In the zone

This cove has no name. It is narrow and the tide moves quickly through it. Rockweed (Ascophyllum) grows prolifically, to a height, mirrored on either side. Its habit is influenced by the environment within which it lives. Space is limited, in this intertidal zone, and organisms have evolved to tolerate water loss rather than avoid it. Seaweeds are sessile organisms and the higher they settle, the longer they will be exposed to the air as the tide recedes. Ascophyllum’s upper reach tells of some maximum amount of time that individuals may be without water during the receding tide.

Competition is the force which limits the growth of Rockweed lower down. Competition from another alga, Irish Moss (Chondrus); which you can just make out as a dark band of reddish-brown on either side of the channel and in its swirling water.

And, what lives above the band of the Rockweed? Look and you will see a thin yellow band and then a black one. It is within the former that one finds barnacles, limpets, and encrusting algae, while the latter represents countless numbers of individual blue-green algae.

All of these organisms have evolved to live and thrive at the tidal height at which they are found, balancing physiological tolerance (mostly to what is above) with the pressures of competition (from below).

The next time you look at a beautiful, seemingly barren, seaside expanse such as this and wonder where all the organisms are … think again.


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