Hugues Lemonnier

Spatial and temporal extension of eutrophication associated with shrimp farm wastewater discharges in the New Caledonia lagoon.

Shrimp farming in New Caledonia typically uses a flow-through system with water exchange rates as a tool to maintain optimum hydrological and biological parameters for the crop. Moreover, the effluent shows hydrobiological characteristics (minerals, phytoplankton biomass and organic matter) significantly higher than that of the receiving environment. Separate surveys were carried out in a bay (CH Bay) with a medium-size intensive farm (30 ha) (PO) and in a mangrove-lined creek (TE Creek) near a larger semi-intensive farm (133 ha) (SO). Net loads of nitrogen exported from the semi-intensive farm and the intensive farm amounted to 0.68 and 1.36 kg ha(-1)day(-1), respectively. At CH Bay, discharge effects were spatially limited and clearly restricted to periods of effluent release. The high residence time at site TE favoured the installation of a feedback system in which organic matter was not exported. Mineralization of organic matter led to the release of nutrients, which in turn, caused in an increased eutrophication of this ecosystem. The study of the pico- and nanophytoplankton assemblages showed (i) a shift in composition from picophytoplankton to nanophytoplankton from offshore towards the coast and (ii) a shift within the picophytoplankton with the disappearance of Prochlorococcus and the increase of picoeucaryotes towards the shoreline. These community changes may partially be related to a nitrogen enrichment of the environment by shrimp farm discharges. Thus, in view of the recent addition of the New Caledonian lagoon to the UNESCO World Heritage list, the data presented here could be a first approach to quantify farm discharges and evaluate their impact on the lagoon.

Dynamics of phytoplankton communities in eutrophying tropical shrimp ponds affected by vibriosis

Tropical shrimp aquaculture systems in New Caledonia regularly face major crises resulting from outbreaks of Vibrio infections. Ponds are highly dynamic and challenging environments and display a wide range of trophic conditions. In farms affected by vibriosis, phytoplankton biomass and composition are highly variable. These conditions may promote the development of harmful algae increasing shrimp susceptibility to bacterial infections. Phytoplankton compartment before and during mortality outbreaks was monitored at a shrimp farm that has been regularly and highly impacted by these diseases. Combining information from flow cytometry, microscopy, pigment and phylogenetic analysis, the presence of Picocyanobacteria, Prasinophyceae and Diatomophyceae were detected as dominant phytoplankton groups and Cryptophyceae, Prymnesiophyceae and Dinophyceae as minor components. At the onset of the first shrimp mortalities, Bacillariophyceae increased while Cyanobacteria, Prymnesiophyceae and Dinophyceae decreased in the water column, followed by proliferation of Prasinophyceae. Several taxa were identified as potential harmful algae (Cyanobacteria, dinoflagellates and Phaeocystis).

Aquaculture Pond Precise Mapping in Perancak Estuary, Bali, Indonesia

ABSTRACT Gusmawati, N.F.; Zhi, C.; Soulard, B.; Lemonnier, H., and Selmaoui-Folcher, N., 2016. Aquaculture ponds precise mapping in Perancak Estuary, Bali, Indonesia. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 637–641. Coconut Creek (Florida), ISSN 0749-0208. Indonesia is one of the biggest producers and exporters of shrimp in the world. Shrimp ponds mapping and monitoring will be of critical importance for supporting decision-making regarding the development of sustainable fisheries. Therefore, automatic processing, acceptable quality, and efficient aquaculture mapping are urgently required. The objective of our work is to develop an automatic classification procedure for aquaculture mapping and monitoring, using the Edge Detection Based (EDB) method on very high spatial resolution satellite image. Then we compare the result obtained with EDB with results given respectively by the unsupervised classification method Isodata implemented using ArcGIS (IUC) and a region growing segmentation (RGT) method implemented in SPRING. The broken structure of embankments, dried-up ponds, ongoing development ponds, also abundance of algae and mangrove vegetation in the ponds present significant challenges to establish an accurate map. The aquaculture map provided by EDB successfully identified a high proportion of the existing ponds (> 95%) and overall accuracy of 84% and a kappa coefficient of 0.68. On the other hand, IUC and RGT produced a lower proportion of ponds (between 60 and 80 %) with lower overall accuracy and needed manual refinements. The present study also showed a potential in discriminating different types of ponds. That could be used for a further objective of analyzing the spatiotemporal changes of the ponds and thus improving shrimp farming development.

Monitoring mangrove forests after aquaculture abandonment using time series of very high spatial resolution satellite images: A case study from the Perancak estuary, Bali, Indonesia

Revegetation of abandoned aquaculture regions should be a priority for any integrated coastal zone management (ICZM). This paper examines the potential of a matchless time series of 20 very high spatial resolution (VHSR) optical satellite images acquired for mapping trends in the evolution of mangrove forests from 2001 to 2015 in an estuary fragmented into aquaculture ponds. Evolution of mangrove extent was quantified through robust multitemporal analysis based on supervised image classification. Results indicated that mangroves are expanding inside and outside ponds and over pond dykes. However, the yearly expansion rate of vegetation cover greatly varied between replanted ponds. Ground truthing showed that only Rhizophora species had been planted, whereas natural mangroves consist of Avicennia and Sonneratia species. In addition, the dense Rhizophora plantations present very low regeneration capabilities compared with natural mangroves. Time series of VHSR images provide comprehensive and intuitive level of information for the support of ICZM.

Surveying shrimp aquaculture pond activity using multitemporal VHSR satellite images - case study from the Perancak estuary, Bali, Indonesia

From the 1980s, Indonesian shrimp production has continuously increased through a large expansion of cultured areas and an intensification of the production. As consequences of diseases and environmental degradations linked to this development, there are currently 250,000ha of abandoned ponds in Indonesia. To implement effective procedure to undertake appropriate aquaculture ecosystem assessment and monitoring, an integrated indicator based on four criteria using very high spatial optical satellite images, has been developed to discriminate active from abandoned ponds. These criteria were: presence of water, aerator, feeding bridge and vegetation. This indicator has then been applied to the Perancak estuary, a production area in decline, to highlight the abandonment dynamic between 2001 and 2015. Two risk factors that could contribute to explain dynamics of abandonment were identified: climate conditions and pond locations within the estuary, suggesting that a spatial approach should be integrated in planning processes to operationalize pond rehabilitation.

13 Years of changes in the extent and physiognomy of mangroves after shrimp farming abandonment, Bali

There is a need to document how fast mangrove coasts are changing. Within the framework of the INDESO project, we are implementing methods for monitoring changes in Indonesian mangroves over the past decade. The Perancak river estuary, Jembrana, Bali was selected as a pilot site to analyze the impact of aquaculture and plantation practices in a 7 km2 mangrove area. During the 80s, most of the mangrove forest was converted to shrimp ponds. However many of shrimp ponds have been abandoned since the 90s and covered by mangroves through plantation programs. We based our analysis on a temporal series of VHR satellite images acquired from 2001 to 2014 aiming to assess the vegetation change over 13 years in the study site. We mapped and quantified the trends of evolution in mangroves in terms of surface extents, forest types and forest structure (young, adult, mature). Our results showed that the Perancak estuary is undergoing the greening, i.e. increasing extent and continuous growing of mangroves. With this approach, we proved that both sustainable and unsustainable coastal zone management practices such as mangrove deforestation, plantation or protection, can be identified and mapped from VHR satellite images.

Suitability of a lumped rainfall–runoff model for flashy tropical watersheds in New Caledonia

ABSTRACT The GR4H lumped hourly rainfall–runoff model was assessed for its integration in a ridge-to-reef modelling framework. Particular attention was paid to rainfall representation, robustness of parameter estimates and ability to reproduce the main runoff features. The study was conducted in four tropical mountainous watersheds in New Caledonia, which are exposed to intense rainfall events, large annual climatic variations triggered by El Niño oscillation, and wildfires. The inverse distance and elevation weighting algorithm outperformed other classical rainfall interpolation methods under data-limited conditions. The time span of data needed for robust calibration was site specific and varied from 6–7 years to 10 years, which may be linked to El Niño events and to wildfires. With sufficient data, simulation quality was equivalent during the calibration and validation periods. The GR4H model was generally able to simulate both flash floods and large annual variations. The model was more reliable when simulating wet years and watersheds not subject to land-cover changes.