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The
introduction of species into habitats outside their normal geographic
range is accellerating as human mobility increases. Introduced species
have the potential to radically alter the structure and function of native
ecosystems and are a leading threat to biodiversity. The Japanese alga
Sargassum muticum has been invading kelp forests in the San Juan Islands
of Washington since its introduction nearly fifty years ago. Subtidal
kelp communities in the San Juan Islands are important habitat for a wide
variety of animals including invertebrates, fish, mammals, and birds.
Furthermore, the kelp species that dominate these plant assemblages add
three-dimensional structure to the habitat and are important sources of
carbon in coastal food webs. Therefore, any widespread effects of S. muticum
on these algal communities are likely to have broader consequences for
the nearshore ecosystem in this region. We are using an experimental approach
to explore the dynamics and consequences of the S. muticum invasion in
the San Juan Islands.
In
2003, our research will focus on three projects: 1) continued monitoring
of removal experiments in order to compare long and short-term responses
of the native community to S. muticum removal, 2) testing the hypothesis
that spatially complex habitats provide a refuge for native kelp species
from competition with S. muticum, 3) investigating the relationship between
the number of invading propagules and recruitment success using S. muticum
as a model system. Our emphasis is on field experiments in each of these
projects, but we also employ field surveys, lab experiments, and other
approaches where appropriate.
Our
results will provide additional insight into the impacts of this ongoing
invasion on the native plant and animal biota of the San Juan Islands.
In particular, our work in 2003 may contribute valuable information about
long versus short-term consequences of invasions. Additionally, our research
into the role of habitat complexity in mediating competition between S.
muticum and native kelp species should provide important information for
resource managers about how to manage habitats and focus eradication efforts
in ways that minimize the effects of invasive species. Finally, experimentally
testing the relationship between the number of invading propagules and
recruitment success will allow resource managers to make more informed
decisions about how to manage potentially invasive species in order to
minimize the risk of them becoming established.
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Britton-Simmons, K. H. and K. C. Abbott. 2008. Short- and long-term effects
of disturbance and propagule pressure on a biological invasion. Journal of
Ecology
96: , 68-77
Britton-Simmons,
K. H. Accepted pending revisions. Direct and indirect effects of the introduced
alga, Sargassum muticum (Yendo), in subtidal kelp communities of
Washington state, USA. Marine Ecology Progress Series.
Britton-Simmons,
K. H. In Preparation. Understanding biotic resistance to non-indigenous
species: Experimental evidence for the importance of functional group
diversity. To be submitted to Ecology Letters.
Klinger,
T., D. K. Padilla and K. H. Britton-Simmons. Accelerated invasion of marine
reserves. In Review. Ecology Letters.
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Britton-Simmons,
K. H. July 2002. Understanding biotic resistance to invasive species:
An experimental approach. American Society of Naturalists Annual Meeting,
Banff, Canada.
Britton-Simmons,
K. H. August 2002. Spread and Impact of the introduced Japanese seaweed,
Sargassum muticum, in native kelp communities of the San Juan Islands.
Marine Ecosystem Health Program Science Symposium, Orcas Island, WA.
Britton-Simmons,
K. H. August 2002. How do native communities resist invasion by non-indigenous
species? Friday Harbor Laboratories Summer Seminar Series, Friday Harbor,
WA.
Britton-Simmons,
K. H. August 2002. How do native communities resist invasion by non-indigenous
species? Presented by Kevin Britton-Simmons. Guest Lecture to Marine Botany
Class, Friday Harbor Laboratories, Friday Harbor, WA, August 2002
Britton-Simmons,
K. H. April 2003. Establishment, spread, and impact of the introduced
Japanese alga, Sargassum muticum, in native kelp communities of the San
Juan Islands. Natural History Seminar Series, The University of Chicago,
Chicago, IL
Britton-Simmons,
K. H. May 2003. Establishment, spread, and impact of the introduced Japanese
alga, Sargassum muticum, in native kelp communities of the San Juan Islands.
Friday Harbor Laboratories, Friday Harbor, WA.
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Spread
and impact of the introduced Japanese seaweed in native kelp forests of
the San Juan Archipelago
Introduced species have the potential to radically alter the structure
and function of native ecosystems and are a leading threat to biodiversity
in the Georgia Basin/Puget Sound region. While it is always better to
prevent the introduction of exotic species, once a species is introduced
it is critical to know the impact of the species on native plants and
animals and if necessary, to try and slow the spread of or eradicate the
invasive species. The Japanese alga Sargassum muticum was introduced and
began invading kelp forests in the San Juan Islands of Washington nearly
fifty years ago, however very little was known about how this introduced
alga affects native species. In 2001, 2002, and 2003, the SDS funded
a research project to assess how introduced Sargassum muticum impacted
native kelp forests and what could be done if the effect was negative.
This research showed that by competing for light, Sargassum
muticum displaces native algae and has a negative, indirect effect on
the native green urchin, (Strongylocentrotus droebachiensis). This is
an important finding and a big concern because kelps are an important
source of food and provide critical habitat for a wide variety of species
in nearshore ecosystems. Similarly green urchins have an influential role
in structuring shallow subtidal communities in this region.
Small scale experiments showed after removing S. muticum,
the native community recovered within about a year, suggesting that Sargassum-induced
changes are reversible. Our experience with this seaweed indicates that
complete eradication is labor intensive and difficult. But small-scale
removals are possible and can be successful, particularly if focused on
specific, limited target areas such as marine reserves. They need to be
repeated every few years in order to stop incipient recolonization of
the area.
Another focus of this research has been to study how
native communities resist invasion by this species. Results suggest that
native communities with all functional components intact (i.e. with high
functional group diversity) will be more resistant to invasion. Because
S. muticum recruitment is a space-limited, disturbance-dependent process,
human activities that increase levels of disturbance in nearshore kelp
communities are likely to facilitate the spread of S. muticum. What this
all means is that human disturbance of nearshore algal communities should
be minimized to help prevent further S. muticum spread and consequent
damage to kelp and green urchins.
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