Pressures affecting pelagic habitats
The main pressures affecting pelagic habitats are human-induced climate change, nutrient and organic enrichment, chemical contaminants, and non-indigenous species. While there is currently insufficient evidence to describe trends in pressures specifically in the context of MSFD pelagic habitats or OSPAR Regions, trends in the human activities exerting the above-mentioned pressures could provide a suitable proxy for trends in the pressures themselves.
NOTE: this is expanded narrative focusing on pelagic habitats - the standard descriptions of the relevant pressures are provided in the DAPI reference list.
The key direct pressures affecting pelagic systems are as follows:
Most importantly, pressures on pelagic systems are increased by Climate change
Human-induced climate change is likely to create the greatest pressures on pelagic systems through changes in ocean temperature, stratification/mixing regimes, potential oxygen depletion, upwellings, atmospheric and oceanographic circulation, and pH (ocean acidification). See: Climate Change , Climate Change Thematic Assessment , Ocean Acidification Other Assessment
Input of nutrients - diffuse sources, point sources, atmospheric deposition [Substances, litter and energy]:
At local scales, inputs of nutrients from farming run-off (driven by society’s need for food), aquaculture, dredging (driven by society’s need for trade and movement of goods) and from industrial and sewage releases can create negative changes in plankton communities. Industrial uses are driven by society’s need for industrial processes, stable economies, health and wellbeing, materials, and trade and movement of goods. Waste treatment and disposal is driven by society’s need for industrial processes and urban uses. Nutrient levels are managed via the EU Water Framework Directive (2000/60/EC) and local equivalents. Effects on hydrodynamics are managed via Environmental Impact Assessments (EIAs), Habitat Regulation Assessments (HRAs) and terrestrial planning processes.
Extraction of, or mortality/injury to, wild species (by commercial and recreational fishing and other activities) [Biological]:
Society’s need for food is a driver of fishing. Mortality/Injury to wild species through overfishing can create imbalances across food webs. The removal of predatory fish can lead to forage fish (plankton consumers) becoming too abundant. In turn, zooplankton are consumed at unsustainable levels, leading to imbalances in plankton communities. Management measures to reduce the impacts of fishing are carried out via the Common Fisheries Policy (CFP) with fishing quotas. However, it should be noted that the drivers for the CFP mostly focus on sustainable fishing levels, rather than on protecting pelagic systems.
Changes to hydrological conditions [Physical]:
Driven by society’s need for economic development, coastal development and the introduction of infrastructure such as offshore wind farms and oil and gas platforms can cause hydrological changes with direct impacts on pelagic habitats at local scale. Hydrodynamic changes can, in turn, can lead to localised changes in stratification / mixing of water column, nutrients, turbidity, currents and plankton distributions.
Input or spread of non-indigenous species [Biological]:
Offshore and coastal development, such as windfarms, can provide a substrate for meroplankton, including non-natives, to settle, while ballast water discharge from shipping can introduce NIS.
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