Marine Birds Thematic Assessment

Impacts on the provision of ecosystem services by marine birds

Marine birds are generally not in good status in all the Regions of the OSPAR Maritime Area. This is likely to cause strong negative impacts on ecosystem services, in particular on services for biotic provisioning, biotic regulation and maintenance and on several cultural services.

Impacts on ecosystem services: method for development of the schematic

This section evaluates the impact of changes in the state of marine birds observed in the QSR assessments on the ecosystem services that the North-East Atlantic provides. It was developed through literature review combined with expert judgement, using the same methodology across all thematic assessments. Several workshops involving ecosystem services experts and marine bird experts were held to discuss and agree the results presented below.

Detailed rationale for the role that marine birds (and their state) play in relation to the provision of ecosystem services

The physical damage or death of organisms (lethal effects directly affecting survival rates), can negatively affect ecosystem services in a relatively straightforward way. Likewise, it should be noted that the alteration of feeding behaviour, reproductive behaviour, fertility, reproductive success, mobility and other factors (i.e., sublethal effects indirectly impacting survival, often with a lagged effect) resulting from different environmental impacts can also affect ecosystem services. It is known that reduced prey availability, the introduction of non-indigenous species, exposure to marine litter or other substances (e.g., PBDEs, PBCs) and many other factors can lead to alterations in birds’ reproductive rates, fecundity and metabolic mechanisms, while visual disturbance and other human activities can cause impacts such as displacement from habitats (see the pressure-related thematic assessments from Non-indigenous Species Thematic Assessment for more details about human-induced pressures and associated environmental impacts), with possible carry-over effects on productivity and survival.

Several traits identified in the literature relating to categories such as morphology, behaviour, demography, physiology are comparable across different groups of marine megafauna (large fishes, marine mammals, and marine birds); they underpin the ecosystem functions performed by these organisms that in turn support the provision of ecosystem services. These traits include, for example, body size, body mass, migration, mortality rate, fecundity, reproductive success, survival rate, reproductive location and feeding strategy. For example, dispersal performance and mortality rate (traits) are associated with nutrient transport (ecosystem function) that, in turn, enables the provision of ecosystem services such as ‘nursery population and habitat maintenance’ (through biodiversity promotion) and ‘regulation and maintenance of marine food webs’ (through the function of nutrient cycling) (Tavares et al., 2019). Consequently, if these traits are adversely affected, for example due to habitat loss or exposure to pollutants, negative consequences for the provision of ecosystem services can be expected. The identification of links between state (changes) and ecosystem services was also based on this reasoning.

As mentioned in the  Pressures  section, various pressures associated with human activities and consequent environmental impacts can affect the breeding performance and abundance of marine birds. Especially in the Norwegian Arctic, Greater North Sea and Celtic Seas, “not good” state has been assigned to more than a quarter of assessed species, the result of insufficient productivity to maintain population sizes and of low abundance compared with baseline values (see: State section). The fact that marine birds are not in good state, as shown schematically in Figure I.1, can in turn negatively impact the provision of several ecosystem services. Indeed, the scientific literature demonstrates a positive relationship between bird abundance and the provision of ecosystem services (Gaston et al., 2018).

Impacts on ecosystem services: key messages

The schematic in Figure I.1 shows that when marine birds are not in good status, widespread and intense negative effects are likely to occur in several ecosystem services. There are instances in which limited positive impacts may also arise from a reduction in marine birds, but these always have low importance and are negligible in comparison with the negative effects.

Figure I.1: Schematic depicting the 'State (changes)’ - ‘Impacts on ES’ linkages for the Marine Birds Thematic Assessment. The ecosystem services shown are those considered most relevant to the Marine Birds Thematic Assessment. Each arrow also denotes an expert estimate of the nature and magnitude of the impact (red arrow = negative impact, green arrow = positive impact, green dashed arrow = potential positive impact; H = high impact, L = low impact)

The following section provides, where deemed necessary, a further elaboration of the identified links between state changes and ecosystem services illustrated in the previous section.

Negative impacts

Figure I.1 shows that a reduction in marine birds might lead to widespread negative impacts on the following ecosystem services: 

Wild fish and other natural aquatic biomass and related raw materials:

Declining abundance of marine bird species can adversely affect this ecosystem service and the associated traditional / local activities. Wild marine birds, being considered game, are sometimes hunted for human consumption, though the contribution by wild bird species to human nutritional needs is very small. As reported by Culhane et al., (2019a), an example can be found in the United Kingdom where, for legal quarry species, as long as quantities are limited to a maximum of 10 000 animals per year any hunter registered as a food business can supply game (including marine birds) in unprocessed form to primary consumers or suppliers such as butchers. This practice is known as 'wildfowling'. At local scale, the collection of marine bird eggs may also be mentioned including, for example the licensed collection of black-headed gull eggs in an EU Special Protection Area in Hampshire (UK) for resale to restaurants (Wood et al., 2009). Unlike the marine bird hunting practices included under recreational services, the consumption of birds and their eggs under this ecosystem service is deemed as being for nutritional purposes (Culhane et al., 2019a). One example of the raw materials provided by seabirds is the use of feathers from hunted birds as fly-fishing tying material (Culhane et al., 2019a). Another is the collection of down from the common eider by both the indigenous people of the Arctic and Europeans (Vestbo et al., 2019). 

Regulation and maintenance of marine food webs:

Declining abundance of marine bird species can adversely affect this ecosystem service by leading to imbalances in the food web. For example, the absence of avian predators from a rocky intertidal community has been observed to increase the abundance of limpet species, which in turn has led to a decrease in algae (Whelan et al., 2008). Other examples could be changes in the status (e.g., abundance) of fish-eating birds that may lead to changes in the trophic structure of fish communities, or seaducks and waders exploiting harvestable size classes of bivalves (Zwarts and Wanink, 1993; Kube and Skov, 1996). Moreover, grazing feeders such as geese play an important role in increasing the diversity of submerged macrophytes and stimulating primary production, which in turn is crucial for maintaining the balance of food webs (Green and Elmberg, 2014).

Water quality regulation:

Marine birds and migratory birds using OSPAR marine areas in their flight routes are known to move nutrients from the shore to the coast and vice versa, as in the case of breeding seabirds and guano. Surface feeders and grazing feeders in particular use both aquatic and terrestrial systems to feed, which results in nutrient cycling along these habitats (Gaston et al., 2018; Noordegraaf, 2020). The nutrient cycling provided by birds contributes to water quality, in turn positively contributing to food web (primary) productivity (the ecosystem service of regulation and maintenance of marine food webs) (Gaston et al., 2018). Declining abundance of marine bird species can therefore adversely affect water quality. 

Pest control:

Some surface feeders such as terns and waders contribute to the reduction and control of mosquitos by consuming their larvae (known to be major pests and vectors of disease; Green and Elmberg 2014). In this sense, a decline in abundance can have a negative effect on this ecosystem service. Moreover, pest control is underpinned by a balanced food web, and therefore all components of the marine ecosystem are relevant to the provision of this ecosystem service, including marine birds (Culhane et al., 2019a).

Recreation-related services:

It is well known that marine birds are the focus of popular recreational activities such as on-site birdwatching (Noordegraaf, 2020). Healthy bird populations, as contributors to the natural seascape, play a key role in ecotourism and the maintenance and enhancement of related economic activity. For example, some species of gulls, the northern gannet and the Atlantic puffin contribute to this benefit by being charismatic species (Burdon et al., 2017). Bird-watching tourism in Europe represents a growing market, especially in countries such as the United Kingdom and the Netherlands. Ornithological organisations such as The Royal Society for the Protection of Birds (UK) and the Dutch Ornithological Organisation have over 1 million members and 141 000 members, respectively (Noordegraaf, 2020). 

Education, scientific, and research services:

Marine birds are a central topic in many scientific research activities. Proof of this is the large number of studies involving marine birds that can be found in various online literature databases (Noordegraaf, 2020). However, precisely because this ecosystem service can be enjoyed offsite, for example by reading a book, it may not be impacted by a decline in seabird abundance as it is not directly influenced by the current state of seabird populations (Culhane et al., 2019a). Seabirds play a key role in education, as they can provide striking examples of certain biological features that are taken as models for demonstrating processes of biological evolution (e.g., explanation of the species formation process; Liebers-Helbig et al., 2010). With regard to education services, reference can also be made to the role of citizen science in bringing volunteers into the activity of monitoring bird species and the consequent role of environmental education (Earp and Liconti, 2020; Kloetzer et al., 2021). Furthermore, the fact that few organisms can provide such long time series of data as birds underscores the value of seabirds to environmental science. Marine birds are also used in many monitoring programmes as indicators, for example in monitoring eggs for contaminants. Finally, research and monitoring activities increase overall knowledge about marine birds and enable them to be protected more efficiently, with possible benefits to their provision of ecosystem services (examples provided by the experts involved in the Marine Birds Thematic Assessment).

Spiritual, artistic, and symbolic services:

The value of birds such as swans in relation to this ecosystem service is reflected in their artistic and historical importance. Birds, including marine birds, are used for taxidermy (which can be considered art) and the feathers from marine birds such as gulls and terns have also been used in the clothing industry, as happened in the past with kittiwakes in Heligoland (Gätke, 1895). In addition, marine birds are often used as symbols by entities such as NGOs, the Lutheran church, and others, and they can have spiritual and ritual identity (Noordegraaf, 2020). However, precisely because this ecosystem service can also be enjoyed offsite, for example through artistic representations, it may not be impacted by the decline in seabird abundance as it is not directly influenced by the current state of seabird populations (Culhane et al., 2019a).

Visual amenity services:

Marine birds provide this service because they can convey a 'sense of place' through their appearance and their vocalisation. For example, the calls of great northern divers are often used as background sound in movies and the vocalisations of seagulls are commonly heard in any film that takes place on the coast (Rüter and Palmer 2012), and they are also used in artistic representations (e.g., works of art that use marine wildlife as inspiration; UK NEA, 2011c). Consequently, a decline in these marine birds may have negative impacts on this ecosystem service. However, precisely because this ecosystem service can be also be enjoyed offsite, for example through artistic representations, it may not be impacted by the decline in seabird abundance as it is not directly influenced by the current state of seabird populations (Culhane et al., 2019a).

Ecosystem and species appreciation:

This ecosystem service represents the value placed on species (charismatic or not) of marine birds simply by knowing that they exist and that they are in good condition, even if perhaps the very people who place this value on them will never see them. This ecosystem service includes knowing that future generations will have the opportunity to enjoy marine birds (Noordegraaf, 2020). Therefore, a significant decline in marine bird populations negatively affects the provision of this service.

Positive impacts

Figure I.1 shows that a reduction in marine birds might lead to limited positive impacts on the following ecosystem services: 

Biomass and raw materials from in-situ aquaculture:

Important aquatic species that provide biomass through aquaculture processes, such as bivalves, are the prey of several species of marine birds, including eider, velvet scoter, common scoter, herring gull, oystercatcher and great black-backed gull. Aquaculture stock losses due to seabird predation can be significant, sometimes up to 30% of the total stock (Varennes et al., 2013; Aquaculture Advisory Council, 2022). The implication of this is that in selected sites a decline in the abundance of some marine bird species can be assumed to have an indirect positive effect on the provision of biomass from in situ aquaculture.

Pest control:

Marine birds can be vectors (as well as victims) of avian influenza, transporting viruses over long distances (Ramey et al., 2010) and eventually infecting domestic poultry (Blagodatski et al., 2021). This can lead to significant economic loss, as well as harm to animal welfare. Marine birds can also play a role in spreading alien species (Signa et al., 2021). Thus, a decline in the abundance of certain marine bird species could – theoretically – have partly positive effects on the control of pathogens and alien species considered to be pests. Such positive effects are counteracted by the fact that marine birds also play an important ecological role in pest control, and therefore their reduction would lead to negative effects on this ecosystem service as well (see "Negative impacts" section).

Visual amenity:

Some seabirds, especially gulls, can evoke negative visual associations in specific contexts, as in urban areas where gulls can be perceived by some to be a nuisance. Thus, their decline could have a (limited) positive effect on this ecosystem service (Rock, 2005). However, it should be noted that negative impacts on this ecosystem service are likely to be much more important, as marine birds generally convey a "sense of place" and are linked to pleasant visual associations (see "Negative impacts" section)

Water quality regulation (potentially):

Facultative scavengers, such as gulls, can contact pathogens and toxins by feeding extensively at landfills, posing hazards to water quality (Whelan et al., 2008). Consequently, a reduction in their abundance could have partly positive effects on beach water quality, for example (Converse et al., 2012). Biomagnification of contaminants has been found in many seabirds, due to their position at the apex of the food web and their wide foraging range. Therefore, seabirds can potentially release various contaminants into the environment through feathers, eggs, guano and carrion, with a consequent negative impact on water quality and the marine food web (Signa et al., 2021). It should be noted that, as marine birds are also a vector of nutrients, their reduction is also associated with negative effects on water quality (see "Negative impacts" section).