Just as trees on land have seasonal growth in the spring and die back, losing their leaves in the fall, so there are seasons in the North Atlantic that affect the growth of marine plants. As spring comes, tiny microscopic marine plants in the top 100 meters of the water column called phytoplankton rapidly grow in response to sunlight, and form the basis of the food chain as they are eaten by zooplankton, which is in turn eaten by other forms of marinelife. The North Atlantic has diverse and varied marine plants, from the small commercially important red seaweed called Irish moss, to big 10-meter-long- broadleaf kelps, to the pink corallike red algae found encrusting rocks in the low intertidal zone. These marine plants, also called algaes, are grazed on by marine snails, sea urchins and other invertebrates, and some fish, which are in turn eaten by larger fish, birds and mammals.
As well as supplying food, the forests of marine algae along the seashore provide places for marine animals to lay eggs, and hiding places for young and vulnerable animals. Lobster when young will use algae as cover, and it is thought that periodic overgrazing of kelp cover by sea urchins leads to increased predatation of young lobster, and subsequently smaller lobster harvests. Seaweeds absorb organic material from seawater and, using the sun's energy plus carbon dioxide in the water, undergo photosynthesis, which results in production of oxygen, energy and growth. A large part of the earth's oxygen supply comes from marine plants.
Marine plants are classified by color as belonging to the red, brown or green algae family. There are hundreds of varieties found inshore along the North Atlantic coastline, some of which, like dulse, are edible. Seaweeds tend to be simpler in structure than terrestrial plants, lacking a circulatory system (like the rings of a tree) because they are bathed in nutrient rich seawater. Some marine plants, such as eelgrass, produce seeds and flowers. The base of the algae does not transfer as in land plants, instead its main function is to anchor the plant, hence the term holdfast for this structure. Algal holdfasts are often good places to look for small invertebrates. The holdfast is attached to a shaft termed the stipe, which connects the blades or fronds of the plant, the location of most of the photosynthetic activity and a common place for snails and other small invertebrates. The plant body can be a wide variety of shapes and sizes, such as stringlike, colanderlike, cylindrical or branched, and often the common name reflects this, as in sea lettuce or cordweed. |
