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Plant culture integration within aquaculture activities is a topic of recent interest with economic and environmental benefits. Shrimp farming activities generate nutrient-rich waste trapped in the sediments of farming ponds or release in the mangrove area. Thus, we investigate if the halophytes species naturally growing around the pond can use nitrogen and carbon from shrimp farming for remediation purposes. Halophyte biomasses and sediments influenced by shrimp farm effluents, were collected in two farms in New-Caledonia. All samples were analyzed for their C and N stable isotopic composition and N content. Higher δ15N values were found in plants influenced by shrimp farm water thus evidenced their abilities to take nutrient derived from shrimp farming. Deep root species Chenopodium murale, Atriplex jubata, Suaeda australis and Enchylaena tomentosa appears more efficient for shrimp pond remediation. This work demonstrates that halophytes cultivation in shrimp ponds with sediments, could be effective for the pond's remediation.

International audience; Background: Most of the 29 Siganidae species are widely distributed through the Indo-Pacific area. In New Caledonia, these family was represented by 12 species. The present report is the first record of Siganus randalli in New Caledonian waters and provide information on its diet. Methods: Three specimens of Siganus randalli were caught in shallow mangrove waters of the southern part of New Caledonia. Their stomach contents and isotopic signatures (carbon and nitrogen) were analyzed and compared to others siganids species. Results and conclusion: This note provides the most southerly record of the rabbitfish Siganus randalli, which extends its distribution range by 1200 km southward and 1300 km southwest. The data on its diet, when compared with other co-occurring or more reef-associated siganid species, provide information on feeding processes and ecological functions associated with its mangrove habitat.

Coastal tropical shrimp farming may impact the adjacent ecosystems through the release of large quantities of effluents rich in nutrients. In New Caledonia, mangroves are considered as a natural biofilter to reduce impacts on the surrounding World Heritage listed lagoon. Our main objective was to understand the influence of effluent discharge on the biogeochemistry of mangrove sediments. A monitoring of the physico-chemical parameters of mangrove sediments was carried out during a whole year, including active and non active periods of the farm. The parameters studied were: i) benthic primary production (Chl-a concentrations), ii) physico-chemical parameters of sediments (redox potential, pH, salinity, TOC, TN, TS, δ13C and δ15N), iii) concentrations of dissolved nitrogen, iron and phosphorus. A mangrove developing in the same physiographic conditions, presenting the same zonation, and free of anthropogenic input was used as reference. The concentration of benthic Chl-a measured at sediment surface in the effluent receiving mangrove was twice to three times that measured in the control zone whatever the season. We thus suggest that nutrients inputs significantly increased the phytobenthic production in the effluent receiving mangrove during the whole year, even after the cessation of discharges and because of natural seasonal dynamic of phytobenthos. Although the flow of surface OM was increased, the OM content at depth was not higher than in the control mangrove. However, the contribution of mangrove detritus to the sedimentary organic pool was higher probably as a result of higher density and much greater individual size of the mangrove trees. Unlike the control mangrove sediment, the effluent receiving mangrove sediment was not stratified, redox potential values were high and presence of Fe3+ was detected down to 50 cm depth, probably as a result of a larger root system, allowing a better sediment oxygenation and accentuated OM decomposition processes, and thus limiting ecosystem saturation.

We have investigated temporal variability in the quantity and biochemical composition of sediment organic matter along with variables proxies of water eutrophication (e.g., inorganic nutrient and chlorophyll-a) at two shrimp farms located in the Southern coast of New Caledonia and characterised by clear differences in shrimp feeding practices and levels of initial trophic conditions. The results of our study reveal that the trophic status of the water column increased during the rearing cycle at both sites, determining a general, though moderated, eutrophication. However, the water column trophic descriptors did not allow to discriminate differences in the trophic status among the investigated sites or between sites in the same farming plant, even if they were subjected to different feeding practices and largely different initial characteristics of the sediment. Temporal variations in biopolymeric C and phytopigment sedimentary contents (used as proxies of benthic eutrophication) varied inconsistently among sites. The multivariate analyses did not identify significant temporal patterns in the benthic trophic status, but allowed discriminating the four investigated sites. The semi-intensive shrimp farming significantly contributed to changing the water column and sediments trophic status of the earthen ponds, but the extent of those changes was not consistently observed in all ponds. In any of the investigated ponds the trophic status exceeded concerning thresholds over which hypoxia or anoxia could occur. We conclude that the established semi-intensive practices adopted so far for shrimp farming activities in the earthen ponds of New Caledonia are able to maintain the status of the ponds below the eutrophication levels over which dystrophic crises could sharply abate most of the reared biomass.

We examined the potential for producing the large numbers of sandfish (Holothuria scabra) needed for restocking programmes by co-culturing juveniles with the shrimp Litopenaeus stylirostris in earthen ponds. Our experiments in hapas within shrimp ponds were designed to detect any deleterious effects of sandfish on shrimp, and vice versa. These experiments showed that a high stocking density of juvenile sandfish had no significant effects on growth and survival of shrimp. However, survival and growth of sandfish reared with shrimp for 3 weeks were significantly lower than for sandfish reared alone. Increased stocking density of shrimp also had a significant negative effect on survival and/or growth of sandfish. A grow-out trial of juvenile sandfish in 0.2-ha earthen ponds stocked with 20 shrimp post-larvae m(-2), and densities of sandfish between 0.8 and 1.6 individuals m(-2), confirmed that co-culture is not viable. All sandfish reared in co-culture were dead or moribund after a month. However, sandfish stocked alone into 0.2-ha earthen ponds survived well and grew to mean weights of similar to 400 g within 12 months without addition of food. The grow-out trial demonstrated that there is potential for profitable pond farming of sandfish in monoculture. Further research is now needed to identify the optimal size of juveniles, stocking densities and pond management regimes. (C) 2007 Elsevier B.V. All rights reserved.