Distribution of the invasive tunicate Styela clava in Long Island

BioInvasions Records (2014) Volume 3, Issue 1: 13–19
doi: http://dx.doi.org/10.3391/bir.2014.3.1.02
Open Access
© 2014 The Author(s). Journal compilation © 2014 REABIC
Research Article
Distribution of the invasive tunicate Styela clava in Long Island Sound,
New England, USA
Nicholas Brunetti and Carmela Cuomo*
University of New Haven, Department of Biology and Environmental Sciences, Marine Biology Program, 300 Boston Post Road,
West Haven, Connecticut 06516, U.S.A.
E-mail: [email protected] (NB), [email protected] (CC)
*Corresponding author
Received: 1 October 2013 / Accepted: 6 February 2014 / Published online: 26 February 2014
Handling editor: Mark Hanson
Abstract
The clubbed tunicate Styela clava (Herdman, 1881) is an invasive, solitary, club-shaped organism native to the western Pacific. S. clava has
spread far beyond its native range into temperate waters worldwide, including those of Long Island Sound (LIS) on the northeastern coast of
the United States. A visual inspection of public and private commercial and recreational marinas and docks located along the shores of LIS
was conducted between June 2011 and September 2013. The wrack lines of public beaches and other public coastal areas were also surveyed.
S. clava was found at 77.8 % of the sites surveyed indicating it has now fully colonized the Sound. It is strongly suggested that managers of
neighboring waters be vigilante, and be prepared to take steps to mitigate negative impacts, should the species spread further south along the
Atlantic Coast of the United States.
Key words: invasion, clubbed tunicate, ascidian, vectors
Introduction
The clubbed tunicate Styela clava (Herdman
1881) is an invasive, solitary, club-shaped tunicate
native to the marine and estuarine waters of the
western Pacific from the Sea of Okhotsk southward
along the coasts of Japan, Korea, and China to
Shanghai (Cohen 2005; Darbyson et al. 2009).
Today, S. clava can be found in temperate marine
waters worldwide, including those of Asia, Europe,
North America, Australia and New Zealand
(Goldstien et al. 2011). The adult tunicate is
easily identifiable by its brown, leathery, outer
covering and the two siphons that protrude from
the top of the tunic (Figure 1). Although considered
a solitary tunicate, it is often found in extremely
dense clusters consisting of thousands of individual
organisms (Osman and Whitlatch 2000; Kluza et
al. 2006). These dense clusters may foul lines,
buoys, pipes, oyster cages, docks and other
submerged natural or artificial objects and can
become serious concerns in regions where Styela
has invaded (Arsenault et al. 2009). Given that
Styela has few known natural predators and is an
effective filter feeder, the introduction and
spread of this species into an area may result in
deleterious effects to the native species and cause
serious economic consequences for boaters,
aquaculture businesses, and marinas.
The spread of S. clava outside of its native
range is thought to have begun in the 1920s in
Newport Bay, California, although it was not
formally identified there until 1932 (Abbott and
Johnson 1972; Cohen 2005). From Newport Bay,
it spread along the eastern Pacific coast of North
America and is now found from Mexico north to
Canada (Clarke and Therriault 2007; BNZ 2008;
Cohen 2005). S. clava made its first appearance
in Great Britain in the 1950s (Carlisle 1954)
where it is assumed to have been transported on
ships returning from Korea. From there it spread
into the waters of Denmark and France in the
1960s, Ireland and the Netherlands in the 1970s,
and Belgium, Germany, and Spain during the last
decades of the 20 th Century (Clarke and Therriault
13
N. Brunetti and C. Cuomo
effort to document the distribution of S. clava
within LIS in order to better understand the
present status of its invasion and to identify the
most likely vectors by which it is spreading in
the Sound.
Methods
Figure 1. Styela clava showing open and partially open siphons.
(N. Sardalla, University of New Haven, Photo Credit).
2007). In the early 1970’s, S. clava was reported
in New York waters (Berman et al. 1992) although
this appears to have been an isolated occurrence.
It was next observed in Beverly, Massachusetts,
in the 1970s (Berman et al. 1992), and in Rhode
Island, New Hampshire, and Maine in the 1980s
(Karney and Rhee 2009). By 1998, S. clava had
entered the waters around Prince Edward Island,
Canada (Clarke and Therriault 2007).
There are some disagreements as to when
S. clava actually reached Long Island Sound (LIS),
a body of water located between the states of
Connecticut (CT) and New York (NY). According
to Whitlatch et al. (1995) and Berman, et al.
(1992), S. clava reached the eastern end of LIS
in 1973 while Clarke and Therriault (2007)
suggest that it did not reach LIS until the 1990s.
Nevertheless, by the year 2000, large populations
of S. clava could be found fouling docks and lines
in Groton, CT (Figure 1; Osman and Whitlatch
2000, Fofonoff, et al. 2003). Pederson et al.
(2005) identified S. clava at three additional sites
within LIS (Mystic, CT, Milford, CT, and
Stamford, CT) and in the Peconic Bay estuary
(Jamesport, NY and Greenport, NY), which is
located at the eastern end of Long Island, NY.
These sightings have resulted in LIS being
classified as a site where S. clava is considered
introduced but not fully colonized (Fofonoff et al.
2003). Anecdotal evidence suggests that S. clava
has spread to other sites in the Sound over the
past decade (Brunetti and Cuomo, personal
observations). This study was undertaken in an
14
A visual inspection of public and private
commercial and recreational marinas and docks
located along the shores of LIS (Figure 3) was
conducted between June 2011 and September 2013
beginning in easternmost Connecticut, extending
west to New York City, and east again along the
southern coast of LIS to Mount Sinai, New York.
Marinas were chosen based on accessibility and
willingness to allow data collection and represent a
range of sizes and types of users. The wrack lines
of public beaches and other public coastal areas
were also surveyed for the presence of S. clava.
A total of 45 sites were surveyed within 25
towns: 29 sites in Connecticut and 16 sites in
New York (Table 1; Figure 3).
Data recorded at the time of the survey included:
location, presence/absence of Styela, average size
of Styela when present, and average density of
Styela when present. A visual inspection was
made of submerged lines, the underside of docks,
submerged marine equipment, and wrack lines for
the presence of S. clava. When found, individuals
were measured and, where possible, density was
determined within a 60 cm diameter circular area
using a single target organism as a centroid.
Abundances were classified as High when > 50
organisms were found, Low when < 10 organisms
were found, and Medium when 10–50 organisms
were found. Multiple measurements were taken at
each site and the average abundance per site was
recorded. In addition, marina owners, workers,
and patrons were shown photographs of S. clava
and interviewed as to whether or not they had
ever seen them on lines or docks in the vicinity
Results
The Connecticut sites covered approximately
110 miles of coastal area while the New York
state sites covered approximately 260 miles of
coastal area. S. clava was found at 77.8% (35 out
of 45) of the sites surveyed (Table 1) and in
97.8% of the towns surveyed (Table 1; Figure 4).
It was common for S. clava to be found at one
marina in a town but not at an adjacent marina in
the same town (Table 1).
New records of invasive tunicate along the United States coast
Figure 2. Historical records of Styela clava in Long Island Sound (data obtained from MIT Sea Grant College Program (MITSG),
Massachusetts Bays National Estuary Program, the U.S. Environmental Protection Agency (EPA) and the U.S. Geological Survey).
Three of the recorded Styela observations
were made with organisms that had been washed
ashore onto beaches in Connecticut (Table 1).
Therefore, abundance data was not recorded for
these three sites as the actual attachment sites for
Styela in these areas was not observed. The
greatest abundance of S. clava was recorded at
three sites located in Stonington and Groton in
eastern Connecticut and at one site, Port Jefferson,
in New York State (Figure 4). Abundance of S.
clava was classified as low at 20 sites while 9
sites contained medium abundances.
The average size (Table 1) of individual
Styela at 29 sites was > 5 cm and these should be
considered as populations with reproducing adults.
Discussion
This study demonstrates that S. clava has fully
invaded the LIS estuary. These tunicates can be
found on both coasts of LIS, and they appear to
have spread to all of these areas within the past
20 years. The spread of S. clava within the Sound
raises several questions: a) what are the main vectors
responsible for its spread; b) how much of a threat
does the presence of S. clava pose to other
organisms living within LIS; c) what are its
potential economic impacts on the LIS region;
and d) what is the likelihood that this tunicate
might spread further south along the eastern
Atlantic coast of the United States?
Once S. clava is established, its expansion and
development within that region is accomplished
via both larval dispersion and adult transport.
Larval dispersion requires an adult breeding
population, temperatures within the range of 15
to 23°C (Buizer 1980; Cohen 2005; Minchin et al.
2006; Global Invasive Species Database 2009;
NIMPIS 2013), salinities of 25 to 35 psu (Cohen
2005; Davis and Davis 2007; Global Invasive
Species Database 2009; NIMPIS 2013), and suitable
habitats for settlement. All of these conditions
are met within the LIS estuary and have no doubt
contributed to the spread of Styela. Ballast water
15
N. Brunetti and C. Cuomo
Table 1. Location, site description, coordinates, Styela clava presence/absence, abundance, and average size of individuals for survey sites in
Long Island Sound.
Site
ID #
State
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
CT
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
Town
Stonington
Groton
Groton
Groton
Waterford
Niantic
Niantic
Westbrook
Clinton
Clinton
Guilford
Branford
Branford
Branford
Branford
Branford
New Haven
New Haven
New Haven
New Haven
West Haven
Milford
Milford
Bridgeport
Bridgeport
Bridgeport
Norwalk
Norwalk
Norwalk
Darien
Mamaroneck
Mamaroneck
City Island
Oyster Bay
Centerport
Northport
Port Jefferson
Port Jefferson
Mount Sinai
South Jamesport
Mattituck
Mattituck
Greenport
Greenport
Orient Point
Site
Type
Marina
Marina
Marina
Dock
Marina
Marina
Beach
Marina
Marina
Marina
Marina
Marina
Marina
Marina
Marina
Dock
Marina
Buoy
Marina
Beach
Beach
Marina
Dock
Dock
Marina
Marina
Marina
Marina
Marina
Dock
Marina
Marina
Marina
Marina
Docks
Marina
Marina
Marina
Marina
Marina
Marina
Marina
Marina
Marina
Marina
S. clava
Present
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
No
Yes
No
Yes
Yes
Yes
Yes
No
Yes
Yes
No
No
Yes
Yes
Yes
No
Yes
Yes
Yes
No
Yes
No
Yes
Yes
Yes
Yes
No
Yes
Yes
transport of Styela larvae into LIS is less likely
owing to their short (~ 48 hour) larval phase
(Clarke and Therriault 2007); however, it cannot
be completely discounted.
Transport of adult Styela on lines, ship hulls,
cages, and other moveable marine equipment is
thought to be the primary long-distance mode by
16
Coordinates
Latitude, N
Longitude, W
S. clava
Abundance
Average Size
of Individuals
41°20'22.23"
41°19'32.82"
41°19'13.87"
41°19'12.41"
41°19'31.00"
41°18'40.42"
41°18'16.30"
41°16'17.97"
41°16'08.94"
41°16'07.98"
41°16'01.50"
41°15'55.32"
41°15'49.89"
41°15'49.46"
41°15'45.84"
41°15'23.07"
41°17'33.06"
41°16'55.23"
41°16'52.65"
41°15'10.62"
41°15'21.85"
41°12'44.96"
41°12'43.78"
41°10'32.87"
41°10'03.59"
41°09'33.16"
41°05'33.39"
41°05'39.18"
41°05'14.40"
41°03'09.08"
40°56'22.77"
40°56'27.52"
40°50'33.00"
40°52'30.22"
40°53'34.74"
40°53'22.37"
40°56'48.04"
40°56'53.66"
40°57'50.36"
40°56'04.20"
41°00'34.20"
40°59'04.45"
41°06'30.00"
41°06'39.66"
41°09'09.60"
71°54'26.46"
72°03'36.78"
72°03'45.86"
72°04'00.99"
72°10'34.47"
72°12'11.11"
72°12'16.69"
72°28'05.03"
72°31'30.48"
72°32'52.80"
72°40'40.80"
72°48'09.66"
72°49'02.41"
72°49'01.23"
72°48'30.96"
72°51'03.84"
72°55'09.77"
72°55'43.44"
72°55'47.64"
72°54'00.00"
72°57'14.82"
73°03'21.16"
73°03'12.86"
73°11'12.78"
73°09'59.29"
73°12'42.44"
73°24'46.04"
73°24'47.64"
73°23'38.10"
73°28'39.24"
73°43'47.85"
73°43'58.97"
73°47'00.00"
73°31'39.85"
73°22'28.86"
73°21'17.32"
73°04'09.72"
73°04'01.81"
73°01'16.18"
72°36'32.40"
72°33'01.20"
72°31'32.42"
72°21'18.00"
72°21'32.82"
72°14'37.38"
High
Medium
High
High
Low
Medium
Unknown
Medium
Low
Low
Low
Low
Low
n/a
Low
Low
n/a
Low
n/a
Unknown
Unknown
Low
Low
n/a
n/a
Low
Medium
n/a
Low
Medium
Medium
n/a
Medium
Medium
Low
n/a
High
n/a
Medium
Low
Low
Low
n/a
Low
Low
> 5 cm
> 5 cm
> 5 cm
> 5 cm
> 5 cm
> 5 cm
Unknown
> 5 cm
> 5 cm
> 5 cm
< 1.2 cm
> 5 cm
> 5 cm
n/a
> 5 cm
< 2.5 cm
n/a
> 5 cm
n/a
Unknown
Unknown
> 5 cm
> 5 cm
n/a
n/a
> 2”
> 2”
n/a
> 1”
> 2”
> 2”
n/a
> 2”
> 2”
> 2”
n/a
> 2”
n/a
> 2”
> 2”
> 2”
> 2”
n/a
> 2”
> 2”
which S. clava spreads from one region to another
(Darbyson et al. 2009). If adults are transported
to an area favoring their survival and reproduction,
they are able to establish new populations there,
which, in turn, grow and expand within the local
area via larval settlement. The spread of Styela in
this manner should result in spatially isolated
New records of invasive tunicate along the United States coast
Figure 3. Long Island Sound
study area with sampling sites
marked by site identification
number listed in Table 1.
Figure 4. Relative abundance
of Styela clava in Long Island
Sound (by site).
17
N. Brunetti and C. Cuomo
populations throughout a region. Such populations
should be associated with recreational and
commercial vessels, marinas, docks, and pilings.
The distribution of Styela populations within LIS
appears to reflect this pattern of spatially
isolated populations associated with marinas and
docks throughout LIS. A close examination of
the data reveal that even within marinas located
in the same town, Styela occurs at one and not at
the other supporting the idea that Styela
colonization of areas within LIS has mainly been
due to adult transport.
The general flow of surface currents in LIS is
from East to West along the North shore of the
Sound and West to East along the South shore of
the Sound (Codiga and Aurin 2007). If Styela was
simply spreading westward via larval dispersal
from the Groton, CT area, one would expect it to
be spreading relatively linearly, in a westward
direction, along the north shore of the Sound. As
well, one might expect denser populations to be
found in the northeastern and north-central
portions of the Sound corresponding to the
length of time a colony was established. The less
dense populations and possibly isolated individuals
would be more typical of the northwestern and
southern regions of the Sound. The present
distribution and abundance of S. clava in LIS
supports the concept that the spread of Styela
along the north shore of LIS was the result of
simple larval dispersion from the initial adult
population located in Groton, CT. Similarly
surface current transport of larvae from West to
East might explain the distribution of S. clava
along the south shore of LIS. Surface current
transport of larvae, however, does not totally
explain the high abundance of Styela found in Port
Jefferson, NY, at a ferry terminal that is situated at
the mid-point, of the sites located along the south
shore of LIS. The number of occurrences of Styela
at marinas observed in this study and the relative
paucity of Styela observed on natural rock
outcrops, along with the fact that Styela often was
found in one marina but not in an adjacent
marina, points to the potential importance of
human-mediated transportation of Styela spread
in the Sound. At this point, it appears highly
likely that both vectors – larval transport and
adult transport - are responsible for the spread of
S. clava throughout the Sound.
Regardless of the vector, S. clava now appears
to be firmly established throughout LIS although
most populations have not yet reached the
fouling densities (> 1000/m2) found elsewhere
18
(Minchin and Duggan 1988). High fouling densities
of Styela are associated, worldwide, with negative
impacts on native populations of filter-feeding
organisms and fouling of docks, lines, pipes and
marine-related equipment (Clarke and Therriault
2007). Dense populations of Styela rapidly
deplete local waters of plankton, leaving little
behind for native filter-feeders in the region,
including many commercially important bivalves
(LeBlanc et al. 2007). Additionally, massive Styela
populations also out-compete native species for
space (Stoecker 1978). At present, few dense Styela
populations have been identified in LIS (this
study). Whether or not the existing LIS populations
of Styela will ever develop into massive
populations remains an open question. At present,
the colony density does not appear to pose a
threat to native filter-feeding organisms nor to
have significant economic impacts in the region.
The invasive tunicate S. clava has fully
invaded the LIS estuary of the United States.
Given that the known temperature tolerances for
breeding populations of S. clava range from 15
to 23°C (Buizer 1980; Cohen 2005; Minchin et
al. 2006; Global Invasive Species Database
2009; NIMPIS 2013), LIS might be expected to
represent the southernmost area likely to be fully
colonized along the east coast of North America.
However, there have already been sightings of S.
clava in the coastal waters of New Jersey,
suggesting that S. clava may be able to invade
even further south along the east coast of the
United States. Preliminary work suggests that
adult Styela may, in fact, be able to tolerate
temperatures as high as 30°C (Cuomo, unpublished
data) although whether or not adults can reproduce
at these temperatures is unknown. It is strongly
suggested that managers responsible for LIS
waters, as well as those of neighboring waters,
closely monitor the status of the populations
within the Sound and be prepared to take steps to
mitigate negative impacts should the populations
become dense or spread further south along the
Atlantic Coast of the United States.
Acknowledgements
This work was supported, in part, by funds from the URS and
SURF programs of the University of New Haven. The authors
would like to acknowledge P. Bartholomew and K. Sandin for
assistance in the field. The authors would also like to thank the
two anonymous reviewers and J.M. Hanson for their helpful
comments.
New records of invasive tunicate along the United States coast
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