Halimeda is responsible for up to 90% of the total sand
deposition on selected shores, that translates to roughly 1
meter height of sand every 500 yrs. After reproduction, the
carbonate exoskeleton of Halimeda is gradually eroded either
via wave action or bioerosion by species such as the irregular
sea urchin Clypeaster rosaceus. Specimens from shallow
turtle grass meadows in the Belize Barrier Reef have been
found to forage primarily on Halimeda debris. Due to its
preference for large particles which are ground to grain sizes
<0.5 mm C. rosaceus plays an important role in bioerosion.
Approximately 5.5 kg of coarse sediment is converted to silty
fine sand by one individual per year
A disease which caused a
Caribbean-wide mortality in the
reef dwelling sea urchin Diadema
antillarum was also shown to
indirectly affect coral reefs. The
sea urchin functions as both a
grazer on algae that can otherwise
smother coral and as a bioeroder
of corals as it feeds on them
Dictyosphaeria
Hypnea musciformis
Cladophora
One of the greatest threats to coral reefs is human expansion and
development. As development continues to alter the landscape,
the amount of freshwater runoff increases. This terriginous
runoff may carry large amounts of sediment from land-clearing
areas, high levels of nutrients from agricultural areas or septic
systems, as well as many pollutants such as petroleum products or
insecticides.
silting
Whether it is direct sedimentation onto the reef or an increase
in the turbidity of the water due to eutrophication, decreases
in the amounts of light reaching corals may cause bleaching.
In addition, increases in the amounts of nutrients enhance the
growth of other reef organisms such as sponges which may
outcompete the corals for space on crowded reefs
Coral bleaching is the whitening of coral colonies due to the loss of
symbiotic zooxanthellae from the tissues of polyps. This loss exposes
the white calcium carbonate skeletons of the coral colony. Corals
naturally lose less than 0.1% of their zooxanthellae during processes
of regulation and replacement. However, adverse changes in a coral's
environment can cause an increase in the number of zooxanthellae
lost.
There are a number of
stresses or environmental
changes that may cause
bleaching including
disease, excess shade,
increased levels of
ultraviolet radiation,
sedimentation, pollution,
salinity changes, and
increased temperatures
Coral Diseases
Several coral conditions have been identified as diseases: white band disease
(WBD), black band disease (BBD), bacterial infection, and shut down reaction.
They are also susceptible to tumors and parasitic worms. These maladies are all
stress related, and anthropogenic stresses can increase a coral's susceptibility to
these diseases.
Diseases such as BBD and WBD actually kill coral tissue while
advancing in a band around the coral and leaving the white coral
skeleton behind. BBD, caused by the cyanophyte Phormidium
corallyticum, may have a role in maintaining coral diversity
because it is most prevalent in coral species that form large
colonies and provide a structural framework for the reef. When
BBD kills part of these colonies, the skeleton is available to be
colonized by other coral species recruits. However, after 25
months, there were not coral recruits among corals infected by
BBD.
CLOD
cyanide
dynamite