Rocky Shores: MBNMS

The Monterey Bay National Marine Sanctuary’s rocky shores are characterized by a fascinating and diverse array of intertidal organisms. The dramatic influence of the mixed, semi-diurnal tidal cycle exposes intertidal invertebrates and algae to large fluctuations in temperature, desiccation (drying out) and wave action, with two high and two low tides per day. This range of environmental variables in turn interacts with biological factors to create the distinct zonation patterns evident on any trip to the rocky shore.

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 striking vertical range occupied by these organisms has long motivated scientists and visitors to investigate the abundant and species-rich assemblage of intertidal organisms that thrive in the sanctuary. Many of the hundreds of marine species found on the rocky shore do not occur subtidally, contributing to the unique nature of this habitat at the interface of land and ocean.

Rocky shores make up about 39 percent of sanctuary shoreline habitat and primarily occur near the tips of and outside Monterey Bay, extending southward along the Big Sur coast and north toward San Francisco. Human use of sanctuary rocky shores ranges from research and education to harvesting, collection, tidepooling and recreation.

Current research and monitoring efforts have two focus areas:

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

Scientists have conducted baseline surveys of rocky-shore communities, and these systems are in turn monitored to understand trends in the abundance and distribution of numerous intertidal organisms. Establishing such baseline data will allow researchers and managers to assess future impacts on this ecosystem.

Various disturbances, which are well-documented occurrences in rocky shore habitats, can impact the typical patchy distributions of invertebrates and algae found in the intertidal zone. Natural forms of disturbance include waves, predation (e.g., sea otters remove mussels from rocky shores), wave-tossed rocks and logs, and substratum weathering and exfoliation. Anthropogenic (human-induced) disturbances include disease, collection and trampling, oils spills, ship groundings, coastal development and road maintenance.

Conservation Concerns

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, including abalone, mussels and limpets.
• The high visitation levels that occur on rocky shores in Southern California have caused changes in the diversity and abundance of intertidal organisms.
• Impacts from oil spills are difficult to generalize because spills vary greatly in amount, chemical composition and degree of weathering before reaching the shore. Research suggests that oil should be kept off shorelines and that cleaning oil from the shoreline can slow intertidal assemblage recovery.
• Physical abrasion from ship groundings can cause very localized damage to organisms and substrates.
• Debris from coastal development and coastal highway maintenance can create periodic disturbances that simulate landslides. These events can immediately eliminate habitat or have long-term impacts related to sand movement and burial on adjacent sites.
• Historically, water quality was a significant issue on sanctuary rocky shores. Primary treated sewage was pumped out on the intertidal shore at Carmel (Mission Point), Point Pinos and Soquel Point until the 1970s. Since then, better sewage treatment and extended sewer lines into the subtidal have eliminated impacts such as altered algal assemblages and waste-strewn areas.

Monitoring

Sanctuary rocky-shore monitoring programs collect information about key population characteristics such as abundance, size, density and diversity. This information helps resource managers and policy makers predict population changes due to both natural and human-induced disturbance and informs decisions about how to best protect these resources.

In the 1700s, whalers followed the gray whale migration to hunt and slaughter the giants for whale oil and other products. Lookouts were placed along points and promontories, and when whales were sighted, shore whaling vessels were launched. Some of California’s coastal towns, including San Simeon and Pacific Grove, were whaling stations.

Disease
PISCO biologists at UC Santa Cruz are monitoring the sanctuary’s black abalone populations. They have documented the decimation of Southern California black abalone by withering syndrome and are monitoring the northward progression of the disease. Populations within the sanctuary appear to be stable, while more southern populations are in decline.

Visitor Use and Marine Reserves
The visitor-use survey project at Point Pinos in Pacific Grove has evaluated how visitors affect rocky-shore communities. This study established baseline data and evaluated visitor impact by comparing the abundance of organisms between high- and low-use areas.

Negative impacts from visitor use were found only in the high intertidal (> +2 ft. MLLW) in the form of reduced algal cover. However, given the likelihood of future increases in visitor use, continued monitoring of this site will provide data and information necessary to develop plans to manage visitor impact in the sanctuary’s rocky shores.

Natural Variability and Long-term Comparisons

• Monitoring of barnacle and mussel recruitment on rocky shores by PISCO biologists has revealed how oceanographic conditions influence the occurrence and distribution of marine organisms. This research is the outcome of several years of monitoring that takes place along the U.S. West Coast; study sites within the sanctuary provide information critical to completing the story of how oceanographic conditions can dramatically affect biological organisms.
• Researchers from Hopkins Marine Station in Pacific Grove have compared rocky-shore species composition between 1931-1933 and 1993-1994. They report a northward shift of southern species that is concurrent with increasing temperature records. Their study indicates how warming waters associated with a changing climate may affect species distributions in the sanctuary.