Food webs Thematic Assessment

Activities affecting marine food webs

Human activities are distributed widely across the North-East Atlantic, but the intensity of activities and of the pressures they impose on the marine environment varies greatly between OSPAR Regions and sub-divisions. Some sea areas are affected by many activities; in others, only a few may be significant. Activities are reflected in the spatial scale of their potential impacts on food webs. The key human activities affecting food webs are extraction of living resources, transport and shipping, water management activities, agriculture, aquaculture, renewable energy and extraction of non-living resources.

Widespread activities

Extraction of living resources:
Society’s need for food is a driver of fishing activity. The different gears and methods used to extract living resources include benthic trawling, scallop dredging, netting (e.g., fixed nets), pelagic trawls, potting / creeling, suction (hydraulic) dredging, bait digging, seaweed and saltmarsh vegetation harvesting, and hand collection of bird eggs and shellfish. These activities directly and/  or indirectly interact with food web components and can alter food web structure and functioning and therefore their balance.

Transport - shipping:
Society’s need for the trade and movement of goods drives transport activities, reflecting the need for stable economies and the supply and demand of goods and services. Transport and shipping involve activities such as the dumping of litter and debris, the production of shipping wastes, particularly emissions of greenhouse gases, and also mooring, beaching and launching, as well as the operation of ferries. Litter and debris (including plastics) can injure or kill marine and coastal wildlife or can be ingested and move through the marine food web. Shipping can introduce non-indigenous species through ballast water discharge, which impacts food web structure and functioning.

Local activities

Physical restructuring of rivers, coastline or seabed (water management):
Dredging the seabed can cause localised increases in nutrients and turbidity. This eutrophication impact can change the pelagic system, including changes in food webs and changes of energy transfer from pelagic systems to higher trophic levels. The dredging and depositing of materials at sea and in local marine areas, predominantly associated with the maintenance of navigable channels and associated disposal at marine sites, will directly interact with benthic habitats and influence bottom-up control in food webs. Furthermore, coastal areas used as spawning areas are negatively impacted by physical disturbance. Benthic communities play a central role in the transfer of materials, from primary production by phytoplankton, microphytobenthos, benthic macrophytes and coastal wetlands through the detrital pool to higher trophic levels in the food web, including commercially exploitable fish.

Agriculture and Aquaculture [Cultivation of living resources]:
Society’s need for food drives marine aquaculture, freshwater aquaculture, and terrestrial agriculture. Agricultural run-off can lead to the input of toxicological substances to the environment, including nutrients and fertilisers. In localised areas, nutrient run-off from industry and sewage can cause significant eutrophication impacts on pelagic habitats, which can alter food web structure and functioning (OSPAR Eutrophication Thematic Assessment). Aquaculture can also provide vectors for the spread of introduced diseases and parasites. Parasites have the potential to uniquely alter food web structure in terms of chain length, interaction strength, and energy transfer.

Renewable energy generation (wind, wave and tidal power), including infrastructure [Production of energy]:
This includes the construction and operation of offshore wind farms and other renewable energy developments designed to harness both wave and tidal energy, including the associated infrastructure. The construction, operation, and decommissioning activities associated with renewable energy developments may directly interact with benthic and pelagic food web components. The introduction of infrastructure to the marine environment alters benthic habitats and can cause hydrological and hydrodynamic changes influencing nutrients, primary production and plankton species distributions. Fish and top-predator communities are impacted by the construction of offshore wind farms and underwater noise. 

Extraction of minerals, Extraction of oil and gas [Extraction of non-living resources]:
The extraction of aggregate materials (mining, polymetallic nodules, sand, gravel and crushed rock), oil and gas from the seabed is necessary for the construction industry and low-carbon technologies. Materials extracted from the seabed directly interact with benthic habitats in the locations where the materials are collected and are likely to modify the consumer-resource (trophic) and substrate-providing (non-trophic) interactions within the food web.

Military operations (subject to Article 2(2)) [Security/defence]:
These activities include the production of contaminants, military training, disposal at sea of munitions and the construction of complex infrastructure projects. They have potential consequences for food web structure and functioning, including habitat degradation, soil erosion, environmental pollution and disturbance, and have contributed to population declines and biodiversity losses arising from both acute and chronic effects in marine systems (Lawrence et al., 2015).