The
cryptofauna
When
walking along an inner reef flat at low tide or swimming around it
at high tide in the daytime, one
cannot help noticing the fossil-like immobility of the reef
invertebrates, which contrasts with the lively movements of the
fish.
By
night, on the contrary, many kinds of fauna emerge from cavities
of all kinds. The cavity-dwellers can be sub-divided into two
groups: the mobile cavity-dwellers, or mobile cryptofauna and the
organisms responsible for the
process of bio-erosion.
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The
mobile cryptofauna
occupy cavities ranging
between a few millimeters to
4 or 5 cm in diameter, which are either gaps in the
overall structure of the blocks, spaces in the
finely-worked substrate, or
crevices hollowed out
by the eroding organisms. |
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The
cryptofauna inhabiting the shelves of the reefs belong to an
extremely wide range of species
(as many as 800 different species have been counted on some reefs),
and there are nearly 500 individuals per dm3 of coral
substrate in the most highly populated places.
The
main zoological groups present are Polychaeta, Mollusca, Crustacea,
Echinodermata and Fish.
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Polychaeta |
Echinodermata |
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Crustacea |
Mollusca |
Studies
on the spatial distribution of these animals have shown that there
exists on the one hand a stock of species common to all the reef
biotopes, and on the other hand, a stock of species the presence
of which depends strictly on specific ecological factors, such as
the hydro-dynamic conditions, prolonged emersion and sudden
changes in the temperature.
Polychaeta
and crustacea have been found to be the largest components of all
the wet organic matter formed by the cryptofauna inhabiting the
Tikehau reefs.
Studies
on the contents of the digestive organs of fish inhabiting the
reefs have shown that the cavity dwellers play an important role
in the trophic food
web. On the one hand, demersal plankton and meroplankton serve as
prey for the mostly nocturnal planktonophagic species, and on the
other hand, the benthic forms, such as Decapods in particular, are
captured by nocturnal carnivores. Mollusca are mainly ingested by
diurnal mesophagic species
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The
cryptofauna therefore constitute a category of fauna which
play an important functional role in the reef ecosystem.
These organisms show a high level of diversity, in terms
of both time (since they include many different juvenile
forms) and space.
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References Peyrot-Clausade,
M.- 1980 Motile cryptofauna of Tuléar reef flats .Mar Biol 56
:43-47. Peyrot-Clausade, M. -1984 . Cryptofaune mobile et
macroforeurs des formations récifales de l'atoll de Tikehau
: étude quantitative préliminaire. Notes et Documents de l'ORSTOM
Oceanogr Tahiti 22 : 127-146. Peyrot-Clausade, M. - 1989
.The carcinological cryptofauna (Brachyura
and Anomura except Paguridae),Tikehau Tuamotu Archipelago, French
Polynesia .Coral Reefs, 8:109-117 |
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