HOLLISTER RANCH SHORELINE PRESERVE

LIFE ON THE EDGE

Point Conception is the traditional center point of a well documented, marine faunal transition zone. This headland separates two different hydrographic climates which differ in water temperature, current direction, wind, swell, and bottom type. It is the center point of a transition zone which marks the boundary between the 'Cold-Temperate' or Oregonian-faunal province from the "Sub-tropical" Californian faunal province. This transition zone is not marked by a fine line but extends over about 5 degrees of latitude centered on Point Conception. Stretching from Monterey in the north, to San Diego in the south, there is a major and marked steepening of the water temperature gradient.  The 'Transition Zone' is characterized by "Warm-Temperate" waters, which contain more species than in the "pure" provinces immediately to the north and south. There are two reasons for this enhanced species diversity. The first is that within this transition zone, species from both provinces overlap. The other is the presence of short range endemics (organisms specifically adapted to this zone).

The largest numbers of overlap and endemic species are found in the subtidal because temperature plays a major role in their distribution and the intertidal zone, relatively speaking, is a harsh environment for temperature sensitive organisms. In fact, many of the species found in the intertidal are "Eurytopic" or broad ranging forms found from Alaska to Baja California. However, even these broad ranging species respond to changes in oceanographic climate by displaying a "Southern Submergence" response. This means that some species, found in the low intertidal within the Hollister Ranch Shoreline Preserve would be found in the subtidal off San Diego and in the middle intertidal in Monterey. One biological example of this "Southern Submergence" phenomena is the Sunflower Star (Pvcnopodia helianthoides).  Although it ranges from Alaska to San Diego, it is commonly found amid the intertidal off the Washington coast, rarely found in the rocky intertidal zone here at Hollister Ranch and exclusively subtidal further south. Endemic species also tend to exhibit "Southern Submergence" within the boundaries of the Transition Zone. Both the Barnacle Balanus aguila and the Turban snail Tegula monterevi are excellent examples of resident species that are intertidal at the northern end of their range and subtidal to the south. Temperature is not the only factor relative to the presence of Transition Zone species. Species presence, and abundance also change in relationship to transitional food sources, predators, competitors, and parasites.

The Hollister Ranch Shoreline intertidal supports excellent examples of both "northern and southern" Transition Zone affinities. The following is a partial list of "northern species" (generally found north of Point Conception) and "southern" species (generally found south of Point Conception).

NORTHERN AFFINITIES:

SOUTHERN AFFINITIES:

In general, the Transition Zone supports a dynamic mix of northern, southern and endemic species. It is a physically and biologically disharmonious setting with shifts in species dominance as common as shifts in predominant current patterns. For example, during an extended "El Nino" event expect to see an increase in southern affinities. During a strong, near shore, California Current event, expect to see more northerly forms. Being so close to the center point of the Transition Zone and its dynamic fluctuations in species composition is part of what makes The Hollister Ranch Shoreline Preserve special.  Please help keep it special by respecting the preserve guidelines which include, no vehicles, keeping animals under control and no taking of living organisms.