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Pratchett M.S.,James Cook University | McCowan D.,James Cook University | Maynard J.A.,CNRS Insular Research Center and Environment Observatory | Maynard J.A.,Center for Marine Science | And 2 more authors.
PLoS ONE | Year: 2013

Background:Climate-induced coral bleaching poses a major threat to coral reef ecosystems, mostly because of the sensitivities of key habitat-forming corals to increasing temperature. However, susceptibility to bleaching varies greatly among coral genera and there are likely to be major changes in the relative abundance of different corals, even if the wholesale loss of corals does not occur for several decades. Here we document variation in bleaching susceptibility among key genera of reef-building corals in Moorea, French Polynesia, and compare bleaching incidence during mass-bleaching events documented in 1991, 1994, 2002 and 2007. Methodology/Principal Findings:This study compared the proportion of colonies that bleached for four major genera of reef-building corals (Acropora, Montipora, Pocillopora and Porites), during each of four well-documented bleaching events from 1991 to 2007. Acropora and Montipora consistently bleached in far greater proportions (up to 98%) than Pocillopora and Porites. However, there was an apparent and sustained decline in the proportion of colonies that bleached during successive bleaching events, especially for Acropora and Montipora. In 2007, only 77% of Acropora colonies bleached compared with 98% in 1991. Temporal variation in the proportion of coral colonies bleached may be attributable to differences in environmental conditions among years. Alternately, the sustained declines in bleaching incidence among highly susceptible corals may be indicative of acclimation or adaptation.Conclusions/Significance:Coral genera that are highly susceptible to coral bleaching, and especially Acropora and Montipora, exhibit temporal declines in their susceptibility to thermal anomalies at Moorea, French Polynesia. One possible explanation for these findings is that gradual removal of highly susceptible genotypes (through selective mortality of individuals, populations, and/or species) is producing a coral assemblage that is more resistant to sustained and ongoing ocean warming. © 2013 Pratchett et al. Source

Vignaud T.,CNRS Insular Research Center and Environment Observatory | Clua E.,Direction Regionale Recherche et Technology | Mourier J.,CNRS Insular Research Center and Environment Observatory | Maynard J.,CNRS Insular Research Center and Environment Observatory | And 2 more authors.
PLoS ONE | Year: 2013

The population dynamics of shark species are generally poorly described because highly mobile marine life is challenging to investigate. Here we investigate the genetic population structure of the blacktip reef shark (Carcharhinus melanopterus) in French Polynesia. Five demes were sampled from five islands with different inter-island distances (50-1500 km). Whether dispersal occurs between islands frequently enough to prevent moderate genetic structure is unknown. We used 11 microsatellites loci from 165 individuals and a strong genetic structure was found among demes with both F-statistics and Bayesian approaches. This differentiation is correlated with the geographic distance between islands. It is likely that the genetic structure seen is the result of all or some combination of the following: low gene flow, time since divergence, small effective population sizes, and the standard issues with the extent to which mutation models actually fit reality. We suggest low levels of gene flow as at least a partial explanation of the level of genetic structure seen among the sampled blacktip demes. This explanation is consistent with the ecological traits of blacktip reef sharks, and that the suitable habitat for blacktips in French Polynesia is highly fragmented. Evidence for spatial genetic structure of the blacktip demes we studied highlights that similar species may have populations with as yet undetected or underestimated structure. Shark biology and the market for their fins make them highly vulnerable and many species are in rapid decline. Our results add weight to the case that total bans on shark fishing are a better conservation approach for sharks than marine protected area networks. © 2013 Vignaud et al. Source

van der Merwe P.,University of Tasmania | Lannuzel D.,University of Tasmania | Lannuzel D.,Center for Marine Science | Bowie A.R.,University of Tasmania | And 3 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2011

Iron is a fundamental nutrient limiting phytoplankton growth in vast regions of the Southern Ocean. Sea ice, which covers ~80% of the Southern Ocean (south of 60°S) during maximum extent, can concentrate iron up to two orders of magnitude higher than in the underlying sea water. The fractionation of iron between the particulate and dissolved fractions depends on the location and type of sea-ice formation and can impact on the bioavailability of this important trace element. This study is the first to document iron fractionation and concentration in both pack and fast ice during a single research study. Sampling was from within the 110-130°E sector of Antarctica. We observed markedly higher concentrations of particulate iron at our fast-ice site (0.96-214. nM) relative to several pack-ice sites (0.87-77.7. nM). A high particulate-to-dissolved iron ratio was observed at the fast-ice site (285:1) relative to the highest observed in pack ice (23:1). This suggests a decoupling between the sources and/or sinks of the dissolved and particulate fractions. Preferential release of dissolved iron (and not particulate iron) into brines at all sites sampled with the sack hole method (and therefore indicative of brine drainage) indicates the diffuse nature of the dissolved fraction. Furthermore, this indicates that there may be a temporal decoupling between the release of the dissolved and the particulate fractions into the water column as sea ice becomes more permeable during the seasonal melt. Implications for phytoplankton production in Antarctic sea ice are discussed. © 2010 Elsevier Ltd. Source

Norman L.,Bangor University | Thomas D.N.,Bangor University | Stedmon C.A.,University of Aarhus | Granskog M.A.,University of Lapland | And 9 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2011

An investigation of coloured dissolved organic matter (CDOM) and its relationships to physical and biogeochemical parameters in Antarctic sea ice and oceanic water have indicated that ice melt may both alter the spectral characteristics of CDOM in Antarctic surface waters and serve as a likely source of fresh autochthonous CDOM and labile DOC. Samples were collected from melted bulk sea ice, sea ice brines, surface gap layer waters, and seawater during three expeditions: one during the spring to summer and two during the winter to spring transition period. Variability in both physical (temperature and salinity) and biogeochemical parameters (dissolved and particulate organic carbon and nitrogen, as well as chlorophyll a) was observed during and between studies, but CDOM absorption coefficients measured at 375nm (a375) did not differ significantly. Distinct peaked absorption spectra were consistently observed for bulk ice, brine, and gap water, but were absent in the seawater samples. Correlation with the measured physical and biogeochemical parameters could not resolve the source of these peaks, but the shoulders and peaks observed between 260 and 280nm and between 320 to 330nm respectively, particularly in the samples taken from high light-exposed gap layer environment, suggest a possible link to aromatic and mycosporine-like amino acids. Sea ice CDOM susceptibility to photo-bleaching was demonstrated in an in situ 120 hour exposure, during which we observed a loss in CDOM absorption of 53% at 280nm, 58% at 330nm, and 30% at 375nm. No overall coincidental loss of DOC or DON was measured during the experimental period. A relationship between the spectral slope (S) and carbon-specific absorption (a* 375) indicated that the characteristics of CDOM can be described by the mixing of two broad end-members; and aged material, present in brine and seawater samples characterised by high S values and low a* 375; and a fresh material, due to elevated in situ production, present in the bulk ice samples characterised by low S and high a* 375. The DOC data reported here have been used to estimate that approximately 8TgCyr-1 (~11% of annual sea ice algae primary production) may be exported to the surface ocean during seasonal sea ice melt in the form of DOC. © 2010 Elsevier Ltd. Source

Van Hooidonk R.,National Oceanic and Atmospheric Administration | Van Hooidonk R.,University of Miami | Maynard J.A.,CNRS Insular Research Center and Environment Observatory | Maynard J.A.,Center for Marine Science | And 3 more authors.
Global Change Biology | Year: 2014

Coral reefs and the services they provide are seriously threatened by ocean acidification and climate change impacts like coral bleaching. Here, we present updated global projections for these key threats to coral reefs based on ensembles of IPCC AR5 climate models using the new Representative Concentration Pathway (RCP) experiments. For all tropical reef locations, we project absolute and percentage changes in aragonite saturation state (Ωarag) for the period between 2006 and the onset of annual severe bleaching (thermal stress >8 degree heating weeks); a point at which it is difficult to believe reefs can persist as we know them. Severe annual bleaching is projected to start 10-15 years later at high-latitude reefs than for reefs in low latitudes under RCP8.5. In these 10-15 years, Ωarag keeps declining and thus any benefits for high-latitude reefs of later onset of annual bleaching may be negated by the effects of acidification. There are no long-term refugia from the effects of both acidification and bleaching. Of all reef locations, 90% are projected to experience severe bleaching annually by 2055. Furthermore, 5% declines in calcification are projected for all reef locations by 2034 under RCP8.5, assuming a 15% decline in calcification per unit of Ωarag. Drastic emissions cuts, such as those represented by RCP6.0, result in an average year for the onset of annual severe bleaching that is ~20 years later (2062 vs. 2044). However, global emissions are tracking above the current worst-case scenario devised by the scientific community, as has happened in previous generations of emission scenarios. The projections here for conditions on coral reefs are dire, but provide the most up-to-date assessment of what the changing climate and ocean acidification mean for the persistence of coral reefs. © 2013 John Wiley & Sons Ltd. Source

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