Research Output

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

  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
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
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.

  • Type:


  • Date:

    30 April 2012

  • Publication Status:


  • Library of Congress:

    Q1 Science (General)

  • Dewey Decimal Classification:

    577.7 Marine ecology


Scherer, C. Developing and testing an index of change in microplankton community structure in temperate shelf seas. (Thesis). Edinburgh Napier University. Retrieved from


Eutrophication; coastal waters; anthropogenic nutrient enrichment; ecosystem health; marine management; microplankton;

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