Finding Yourself in the Infralittoral Fringe


The sandy beaches where surfperch live much of their lives can be vast and featureless.  The sand is constantly on the move so we don’t see plant and animal landmarks indicating the zones so familiar in the rocky intertidal.  In the shot above, could you place yourself with respect to mean lower low water (0.0′ on your tide table)?


Intertidal habitats are stacked vertically along a gradient of tidal exposure.  There are lots of classifications for intertidal zones.  I use a 4 zone scheme with origins dating back to some of Ed Ricketts’ unpublished work in the 1930s.  You can get some of the history in Ricketts et al. 1968.  Two works I frequently refer to (The Light & Smith Manual and Kozloff’s Seashore Life of the Northern Pacific Coast) adopt this scheme, so it’s good enough for me.  The Light and Smith Manual describes the zones like this:

  1.  the high intertidal zone, which includes the uppermost area wetted by the sea down to 5 feet above mean lower low water
  2.  the upper intertidal zone, which includes the tidal elevations from 5 to 2.5 feet above mean lower low water
  3.  the middle intertidal zone, which extends from 2.5 down to 0 feet mean lower low water
  4.  the low intertidal zone, which extends from 0 feet mean lower low water to the lowest level the tides reach

Surfperch are among the most mobile surf-dwellers and and live in all of these zones, when they are available, which, from the surfperch point of view, means when they are inundated.  When the sandy beaches lie exposed, there are few landmarks to the intertidal zones other than occasional shows of burrowing animals.  Organisms like barnacles, mussels and algae need to be attached to the substrate.  For them, sand is inadequate, so they associate with rocks and are more or less stuck in a particular zone.

A pool bounded by rocks with starfish and kelp
A low sand-filled tide pool

In happy instances where rock and sand are interspersed we can see indications of tidal zonation not evident on a purely sandy beach. The photo above shows a rock jutting out of the sand on one side of a low tide pool. The tide in this scene is just less than two feet below mean lower low water. Check out the brown algae along the bottom of the rock. To get oriented, it starts on the left by the large sea star and extends along the bottom of the rock all the way out to the tip. That’s dense-clumped kelp, Laminaria sinclairii. You can be sure that the rock it’s living on is jutting out of a sandy beach because dense-clumped kelp is partial to sand scour. Ouch. One other thing about this photo; the top of the dense-clumped kelp is just about mean lower low water. You’re not going to see Laminaria above this level. It’s a great landmark and if you see it you can be sure you are in the low intertidal zone, or what some people call the infralittoral fringe.

intimate view
Dense-clumped Kelp, Laminaria sinclairii

James Markham has done some nice ecological work on Laminaria sinclairii.  If you are interested, you can check out the abstract of his 1973 paper in the Journal of Phycology. Markham found that L. sinclairii is most prevalent where surf action and sand burial are greatest.  I’ve illustrated seasonal fluctuation in sand level and burying in River of Sand.

Markham described this basic progression.  “The sand level begins to build up on the beach in April and continues to rise, burying the plants, throughout the summer, until the first, heavy storms in fall again remove the sand. Maximum growth occurs in early summer, prior to burial.”  The young blades you see in the photo above will be buried by October and lost in December.  New growth begins in January and regeneration is in full swing by March and April.


Laminaria‘s frequent companion in the infralittoral fringe is the surfgrass, Phyllospadix scouleri.  All things being equal, you won’t find it growing much higher than mean lower low water. The lower intertidal zone is rich in sea life and beds of Laminaria and Phyllospadix are more than just a landmark for us humans.  They are home for countless worms, crustaceans and mollusks, some of which get eaten by surfperch, tides and surf permitting.


Kozloff, E. N. 1993. Seashore Life of the Northern Pacific Coast. 3rd ed. University of Washington Press.

Light, S. F., 2007. The Light & Smith Manual: Intertidal Invertebrates from Central California to Oregon. 4th ed., edited by J. T. Carlton. University of California Press.

Ricketts, E. W., and J. Calvin. 1968. Between Pacific Tides. 4th ed., revised by J. W. Hedgpeth.    Stanford University Press.

Note: This post was lightly edited and some photos updated on June 6, 2018.

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