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The zoobenthos : macrofauna biomass 
in sediments at Tikehau

Marie José Langlade , IRD

(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 

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.

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:

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.

 

zooben3.jpg (28532 octets)

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.

 

 

Trophic structure 

 

zooben4.jpg (25955 octets)

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).

 

References

Intès A., 1994, Atoll Research Bulletin, National Museum of Natural History Washington D.C., N°415 part II.

 

update : 07/10/08

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