Pacific Rocky Intertidal Monitoring: Trends and Synthesis
The California Channel Islands North region falls entirely within Channel Islands National Park, which encompasses the four northern Channel Islands (San Miguel, Santa Rosa, Santa Cruz, Anacapa), plus one southern island (Santa Barbara) and their surrounding waters. Designated by congress to have controlled, low-impact visitation, the islands receive less than 300,000 visitors per year, most of whom are restricted to a few areas serviced regularly by a local boat tour concessionaire. The waters surrounding the four Northern Channel Islands constitute the major portion of the Channel Islands National Marine Sanctuary, which also includes the waters surrounding Santa Barbara Island to the south. The Sanctuary presence helps to protect rocky intertidal resources primarily by 1) restricting new hydrocarbon exploration and development, 2) prohibiting most types of vessel discharge in near shore waters, and 3) limiting motorized vehicle traffic near the islands (tankers & aircraft). The region includes ten State Marine Reserves, in which all fishing is prohibited, and two State Marine Conservation Areas, in which limited commercial or recreational take is allowed.
The Northern Channel Islands span the transition between two major biogeographic provinces, the cooler Oregonian Province, and the warmer Californian Province, resulting in high species diversity, and substantial differences in species composition over short distances (e.g. east/west sides of islands). Water circulation patterns are complex around the islands, and vary seasonally, but in general, cold, oxygen-rich water flows in from the north, and warm, oxygen poor water flows in from the south. Currents in the Santa Barbara Channel between the islands and the mainland are generally cyclonic (counterclockwise), flowing westward close to the mainland, with a weaker return current flowing eastward past the northern edges of the islands. Sea surface temperature is generally cool during winter and spring and warmer during summer and fall months, with the warmest water bathing the south-eastern sides of the islands. San Miguel, the westernmost island, is subject to frequent upwelling, and rough, windy conditions. It is the only place in the world where up to six species of pinnipeds can be found together on a single beach (Point Bennett). The islands serve as rookeries for seals & sea lions, and are important nesting and roosting sites for numerous seabirds, including several threatened or endangered species.
Rocky shores are the dominant coastal habitat type on the islands, with approximately 60-70% of the total shoreline of each island classified as bedrock. Interspersed among rocky shores are boulder/cobble/sandy beaches, and a few small coastal wetlands.
One of the biggest threats to Northern Channel Island intertidal and near shore marine communities is oil spills. There is a great deal of oil-related activity in the waters surrounding the islands, with over 20 active offshore oil platforms, and pipelines to transport oil onshore to storage facilities. Historically, overharvesting was a concern for some intertidal species, particularly the black abalone, which was included in commercial harvest. Overharvesting has substantially impacted the abundances of many near shore species, such as red, pink and white abalone, lobster, red urchins, sea cucumbers, and rock fish. Disease is another important threat to rocky intertidal communities. The black abalone has experienced catastrophic declines due to a disease called withering syndrome, and is now a federally listed endangered species. Seastars have also been victims of a wasting disease, particularly during El Niño events when the water is warm, and populations have fluctuated substantially.
Previous monitoring studies include surveys at 8 northern island locations done in the 1970’s by the U.S. Bureau of Land Management (now BOEM) for the Southern California Bight Baseline Study. Kanter and Straughan characterized mussel bed communities at several sites on the islands in the 1970’s. MARINe Long-Term monitoring has been done in this region since 1982, and Biodiversity surveys were first done in 2001, with precursor “1-time surveys” conducted at 19 sites in the 1990’s.
The Pacific Rocky Intertidal Monitoring sites located within the California Channel Islands North region are listed below (arranged by island):
San Miguel Island
Santa Rosa Island
Santa Cruz Island
Anacapa IslandS Frenchys Cove