Common Types of Marine Algae

Algae are not true plants, but form a kingdom of their own; however, they are just as important as plants to any reef set-up. Some colonize rocks, while others live within anemones, providing them with nourishment and utilizing their waste. Small encrusting and filamentous algal species may be inadvertently introduced to the aquarium, along with tiny invertebrates, when adding rock collected from the sea. The larger, more decorative varieties, as pictured below, are sold like freshwater plants.

Green, brown, or red algae are beneficial to the tank, and many invertebrates and fish love grazing on them. However, the development of film-like, brownish-purple algae can indicate a variety of problems in the aquarium, including overstocking, poor water quality, overfeeding, or incorrect lighting. Promptly siphon out this type of algal growth and rectify the causes.

Algae need strong light, the waste products from fish and invertebrates, and various trace elements found in seawater. Of all algae, members of the genus Caulerpa are the most numerous; these can be difficult to identify, since a single species may assume different forms. Factors such lighting, substrate, and nutrients all contribute to this diversity of growth. Some species of algae are sensitive to temperature changes, with a 5°C (9°F) fluctuation proving fatal, while others, such as Caulerpa prolifera, can withstand substantial variation.

Caulerpa prolifera
The most commonly seen green algae in marine aquaria, this hardy species is ideal for novices, although, once established, it can become rampant! Maintain control with regular harvests.

Codiacea spp. Calcareous Algae
Calcareous Algae are so-called because they absorb calcium from seawater to reinforce their leaves, a process that makes them more rigid than Caulerpa species. Given strong lighting and high pH levels, they are easy to keep.

Rhodophyceae spp. Red Algae
Red Algae are firm favourites, since they contrast well in a reef aquarium. In healthy plants, the red color extends to the very edges of the fronds. Specimens are best purchased attached to a rock, but even so can be difficult to maintain.

Pencillus Capitatus Shaving Brush
Popular for its unusual shape, this algae is usually imported from the Caribbean, where it is found on sand or mud substrates. Before buying a specimen, check that it is undamaged. With luck, it will propagate via small shoots near the base.

Valonia Ventricosa Sailor's Eyeballs
Each of the ball-shaped growths on this alga is a single cell reaching up to 5 cm (2 in) in diameter, the largest single-celled development in nature. The cells are readily punctured; take extra care when handling the plant or working in the tank.