Rocky Shores

In Greater Farallones and Monterey Bay National Marine Sanctuaries, the rocky shores are characterized by a fascinating and diverse array of intertidal organisms. The dramatic influence of the tidal cycle exposes this region’s inhabitants to large fluctuations in temperature, desiccation (drying out) and wave action twice per day.


Rocky shores are divided into a series of zones that are defined by the amount of time the rocks are exposed to air and water. Individual species tend to occupy different parts of the intertidal gradient from the high intertidal zone, where environmental stress is highest, to the low intertidal zone, where biological interactions prevail.

The Splash Zone: Few organisms survive here. Those that can (e.g., barnacles, limpets and a type of green algae) are almost always exposed to the air and are rarely submerged by water.

The High Zone: Organisms that inhabit this zone are exposed to air more than 70 percent of the time and must develop adaptations to survive the long dry periods. For example, limpets, chitons and black turban snails form a watertight seal onto the rocks with their shells to protect themselves from drying out.

The Mid Zone: This zone is densely populated. California mussels often form large beds that provide important refuge and habitat for a variety of other invertebrates and algae.

The Low Zone: In this zone, organisms may be exposed to air just a few times a month so they are more resilient to waves and less resilient to air exposure. Inhabitants include the giant green anemone, the purple sea urchin, the sunflower star and the beautiful sea palm.

Conservation and Management Issues

There are a number of conservation concerns relative to this habitat. These include the following:

  • Harvesting pressure and disease can cause declines in rocky-shore invertebrates.
  • The high visitation levels that occur on rocky shores can cause changes in the diversity and abundance of intertidal organisms.
  • Oil spills pose a significant threat; oil can smother mussel beds and kill acorn barnacles, limpets and other species.
  • Physical abrasion from ship groundings can cause very localized damage to organisms and substrates.
  • Debris from coastal development and highway maintenance can create disturbances, similar to landslides, that can immediately eliminate habitat or have long-term impacts related to sand movement and burial on adjacent sites.
  • The introduction of non-native invertebrates is a major concern. These newcomers threaten the abundance and/or diversity of native species, disrupt ecosystem balance and threaten local marine-based economies.
  • Water from streams and culverts that drain onto the sanctuary’s rocky shores often bring contaminants that can have a variety of biological effects.


Monitoring programs are essential to understanding short- and long-term natural variability and for assessing the health of the region’s rocky shores. Most current research and monitoring efforts have two main focus areas:

  • establishing the health of this ecosystem
  • determining how rocky shores respond to various disturbances

Staff from both the Greater Farallones and Monterey Bay sanctuaries are involved in two rocky-shore research projects:

  • Long-term Monitoring Program and Experiential Training for Students (LiMPETS)
  • The Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO)

In the Monterey Bay sanctuary, a study on visitor use and marine reserves at Point Pinos in Pacific Grove has evaluated how visitors affect rocky-shore communities.

In the Greater Farallones sanctuary, the Duxbury Reef Restoration Program analyzes visitor data, determines baseline species diversity patterns and abundance on the reef, and identifies high- and low-impact areas regarding visitor use.