INTERTIDAL PLANT COMMUNITIES

Flora

Although frequently overlooked as a plant community, there is an abundance of life in the intertidal zone along the coast. Most marine plants are a species of algae--absent of true flowers, leaves or roots. In place of the usual plant structure, algae is characterized by blades, stipes and holdfasts. The blades are like leaves, stipes are much like the stem, and holdfasts act similar to the root system of a terrestrial plant (Dawson and Foster 1982; Evens 1993).

There are three types of algae found along the California Coast: green, brown and red (Dawson and Foster 1982; Evens 1993). There are few green algae species found in the intertidal zone but, perhaps, the most visible and abundant is the bright green sea lettuce (Ulva lactuca) that is found in shallow bays, lagoons, harbors and marshes. The brown algae are larger and include giant kelps (Nereocystis), oar weeds (Laminaria) and sea palms (Postelsia palmaeformis). Brown algae is particularly suited for the cold Pacific Ocean. Red algae is still more abundant and comprises most species of seaweed in the world. Two of the most notable along the California Coast and around the Peninsula include nori (Porphyra) and Turkish towel plant (Gigartina exasperata). The former is a purple colored seaweed that is also cultivated in east Asia and routinely used in Japanese cooking. The latter is a large, flat seaweed covered with papillae and common in the intertidal and low subtidal zone. The only true flowering plants are eelgrass (Zostera marina) and scouler surfgrass (Phyllospadix scouleri). Z. marina occurs in the subtidal zone of protected bays and lagoons; and P. scouleri emerge in the intertidal zone along rocky shores (Dawson and Foster 1982; Evens 1993).

The intertidal plant community consists of four zones: the splash or top zone, the high midlittoral or intertidal zone exposed and covered twice per day by low and high tides, the low midlittoral or intertidal zone that is exposed only once per day by low tide, and the subtidal zone which remains submerged. Unlike terrestrial zones, however, intertidal zonation occurs in nine vertical feet requiring all species to be uniquely adapted for these extreme conditions. (Baker 1984, Dawson and Foster 1982; Evens 1993).

Species differ in their ability to tolerate exposure to extreme wet or dry conditions, and thus occur at different locations along the intertidal gradient. The intertidal plant community is characterized by high and low stress conditions. The former consists of an almost completely terrestrial environment, and the latter is mainly dominated by an aquatic habitat. For example, the splash zone consists of plants and animals that are actually more adapted for air than water or prefer desiccating conditions or only require an occasional wetting. What happens when algae that is primarily adapted for the wet intertidal zone becomes exposed to air for prolonged periods of time during low tide? It may experience a lack of nutrients, desiccation, increased radiation, increased or decreased temperature and salinity. If you have ever been tide pooling, you have probably observed some of these difference that are particularly evident during high and low tide (Baker 1984; Dawson and Foster 1982). How does a species adapt to survive these harsh environmental conditions?

Fauna

Similar to the flora in the intertidal community, animal life is highly specialized and survives in a very narrow, vertical geographic area between the splash zone which is dominated by species better or equally suited for a terrestrial environment, and the subtidal zone with species exclusively adapted for aquatic life.

In the splash or top zone, you are likely to find giant acorn barnacles (Balanus nubilis) and purple shore crabs (Hemigrapsus nudus). At the edge of the littoral zone, California (Mytilus californianus) and blue mussels (Mytilus edulis) begin to dominate and increase upon entering the higher midlittoral zone (Kavanaugh 1994; McConnaughey and McConnaughey 1985). Other species found in the midlittoral zone include the leaf barnacle (Pollicipes polymerus), ochre sea star (Pisaster ochraceus), and giant green anemone (Anthopleura xanthogrammica). As we go deeper into the water and enter the lower midlittoral zone, we are likely to encounter purple sea urchins (Strongylocentrotus purpuratus), stiff-footed sea cucumbers (Eupentacta quinquesemita), sunflower stars (Pycnopodia helianthoides) and giant Pacific chiton (Cryptochiton stelleri). Still deeper, in the subtidal zone, increasing numbers of aquatic animals are observed including the dungeness crab (Cancer magister), eccentric sand dollar (Dendraster excentricus), red abalone (Haliotis rufescens), and giant rock scallop (Hinnites giganteus), as well as the occasional giant Pacific octoposus (Octopus dofleini) and vermillion rockfish (Sebastes miniatus) (Kavanaugh 1994; Kozloff 1983; McConnaughey and McConnaughey 1985).