Seagrass meadows
The seagrass meadows in Basque estuaries are represented by only one species (Zostera noltei), which is classified as endangered. Due to its intertidal nature, it is considered to be especially vulnerable to the impact of climate change, particularly to rising sea levels. As a vulnerable species in the Basque Country, it is considered to be an indicator of the resilience of the intertidal estuarine system due to the ecosystem services it provides.
Figure 1. Zostera noltei seagrass meadows in estuaries in the Basque Country.
- Zostera noltei seagrass meadows are considered to be indicators of the resilience of the intertidal estuarine system of Basque estuaries.
- They are vulnerable to rising sea levels and changing physical and chemical sea conditions
Relationship of the indicator to climate change
They are an indicator of the resilience of the system due to the ecosystem services they provide: they retain sediment, prevent erosion in estuaries, act as a blue carbon sink and an ecosystem engineer. They are also considered to be vulnerable because of the expected displacement of their grasslands in response to rising sea levels and the changing physical and chemical conditions of the sea, with a probable limitation in the space available for them to develop (Valle et al. 2014).
Figure 4. Trends over time for the area occupied by Z. noltei mapped in 2008, 2012 and 2021.
The mapped occupied area has increased for all estuaries (Figure 4).
Zostera noltei is the only species of marine phanerogams that can be found in Basque estuaries (Figure1). This species is currently listed as an endangered species in the Basque Catalogue of Endangered Species of Wild and Marine Fauna and Flora (Official Gazette of the Basque Country (BOPV) no. 37, of February 23, 2011).
The distribution of Zostera noltei seagrass meadows has been documented by means of sampling campaigns carried out in estuaries where the species is naturally present (Oka, Lea and Bidasoa estuaries) and where it has been introduced through restoration work using root balls and by sowing seeds (Butron and Oria estuaries). Data on position, patch size and relative density were collected during the sampling campaigns. Position and altitude data were collected using a high-precision Trimble R6 GPS (Figure2).
Figure 2. Images of mapping data taken with a Trimble R6 GPS. Map showing estuaries on the Basque coast where Zostera noltei meadows have been mapped in green circles.
Sampling was carried out in summer and autumn 2021. Once all the sampling has been carried out, the GPS data are incorporated into a geographic information system (GIS) where the polygons corresponding to the identified patches are being delimited, assigning the sizes and densities observed in the field to them (Figure3).
Figure 3. View of the 5 estuaries where Zostera noltei patches have been mapped (data points are shown in orange on the maps). Estuaries of A) Butron; B) Oria; C) Lea; D) Bidasoa; E) Oka.
The total area mapped in the 2021 campaign was 56.47 ha. Most of this area was around the Oka estuary (47.75 ha). New areas were located in this estuary that had not been mapped in previous campaigns: Murueta, Portuondo and San Antonio, as they were previously unknown.
The trend analysis was carried out by comparing the distribution data collected in the 2021 mapping with the data from the 2008 and 2012 mappings (Garmendia et al. 2013).
Garmendia, J. M., M. Valle, Á. Borja, G. Chust, and J. Franco. 2013. Cartografía de Zostera noltii en la costa vasca: cambios recientes en su distribución (2008-2012). Revista de Investigación Marina, AZTI-Tecnalia 20:1-22.
Valle, M., G. Chust, A. del Campo, M. S. Wisz, S. M. Olsen, J. M. Garmendia, and Á. Borja. 2014. Projecting future distribution of the seagrass Zostera noltii under global warming and sea level rise. Biological Conservation 170:74-85.
