Zonation

The marine environment rivals that of the tropical rain forests as regards biodiversity. It acts as a reservoir for dissolved carbon dioxide, helping to maintain a constant atmospheric carbon dioxide concentration. A significant amount of photosynthetic activity occurs carried out by marine organisms. The biodiversity of our marine environment has an important direct economic value such as food, drugs, and raw materials. It's great offering is also in an indirect economic value by way of photosynthesis.

Zonation - horizontal bands or zones of organisms and animals.

Physical and biological factors create regular patterns in the ecology of the rocky littoral zone. These effects are displayed as wide bands, each containing certain species. The upper limits of each band are maintained by physical constraints, such as resistance (or lack thereof) to desiccation and/or hypersaline conditions, while lower limits are set by biological constraints, such as competition and predation/herbivorous grazing.

Few features of the shore are more obvious than zonation and all shorelines have some degree of it. In mountain areas, plants occupy definite bands or zones that exist mainly according to temperature, elevations and lighting conditions. The same is true in our ocean shorelines. The zones are by no means constant in composition, number, width and these factors vary from season to season, year to year, shore to shore, and even rock to rock. When the range of tides are shallow, and the slope of the beach is flat, the tidal zonation is wide. Heavy waves widen the zones and upper and lower borders of the zone become less obvious.

Physical and biological factors create regular patterns in the ecology of the rocky littoral zone. These effects are displayed as wide bands, each containing certain species. The upper limits of each band are maintained by physical constraints, such as resistance (or lack thereof) to desiccation and/or hypersaline conditions, while lower limits are set by biological constraints, such as competition and predation/herbivorous grazing.

Each zone has a particular color or texture from the organisms inhabiting that particular zone. These effects are displayed as wide bands, each containing certain species. Universal patterns of zonation, occurring throughout the world, have been recognized, such that no matter where you might be observing the exposed intertidal, the middle littoral zone will often have a community of barnacles, mussels, and rockweeds. Almost all organisms in this intertidal area have evolved from their marine ancestors and some have adapted well to exposing themselves to air.

During low tides most animals hide away in damp crevices or take refuge under rocks. Some animals like the shore crab, can keep from drying out by actually holding small amounts of water in their gill chambers. The mussel "clams-up" to retain it's moisture.

click above on a zone to go to it

The shores are either rocky or sandy and can be divided into specific areas. In 1949 a husband and wife team T.A. and Anne Stephenson published their "Universal Scheme of Zonation." They studied coastlines in various parts of the world. Their theory is related to the air and water interface with other factors such as light penetration, sedimentation and moisture. It relies on relies on the deposition of organisms in the defined areas and not on tidal levels. They found features of zonation that were of universal occurrence and universal application and came up with the following terminology for rocky coasts:

  • 1. Supralittoral zone ..near sea but above the high tide mark with some marine influence (spray)
  • 2. Supralittoral fringe...upper limit of barnacles (in quantity) to nearest higher convenient landmark (upper limit of Littorina
    or lower limit of land lichens. Spring tides invade part of this zone.
  • 3. Midlittoral zone: the entire intertidal areas, from the upper limit of barnacles to upper limits of large brown algae at the
    lower part of the shore. The barnacle demarcation is an important reference point in the universal scheme.
  • 4. Infralittoral fringe: the lower fringe of the intertidal ..an area extending from the upper limit of whatever organism sets
    the lower limit of the midlittoral zone, to the ELWS (extreme low water spring) tide mark, or in areas of waves, to the
    lowest level visible between waves. Organisms living here cannot tolerate complete immersion but can live in an area of
    broken emergence through wave action.
  • 5. Infralittoral zone: the area between ELWS tidal level and corresponding more or less to the more commonly used
    "sublittoral" term.

The highest zone, toward the shore side is the "Supralittoral Zone and Fringe often called the "splash zone." This area consists of acorn barnacles in the upper splash zone to terrestrial lichens in the lower limits. During certain seasons, high level algae, Porphya, can be found. It is frequently exposed to ocean spray and often appears black. The color is due to the growth of cyanobacteria a photosynthetic relative of bacteria. On almost every shore of the world you will find barnacles such as Orthamalus dalli and Balanus glandula. Mussels and Chitons also call this home.

The next stage is the "Midlittoral zone." Usually in this upper level of the midlittoral zone it is covered with barnacles and the in lower limits of this zone, large brown algae, Pelvetiopsis and some red algae, Gigartinecan, be found. The barnacle demarcation is an important reference point in the universal scheme. Here you can find mussels, and goose neck barnacles, as well as species of crabs, periwnkles, chitons, snails and limpets. Sea anenomes and whelks also can call this area home.

"Infrallittoral Zone and Fringe" also known as the "Sublittorial Zone," extends from the it's upper most point competes for space of the organisms such as large brown algae. It extends it's lower limits to tide mark or ares of waves. The organisms that live here cannot tolerate complete submersion and thrive by the constant motion of the wave action. This area contains another zone of barnacles, as well as sea stars, chitons, limpets, brown algae, sea cabbage and much more.

Many factors effect the tidal areas such as desiccation, heat, shortage of oxygen and competition for feeding. Such causes of intertidal zone were tested in 1961 by Joseph Connell from the University of California with barnacles.

Zonation | Intertidal Pools | Collection Etiquette

Kelp & Algae | Fungi | Porifera | Cnidaria

Mollusca | Echinodermata | Osteichthyes

Tides | References