-in reality, few reefs are dominated solely by corals, hence the term

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coral reefs
-in reality, few reefs are dominated solely by
corals, hence the term coral reef is often a
misnomer. -corals are largest, most showy,
obvious, easiest to recognize on many reefs
however, few people realize that red algae
generally exceed corals in importance as
reef-building organisms.
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-therefore, instead of term coral reefs, tropical
reefs or biotic reefs is preferred.
-without certain spp. of calcareous coralline red
algae, most reefs would not exist.
These coralline red algae are harder than most
corals, and this durability enables them to
withstand the tremendous power of the huge
breakers on oceanic islands. -within such
extreme high-energy systems, coralline algae form
an algal ridge that absorbs wave energy and hence
protects the more delicate corals, fleshy algae,
sponges, other organisms that inhabit the
protected lagoons and back-reef habitats.
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-cement, holding everything together, is what
makes it all work - and the red calcareous red
algae are the principal cementing agents of
nearly all tropical reefs. -many reefs,
especially in the Pacific, are almost entirely
formed by calcified plants
-there is no significant fossil record of the
evolutionary history of the marine red algae,
except for the order Corallinales which extends
back as far as the Jurassic.
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also algal nodules (rhodoliths, maerl)
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-Red Algae or Rhodophyta is by far the largest
most diversified of tropical reef plants -largely
restricted to hard-bottom -predominantly
macroscopic in all tropical reefs -equally
abundant in Atlantic, Pacific, Indian oceans
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The red color is due to the presence of
phycoerythrin which reflects red light and
absorbs blue light.
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- color varies according to the ratio of
phycoerythrin to phycocyanin they may appear
green or bluish from the chlorophyll and other
masking pigments.
-because blue light penetrates water to a greater
depth than light of longer wavelengths, these
pigments allow red algae to photo- synthesize
live at somewhat greater depths than most other
algae.
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-occupy entire range of depths inhabitable by
photosynthetic organisms, from high-intertidal to
depth as great as 300 M (San Salvador I. Bahamas,
greatest depth for known plant life)
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Biologically active compounds produced by reef
dwelling organisms possess antimicrobial and
antiviral activity. These compounds may be
important sources for natural product based drugs
and medicines
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1. Beach
2. Reef flat
3. Algal Ridge
4. Sub-Terrace
5. Terrace
6. Reef Slope

The reef flat is a rigorous environment. The
organisms that live here must be adapted to
withstand intense ultraviolet radiation, high
salinities, and elevated water temperatures.
Although some areas of the reef flat are barren
pavement, pockets of branching corals do occur
where there is sufficient water flow to prevent
over-heating or desiccation.
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Encrusting coralline algae flourish where waves
break on the reef, forming an elevated bank known
as the algal ridge. As water from the waves
returns seaward, its load of suspended sand and
gravel scours a series of narrow ridges. The
alternating ridges and valleys are known as spurs
and grooves.
Corals growing on top of the spurs are stoutly
formed and compressed in shape to withstand the
extreme force of breaking waves.
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On many reefs there is a terrace below the algal
ridge. In this zone we often find stout fire
corals which are able to withstand the wave surge
and strong currents which characterize this area.
Here surgeon fishes and parrotfishes rove over
the submarine terrace grazing on benthic algae
As we move down the slope from the submarine
terrace, we find increasing coral cover and
fishes that prefer areas of rich coral growth,
like this regal angelfish
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Some outer reefs have flattened terraces that
interrupt the gradient of the reef slope. It is
here, protected from the wave surge overhead yet
still exposed to abundant sunlight, that we find
lush gardens of corals with expansive body forms
designed to maximize their exposure to sunlight.
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Descending the slope, we find corals continue to
expand horizontally in shape in order to capture
as much sunlight as possible.
Branching forms found in shallow water are
largely replaced by plate like forms below a
depth of sixty meters.
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-reef-building (hermatypic) corals are of the
order Scleractinia in the class Anthozoa of the
phylum Cnidaria. 6,000 species -
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-contain large quantities of unicellular
microalgae called zooxanthellae
(dinoflagellates), living symbiotically in the
gastrodermis of reef-building corals. -nutrients
supplied by the zooxanthellae make it possible
for the corals to grow and reproduce quickly
enough to create reefs. Zooxanthellae provide
the corals with food in the form of
photosynthetic products. In turn, the coral
provides protection and access to light for the
zooxanthellae. -the role of macroalgae is
mainly photosynthetic as well as providing bulk
materials, similar to bricks or blocks in
construction.
Symbiodinium
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Coral reefs --Corals need warm water, between
18C 30C. If the water is colder, the reefs
are poorly developed or nonexistent. Most coral
reefs lie between the latitudes of 30 degrees N
S where sea temperatures are warmest. Corals
need access to sunlight (the algae living in
their cells need light for photosynthesis) so the
water where they grow needs to be shallow and
clear. Too much sediment in the water can smother
the coral polyps and too much fresh water kills
them. That is why coral reefs don't grow close to
the mouths of rivers.
Orange atolls / Red fringing reefs / Green
barrier reefs
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Coral reefs are divided into 3 basic types
fringing reefs, barrier reefs and atolls.
  Fringing reefs grow in shallow waters and
border the coast closely or are separated from it
by a narrow stretch of water. Fringing reefs
consist of several zones that are characterized
by their depth, the structure of the reef, and
its plant and animal communities. These regions
include the reef crest (the part of the reef the
waves break over), the fore reef (the region of
medium energy), and the spur and groove or
buttress zone (the region of coral growth which
includes rows of corals with sandy canyons or
passages between each row)
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Barrier reefs are reefs that are separated from
land by a lagoon. These reefs grow parallel to
the coast and are large and continuous. Barrier
reefs also include regions of coral formation
that include the zones found in fringing reefs
along with patch reefs (small reefs), back reefs
(the shoreward side of the reef), as well as bank
reefs (reefs that occur on deep bottom
irregularities). Coral reefs also include reef
flats, the reef crest, and a coral terrace (a
slope of sand with isolated coral peaks). These
features are followed by another coral terrace
and a vertical drop into deeper waters. Great
Barrier Reef in Australia. Belize, C.Am.
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- third type of coral reefs are atolls, annular
reefs that develop at or near the surface of the
sea when islands that are surrounded by reefs
subside. Atolls separate a central lagoon and are
circular or sub-circular. - two types of atolls
deep sea atolls that rise from deep sea and those
found on the continental shelf. - mostly limited
to the oceanic basins of the Pacific
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Reef morphology -- Reefs are often referred to as
the "rainforests of the oceans". Coral reefs host
an extraordinary variety of marine plants and
animals (perhaps up to 2 million) including 1/4
of all marine fish species. The wide variety of
habitats depends a lot on the morphology of the
coral reef. Differences in temperatures, light,
exposure to waves and tides, currents and the
amount of food available result in different
habitats and niches.
A) Mud flats close to shore with tide pools - B)
Mangroves - C) Seagrass bed - D) Patch reefs on
inner reef slope - E) Inner lagoon - F) bottom
with mud - G) Pinnacle - H) Outer lagoon - I)
Fine sand - K) Acropora corals - L) Algae ridge -
M) Sand and rubble - N) Gorgonians and black
corals - O) Cave or overhang
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Coastal bays Mangroves often live along the
edge of bays and river mouths. The water is often
turbid with silty bottoms. Mangroves provide
shelter with their root system and are a nursing
ground for many species of coral reef
fishes. Lagoons  Depths my vary from less than
a meter to 90m. If there is good circulation of
water there may be many patch reefs or just large
stands of Acropora corals growing there. There
may be seagrass beds or mud flats. Lagoons can
trap many fish varieties as tide recedes.
A coarse sedimentation   B fine sedimentation
  C  daily variation of temperatures   D 
number of different species