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Impact of the introduced New Zealand screwshell Maoricolpus Roseus on soft-sediment assemblages in southeast Tasmania

Reid, AP 2010 , 'Impact of the introduced New Zealand screwshell Maoricolpus Roseus on soft-sediment assemblages in southeast Tasmania', PhD thesis, University of Tasmania.

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Non-indigenous species (NIS) continue to have major impacts on the integrity,
diversity and health of native terrestrial, freshwater and marine ecosystems globally.
The New Zealand Screwshell (Maoricolpus roseus) is a turritellid gastropod
inadvertently introduced to Tasmania during the 1920s. It has since become one of
Australia's most widespread marine invasive species, occupying vast areas of
benthic habitat along Australia's SE coast. In Australia, M roseus occupies a range
of habitats from muddy silts to rocky reef although it is most common on shelly
substrates and course sands over a depth range of 0 - 200 m, and regularly attains
densities of `600 - 2500 m^-2`.
Given that M roseus has occupied vast areas of sea floor at high densities for extensive periods of time, the potential exists for this species to invoke large ecological changes to its recipient communities. Despite this, the impact of the screwshells is yet to be either qualitatively or quantitatively examined.
Due to the absence of baseline data on the abundance and distribution of native
species prior to the arrival M roseus ea. 90 years ago, assessing impacts of the
species using a before-after comparison was not possible. In this study I employed a
combination of qualitative surveys and in situ manipulative experiments at a variety
of spatial, temporal and conceptual scales in order to develop a robust quantitative
assessment of the impact of M roseus. This approach involved employing several
independent assessments of impact: (a) experiments in which impacts of M roseus to community structure are assessed and separated; (b) experiments in which impacts of M roseus to benthic community function are quantified using in situ
metabolic chambers; ( c) quantitative surveys which examine the relationship
between screwshells and commercially important scallop species; and ( d)
experiments in which the impacts of M roseus on growth and development of
commercially important scallops are assessed. Importantly, the experimental and
survey designs used were developed to address two unique facets. Firstly, the design
of the experiments and surveys allowed identification of the spatial and temporal
variability of M roseus' impacts. Secondly, the designs allowed for quantification
of the separate impacts of M roseus on the structure and function of native soft-sediment
In the D'Entrecasteaux Channel (SE Tasmania) where M roseus is known to be
patchily distributed at a range of densities from 0 - 2000 m-2, in situ experiments
clearly demonstrated a marked impact on the structure and metabolism of the
benthic community due to the presence of the screwshells. Typically, communities
associated with high densities of screwshells exhibited elevated species richness and
abundances of total macroinvertebrates when compared to patches of benthos with
low densities of screwshells, and areas devoid of the species. Further, such
communities exhibited significantly higher metabolic rates (both respiration and
production), although the specific metabolic rates fundamentally depended upon
whether screwshells were alive, dead and empty, or supporting hermit crabs.
Observations from surveys combined with in situ experiments also highlighted
impacts of M roseus on .commercial species. The distribution of three native scallop
species in the D 'Entrecasteaux Channel depended upon the distribution and density
of M roseus, in addition to the coarseness of the sediments. Further, Pecten
fumatus, the most common of the scallop species, actively avoided areas of benthos
supporting screwshells at densities `> 200 m^-2`. Caging experiments also revealed that
the condition, growth and weight of P. fumatus were significantly impacted by the
presence of M roseus.
I collate and interpret the results from in situ experimental manipulations and large
and small scale surveys to provide a robust estimate of the immediate and potential
impacts of M roseus on native soft-sediment ecosystems and commercially
important species. The results have highlighted the importance of using multiple
methodologies when assessing impacts of NIS, as undoubtedly the most robust
information is attained through the use of multiple independent assessments of
impact. There is clear evidence that M roseus has drastically altered the structural
complexity and integrity of recipient soft-sediment benthic habitats, and the
structure and function of the community it supports. Given the magnitude of impact
of M roseus on native communities and commercially important species, there is a
clear need for a management strategy to be developed for this species. Not only is
M roseus a potential threat to the integrity and natural function of native softsediment
communities, but it is also has the potential to put important recreational and commercial scallop fisheries in Tasmania at risk.

Item Type: Thesis - PhD
Authors/Creators:Reid, AP
Keywords: Introduced mollusks, Maoricolpus roseus
Copyright Information:

Copyright 2010 the author

Additional Information:

Thesis (PhD)--University of Tasmania, 2010.
Includes bibliographical references.
Partial contents: 2. Impacts of introduced New Zealand screwshells on native soft sediment communities -- 3. Immediate and long term impacts of an invasive ecosystem engineer on community metabolism -- 4. Impacts of New Zealand screwshells on scallop distribution and behaviour: a multiscale approach -- 5. Impacts of New Zealand screwshells on juvenile commercial scallops (Pecten fumatus)

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