Intertidal Environment (Littoral) 



147 



crabs, chief of which is Pachygrapsus cras- 

 sipes which rattles noisily as it scurries away 

 to hide from visitors walking over the rocks. 

 Even more common but less obvious are 

 hermit crabs, mostly species of Pagurus, 

 which occupy the shells usually of Littorina 

 and Tegula but may sometimes be found in 

 other discarded shells, tubes, or miscellane- 

 ous containers (MacGinitie and MacGinitie, 

 1949, pp. 293-299). 



In the next, the midtide zone, are in- 

 creased numbers of species and individuals 

 of algae. Among the more common are the 

 small calcareous red Corallina vancouveren- 

 sis, the larger species of the green Ulva, and 

 several red algae including Gigartina canali- 

 culata and G. leptorhynchos. These plants 

 are large enough that they provide protec- 

 tion as well as food for animals of the zone. 

 In shady areas a crustose red alga, Litho- 

 thamnium, commonly forms a relatively 

 smooth pink belt, 30 to 60 cm wide, under 

 which many small animals may hide. The 

 animals as well as the plants of this zone are 

 more highly varied than in the two higher 

 zones. One of the most typical is the black 

 mussel, Mytilus calif ornianus, which lives in 

 dense clusters in areas of strong surf and on 

 pilings of piers fronting the open sea. Meas- 

 urements by Fox and Coe (1943) show that 

 individuals filter as much as 22,000 liters of 

 water per year, separating large quantities 

 of suspended sand in the process. Associ- 

 ated with the mussel are large barnacles, 

 Balanus tintinnabulum, and the gooseneck 

 Mitella polymerus. Living on the rocks are 

 many chitons, of which Nuttallina califor- 

 nica is the most common. Like the limpet, 

 this chiton erodes a hole in the rock, locally 

 as deep as 2 cm. During the night when the 

 Tock surface is cool and moist the chiton 

 wanders about grazing, and then it returns 

 by dawn, usually to its home depression in 

 the rock (Lane, 1956). A sea anemone, 

 Bunodactis elegantissima, is also common, 

 living in closely packed colonies poorly dis- 

 guised by attached shells and sand grains. 



The lowest zone, exposed only at minus 

 tides, grades seaward into the sublittoral 

 area of the inner continental shelf. Because 

 of the extremely wide variety of plants and 



animals as compared to the rest of the in- 

 tertidal area, collection from this zone is so 

 highly prized by biologists that they are will- 

 ing to go to great lengths to be present at 

 minus tides. Collecting from it at higher 

 tides by swimming is difficult, largely be- 

 cause of surf action. Plants are dominated 

 by the large brown alga, Egregia laevigata, 

 although red algae are represented by the 

 large Gigartina spinosa, by Gelidium carti- 

 ligineum which is sometimes picked for agar, 

 and by a wide variety of smaller forms. In 

 this zone also is the grass-like Phyllospadix 

 torryi, a marine seed plant closely related to 

 Zostera which lives in the minus-tide region 

 of marshes and bays as well as the open sea. 

 A calcareous red alga, Melobesia mediocris, 

 is commonly present as an encrustation on 

 the blades of Phyllospadix. Prominent 

 among the animals is the large green soli- 

 tary sea anemone, Anthopleura xanthogram- 

 mica. Starfishes are also common; chief 

 among them is the large Pisaster ochraceus 

 which may be seen chnging to rocks or pil- 

 ings just below the horizon of abundant 

 mussels which also serve as part of its food 

 supply. An animal closely related to the 

 starfish, although outwardly diff'erent in ap- 

 pearance, is the spiny and purple sea urchin. 

 Strongylocentrotus franciscanus and S. purpu- 

 ratus are the most common species, and 

 they, like many of the other urchins, are 

 capable of drilling hemispherical holes in 

 rock and concrete and reportedly even in 

 steel pilings. The best rock borers, how- 

 ever, are several species of Pholadidea whose 

 habitat ranges downward from this zone. 

 Another animal, likely to be overlooked or 

 mistaken for a plant, is the hydroid, a small 

 attached linear colony of individuals which 

 forms a life phase of medusae. Among 

 other animals occasionally seen in this zone 

 are solitary corals, sponges, abalones (Fig. 

 130), tunicates, bryozoans, worms, crabs, 

 and others too numerous even to mention 

 here. 



A special environment more closely related 

 to rocky shores than to sandy beaches or 

 marshes is provided by wooden pilings of 

 piers. Here lives a group of wood-boring 

 animals, prominent among which are the 



