Unless stated otherwise, the material in this Seashore and Ocean section was taken from “Seashore Life at Torrey Pines State Natural Reserve” by Carol and Peter Lucic
Torrey Pines State Natural Reserve is located in an area which lies closer to the equator than to the north pole. Because of this, our waters are almost semi-tropical and possess many marine organisms with close relatives from farther south. Our coastal climate is characterized as Mediterranean – that is, with mild winters and temperate summers, which encourages the occurrence of marine flora and fauna that are transitional between true tropical and true temperate.
The general circulation of ocean water in the northern hemisphere of the Pacific is clockwise around the entire ocean basin. Therefore, the overall current off the coast of California and Torrey Pines State Natural Reserve is from north to south and is known as the California Current. This current brings water from the higher latitudes–off Alaska, the Aleutian Islands, and Siberia. This makes for cool water along our coast, especially at depth, and therefore some cool water types of plants and animals are able to live here despite our relatively warm climate.
Because of several factors, surface water off Southern California (including Torrey Pines) often does not move parallel to shore but slightly away from it and ends up going out to sea. Because there is no water on the land to move in and replace this water, colder water comes up from below to take its place near the shore. This process is called “upwelling” and causes the near shore water to be much cooler than would otherwise be the case.
Upwelling can cause local coastal fog. When a mass of warm dry air, known as a Santa Ana, moves from the land to the sea, it comes to rest several miles out from the coast. The lower part of this air becomes cooled and moistened by the ocean water and forms what is called a stable marine layer. In time the airflow reverses and moves this layer back toward land. As it approaches the shore, it encounters the colder upwelled water which further cools this air to the point at which fog is formed. The advancing fog bank envelops the coast and delivers large quantities of life-giving water to the shoreline flora. It is thought that the Torrey pines would not have survived our Mediterranean climate without such fogs.
If your feet were anchored to the beach and the tide came in and covered your head, could you hold your breath until the tide went out again? The reverse of this is what many intertidal animals must do twice each day, as they are able to “breathe” only when covered by seawater. Some marine animals such as fish last but a short time out of the water and others, such as the periwinkle, can survive out of water for as long as two months. Most of these “long breath holders” have discovered a way of trapping small quantities of water within their shells to help them survive in the reverse way that a SCUBA diver carries air in tanks to breathe underwater.
The intertidal area may be subdivided into four zones:
- Splash Zone: e.g. the top of Flat Rock and several feet higher
- High Intertidal: top to side of Flat Rock
- Medium Intertidal: side to below bottom of Flat Rock
- Low intertidal: below bottom of Flat Rock
Examples of benchmark plants and animals and their zones are given below.
When the tide is out, the animals left high and dry are, for the most part, under varying degrees of stress. First, they are starved for oxygen; second, they are exposed to terrestrial predators (such as humans); and third, many cannot eat. They seek shelter in crevices, under rocks, beneath the sand, or in their shells and wait until the tide covers them and lets them become active again.
Next topic: Rocky shore biota