• Bacteria

• Protists  

• Micro and meso zooplancton

• Trophic food web

The protists

General background

Protists constitute one of the five kingdoms in Whittaker's system of classification (1969), namely procaryots, protists, plants, fungi and animals. They used to be subdivided depending on their mode of nutrition into protozoa, which belonged to the animal kingdom, and protophyta, which belonged to the plant kingdom. However, protists of some kinds, especially among the flagellata, can be either autotrophic or heterotrophic. In addition, mycologists have claimed that they have identified a further group, the myxomycetes, which are characterised by their strange pedunculate aerial fructifications several millimetres long. However, the fact that their cycle includes a long amoeboid phase means that they should be classified as  protists and given the name mycetozoa. On the other hand, protophytes overlap somewhat with some colonial forms of algae, with which no very clear-cut distinctions can be made: the protist kingdom therefore merges partly with the plant kingdom. One feature common to all protists is their unicellular structure. Most of them live in aquatic habitats, and some of them are parasites. Protists are thought to include more than 30 000 species. Systematic descriptions of their morphological features differ considerably from one author to another. They include several clearly distinguishable branches.

For more information on the protists.

In the atoll lagoons

The lagoon waters were found to contain both ciliata and flagellata. 

• The ciliata belonged mostly to the following 3 orders: Choretotrichida (length: 70 – 136 µm), Oligotrichida (50 – 132 µm) and Pleurostomatida (55 – 136 µm). 

• The dinoflagellata belonged mostly to the following 3 orders : Peridiniales (30 – 83 µm), Gymnodiniales (18 µm) and Prorocentrales (40 µm). The 2  main species identified were the heterotrophic flagellata Protoperidium sp. and Gymnodinium sp.  

Biomass measurements on Tikehau et Takapoto    

The abundance and biomasses of the protists in the 2 lagoons at which measurements were made are given in the following table :

In the Tikehau lagoon, considerable time-related variations were observed in the biomass of the protists.

Data obtained on Tikehau in october 94
Abundance as number of dinoflagellata   per ml	Abundance as number of ciliata per ml

Abundance of the flagellata in the waters of 10 Tuamotu atolls

In the waters of the 10 lagoons prospected in the framework of the TYPATOLL project, the autotrophic and heterotrophic flagellata were counted at two different times of year, in November 95 and March 96.

The heterotrophic flagellata were found to be generally more abundant than the autotrophic flagellata. The former species were particularly abundant on both of the above dates in the Reka-Reka and South Tepoto lagoons, and in March 96 in the Haraiki and Tairao lagoons.
The following table gives the mean values obtained at each season in the two kinds of waters (atoll lagoon waters and surrounding ocean waters) not including the very widely open atoll of Tekokota:
In November 95 : in atoll lagoon waters 2 400 autotrophic flagellata  / ml , 4 300 heterotrophic flagellata /ml in surrounding ocean waters 1 000 autotrophic flagellata  / ml , 1 400 heterotrophic flagellata /ml	In March 96 : in atoll lagoon waters 2 500 autotrophic flagellata / ml , 6 500 heterotrophic flagellata /ml in surrounding ocean waters 330 autotrophic flagellata / ml , 2 200 heterotrophic flagellata /ml

Bibliography :

Gonzalez J.M., Torréton J.-P., Dufour P., Charpy L. (1998) Temporal and spatial dynamics of the pelagic microbial food web in atoll lagoon. Aquatic Microbial Ecology 16: 53-64

Loret P, Le Gall S, Dupuy C, Blanchot J, Pastoureaud A, Delesalle B, Caisey X, Jonquieres G (2000). Heterotrophic protists as a trophic link between picocyanobacteria and the pearl yoster Pinctada margaritifera in the Takapoto lagoon (Tuiaomotu Archipelago, French Polynesia). Aquatic Microbial Ecology 22: 215-226

Sakka A, Legendre L, Gosselin M,Delesalle B (2000). Structure of the oligotrophic planktonic food web under low grazing of heterotrophic bacteria: Takapoto Atoll, French Polynesia. Marine Ecology-Progress Series 197: 1-17