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Intertidal Zone

The Convergence of Land, Air, and Sea


Located at the junction of the atmosphere, hydrosphere, and lithosphere, the intertidal zone is where air, earth, and land interact. It is a zone between high tide and low tide where an abundance of marine life thrives. Unfortunately, it's a place where changes to the climate or human impact make their greatest impact.

A 1933 study documented the life in California's intertidal zone at Pacific Grove. Sixty years later, doctoral student Raphael Sagarin examined the same exact area and found, in the words of the Los Angeles Times, "It was almost as if Malibu had moved to Monterey Bay."

The biogeography of the area had dramatically transformed over the last six decades. Flora and fauna associated with warmer Southern California had moved northward. The explanation was that increased temperatures were the culprit. Using temperatures averaged over a 13-year period (climate data typically relies upon 30-year spans of data), researchers discovered that the study site had risen 4 degrees Fahrenheit over the 60 years and annual temperature increased 2 degrees.

In addition to climatic impacts, people have a dramatic impact on the intertidal zones. While it's illegal to remove as much as a shell from many tidal pools, there is very limited enforcement so buckets of marine plants and animals are carried away from intertidal zones each day. That which is not carried away is often crushed or destroyed by sightseers who visit tidal pools and rocky intertidal zones. This loss and damage affects the biodiversity and food cycle of these precious marine environments.

The intertidal zone is further divided into four key zones:

  • Lower intertidal zone - dry only during the lowest tides and contains the highest biodiversity within the intertidal zone.
  • Middle intertidal zone - regularly covered with sea water.
  • Upper intertidal zone - covered by water during high tide so it experiences dry periods daily.
  • Spray zone - the "desert" of the intertidal zone, this area survives on the mist and spray of the ocean.

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