C5: Diverse seas: condition of pelagic habitats
Short Description
This indicator of marine biodiversity tracks changes in the Good Environmental Status (GES) of pelagic (water column) habitats. The assessment is based on (a) changes in lifeforms (groups of plankton species that perform the same function in the marine environment) that make up plankton communities, and (b) changes in the biomass of phytoplankton and the abundance of zooplankton. These assessments have been used to inform the assessment of GES for the updated UK Marine Strategy (UKMS) Part One (2019) and to fulfil reporting commitments under the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR). The changes experienced by plankton communities could have implications for the health (functioning, dynamics and structure) of the whole marine ecosystem.
Readiness and links to data
This indicator is not available for reporting in 2024 in a finalised form. An interim indicator is presented here that shows GES assessments conducted for the OSPAR Quality Status Report (QSR) 2023. Status of plankton lifeforms from Changes in Phytoplankton and Zooplankton Communities is presented in C5a, and the status of broad habitat from Changes in Phytoplankton Biomass and Zooplankton Abundance is presented in C5b. The 2 components are presented at differing levels (lifeforms versus habitat) due to the nature of the underlying assessments.
Previous assessments of pelagic habitats have been reported under the updated UKMS Part One (2019). UKMS Part One will be updated in 2024 by adopting the results of the OSPAR QSR 2023 to carry out the regional pelagic habitats assessment for UK waters.
Additional data on trends in individual lifeforms is available via the Plankton Lifeform Indicator Tool.
Notes on indicator
The status of phytoplankton and zooplankton communities has been assessed by analysing trends in the abundance of planktonic lifeforms (those organisms that spend all or part of their lives in the water column as plankton). GES is assessed by identifying the primary drivers for observed changes – if these changes are closely linked to increasing anthropogenic pressure (identified via statistical analyses), the status is determined to be ‘not good’. However, the complexity of these systems means that in many instances the indicator exhibits a change, but it is unclear whether this change is associated with an anthropogenic pressure (for example, climate change, or nutrient pollution) or a reduction in anthropogenic pressure (such as a reduction in nutrient pollution). This means that for many of the component parts of this indicator it is not currently possible to identify whether GES has been met.
Both components of C5 have been disaggregated by 3 major pelagic habitat types in the Greater North Sea and Celtic Seas: variable salinity (which correspond to river plumes and regions of freshwater influence), coastal (nearshore areas adjacent regions of freshwater influence with mean salinity of less than 34.5 parts per thousand), and shelf (habitats that are offshore with an average depth of less than 200m and a salinity of greater than 34.5 parts per thousand). The assessment has been organised this way because these habitats have differing properties and are subject to different pressures.
Indicator components
Figure C5a: Changes in phytoplankton and zooplankton communities: proportion of lifeforms consistent with Good Environmental Status, Greater North Sea and Celtic Seas, 1960 to 2019
Table C5a: Changes in phytoplankton and zooplankton communities: proportion of lifeforms consistent with Good Environmental Status, Greater North Sea and Celtic Seas, 1960 to 2019
| OSPAR Region | Habitat | Not assessed | Not good | Unknown |
|---|---|---|---|---|
| Celtic Seas | Coastal | 1 | 4 | 3 |
| Celtic Seas | Shelf | 1 | 3 | 4 |
| Celtic Seas | Variable salinity | 0 | 1 | 7 |
| Greater North Sea | Coastal | 0 | 0 | 8 |
| Greater North Sea | Shelf | 1 | 2 | 5 |
| Greater North Sea | Variable salinity | 1 | 0 | 7 |
Trend description for C5a
The results from the OSPAR QSR 2023 vary by OSPAR region and by broad habitat type. In the Greater North Sea, change in the majority of lifeforms could not be identified as being in either ‘good’ or ‘not good’ status. In shelf habitats, 2 of the 8 lifeforms were assessed as ‘not good’, with the remainder being ‘unknown’, or ‘not assessed’.
In the Celtic Seas, coastal habitats were identified as having the most lifeforms in ‘not good’ status (4 of 8). Whereas shelf and variable salinity habitats had 3 and one lifeform assessed as ‘not good’, respectively.
There are currently no 'good' results in the recent assessment as there is not enough historical data to identify what represents GES in pelagic habitats. The drivers of change for lifeforms in ‘not good’ status are sea surface temperature and pH (related to ocean acidification) and changes in the ratio of nitrogen and phosphorous (related to nutrient pollution). Plankton lifeforms linked to anthropogenic pressures are generally exhibiting decreasing trends, however meroplankton (lifeforms which spend part of their lives as plankton, such as crabs and lobster) abundance in shelf habitats is increasing in both regional seas, which has been associated with increases in sea surface temperature.
Assessment of change
No assessment of change was undertaken for this indicator as a suitable time series is not yet available in the Outcome Indicator Framework.
Figure C5b: Changes in phytoplankton biomass and zooplankton abundance: number of broad habitat types consistent with Good Environmental Status 1960 to 2019
Table C5b: Changes in phytoplankton biomass and zooplankton abundance: number of broad habitat types consistent with Good Environmental Status 1960 to 2019
| OSPAR Region | Not good | Unknown |
|---|---|---|
| Celtic Seas | 2 | 1 |
| Greater North Sea | 2 | 1 |
Trend description for C5b
In the both the Greater North Sea and the Celtic Seas the Coastal and Shelf habitats were assessed as being in ‘not good’ status as changes in phytoplankton biomass and zooplankton abundance were found to be in response to anthropogenic pressure. The environmental status of variable salinity habitats is currently unknown.
Changes in phytoplankton biomass and zooplankton abundance were evident across the Greater North Sea and Celtic Seas. The primary drivers attributed to these changes are changes in the ratio of nitrogen and phosphorous, the mixed layer depth, pH and the Atlantic Multidecadal Oscillation.
Assessment of change
No assessment of change was undertaken for this indicator as a suitable time series is not yet available in the Outcome Indicator Framework.