Marine algae are among the most ancient members of the plant kingdom, and vital components of the ecosystem of marine life. These plants are abundant in coastal areas, usually anchoring themselves to a hard surface using specialized “holdfast” structures. These structures are not true roots, and there are also no true shoots, leaves, seeds, water-conducting tissues, or flowers. Species can range in size from very small (3 -10 microns) to very large (over 200 feet long) and some can grow more than 10 inches per day. The three best known types of marine algae are red algae (Rhodophyta), green algae (Chlorophyta and others) and brown algae (Phaeophyceae).

Sargassum Algae

Sargassum Algae

In the Gulf of Mexico, marine algae play an irreplaceable role in maintaining marine life and habitats. In reef environments, some species of red algae “exceed corals in importance as reef building organisms.”[1] Hence, the term “tropical reef” is sometimes used instead of "coral reef" to reflect this diversity.

Marine algae often live alongside seagrasses, which have flattened leaves that allow easy attachment for the algae. These two types of plants combine to create diverse ecosystems. Marine animals use these mats of algae and seagrass to rest, spawn, feed, and hide from predators. Examples of such animals are pipefish and snapper, shrimps and crabs, and tiny snails and clams.

Zooxanthellae

Zooxanthellae

A common species of brown algae in the Gulf of Mexico is Sargassum. This brown alga lends its name to the Sargasso Sea, a region in the North Atlantic Ocean between North America and Africa where large mats of Sargassum are concentrated. Some Sargassum species, like that in the Sargasso Sea, never anchor; other species attach to hard surfaces in shallow waters, near coral reefs and in mangrove thickets. Sargassum can be considered a habitat in addition to a species because fish and other animals use it as a refuge, as is true for other marine plants. There are actually several species of animals – crabs, shrimps, snails, and even a nudibranch – that live no where else. Since the oil spill, oily patches of Sargassum have been reported washing ashore on Gulf coastlines. The animals that take refuge in these plants will likely die from either the physical effects of the oil or from ingesting the oily residue that clings to the algae.

Some marine algae are necessary for coral growth. Many reef-building coral species have algal cells called zooxanthellae that live within its tissues in a symbiotic relationship. The zooxanthellae photosynthesize and provide supplemental energy to the coral. "Bleached" corals that have lost their zooxanthellae (through disease or stress) often die as a result.

Algae can also be detrimental to coral growth. If marine algae are allowed to physically overgrow the coral, shading it from sunlight, the zooxanthellae can die or leave the coral, in turn putting the coral at risk. Overgrowth of algae can be caused by increased nutrients in the water or by decreased populations of animals (such as sea urchins) that normally graze upon the algae.

Resources for marine algae

[1]“Gulf of Mexico: Origin, Waters, and Biota, Volume 1 – Biodiversity, edited by D. L. Felder and D. K. Camp, Texas A&M Press, 2009, pg 189