Lesson #1: Intertidal habitats
“To understand the life of the shore, it is not enough to pick up an empty shell and say -This is a murex, or “That is an angel wing.” True understanding demands intuitive comprehension of the whole life of the creature that once inhabited this empty shell: how it survived amid surf and storms, what were its enemies, how it found food and reproduced its kind, what were its relations to the particular sea world in which it lived.”
Excerpt from the THE EDGE OF THE SEA,
by Rachel Carson
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Description of Study Location
The south half of the shoreline within MacKerricher State Park consists of a series of rocky headlands separated by sandy beaches and coves, while the north half is comprised of miles of long gentle sloping beach backed by the extensive Ten Mile River Dunes complex.
The organisms that inhabit this intertidal environment have adapted to the extreme conditions created by the daily movement of the tides. Intertidal organisms must endure submersion in saltwater, and exposure to fresh rainwater. They endure drying out from exposure to sun and wind, and survive wave shock during high tides and raging storms. They experience different sets of predators when covered with water and when exposed.
The positions of organisms inhabiting intertidal environments are determined by physical and biological factors. The upper limit of distribution of any intertidal organism is largely determined by physical factors, such as desiccation due to exposure. The lower limit is usually determined by biological factors, such as predator-prey relationships and competition for space.
Physical Factors
The primary factor determining the biological characteristics of the MacKerricher State Park shoreline is the substrate (the surface on which a plant or animal grows on or is attached to), which can be classified as either rocky shores or sandy beach. The rocky shoreline of the Laguna Point headland exhibits a greater variety of marine organisms than the intertidal beach near the Ten Mile River primarily for the following reasons.
Substrate Heterogeneity
This term is from the Greek terms hetero which means other and genea which means race or kind. Rocky shorelines provide a large variety of habitats. Within the intertidal region at Laguna Point can be found protective crevices, tide pools, drainage or surge channels. Most rocky-shore organisms live on the substrate surface and are referred to as being epibenthic from the Greek terms epi-which means (on or upon) and bethos which means (depth of the sea). Within the rocky shore environment any number of different habitats can be identified such as rock/mud aggregate, tidepools, boulder, and cobble. Substrate heterogeneity is further enhanced if the rocks present are light colored and composed of a softer rock that erodes to a rough textured surface. Typically, harder rocks tend to be relatively smooth thus providing fewer cracks and holes for home sites. Additionally, smooth dark rock surfaces tend to retain heat from the sun during tidal exposure and reach a much higher temperature than lighter colored, rough surfaced rock.
Substrate Stability
A shoreline composed of large rocks and boulders is physically more stable and less likely to be changed during periods of heavy wave action than a beach composed of sand, smaller rocks or flat cobbles. Habitats composed of these smaller materials are rearranged during every heavy wave action.
Upwelling
Upwelling is the localized occurrence of seasonal upwelling provides nutrient and oxygen rich waters to intertidal organisms inhabiting headlands that project westward into the ocean, such as is the Laguna Point headlands.
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