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Serge Andrefouet - One of the best experts on this subject based on the ideXlab platform.
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The wave regimes of the Central Pacific Ocean with a focus on pearl farming Atolls
Marine Pollution Bulletin, 2021Co-Authors: Cyril Dutheil, Swen Jullien, Jérôme Aucan, Christope E. Menkès, Romain Le Gendre, Serge AndrefouetAbstract:Pearl farming sustainability in South Central Pacific (SCP) Atolls strongly depends on water quality and renewal. These factors are partly controlled by the wave conditions that impact the lagoon circulation. To characterize the wave conditions around 83 SCP Atolls including those hosting pearl farming activities, we used 18 years of WaveWatchIII simulation with a grid refined from 50 to 5 km resolution. Three regional wave regimes are statistically identified: two associated with long distant swells originating from mid-latitude storms, and one with local trade winds. All regimes occur with a relatively high frequency (22–44%), but with a marked seasonality. Wave conditions are also strongly modified locally during their propagation between the archipelagoes. Western and southern isolated Atolls generally have a single regime all around their rims. In contrast, central Tuamotu Atolls experience different regimes depending on their levels of protection. These results help understanding atoll hydrodynamics, which has implications for their management.
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assembly rules of fish communities in tuamotu archipelago atoll lagoons the case of fangatau a lagoon dominated by giant clam habitats
Marine Biodiversity, 2018Co-Authors: Gerard Moutham, Michel Kulbicki, Antoine Gilbert, Jonas Tuahine, Serge AndrefouetAbstract:Assembly rules of fish communities in Tuamotu Archipelago lagoons have been previously investigated but without considering lagoons where shallow habitats are dominated by giant clam populations. We tested if assembly rules for 14 Atolls were challenged by such an atoll (Fangatau), and in doing so investigated the robustness of inter-island population patterns to specialized habitats. Fangatau had significantly higher proportions of Pomacentridae and Scaridae, but lower proportions of Labridae, Acanthuridae, Balistidae and Serranidae. Functionally, herbivores, omnivores, species <7 cm or between 50 and 80 cm, and species forming schools were found in higher proportions, while sessile invertebrate feeders, medium-size species (30–50 cm) and solitary species were lower. These differences were rather related to Fangatau isolation, as no other physical or ecological feature could explain them. Total richness, functional richness, and functional redundancy remained correlated mainly to atoll size, without outliers related to high clam abundance and presence of peculiar habitats.
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Revisiting wild stocks of black lip oyster Pinctada margaritifera in the Tuamotu Archipelago: The case of Ahe and Takaroa Atolls and implications for the cultured pearl industry
Estuarine Coastal and Shelf Science, 2016Co-Authors: Serge Andrefouet, Yoann Thomas, Franck DumasAbstract:Spat collecting of the black lip oyster (Pinctada margaritifera) is the foundation of cultured black pearl production, the second source of income for French Polynesia. To understand spat collecting temporal and spatial variations, larval supply and its origin need to be characterized. To achieve this, it is necessary to account for the stock of oysters, its distribution and population characteristics (size distribution, sex ratio). While the farmed stock in concessions can be easily characterized, the wild stock is elusive. Here, we investigate the distribution and population structure of the wild stock of Ahe and Takaroa Atolls using fine-scale bathymetry and in situ census data. Stocks were surprisingly low (similar to 666,000 and similar to 1,030,000 oysters for Ahe and Takaroa respectively) considering these two Atolls have both been very successful spat collecting Atolls in the past. Furthermore, in Ahe atoll, wild populations are aging with a dominant but small female population. Comparison with the cultured stock population (-14 millions oysters) and its dominant young male population suggests that to maximize larval supply and spat collecting on the long term, it would be useful to increase the number of females in selected sanctuaries. We discuss the implication of our findings for the long-term management of stocks and for spat collection in pearl farming Atolls, and for on-going numerical modelling studies on larval dispersal.
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Mass mortality events in atoll lagoons: environmental control and increased future vulnerability
Global Change Biology, 2015Co-Authors: Serge Andrefouet, Cyril Dutheil, Christophe E. Menkès, Margot Bador, Matthieu LengaigneAbstract:Coral reefs and lagoons worldwide are vulnerable environments. However, specific geomorphological reef types (fringing, barrier, atoll, bank for the main ones) can be vulnerable to specific disturbances that will not affect most other reefs. This has implications for local management and science priorities. Several geomorphologically closed Atolls of the Pacific Ocean have experienced in recent decades mass benthic and pelagic lagoonal life mortalities, likely triggered by unusually calm weather conditions lasting for several weeks. These events, although poorly known, reported, and characterized, pose a major threat for resource sustainability. Based on a sample of eleven events on eight Atolls from the central South Pacific occurring between 1993 and 2012, the conservative environmental thresholds required to trigger such events are identified using sea surface temperature, significant wave height and wind stress satellite data. Using these thresholds, spatial maps of potential risk are produced for the central South Pacific region, with the highest risk zone lying north of Tuamotu Archipelago. A regional climate model, which risk map compares well with observations over the recent period (r = 0.97), is then used to downscale the projected future climate. This allows us to estimate the potential change in risk by the end of the 21st century and highlights a relative risk increase of up to 60% for the eastern Tuamotu Atolls. However, the small sample size used to train the analysis led to the identification of conservative thresholds that overestimated the observed risk. The results of this study suggest that long-term monitoring of the biophysical conditions of the lagoons at risk would enable more precise identification of the physical thresholds and better understanding of the biological processes involved in these rare, but consequential, mass mortality events.
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climate variability and massive mortalities challenge giant clam conservation and management efforts in french polynesia Atolls
Biological Conservation, 2013Co-Authors: Serge Andrefouet, Antoine Gilbert, Christophe E. Menkès, Simon Van Wynsberge, Nabila Gaertnermazouni, Georges RemoissenetAbstract:Abstract In 2004, the first no-take area (NTA) dedicated to the conservation of giant clams Tridacna maxima was implemented in Tatakoto Atoll, French Polynesia. This NTA protected a unique area worldwide, with extraordinarily high giant clam densities (up to 337 individuals per m2 on 20-m transect). In 2012, a stock assessment survey revealed a dramatic decrease of the clam population. The reduced densities peaked at 38 ind m−2 and the stock in the NTA decreased from 20.1 ± 6.0 million to 1.9 ± 0.55 million clams (mean ± 95% confidence interval). Losses of similar proportions were observed throughout the atoll. Remarkably, the 83% overall loss of this natural resource used daily for consumption and for exports of clam meat to Tahiti Island went unnoticed by the local population. Field clues, including the size of live juveniles attached to the inside of dead shells, pointed to a massive mortality occurring about 3 years before the 2012 survey. Examinations of sea surface temperature satellite data identified a high range of temperature variations before March 2009. In agreement with past and recent events in other Atolls, this anomaly is the most likely explanation of the massive loss of giant clams in Tatakoto Atoll, although the exact hydrological and biological secondary mechanisms that occurred in the lagoon remain unclear. The consequences of the massive die-off inside and outside the NTA require new long-term management strategies, by reinforcing the top-down national giant clam management arrangements and by setting flexible management objectives across a network of islands.
Georges Remoissenet - One of the best experts on this subject based on the ideXlab platform.
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climate variability and massive mortalities challenge giant clam conservation and management efforts in french polynesia Atolls
Biological Conservation, 2013Co-Authors: Serge Andrefouet, Antoine Gilbert, Christophe E. Menkès, Simon Van Wynsberge, Nabila Gaertnermazouni, Georges RemoissenetAbstract:Abstract In 2004, the first no-take area (NTA) dedicated to the conservation of giant clams Tridacna maxima was implemented in Tatakoto Atoll, French Polynesia. This NTA protected a unique area worldwide, with extraordinarily high giant clam densities (up to 337 individuals per m2 on 20-m transect). In 2012, a stock assessment survey revealed a dramatic decrease of the clam population. The reduced densities peaked at 38 ind m−2 and the stock in the NTA decreased from 20.1 ± 6.0 million to 1.9 ± 0.55 million clams (mean ± 95% confidence interval). Losses of similar proportions were observed throughout the atoll. Remarkably, the 83% overall loss of this natural resource used daily for consumption and for exports of clam meat to Tahiti Island went unnoticed by the local population. Field clues, including the size of live juveniles attached to the inside of dead shells, pointed to a massive mortality occurring about 3 years before the 2012 survey. Examinations of sea surface temperature satellite data identified a high range of temperature variations before March 2009. In agreement with past and recent events in other Atolls, this anomaly is the most likely explanation of the massive loss of giant clams in Tatakoto Atoll, although the exact hydrological and biological secondary mechanisms that occurred in the lagoon remain unclear. The consequences of the massive die-off inside and outside the NTA require new long-term management strategies, by reinforcing the top-down national giant clam management arrangements and by setting flexible management objectives across a network of islands.
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the giant clam tridacna maxima communities of three french polynesia islands comparison of their population sizes and structures at early stages of their exploitation
Ices Journal of Marine Science, 2006Co-Authors: Antoine Gilbert, Serge Andrefouet, Laurent Yan, Georges RemoissenetAbstract:feed Tahiti’s market (up to 50 t of wet matter y � 1 ), combined with the relatively small size of these lagoons, will soon call for management action to sustain a fishery that currently targets a large, virtually pristine stock. Hence, we present T. maxima population sizes and structures for two Atolls (Fangatau and Tatakoto) and one island (Tubuai), where high clam densities and population sizes have promoted a small-scale, but growing, commercial fishery since the late 1990s. We followed an earlier pilot study, in which a combination of remote sensing and in situ data provided an estimate of the Fangatau clam population size (23.6 � 5.3 million clams, mean � 95% confidence interval, for 4.05 km 2 of mapped lagoon). We obtain 88.3 � 10.5 and 47.5 � 5.2 million clams for Tatakoto (mapped area of 11.46 km 2 ) and Tubuai (mapped area of 16.3 km 2 ), respectively. Accounting for contrasted length frequency distribution curves and one common sizeeweight relationship, the total biomasses are 1485 � 177 t, 1162 � 272 t, and 2173 � 232 t of commercial flesh for Tatakoto, Fangatau, and Tubuai, respectively. In addition, given the legal restriction on collecting clams smaller than 12 cm, the legally harvestable biomasses are 958 � 114 t, 1038 � 247 t, and 1971 � 210 t of flesh for Tatakoto, Fangatau, and Tubuai, respectively. The ratio between legal and total stock is much smaller for Tatakoto because this atoll is dominated by small clams, unlike the other two sites. The differences in population size and structure are discussed in terms of natural environment (habitats, degree of aperture to the ocean, temperature variations), providing insights on the natural variability between two similar systems (Tatakoto and Fangatau), and between different systems (the two Atolls and the volcanic island of Tubuai), suggesting that future management schemes will have to be optimized locally.
Masayuki Fujikawa - One of the best experts on this subject based on the ideXlab platform.
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middle permian sponge microencruster bioherms in the akiyoshi limestone sw japan implications for late palaeozoic reef evolution on mid panthalassan Atolls
Geological Journal, 2012Co-Authors: Tsutomu Nakazawa, Katsumi Ueno, Masayuki FujikawaAbstract:Middle Permian lagoonal bioherms are described from mid-Panthalassan atoll carbonates (Akiyoshi Limestone) in the Akiyoshi accretionary complex, SW Japan. The bioherms are composed of frame-building sphinctozoan and inozoan sponges, together with encrusting organisms, including chaetetids, Shamovella, calcareous red algae, and other microbes. Of them, sphinctozoan sponges, Shamovella, and microbes (forming microbialites) are the most dominant. Chaetetids, which were predominant in the Early Pennsylvanian but rapidly decreased in the late Moscovian, are also common in these bioherms. Archaeolithoporella and bryozoans are rare, probably due to the low-energy lagoonal environment. This sponge–microencruster community replaced the Gzhelian–Asselian Palaeoaplysina–microencruster community on the Akiyoshi Atolls during the Sakmarian–Kubergandian interval. This drastic change in the reef-building community type almost coincides with the rapid deglaciation of the Gondwanan ice sheet and superplume activity beneath the mid-Panthalassan ocean. The prosperity of calcareous sponges was possibly controlled by environmental factors such as warming and eutrophication after the Gondwanan glaciation. Copyright © 2012 John Wiley & Sons, Ltd.
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gzhelian asselian palaeoaplysina microencruster reef community in the taishaku and akiyoshi limestones sw japan implications for late paleozoic reef evolution on mid panthalassan Atolls
Palaeogeography Palaeoclimatology Palaeoecology, 2011Co-Authors: Tsutomu Nakazawa, Katsumi Ueno, Hodaka Kawahata, Masayuki FujikawaAbstract:Abstract A Palaeoaplysina–microencruster reef community is recognized in the Gzhelian–Asselian interval of the Taishaku and Akiyoshi limestones in SW Japan, which represent accreted Panthalassan atoll carbonates. In a reef-core area of the atoll, the alga Palaeoaplysina acted as a framebuilder and was associated with various binders (e.g., Tubiphytes, Archaeolithoporella, cystoporate bryozoans, and microbialites) and sediment-bafflers such as fenestrate and cryptostomate bryozoans and phylloid algae. In a subtidal environment of the back-reef area, Palaeoaplysina and phylloid algae flourished as sediment-bafflers. A microbial community, including Tubiphytes and sessile foraminifers, was predominant in a very shallow, peritidal environment of the back-reef area. Palaeoaplysina was distributed mainly along the northern margin of Pangea and is regarded as a boreal element. During Gzhelian–Asselian time, its distribution extended to the tropical or subtropical Panthalassa Ocean due to global cooling. On the Akiyoshi Atolls, the Palaeoaplysina–microencruster community was succeeded by a sponge–microencruster community in the late Early Permian. The timing of this biotic turnover is similar to that of a change in climate from icehouse to greenhouse conditions, and coincides with superplume activity beneath the mid-Panthalassa Ocean.
Andréfouët Serge - One of the best experts on this subject based on the ideXlab platform.
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The wave regimes of the Central Pacific Ocean with a focus on pearl farming Atolls
'Elsevier BV', 2021Co-Authors: Dutheil Cyril, Jullien Swen, Aucan Jérôme, Menkès, Christope E., Le Gendre Romain, Andréfouët SergeAbstract:International audiencePearl farming sustainability in South Central Pacific (SCP) Atolls strongly depends on water quality and renewal. These factors are partly controlled by the wave conditions that impact the lagoon circulation. To characterize the wave conditions around 83 SCP Atolls including those hosting pearl farming activities, we used 18 years of WaveWatchIII simulation with a grid refined from 50 to 5 km resolution. Three regional wave regimes are statistically identified: two associated with long distant swells originating from mid-latitude storms, and one with local trade winds. All regimes occur with a relatively high frequency (22–44%), but with a marked seasonality. Wave conditions are also strongly modified locally during their propagation between the archipelagoes. Western and southern isolated Atolls generally have a single regime all around their rims. In contrast, central Tuamotu Atolls experience different regimes depending on their levels of protection. These results help understanding atoll hydrodynamics, which has implications for their management
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The lagoon geomorphology of pearl farming Atolls in the Central Pacific Ocean revisited using detailed bathymetry data
2020Co-Authors: Andréfouët Serge, Genthon Pierre, Pelletier Bernard, Le Gendre R., Friot C., Smith R.Abstract:The lagoons of seven French Polynesia and Cook Islands pearl farming Atolls (Raroia, Takume, Mopelia, Takapoto, Ahe, Takaroa and Manihiki) were surveyed using multibeam and mono-beam sounders. From the detailed bathymetry, morphometric variables (average and maximum depth, frequency-area of depth, lagoon area and volume) are computed and compared. Remarkable geomorphological structures highlighted by bathymetric variations include deep reticulated structures and pinnacles. The seven Atolls appear very different in abundance, size and density of these entities. Considering them as markers of the geological, sedimentological and eustatic processes that shape atoll lagoons, they are discussed in the context of the general theory of atoll lagoon formations involving karstic dissolution during Pleistocene or earlier low sea-level stands. In terms of pearl farming management, accurate bathymetric maps help pearl oyster wild stock assessment, development of circulation and biogeochemical models, better lagoon zoning and strategy to remove pearl farming derelict gears
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Monitoring pearl farming lagoon temperature with global high resolution satellite-derived products: An evaluation using Raroia Atoll, French Polynesia
'Elsevier BV', 2020Co-Authors: Van Wynsberge Simon, Aucan Jérôme, Le Gendre Romain, Sangare Nathanaël, Menkes Christophe, Liao Vetea, Andréfouët SergeAbstract:Temperature is important for pearl oyster reproduction, pelagic larval duration, and growth in the context of pearl farming, but has seldom been monitored over long periods in remote Atolls. To test if satellite-derived Sea Surface Temperature (SST) could provide a solution, two daily global SST products were compared with 18 high-precision loggers deployed during 10-months in the wide Raroia atoll (Tuamotu Archipelago, French Polynesia). The Multi-scale-Ultra-high-Resolution (MUR) SST was better correlated with lagoon temperature (r > 0.97) than the Global-Foundation-Sea-Surface-Temperature-Analysis (G1SST) SST (r
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Assembly rules of fish communities in Tuamotu archipelago atoll lagoons : the case of Fangatau, a lagoon dominated by giant clam habitats
2018Co-Authors: Mou-tham Gérard, Kulbicki Michel, Gilbert A., Tuahine J., Andréfouët SergeAbstract:Assembly rules of fish communities in Tuamotu Archipelago lagoons have been previously investigated but without considering lagoons where shallow habitats are dominated by giant clam populations. We tested if assembly rules for 14 Atolls were challenged by such an atoll (Fangatau), and in doing so investigated the robustness of inter-island population patterns to specialized habitats. Fangatau had significantly higher proportions of Pomacentridae and Scaridae, but lower proportions of Labridae, Acanthuridae, Balistidae and Serranidae. Functionally, herbivores, omnivores, species
Yannis P Papastamatiou - One of the best experts on this subject based on the ideXlab platform.
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Seasonal, diel, and tidal movements of green jobfish (Aprion virescens, Lutjanidae) at remote Hawaiian Atolls: implications for marine protected area design
Marine Biology, 2007Co-Authors: Carl G Meyer, Yannis P Papastamatiou, Kim N HollandAbstract:Empirical data quantifying the long-term movement patterns of coral reef top predators are needed in order to design marine protected areas (MPAs) that will provide these fishes with effective, long-term protection. Acoustic telemetry was used to quantify the movements of a large coral reef top predator (Aprion virescens, Lutjanidae; Hawaiian name ‘uku’) at five Atolls in the Northwestern Hawaiian Islands Marine National Monument (NWHIMNM) from May 2005 to September 2006. The study Atolls were located between 23.8°N, 166.2°W and 28.5°N, 178.3°W, and were separated from their nearest receiver-equipped neighbor by distances ranging from 100 to 478 km. No inter-atoll movements by uku were detected but individuals were seasonally site-attached to core activity areas of up to 12 km in length, and ranged up to 19 km across Atolls. Within their core areas, tagged uku exhibited diel and tidal habitat shifts, with the latter resulting in round trips of up to 24 km in 24 h. Seasonal uku migrations resulted in extended winter (October–April) absences from summer (May–September) core activity areas and may be linked to summer spawning. Large MPAs (i.e., entire islands, Atolls or banks) would probably be required for full protection of resident populations of adult uku, but such ‘island-scale’ MPAs will not benefit fisheries unless there is significant larval supply from MPAs to neighboring fished areas, or adult emigration over time scales exceeding the 16-month monitoring period of this study. A mixed management strategy of combining smaller MPAs with conventional measures (e.g., minimum size limits, catch, and effort restrictions) may be the best approach for sustaining uku fisheries. However, this would still require relatively large MPAs (12 km in length) to contain uku short-term (diel and tidal) movements, and seasonal migrations would still take uku beyond the boundaries of MPAs of this size. These fluxes across MPA boundaries could supply fish to fisheries but, if high exploitation rates exist, fishing could eliminate key MPA benefits such as increased numbers of large, highly fecund individuals.
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seasonal and diel movements of giant trevally caranx ignobilis at remote hawaiian Atolls implications for the design of marine protected areas
Marine Ecology Progress Series, 2007Co-Authors: Carl G Meyer, Kim N Holland, Yannis P PapastamatiouAbstract:We need to understand the long-term movement patterns of coral reef top predators in order to design marine protected areas that will provide these animals with effective, long-term pro- tection. We used acoustic telemetry to quantify the movements of giant trevally, a large coral reef top predator, at 5 Atolls in the Northwestern Hawaiian Islands Marine National Monument. We did not observe any inter-atoll movements but found that giant trevally were attached to core activity areas from which they made periodic atoll-wide excursions of up to 29 km. Within the core areas, the tagged fish exhibited diel habitat shifts. We identified Rapture Reef at French Frigate Shoals (FFS) atoll as a spawning site, where giant trevally form seasonal mating aggregations. Giant trevally that use Rapture Reef as their core daytime area live there year-round, whereas those that occupy other areas of FFS migrate to Rapture Reef in the summertime during specific phases of the moon. Although giant trevally were wide-ranging and would require large marine protected areas (e.g. entire Atolls or islands) to protect their entire range, core activity areas and spawning sites for giant trevally could be contained within relatively small marine protected areas. Identification of spawning sites could assist in the establishment of focused marine protected areas that, while quite small in size, could have significant impact in preserving the spawning biomass of this species. Very large marine protected areas are not feasible in most heavily populated areas, hence effective alternative management strategies must be found for this fishery-targeted, wide-ranging top predator. We sug- gest using a combination of relatively small marine protected areas, to protect core activity areas and spawning sites for giant trevally, and conventional measures such as minimum size or 'slot' limits to further safeguard spawning stocks.