Comparison of Feeding Strategies among Three Intertidal Sites

San Juan Island includes a wide variety of habitats that have some animal species in common and some that are found only in specific habitats.  This page summarizes feeding strategies by the most prominent fauna at three field sites surveyed during the MIZ 2004 marine habitats project.  We visited one field site on each of three low tides to work with the habitat team, in order to gain a better understanding of differences among these three intertidal habitats.  We used these visits to gain an understanding of physical differences among sites as well as the most abundant or prominent animals encountered using typical survey methods for each site.  For a reference to common terms used in comparing feeding strategies, click here.

The Cobble Beach at Snug Harbor
is a north-west facing shore made up of various sized rocks, most of which can be turned over by hand. Water surge is variable depending on the weather, and some stones may be turned over by high wave action.

Upon the Rocky surface

When looking closely at the surface of the beach, almost every rock is littered with a combination of limpets, snails, barnacles, and chitons. With the exception of a few snail species that prey on shelled organisms, these animals from the upper rocky surface feed on small particles that are suspended in the water column, or organisms and material that have settled onto the rocks (such as algae, or the very young stages of other animals) and can be grazed off.

Rocky Promontory of Eagle Cove
is a south-facing cove exposed to the rough waters of the Strait of Juan de Fuca.

Mid Intertidal With Tide Pools

Both Eagle Cove and Cobble Beach are predominantly rocky substrates and therefore share many of the same species of limpets, snails, barnacles, chitons, and sea stars. Some others (described below) were prominent at Eagle Cove but not at Cobble Beach.

Mud Flats of Garrison Bay
are soft sediments within a protected bay with very calm waters that slowly creep in and out with the tidal oscillations.

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