIC
Open Access
Research Article
Fouling around: vessel sea-chests as a vector for the introduction
and spread of aquatic invasive species
Melissa A. Frey1*, Nathalie Simard2, David D. Robichaud3, Jennifer L. Martin4 and Thomas W. Therriault5
1Royal British Columbia Museum, 675 Belleville Street, Victoria BC, V8W 9W2, Canada
2Maurice Lamontagne Institute, Fisheries and Oceans Canada, 850 Route de la Mer, Mont-Joli QC, G5H 3Z4, Canada
3LGL Limited, 9768 Second Street, Sidney BC, V8L 3Y8, Canada
4St. Andrews Biological Station, Fisheries and Oceans Canada, 531 Brandy Cove Road, St. Andrews NB, E5B 2L9, Canada
5Pacific Biological Station, Fisheries and Oceans Canada, 3190 Hammond Bay Road, Nanaimo BC, V9T 6N7, Canada
E-mail: (MAF), (NS), (DDR), (JLM), (TWT)
*Corresponding author
Received: 20 July 2013 / Accepted: 19 November 2013 / Published online: 1 February 2014
Handling editor: Alisha Dahlstrom
Sea-chests, recesses built into the hull of a vessel, have been recently identified as hotspots for fouling organisms. In this study, we examined
the types and abundances of taxa found in sea-chests of commercial vessels, and investigated whether vessel specifications and voyage
histories influenced the nature and extent of sea-chest fouling. Eighty-two sea-chests were sampled from 39 commercial vessels while in dry
dock on the West or East Coast of Canada. Overall, 80% of the vessels showed evidence of sea-chest fouling, and 46% harboured at least one
non-indigenous species. In total, 299 unique taxa were recorded, including a number of non-indigenous and cryptogenic organisms that
collectively made up 20.5% and 14.4% of the taxa sampled from West and East Coast vessels, respectively. Additional results suggested that
in-service period (i.e., duration since last sea-chest cleaning) and vessel origin (i.e., domestic versus international) may, in part, determine the
nature and extent of sea-chest fouling. By contrast, vessel size and port duration were unable to explain taxonomic richness or abundance of
fouling organisms in sea-chests. Taken together, these findings highlight the role of sea-chests as an important vector responsible for the
introduction and spread of a variety of taxa, including aquatic invasive species, but also suggest that the factors that influence sea-chest
fouling in commercial vessels are complex. Further research, aimed at better understanding the determinants of sea-chest fouling and the
efficacy of anti-fouling systems, would help further refine management strategies and reduce the risks associated with sea-chest fouling.
Key words: biofouling, biological invasions, dispersal, non-indigenous, seachests, shipping, vessels
For centuries, shipping has served as the
principal vector for the introduction and spread
of aquatic invasive species worldwide (e.g.,
Cohen and Carlton 1998; Ruiz et al. 2000; Hewitt
et al. 2004). Historical, slow ocean-going vessels
transported aquatic species that fouled or bored
into the hulls of vessels, likely extending the
distributions of numerous “fouling” organisms
across oceans and along coastlines (Carlton and
Hodder 1995). Today, contemporary shipping is
generally characterized by relatively faster
vessel speeds, shorter port residence times, and
routine hull husbandry, which in turn, may
minimize the extent of biofouling on vessel hulls.
However, given increased levels of global trade,
associated shipping traffic, and new regulations
for anti-fouling agents (e.g., a worldwide ban of
tributyltin (TBT) compounds), biofouling continues
to pose serious invasion risks, particularly if
aquatic organisms are still able to readily
hitchhike from port to port on vessels (Carlton
1996; Gollasch 2002; Minchin and Gollasch 2003).
In addition to the flat surfaces of a vessel’s
hull, there are several specialized ‘niche’ areas
M.A. Frey et al.
on which organisms can attach, including bow
thrusters, rudders, propellers, intakes, and sea-
chests. Sea-chests are protected, cavity-like
structures, built into the hull of a vessel and
typically covered with metal grates (Coutts et al.
2003). Despite housing water intakes used for
engine cooling, ballast water operations, and
emergency fire-fighting, sea-chests are typically
characterized by relatively low water flows
compared to higher velocities and shear stresses
experienced on the exposed, flat surfaces of the
hull. Such low-flow environments provide a
relatively protected refuge for many fouling
organisms, leading to increased survivorship and
thriving communities (Coutts and Dodgshun
2007). Indeed, recent studies suggest that sea-
chests and sea-chest grates are hotspots for
biofouling, and by extension, may serve as an
important vector for the introduction and spread
of non-indigenous species (Coutts and Taylor
2004; Coutts and Dodgshun 2007; Sylvester and
MacIsaac 2010).
Anecdotally, sea-chests have been implicated
in the transport and potential spread of several
non-indigenous species, including Mytilus gallo-
provincialis, a well-known invasive mussel that
was found in large numbers in the sea-chests of
an Antarctic supply vessel (Lee and Chown 2007);
Caprella mutica, another widely introduced
species that has spread throughout the North
Atlantic, Northeast Pacific and South Pacific,
possibly as a hitch-hiker in the sea-chests of
commercial vessels (Ashton et al. 2007; Frey et
al. 2009); and Molgula citrina, a North Atlantic
ascidian that recently has been discovered in the
North Pacific, and potentially introduced to the
region via sea-chests (Lambert et al. 2010).
However to date, only a few detailed studies
have quantified the magnitude of biofouling
within sea-chests (Coutts et al. 2003; Coutts and
Dodgshun 2007), thus providing only some of
the information needed to make sound policies
on vector regulation and invasive species
management. The objective of this current study
is to further assess the role of sea-chests as a
potential vector for the introduction and spread
of fouling organisms, including aquatic invasive
species. Specifically, we examined the types and
abundances of taxa found in sea-chests of commer-
cial vessels visiting or operating in Canadian
waters, and whether certain vessel specifications
and voyage histories influenced the nature and
extent of sea-chest fouling.
Vessel sampling and characteristics
Between 2006 and 2009, we sampled sea-chests
from 39 commercial vessels in dry dock on the
West (n = 25) and East (n = 14) Coasts of
Canada (sampling locations: Victoria, British
Columbia; Les Méchins, Québec; Halifax, Nova
Scotia). For each vessel, we obtained available
data related to vessel specifications and voyage
history by interviewing ship personnel; vessels
with specific data gaps (e.g., unreported port
durations) were sampled but excluded from
respective statistical analyses (see Appendix 1).
Sampled vessels represented a variety of types
and size classes, including barge (n = 2), general
cargo (n = 9), passenger (cruise) (n = 2), ferry (n
= 13), fishing (n = 3), research (n = 9), and tug
(n = 1), and ranged from 139 to 109,000 gross
tonnage (gt). Port duration was estimated as the
average number of days spent in the last five
ports of call (mean = 4.3 days, sd = 4.4, min. =
0, max. = 16.6, n = 30). In-service period was
measured as the number of months since last
inspection and cleaning of sea-chests, including
the complete removal of all fouling organisms.
While the majority of these vessels were in dry
dock for routine maintenance following several
consecutive years at sea, a few ships were
docked for emergency repairs, providing the
opportunity to sample vessels over a broad range
of in-service periods (mean = 29.6 months, sd =
15.5, min. = 0.5, max. = 59.1, n = 28). We
classified vessel origin as ‘domestic’ (n = 23) if
travel occurred exclusively in Canadian waters
(i.e., along each coast), or ‘international’ (n =
16) if the vessel sailed to a foreign port within
the previous five ports visited. Based on
interview responses and visual inspections, all
sampled vessels and associated sea-chests appeared
to have been fitted with cathodic protection
systems (e.g., Cathelco®) and/or treated with anti-
fouling coatings (e.g., Interspeed 640 Red A/F)
to control biofouling. Unfortunately detailed
records for these anti-fouling systems (e.g., type,
location, and age) were unavailable for most
vessels, and therefore not suitable for further
Sea-chest sampling and characteristics
Shortly after the arrival of each vessel, we
sampled between one and four sea-chests (mean
= 2.1 sea-chests per ship, sd = 0.8), depending on
Sea-chests as a vector for aquatic invasive species
permitted access and time; in total 82 sea-chests
were examined. Preliminary sea-chest surveys
conducted prior to this study (Couture and
Simard 2007) suggested that, in general, fouling
organisms are not evenly distributed within sea-
chests, but rather in patches. To account for
spatial heterogeneity, we implemented a sampling
design that consisted of quadrat sampling, timed
searches, and visual estimates. Within each sea-
chest, three 0.01m2 quadrats were placed on
surfaces with the greatest amount of biofouling,
and all organisms within each quadrat were
collected using a putty scraper (Ardisson et al.
1990). We then conducted timed inspections (5
minutes) to search for rarer taxa potentially not
sampled within the quadrats. To assess whether
the sampled organisms were alive, specimens
were examined prior to preservation in 70%
ethanol. Within each entire sea-chest, we also
relied on visual estimates of percentage cover to
quantify the overall extent of biofouling. To
minimize observer biases on different coasts,
estimates made in the field were later verified by
a single investigator using photos. Although sea-
chests varied in size as characterized by total
surface area (mean = 7.6 m2, sd = 9.5, min. =
0.2, max. = 53.5), this standardized sampling
approach ensured equal sampling effort among
sea-chests. Sea-chest grates were occasionally
sampled by taking scrapings or bulk collections
(taxonomic data available upon request), but
ultimately these samples were not included in the
following analyses.
Classification of taxa
Individuals larger than 1 mm were examined
with dissecting and compound microscopes and
subsequently identified to species or the lowest
taxonomic level possible using available taxonomic
keys and species descriptions (e.g., Carlton
2007). Taxa were further categorized as either
‘indigenous’ (taxa that are native to each respective
coast), ‘non-indigenous (non-established)’ (non-
native taxa that have not been reported previously in
the region), ‘non-indigenous (established)’ (non-
native taxa that are presently established in the
region), ‘cryptogenic’ (taxa of unknown origin),
or ‘unknown’ (taxa that have been identified to
genus or higher, and whose origin remains
unclear). For certain groups, we consulted with
additional taxonomic experts to confirm the
identity and origin of each species (see
acknowledgements). Specimens that appeared
dead upon collection and already represented by
live individuals (e.g., empty shells of mussels
(Mytilus sp.) and tests of barnacles (Balanomorpha))
were excluded from further analyses.
Data analysis
To quantify the extent of biofouling, we
calculated both taxonomic richness (i.e., number
of unique taxa) and abundance (i.e., average
percentage cover) of organisms for each vessel.
We then examined whether either of these measures
were influenced by vessel specifications or voyage
histories. Linear models were implemented to
separately test the effects of each factor:
regression was used to examine vessel size, port
duration, and in-service period, while an analysis
of variance (ANOVA) was used to evaluate
vessel origin. For the purposes of testing the
effect of these factors on taxonomic richness, we
randomly selected a single sea-chest per vessel
to avoid biases that may have been introduced by
uneven sampling of multiple sea-chests among
vessels. To test their effect on abundance, we
used the average percentage cover of all sea-
chests sampled within each vessel. Taxonomic
richness and abundance data were square-root and
arcsine transformed, respectively, to meet statistical
assumptions. We recognize that these factors
could be confounded by complex interactions;
however, data gaps reduced the usefulness of a
full-factorial multiple regression. Analysis of
similarity (ANOSIM) tests, based on Bray-Curtis
similarity matrices calculated from presence/absence
of taxa, were also performed to evaluate
similarities of taxonomic composition between
and within vessels. Separate tests were performed
for each coast, and rather than creating zero-
adjusted coefficients, samples that contained no
species were removed from the analyses (Clarke
and Gorley 2006). Analyses were carried out
using JMP v4.0.2 (SAS Institute) and PRIMER
v6.1.9 (PRIMER-E Ltd.).
Extent of biofouling in sea-chests
Overall, 80% of sampled vessels showed
evidence of sea-chest fouling. The number of
unique taxa found in each sea-chest ranged from
0 to 47 with an average of 8.9 ± 12.1 taxa (mean
± sd); within each vessel, taxonomic richness
ranged widely from 0 to 61 (Figure 1A) with an
average of 14.9 ± 16.8 taxa (mean ± sd). The
extent of biofouling as measured by surface area
M.A. Frey et al.
Figure 1. Distribution of A) taxonomic richness (number of
taxa) shown with B) corresponding abundance (average
percentage cover) in sea-chests for sampled vessels. Vessels
ordered by increasing taxonomic richness, and do not correspond
to codes in Appendix 1.
Figure 2. Relationship between in-service period (i.e., duration
since last sea-chest cleaning) and extent of fouling as measured
by: A) taxonomic richness (number of taxa), and B) abundance
(average percentage cover) in sea-chests for each sampled vessel.
Regression line shows back-transformed model fit.
coverage varied from 0 to 90% (Figure 1B) and,
across all vessels, averaged 17.8 ± 24.6% (mean
± sd). Interestingly, vessels with heavily fouled
sea-chests (i.e., high average percentage cover)
did not necessarily equate to those with elevated
taxonomic richness (i.e., large number of taxa)
(Figure 1).
In total, we collected 299 distinct taxa (see
Appendix 2), representing a broad spectrum of
invertebrates, algae, and sea-grass, and including
54 non-indigenous (both non-established and
established) and cryptogenic species. Communities
were dominated by arthropods (primarily
barnacles and amphipods, found in 63% of sea-
chests), molluscs (bivalves and gastropods,
55%), cnidarians (primarily hydrozoans, 45%),
polychaetes (45%), and bryozoans (30%). While
the majority of these taxa were recognized as
indigenous, we also identified a substantial
number of non-indigenous and cryptogenic
organisms that collectively, comprised 20.5% and
14.4% of the taxa sampled from West and East
Coast vessels, respectively (Table 1). Non-
indigenous species were found more frequently
on international vessels (63% of those sampled)
than on domestic vessels (35%). Overall, 46% of
all vessels sampled (43% of West Coast vessels;
48% of East Coast vessels) harboured at least
one non-indigenous species within a sea-chest.
Effects of vessel specification and voyage history
on biofouling
Only a few of the factors related to vessel
specification or voyage history, when analyzed
separately, explained taxonomic richness or
abundance in sea-chests (Table 2). Vessel size
appeared to have a marginally significant effect
on biofouling (p = 0.08); however, when the two
largest vessels (both cruise ships) were excluded
from the analysis this weak effect was not
statistically significant (taxonomic richness: R2 =
0.042, F[1, 34] = 1.480, p = 0.23; abundance: R2 =
0.030, F[1, 34] = 1.043, p = 0.31). Port duration
also had no significant effect on biofouling. By
contrast, in-service period, defined as the number
of months since previous cleaning of sea-chests,
showed a significant positive relationship with
taxonomic richness, but not abundance (Figure 2,
Table 2). For both measures, however, sea-chest
fouling appeared to significantly increase on
vessels with in-service periods greater than 24
months (taxonomic richness: t = -2.509, df = 26,
p = 0.02; abundance: t = -2.110, df = 26, p =
Sea-chests as a vector for aquatic invasive species
Table 1. Number and percentage of indigenous, non-indigenous (non-established), non-indigenous (established), cryptogenic, and unknown
taxa sampled from the sea-chests of West and East Coast vessels.
West Coast Vessels East Coast Vessels
Origin of Taxa # of Taxa % of Taxa # of Taxa % of Taxa
Indigenous 82 42.1 51 36.7
Non-indigenous (non-established) 26 13.3 14 10.1
Non-indigenous (established) 9 4.6 2 1.4
Cryptogenic 5 2.6 4 2.9
Unknown 73 37.4 68 48.9
Total 201 139
Table 2. Summary of linear model results of the effects of vessel specifications and voyage histories on: A) taxonomic richness (number of
taxa, square-root transformed), and B) abundance (average percentage cover, arcsine transformed) in sea-chests. Effect size for vessel size
(gross tonnage), port duration (average number of days in port), and in-service period (number of months since last sea-chest cleaning) is the
slope (linear regression); effect size for vessel origin (domestic vs. international) is the mean difference (ANOVA). Significance level, α =
Factor R2 Effect Size F df (n-2) p
A) Taxonomic richness
Vessel size 0.080 2.61 x 10-5 3.149 36 0.08
Port duration 0.003 0.025 0.079 28 0.78
In-service period 0.183 0.059 5.840 26 0.02
Vessel origin 0.050 0.886 1.946 37 0.17
B) Abundance
Vessel size 0.083 4.55 x 10-6 3.268 36 0.08
Port duration 0.007 -0.006 0.186 28 0.67
In-service period 0.027 0.003 0.724 26 0.40
Vessel origin 0.062 0.172 2.360 36 0.13
Figure 3. Average (± standard error)
number of indigenous, non-
indigenous (non-established), non-
indigenous (established), cryptogenic,
and unknown taxa sampled from a
single sea-chest in domestic and
international vessels. Asterisk
highlights significant difference in
average number of taxa between
domestic and international vessels (p
= 0.01).
The overall effect of vessel origin was not
statistically significant, although international
vessels harboured more taxa (15.2 ± 3.4, mean ±
se) and had a higher average percentage cover
(25.0 ± 8.5) relative to domestic vessels (10.9 ±
3.1 taxa, 13.1 ± 3.4 % cover). Moreover, non-
indigenous (both non-established and established),
cryptogenic, and unknown taxa were on average
more prevalent on international vessels (Figure
3), albeit this difference was only statistically
significant for non-indigenous species (F[1, 37] =
6.74, p = 0.01). By contrast, indigenous taxa
were found in similar numbers on both
international and domestic vessels. Further analysis
(ANOSIM) revealed that taxonomic composition
was more similar within a vessel relative to
among vessels (West Coast: R = 0.59, p = 0.001;
East Coast: R = 0.72, p = 0.001). The same
analyses for vessels grouped by origin suggested
that sea-chests of domestic and international
M.A. Frey et al.
vessels did not significantly differ in overall
taxonomic assemblage (West Coast: R = 0.04, p
= 0.22; East Coast: R = 0.04, p = 0.34).
Similar to earlier investigations (Coutts et al.
2003; Coutts and Dodgshun 2007), our findings
confirm that commercial vessels can harbour
both an abundance and a diversity of fouling
organisms, including many non-indigenous and
cryptogenic taxa, within their sea-chests. While
the above results indicate that the extent of
biofouling, as measured by both percentage cover
and taxonomic richness, is quite variable across
vessels, the frequency of biofouling, as estimated
by the percentage of vessels with sea-chest
fouling, is relatively high with 80% of the
sampled vessels exhibiting some level of biofouling.
In general, these findings are consistent with the
few other studies that have quantified fouling in
sea-chests or on sea-chest gratings, and highlight
the role of this niche area as a hotspot for
biofouling (Coutts and Taylor 2004; Coutts and
Dodgshun 2007; Sylvester and MacIsaac 2010).
The number of non-indigenous species found
in this study further underscores the notion that
sea-chests pose a serious risk for the introduction
and spread of aquatic invasive species (Coutts
and Dodgshun 2007). On both coasts a sizeable
proportion (~15–20%) of the sea-chest community
was identified as non-indigenous or cryptogenic.
These results are lower than those reported in a
recent hull fouling study that also sampled
vessels on both coasts of Canada (~40-46%)
(Sylvester et al. 2011); however, it is important
to note that this latter investigation focused on
international vessels only. By contrast, our estimates
are comparable to those found in a similar sea-
chest study (~25%), which surveyed both
international and domestic vessels (Coutts and
Dodgshun 2007). In addition to these findings,
nearly half of all vessels sampled here carried at
least one non-indigenous species within their
sea-chests. We documented a number of non-
indigenous taxa that have already successfully
invaded other areas of the world, and may be
well-adapted to the temperate waters of Canada.
For example, the gammarid amphipod Elasmopus
rapax was found in significant numbers (>1,500
individuals/m2) in the sea-chests of an international
vessel arriving from Hawaii to the West Coast of
Canada. This small amphipod has been reportedly
introduced in Hawaii (Coles et al. 1999; but see
Hughes and Lowry 2010), California (Chapman
in Carlton 2007), and in temperate ports throughout
southern Australia (Hughes and Lowry 2010).
Similarly the bryozoan Bugula neritina, a well-
known fouling organism widely introduced and
expanding on both coasts of North America (e.g.,
Cohen and Carlton 1995; Pederson et al. 2005),
was discovered in the sea-chests of an international
vessel that had traveled extensively throughout
the Atlantic prior to arrival on the East Coast of
Canada. Given these invasion histories, such
fouling species seem primed for establishing
populations in the temperate waters of Canada;
and based on our observations, sea-chests could
serve as the primary vector of introduction for
these non-indigenous species.
Sea-chests may also play an important role in
the secondary spread of already established non-
indigenous or cryptogenic species. During this
study, we discovered large numbers (100–4,300
individuals/m2) of the invasive caprellid amphipod
Caprella mutica in the sea-chests of several
domestic vessels, each exclusively operating in
the West Coast or in the East Coast of Canada.
While we proposed that sea-chests may have
facilitated the spread of this species, at least
along the West Coast (Frey et al. 2009), a similar
argument may hold for many of the other non-
indigenous and cryptogenic species found in the
sea-chests of domestic vessels, including the
invasive tunicate Ciona intestinalis – a species
already present on both coasts of North America
and whose spread is of concern to managers and
policy-makers (Therriault and Herborg 2008;
Locke et al. 2009). The above results confirm
that the sea-chests of international vessels are
more likely to harbour non-indigenous species
(and more of them). However once established,
domestic vessels may play an equally significant
role by spreading these species via intra-coastal
voyages (Simkanin et al. 2009; for examples
from recreational boats, see Clarke Murray et al.
2011; Lacoursière-Roussel et al. 2012).
Previous investigations have demonstrated that
certain factors, related to vessel specifications and
voyage histories, likely play a major role in
contributing to the nature and extent of biofouling
(e.g., Coutts and Dodgshun 2007; Davidson et al.
2009; Sylvester and MacIsaac 2010). Accordingly,
we expected vessels with longer port durations
and longer in-service periods to show increased
taxonomic richness and abundance. However, we
found no significant relationship between port
duration and the extent of biofouling in this
study, and contrary to prediction, observed relatively
high levels of sea-chest fouling in some vessels
Sea-chests as a vector for aquatic invasive species
that had brief port residency times (e.g., averaging
one day or less). Admittedly the available data
was limited to the last five ports, and may not
accurately reflect typical port durations since last
dry docking. As an additional caveat, it is important
to note that anti-fouling systems were not evaluated
in our analyses, and may have confounded some
of our findings. By contrast, in-service period
did appear as an important determinant for sea-
chest fouling, which is consistent with other
biofouling studies (Coutts 1999; Davidson et al.
2009; but see Sylvester and MacIsaac 2010). On
average, vessels operating for more than approxi-
mately 24 months since last dry docking had
significantly higher taxonomic richness and
abundance. These results, coupled with comparable
findings from recent hull fouling investigations
(Davidson et al. 2009; Sylvester et al. 2011),
demonstrate that current cleaning and maintenance
practices may not sufficiently control biofouling.
They also suggest that shorter periods between
scheduled maintenance may be an effective
management strategy to prevent excessive levels
of biofouling (Sylvester et al. 2011). Although
we were unable to examine other factors, including
sailing speed, voyage routes, extensive port
history, sea-chest environmental conditions, and
anti-fouling systems due to data limitations, such
factors may be important determinants of sea-
chest fouling (Coutts et al. 2010; Sylvester et al.
2011), and represent vital areas for further
Indeed, a comprehensive understanding of the
factors that significantly influence sea-chest
fouling would likely improve our ability to
identify and manage associated invasion risks.
For example, although vessel origin may not account
for overall taxonomic richness or abundance, our
results show that origin does influence the type
of species that are associated with sea-chests.
International vessels are more likely to harbour
non-indigenous (both non-established and
established) species, and on average, carry signi-
ficantly more non-indigenous (non-established)
species than domestic vessels. In Canada, more
than half of recent commercial shipping traffic is
international (Statistics Canada 2012), with the
majority of West Coast arrivals originating in
Asia or the West Coast of the United States, and
East Coast arrivals coming from the East Coast
of the United States or Europe (Lo et al. 2012).
Lo et al. (2012) also showed that wetted
(immerged) surface area, used as a proxy for
potential propagule pressure of biofouling, was
significantly correlated with vessel arrivals.
However it is important to consider that, as
found with ballast water (Verling et al. 2005),
the large variation of sea-chest fouling among
vessels observed in this study suggests that
invasion risk may not be a simple function of
total vessel arrivals, but rather dependent on a
complexity of factors involving various vessel
specifications and voyage histories. Under-
standing which factors contribute most to sea-
chest fouling remains essential for developing
effective invasion management strategies.
Collectively, our findings support the notion
that sea-chests represent a greater source of non-
indigenous species than previously thought
(Coutts et al. 2003). Vessel biofouling is the
oldest, most important vector contributing to the
introduction and spread of aquatic invasive species,
accounting for more than 40% of all marine
invasions (Hewitt and Campbell 2010). Indeed,
hull fouling has been directly attributed to a large
number of non-indigenous species in different
regions of the world (e.g., Gollasch 2002;
Simkanin et al. 2009; Rocha Farrapeira et al.
2011), and may pose a greater invasion risk than
all other vectors, including ballast water
(Gollasch 2002; but for freshwater environments,
see Sylvester and MacIsaac 2010). Among the
various niche areas along the hull of a vessel,
sea-chests have been identified as a major hotspot
for biofouling (Coutts and Taylor 2004; Sylvester
and MacIsaac 2010), suggesting that this vector
alone may present a significant invasion risk. In
the present study, we found 47 distinct taxa in a
single sea-chest, comparable to the maximum
taxonomic richness reported in a similar
investigation (Coutts and Dodgshun 2007). By
sampling a second sea-chest in the same vessel,
richness increased to 61 distinct taxa, a level
comparable to that found in more general hull
fouling studies (Drake and Lodge 2007; Sylvester
and MacIsaac 2010). Admittedly, these numbers
represent maximum levels recorded; however, it
has been argued that such extreme cases likely
pose the greatest invasion risk (Drake and Lodge
2007; Sylvester and MacIsaac 2010). We note
that sampling additional sea-chests and vessels
would likely result in increased taxonomic
richness, as species accumulation curves (not
presented here) have yet to reach an asymptote.
Moreover, the ANOSIM results showed that
biotic communities in sea-chests are more
similar within vessels than among vessels,
suggesting that each vessel may deliver a relatively
unique assemblage of organisms to recipient ports.
Vessels with such rich fouling communities can
M.A. Frey et al.
rival those found in ballast water (Drake and Lodge
2007), further underscoring the relative importance
of sea-chests as a major vector for aquatic
invasive species.
Despite the associated invasion risks, relatively
few policies and management strategies are
currently in place to regulate sea-chests and other
vectors of biofouling. Certain regional guidelines
have been developed by some governments
(Hewitt and Campbell 2007), but a more global
approach that controls biofouling across all regions
and all vessels has not been implemented yet.
While mandatory regulations for ballast water
management may have reduced invasion risk
(albeit not completely, Bailey et al. 2011), a lack
of comparable strategies for hull and sea-chest
fouling allows for continued transport of biota
and potential shipping-mediated biological invasions
(Davidson and Simkanin 2012). Developing
effective vessel fouling management strategies is
essential, particularly given emergent trends in
shipping activity (e.g., increased port residency
for vessels during global economic downturns)
and recent changes to regulations of anti-fouling
coatings (e.g., ban of TBT), each of which may
ultimately lead to increased levels of vessel
fouling across the globe (Floerl and Coutts 2009;
Piola and Hopkins 2012). In this study, all
vessels reportedly employed an anti-fouling
system to control biofouling within sea-chests
(e.g., cathodic protection systems and/or anti-
fouling coatings). Yet similar to other investigations
(Coutts and Taylor 2004; Coutts and Dodgshun
2007; Davidson et al. 2009), biofouling was still
substantial in some cases, suggesting that current
treatments are not always effective. Even the most
commonly employed marine growth prevention
systems (i.e., sacrificial anodic copper dosing
(Cathelco®) and electrochlorination (Chloropac®))
have operational limitations that in turn can
influence efficacy (Grandison et al. 2011). Thermal
treatment that uses heated seawater offers promise
as an alternative method to control biofouling
within sea-chests; however, this technology needs
further refinement before being implemented
under actual conditions (Piola and Hopkins 2012).
In conclusion, sea-chests serve as an important
vector for the introduction and spread of aquatic
invasive species. Indeed, sea-chests can rival
other major transfer mechanisms such as ballast
water, and similarly, would benefit from the
development of effective biofouling management
strategies. To promote a comprehensive approach
to the control of vessel fouling, the International
Maritime Organization recently outlined voluntary
guidelines centered on management plans, docu-
mentation, inspections, maintenance, anti-fouling
systems, and new design and construction (IMO
2011). These include practical recommendations
for managing sea-chests and other niche areas,
including the installation and upkeep of anti-
fouling systems (e.g., marine growth prevention
systems or thermal treatment systems). Following
the adoption of these guidelines, it will be
important to assess whether the voluntary measures
translate into increased prevention of vessel-
mediated biological invasions (Baily et al. 2011).
For example, just prior to mandatory regulations
in the United States, voluntary compliance with
ballast water management guidelines was relatively
high among vessels that reported; but overall
compliance remained unknown due to vast under-
reporting (Miller et al. 2005). Fortunately, education
and inspection programs appear to result in
increased compliance and improved management
practices (Baily et al. 2011). Additional research,
aimed at better understanding the factors that
influence sea-chest fouling and testing the efficacy
of anti-fouling systems, will help further refine
management strategies and reduce the invasion
risks associated with sea-chest fouling.
We thank the following for logistical and technical support:
Transport Canada, Public Works and Government Services
Canada (Esquimalt Graving Dock), Victoria Shipyards, Esquimalt
Drydock, Canadian Maritime Engineering, Point Hope Maritime,
Halifax Shipyards, Verreault Navigation, Ocean Drydock,
shipping companies and crew, Biologica Environmental Services,
C. Carver and A. Mallet (Mallet Research Services), I. Bérubé, R.
Brown, J.-Y. Couture, I. Davidson, M. Galbraith, M. Huot, S.
Lindstrom, D. Mackas, N. Pellegrin, C. Simkanin and D. Sephton.
We especially thank L. Treau de Coeli and B. Ranns for their
assistance in the field and the lab, and J. Carlton, I. Davidson, H.
Gartner, A. Locke, C. Simkanin, and the reviewers for helpful
discussions and comments. Funding for this research was granted
by Fisheries and Oceans Canada’s Aquatic Invasive Species
Program; MAF was supported as a post-doctoral researcher
through the NSERC Visiting Fellowship in Canadian Government
Laboratories Program.
Ardisson P-L, Bourget E, Legendre P (1990) Multivariate
approach to study species assemblages at large spatio-
temporal scales: the community structure of the epibenthic
fauna of the Estuary and Gulf of St. Lawrence. Canadian
Journal of Fisheries and Aquatic Sciences 47: 1364–1377,
Ashton GV, Willis KJ, Cook EJ, Burrow M (2007) Distribution
of the introduced amphipod Caprella mutica Shurin, 1935
(Amphipoda: Caprellida: Caprellidae) on the west coast of
Sea-chests as a vector for aquatic invasive species
Scotland and a review of its global distribution. Hydro-
biologia 590: 31–41,
Baily SA, Deneau MG, Jean L, Wiley CJ, Leung B, MacIsaac HJ
(2011) Evaluating efficacy of an environmental policy to
prevent biological invasions. Environmental Science and
Technology 45: 2554–2561,
Carlton JT (1996) Pattern, process, and prediction in marine
invasion ecology. Biological Conservation 78: 97–106,
Carlton JT (ed) (2007) The Light and Smith Manual: Intertidal
Invertebrates from Central California to Oregon. 4th ed. The
University of California Press, Berkeley, 1019 pp
Carlton JT, Hodder J (1995) Biogeography and dispersal of
coastal marine organisms: experimental studies on a replica
of a 16th-century sailing vessel. Marine Biology 121: 721–
Chapman JW (2007) Gammaridea. In: Carlton JT (ed), The Light
and Smith Manual: Intertidal Invertebrates from Central
California to Oregon. 4th ed. The University of California
Press, Berkeley, pp 545–618
Clarke KR, Gorley RN (2006) PRIMER v6: User
Manual/Tutorial. PRIMER-E, Plymouth UK.
Clarke Murray C, Pakhomov EA, Therriault TW (2011)
Recreational boating: a large unregulated vector transporting
marine invasive species. Diversity and Distributions 17:
Cohen AN, Carlton JT (1995) Nonindigenous aquatic species in a
United States estuary: a case study of the biological invasions
of the San Francisco Bay and Delta. US Fish and Wildlife
Service, Washington DC
Cohen AN, Carlton JT (1998) Accelerating invasion rate in a
highly invaded estuary. Science 279: 555–558,
Coles SL, DeFelice RC, Eldridge LG, Carlton JT (1999)
Historical and recent introductions of non-indigenous marine
species into Pearl Harbor, Oahu, Hawaiian Islands. Marine
Biology 135: 147–158,
Coutre J-Y, Simard N (2007) Évaluation préliminaire des risques
potentiels d’introduction d’espèces non indigènes dans les
eaux de la côte est canadienne par l’intermédiaire des
caissons de prise d’eau des navires. Rapport manuscrit
Canadien des sciences halieutiques et aquatiques 2824: 25 pp
Coutts, ADM (1999) Hull fouling as a modern vector for marine
biological invasions: investigation of merchant vessels
visiting northern Tasmania. MSc Thesis, Australian Maritime
College, Tasmania, 283 pp
Coutts ADM, Moore KM, Hewitt CL (2003) Ships’ sea-chests: an
overlooked transfer mechanism for non-indigenous marine
species? Marine Pollution Bulletin 46: 1504–1515,
Coutts ADM, Taylor MD (2004) A preliminary investigation of
biosecurity risks associated with biofouling on merchant
vessels in New Zealand. New Zealand Journal of Marine and
Freshwater Research 38: 215–229,
Coutts ADM, Dodgshun TJ (2007) The nature and extent of
organisms in vessel sea-chests: A protected mechanism for
marine bioinvasions. Marine Pollution Bulletin 54: 875–886,
Coutts ADM, Piola RF, Hewitt CL, Connell SD, Gardner JP
(2010) Effect of vessel voyage speed on survival of
biofouling organisms: implications for translocation of non-
indigenous marine species. Biofouling 26: 1–13,
Davidson IC, Brown CW, Sytsma MD, Ruiz GM (2009) The role
of containerships as transfer mechanisms of marine
biofouling species. Biofouling 25: 645–655,
Davidson IC, Simkanin C (2012) The biology of ballast water 25
years later. Biological Invasions 14: 9–13,
Drake JM, Lodge DM (2007) Hull fouling is a risk factor for
intercontinental species exchange in aquatic ecosystems.
Aquatic Invasions 2: 121–131,
Floerl O, Coutts A (2009) Potential ramifications of the global
economic crisis on human-mediated dispersal of marine non-
indigenous species. Marine Pollution Bulletin 58: 1595–
Frey MA, Gartner HN, Clarke Murray C, Therriault TW (2009)
First confirmed records of the non-native amphipod Caprella
mutica (Schurin 1935) along the coast of British Columbia,
Canada, and the potential for secondary spread via hull
fouling. Aquatic Invasions 4: 495–499,
Gollasch S (2002) The importance of ship hull fouling as a vector
of species introductions into the North Sea. Biofouling 18:
Grandison C, Piola R, Fletcher L (2011) A review of Marine
Growth Prevention System (MGPS) options for the Royal
Australian Navy. Commissioned by the Department of
Defence, Marine Platforms Division, Defence Science and
Technology Organisation, Victoria, 28 pp
Hewitt CL, Campbell ML, Thresher RE, Martin RB, Boyd S,
Cohen BF, Currie DR, Gomon MF, Keough MJ, Lewis JA,
Lockett MM, Mays N, McArthur MA, O’Hara TD, Poore
GCB, Ross DJ, Storey MJ, Watson JE, Wilson RS (2004)
Introduced and cryptogenic species in Port Phillip Bay,
Victoria, Australia. Marine Biology 144: 183–202,
Hewitt CL, Campbell ML (2007) Mechanisms for the prevention
of marine bioinvasions for better biosecurity. Marine
Pollution Bulletin 55: 395–401,
Hewitt CL, Campbell ML (2010) The relative contribution of
vectors to the introduction and translocation of invasive
marine species. Commissioned by the Department of
Agriculture, Fisheries and Forestry, Canberra, 56 pp
Hughes LE, Lowry JK (2010) Establishing a neotype for
Elasmopus rapax Costa, 1853 and its presence as an invasive
species in temperate Australian waters. Journal of Crusta-
cean Biology 30: 699–709,
IMO (International Maritime Organization) (2011) Guidelines for
the control and management of ships’ biofouling to minimize
the transfer of invasive aquatic species. Annex 26, Resolution
MEPC.207(62), London
Lacoursière-Roussel A, Forrest BM, Guichard F, Piola RF,
McKindsey CW (2012) Modeling biofouling from boat and
source characteristics: a comparative study between Canada
and New Zealand. Biological Invasions 14: 2301–2314,
Lambert G, Shenkar N, Swalla B (2010) First Pacific record of
the north Atlantic ascidian Molgula citrina – bioinvasion or
circumpolar distribution? Aquatic Invasions 5: 369–378,
Lee JE, Chown SL (2007) Mytilus on the move: transport of an
invasive bivalve to the Antarctic. Marine Ecology Progress
Series 339: 307–310,
Lo VB, Levings CD, Chan KMA (2012) Quantifying potential
propagule pressure of aquatic invasive species from the
commercial shipping industry in Canada. Marine Pollution
Bulletin 64: 295–302,
Locke A, Hanson JM, MacNair NG, Smith AH (2009) Rapid
response to non-indigenous species. 2. Case studies of
invasive tunicates in Prince Edward Island. Aquatic Invasions
4: 249–258,
M.A. Frey et al.
Miller AW, Ruiz GM, Lion K (2005) Status and trends of ballast
water management in the United States. Second biennial
report of the National Ballast Information Clearinghouse,
Submitted to the United States Coast Guard, 2004.
Smithsonian Environmental Research Center, Edgewater,
Maryland, 31 pp
Minchin D, Gollasch S (2003) Fouling and ships’ hulls: How
changing circumstances and spawning events may result in
the spread of exotic species. Biofouling 19: 111–122,
Pederson J, Bullock R, Carlton J, Dijkstra J, Dobroski N,
Dyrynda P, Fisher R, Harris L, Hobbs N, Lambert G, Lazo-
Wasem E, Mathieson A, Miglietta M-P, Smith J, Smith III J,
Tyrrell M (2005) Marine Invaders in the Northeast: Rapid
Assessment Survey of Non-native and Native Marine Species
of Floating Dock Communities, August 2003 MIT SeaGrant,
40 pp
Piola RF, Hopkins GA (2012) Thermal treatment as a method to
control transfers of invasive biofouling species via vessel sea
chests. Marine Pollution Bulletin 64: 1620–1630,
Rocha Farrapeira CM, de Oliveira Tenório D, Duarte do Amaral
F (2011) Vessel biofouling as an inadvertent vector of
benthic invertebrates occurring Brazil. Marine Pollution
Bulletin 62: 832–839,
Ruiz GM, Fofonoff PW, Carlton JT, Wonham MJ, Hines AH
(2000) Invasion of coastal marine communities in North
America: apparent patterns, processes, and biases. Annual
Review of Ecology and Systematics 31: 481–531,
Simkanin C, Davidson I, Falkner M, Sytsma M, Ruiz G (2009)
Intra-coastal ballast water flux and the potential for secon-
dary spread of non-native species on the US West Coast.
Marine Pollution Bulletin 58: 366–374,
Statistics Canada (2012) Shipping in Canada 2011. Ottawa, 191
Sylvester F, MacIsaac HJ (2010) Is vessel hull fouling an invasion
threat to the Great Lakes? Diversity and Distributions 16:
Sylvester F, Kalaci O, Leung B, Lacoursière-Roussel A, Clarke
Murray C, Choi FM, Bravo MA, Therriault TW, MacIsaac
HJ (2011) Hull fouling as an invasion vector: can simple
models explain a complex problem? Journal of Applied
Ecology 48: 415–423,
Therriault TW, Herborg L-M (2008) A qualitative biological risk
assessment for vase tunicate Ciona intestinalis in Canadian
waters: using expert knowledge. ICES Journal of Marine
Science 65: 781–787,
Verling E, Ruiz GM, Smith LD, Galil B, Miller AW, Murphy KR
(2005) Supply-side invasion ecology: characterizing
propagule pressure in coastal ecosystems. Proceedings of the
Royal Society B 272: 1249–1257,
Supplementary material
The following supplementary material is available for this article:
Appendix 1. Supplementary data for vessels and sea-chests sampled.
Appendix 2. Non-indigenous (including non-established and established), cryptogenic, indigenous, and unknown taxa found in the sea-
chests of vessels sampled while in dry dock on the West Coast and East Coast of Canada.
This material is available as part of online article from:
... ISS are integral to vessel function and their design and construction are complex components of shipbuilding and a significant part of a ship's capital costs (P erez et al. 2020). Available colonisation space for biofouling within ISS is orders of magnitude lower than external hull surfaces, but ships' ISS can be more prone to biofouling due to their sheltered nature and inherent challenges to effective antifouling system protection (Coutts and Dodgshun 2007;Frey et al. 2014;Lewis 2016). In addition, restricted spaces within ISS means relatively modest biofouling accumulation can exert strong impacts on system integrity and operations . ...
... Sea chests, sea strainers, and heat exchangers have been examined in some instances based on periodic available access. Sea chests provide distinctive habitat for diverse assemblages of biofouling and mobile species, supporting organism types that are usually absent elsewhere on ship surfaces (Coutts and Dodgshun 2007;Frey et al. 2014). Sea chest biofouling offers unique opportunities for species transfers (Coutts et al. 2003) and operational impact to ISS seawater intake (Lewis 2016; Figure 1), though this impact is not well quantified. ...
... However, there is uncertainty surrounding MGPS efficacy throughout ISS spaces from intakes to discharges (e.g. Lewis and Smith 1991;Frey et al. 2014;Lewis 2016;Gust et al. 2018b) because access for sampling is limited . Biofouling organisms' tolerance of proactive and reactive treatment approaches may differ among species and applied research of impacts on ISS has informed renewed strategies to combat the problem (Lewis and Smith 1991;Piola and Grandison 2017;Salters and Piola 2017;Piola et al. 2022). ...
Biofouling of ships' internal seawater systems (ISS) can cause significant operational issues and is a potential transfer mechanism for marine nonindigenous species. This study used an engine room simulator and economic evaluation to quantify impacts on commercial ship performance of biofouling occlusion within various ISS nodes (sea chest, strainer, and heat exchangers). A characteristic hockey-stick relationship between occlusion and impact emerged, whereby engine room systems could tolerate up to 55% occlusion of a single node without operational impact, followed by rapid performance deterioration. The relative magnitude of impacts varied by ISS node and in response to changes in ambient seawater temperatures. System tolerance was much lower when simultaneous occlusion of multiple nodes was assessed. In economic terms, consequences included required freight rate increases of 1-26% prior to forced (automatic) slowdown of the ship and up to 82% increases if slowdown conditions were required.
... These data are the best-available for biofouling on vessels entering Canada, and are considered representative of current vessel biofouling communities as no major changes in vessel routes or biofouling management practices have been reported. In addition, data from drydock inspections examining fouling inside vessel seachests were included from vessels sampled in the Pacific coast (n = 6) and the Atlantic coast (n = 2) (Frey et al. 2014). The biological data were pooled across regions (rather than kept as region-specific datasets) due to small sample sizes for each of the individual regions, although analysis using regional separation was performed as part of the sensitivity analysis. ...
... Internal seachest data from navy vessels were excluded to keep vessel types consistent across studies. Full sampling details and analysis of the internal seachest study can be found in Frey et al. (2014). Information on last ports-of-call were available for vessel sampling data, and were used for the port history analysis (described later). ...
... Both species-level and higher order distinct taxa data were used to create species abundance distributions, as species identity was not important for this analysis. Taxa were also classified as NIS, or non-NIS, in the original studies according to their population status in the specific regions where sampling occurred (Sylvester and MacIsaac 2010;Sylvester et al. 2011;Frey et al. 2014;Chan et al. 2015). If specimens were unable to be identified to species level, but the taxon was listed by the original authors as a 'non-established taxon', it was considered a NIS. ...
Technical Report
Full-text available
Biofouling is the accumulation of organisms (such as algae, mussels, barnacles, and other taxa) on underwater surfaces. Biofouling on vessels is seen as undesirable, as it reduces vessel fuel efficiency through increased drag, and has potential to transfer organisms over long distances to locations outside their natural biogeographic region. Compared to other vectors that transfer aquatic organisms, such as ballast water, biofouling is relatively understudied despite being a major contributing vector of aquatic nonindigenous species (NIS) to coastal ecosystems globally. As a result, Transport Canada requested science advice from Fisheries and Oceans Canada, seeking an updated national assessment of the probability of NIS introduction and establishment via biofouling on vessels, to inform the development of biofouling management policies. This study used a multistage mechanistic model (a multiple-step model describing the parts or stages of the invasion process) to assess the probability of introduction and establishment of NIS into Canada based on one year of data on first arrivals of foreign-flagged commercial vessels. The stages in the model included arrival, survival, and establishment of NIS, but throughout this document the term ‘establishment’ denotes the cumulative success through all three stages to result in a self-sustaining population in Canadian waters. Separate assessments were conducted for vessels’ main hull surfaces and combined niche areas (such as the sea-chest, propeller, and thruster tunnels, where biofouling may be more concentrated). Results were summarized for the four coastal regions of Canada based on the destination/arrival port of the vessels: Atlantic, Pacific, Great Lakes-St. Lawrence River, and Arctic regions. The model parameters were based on empirical vessel biofouling and environmental data, as well as estimates of biological processes with variability introduced. Estimates of mean NIS primary establishments per year via vessel hulls ranged from <1 (Arctic region) to 2.2 (Pacific region). Similarly, the mean number of trips until at least one NIS establishment is successful via the hull ranged from 94 (Pacific region) to 174 (Great Lakes-St. Lawrence River region). Primary NIS establishments via vessel niche areas were generally higher than those associated with the hull, with the highest species establishments per year being 8.4, with 23 trips until establishment occurs (Pacific region). While there is uncertainty associated with these estimates, these results indicate a meaningful probability of NIS establishments by vessel biofouling in all regions of Canada. The Atlantic and Pacific coasts are expected to receive the greatest numbers of NIS establishments, driven by the higher number of vessel arrivals to these regions. NIS establishment rates via the main hull areas of vessels were lower compared to niche areas, with the niche areas (all combined) having higher abundance of biofouling but smaller wetted surface area. Vessel biofouling should be considered as a dominant, active vector for introduction of NIS to Canada.
... Ship systems are impacted negatively by seawater due to corrosion and biofouling in ship hulls, internal pipes, filters, grids, and valves. Due to its working regime, the gratings used in the sea chests have been identified are hotspots for Biofouling accumulation [2] and hence, it must be treated as a critical part of the maintenance to avoid ship malfunction. ...
... In both films, the preferential direction of this structure was the (111) plane, similar to the one described by Carvalho et al. [49] when substoichiometric ZrN is formed. Furthermore, the Cu-ZrN film revealed a slight displacement to higher 2θ positions, which could be due to (1) the oxygen content present in this film [49] or (2) substitutional Cu in the ZrN lattice [50] or (3) a combination of the mentioned. Another aspect to emphasize is the crystallite size in the (111) plane, which increased from 8 nm to 26 nm with the copper addition in the nitride film. ...
... This research is sponsored by national funds through FCT -Fundação para a Ciência e a Tecnologia, under the PhD Research Scholarship with reference 2020.09436.BD. Also, this work was financially supported by the On-SURF project (co-financed via FEDER (PT2020) POCI-01-0247- [2]FEDER-546024521), the HEALTHYDENT project (co-financed via FEDER (PT2020) POCI-01-0145-FEDER-030708 and FCT (PIDDAC)), the COMPETE program -Competitive Factors Operational Program -and by national funds through FCT -within the scope of the UIDB/00285/ 2020 project. ...
Corrosion and antibiofouling protection of maritime transport are important to improve lifetime usage and reduce maintenance costs. Tributyltin (TBT) paint was the most widely used solution, but it was banned due to environmental toxicity in 2008. Multifunctional coatings can be the solution for many current issues, particularly in situations where it is necessary to combine dissimilar properties such as anticorrosion and antibacterial. Zirconium (oxy)nitrides (coatings with great corrosion resistance) doped with copper (proved already to show antibiofouling activity) were obtained by unbalanced magnetron sputtering with a reactive atmosphere to add the anticipated multifunctional characteristics. The properties of obtained films were assessed by SEM, EDS, XRD, AFM, and contact angle measurements. EIS and potentiodynamic polarization tests were performed in NaCl (3.5 % wt.) solution for 168 h to simulate seawater exposure. The results demonstrated that Cu did not form, with Zr(O)N, a crystalline phase. Moreover, Cu incorporation promotes voids among column boundaries of ZrON films, directly influencing their roughness, surface energy, porosity index, and wettability. Regarding corrosion resistance, the inclusion of Cu worsens the Zr(O)N chemical stability against seawater. The obtained results demonstrated the incapability of Cu-Zr(O)N films to be applied as unique coatings to avoid biofouling under seawater exposure due to copper addition.
... The loss of ecological balance results in the extinction of certain species and the overproduction of others, such as marine creatures . Both sessile and mobile marine creatures have been found to congregate in seawater connected parts of the ships (Lee and Chown 2007;Frey et al. 2014). Barnacles, bryozoans, sea stars, polychaetes, gastropods, ascidians, hydroids, seagrass, amphipods, mytilus galloprovincialis, algae, hydroids, caprella mutica, crustaceans, molgula and bivalves are some of proliferating and harmful marine creatures associated with ship sea chests (Lee and Chown 2007;Ashton et al. 2007;Coutts and Dodgshun 2007;McDonald 2012;Frey et al. 2014) Specifically, mucilage is one of the mentioned clogging materials which has become increasingly common in some narrow sea channels in recent years, owing to the effects of global warming (Danovaro, Fonda Umani, and Pusceddu 2009;Tas, Kus, and Yilmaz 2020). ...
... Both sessile and mobile marine creatures have been found to congregate in seawater connected parts of the ships (Lee and Chown 2007;Frey et al. 2014). Barnacles, bryozoans, sea stars, polychaetes, gastropods, ascidians, hydroids, seagrass, amphipods, mytilus galloprovincialis, algae, hydroids, caprella mutica, crustaceans, molgula and bivalves are some of proliferating and harmful marine creatures associated with ship sea chests (Lee and Chown 2007;Ashton et al. 2007;Coutts and Dodgshun 2007;McDonald 2012;Frey et al. 2014) Specifically, mucilage is one of the mentioned clogging materials which has become increasingly common in some narrow sea channels in recent years, owing to the effects of global warming (Danovaro, Fonda Umani, and Pusceddu 2009;Tas, Kus, and Yilmaz 2020). On the other hand, there may be inanimate pollutants such as sediment and human-derived materials that cause fouling or blockage in sea chests. ...
... On the other hand, seawater cooling water system and sea chest fouling risks of the ships are not a widely researched subject. Researchers have generally examined the formation, distribution, and transfer mechanism of NIS organisms by means of ship transportation (Piola and Hopkins 2012;Coutts and Dodgshun 2007;Coutts, Moore, and Hewitt 2003;Frey et al. 2014;Piola and Grandison 2017;Coutts and Taylor 2004;Chan, MacIsaac, and Bailey 2015;Meloni et al. 2021). However, to the authors' knowledge, a detailed risk analysis study of ship's machinery systems related to the sea chests fouling was not found in the literature. ...
Sea pollution has negative consequences and has an impact on the marine ecosystem and ship machinery processes. The main risk of sea pollution on ship is based on sea chests that are used for ballast water and firefighting. In addition to this, sea chest fouling, which primarily forms as a result of pollution, has an impact on the ship machinery, navigation in waterways, and the environment. The possibility of failure related to sea chest fouling issues in seawater cooling systems used to cool ship machinery parts were investigated in this study. Significant defects in the cooling and related engine systems were determined using both a full-mission Kongsberg engine room simulator (ERS) process and failure modes and effects (FMEA) technique, which relied on expert judgments within the cause–effect relationship. According to the findings, sea chest pollution has a direct impact on the ships’ cooling water systems and other related components, causes power losses, and leads the main engine to shut down, resulting in the ship losing maneuverability. As a result of these circumstances, the risk of catastrophic events such as grounding, contact, collision, flooding, fire explosion, and others was determined.
... Some less obvious consequences of IWC include the creation of conditions conducive to NIS establishment [e.g., copper contaminated ports or marinas favoring survival of copper tolerant species (Piola and Johnston, 2006;Piola and Johnston, 2007)], premature deterioration of biocidal antifouling coatings leading to a higher likelihood of refouling and the acceleration of re-cleaning cycles (Earley et al., 2014;Oliveira and Granhag, 2020;Swain et al., 2022), and a focus on cleaning the main hull at the expense of managing all submerged surfaces, including niche areas (Growcott et al., 2019;Davidson et al., 2023). Focusing attention away from niche areas is particularly troubling, as these areas are important hotspots for the accumulation and transfer of NIS (Coutts and Dodgshun, 2007;Frey et al., 2014). ...
... For niche areas, a combination of biocidal coatings and marine growth prevention systems (MGPS) may still offer the best chance of fouling prevention, where applicable (Lewis, 2016;Georgiades et al., 2018). However, the efficacy of MGPS has long been questioned (Lewis and Smith, 1991;Frey et al., 2014;Lewis, 2016;MPI, 2020), and thus should also be subject to independent testing. ...
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Effective environmental policy often involves introducing and maintaining important activities with positive outcomes while minimizing environmental consequences; essentially decoupling a positive activity from its negative impacts. In-water cleaning (IWC) of biofouling from ships’ submerged surfaces is an example of an activity with positive outcomes (e.g., maintaining optimal ship energy efficiency and decreased biosecurity risk) and unintended negative consequences (e.g., release of living organisms, biocides, and microplastics). Several approaches exist to mitigate these negative consequences, including debris capture, with primary and secondary treatment of removed particulate and dissolved materials. However, it is unlikely that these approaches will eliminate environmental risk. Policy makers should be aware of the full suite of risks related to ship IWC and the tradeoffs to consider when balancing mitigation approaches.
... Furthermore, antifouling coating systems are generally more effective on the hull when exposed to higher water velocities experienced during sailing (Coutts and Taylor, 2004). Conversely, niche areas tend to become more heavily fouled with organisms since the antifouling coating systems cannot be applied (e.g., sacrificial anodes) or they are typically less effective in these physically complex areas (Coutts and Taylor, 2004;Davidson et al., 2009;Frey et al., 2014). Marine growth prevention systems (e.g., anodic copper dosing and electrolysis) deliver antifouling agents to reduce fouling in recessed or internal niche areas, such as sea chests and water cooling systems (Coutts and Dodgshun, 2007;Grandison et al., 2011). ...
... For example, it has been hypothesized that larger ships have a higher likelihood of non-indigenous species introduction than smaller ships as they have more wetted surface area to accumulate a larger number of fouling organisms (Lo et al., 2012;Moser et al., 2016;Miller et al., 2018). However, the wetted surface area of a ship may not directly indicate the abundance of fouling organisms, since fouling organisms are typically concentrated in niche areas, which make up between 7 and 27% of a ship's total wetted surface area and do not normally increase proportionally with wetted surface area (Frey et al., 2014;Chan et al., 2015;Moser et al., 2017). The operational profile of a ship includes time between dry-docking visits, sailing speed, residence time in ports, and travel history. ...
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Ship biofouling is a major vector for the introduction and spread of harmful marine species globally; however, its importance in Arctic coastal ecosystems is understudied. The objective of this study was to provide insight regarding the extent of biofouling (i.e., percent cover, abundance, and species richness) on commercial ships operating in the Canadian Arctic. A questionnaire was used to collect information on travel history, antifouling practices, and self-reported estimates of biofouling extent from ships operating in the region during 2015–2016. Twenty-five percent of ships operating in the region during the study period completed the questionnaire ( n = 50). Regression trees were developed to infer the percent cover of biofouling, total abundance of fouling invertebrates, and fouling species richness on respondent ships based on previous underwater wetted surface assessments of commercial ships in Canada. Age of antifouling coating system was the only significant predictor of percent cover and total abundance of biofouling invertebrates, while the number of biogeographic realms previously visited and port residence time were significant predictors for fouling species richness. Comparison of relevant travel history features reported through the questionnaire to the regression tree models revealed that 41.9% of 43 respondent ships had antifouling coating systems older than 630 days and are therefore inferred to have relatively high (> 9.3%) biofouling percent cover. More than half of respondent ships (62.8%) had antifouling coating systems older than 354 days and are therefore inferred to have a relatively high total abundance (over 6,500 individuals) of fouling invertebrates. Nearly half of respondent ships (45.9% of 37 ships) had visited at least three biogeographic realms during their last 10 ports-of-call and are therefore inferred to have relatively high fouling species richness (mean 42 taxa). Self-reported estimates of biofouling cover were unreliable, being much lower than model inferences. Although the regression tree models have relatively low predictive power, explaining only 15–33% of the variance in biofouling extent, this study indicates that commercial ships are an active pathway for the transportation of non-indigenous aquatic species to Canadian Arctic coastal ecosystems via biofouling.
... Here, the use of proactive in-water cleaning (PIC) as a preventative measure to control the growth of microfouling (slime) can help to minimize biosecurity risks (reviewed in Scianni and Georgiades 2019). If patches of macrofouling organisms (potential basibionts) have already grown on the structure, the desirable reactive approach is through dry-docking and re-application of anti-fouling substances, including careful inspection of niche areas, which have been found to host considerably higher amounts of fouling (Coutts and Taylor 2004;Davidson et al. 2010;Clarke-Murray et al. 2011;Frey et al. 2014). In-water cleaning via encapsulating systems would also be an alternative for macrofouling removal, although these techniques are still under evaluation for feasibility and environmental safety (Hopkins and Forrest 2008;Roche et al. 2015;Keanly and Robinson 2020). ...
Vessel hull-fouling is responsible for most bioinvasion events in the marine environment, yet it lacks regulation in most countries. Although experts advocate a preventative approach, research efforts on pre-arrival processes are limited. The performance of mobile epifauna during vessel transport was evaluated via laboratory simulations, using the well-known invasive Japanese skeleton shrimp (Caprella mutica), and its native congener C. laeviuscula as case study. The invader did not possess any advantage in terms of inherent resistance to drag. Instead, its performance was conditioned by the complexity of secondary substrate. Dislodgement risk was significantly reduced when sessile fouling basibionts were added, which provided refugia and boosted the probability of C. mutica remaining attached from 7 to 65% in flow exposure trials. Interestingly, the invader exhibited significantly higher exploratory tendency and motility than its native con-gener at zero-flow conditions. Implications in terms of en-route survivorship, invasion success and macrofouling management are discussed.
... However, in reality, structural and functional design features such as bulkheads, stiffeners, ribs, pipework and anodes can add significant geometric constraints to sea chest design (MPI, 2016). Sea chests are frequently reported to harbour complex biofouling assemblages (Coutts and Dodgshun, 2007;Frey et al., 2014;Inglis et al., 2010) as they provide a protected environment removed from the strong current flow experienced over the exposed hull, with steady supplies of nutrients and clean oxygenated seawater (Jones and Little, 1990). These conditions often negatively impact the performance of antifouling coatings, with reduced water flow and static pockets leading to insufficient biocide release through a lack of polishing or ablation, or inadequate over-the-surface flow to detach settled organisms from FRCs (Arndt et al., 2021;Georgiades et al., 2018;Leary et al., 2016). ...
Sea chests are arguably the most problematic vessel niche areas with respect to managing and preventing marine biofouling. This is partly due to the design and location of these structures, as well as the difficulty in managing them with conventional antifouling technologies. Antifouling coatings are typically designed for use on flat exposed hull surfaces that experience predictable flow conditions, and often perform poorly under variable flow conditions found in sea chest environments. This study examined whether custom-designed inserts retrofitted to experimental sea chests to alter their internal geometry and flow characteristics could improve antifouling coating performance. For in-laboratory sea chests coated with self-polishing copolymer (SPC) antifouling coatings, retrofitted inserts improved the polishing rate and erosion consistency of the coating; likely due to enhanced laminar flow and greater uniform wall shear stress over the surface of the sea chest, and the elimination of circulation zones and/or pockets of static water. For in-field sea chests coated with fouling-release coatings, inserts had little direct impact on biofouling accumulation compared to unmodified sea chests, with similar levels of fouling recorded per cm² of sea chest surface. Inserts did however reduce the overall biomass of biofouling accumulated, through a reduction in available settlement area.
... The availability of protected niche areas along the vessel's hull is especially important. Areas like the propellers, sea chests, and rudders provide a safe zone from currents and shear forces, enabling an extensive accumulation of fouling organisms (Frey et al., 2014;Gewing and Shenkar, 2017). The extent of WSA and niche areas varies with the specific build and design of the different vessel categories (Moser et al., 2017;Miller et al., 2018). ...
The shipping industry is considered the main vector of introduction of marine non-indigenous species (NIS). NIS distributions are often a consequence of frequent trade activities that are affected by economic trends. A dominant trend in the shipping industry is the operation of Ultra Large Container Vessels (ULCV), which are over 395 m long and sail mostly on the East-Asia – northern-Europe route. Understanding the risk of NIS introduction by this emerging shipping category is needed for devising strategies for sustainable shipping. Here, we conducted a controlled simulation of key abiotic factors that determine marine bioinvasion success: temperature, salinity, and food availability along selected routes, under two treatments: ULCV and intermediate-size vessels. We tested the effect of each treatment and the varying environmental conditions on the survival of two invasive ascidians (Chordata, Ascidiacea). We used survival analysis methods to locate predictors of ascidian mortality; Environmental conditions at ports with high mortality were used to identify similar major ports on a global scale as potential abiotic barriers. The key factors in ascidian mortality varied between the two species, but for both species, the treatment and salinity were dominant predictors for survival. We identified Port Klang, Rotterdam, and Dammam as ports with high mortality and located several globally distributed major ports that present similar environmental conditions. Our results highlight the potential role of selected major ports as abiotic barriers to fouling organisms during ocean voyages. The tolerance of the tropical-origin Microcosmus exasperatus to the northern-Europe conditions, and of the temperate/sub-tropical origin Styela plicata, to high temperature conditions, point out the urgent need to modify international fouling regulations in view of global change. Further studies on the survival of fouling organisms during a cascade of changing environmental conditions will contribute to the advancement of science-based regulations to reduce the adverse effects of NIS.
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valuation préliminaire des risques potentiels d'introduction d'espèces non indigènes dans les eaux de la côte est canadienne par l'intermédiaire des caissons de prise d'eau des navires Jean-Yves Couture et Nathalie Simard Direction régionale des sciences Pêches et Océans Canada Institut Maurice-Lamontagne 850, route de la Mer Mont-Joli, Québec, G5H 3Z4 2007 Rapport manuscrit canadien des sciences halieutiques et aquatiques 2824 Pêches et Océans Canada Fisheries and Oceans Canada Rapport manuscrit canadien des sciences halieutiques et aquatiques Les rapports manuscrits contiennent des renseignements scientifiques et techniques qui constituent une contribution aux connaissances actuelles, mais qui traitent de problèmes nationaux ou régionaux. La distribution en est limitée aux organismes et aux personnes de régions particulières du Canada. II n'y a aucune restriction quant au sujet; de fait, la série reflète la vaste gamme des intérêts et des politiques de Pêches et Océans Canada, c'est-à-dire les sciences halieutiques et aquatiques. Les rapports manuscrits peuvent être cités comme des publications à part entière. Le titre exact figure au-dessus du résumé de chaque rapport. Les rapports manuscrits sont résumés dans la base de données Résumés des sciences aquatiques et halieutiques. Les rapports manuscrits sont produits à l'échelon régional, mais numérotés à l'échelon national. Les demandes de rapports seront satisfaites par l'établissement auteur dont le nom figure sur la couverture et la page du titre. Les numéros 1 à 900 de cette série ont été publiés à titre de Manuscrits (série biologique) de l'Office de biologie du Canada, et après le changement de la désignation de cet organisme par décret du Parlement, en 1937, ont été classés comme Manuscrits (série biologique) de l'Office des recherches sur les pêcheries du Canada. Les numéros 901 à 1425 ont été publiés à titre de Rapports manuscrits de l'Office des recherches sur les pêcheries du Canada. Les numéros 1426 à 1550 sont parus à titre de Rapports manuscrits du Service des pêches et de la mer, ministère des Pêches et de l'Environnement. Le nom actuel de la série a été établi lors de la parution du numéro 1551.
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Therriault, T. W., and Herborg, L-M. 2008. A qualitative biological risk assessment for vase tunicate Ciona intestinalis in Canadian waters: using expert knowledge. – ICES Journal of Marine Science, 65: 781–787. Non-indigenous species (NIS) can pose a significant level of risk, through potential ecological or genetic consequences, to environments to which they are introduced. One way to characterize the overall risk posed by a NIS is to combine the probability and consequences of its establishment in a risk assessment that can be used to inform managers and policy-makers. The vase tunicate Ciona intestinalis is considered to be a cryptogenic species in eastern Canadian waters, but has not yet been reported from Pacific Canada. Because it is unclear what level of risk it poses for Canadian waters, we conducted a biological risk assessment for C. intestinalis and its potential pathogens, parasites, and fellow travellers. An expert survey was conducted to inform the risk assessment. The ecological risk posed by C. intestinalis was considered high (moderate uncertainty) on the Atlantic coast, and moderate (high uncertainty) on the Pacific coast. The genetic risk posed by C. intestinalis was considered moderate on both coasts, with low uncertainty on the Atlantic coast and high uncertainty on the Pacific coast, where hybridization with Ciona savignyi may be possible. Pathogens, parasites, and fellow travellers were considered to be a moderate ecological risk and a low genetic risk (with high uncertainty) for both coasts.
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Biofouling on international vessels is an important mechanism for the inadvertent transfer of non‐indigenous marine species around the globe. This paper describes the nature and extent of biofouling on 30 merchant vessels (ranging from 1400 to 32 000 gross registered tonnes) based on analysis of hull inspection video footage collected by two New Zealand commercial diving companies. A new method for measuring biofouling communities is applied, which aims to incorporate the potential for various hull locations to house non‐indigenous marine species. Our analysis revealed that out‐of‐service vessels and vessels plying trans‐Tasman routes possessed greater levels of biofouling than more active vessels. Dry‐docking support strips and sea‐chest gratings generally had the highest levels of biofouling and may pose relatively high biosecurity risks. Any future biosecurity surveillance should target these hull locations for non‐indigenous species.
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A milestone in understanding a globally significant mechanism of marine bioinvasions was published 25 years ago. The transformative paper on ballast water provided a baseline of patterns, processes and predictions of marine introductions, underpinned a dramatic increase in research on the topic, and presented a foundational insight for an international approach to vector management. The 25 year anniversary of JT Carlton’s ‘Transoceanic and interoceanic dispersal of coastal marine organisms: the biology of ballast water’ coincides with an International Maritime Organization (IMO) convention for management of ballast water that has not been fully ratified. The emergence of ship biofouling as a vector of management concern worldwide has also prompted renewed efforts to reduce species transfers by ships through new policy initiatives.
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In marine systems subject to vessel traffic, the likelihood of an invasion by an exotic species typically increases with the arrival of each infested boat. In this paper, recreational boating activity patterns and boat fouling by tunicates were compared between eastern Canada and central New Zealand, and the relative importance of boat characteristics on fouling was evaluated using Boosted Regression Tree analysis. For Canada, we also determined the relative importance of boat characteristics and propagule exposure (i.e., the interaction between tunicate density in source region and time in water) on patterns of boat fouling. Approximately half of boats examined during the fall in eastern Canada and during the summer in central New Zealand were fouled by tunicates. Although there was a greater richness of tunicate species on New Zealand boats, the two countries had several species or genera in common, including Botryllus schlosseri, Ciona spp. and Botrylloides spp. The time since last boat maintenance was longer in New Zealand than in Canada. However, boat fouling and boat-mediated spread may be facilitated in Canada by boating activity patterns there, as the movement of boats among multiple marinas is considerably greater than in New Zealand. Among the boat characteristics, voyage type, the time that boats spent in water (Canada) and time since last application of antifouling paint (New Zealand) were among the best predictors of boat fouling. However, our results from Canada showed that propagule exposure was more important than boat characteristics in predicting the presence of the invasive colonial tunicate, B. schlosseri. This study shows the importance of small boats as potential vectors for tunicates and demonstrates that predictive models for the spread of biofouling species should be based on regional boating patterns, boating characteristics, and local propagule exposure.
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We investigated hierarchical organization and spatiotemporal discontinuities in species abundances in the epibenthic community of the Estuary and Gulf of St. Lawrence. Quantitative samples were obtained from 1975 to 1984, on 161 collectors (navigation buoys) moored yearly from May through November. Maximum biomass values of the dominant species, common to all regions studied, were used to assess epibenthic community structure. Numerical methods were used to characterize spatial structure and temporal variability of the dominant assemblage. Spatially constrained clustering and ordination techniques revealed six broad biogeographic zones whose limits vary yearly. However, spatially unconstrained clustering and ordination techniques showed two major sets of non-continguous localities, each characterized by a singular biotic structure. Further, spatial autocorrelation analyses showed a significant relationship between biomass and geographic distance. The resulting spatial structure of biomass was dependent on the species considered. The multidimensional Mantel technique showed an 8-yr period of variation in community structure at large (whole system, Gulf) and intermediate (North Shore plus Lower North Shore) spatial scales. The amplitude and asymmetry of this temporal cycle increased as the spatial scale decreased. In spite of the observed discontinuous spatial patterns, the temporal oscillations in community structure detected at different spatial scales suggest that the Estuary-Gulf system responds to the external input of auxiliary energy as an integrated system.
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Ships have long been recognized as a major vector for the introduction of non-native and harmful organisms. From 1992 to 1996 a shipping study was undertaken in Germany, focusing on the fauna transported by ships, to assess the importance of species introductions by international shipping traffic. Ballast water, tank sediment or hull fouling of 186 vessels was sampled. A total of 257 species were identified, ranging from Foraminifera to Teleostei, and 57% of the species sampled were considered to be non-native to the North Sea region, originating from elsewhere in the world including the north eastern Atlantic (west of the English Channel). Non-native species were recorded in 38% of all ballast water samples, 57% of all sediment samples and 96% of all hull samples, indicating that hull fouling is an important vector of introduction. Four species (1.6%) of unknown origin (cryptogenic species) were identified. The potential for establishment in the North Sea region of all non-native species found was classified into three categories based on the degree of similarity of climatic conditions in the North Sea and the donor region. Based on this criterion 19 of the species found in the fouling communities on ships' hulls were deemed to have a high potential for establishment in the North Sea.
Increasing numbers of scientific and tourist vessels are entering the Antarctic region and have the potential to bring with them a range of organisms that are not currently found in the region. Little is known about the frequency of such introductions or the identity and survivorship of the species associated with them. In this study, we report the findings of an inspection of the sea chests of the South African National Antarctic Programme supply vessel, the SA 'Agulhas', while the vessel was in dry dock in June 2006. Large populations of a known invasive mussel, Mytilus gallo-provincialis (Lamarck), were found. By extrapolating from shell length, the age of individuals was estimated, the results of which suggest that some specimens have survived transportation to the Antarctic region on multiple occasions. These findings are cause for concern and demonstrate that Antarctic research and supply vessels are important vectors for marine non-indigenous species into the region.
Anthropogenic biological invasions are a leading threat to aquatic biodiversity in marine, estuarine, and freshwater ecosystems worldwide. Ballast water discharged from transoceanic ships is commonly believed to be the dominant pathway for species introduction and is therefore increasingly subject to domestic and international regulation. However, compared to species introductions from ballast, trans-location by biofouling of ships' exposed surfaces has been poorly quantified. We report translocation of species by a transoceanic bulk carrier intercepted in the North American Great Lakes in fall 2001. We collected 944 individuals of at least 74 distinct freshwater and marine taxa. Eight of 29 taxa identified to species have never been observed in the Great Lakes. Employing five different statistical techniques, we estimated that the biofouling community of this ship comprised from 100 to 200 species. These findings adjust upward by an order of magnitude the number of species collected from a single ship. Thus, overall invasion risk from biofouling may be comparable or exceed that of ballast water discharge.