Balearic seaweeds

Seaweeds are a key element of our marine ecosystems; a distinctive feature of our seascapes. They provide food and shelter to several creatures; sequester carbon and other nutrients; oxygenate coastal waters and neutralize ocean acidification. Yet they remain as one of the least known elements of our seas. Let’s learn more about them and some of the species living in the Balearic waters.

Seaweeds differ from plants in that they don’t have differentiated tissues. Unlike marine plants like the seagrass Posidonia oceanica, seaweeds do not have root, stem, leaves, flowers and fruits. Instead they absorb nutrients through their leaf-like tissues.

Seaweed are mainly found in coastal environments as they need light to survive. Based on their color they are classified as green, brown and red algae. Brown and red seaweed have extra pigments allowing them to photosynthesize at higher water depths.

We can learn lots about the state of marine ecosystems throughout seaweed. Some green algae like Ulva and Enteromorpha are fast-growers and can sign an excess of nutrients in water; whereas the presence of brown algae like Cystoseirais often a good indicator of water quality. Some calcareous red algae look like stones often referred to as “rhodolith” and form one of the most fragile and richly diverse marine habitats in Mediterranean waters.

Seaweed species around the Balearic Islands can have a native or invasive origin. Some common native species include: 

• Caulerpa prolifera (green): found in shallow muddy sediments of less than 20 m. Present in Pollença, Alcúdia, Portocolom, Fornells, Addaia, Talamanca and Estany des Peix;
• Cystoseira (brown): needs good seawater quality to grow and therefore can serve as a bioindicator. Some of their species contain air vesicles in their structures that helps them to stand strong currents;
• coralline algae Phymatholithon, Lithothamnion, Lythophyllum (red): found up to 100 m water depth. The carbonates stored in their cell walls gives them a pink stone-like appearance. They form maërl beds a scenic and rich habitat protected by law.

Observations of invasive species around the Balearic Islands were reported more than 30 years ago. Invasive species may arrive in many ways, such as water filters from some aquariums, ballast water from ships, or transported in anchors. Rising water temperatures has favored the spread of invasive species. Some examples of invasive species common in the Balearics include:

• Acrothamnion preissii (red): of Indo-Pacific origin, filamentous, colonizes other vegetation by forming dense cotton-like mats, found between 5–70m water depth in all the islands;
• Asparagopsis taxiformis (red): from west Australia, observed in all the Balearic islands mostly within 10–30m, low invasive potential;
• Caulerpa cylindracea (green): from southwest Australia, it has one of the highest invasive potential of the Balearic Sea, most commonly found within 40–45 m;
• Halimeda incrassata (green): from the Atlantic and Indo-Pacific oceans, calcareous, can threaten the native ecosystem, found in southwestern Mallorca and Cabrera;
• Lophocladia lallemandii (red): from the Red Sea, found in all islands up to 25 m;
• Womersleyella setacea (red): Hawaiian Islands origin, filamentous, produces biodiversity loss in coralligeneous habitats, found in all the islands within 25–45 m.

Keeping an eye on the arrival and expansion of invasive seaweed species is important as they can rapidly transform our marine habitats and have the potential to have a big impact on fish populations and diversity of species. Tracking the presence and occurrence of invasive species in Balearic waters is the aim of “Invasive seaweed” (Algas Invasoras) project of the Marine Citizen Science platform www.observadoresdelmar.es. Marilles Foundation is working closely with Observadores del Mar (SeaWatchers) to develop a broad marine citizen science programme in the Balearics.