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 recognised as healthy in terms of ecosystem 'organisation' and 'vigour'. 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.
Highlights
The Marine Strategy Framework Directive (2008) is the most recent European Union legislation designed to safeguard the environment and ensure the sustainable use of ecosystem services in marine waters within the exclusive economic zone of EU member states
Observations of the stomach contents of squid and fish show that the pelagic web is well linked to higher trophic levels, the euphausiid Meganyctiphanes playing an important role in nourishing small nektonic predators
The main difference from expectation is that Calanus spp. are in most years less abundant than expected; it may be that the bottom water of the Western Irish Sea (WIS) in winter is neither sufficiently cold nor sufficiently well isolated to provide a refuge for the large copepods
Summary
The Marine Strategy Framework Directive (2008) is the most recent European Union legislation designed to safeguard the environment and ensure the sustainable use of ecosystem services in marine waters within the exclusive economic zone of EU member states. Article 1 of the Directive states that the overarching aim is: “to achieve or maintain good environmental status in the marine environment by 2020 at the latest.”. The Directive expands its definition of Good Environmental Status (GES) by means of 11 “Qualitative Descriptors” and a European Commission document (Commission Decision 2010/477/EU, 2010) provides assessment criteria for each descriptor. Four of these descriptors relate to the “pelagic habitat.”. We understand the condition of the “pelagic habitat” as including the physical and chemical characteristics of the sea-water and the biological and ecological characteristics of the plankton found in that water: in effect, as a sub-system within a specified marine ecosystem
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