The
zoobenthos : macrofauna biomass
in sediments at Tikehau
(a
review from article referenced)
A
survey of 20 random stations was realised in the lagoon to provide
a first assessment of the macro-zoobenthos of the soft bottoms.
Taxonomic
structure
In
terms of abundance
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The
Molluscs and the Polychaetes dominate the endofauna with a
mean density of 11.3 and 10.4 ind m-2
respectively. The Crustaceans count for less than 2 ind m-2
and the Echinoderms as well as the lancelets less than 1
ind m-2. The abundance of the Crustaceans is
probably under estimated as only large apparent
Invertebrates were counted. The average density of the big
burrowing species can be estimated to stand around 0.3 ind
m-2 as revealed by hole density.
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The
Sponges clearly dominate with around 0.5 colony m-2.
The other organisms are generally scarce except in some very
localised areas harbouring high densities of holothuroid (Halodeima atra).
In
terms of biomass
The
global structure is not very different, as it can be seen on the
diagram below:
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The
Molluscs (36%) and the Sponges (27%) are the most present.
The class "others" (25% of animal organic matter
-AOM- ) include the Sipunculids but also the fauna living
in the dead shells and some micro molluscs.
The other groups stand far behind in importance : the
Polychaetes are mainly small animals and contribute for
only 9% to AOM. The Crustaceans are essentially little
species such as Tanaidacae or Mysidacae. Some crabs (mostly
Portunids) are rarely collected in the endofauna and the
contribution of the group to the biomass is poor : 2% of
AOM. The Echinoderms are very few represented on the soft
bottoms (Ophiuroids) with only 1 % of AOM.
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Considering
the total living biomass, the primary producers largely
dominate with about 60% of the total organic matter. They
are sea weeds such as Halimeda
or Caulerpa belonging
to several species, but they may also be Phanerogams Halophila
ovalis. (the
sole species encountered in this lagoon.
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Trophic
structure
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The
deposit feeders are considered as a unique group.
No
distinction between the surface deposit feeders and the
burrowing deposit feeders is made. They are slightly the
best represented with 46% of AOM.The suspension feeders
stand in the same order of magnitude with 42% of AOM.The
carnivores are the leadt represented with only 12% of
AOM.They are collected in the epifauna (Molluscs as Strombus
spp. or Nassarius
spp.) as well as in the endofauna (some
Crustaceans and Polychaeta).
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References
Intès
A., 1994, Atoll Research Bulletin, National Museum of Natural
History Washington D.C., N°415 part II.
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