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Green grow the grasses beneath the waves

Considering that grasses now represent about 20 percent of Earth’s vegetational cover, it may not be so surprising that some grasses saw the future and chose not to compete. Our local surfgrass (Phyllospadix scouleri) and eelgrass (Zostera marina) species, though not true grasses, are thought to have evolved from terrestrial plants that invaded the sea 140 to 40 million years ago. In other words, though all land plants first evolved from the sea, seagrasses returned to their roots, as it were. Being true-rooted, flowering plants (kelp and other algae have no such characteristics), seagrasses self-pollinate, then eject their seeds while completely submerged. While many people have trouble telling surfgrass from eelgrass, there are clear distinctions.

Surfgrass is found where surf and rocks abound. During low tides it may be exposed to air where the brilliant, shiny emerald-green strands, which grow to 4 feet tall, densely carpet nearshore rocks and boulders. Under the water’s surface, tidal surge and swell whip up the long blades to shape them into verdant wave shapes that mimic the look of water waves. The lush grass copes with its turbulent surroundings via each individual strand’s awesome anchoring powers. Each strand’s base comprises tangled, brown roots that weld like concrete to rock substrate. The individual, compressed (1/16-inch wide) blades flex easily with little resistance. Shapewise, surfgass strands somewhat resemble fine spaghettini noodles. When I enter the water at the Cove and a set of waves rolls in, I dive down and grab onto a hunk of surfgrass, confident that I won’t be washed back to shore. It’s a strategy that works every time.

Contrarily, eelgrass generates tranquil, grassy islands or oases in the white sand expanse off La Jolla Shores. Growing in bundles on the sheltered bottom at 25 to 50 feet deep, individual blades grow to 3 feet tall and measure 1/8-inch wide. Shapewise, eelgrass strands somewhat resemble flat, wide fettuccini noodles. The stem of each bundle is loosely submerged in sand, where it is further anchored by many fine roots. Although eelgrass grows well beyond the breaking waves, surge from heavy surf may uproot these delicately positioned plants so beach walkers may see some wash in.

As with all plant life, seagrasses provide food and substrate to a variety of animals. Like many local plants at this season, seagrasses are also not in bloom. Come summer, they will send up flowers but none that are colorful or fragrant because, as self-pollinators, they have no need to attract birds or bees.

To find surfgrass flowers, move in close and wade through the strands to discover singular green blades with individual brown seedpods attached.

To locate eelgrass flowers, maintain some distance and look for seedpod structures that project a foot above the grass meadows themselves.

Once seagrass seeds have developed, the pods burst open and the numerous seeds pop out, drop down and root within 3 feet of where they were ejected. This is a particularly good trick for grasses in the surfzone. The reseeding method is not obvious for surfgrass because of its rocky and otherwise chaotic environment, but it explains why eelgrass forms distinct islands. Each island is composed of a solitary plant, its progeny, their progeny and so on.

Seagrasses are an important food source for many animals such as snails, some fish, birds and mammals, and they play a critical role in providing a safe haven for various animals to hide, hunt and reproduce. Cormorant birds use surfgrass to build their nests, as can be seen in their rookery area above the caves. These attributes aside, we want to be mindful of seagrasses because their sensitivity to pollution makes them an excellent barometer of the health of the nearshore environment.


— Judith Lea Garfield, naturalist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. Send comments to