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Predicting the impact of an invasive seaweed on the fitness of native fauna

Wright, JT and Gribben, PE 2008 , 'Predicting the impact of an invasive seaweed on the fitness of native fauna' , Journal of Applied Ecology, vol. 45, no. 5 , pp. 1540-1549 , doi:

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Understanding the impacts of invasive species on natural ecosystems is an important component
of developing management strategies. Habitat-forming invasive plants and sessile invertebrates
often support a high diversity and abundance of native fauna, suggesting some benefits of invasion.
However, the fitness responses of these native fauna, and thus the net benefit from their association
with habitat-forming invasive species, are not well understood.
We determined how fitness-related life-history traits, patterns of resource allocation among
life-history traits, and survivorship of an abundant bivalve,
Anadara trapezia
, responded to invasion
by the habitat-forming seaweed,
Caulerpa taxifolia
, by transplanting
A. trapezia
into invaded and
uninvaded habitats over a 12-month period.
A. trapezia
recruits into
C. taxifolia
in high numbers, adult growth, body condition,
shell condition, female reproduction and survivorship were all significantly lower in
C. taxifolia
compared to unvegetated sediment. Notably, we observed high mortality in
C. taxifolia
after heavy
rainfall events, highlighting a potential link between sublethal effects on condition, stochastic
environmental perturbation and survivorship.
In addition to the overall reduction in fitness, there were changes in scaling relationships between
reproduction and body size following invasion. Female
A. trapezia
C. taxifolia
habitat allocated
proportionally more resources to reproduction (including reproductive tissue and number of eggs
per follicle) than those in unvegetated sediment despite their poor condition. Maximizing
reproduction following invasion may impose a further cost to already stressed
A. trapezia
contribute to the higher mortality observed when living in
C. taxifolia
Synthesis and applications
. The full impact of habitat-forming invasive species is complex and
understanding it cannot be based solely on descriptions of native species diversity or abundance.
Our study has identified how the presence of long-lived species within habitat-forming invasive
species may simply indicate an extinction debt. A decline in the fitness of
A. trapezia
C. taxifolia
appears to increase its probability of mortality in the long-term. We recommend that management
approaches for
C. taxifolia
and other habitat-forming invasive species combine an understanding
of impacts on species diversity, abundance and the fitness of associated fauna to provide a more
pluralistic understanding of their effects.

Item Type: Article
Authors/Creators:Wright, JT and Gribben, PE
Keywords: Anadara trapezia • bivalve • Caulerpa taxifolia • fitness • invasive species • life-history traits • marine algae • reproduction allocation • scaling relationships • survivorship
Journal or Publication Title: Journal of Applied Ecology
ISSN: 0021-8901
DOI / ID Number:
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