Particulate organic matter in sixteen Tuamotu atoll lagoons (French Polynesia)

Abstract

ABSTRACT. The s t a n d~n g stock and chemical composition of suspended particles were monitored In 16 Tuamotu atoll lagoons and surrounding oceanic water between 1983 and 1996 Temporal and spatial variability was estimated from 18 surveys performed in Takapoto. Atoll lagoon partlculate organic matter (POM) concentrations were compared using data taken during the same months (March and November) and at the same time (morning). It appears that the lagoonal particulate organic carbon concentration depends on the latltude of each lagoon. We interpret this result as a n influence of the waters deriving from the Peruvian and equatorial upwellings. Phytoplankton biomass (chlorophyll) concentration was inversely related to the water exchange between lagoon and ocean. Therefore, the best atolls for pearl oyster farming seem to be those located north of the Tuamotu Archipelago and with snlall exchange with the occan. POM concentration cvas 2 to 5 tunes higher in the atoll lagoons than in the surrounding oceanlc water, wlth a hlgher C:N ratio and a lower N:P ratio. The small size of organic particles (70'% < 3 pm) and the low contl-ibution of phytoplankton to particulate organlc carbon (POC) (S to 19%) in the lagoons must be taken into account when calculating the potential of pearl oysters, which cannot exceed the nutritional potential of Tuamotu atoll lagoons.

Phytoplankton composition and selective feeding of the pearl oyster Pinctada margaritifera in the Takapoto lagoon (Tuamotu Archipelago, French Polynesia):in situ study using optical microscopy and HPLC pigment analysis

“…3) and is in agreement with the lack of spatial variability mentioned by Buestel & Pouvreau (2000) at the lagoon scale. The differences observed in the composition of these communities at Stn 1 could be explained by the influence of anthropic outputs from the village, located in the south part of the atoll (Charpy et al 1997). No significant differences (ANOVA, a = 5 %)…”

Relationships between bacterioplankton and phytoplankton biomass, production and turnover rate in Tuamotu atoll lagoons

“…General water column characteristics in the lagoons have been described (Charpy et al 1997, Charpy & Blanchot 1998, Dufour et al 2001. In relation to the present study, we might underline, first, the importance of dissolved organic nutrients, with ~1 mg dissolved organic carbon (DOC) l -1 ), a high proportion of dissolved organic nitrogen (DON) (> 90% of total dissolved nitrogen) and a sizeable fraction (~50%) of dissolved organic phosphorus (DOP) in the total dissolved phosphorus and, second, an overall trophic gradient, exhibited by practically all descriptors (which are inter-correlated).…”

“…Chlorophyll a (chl a) concentrations were determined by fluorometry (Charpy & Blanchot 1998). Phytoplankton carbon (PhytoC) was calculated from chl a concentrations using a carbon-to-chlorophyll ratio of 108 (Charpy et al 1997, see also 'Discussion').…”

“…Normalized by average depth (Table 1) Depth-averaged primary production was negatively correlated with permeability (r 2 = 0.47, p < 0.001). Chlorophyll concentrations (taken from Charpy et al 1997) were negatively correlated with permeability (r 2 = 0.45, p < 0.001). Table 2.…”

Temporal and spatial dynamics of the pelagic microbial food web in an atoll lagoon

“…Thus, the scale and source of such variability are likely to play a significant role in the long-term equilibrium of an ecosystem (Haury et al 1978, Steele 1991. Atoll lagoons have been reported as systems showing distinct characteristics relative to the adjacent oceanic waters (Le Borgne et al 1989, Charpy-Roubaud et al 1990, Charpy et al 1997, Pages et al 1997, with higher abundances of autotrophic picoplankton (Charpy 1996, Charpy & Blanchot 1998 and elevated bacterial biomass and activity (Yoshinaga et al 1991, Torreton & Dufour 1996a compared to the surrounding oceanic waters. Tikehau lagoon is one example where lagoon waters were stable over several years of investigation (Blanchot et al 1989, Charpy & Charpy-Roubaud 1991, Torreton & Dufour 1996b) with day-to-day variability in the same range as long-term (seasons) variability.…”