Special Issue: Proceedings of the 5th International Invasive Sea Squirt Conference (October 29–31, 2014, Woods Hole, USA)
Edited by Mary Carman and Stephan Bullard
Published in March 2016
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Editorial
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Stephan G. Bullard and Mary R. Carman
Introduction to the proceedings of the 5th International Invasive Sea Squirt Conference, 2014 (pp 1-3) |
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Research articles
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Luciana Vieira Granthom-Costa, Carlos Gustavo Werner Ferreira and Gustavo Muniz Dias
Biodiversity of ascidians in a heterogeneous bay from southeastern Brazil (pp 5-12) |
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Ascidians are fast-growing sessile animals, frequently observed on artificial and natural substrata. Several introduced ascidians
are known for monopolizing space in benthic communities, mainly in urbanized areas, where harbours act as gateways for exotic species.
In the southeastern Brazil, the Arraial do Cabo Bay is the main point of coastal upwelling and one of the most visited localities during
the summer due to beaches and dive sites. While the region of the botton of the bay is close to the city, being exposed to anthropogenic
disturbances but warm waters, the area outside the bay is a pristine site, exposed to cold waters caused by the upwelling system.
To understand how ascidian species are distributed through the temperature and anthropogenic gradients, we sampled ascidian specimens
at 11 sites from three distinct regions: (1) inner bay, a harbor area exposed to intense ship and boat/platform traffic; (2) external bay,
a pristine and warm area and (3) outside of the bay, a region exposed to coastal upwelling and cold water. We recorded 31 species of ascidians
of which the Didemnidae and Styelidae families were the most speciose. Symplegma rubra and Phallusia nigra were the most common
species. We found 22 species in the inner bay, of which nine were exclusive to this region (Styela canopus, Clavelina oblonga,
Polyclinum constellatum, Polyclinum molle, Didemnum speciosum, Botrylloides giganteum, Ascidia curvata,
Ascidia sydneiensis and Rhodosoma turcicum). In the external bay, we found 19 species, five exclusive to this region
(Didemnum vanderhorsti, Didemnum galacteum, Eusynstyela tincta, Eusynstyela sp. and Botryllus sp.).
Outside of the bay, three of the four species found (Cystodytes dellechiajei, Didemnum granulatum and Didemnum rodriguesi)
were exclusive. Sixteen species were categorized as cryptogenic, seven as native and five as invasive to the Brazilian Coast. Four of the five
invasive species were found only in the inner bay (R. turcicum, S. canopus, A. sydneiensis and A. curvata) close
to man-made structures, while Styela plicata, an invasive ascidian with worldwide distribution, was also observed in the external bay.
Seventeen of the 31 species were exclusive to one of the three regions, suggesting that anthropogenic impacts in the inner bay and the upwelling
outside of the bay may be influencing the occurrence of different species, and increasing the local diversity of ascidians.
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Luís F. Skinner, Danielle F. Barboza and Rosana M. Rocha
Rapid Assessment Survey of introduced ascidians in a region with many marinas in the southwest Atlantic Ocean, Brazil (pp 13-20) |
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In August 2014, we performed Rapid Assessment Surveys (RAS) in seven marinas along circa 70 km of the coastline of Ilha Grande Bay (IGB),
southeastern Brazil to evaluate diversity in the Ascidiacea and of introduced species. This region is very important for marine biodiversity
and includes many protected areas. However, urbanization, tourism and economic development (aquaculture, fisheries, commercial ports and
nuclear energy generation) are some of the impacts and drivers of species introduction. Our survey found 16 species, only one native,
two introduced and eleven cryptogenic. Two species could not be identified precisely. The most species-rich marina had 11 species and
the most polluted three marinas had only six species each. Comparisons with literature indicated that marinas in the IGB had fewer species
and fewer introductions than marinas in the São Sebastião Channel (São Paulo), in the same biogeographic region. Future monitoring should
consider complementary methods such as passive collectors deployed during summer time and RAS in at least two different times of the year.
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Cynthia H. McKenzie, Kyle Matheson, Scott Caines and Terri Wells
Surveys for non-indigenous tunicate species in Newfoundland, Canada (2006 – 2014): a first step towards understanding impact and control (pp 21-32) |
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Fisheries and Oceans Canada initiated survey and monitoring programs in 2006 to determine presence, geographic range, and subsequent spread
of non-indigenous tunicates in Atlantic Canada. Although non-indigenous tunicates have impacted aquaculture industries in Atlantic Canada
for over a decade, aquaculture operations in Newfoundland and Labrador (NL) have not yet been affected. In this report, we document
and explain results from biofouling collectors and various underwater techniques to survey and monitor for non-indigenous tunicates
in NL between 2006 and 2014. During early surveys (2006–2007) we only observed low-impact invaders, Botryllus schlosseri and
Botrylloides violaceus, at locations along the south coast of NL. Botryllus schlosseri became the most widely distributed
species (18 locations within Placentia Bay) and evidence demonstrated spread to locations on the northeast (2011) and west (2013) coasts of NL.
In 2012, we detected Ciona intestinalis in a single harbour in southern NL (Placentia Bay). In contrast to southern regions of Atlantic
Canada, Styela clava and Didemnum vexillum, two high-impact invasive tunicates, were not observed during these surveys.
Newfoundland and Labrador represents the northern range limit of non-indigenous tunicates in Atlantic Canada, but seawater temperatures
are unlikely to prevent further expansion or introduction of non-indigenous tunicates throughout the province.
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Phil Colarusso, Eric Nelson, Suzanne Ayvazian, Mary R. Carman, Marty Chintala, Sinead Grabbert and David Grunden
Quantifying the ecological impact of invasive tunicates to shallow coastal water systems (pp 33-42) |
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Coastal ponds, due to their proximity to human activity, may be particularly vulnerable to invasions
by non-native species. A number of invasive tunicate species have been documented in several of
the coastal ponds on the island of Martha’s Vineyard, Massachusetts. Tunicates are voracious
filter feeders, thus our study attempted to examine the impact of their feeding on the normal
food web in a coastal pond. In 2012 and 2013, we sampled Stonewall (high tunicate abundance)
and Lagoon Ponds (tunicates absent) on Martha’s Vineyard. We used quadrat sampling to quantify
tunicate abundance, eelgrass shoot density and eelgrass canopy height. Fish, invertebrates and
aquatic vegetation were collected via beach seine, minnow trap, crab traps or by hand. Water
samples were run through a filter to collect phytoplankton. These biota samples were processed
for carbon and nitrogen isotopic analysis. Temperature loggers were deployed in both ponds
to collect water temperature. Detailed bathymetric readings were taken to generate an estimate
of the volume of each pond. Tunicate filtration rates from published scientific literature, our
volume estimate of Stonewall Pond and our measured tunicate abundance were used in a model
to estimate the time needed by tunicates to filter a volume of water equal to Stonewall Pond.
That time varied from less than an hour to over 17 hours. Isotopic analysis showed that tunicates
were feeding on similar resources as the commercial shellfish species. There was broad overlap
in the isotopic signatures between the biota from both ponds, suggesting that tunicates were
not having a measurable impact to the food web. Tunicates exhibit significant seasonal abundance changes,
with the peak occurring late summer into the early fall. The limited duration of this peak may
not be sufficient to be reflected in the isotopic signature of resident biota. As water temperature
continues to increase with climate change, the current assemblage of tunicates in these shallow water
systems on Martha’s Vineyard will likely change in response.
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Gil Koplovitz, Yaniv Shmuel and Noa Shenkar
Floating docks in tropical environments - a reservoir for the opportunistic ascidian Herdmania momus (pp 43-50) |
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The solitary ascidian Herdmania momus is considered native to the Red Sea, and invasive in the Mediterranean. Periodic surveys
have revealed high recruitment and growth rates of this species on floating docks in the Gulf of Aqaba, Red Sea, following the annual
vertical mixing event. In order to ascertain the length of time taken by H. momus individuals to settle on new artificial substrates,
and the pace at which they grow and reach the reproductive stage, we monitored a newly-deployed floating dock for two years following
its deployment. The number of individuals and their sizes were recorded weekly in March-June 2013 (spring-early summer), in June-August (summer),
and re-visited each spring (April 2014, 2015). In addition, seven fixed quadrates were artificially cleaned and monitored in summer 2013.
Ascidians were visible after eight weeks in the spring and five weeks in the summer. Growth rate in spring was twice as fast as in summer
(0.275 and 0.106 cm/week respectively). Recruitment was higher during spring, reaching a density of 34.3 ± 7.1 in June, with fully reproductive
individuals, dropping to 0.86 ± 0.46 individuals per quadrate in August. Field surveys of additional floating docks revealed significantly higher
densities at the northern sites during spring. Following a nutrient enrichment event such an opportunistic filter-feeder can potentially release
and distribute propagules to natural reefs, inducing a shift in community assemblage. In addition, its ability to colonize artificial substrates
within its native range sheds light on its success as an invasive species in the Mediterranean.
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Mary R. Carman, Philip D. Colarusso, Eric P. Nelson, David W. Grunden, Melisa C. Wong, Cynthia McKenzie, Kyle Matheson, Jeff Davidson, Sophia Fox, Hilary A. Neckles, Holly Bayley, Stephen Schott, Jennifer A. Dijkstra and Sarah Stewart-Clark
Distribution and diversity of tunicates utilizing eelgrass as substrate in the western North Atlantic between 39° and 47° north latitude (New Jersey to Newfoundland) (pp 51-57) |
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Seagrass meadows are ecologically important habitats that are declining globally at an accelerating rate due
to natural and anthropogenic stressors. Their decline is a serious concern as this habitat provides many ecosystem
services. Eelgrass (Zostera marina) is the dominant seagrass species in the western North Atlantic. It has
recently been established that invasive tunicate species possibly threaten the health of eelgrass beds. Colonization
of eelgrass leaves by tunicates can inhibit eelgrass growth and may cause shoot mortality. To document the distribution
and diversity of tunicate species that attach to eelgrass in the western North Atlantic, we surveyed twenty-one eelgrass
sites from New Jersey to Newfoundland. Eight species of tunicates were found to be colonizing eelgrass, of which 6 are
considered invasive. Botrylloides violaceus and Botryllus schlosseri were most commonly attached
to eelgrass, with B. schlosseri having the largest latitudinal range of any species. Tunicate faunas attached
to eelgrass were less diverse north of Gloucester, Massachusetts, where individual survey sites exhibited two species
at most and only 4 of the 8 species observed in this study. Percent tunicate cover on eelgrass tended to fall within
the 1–25 range, with occasional coverage up to >75–100. Density of eelgrass was highly variable among sites, ranging
from <1 to 820 shoots/m². The solitary tunicate Ciona intestinalis was only found on eelgrass at the highest latitude
sampled, in Newfoundland, where it is a new invader. The tunicates observed in this study, both solitary and colonial,
are viable when attached to eelgrass and pose a potential threat to overgrow and weaken seagrass shoots and reduce
the sustainability of seagrass meadows.
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Gretchen Lambert, Richard C. Karney, Walter Y. Rhee and Mary R. Carman
Wild and cultured edible tunicates: a review (pp 59-66) |
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Most tunicate species are not edible but some solitary stolidobranchs in the Styelidae and Pyuridae families
are wild-harvested or cultured. The main species are Halocynthia aurantium, H. roretzi,
Microcosmus hartmeyeri, M. sabatieri, M. vulgaris, Polycarpa pomaria,
Pyura chilensis, Styela clava, and S. plicata, and they may be eaten raw, cooked,
dried or pickled. Historically the Maoris ate Pyura pachydermatina in New Zealand. Aboriginal people
ate P. praeputialis in Australia, and although it is now only used for fishing bait in that country,
it is eaten in Chile where it has invaded Antofagasta Bay. There is a large market for cultured tunicates,
especially among Asian populations. Styela clava and S. plicata have become extremely abundant
in many countries as non-native introductions; they could easily be harvested and sold as seafood in these newly
colonized regions, as could other common solitary stolidobranchs that have not previously been consumed. However,
hurdles remain; diseases and overexploitation can significantly reduce cultured product and wild populations.
Recently, the disease ‘soft tunic syndrome’ caused up to a 70% loss of H. roretzi crop in Korea, and
harvesting wild P. chilensis reduced their numbers three fold in some parts of Chile. Most aquaculture
operations are located in bays with urban runoff where pollutants including heavy metals and toxic substances
could accumulate in tunicates. Natural disasters like tsunamis can also negatively impact aquaculture,
as happened in Japan in 2011. Nevertheless, with proper culturing, monitoring, and preparation certain
edible tunicate species that are currently an underutilized but highly nutritive food in many parts
of the world could be easily cultivated, and the huge numbers of invaders could be harvested and marketed.
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Vanessa Reid, Cynthia McKenzie, Kyle Matheson, Terri Wells and Cyr Couturier
Post-metamorphic attachment by solitary ascidian Ciona intestinalis (Linnaeus, 1767) juveniles from Newfoundland and Labrador, Canada (pp 67-76) |
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Ciona intestinalis is an invasive marine biofouling organism first detected in coastal waters of Newfoundland
and Labrador in 2012. As a sessile animal, it is essential that larvae locate a suitable substrate for attachment
in an adequate environment, but the timing of this critical event may not be as important as once believed.
We demonstrate that while swimming larvae may have limited time to locate and attach to a substrate, development into
juvenile stages and prolonged survival is possible without substrate attachment. In laboratory experiments we demonstrate
that between 38 and 61% of tadpole larvae undergo pre-attached metamorphosis at the water surface or free floating.
These are the first experiments to confirm the ability of C. intestinalis juveniles to initiate post-metamorphic
attachment when substrate is available. In the early stages of juvenile development (i.e. Rotation, FAS I, and FAS II)
there are no differences in post-metamorphic attachment ability. Postponing attachment until after the onset of metamorphosis
allows C. intestinalis larvae and juveniles to effectively prolong the planktonic stage and increase their dispersal potential.
This information is of particular concern to aquaculture industries, but also may have implications for management efforts in regions
where C. intestinalis has successfully invaded.
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Xavier Turon, Juan I. Cañete, Javier Sellanes, Rosana M. Rocha and Susanna López-Legentil
Too cold for invasions? Contrasting patterns of native and introduced ascidians in subantarctic and temperate Chile (pp 77-86) |
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We analysed the biodiversity of ascidians in two areas located in southern and northern Chile: Punta Arenas
in the Strait of Magellan (53º latitude, subantarctic) and Coquimbo (29º latitude, temperate). The oceanographic
features of the two zones are markedly different, with influence of the Humboldt Current in the north, and the Cape Horn
Current System, together with freshwater influxes, in the Magellanic zone. Both regions were surveyed twice during 2013
by SCUBA diving and pulling ropes and aquaculture cages. Both artificial structures and natural communities were sampled.
A total of 22 species were identified, three of them reported for the first time in Chilean waters: Lissoclinum perforatum,
Synoicum georgianum, and Polyzoa minor. The first is an introduced species found here for the first time in the Pacific.
No species occurred in both regions, highlighting the very different environmental conditions of subantarctic vs. temperate waters.
In spite of exhaustive searches in aquaculture facilities and on artificial structures such as harbour docks and piers, no introduced
species were found in the Punta Arenas area. Conversely, 5 out of 11 (45%) species found in northern Chile were introduced. The Coquimbo
area has a history of ship traffic dating back at least 150 years, and cultures of native (e.g. scallop) as well as exotic species
(e.g. abalone) have been deployed for ca. 35 years. Some of the introduced species, such as Ciona robusta (formerly
C. intestinalis sp. A), constitute pests for scallop culture facilities in the area, causing serious losses to local farmers.
It is surprising that the Punta Arenas zone, with a history of ship traffic dating back ca. 500 years and over 25 years of sustained
mussel and salmon aquaculture activity, is apparently free from introduced species. The ascidian cover on artificial structures is high,
but it is made up of native species such as Paramolgula sp., Cnemidocarpa verrucosa, or Polyzoa opuntia.
It is hypothesized that cold waters (5 to 11ºC) are the determining factor hindering the development of introduced ascidians,
which tend to be temperate-warm water species. The ongoing warming in the Southern Cone may change this picture and continued monitoring
is strongly advised.
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Cynthia H. McKenzie, Kyle Matheson, Vanessa Reid, Terri Wells, Derek Mouland, Darrell Green, Brooks Pilgrim and Geoff Perry
The development of a rapid response plan to control the spread of the solitary invasive tunicate, Ciona intestinalis (Linnaeus, 1767), in Newfoundland and Labrador, Canada (pp 87-100) |
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The vase tunicate, Ciona intestinalis, was first confirmed in Newfoundland and Labrador (NL) waters in September 2012. The Department
of Fisheries and Oceans (DFO) Aquatic Invasive Species (AIS) monitoring program, in collaboration with the Department of Ocean Sciences at Memorial
University of Newfoundland (MUN), detected an isolated infestation of vase tunicate in Little Bay, Placentia Bay. The solitary tunicate was attached
to wharf structures, eel grass, and some vessels in the area. Early detection of AIS is one of the primary goals of the DFO AIS monitoring program.
This early detection, with the species currently confined to a small area of Placentia Bay, provided a unique opportunity for mitigation activities.
This study details the various stages of a rapid response plan, its development through responses to two colonial tunicates, Botryllus schlosseri
and Botrylloides violaceus, and its application to control the spread of solitary tunicate, C. intestinalis. Pre-invasion planning and
the response plan include key phases of communication, detection and demarcation, containment and risk assessment, mitigation implementation and evaluation.
Mitigation trials in Little Bay, Placentia Bay (2013 and 2014) have included floating dock removal, permanent structure cleaning, and recreational and
commercial vessel cleaning with application of antifouling paint. Mitigated and unmitigated harbours have been monitored to evaluate the effectiveness
of the control efforts. As of 2015, surveys of the mitigated area have only detected very small numbers of C. intestinalis, which were removed.
A rapid response plan based on experience, good communication, strong partnerships, and common goals has allowed NL to respond to a high impact AIS
tunicate in an effective manner. The new Aquatic Invasive Species Regulations in the Canadian Fisheries Act will provide authority for response,
but monitoring, vigilance, prior planning, collaboration between stakeholders and rapid action are the real tools for an effective control plan.
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Mary R. Carman, Scott Lindell, Emma Green-Beach and Victoria R. Starczak
Treatments to eradicate invasive tunicate fouling from blue mussel seed and aquaculture socks (pp 101-110) |
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Tunicates can foul blue mussels and negatively affect productivity on mussel farms. In New England and elsewhere, invasive species of colonial
tunicates commonly foul wild and cultured blue mussels and aquaculture gear. Eco-friendly experimental treatments that meet industry guidelines
were selected for trial application. Chemical (acetic acid) and water (brine and freshwater) treatments were applied in short-term and long-term
applications to juvenile mussels that either were or were not exposed to tunicates. Acetic acid baths (5 mins and 10 mins) were lethal to juvenile
mussels. Brine baths killed tunicates, but caused relatively high mussel mortality, though less mussel death occurred in the short-term (10 sec)
brine bath (6–17%) compared to the long-term (20 sec) brine bath (8–30%). Both long-term (24 hr) and short-term (8 hr) freshwater baths were
effective against tunicates, with less mussel mortality (2%) occurring in the short-term bath. Tunicates survived short-term freshwater sprays
but not long-term freshwater sprays. Long-term (10 mins) freshwater sprays caused slightly more mussel mortality (4%) than short-term (5 mins)
freshwater sprays. Each treatment demonstrated varying degrees of effectiveness, yet the freshwater short-term baths and sprays were able to remove
tunicates while maintaining high survivorship among juvenile mussels. Additionally, freshwater treatments do not require the use or disposal of chemicals.
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Lauren M. Stefaniak and Johann Heupel
Alternative menthol sources for ascidian relaxation (pp 111-114) |
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Rapidly changing environmental conditions and the increasing establishment of invasive alien species present many challenges for policy makers,
managers and researchers. The traditional policies for data management, or lack thereof, are obstructing an adequate response to invasive alien species,
which requires accurate and up-to-date information. This information can only be provided if data regarding invasive alien species are available and
useable by all, irrespective of country, status or purpose. The best way forward is for researchers to publish their data openly, by making use
of repositories in which the data are licenced in a permissive manner, while making sure they are credited by the adequate provision of citation.
Reducing the barriers to data sharing will improve our ability to respond to the growing issue of biological invasions.
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Page Valentine, Mary R. Carman and Dann Blackwood
Observations of recruitment and colonization by tunicates and associated invertebrates using giant one-meter² recruitment plates at Woods Hole, Massachusetts (pp 115-130) |
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Large recruitment plates measuring 1 × 1 m were deployed over an 18-month period from September 2013 to March 2015
for the purpose of documenting recruitment and colonization processes of marine invertebrate species at Woods Hole,
Massachusetts. Each side of two plates was subdivided into 16 subareas (25 × 25 cm), and an observational strategy
was developed whereby, at approximately two-week intervals, a different subarea was cleaned. Using this approach,
we were able to photographically document species recruitment and growth interactions. Water temperature records
from the site show that steady warming and cooling between 3 and 20° C changed at a mean rate of 0.2° C d-1.
However, temperature changes during the coolest and warmest parts of the temperature cycle were highly variable.
In 2014, between the first and last occurrence of 0° C, temperatures were ≤0° C 15 percent of the time, but in 2015
temperatures were ≤0° C 93 percent of the time. In 2014, between the first and last occurrence of 21° C, temperatures
were ≥21° C 88 percent of the time, and this warm period correlated with the disappearance of the hydroid
Ectopleura crocea, the solitary tunicates Ascidiella aspersa and Ciona intestinalis,
and the 2013 generation of Botrylloides violaceus. In Woods Hole, large plates provided enough space
to accommodate both fast- and slow-colonizing species, resulting in the establishment of a diverse assemblage
that was observed over a long time period. The most successful colonizing species had relatively long reproductive
and recruitment periods, grew rapidly, repelled settlement onto their surfaces by larvae of any species,
defended themselves against overgrowth by any species, overwintered, and lived a long time. Of the three dominant
species observed in this study, the colonial tunicates Didemnum vexillum and Botrylloides violaceus
had these qualities; the encrusting colonial bryozoan Schizoporella unicornis had all but one, it grew more
slowly than the others. Barnacles constituted the only biological substrate that was effectively colonized by other
species, both by larval recruitment and overgrowth. In Woods Hole, after a substrate had become fully colonized,
there was very little opportunity for new recruitment or colony growth until new substrate opened after the death
of colonies and individuals and the disappearance of biogenic structures such as amphipod tubes. An understanding
of colonization processes utilized by invasive species allows prediction of their potential effects on ecosystems
in areas where they are not yet present.
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