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Developing and testing an index of change in microplankton community structure in temperate shelf seas.

Scherer, Cordula (2012) Developing and testing an index of change in microplankton community structure in temperate shelf seas. PhD thesis, Edinburgh Napier University.

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      Abstract/Description

      Assessment of eutrophication of coastal waters has traditionally relied on bulk indicators
      of ecosystem state (e.g. nutrients and phytoplankton biomass as chlorophyll)
      and changes in phytoplankton
      oristic composition such as the occurrence of nuisance
      and harmful species. Information on these variables does not allow adequate
      insight into the effects of anthropogenic nutrient enrichment on ecosystem "health":
      i.e. the structure and functioning of the biological community. Environmental policies
      like the Marine Strategy Framework Directive (MSFD) require an ecosystem
      approach to marine management, suggesting the need for a holistic approach to
      assessing environmental status. Autotrophic species of microplankton are primary
      producers and form the base of the pelagic food web. Microheterotrophs are their
      immediate consumers, and this suggests that changes in microplankton community
      structure may be a useful indicator of pelagic ecosystem health.
      The aim of this study was to develop and test an indicator to detect change in
      microplankton community structure in the context of eutrophication. The theoretic
      approach of an existing phytoplankton community index (PCI) was used to
      develop a microplankton community index (MCI). The theory involved the use of
      "lifeforms" (functional groups) and system state space theory. The approach was
      to select lifeforms that provided information on eutrophication, biodiversity and energy flow.
      These lifeforms included diatoms, dino
      agellates, micro-
      agellates, and
      ciliates. Pairs of lifeforms were used as state variables to describe the state of the
      ecosystem. For each pair of lifeforms, data on abundance or carbon biomass were
      mapped into state space. The resulting "cloud" of points incorporated the inherent
      variability of microplankton populations. The index calculated as the difference between
      "clouds", can be used to determine whether differences occur between diffrent
      sites (with different degrees of pressure) or at the same site over time (response to
      pressure at a single site). Three moored instrument sites were selected to develop
      and test the MCI. High temporal resolution sampling of physical, chemical, and microplankton
      components was carried out for two years (February 2008 - December
      2009) in the western Irish Sea (WIS). For the mooring sites in Liverpool Bay (LBay)
      in the eastern Irish Sea and the West Gabbard (WGabb) in the southern North Sea
      data of those components were provided for the same frequency and period.
      Microplankton cell abundance and carbon biomass showed that the expected seasonal
      cycle was coupled to hydrodynamic conditions at each site with the sub-surface
      light climate considered to be the main factor that controlled the start and duration
      of the production season at all three sites. At WIS, diatoms dominated the spring
      bloom and autumn period. Succession from diatoms to dino
      agellates was associated
      with increased stratiffication and micro-
      agellates were abundant but without an obvious
      seasonal pattern. Diatoms dominated the microplankton throughout the year at LBay and WGabb due to high nutrient concentrations and intermittently stratifying
      conditions. The influence of nutrient enrichment on microplankton community
      was investigated at the LBay (� 30�M winter DIN) and WGabb (� 15µM winter
      DIN) sites by using five pairs of lifeform state space plots (diatoms/dino
      agellates,
      autotrophs/heterotrophs, autotrophs /mixotrophs, mixotrophs/heterotrophs, and
      small/large sized microplankton). A clear increase in the autotroph biomass at
      LBay station in the autotrophs/mixotrophs comparison was observed and the MCI
      value of the small/large sized microplankton comparison suggested a difference between
      the communities at the two sites with higher biomass of the large sized lifeform
      at LBay. Comparisons with the heterotrophic lifeform were difficult, because few
      data points were available.
      By including additional microplankton lifeforms the MCI extended the PCI approach
      and can be used to provide a more complete assessment of change in microplankton
      community structure. Further development and assessment is required such as
      what represents the optimum size of datasets for reliable application of the index
      and the distinction of the nutritional mode in long-term preserved microplankton
      samples.
      A key element of the MCI application is the comparison to a reference condition.
      According to the MSFD such conditions should be representative of good environmental
      status (GES). On the basis of current understanding of microplankton ecology
      (biogeography, seasonal dynamics and succession) the results from this study
      suggest that the microplankton community at station WIS represents GES and this
      station is therefore proposed as a reference site for seasonally stratifying temperate
      shelf seas.

      Item Type: Thesis (PhD)
      Uncontrolled Keywords: Eutrophication; coastal waters; anthropogenic nutrient enrichment; ecosystem health; marine management; microplankton;
      University Divisions/Research Centres: Faculty of Health, Life & Social Sciences > School of Life, Sport and Social Sciences
      Dewey Decimal Subjects: 500 Science > 570 Life sciences; biology > 577 Ecology > 577.7 Marine ecology
      Library of Congress Subjects: Q Science > Q Science (General)
      Item ID: 5640
      Depositing User: Ms Cordula Scherer
      Date Deposited: 07 Sep 2012 15:11
      Last Modified: 11 Jul 2013 16:55
      URI: http://researchrepository.napier.ac.uk/id/eprint/5640

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