3.4 Biological Resources
with moderately fine grain size. Grunion are managed as a game species by the California Department of
Fish and Game. Their spawning season occurs from March to August.
Hard Bottom Communities
Rocky habitats often are very productive ecosystems that support a variety of plants and animals. Hard
bottom habitats include rocky intertidal shores and hard bottom subtidal reef. (The intertidal zone is the
area between the highest high tide and the lowest low tide. Areas that are permanently inundated are
defined as subtidal.) Approximately 14 percent of the coastline in San Diego County is estimated to be
rocky, but the distribution of subtidal reefs is less well known than the rocky intertidal because large-scale
mapping studies have not been undertaken. The proportion of hard substrate habitat at any given time
relates to the amount of sand in the littoral cell and relief height. An increase in the proportion of hard-
bottom habitat may be occurring in conjunction with sand loss and degradation of beaches by erosion.
Several physical factors influence the types and diversity of marine life associated with rocky habitats.
Important substrate qualities include relief height (low, high), texture (smooth, pitted, cracked), size, and
composition(sandstone, mudstone, basalt, granite). Substrates that are of higher relief, greater texture, and
size generally have the richest assemblages of marine species. Cobbles, which roll and move about within
the wash zone, are dangerous to small organisms and empty of life. Rocks and reefs of low height are
subjected to seasonal burial and uncovering associated with the onshore and offshore migration of sand.
Suchlowlying substrate tends to be devoid of organisms and is dominated by opportunistic annuals or sand
tolerant species. The hardness of the substrate also is important; organisms growing on soft rock substrates
(e.g., mudstones, sandstones) may be dislodged when water movement fractures or erodes the rock.
In addition to relationship with substrate characteristics, marine life also differs with water level. The upper
intertidal or splash zone is characterized by simple green algae (Chaetomorpha, Enteromorpha, Ulva),
barnacles (Cthamalus), limpets (Collisella, Lottia), and periwinkles (Littorina). Coralline algae
(Corallina spp.) is a dominant algae on low relief rocky substrate in the mid-to-low intertidal zone.
Intertidal substrates less influenced by sand burial and abrasion often support California mussel (Mytilus
californus), gooseneck barnacle (Pollicipes polymerus), aggregating sea anemones (Anthopleura
elegantissima), he rmit crabs (e.g., Pagurus), a variety of snails (e.g., Lithopoma, Kelletia, Tegula),
chitons (e.g., Mopalia), and annual species of algae.
Along the northern coast of San Diego County, the most common algae on exposed rocky substrate are
coralline algal turf and seasonal species that can develop rapidly whenever a surface is free from sand, but
Regional Beach Sand Project EIR/EA
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