Assessing pelagic habitats: Changes in plankton diversity

EU Member States are required to assess the Good Environmental Status (GES) of their pelagic habitats under the Marine Strategy Framework Directive (MSFD). OSPAR has coordinated this process in the Northeast Atlantic, supporting the development of a suite of three plankton indicators, which were published as part of the OSPAR Initial Assessment and remain in further development:

PH1/FW5: Changes in phytoplankton and zooplankton communities

PH2: Changes in phytoplankton biomass and zooplankton abundance

PH3: Changes in plankton diversity (pilot study)

The last indicator, PH3, is currently in its pilot phase, and focuses on phytoplankton change. Our new paper, led by Dr Isabelle Rombouts, reviews our method and the first application of the indicator.

First, the technical information: PH3 is a multi-metric indicator describes the structure of the phytoplankton community (alpha diversity) and detects significant temporal changes (beta diversity) in the three stations in the Western Channel. We selected the Menhinick (taxa richness) and Hulbert (dominance) Indices as two complementary alpha diversity indices which are strongly related to habitat characteristics and which are easy to communicate to non-scientists. Temporal shifts (species turnover) in phytoplankton community structure were examined using the Local Contribution to Beta Diversity (LCBD; a beta diversity index), followed by the Importance Value Index (IVI) which identified taxa with the highest contribution to the “unusual” community structure.

Figure 1: Contour plots of genus dominance (Hulburt’s Index) for three French stations. Figure modified from Rombouts et al. 2019.

So what did we find?

This first application of the PH3 indicator is a pilot study, or proof of concept. We used data from three French stations to develop, test, and validate the indicator. This is a surveillance indicator which is useful to describe the phytoplankton community structure and detect temporal changes (species turnover) within a time-series. We found that periods of high dominance were also identified as periods of significant turnover in species. In these cases the IVI indicated dominance of a single species, as a monospecific bloom. Such high biomass of a single taxa can be the result of either nutrient inputs or changing environmental conditions. The pressures causing such change may be species specific, and pressure data are required to further investigate what causes of change. Once drivers of change are identified, the policy measures needed to maintain or achieve GES can be examined.

As with any indicator, appropriate data are required to ensure confidence in detecting and interpreting change. Maintaining taxonomic expertise is critical to analysing the plankton data needed for PH3. Without this important skill base it would be impossible to construct and populate any plankton indicators. This work demonstrates how our indicator works with phytoplankton data from fixed point stations. In the future it would be useful to test this method with zooplankton data as well as spatially extensive datasets, such as the Continuous Plankton Recorder survey.

As we further develop and better interpret our suite of plankton indicators the robustness of the evidence base used for decision making increases. It is this evidence base that is required to support good decision making about how we use and manage the Northeast Atlantic marine environment.

Abigail, Plankton and Policy

Read more: Rombouts, I., Simon, N., Aubert, A., Cariou, T., Feunteun, E., Guérin, L., Hoebeke, M., McQuatters-Gollop, A., Rigaut-Jalabert, F. and Artigas, L.F., (2019). Changes in marine phytoplankton diversity: Assessment under the Marine Strategy Framework Directive. Ecological Indicators, 102: 265-277.

About Abigail McQuatters-Gollop

Marine biologist, guitarist, cat lover, red wine drinker. I like plankton.
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