Ria de Aveiro Coastal Lagoon

Ria de Aveiro is a shallow coastal lagoon located on the northwest coast of Portugal, near the city of Aveiro. Formed by the Vouga River and connected to the Atlantic Ocean through an artificial inlet, the lagoon is characterized by a complex network of channels, mudflats, and salt marshes. Its wide intertidal zones host extensive seagrass meadows, mainly composed of Zostera noltei, which are most abundant in the inner, sheltered areas of the lagoon. These meadows are typically visible at low tide and contribute to the high ecological value of the system. As shown in Figure 1, the area considered in this study spans approximately 12 km², spread over 14 study sites. Study sites have been chosen to match sites of Sousa et al. (2019)

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⚠️ Warning

The Ria de Aveiro Lagoon meadows are not monospecific! The intertidal mask for this site was created by photointerpreting the presence of seagrass from Sentinel-2 images; therefore, other types of vegetation may have been included in the analysis.

Figure 1: Intertidal Mask of Ria de Aveiro

For this site, a time series of the Sentinel-2 missions has been used to monitor the seagrass meadow since 2017 (Table 1). This work was published by Zoffoli et al. (2021). The present work updates the time series from Zoffoli et al. (2021) by incorporating newly available images and computing additional metrics (see Methodology).

Table 1

Date	Capteur	Date	Capteur	Date	Capteur
juillet 24, 2017	Sentinel-2	juillet 26, 2020	Sentinel-2	août 05, 2023	Sentinel-2
juillet 17, 2018	Sentinel-2	juillet 13, 2021	Sentinel-2	juillet 22, 2024	Sentinel-2
août 03, 2019	Sentinel-2	juillet 31, 2022	Sentinel-2

List of Satellite images used to follow the meadows in Aveiro Lagoon

Figure 2: Seagrass Cover in Percent over the years of the meadow of Ria de Aveiro Lagoon. Only pixels with an SPC above 20 % are displayed.

Figure 2 is show the evolution of the Seagrass Cover over time, since 20175. The minimum density was recorded in 2022 with 40% of average cover, while the maximum density has been recorded in 2024 with 51% of average cover.

Figure 3: Boxplot of SPC for each site of Aveiro Lagoon.

Historical seagrass patches of the meadow

Figure 4: Consecutive years with ≥50% seagrass cover since 2024. The value X for each pixel indicates that the meadow has maintained a Seagrass Percentage Cover (SPC) above 50% every year for the past X years, counting backward from 2024.

Year of the maximum of cover

Figure 5: Map of the year of maximum cover of the meadow

Figure 6: Area of the meadow reaching its maximum cover value ever for each year.

Rate of decline since the date of maximum

Figure 7: Map of the rate of decline (in Percent Cover per Year) since the date of maximum shown in Figure 5

Amount of time above 50% since the start of the time serie

Figure 8: Map of the amount of time each pixel had SPC values above 50% since the start of the time serie