ALGAE

Algae are incredibly widespread and diverse, with several hundred species being recorded in the Mediterranean, and more being discovered each year as migrants from other, more distant seas. Some are single-celled, living in the tissue of some hard coral polyps, others are multicellular, spreading over rocky surfaces. Many grow in tufts and some are so delicate, it is hard to imagine that they are in fact algae. Most species have specific predators, which browse on them, such as fish, sea urchins or snails. Algae can be split into three groups depending on their pigmentation. These are green, red and brown algae, most of which have relatives in other oceans of the world.

GREEN ALGAE

CHLOROPHYTA or MERMAID’S CUP

Acetabularia mediterranea

This unmistakable alga consists of clumps of thin green or white stalks topped with a thallus of a light green, rayed disc hardened by encrusted limestone. Umbrella shaped, it grows around 8cm (3in) tall with the disc being around 1.2cm (½in). In the growing season, it is preyed upon by various wrasse and bream species which eat the tops, leaving many empty stalks. Large clumps are concentrated on a stone or rocky substrate. It is quite often found on the lower shore and can grow as deep as 30m (100ft).

COMMON CAULERPA

Caulerpa prolifera

This indigenous species of Caulerpa is still fairly common around the Mediterranean, particularly in southern and central areas where its cousin C. taxifolia (see below) is not as rampant as it is in the north. The two species have similar ways of spreading over all substrata by way of a common robust stolon or stalk. C. prolifera has wide branching blades protruding perpendicularly into the water. The blades reach over 15cm (6in) long and can be as broad as 13cm (5cm). C. prolifera is also very common in the Caribbean and is one of the species favoured by marine aquarists.

CREEPING CAULERPA

Caulerpa racemosa var. occidentalis

This is another highly invasive species, originally thought to have come through the Suez Canal from the Red Sea. However, indications are that the species is actually Australian in origin. Interestingly, C. racemosa is very prolific in the Caribbean and is located as far north in the Atlantic as Bermuda. It is also common in the Pacific and is used as a food source by Polynesians, who eat it raw with grated coconut and coconut milk. This alga spreads by means of long stolons. Its racemous rhyzoids point downwards and photosynthesis occurs in the clustered aggregations, which reach around 5cm (2in) in height. Bright green, with rounded lobes to each branch, this species appears to be both warm- and cold-water tolerant, occurring from 5m (17ft) to over 50m (165ft) depths.

CARPET ALGA

Caulerpa taxifolia

First introduced accidentally in 1984 in Monaco, this virulent alga has leaves that are small and paired, with the new growth being a pale green or even yellow. With no natural predators in the region, it is growing at such an alarming rate that the entire Mediterranean is at risk. It spreads from a single stalk, and the enzyme in the alga is toxic. Leaves can be from 6–65cm (2½in–2ft 2in) long and in 1m² (11 sq ft) of seabed an individual plant can have a stolon of over 3m (10ft) in length, with over 200 leaf fronds; in total, over 220m (240yd) of plant with 8,000 leafy fronds weighing 12kg (26lb) have been found in 1m² of new Caulerpa meadow. Caulerpa taxifolia is very similar to Caulerpa sertularoides, which is often used in salads in the Philippines and is not in the least bit toxic.

FINGER CODIUM

Codium vermilara

Noted by the small clumps of ‘fuzzy’ fingers, this alga has a common root stalk and branches widely at its base to form many small rounded clumps of stalks. Quite often coated in a filamentous, slimy alga, Finger Codium is grazed on by a few species of nudibranch. This species enjoys aerated, shallow water conditions where wave surge and high light are present.

PURSE CODIUM

Codium bursa

Unmistakable rounded shape in various shades of green. Growing up to 40cm (1ft 4in) in diameter, as it gets older, the more uniform spherical ball develops a central depression. Found singularly or in small groups of various sizes on a rocky substrate, the exterior of the alga can get rather scruffy in appearance and quite often has other species of algae adhered to its surface.

SEA CACTUS

Halimeda tuna

Very similar in formation to Halimeda species found in the Caribbean, the Sea Cactus is made up of a series of distinct small rounded discs approximately 10cm (4in) long, which are joined together by a narrow strand. Coloured from a pale brownish-green to a brilliant green of new growth, the plant resembles the terrestrial ‘Prickly Pear Cactus’. Often found under overhangs, it prefers shaded or deeper water conditions.

SEA FAN

Udotea petiolata

Typically fan-shaped with a convoluted, rounded edge, attached to rocky surfaces by a short peduncle. Quite often, there are darker green growth lines over the leaf which can grow up to 10cm (4in) high and during reproduction, the outer edge is tinged white. Growing in clumps and widely spread out over rocks, this alga is photo-phobic, preferring shallow light-filled, warm water. It is found in depths from 5 to 10m (17–33ft).

RED ALGAE

RHODOPHYTA or ROUGH CORAL MOSS

Corallina elongata

Red or pale-pink seaweed made up of calcified parts loosely connected into a feather-like shape. Whilst growing, the new growth may appear lighter in colour than the stem. Often growing through other species of algae and small sponges, the tips of the ‘feathers’ are quite often all that you may see. However, it can also grow to form quite dense carpets of algae. Preferring shallow water, the fronds are 2–6cm (¾–2½in) long. It is able to resist rough seas and moderate pollution. This alga, when dried, was formerly used medicinally with other red algae for the treatment of intestinal worms.

JANIA

Jania rubens

Similar in structure to Corallina elongata, but much paler and thinner, Jania rubens comprises a large clump of calcareous and jointed fronds, which branch off dichotomously. The reproductive organs are in the form of a swelling at the joints and difficult to see. Growing from 1.5 to 4cm (½–1½in) in diameter, the rosy red alga forms circular clumps in shallow water and is quite often associated with numerous other algae which it tends to colonize.

STONE WEED

Lithophyllum lichonoides

Sometimes referred to as footpath alga or ‘trattoirs’, Stone Weed is strongly calcified and is common in surface waters where it forms a developing rim or cornice around shoreline rocks. The growth is determined by tidal movement and the cornices can be quite wide. Wherever it occurs in deeper water, it can be found on rocky bottoms in areas of strong tidal movement. Coral-like, with numerous hard and flattened fronds, it is purple in colour with white or pink new growth lines at the edges. It is very tolerant of wave action, preferring shallow water where it can become exposed at low tide. Similar in shape to Pseudolithophyllum expansum, the individual parts of this alga grow to around 7cm (2¾in) and fuse with other, similar-sized parts to form a large ‘reef-like’ structure.

SEA ROSE

Peyssonnelia squamaria

Bright and colourful, the Sea Rose is brownish-red in colour and each part forms a small fan progressively getting larger as the fan grows out in petal-like formations. Pale yellow at the base of each petal, striated lines grow stronger in colour as they expand to the outer rim. Often appearing almost luminescent underwater, each rose may grow as much as 10cm (4in) in diameter and is often associated with a brilliant green alga. This colourful species prefers low light conditions either at the entrances to caves and caverns or on poorly illuminated hard rock bottoms where its range can extend to over 50m (165ft) depth.

SEA MAT

Pseudolithophyllum expansum

The sea mat is quite distinctive in shape and colour form, being a pale purplish-pink with a light outer rim. This very hard coralline alga encrusts large areas of poor light and is found on most rocky substrates from shallow waters down to over 60m (200ft). The growing edge of the alga can be deeply convoluted and is one of the contributory alga, which forms the Mediterranean reefs, cementing detritus, algae and rock together.

RED SEAWEED

Sphaerococcus coronpifolius

This species is particularly common in most coastal regions of the Mediterranean. Dark ruby red in colour and forming small clumps widely branching from a single stalk, these seaweeds prefer well-aerated, light-filled, shallow water. Quite often, wherever there has been damage to the rock surface by anchor or boat groundings, this alga is one of the first to take hold. Extremely opportunistic, it is not uncommon for entire rocky surface areas to be dominated by this quick-growing alga.

BROWN ALGAE

PHAEOPHYTA or FORKED RIBBONS

Dictyota dichotoma

This is a delicate alga, the green chlorophyll masked by brown pigments, changing to a brilliant iridescent blue at the outer edge of its tips. Usually only growing to around 15cm (6in) high with dichotomously branching, ribbon-like fronds 2–12mm (¹/₁₀–½in) wide. With no mid rib to support the alga, it wafts in whatever current assails it. Fragile in nature, it is easily broken apart or knocked off its rocky base sand. Quite often found washed up on the shore.

SEA FERN

Halopteris scoporici

Widespread on all well-illuminated rock surfaces in central and eastern Mediterranean regions, the Sea Fern grows to around 15–20cm (6–8in) tall and has a thick, dark brown (almost black), single stalk branching to dense feather-like tufts which are rough in texture. Found in all depths, this alga is often overgrown by other species.

PEACOCK’S TAIL

Padina pavonica

Calcareous in nature, the fronds have a parchment-like feel to them. Each frond is flat and fan-shaped, changing to become funnel-like as it matures. Coloured light brown to white, it has darker, horizontal, striped growth lines. Tolerant of some freshwater run-off, it is quite often found on jetty slipways and pilings. Enjoying sunlight and warm calm waters, it is rarely found below 20m (66ft).

COMMON SARGASSUM

Sargassum vulgare

Sargassum weed can grow up to 1m (3ft 3in) in height and is widely distributed around the Mediterranean. It is fast growing and attaches to a rocky substrate. It has long, crinkly fronds with short, lateral, leaf-like structure branches, interspersed with small air bladders. It will tolerate some pollution and if broken free from its rocky base, the alga survives quite happily on surface waters buoyed by its air bladders. It provides a home and shelter for many small pelagic creatures.