Seaweed
"Seaweed" is a colloquial term and lacks a formal definition. A seaweed may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae. As these three groups do not have a common multicellular ancestor, the seaweed are in a polyphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered to be seaweed.
Zostera muelleri
Seagrasses are a flowering plant species, not to be confused with seaweed, which do not form flowers, fruits, and seeds to reproduce. Seagrasses are important to the marine ecosystem for many reasons. For one, they provide food, homes, and breeding grounds to a variety of marine species. Secondly, meadows of seagrass are important carbon reservoirs or sinks, sequestering 10-18% of the ocean's carbon accumulation for long-term storage. Seagrasses also enhance sediment accretion, and protect coastlines from destructive wave energy.