Phyllospadix scouleri
Scouler’s Surfgrass Southern Alaska to Mexico
Family Potomogetonaceae

Surfgrass is not a seaweed, nor is it a grass. It is a flowering monocot in the family Potomogetonaceae. There are three species of Phyllospadix along the northern Pacific coastline, the most common of which is P. scouleri. You can identify it by its long, smooth and somewhat flattened leaves. The other two species, P. serrulatus and P. torreyi have, respectively, serrations along the leaf margins or round leaves. It also has three vascular bundles per leaf, one along the center and one near each margin. Phyllospadix serrulatus has five to seven. These, however, can only be seen with a microscope. The plant has rhizomes with numerous roots per node. It is usually attached to rocks in the mid- to lower intertidal zones. Sometimes sand will wash over the rocks, giving the appearance that the surfgrass is growing out of the sand. You may find large amounts of surfgrass washed onto the beaches after strong waves have dislodged it during winter storms. 
 

Zostera marina
Eel Grass
Alaska to Baja California
Family Zosteraceae

Eelgrass is one of the dominant and most important plants in Netarts Bay. There are two species of eelgrass in the bay, Zostera marina, a native, and Zostera japonica, an invasive species from Japan. Pictured are both, the larger native and the smaller invasive. Unlike most plants in the mudflats, eelgrass is not an alga or “seaweed.” Rather, it is a vascular plant, a monocot in the phylum Anthophyta and in the family Zosteraceae. Despite its common name, eelgrass, Zostera is not a true grass (true grasses are in the family Poaceae), but may be more closely related to lilies.

Eelgrasses mark the gradation from sea to wetland in Oregon's quiet bays and estuaries. They form dense beds that can cover acres of shallow bay bottom, their roots and rhizomes holding the sands and muds in place and providing both temporary and permanent homes for scores of associated plants and animals. Eelgrass beds are considered some of the most productive areas in estuaries, serving as a nursery for many invertebrates and fish.

Eelgrass is a primary producer that supplies and traps organic matter that provides food for animals and gives nutrients to algae. Primary productivity is a measure of the rate at which radiant energy (sunlight) is converted through photosynthesis by green plants to organic carbon – carbon that can then be used as food by both the plants and other organisms (see footnote). Primary productivity of Zostera marina has been measured at 1450 grams of carbon per square meter per year, almost as much as a field of alfalfa. In addition to making food, eelgrass furnishes shelter, protection, and a safe place to live to other organisms. During storms, Z. marina will break loose from the beds in Netarts Bay, wash into the ocean on the outgoing tide, and come ashore with the waves to the beach between Netarts and Oceanside in jumbled heaps and rows.

¹ This is a limited definition that ignores chemosythesis

Zostera japonica
Japanese or Dwarf Eel Grass
British Columbia to southern Oregon
Family Zosteraceae

The non-native Zostera japonica, once used as packing for imported Japanese oysters that were shipped to the United States from eastern Asia, was introduced to Washington State in the late 1950s (it was first observed in 1957) and has spread to estuaries in the Pacific Northwest from British Columbia to Southern Oregon. Called the dwarf eelgrass, it has a shorter and narrower blade than Z. marina and it grows at a higher elevation, above the 0.0 MLLW tide level, whereas Z. marina lives from a couple of feet above MLLW down to -30 feet. Dwarf eelgrass can be found on both sides of Netarts Bay in the mud and sand flats near its edges and on some of the high sand bars in the middle of the bay. In other Oregon estuaries, the two species of Zostera maintain their vertical separation, generally not mixing. The large, almost level tidal flats of Netarts Bay, however, allow the two eelgrasses to overlap, and Z. japonica can be found growing next to and sometimes intermingled with Z. marina (as shown in the picture).

Algal Symbionts in Sea Anemones

Though certainly not seaweeds, it is worth mentioning some symbiotic microalgae – zoochlorellae and zooanthellae - that are harbored in the epidermis and gut lining of certain sea anemones, especially Anthopleura xanthogrammica, the giant green anemone found in local tide pools and on the vertical faces of intertidal rocks. The zoochlorellae (family Chlorophyceae) are Chlorella-like algae that give this sea anemone much of its bright green color. The zooanthellae (in the family Dinophyceae) are actually dinoflagellates of the genus Symbiodinium and are cosymbionts. The presences of these algae are influenced by both temperature and light. They prefer cool, illuminated environments. Giant green anemones living in caves, such as Lost Boy Cave just north of Oceanside, lack zoochlorellae and appear pale and are without the rich green color of those living in sunlight.  Carbon-14 studies have shown that these symbionts provide its host with some food, but it is less than four percent of the anemone’s nutritional needs.
 

Vaucheria (Derbesia?) sp.
No Common Name
Alaska to southern California
Family Vaucheriaceae (Bryopsiaceae?)

This green, velvet-looking alga spreads across the mudflats of Netarts Bay. It is not grouped with the macroalgae. It is a member of the Xanthophyceae (yellow-green algae). It is filamentous and coenocytic, that is there are no cell walls between nuclei, and the filaments consist of long, hollow tubes. Growth takes place at their tips, and there are regions of the filaments that can serve as holdfasts. There are numerous species of Vaucheria that live in marine, freshwater, and terrestrial ecosystems. It reproduces asexually by fragmentation and sexually by eggs and sperm produced at specialized sites called, respectively, the oogonium and antheridium. The genus is named after Jean-Pierre-Etienne Vaucher, an early nineteenth century French botanist.