Status Assessment 2024 - Cymodocea meadows

Confidence

Medium

Background Information

• Year added to OSPAR List: Cymodocea meadows habitat was added to the OSPAR List of Threatened and/or Declining Species and Habitats in 2008 (OSPAR Agreement 2008-06) following its nomination in 2008 supported by the Case Report (OSPAR Publication 2008/358).
• The original assessment of Cymodocea meadows against the following Texel-Faial Criteria led to the listing of the habitat (OSPAR Publication 2010/487): a) not considered of global but of regional importance; b) considered a rarity because there are a limited number of sites where it occurs; c) considered sensitive for several reasons, such as vulnerability to many stresses (physical, turbidity, water pollution) and limited ability to reproduce sexually; d) considered of ecological importance because of its key role in coastal ecosystems in terms of productivity, water filtration and associated fauna; e) status of decline considered significant.
• The anthropogenic pressures and biological factors that are affecting the habitat: pressures are directly related to human activities. The pressures identified in the Background Document (OSPAR Publication 2010/487) and the Case Report (OSPAR Publication 2008/358) are summarised in the following categories of Annex III of the JAMP/MSFD: a) hydrological changes (construction works); b) nutrient and organic enrichments (eutrophication, urban sewage inputs, industrial pollution); c) habitat damage (anchoring, construction works, dredging, shell fishing and other fishing practices). An additional factor identified was the spread of Caulerpa prolifera (in the Bay of Cadiz).
• Last status assessment and brief outcome: 2010. The assessment concluded that: a) in Spain, the status of Cymodocea meadows in the Bay of Cadiz was good, but the other sites were vulnerable or at risk of disappearing; b) in Portugal, Cymodocea nodosa had very low genetic diversity, which increased its vulnerability and need for protection.

Geographical Range and Distribution

Cymodocea nodosa is distributed in the Mediterranean Sea and in the temperate and subtropical north-east Atlantic Ocean, from central Portugal and southern Spain to north-west Africa, including the Canary Islands and Madeira. Since the publication of the Background Document (OSPAR publication 2010/487), the southern limit of its distribution has shifted southwards, from Senegal to the Gambia.

In the OSPAR maritime area, the range of distribution is entirely located in the southwest of the Iberian Peninsula coast, restricted to Portugal and Spain, with the Sado estuary as the northern limit of its distribution (Figure 1). In Spain, it is or has been distributed along the Andalusian coast (Cadiz and Huelva). In the Bay of Cadiz there is a fairly widespread population, with small patches in Bajo de la Cabezuela and Cortadura beach, in the outer area of the Bay. In El Estrecho Natural Park, Cymodocea meadows have been found in the subtidal areas of different beaches near Tarifa (Valdevaqueros, Bolonia, Playa de Los Lances). Cymodocea meadows have also been cited in Barbate, Corrales de Rota, Caños de Meca, Punta Peginas, Caño de Cortadura, Roche, Zahara and Chipiona, although their presence has not been evidenced recently and it is believed to have disappeared in Corrales de Rota (Figure 1). Although there is evidence of their historical presence in Huelva, on one of the banks of the Piedras river, these meadows disappeared in 2010 and there is no evidence of their recovery. In Portugal, Cymodocea meadows are present in the Sado estuary, in the Ria Formosa lagoon and on some isolated beaches (Alporchinhos beach, Marinha beach, Santa Eulalia beach, Arrifes beach, Senhora da Rocha beach, Gale beach and Sendil) on the south coast of the Algarve region. Its presence is confirmed in the Sado estuary and in the Ria Formosa, but on beaches it can only be confirmed at Arrifes beach.

Based on this information, the distribution trend in Region IV is considered to be decreasing due to its disappearance in some locations, although there are also many uncertainties in other locations.

Methods of assessment: 1, 2.

Extent

The extent of seagrass meadows is usually measured as meadow area. Since the first existing surveys of Cymodocea meadows in Region IV, the extent of most locations has declined. The trend since 2010 is uncertain for most locations due to the lack of a systematic mapping approach, but there is evidence that meadows have shrunk in others, or even disappeared.

In Spain, the extent of Cymodocea meadows in Bolonia and Valdevaqueros (El Estrecho Natural Park) was 89 ha in 2016-2018, and in the Bay of Cadiz the extent was 327 ha in 2019 (including the 247.8 ha Bay of Cadiz Natural Park and the 79.3 ha of the Marine bottoms of the Bay). Protected areas in Caños de Meca (Punta de Trafalgar) and Barbate accounted for 14.20 and 1.57 ha, respectively. Between 2019 and 2021, a series of surveys have been carried out to confirm its presence in the Bay of Cadiz. Comparing these data with the 1990 reference map, the presence of C. nodosa was confirmed in 80 % of the transects sampled and the remaining 20 % corresponded to Caulerpa prolifera, a widespread species throughout the bay. In a shorter decadal perspective, the current extent of most of the Cymodocea meadows in the exposed areas of the Cadiz coasts, corresponding to very small and isolated patches (e.g. Caños de Meca, Barbate), as well as in other areas (e.g. Chiclana, Playa de Cortadura, Punta Peginas), is currently unknown. The meadows of Huelva (Piedras river) and Corrales de Rota disappeared in 2010, with the consequent loss of habitat extent.

In Portugal, the extent of Cymodocea meadows was mapped in 2007-2009 at all sites (91 ha in Ria Formosa, 2.2 ha in the Sado estuary, 15 ha in Santa Eulalia and 0.24 ha in the remaining sites). Subtidal seagrass meadows, including Cymodocea meadows, but also other species, have been recently mapped in the Ria Formosa (186 ha, 2019) and in the Sado estuary (15.9 ha, 2022). However, past and present areas are not comparable due to the use of different mapping approaches, which makes it difficult to know the trend in extent. The current area of Cymodocea meadows on isolated beaches in southern Portugal is currently unknown.

Methods of assessment: 1, 2, 4.

Condition

The overall condition of the Cymodocea meadows in Region IV is unknown due to the lack of direct evidence in most of the locations, as direct and continuous monitoring is generally not carried out. However, the quality of the water bodies in which they are found is regularly monitored by government agencies to assess the ecological status of coastal and transitional waters within the scope of the Water Framework Directive. In the last published reports (cycle 2022-2027), the ecological status of these water bodies was generally classified as Good or Moderate (seagrasses being used as biological indicators in some water bodies), except in two locations (Chipiona and Bahía Interna de Cadiz), where the status was Poor.

In Spain, the regional government of Andalusia has had a monitoring programme for Cymodocea meadows since 2004, although it focuses more on the presence and distribution of the species than on its condition (in terms, for example, of seagrass abundance, biomass, or density of shoots) and seems to have been discontinued as of 2020. The 2019 report, the last to include an assessment of the status of this habitat, concluded that, since 2004, a strong generalised regression and disappearance of many of the Cymodocea meadows in Andalusia has been observed. The only long-term monitoring programme of the condition of Cymodocea meadows currently underway is carried out in the Bay of Cadiz (Spain) on a seasonal basis, where they show a stable trend (Figure 2). The current condition of Cymodocea meadows elsewhere is unknown. Future prospects are not favourable at some sites (e.g. Ria Formosa) due to the rapid expansion of the green alga Caulerpa prolifera and other human threats.

There is an urgent need to establish long-term monitoring programmes at sites where their status is unknown, to assess the effectiveness of protection measures and responses to threats and pressures.

Method of assessment: 1, 2, 5.

Threats and impacts

The impacts and threats identified in the Background Document (OSPAR publication 2010/487) that cause damage to Cymodocea meadows continue to exist today, some have recently increased, and new ones have emerged in some locations, in particular in relation to the impacts of climate change and the spread of algae displacing seagrass meadows.

Impacts related to coastal development (construction of coastal infrastructure) and physical damage (navigation, dredging, boat anchoring, shell fishing) are a consequence of urban pressure in the coastal zone, causing both direct loss of meadows and indirect adverse effects such as alteration of coastal dynamics (e.g. the disappearance of Cymodocea meadow in the Piedras river was probably caused by dredging works carried out in 2009). These impacts have been increasing in many locations, for example in the Ria Formosa.

Loss of water quality due to the discharge of insufficiently treated sewage, pollution from industrial activities and diffuse pollution from intensive agriculture and maritime traffic continue to affect Cymodocea meadows. For example, there is strong environmental pressure on the meadows in El Estrecho Natural Park, with the risk of accidental dumping or illegal cleaning of boat tanks. In some areas (e.g. Ria Formosa), the establishment of sewage treatment plants reduced the threat of water pollution.

New impacts and threats have emerged, such as marine heat waves or the massive expansion of the green alga Caulerpa prolifera, which is out-competing the Cymodocea meadows in Ria Formosa. The arrival of the invasive seaweed Rugulopteryx okamurae is also a potential threat in Region IV.

The continuing or increasing magnitude of past and new impacts and threats is exacerbated by the fact that the recovery of Cymodocea meadows is either entirely dependent on vegetative reproduction (in Portugal) or they are isolated and unique. The unknown consequences of the combination of impacts and threats may also exacerbate their consequences on Cymodocea meadows.

Method of assessment: 1, 2.

Measures that address key pressures from human activities or conserve the habitat

Several measures have been taken in Portugal and Spain to address the main pressures from human activities and to conserve Cymodocea meadows in Region IV.

In both countries there are national, European, and international legal frameworks to protect Cymodocea meadows as a habitat or Cymodocea nodosa as a species. Most of the Cymodocea meadows in Spain (98 %) and Portugal (2 main locations) are currently under legal protection. Since 2010, monitoring of the distribution, extent, and condition of Cymodocea meadows has not been carried out systematically across the region, although there are some programmes and surveys in the main locations. These studies are carried out by different institutions, with different methods and tend to focus on the evaluation of extent, which makes it difficult to assess the overall status in Region IV. Community and citizen science projects are supporting distribution and extent assessments. Monitoring of the condition of seagrass meadows is rare and only carried out at one site on a long-term basis. Standardised protocols for systematic, long-term monitoring of Cymodocea meadows in this region, including their distribution, extent, condition, and habitat quality, should be adopted.

Measures to restore the habitat are based on a few small-scale and experimental restoration research projects, but the results have not been satisfactory, or it is too early to assess their success. European and national legislation is in place to address and minimise adverse impacts on Cymodocea meadows from human activities, such as establishing protected areas, controlling inputs of pollutants, and carrying out impact assessments. A wide range of campaigns and actions have been carried out in the region to raise awareness of the importance of Cymodocea meadows, targeting a wide range of audiences.

Although the effectiveness of the measures is not always known, they may have contributed to reversing the trend of seagrass decline in Europe at the continental level. Further management measures may be needed in relation to climate change and biological invasions.

Method of assessment: 1, 2, 4, 5.

Conclusion (including management considerations)

The overall status of Cymodocea meadows in the OSPAR maritime area is poor due to a decreasing trend in their distribution and extent in some locations, and an unknown generalised trend in their condition. There are at least two sites in Spain where the meadows have disappeared since the last assessment. Elsewhere, the trend is unknown or stable, with no indication that the status of any site has improved. The poor status is exacerbated in isolated meadows throughout the whole region and due to the low genetic diversity of Cymodocea meadows in Portugal, which makes them more sensitive to impacts and in need of specific management measures. Previously identified threats and impacts continue to exist and new ones have emerged or accelerated (climate change and algal outcompeting). Measures are in place to minimise and avoid impacts, but their effectiveness is not always known. The Texel-Faial criteria used for inclusion of this habitat in the OSPAR list continue to be met, as indicated in the Background Document (OSPAR publication 2010/487).

The information available on the status of Cymodocea meadows since the publication of the Background Document (OSPAR Publication 2010/487) has improved through national or regional monitoring programmes and quality assessments under the European Directives, mainly on distribution and extent, but rarely on condition (only one location, the Bay of Cadiz, has been assessed for condition trend). However, it remains insufficient for a comprehensive assessment of its overall status in the OSPAR maritime area at a high level of confidence due to its focus on a few locations, the lack of systematic long-term surveys across the region or over time, and the fact that it is a fast-growing species with a high dynamism in some locations. Therefore, this assessment has a medium level of confidence.

Although a wide range of protection and management measures are already in place, these need to be strengthened to address ongoing and newly identified pressures and threats, to prevent further losses and to restore, where possible, lost, and degraded meadows. The establishment of systematic long-term surveys is essential to monitor the distribution, extent, and condition of Cymodocea meadows and to identify the specific causes of their loss and decline.

The status of Cymodocea meadows in the OSPAR maritime area should be reassessed on a short-term cycle (< 10 years) if new evidence of status becomes available.

      Knowledge Gaps

There are significant data and knowledge gaps on the status of Cymodocea meadows in the OSPAR maritime area.

Data availability is insufficient for a high confidence assessment. Pre-2010 records in the OSPAR maritime area include a total of 24 locations (Figure 1). Recent distribution (2017-2023) is only confirmed at 10 localities (3 out of 9 in Portugal, and 7 out of 15 in Spain). The current status of the extent is based on a medium confidence assessment, as many locations have not been mapped since 2010 or methodological approaches are not systematic between localities or over time, so data cannot be compared.

In order to have a more accurate assessment of the status of Cymodocea meadows across the OSPAR maritime area, it would be necessary to establish a systematic long-term monitoring protocol, especially for those locations which conservation status has been unknown since 2010. Given that in most locations no previous data on the extent or status of Cymodocea meadows are available, or the available data show a large variability, the initial results of the recommended surveys could not be used to analyse the evolution of the meadows since the last status assessment, but the presence or disappearance of these meadows could be confirmed, and the data cross-checked with future results. Emerging methodological approaches developed in recent years (mapping using machine learning techniques on satellite or unmanned aerial vehicles imagery) could provide accurate and standardised information on the distribution and extent of Cymodocea meadows.

Method used

The assessment is mainly based on a compilation and revision of scientific publications published since the last state assessment, plus previous studies that are still relevant (1), as well as on published and unpublished technical reports (2). Scarce and non-published information (4) and expert assessment (5) were minority methods used.

Evidence of decline required an integration rule when locations in the OSPAR maritime area showed different trends. Following a precautionary principle, the worst trend was used to define the status, and the unknown status at the locations was not considered.

Main source of information:

3. Assessment derived from a mix of OSPAR data assessment and assessments from third parties.

Assessment is based upon:

b) based mainly on extrapolation from a limited amount of data (e.g. other predictive models or extrapolation using less complete sample of occurrence and environmental data);

c) based mainly on expert opinion with very limited data;

d) insufficient or no data available.

Sheet reference:

BDC2024/Cymodocea meadows