Pelagic habitats
Assessment of progress towards the achievement of Good Environmental Status for pelagic biodiversity.
Extent to which Good Environmental Status has been achieved
Prevailing environmental conditions are likely to be driving the observed changes in plankton communities, but human activities cannot be ruled out. It is uncertain whether Good Environmental Status has been achieved.
How progress has been assessed
In the UK Marine Strategy Part One (HM Government, 2012), the UK set out the following “Characteristics of Good Environmental Status” for biodiversity:
“At the scale of the Marine Strategy Framework Directive sub-regions, and in line with prevailing conditions, the loss of biodiversity has been halted and, where practicable, restoration is underway.
The abundance, distribution, extent and condition of species and habitats in UK waters are in line with prevailing environmental conditions as defined by specific targets for species and habitats.
Marine ecosystems and their constituent species and habitats are not significantly impacted by human activities such that the specific structures and functions for their long-term maintenance exist for the foreseeable future.
Habitats and species identified as requiring protection under existing national or international agreements are conserved effectively through appropriate national or regional mechanisms.”
The extent that Good Environmental Status had been achieved, as articulated in the criteria for biodiversity (European Commission, 2010), was assessed using targets set out for pelagic habitats in the UK Marine Strategy Part One (HM Government, 2012). The status of plankton communities was assessed against two targets: habitat distribution and habitat condition. Both targets would need to be met for Good Environmental Status to be achieved for pelagic habitats.
Progress towards the target for habitat distribution was assessed by examining changes in plankton communities. This was done using a specially developed plankton index approach (Tett and others, 2008, which compares changes in a suite of plankton lifeforms (functional groups of species) and can provide an indication of change in the ecological functioning of the plankton community.
Progress towards the target for habitat condition was assessed by examining changes in plankton biomass and zooplankton abundance. Unlike the Initial Assessment (HM Government, 2012), this assessment included indicators of change in zooplankton abundance as well as of change in phytoplankton biomass.
Indicators relevant to the targets were agreed by OSPAR, and used data collected by selected monitoring programmes in the UK and by neighbouring countries within the Celtic Seas and the Greater North Sea. This is the first time that plankton data from a number of fixed-point monitoring stations and the Continuous Plankton Recorder have been assessed together at a sub-regional scale.
Progress since 2012
Since the UK Initial Assessment 2012 (HM Government, 2012), new indicators of zooplankton and phytoplankton community structure and biomass have been developed (Tett and others, 2008; OSPAR Commission, 2017). These are the first operational plankton biodiversity indicators in the North East Atlantic. Phytoplankton communities continue to vary considerably over space and time, and phytoplankton biomass has continued to increase in most areas.
Outstanding issues
It is still unclear to what extent natural variability, climate change, ocean acidification, eutrophication and the impacts of fishing on the food web may be contributing to changes in abundance, biomass and composition of plankton communities.
Achievement of targets and indicators used to assess progress
|
Targets |
Indicator |
Assessment Results |
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Habitat distribution: At the scale of the Marine Strategy Framework Directive sub-regions, the plankton community distribution is not significantly adversely influenced by anthropogenic drivers, as assessed by indicators of changes in plankton functional types (lifeforms). |
Change in plankton communities |
The lifeforms (functional groups of species) that make up the plankton communities changed between the starting conditions period (2004-2008) and the current assessment period (2009-2014). |
|
Habitat condition: At the scale of the Marine Strategy Framework Directive sub-regions, condition of plankton community is not significantly adversely influenced by anthropogenic drivers. |
Change in plankton biomass and abundance |
In most areas, phytoplankton biomass (chlorophyll-a) has increased between the starting conditions period (2004-2008) and the current assessment period (2009-2014). Changes in zooplankton abundance varied across the two sub-regions assessed, with increases in some areas, decreases in others, and no change in some. |
Further information
Assessment of the extent that the target on habitat distribution has been met
In both sub-regions, the lifeforms (functional groups of species) that make up the plankton communities changed between the starting conditions period (2004-2008) and the current assessment period (2009-2014). These changes could have implications for ecosystem functioning. It is unclear if observed changes are a result of pressures from human activities. Therefore, it is not yet possible to say with confidence if the UK target has or has not been met.
Evidence to support the above evaluation of habitat distribution
The supporting evidence for this target evaluation comes from the assessment of the indicators: change in plankton communities and change in plankton biomass and abundance The indicator assessments have been undertaken as part of the OSPAR Intermediate Assessment (OSPAR Commission, 2017). As such, the indicator assessments were undertaken in each OSPAR Region (approximate to each Marine Strategy Framework Directive sub-region). This UK assessment differs slightly from the OSPAR assessment, because it uses only data collected by the UK although these data were collected throughout the sub-regions, not just in UK waters.
Change in plankton communities was assessed using the novel Plankton Index approach which examines change in plankton lifeforms. This approach can be used to reveal plankton community responses to pressures and prevailing conditions. Lifeforms are comprised of organisms with the same functional traits. Changes in the relative abundance of two contrasting lifeforms (called ‘lifeform pairs’) can indicate changes to ecosystem functions, including links between the biological communities of the water column and sea floor, ecosystem energy flows and pathways, and food web interactions. The use of the plankton lifeform approach can overcome difficulties in plankton taxonomy and identification and allow comparison of data generated by different laboratories and methodologies.
The UK assessment for plankton community change provided the first opportunity to bring plankton data sets from a variety of sources to be examined using a novel Plankton Index approach. Results of this analysis indicate variability in the UK plankton community. The aggregated Plankton Index values across the lifeform pairs showed changes to lifeforms in both sub-regions between the starting conditions period (2004-2008) and the current assessment period (2009-2014). These findings are in agreement with published scientific literature on plankton dynamics.
While the indicator assessment showed there has been change in plankton communities (medium-high confidence), it is not yet possible to determine the magnitude and the direction of this change. It is also unclear if these changes are being driven by pressures from human activities or by environmental factors. Extensive peer-reviewed research, however, suggests that prevailing oceanographic and climatic conditions are likely to be the overall driver of change in the indicator in both sub-regions. More work is needed to understand the influence of anthropogenic pressures.
Assessment of the extent that the target on habitat condition has been met
In both sub-regions, this assessment identified changes in biomass and abundance of plankton, which may have consequences on the functioning, dynamics and structure of the whole marine ecosystem. In most areas, phytoplankton biomass (chlorophyll-a) has increased between the starting conditions period (2004-2008) and the current assessment period (2009-2014). Changes in zooplankton abundance varied across the two sub-regions, with increases in some areas, decreases in others and no change in some. It is unclear if these changes are a result of pressures from human activities. It is therefore not yet possible to say with confidence if the UK target has or has not been met.
Evidence to support the above evaluation of habitat condition
The supporting evidence for this target evaluation comes from the assessment of the indicator: change in plankton biomass and abundance. This indicator assessment has been undertaken as part of the OSPAR Intermediate Assessment (OSPAR Commission, 2017). As such, the indicator assessment was undertaken in each OSPAR region (approximate to each Marine Strategy Framework Directive sub-region). This UK assessment differs slightly from the OSPAR assessment, because it uses only data collected by the UK although these data were collected throughout the sub-regions, not just in UK waters.
The indicator of change in plankton biomass and zooplankton abundance identifies changes (classified as small, important or extreme) in the production and losses of plankton over time, to reflect the state of the marine ecosystem, which may help us to better understand changes in other parts of the food web. Total phytoplankton biomass and abundance of zooplankton are used to represent phytoplankton and zooplankton production and losses. The assessment was conducted within a series of ecohydrodynamic areas (van Leeuwen and others, 2015), which account for the physical features of the water column.
In the Greater North Sea, the pattern of yearly changes in zooplankton abundance was similar in each ecohydrodynamic area. Extreme negative changes in zooplankton abundance occurred between 1975 and 1985 in most areas, indicating a decrease in zooplankton abundance, in accordance with a previously-identified regime shift. From 2004 to 2012, the abundance of zooplankton showed some important changes for several years in all ecohydrodynamic areas except in permanently stratified waters. There were fewer important changes in zooplankton abundance in permanently stratified waters compared to the other ecohydrodynamic areas. Phytoplankton biomass has increased, since 1994, in most ecohydrodynamic areas of the Greater North Sea.
In the Celtic Seas, the seasonally stratified waters and the regions of freshwater influence showed similar changes in zooplankton abundance, with some notably important changes in zooplankton abundance in the 1990s and after 2004. Phytoplankton biomass was not assessed for each ecohydrodynamic area of the Celtic Seas but in the sub-region as whole, where phytoplankton biomass showed variability across years with an increase since the 1980s.
Moving forward
The methods developed so far mean we can continue to monitor changes in the plankton community. The assessment of Good Environmental Status in pelagic habitats would be improved by research into the effects of the key anthropogenic pressures and climatic drivers on this component of the ecosystem.
Further information
Several knowledge and data gaps have been identified in the individual indicator assessments that will need to be addressed in the most appropriate forum (UK Marine Monitoring and Assessment Strategy, OSPAR or the EU). Filling these gaps will increase the confidence of the assessments.
This has been the first assessment of plankton and pelagic habitats at the sub-regional scale in the North East Atlantic. This was possible through international co-operation and data exchange, facilitated by OSPAR. Going forward, future assessments would be more efficient if various inconsistencies between the different national datasets of neighbouring countries could be successfully addressed.
Changes in plankton communities were assessed using the novel Plankton Index approach which examined change in plankton lifeforms (Tett and others, 2008). This approach has added value to previous assessments that were based solely on changes in phytoplankton biomass and zooplankton abundance. However, the current assessment was limited in that it was unable to distinguish changes caused by pressures from human activities from those driven by changes in climate and prevailing conditions. Going forward, monitoring Plankton Index along with plankton biomass and abundance will provide greater potential for determining impacts of human activities on pelagic habitats. The next steps will aim to increase the robustness and confidence of future assessments by building a quantitative evidence base that can link changes in the plankton indicators to prevailing conditions and anthropogenic pressures.
The Plankton Index approach to assessing plankton communities could benefit from the addition of a lifeform pair that includes taxa responsible for harmful algal blooms. Such a lifeform pair could add value by representing socio-economic impacts on industries and on human health, as well as impacts on biological functioning of the marine ecosystem.
Finally, it is worth noting that the current assessment focuses solely on the plankton component of the pelagic habitat. Future assessment could include microbial components such as environmental bacteria and viruses.
References
Acknowledgements
European Commission (2010) ‘Commission Decision of 1 September 2010 on criteria and methodological standards on Good Environmental Status of marine waters’ (notified under document C (2010) 5956) (Text with EEA Relevance) (2010/477/EU). Official Journal of the European Union L232, 2.9.2010, pages 14-24 (viewed on 5 July 2018)
HM Government (2012) ‘Marine Strategy Part One: UK Initial Assessment and Good Environmental Status’ (viewed on 5 July 2018)
OSPAR Commission (2017) ‘Intermediate Assessment 2017’ (viewed on 21 September 2018)
Tett P, Carreira C, Mills DK, van Leeuwen S, Foden J, Bresnan E and Gowen RJ (2008) ‘Use of a phytoplankton community index to assess the health of coastal waters’ ICES Journal of Marine Science, 65: 1475-1482 (viewed on 26 October 2018)
van Leeuwen S, Tett P, Mills D, Van der Molen J (2015) ‘Stratified and non-stratified areas in the North Sea: Long-term variability and biological and policy implications’ Journal of Geophysical Research: Oceans: volume 120, pages 1–17 doi:10.1002/2014JC010485 (viewed on 26 October 2018)