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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.
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