Assessing the State of the Pelagic Habitat: A Case Study of Plankton and Its Environment in the Western Irish Sea

Abstract

Much work had been undertaken on tracking change in the condition of marine pelagic ecosystems and on identifying regime shifts. However, it is also necessary to relate change to states of good ecosystem health or what the European Marine Strategy Framework Directive (MSFD) calls "Good Environmental Status" (GES). Drawing on existing scientific and legislative principles, including those of OSPAR's "Strategy to Combat Eutrophication," we propose a framework for assessing the status of what the MSFD calls the "pelagic habitat" in temperate coastal seas. The framework uses knowledge of local ecohydrodynamic conditions, especially those relating to the stratification and optical environment, to guide expectations of what would be recognized as healthy in terms of ecosystem "organization" and "vigor." We apply this framework to the seasonally stratified regime of the Western Irish Sea, drawing on published and new work on stratification, nutrient, and phytoplankton seasonal cycles, zooplankton, and the implications of plankton community structure and production for higher trophic levels. We conclude that, despite human pressures including nutrient enrichment, and the food-web effects of fisheries, the pelagic ecosystem here is in GES, and hence may be used as a reference for the "Plankton Index" method of tracking change in state space in seasonally stratified waters.

The Plankton Lifeform Extraction Tool: a digital tool to increase the discoverability and usability of plankton time-series data

“…For example, Bedford et al (2020a) identified regional-scale trends in lifeform changes (increasing diatom abundance in the northern North Sea and increasing mesozooplankton abundance across almost the whole northwest European shelf) using time-series data from five different UK plankton surveys and linked some of these changes to changing sea surface temperature. Assessment of the status of the marine pelagic habitat requires linking changes to pressures (Scherer et al, 2016), which relies on high-temporal-and high-spatial-resolution, good-quality observations, such as climate (Bedford et al, 2020a) and eutrophication (Gowen et al, 2015;Greenwood, 2019).…”

The Plankton Lifeform Extraction Tool: a digital tool to increase the discoverability and usability of plankton time-series data

“…For example, Bedford et al (2020a) identified regional-scale trends in lifeform changes (increasing diatom abundance in the northern North Sea and increasing mesozooplankton abundance across almost the whole northwest European shelf) using time-series data from five different UK plankton surveys and linked some of these changes to changing sea surface temperature. Assessment of the status of the marine pelagic habitat requires linking changes to pressures (Scherer et al, 2016), which relies on high-temporal-and high-spatial-resolution, good-quality observations, such as climate (Bedford et al, 2020a) and eutrophication (Gowen et al, 2015;Greenwood, 2019).…”

The Plankton Lifeform Extraction Tool: A digital tool to increase the discoverability and usability of plankton time-series data

“…For example, Bedford et al, 2020a identified regional-scale trends in lifeform changes (increasing diatom abundance West European shelf) using timeseries data from 5 different UK plankton surveys and linked some of these changes to changing sea surface temperature. Assessment of the status of the marine pelagic habitat (McQuatters-Gollop et al, 2019) requires linking changes to pressures (Scherer et al, 2016), which relies on high temporal and spatial resolution good quality observations, such as climate (Bedford 495 et al, 2020a) and eutrophication (Gowen et al, 2015;Greenwood, 2019). Scores of zero are equal to the long-term mean, positive scores (in green/yellow) signify values above the long-term mean and negative scores values below the long-term mean (in blue).…”

Plankton lifeforms as a biodiversity indicator for regional-scale assessment of pelagic habitats for policy

“…Ideally, the envelope used to calculate a value of the PI would be drawn around a set of points from a marine ecosystem known to be in GES. Scherer et al (2016) have proposed a method for determining pelagic GES independent of the PI tool, but in default of application of this method to all EHD types in UK waters, the PI only provides an indication of change. However, such change in PI can be used as a 'flag' to trigger further investigation into the pressures that may be causing this change in ecosystem state.…”

“…Observationally-informed designations of the seasonal stratification from fixed point stations in some regions such as the Western English Channel do not always agree perfectly with the EHDs defined in Figure 1. In some cases, such as the Irish Sea, it is likely that numerous EHD zones occur in a relatively small region of complex hydrography (Gowen et al, 1995;Scherer et al, 2016) and so may need revisiting. In addition, some EHDs (e.g.…”

The Plankton Lifeform Extraction Tool: a digital tool to increase the discoverability and usability of plankton time-series data

“…For example, Bedford et al (2020a) identified regional-scale trends in lifeform changes (increasing diatom abundance in the northern North Sea and increasing mesozooplankton abundance across almost the whole northwest European shelf) using time-series data from five different UK plankton surveys and linked some of these changes to changing sea surface temperature. Assessment of the status of the marine pelagic habitat requires linking changes to pressures (Scherer et al, 2016), which relies on high-temporal-and high-spatial-resolution, good-quality observations, such as climate (Bedford et al, 2020a) and eutrophication (Gowen et al, 2015;Greenwood, 2019).…”

The Plankton Lifeform Extraction Tool: A digital tool to increase the discoverability and usability of plankton time-series data

“…For example, Bedford et al, 2020a identified regional-scale trends in lifeform changes (increasing diatom abundance West European shelf) using timeseries data from 5 different UK plankton surveys and linked some of these changes to changing sea surface temperature. Assessment of the status of the marine pelagic habitat (McQuatters-Gollop et al, 2019) requires linking changes to pressures (Scherer et al, 2016), which relies on high temporal and spatial resolution good quality observations, such as climate (Bedford 495 et al, 2020a) and eutrophication (Gowen et al, 2015;Greenwood, 2019). Scores of zero are equal to the long-term mean, positive scores (in green/yellow) signify values above the long-term mean and negative scores values below the long-term mean (in blue).…”

Plankton lifeforms as a biodiversity indicator for regional-scale assessment of pelagic habitats for policy

“…Ideally, the envelope used to calculate a value of the PI would be drawn around a set of points from a marine ecosystem known to be in GES. Scherer et al (2016) have proposed a method for determining pelagic GES independent of the PI tool, but in default of application of this method to all EHD types in UK waters, the PI only provides an indication of change. However, such change in PI can be used as a 'flag' to trigger further investigation into the pressures that may be causing this change in ecosystem state.…”

“…Observationally-informed designations of the seasonal stratification from fixed point stations in some regions such as the Western English Channel do not always agree perfectly with the EHDs defined in Figure 1. In some cases, such as the Irish Sea, it is likely that numerous EHD zones occur in a relatively small region of complex hydrography (Gowen et al, 1995;Scherer et al, 2016) and so may need revisiting. In addition, some EHDs (e.g.…”

The Plankton Lifeform Extraction Tool: a digital tool to increase the discoverability and usability of plankton time-series data

“…For example, Bedford et al (2020a) identified regional-scale trends in lifeform changes (increasing diatom abundance in the northern North Sea and increasing mesozooplankton abundance across almost the whole northwest European shelf) using time-series data from five different UK plankton surveys and linked some of these changes to changing sea surface temperature. Assessment of the status of the marine pelagic habitat requires linking changes to pressures (Scherer et al, 2016), which relies on high-temporal-and high-spatial-resolution, good-quality observations, such as climate (Bedford et al, 2020a) and eutrophication (Gowen et al, 2015;Greenwood, 2019).…”

The Plankton Lifeform Extraction Tool: A digital tool to increase the discoverability and usability of plankton time-series data

“…For example, Bedford et al, 2020a identified regional-scale trends in lifeform changes (increasing diatom abundance West European shelf) using timeseries data from 5 different UK plankton surveys and linked some of these changes to changing sea surface temperature. Assessment of the status of the marine pelagic habitat (McQuatters-Gollop et al, 2019) requires linking changes to pressures (Scherer et al, 2016), which relies on high temporal and spatial resolution good quality observations, such as climate (Bedford 495 et al, 2020a) and eutrophication (Gowen et al, 2015;Greenwood, 2019). Scores of zero are equal to the long-term mean, positive scores (in green/yellow) signify values above the long-term mean and negative scores values below the long-term mean (in blue).…”

Plankton lifeforms as a biodiversity indicator for regional-scale assessment of pelagic habitats for policy

“…Ideally, the envelope used to calculate a value of the PI would be drawn around a set of points from a marine ecosystem known to be in GES. Scherer et al (2016) have proposed a method for determining pelagic GES independent of the PI tool, but in default of application of this method to all EHD types in UK waters, the PI only provides an indication of change. However, such change in PI can be used as a 'flag' to trigger further investigation into the pressures that may be causing this change in ecosystem state.…”

“…Observationally-informed designations of the seasonal stratification from fixed point stations in some regions such as the Western English Channel do not always agree perfectly with the EHDs defined in Figure 1. In some cases, such as the Irish Sea, it is likely that numerous EHD zones occur in a relatively small region of complex hydrography (Gowen et al, 1995;Scherer et al, 2016) and so may need revisiting. In addition, some EHDs (e.g.…”