Zoobenthos : meiofauna

from Patrick Buat thesis

This study has allowed to describe the meiofauna compartment and to specify its integration in the matter and energy cycle in soft bottoms of Tikehau atoll ( French Polynesia ). Environmental and biological parameters which characterise the sediments on the periphery of the pinnacles and in the whole lagoon have been measured together with the composition and density of the main groups of the meiobenthos. The pinnacles enrich the adjoining areas by exporting materiel in various forms. In the lagoon, three types of sediments can be distinguished based on the percentage of silt content. Each type of sediment bas its own meiobenthic community which is dominated by four taxonomie groups.

Nematodes dominate all communities, followed by copepods and turbellaria. Polychetes are the last group which is of any importance and the main representative of the mixofauna. The different types of sediments are all present on the detrital cones of the pinnacles and make them appear to be a small scale reproduction of the system found in the lagoon. Therefore. the detrital cones of the pinnacles is a valuable tool for studying the ecology of meiofauna in atoll lagoons.

The results show that meiofauna of Tikehau atoll exhibits metabolic compensation against temperature. The oxygen demand of meiofauna is not any higher than in temperate regions and it makes up for 5% of the total oxygen demand of the sediment. The efficiency of production is weak (40%) for the three groups considered and the total annual production of the meiofauna of Tikehau is small (P/B=5). Nevertheless productivity varies with taxonomic groups. Nematodes and polychetes have small annual productions (P/B =3), while copepods have a production comparable to what has been observed in other places (P/B=15). The production of meiofauna will depend on the structure of the community, hence on the type of sediment, but it will be small in general. The average annual production of the meiobenthos in the lagoon is 1 g  C^-2 year^-1.

Measurements of both nitrogen excretion and faeces production show that the direct remineralisation of carbon and organic nitrogen is not very important for the three groups considered though it is much higher than the flux measured at the water-sediment interface. The largest part of the organic matter which transit through the gut, is released nearly undegraded into the environment.

The results suggest that meiofauna is playing an important role in transforming organic matter and making it available to the bacteria compartment much quicker. Ammonia excretion could also favour bacterial production. As a consequence, the small productivity of meiofauna might not allow its usage by higher trophic levels with the exception of areas close to pinnacles.

References

Buat P, 1996, Importance et rôle de la méiofaune dans le cycle de la matière et de l'énergie des lagons d'atoll, ORSTOM, Papeete (PYF), 1996, 203 p. multigr., bibl., ill., tabl., graph. - Th. univ. : Océanol., Université Française du Pacifique : Papeete, Cote : F A010013629/2; PT OCEA.BUA/1; M 032MILPHY BUA/1
Key-words : French Polynesia - Tuamotu - Atoll - Meiobenthos - Respiration - Defecation - Excretion - Production - Carbon budget