# Mapping Subtidal Marine Forests in the Mediterranean Sea Using Copernicus Contributing Mission
###### Abstract  
Mediterranean subtidal reefs host ecologically significant habitats, including forests of _Cystoseira_ spp., which form complex benthic communities within the photic zone. These habitats are increasingly degraded due to climate change, invasive species, and anthropogenic pressures, particularly in the eastern Mediterranean. In support of habitat monitoring under the EU Natura 2000 directive and the Nature Restoration Regulation, this study investigates the utility of high-resolution satellite remote sensing for mapping subtidal brown algae and associated benthic classes. Using imagery from the SuperDove sensor (Planet Labs, San Francisco, CA, USA), we developed an integrated mapping workflow at the Natura 2000 site GR2420009. Aquatic reflectance was derived using ACOLITE v.20250114.0, and both supervised classification and spectral unmixing were implemented in the EnMAP Toolbox v.3.16.3 within QGIS. A Random Forest classifier (100 fully grown trees) achieved high thematic accuracy across all habitat types (F1 scores: 0.87-1.00), with perfect classification of shallow soft bottoms and strong performance for _Cystoseira_ s.l. (F1 = 0.94) and _Seagrass_ (F1 = 0.93). Spectral unmixing further enabled quantitative estimation of fractional cover, with high predictive accuracy for deep soft bottoms (R\({}^{2}\) = 0.99; RPD = 18.66), shallow soft bottoms (R\({}^{2}\) = 0.98; RPD = 8.72), _Seagrass_ (R\({}^{2}\) = 0.88; RPD = 3.01) and _Cystoseira_ s.l. (R\({}^{2}\) = 0.82; RPD = 2.37). The lower performance for rocky reefs with other cover (R\({}^{2}\) = 0.71) reflects spectral heterogeneity and shadowing effects. The results highlight the effectiveness of combining classification and unmixing approaches for benthic habitat mapping using CubeSat constellations, offering scalable tools for large-area monitoring and ecosystem assessment. Despite challenges in field data acquisition, the presented framework provides a robust foundation for remote sensing-based conservation planning in optically shallow marine environments. brown algae; coastal reefs; Earth observation; climate change 2025172398  
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in biodiversity, habitat complexity, and trophic stability due to these combined stressors. Coral reefs, kelp forests, and _Seagrass_ meadows are particularly vulnerable, with some regions already experiencing severe degradation [3; 4]. Coastal communities dependent on fisheries and tourism are especially at risk due to declining fish stocks and habitat loss [5]. The Mediterranean Sea, a global biodiversity hotspot, is disproportionally affected by climate change [6; 7; 8; 9; 10; 11; 12]. Marine heat waves, invasive species, and habitat loss due to coastal development linked to tourism are key factors shaping the current situation [12; 13]. Shallow reefs, once supporting rich biodiversity, have seen a decline in foundation species notably within the order Fucales, [PERSON], 1827, particularly the _Cystoseira_ genus, [PERSON], 1820, _Sensu lato_ (s.l. ), which includes the _Cystoseira_, _Ericaria_, and _Gongolaria_ genera. _Cystoseira_ s.l. forests are among the most important foundation species in the shallow rocky reefs of the Mediterranean Sea and the warm temperate northeast Atlantic Ocean [14]. They create complex habitats and are essential for biodiversity and ecosystem functioning. In the Mediterranean Sea, approximately two-thirds of the estimated 28 _Cystoseira_ s.l. species are endemic, with new species still being described [15; 16]. Over the last few decades, Mediterranean _Cystoseira_ s.l. populations have sharply declined due to human and climate-driven pressures [17]. Recent studies have highlighted the vulnerability of _Cystoseira_ s.l. species to habitat destruction, eutrophication, pollution, invasive species, and trophic cascades from overfishing [18]. Most of the _Cystoseira_ s.l.