Cascais, Mafra, Sintra I Scientific Expedition

A Unique Sea on the Doorstep of Portugal’s Capital

A woman in a green jacket examines a device on a boat, aided by a man in a blue fishing outfit. They appear focused and engaged in their task.

The coast between Cascais, Mafra and Sintra holds one of Portugal’s most valuable, yet least known, marine natural heritages. With diverse ecosystems, intense human pressures, and exceptional ecological, economic and social importance, this region represents a unique opportunity to align marine conservation with sustainable development.

In October 2022, Oceano Azul Foundation, in partnership with the municipalities of Cascais, Mafra, and Sintra, led the largest scientific expedition ever undertaken in this area: the Oceano Azul Expedition – Cascais | Mafra | Sintra. Its goal: to study and protect this marine territory, and to lay the groundwork for a Community-led Marine Protected Area.

For 12 days, a multidisciplinary team of 58 scientists from 7 national institutions, 17 local fishers, institutional partners and over 150 participants sailed aboard the Santa Maria Manuela to study the region’s biodiversity and habitats. Collaboration with the fishing communities of Ericeira and Cascais was a cornerstone of the expedition – a living example of how science and traditional knowledge can move forward together. The expedition was also supported by the Government of Portugal, reinforcing the role of science in shaping public policy.

Santa Maria Manuela vessel
© Oceano Azul Foundation _ Nuno Vasco Rodrigues

Why this sea matters

Unique ecosystems – including beaches, intertidal zones, rocky reefs, seamounts and shelf habitats.
High human pressure – proximity to major urban centers makes monitoring and protection essential.
Natural and economic value – biodiversity here sustains livelihoods through fishing, coastal tourism and recreation.

Scientific components

1. Intertidal zone

Surface observations at low tide using drones, transects and sampling grids to catalogue flora and fauna (algae, invertebrates, fish) and map intertidal communities.

Two divers in wetsuits and scuba gear study an underwater grid on a seabed

2. Coastal benthic ecosystems (5–100 m depth)

Diving surveys, baited remote underwater video systems (BRUVS) and remotely operated vehicles (ROVs) to study fauna, flora and habitats such as kelp forests, Sabellaria reefs, gorgonian gardens and coral–sponge communities.

3. Coastal pelagic ecosystems (water column up to 12 m depth)

Seabird and marine mammal censuses (ESAS methodology), complemented by pelagic BRUVS to record fish, cetaceans and megafauna.

Natural values identified

Marine environments influenced by key systems such as the Camões Seamount, Tagus Estuary, and the Nazaré and Lisbon–Setúbal canyons.
Hundreds of marine species, including threatened and ecologically or commercially important species.
Priority habitats protected under EU directives: Sabellaria reefs, kelp forests, gorgonian gardens.
20 species of seabirds recorded, including four threatened in Portugal: the European storm petrel, Cory’s shearwater, Balearic shearwater and common tern.
Sightings of dolphins, including bottlenose and common dolphins.

From discovery to commitment

The expedition’s findings are consolidated in a scientific report, providing the technical foundation for the proposed Marine Protected Area of Community Interest – Cascais | Mafra | Sintra.

This document confirms the region’s ecological richness, identifies priority habitats and species for conservation, and equips civil society, municipalities and Government with the knowledge needed to move forward with the participatory process that will secure lasting protection.

Read the Expedition’s scientific report

Putting the ocean at center stage

The expedition was also conceived as an opportunity to bring visibility to the sea of Cascais, Mafra and Sintra – a natural heritage still unknown to many.

The documentary produced during the expedition showcases the scientists, fishers and discoveries made during the mission. More than a record, it positions the ocean as part of the identity of this dynamic region, and highlights how marine protection can and must begin with local communities.