Homework-Answer this question and email it to
1. What factors account for the vast majority of atolls in the Indian and
Pacific oceans and that atolls are rare in the Atlantic ocean and b. Why are
there no coral reefs off the Northeastern coast of Brazil even though it lies in
2. Some of the organic material manufactured in the estuarine
communities is exported to other ecosystems. What type of ecosystems receive
this material? How is this material transported?
reefs may cover over 100 sq km: massive structures that have been built almost
entirely by marine plants and animals. The material of the reef is calcium carbonate:
limestone derived from the surrounding waters by the reef organisms.
reef forms the top layer of the reef adding new limestone to these massive structures
at rates that can be measured annually at KG's for every square meter of the
are probably the most oblivious life forms on the reefs. All the different
colors and shapes made up of thousands of individual polyps, each secreting its
own small cup of coral limestone, which provide the building blocks for reef
construction. But plants are also important in the development of this system
as many secrete limestone!
*Coralline algae, in particular, form
cementing crusts that act as 'mortar' for the coral 'blocks'.
*Coral reefs have existed in the earth's
shallow seas for a long time, probably in excess of 450 million years;
The scleractinian corals that
succeeded the rugose forms probably evolved in the
warm waters of the Tethys Sea,
It was eventually closed by the gradual northward migration of
the southern continents, a process known as continental drift.
*The Australian continent was also on the
move and slowly drifting northwards from the cold polar latitudes and into the
warmer waters of the tropics and by chance ventured into this area rich in
coral growth...its northeastern shores in particular were bathed in the ocean
waters passing through the coral rich seas. (Great Barrier
*With the great environmental fluctuations
in the earth's history, sea levels have oscillated from positions slightly
higher than the present to at least 150m below the present level.
*Florida is the only state in the Continental US
to have extensive shallow coral reef formations near its coasts. The reefs
extend from near Stuart on the Atlantic east coast to the Dry Tortugas, west of
Key West in the Gulf of
Mexico. The best reef development occurs in the Florida
*These reefs may rival some of the
Caribbean areas and number about 6000 between Key Biscayne and the Dry Tortugas
These reefs came into existence 5-7000 years ago when the
Wisconsin Ice Age ended and the sea level rose. The growth is slow and
estimates range from one to 16' every 1000 years.
WORM REEFS Aggregations of the tropical reef worm (Phragmatopoma lapidosa ) construct low reefs of tubes consisting of sand grains
cemented together by protein. The reefs expand as worm larva settle on existing
The reef growth is controlled by waves bringing planktonic food and sand to the worms. Found from Cape
Canaveral to Key Biscayne and best developed off St. Lucie and Martin Counties...Bath
Coral banks that occur offshore from JAX to St Lucie inlet at
depths of 50-100m are another of Floridas little known reef types. The banks are
constructed by the ivory tree coral (Oculina
*Stony corals are the major reef
architects. These small marine animals, called polyps, produce a hard skeleton
made of calcium carbonate, which they extract from the seawater and combine
with CO2 for limestone
*Some corals grow in colonies that
continue to enlarge year after year, and some are solitary and live alone.
Together they can form enormous colonies that are called coral reefs, coral
islands and coral atolls. The largest, being the Great
Barrier Reef, is 1,250 miles long.
*They can exhibit many shapes, sizes, and
colors and reefs look like underwater gardens (although they usually lose their
colors when removed from the water except red coral).
*And though reef corals are classified as
animals, there is a complex of microscopic plants called zooxanthellae,
which live within the animal tissues (symbiosis) and the animals benefit from the
energy that the plants provide through photosynthesis.
These dinoflagellates gain nutrients
from the corals nitrogen and phosphorus wastes. They are also responsible for
most of the colors of the reef.
These specialized habitats provide shelter, food, and breeding
sites for numerous plants and animals and form a breakwater for the adjacent
coast, providing natural storm protection.
*They are also important to South East
*Reef development occurs only in areas
with specific environmental characteristics:
solid structure for the base,
2.warm and predictable water temperatures and
transparent waters low in phosphate and nitrogen nutrients,
4.and moderate wave action to disperse wastes
and bring oxygen and plankton to the reef.
*Corals live in all oceans of the world
from the Arctic and Antarctic to the tropics.
The largest reefs occur in the warmer portions of the Pacific and Indian oceans
however they are also found in the Caribbean and Gulf of Mexico and southern Florida.
*Numerous species occur in the different
areas ranging from 40 or more in the West Indies to 200 or more on the Great
Barrier Reef (because of their great skeletons, their fossils have yielded more
than 6000 extinct species.)
*Corals can live in water below 68-70
degrees (reef min. temps) but don't form reefs, just like some corals which can
live 19,000 feet below the surface, but reef-building corals are in water
usually less than 300'.
*There are three types of reefs,
fringing, which follow the coastline and form along the coast,
2. barrier reefs, which lie parallel
to the coast and separated by a narrow lagoon, and
3. atolls, which are associated with
rims of extinct volcanoes which sunk back into the ocean leaving a circular rim
of coral around a deep lagoon.
*Every year careless boaters run aground
destroying coral colonies hundreds of years old. From the surface reefs have a
unique golden brown color. If you see brown, you may
be about to run aground. Anchors, hooks traps and touching all injure or damage
or destroy corals by leaving it vulnerable to infection by microscopic
organisms that can kill the animals.
The adult coral, stationary at this stage in life is called a
polyp which can reproduce in two different ways. One is by means of eggs that,
when fertilized by sperm, develop into tiny swimming larval organisms called planulae.
*They eventually settle down on the bottom
of the ocean, on a rock etc. and develop into polyps. Each polyp builds a
limestone skeleton attached to the surface on which the polyp has landed. After
establishment, the upper part of the polyp becomes domed shaped, develops a
body and a mouth with tentacles around the mouth used to draw in food from the
*The tentacles are armed with specialized
stinging cells called nematocysts that paralyze tiny prey. (mostly
*Another process is by budding
which offshoots called buds grow out from the body and remain attached sending
out more buds.
*The coral reef has a very high order of
internal organization, greater even than the tropical rain forests they are
often compared to. Both receive high levels of solar radiation, the ultimate
source of all ecosystem energy.
*2 CLASSES of reef corals exist, HYDROZOA
AND ANTHOZOA. In the keys, Millepora (fire coral) is
the only hydrozoan coral on shallow reefs. Stylaster and Distichophora are
found in deep habitats.
The anthozoans include octocorals, zoanthids, stony
corals, false corals, and anemones.
stinging/burning comes from nematocysts. 2 species of firecoral
are found in Florida
reef. The bladed is a keel shaped (M. complanata)
restricted to shallow windward reef tops. Crenulated (M. alcicornis)
is a branching species found in a much wider range of reef habitats.
*Fire corals are successful in colonizing
living octocoral branches.
* Coral reefs can only grow up to about the
level of a low spring tide, and reefs (as opposed to individual corals) will
probably not develop in water more than 40m deep. Reefs are, therefore,
strongly influenced by sea level. Over the time that most of the world's reefs
have grown, there have been major sea level changes.
*There were two main reasons for sea level
changes. One, the worlds ocean basins have changed in
size and shape because of sea floor spreading and plate tectonics and the other
is the ice ages.
*ZONES OF THE MODERN REEF.
In the last 8000 years, reefs have grown to what they are
today. They have grown from the older reef platforms about 15-20m deep. The
modern reefs are relatively thin and their shape reflects accurately the shape
of the surface over which they are growing.
*To understand the growth of modern reefs,
its best to begin at the surface, where five easily defined zones can be
*1. the reef
2. the reef crest,
3. the coral flat,
4. the sand flat, and
5. the lagoon.
*The upper slope of the modern reef front
extends from the mean low-water level of spring tides down to a depth of 10 to
20m. Fairly steep, sometimes vertical, sometimes terraced, and often serrated
by coral covered spurs and channels, the area has a lot of coral cover.
* On some reefs, the front is protected by
a line of patch reefs, many of which are joined to form an outer front.
*The exposed windward reef crest, or outer
reef flat, lies above the mean low-water level of spring tides. It is composed
of either a seaweed, stepped surface of encrusted coralline algae and devoid of
corals, or a flat coralline-encrusted surface that may reach half a meter above
the mean low-water level of spring tides, as on a ribbon reef.
*The upper surface of the reef crest is
sometimes covered by a green turf of fleshy algae, which provide a home for
countless small organisms, particularly foraminifera. These algae pavements can
reach 200-300m wide and form in response to the high energy conditions typical
of windward edges.
*These algal pavements are replaced by
extensive coral development in lower energy or more leeward parts of the edge
of the reef.
The coral flat or reef flat, occurs
on the sheltered or lee side of the algal flat. It usually consists of an
aligned coral zone where most corals are encrusted by coralline algae.
*These aligned corals occur in patches 1
to 2 m wide and 20m long formed by coral growing parallel to the direction of waves
refracted across the top of the reef. The water movement is channeled across
the grooves between the aligned assemblages of coral and in this way, coral
growth on the reef top controls the backward flow of water across the reef.
*Nutrients and sediments are carried back
through these channels to the sand flat and lagoon areas. This zone is usually
separated from the lagoon by a sand flat, sometimes up to 500m wide. The sand
flat is made up of broken skeletons of corals, coralline algae, and other reef
organisms derived from the reef front and coral flat and transported toward the
lagoon as sands and gravels
*Foraminifera from the algal turf of the
reef crest also form part of this sediment.
Sand flats have been built by prevailing swell and waves that
continually destroy the reef front and transport the broken products backwards.
*The surface of the sand flat, covered by
one half to two meters of water, depending upon the tides, is often sparsely
covered by small colonies of branching corals which can grow from fragments
brought from the coral flat which grow when they come to rest.
*In this way, the coral flat extends
backward across the sand flat, and the sand flat will migrate into the lagoon
The lagoon is best seen in platform reefs, where they reach
5-10m deep with the deepest part on the leeward side of the reef
*Lagoons are sometimes open with very few patch
reefs rising from the floor or often very crowded with patch reefs making
navigation of the lagoon difficult...
*They are made up of many species of
branching and massive corals, the dead parts of which are encrusted by
coralline algae. The lagoon floor consists of coral sand, which becomes finer
away from the windward margin and patches of mud (very fine) sometimes occur in
the quiet waters of the leeward margins.
*Because the lagoons are depositories for
sediments and organic material created on the windward margin, they are slowly
*About 6000 yrs ago, sea level established
and maintained a position close to what it is today.
*The composition of the reef also varies
with the position of the reef on the continental shelf. The structure of the
outer shelf-reefs generally reflects the influence of powerful waves, and here
most of the reef consists of coral skeletons forming a porous, but relatively
*Reefs in the middle and inner parts are
dominated by accumulations of sand, and the coral framework forms a much
smaller proportion of the reef, reflecting the calmer sea, or lower energy
conditions compared with the outer reef.
*3 stages of reef development can be seen.
1. vertical growth to sea level...a
reef growing slowly from a deep substrate may not yet have reached sea level or
only recently have reached sea level and is characterized by vigorous growth of
free-standing branching or massive corals upwards to sea level. Such a reef is
*2.A reef growing from relatively shallow
substrate, or one growing rapidly from a deeper substrate, will reach sea level
quickly and will be subject to the influences of shallow water for a long
time...many have been at sea level for 4 to 6000years. Swell, waves and
currents help develop these and these reefs are called mature.
*3. Reefs growing from very shallow
substrates, or small reefs that have grown rapidly from deeper substrates, may
have been at sea level even longer than mature reefs and because a long time at
the surface leads to destruction of the reef, lagoons will have been filled in
and the typical zonation destroyed. Erosion is
thought to exceed production, and such reefs are called senile.
*Its believed that reefs progress through the growth stages from
juvenile to mature to senile. Different reefs require different lengths of time
to follow this progression, the time being dependant on depth and size of
substrate, rates of growth, length of time at sea level, and intensity of the
processes operating at sea level.
*As reef growth has seldom lasted for more
than 5000-15000 years, some large lagoon reefs may not have sufficient time to progress
through the complete cycle in one high-sea-level growth phase and could need
more than one growth phase to reach a senile condition.
*Maintenance and Destruction
Reefs come in a vast array of shapes and sizes and many of these
differences result from erosion while periodically exposed during
low-sea-levels rather than from growth differences
A coral reef requires only the basic plant nutrients plus a
copious supply of calcium for the construction of the calcium carbonate of the
coral skeletons and other limestone forming materials of the reef. Carbon
dioxide and calcium are abundant in sea water.
*N, P and some trace elements may only be
present in limited quantities in the clear oceanic waters and the reef must
recycle these materials to maintain its intense biological activity.
*All plant and animal matter grown must be
totally consumed or fully degraded within the reef community to prevent the
loss of any nutrients. Extensive mats of blue-green algae on the reef may
provide the reef with N by converting the N in the atmosphere to the soluble
inorganic N nutrients.
*There are very small but important losses
and gains from any reef system and that is the exchange of larval forms with
other reefs. This ensures inbreeding and that any species depleted by disease
or other stress will be replaced by larval input from another reef or reefs.
*About 3/4 of the CO2 that is removed from
sea water by a coral reef in each 24hr period is used directly in
photosynthesis within the reef algae. This creates about 20g of new organic
matter for every square meter of shallow, reef-flat environment per day and can
be up to 50g a day in areas of intense biological activity. This is the reefs
*Most of the limestone making up the solid
underlying mass of the coral reef consists of skeletons of once living corals.
*They provide the aggregate of the reef
concrete. At least some of the corals in this rich surface growth are likely
top add to the structural framework of their own reef when they die.
The encrusting coralline algae hold together the sand and
framework materials of the reef to create a solid surface.
*They have a role in building a real reef
rather than a pile of uncemented coral debris and
sand. Once the reef has been totally consolidated by these algae, chemical
precipitation of more carbonates in the reef structure provides additional
cementing of the remaining loose calcium carbonate materials.
*Its a slow process but it makes the entire structure more rigid.
The final reef material is a porous but strong limestone, though it frequently
contains uncemented regions.
*NUTRIENTS AND REEF PRODUCTIVITY
Direct feeding by the polyps usually
only supplies only 10 per cent of the corals energy needs. In such cases, most
energy comes from photosynthesis by zooxanthellae,
which obtain nutrients from metabolic waste products of the coral host as well
as from the seawater or detritus.
*Coral reef primary productivity is
usually very much higher than areas where these nutrients are more abundant but
recycling rates of the corals and zooxanthellae are
high but the harvestable primary productivity is low because most of the
organic matter produced is metabolized and nutrients are freed to be reused in
*Almost every gram of organic matter
created by a coral reef is consumed and eventually finds its way back to the
seawater as carbon dioxide. Before most of the organic matter is finally
degraded back to CO2, it may move through all or part of the complex and finely
balanced coral reef food web.
*Reefs may be thought of as assemblages of
beautiful animals but in fact they are dominated by the activities of plants.
The whole system is driven by the photosynthetic activities of plants, just
like most ecosystems existing in light.
*Even the corals function principally as
plants, deriving as much as 90% of their total and energy requirements from the
tiny algae, known as ZOOXANTHELLAE, contained within their coral tissues. The
remaining requirements are met through feeding on reef plankton.
*Apart from the corals, the major plants
providing the food supply of the reef are fine filamentous algae that form a
rapid growing fuzz or turf over almost all available surfaces within the reef.
This turf is grazed by animals, which in turn are preyed on by larger animals
and so the food web expands.
*Also, all living materials die and
undergo microbial decay, forming the basis of yet another component of the
complex food web.
.The reef also creates and consumes its own plankton. Each
animal and plant serves a vital role in the reef's finely tuned balance.
*. The Factory
The 10 to 30 grams of calcium carbonate or limestone created
everyday for each square meter of the active parts of the reef are retained somewhere
within the general reef environment. The reef thus exhibits real, measurable
growth over hundreds of years.
*. The energy to enable the creation of
all this limestone comes into the system through algal photosynthesis. Much of
the limestone originates as growing coral but other organisms, such as many
algae, tiny single celled forams, and shells make
*. Photosynthesis by zooxanthellae
also promotes production of skeletal limestones that
make up the reef framework. Zooxanthellae provide
coral with the energy needed to calcify.
*. Photosynthesis uses CO2 and water from
respiration raising the pH of the system end enhancing aragonite precipitation.
During calcification, calcium ions, which are abundant in
seawater, combine with bicarbonate ions, also found in the environment and the
following reaction occurs...
*1 -Ca2 + 2HCO3 -----> Ca(HCO3)2 and then calcium carbonate and carbonic acid are
2- Ca(HCO3)2----->CaCO3 + H2CO3
but carbonic acid can't exist so carbonic
acid must be ionized
3- H2CO3---> H+ + HCO3- or converted to water and CO2
4- H2CO3----> H2) + CO2
One of the obvious of all reef destroying processes are
storms. But not all reef destruction is caused by physical forces. Many animals
and even some algae live out their lives inside the reef structure and even in
the skeletons of still-living corals and other organisms with hard skeletons.
*. Some of these graze off of the reef
surfaces and remove considerable amounts of the limestone at the same time.
These boring and grazing organisms weaken the structure of their host or the
reef itself by physically disrupting the limestone materials.
*. This in turn, forms more fine sand and
calcium carbonate detritus in the reef system. But the boring organisms also
dissolve, using acid secretions, much of the calcium carbonate they remove
(about 5-25% of total CaCO3 deposited by the reef)..
*. BIOLOGICAL INTERACTIONS
Of course, grazing and predation can be
readily observed but on coral reefs, disease, competition, chemical warfare, bioerosion and symbioses are also common.
Pathogens may injure and kill corals, and black band, one such
pathogen usually attaches to a coral following tissue damage.
overgrowth denying light and water movement.
Allelopathy (chemical defense and offense) is also
used to prevent overgrowth and gain living space.
Damselfish destroy coral tissue and farm/defend algae on the
The black sea urchin crops algae from the reef and this
provides settlement habitat for coral larvae.
*. Sponges bore into coral skeletons,
weakening them, some bind to them and some protect the undersurface from
attacks by boring organisms.
hobbyist idea of "soft corals"
is quite different than the actual definition. True soft corals, according to
the definition, all belong to the subclass Octocorallia.
The name "Octocorallia" refers to the fact
that each polyp has eight tentacles.
can be confusing since many 'soft corals' are not actually soft. This
definition includes such corals as the "Blue Coral", Heliopora coerulea,
the Pipe Organ coral Tubipora musica, and the Gorgonians, all of which produce hard shells
characteristic of true soft corals are the side branches of the polyp tentacle,
', which give
the polyps a feathery look. Although pinnules are a
sure sign of a soft coral, not all soft corals have them.
Estuaries and Corals Review Answers
1. the sea invaded lowlands and river mouths as a result of
rising sea level
4 up the
5. soft mud
6 can cope within a wide range of
7. take on water
8. height of the
11 plants and
seaweeds diatoms phytoplankton
12 dead organic matter
forests saltwater and freshwater marshes saltwater marshes tidal marshes
14 calcium carbonate
15 a planula
16. perform photosynthesis, and thus provide nourishment help the corals produce their skeletons
17 capture of zooplankton with tentacles
or mucus nets zooxanthellaeabsorption of DOM
(dissolved organic material) from wateruse of mesenterial filaments
19 it forms calcium carbonate sediment
20 the zooxanthellae
need light to photosynthesize
21 fringing reef
22 reef crest
23 along the coasts
24 spur and groove formations
25 the Indo-west Pacific region
26 turf algae