The majority of plants that are found in the ocean are in the surface zone. This zone, also called the sunlit zone, extends approximately 650 feet and is characterized by the amount of sunlight that passes through it. At this level, there is enough sunlight for plants to conduct photosynthesis. Beyond that, the sunlight continues to penetrate but not enough for plants to comfortably thrive.
Kelp is the largest member of the algae family. It resembles some land plants in that they have long bladed leaves, but they also have bladders that help keep them afloat. A long-lived plant, a strand of kelp can live up to 10 years, with individual blades that are replaced every few months.
Kelp form one of the most impressive underwater sights, the kelp forests. These forests, just like land forests, have a number of different layers from the canopy to the forest floor. These forests shelter an entire ecosystem, providing food and shelter for a number of different marine animals from fish and shellfish to microscopic organisms.
Programs have been put in place to monitor these underwater forests to see if they can monitor the life cycles of long-lived ecosystems. Organizations such as the California Department of Fish and Game and the Channel Islands National Park are closely monitoring not only the kelp forests but also the life within.
Phytoplanktons are tiny, microscopic organisms that form one of the important building blocks for ocean life. These single-celled organisms are consumed by fish of all size, beginning a trend that continues up the food chain. Because they contain chlorophyll, phytoplanktons are green in color.
These organisms are found at the surface because, like land plants, they require sunlight and nutrients to survive. Fresh nutrients are supplied by the currents and tides and consequently are a good indicator as to ocean conditions. If the oceans are not sufficiently warm, new water does not come up to the surface and does not bring fresh nutrients with it. When the phytoplanktons begin to starve, they affect every other animal in the food chain; prolonged changes in the waters can be devastating.
Seagrasses are flowering grasses that are rooted in the sea floor and grow completely underwater. There are a number of different types, many of which thrive in the saltwater ocean environment. Because they need plenty of sunlight, they are mostly found along the shorelines in the shallows.
Not only do seagrasses provide food and shelter to a number of different marine animals including fish and insects, but they also help to maintain water clarity. Loose sand and silt is trapped in their grassy leaves, which also helps more sunlight penetrate the water. The roots of seagrasses also trap dirt and sand, helping to prevent coastal erosion.
Because of their close proximity to land, seagrasses are in danger from not only the boats that troll the shallows but also from pollution running off the land. Measuring the decline of the seagrasses can present a telling picture of the coastal environment as a whole.