Enabling an Ecosystem Service and Natural Capital Approach

Ashley, M., Rees, S., Mullier, T., 2021 Exe Estuary Management Plan 2022-2027: Enabling an Ecosystem Service and Natural Capital Approach within the Exe Estuary Management Plan. Summary text provided by research staff at the University of Plymouth

Author and affiliation: Matthew Ashley, Siân Rees, Tom Mullier

School of Biological and Marine Science, University of Plymouth.

This report has been compiled by staff at The Marine Institute, School of Biological and Marine Science, University of Plymouth.

Contact Details:

Dr Matthew Ashley / Dr Siân Rees

School of Biological and Marine Science,

Marine Institute

Marine Building

Level 3

University of Plymouth.

Drake Circus



Tel 00 44 (0) 1752 584732

Web: http://www.plymouth.ac.uk/marine

The habitats and species populations within the Exe estuary provide ‘natural capital’ that supports multiple ecosystem services (ES), defined as the ‘the benefits provided by ecosystems that contribute to making human life both possible and worth living’ (UK National Ecosystem Assessment, 2011) (Figure 1; Table 1). Associated marine cultural heritage assets represent interaction between people and the marine environment in the Exe estuary area through time.

The Natural Capital Approach (NCA) is a tool to assess and identify where and how to improve the natural environment and maintain flows of ES benefits. The Natural Capital Approach provides a means to achieve the UK government’s vision to ‘to be the first generation to leave the natural environment in a better state than it inherited’ (Natural Capital Committee, 2015; HM Government, 2018). The Natural Capital Approach relates the state of natural capital stocks (elements of nature that have value to society, such as forests, fisheries, rivers, biodiversity, land and minerals) to the flow of environmental or ‘ecosystem’ services over time (Natural Capital Committee, 2013; Natural Capital Committee, 2017; ONS, 2017).

Within the Exe estuary the habitat and species assets, including the water column provide an array of structures and functions that, combined, provide services and benefits that are linked to the Environment and People elements considered in the Exe Estuary Management Plan 2022-2027 (Figure 1; Table 1). The reviewed level of delivery of these benefits depends on the extent of related habitats and health of those habitats not being adversely impacted by human activities. The implication of activities on level of delivery of benefits can thereby be assessed within the management plan. 5 key ES benefits, considered in the Exe Estuary Management Plan 2022-2027 include:

Regulating service: healthy climate (Environment 3, Climate Change)

A healthy climate is dependent on the balance and maintenance of the chemical composition of the atmosphere and the oceans by marine living organisms. The capture and export of carbon is central to this process. Within the Exe estuary, saltmarsh and seagrass plant communities with root systems capture and store carbon in situ. Algae and kelp communities on intertidal habitats and infralittoral rock habitats capture carbon which is exported in detritus, and a proportion stored/sequestered in offshore soft substratum sediments. The water column supports the carbon cycle though oceanic primary production harvesting light to convert inorganic to organic carbon. River and estuaries provide relatively large C efflux through terrestrial detritus and sewage inputs to the coastal zone coastal ocean.

Regulating service: clean water and sediments (Environment 5.1, Water Quality)

Marine living organisms store, bury and transform waste though assimilation and chemical decomposition and re-composition. Vegetation within saltmarsh and seagrass habitats within the Exe estuary has the ability to baffle water currents and stabilize sediments, resulting in organic matter and nutrients becoming stored within the accreting sediments, sequestering carbon, nitrogen and phosphorous, while the remaining organic material is recycled or exported. Bioturbation (biogenic modification of sediments through particle reworking and burrow ventilation) by benthic organisms living within soft substratum habitats provides a mechanism for nutrient cycling (Queirós et al., 2013). Filter feeding bivalves, such as mussels pump water and contaminants such as bacteria, algae, microplastics and detritus into their gill chambers, as they feed, effectively reducing concentrations within the water column (Scott et al., 2019; Viarengo and Canesi, 1991).

Regulating service: sea defence (flood prevention, storm defence and alleviation of coastal erosion) (Environment 5.4, Flood and Coastal Risk Management)

Estuarine habitats within the Exe estuary play a valuable role in the defence of coastal regions. Physical barriers such as those provided by littoral rock habitats dampen wave energy and contain rising water. Saltmarsh habitats attenuate currents, dampen wave energy, and store large volumes of water. Soft substratum habitats dissipate wave energy and provide barriers reducing risk of damage to coastal defences and low lying land and infrastructure. Intertidal habitats not only provide sea defence ES benefits in relation to present sea level (and sea conditions), but unlike man-made defences, if unimpeded by coastal development, natural intertidal habitats such as saltmarsh will migrate with rising sea levels, predicted under future climate scenarios.

Provisioning service: wild food (People 6.2, Fisheries)

Commercial fisheries, aquaculture and hand gathering directly benefit from flow of ‘wild food’ ecosystem service benefits, related to stocks of fish and shellfish species within the Exe estuary. Habitats such as: estuarine saltmarsh, sublittoral seagrass beds and coastal infralittoral rock habitats, and also littoral sediments, provide important nursery habitat, supporting shelter and food resources for the main commercially and recreationally gathered fish and shellfish species Deeper circalittoral rock habitats support adult life stages of shellfish species and fish species such as pollack P. pollachius and bass Decentrarshus laborax. Outside MPAs sublittoral soft substratum habitats provide important habitats supporting adult life stages of all commercially targeted species. Water quality within the site is essential to supporting aquaculture resources and availability of blue mussel M. edulis for hand gathering, as well as supporting healthy fish and shellfish populations.

Cultural service: recreation and tourism (People 6.3, Water Based Recreation, 6.4, Tourism)

Marine natural capital assets provide the basis for a wide range of recreation and tourism activities. Recreation and tourism opportunities include watersports, wildlife watching, recreational fishing, appreciating scenery (e.g. from a viewpoint), swimming outdoors, visits to a beach (sunbathing or paddling in the sea), walking (e.g. walking the coast path) (Natural England, 2021). Saltmarsh (in relation to coastal access points, nature watching, aesthetic interest and supporting species of interest to recreational fishing and foraging) and littoral sand, coarse and mixed sediments (in relation to beaches and coastal access points) within the Exe estuary, combine to provide significant contributions to the provision of the ES benefits of Recreation and Tourism.

Map of the Exe Estuary showing broad scale habitats
Figure 1. Estuarine habitats within the Exe estuary
A table displaying the scale of ecosystem service contribution relative to other features
Table 1
A table displaying confidence in evidence available to assign ES provision.
Table 2

Contribution of habitat features (aggregated to Eunis level 3) and associated species communities to 5 key ES benefits: wild food, sea defence, clean water and sediments, healthy climate, tourism including recreation and nature watching (reviewed evidence from Potts et al (2014) and Rees et al. (2019)).

Broad scale habitat Natural Capital Asset: Habitats in Exe Estuary  


Extent (km²)

Contribution to ES Goods/Benefits
Food (wild food) Tourism, nature watching and recreation Sea Defence Healthy climate Clean water and sediments
 Marine Intertidal reef A1: Littoral rock and other hard substrata 0.24 3 1 1 2
Intertidal sediments A2.1 Littoral coarse sediment 0.05 1 1 3
A2.2: Littoral sand and muddy sand 3.17 1 1 3 2
A2.3: Littoral mud 5.68 3 1 3 3 3
A2.4: Littoral mixed sediment 0.05 1 1 3 2
A2.5 Coastal saltmarshes and saline reedbeds 0.2 3 3 3 3 3
A2.6 Littoral sediments dominated by aquatic angiosperms (seagrass bed) 1.65 3 1 1 1 1
A2.7 Littoral biogenic reefs (A2.72 Blue mussel beds) 0.49 2 1 1 1 1
Subtidal sediment A5.1: Sublittoral coarse sediment 0.16 2 3 2 3
A5.2: Sublittoral sand 0.08 2 3 2 3
A5.3: Sublittoral mud 3.95 2 3 2 3
A5.4: Sublittoral mixed sediment 2.34 2 3 2 3
Water column N/A  Areas of high planktonic primary productivity  – 2 1 1 2 1
N/A  Tide swept channels  – 1


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