Seaweeds are another important group of plants in Long Island waters.  Seaweeds (a.k.a. – macroalgae) are a diverse group of organisms represented by a wide range of growth forms.  In general, seaweeds are divided into 3 groups based on their color – green, brown or red – though even within groups, color ranges greatly.  While seaweeds share some characteristics of “higher” plants, they lack the complex reproductive structures (flowers) and specialized functional tissues (roots, stems, and leaves) of seagrasses and land plants.  Seaweeds reproduce asexually (vegetative growth) and sexually (release of spores).  Seaweeds also display a wide range of growth strategies.  Some species, especially green seaweeds grow rapidly in response to nutrients (nitrogen) and may “bloom” in nutrient rich waters, only to reproduce and die after all the nutrients have been depleted.  Other species are more perennial.  These perennial species either never seem to die back (almost like evergreens) or die back under adverse conditions (e.g., high water temperatures, low light, etc.) but regrow when stress is alleviated.

Seaweeds are found in all of our coastal waters, with over 100 species represented.  Most seaweeds require a hard surface to which they can anchor, like rocks and shells, however, there are a few species that can be found over mud or sandy bottoms in the quiet back bays and creeks.  Seaweeds, like eelgrass, have the potential to form extensive beds that provide structure and habitat for marine animals.  Bed-forming seaweeds on Long Island include the perennial, brown seaweeds Sargassum (gulfweed) and Laminaria (kelp).  Long Island also supports seaweed species that are non-native and invasive.  The first documented seaweed invasion on Long Island was by the green seaweed Codium (oysterthief, Sputnik-weed, deadman’s fingers) in 1957 in Orient Harbor.  The most recent introduction of a non-native seaweed was the discovery of the red seaweed Grateloupia on Montauk Point in 2001.  Currently, Long Island supports seven species of seaweed that are thought to be non-native.