Depleted dissolved organic carbon and distinct bacterial communities in the water column of a rapid-flushing coral reef ecosystem

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in The ISME Journal 5 (2011): 1374–1387, doi:10.1038/ismej.2011.12.Coral reefs are highly productive ecosystems bathed in unproductive, low-nutrient oceanic waters, where microbially-dominated food webs are supported largely by bacterioplankton recycling of dissolved compounds. Despite evidence that benthic reef organisms efficiently scavenge particulate organic matter and inorganic nutrients from advected oceanic waters, our understanding of the role of bacterioplankton and dissolved organic matter in the interaction between reefs and the surrounding ocean remains limited. Here we present the results of a four-year study conducted in a well-characterized coral reef ecosystem (Paopao Bay, Moorea, French Polynesia) where changes in bacterioplankton abundance and dissolved organic carbon (DOC) concentrations were quantified and bacterial community structure variation was examined along spatial gradients of the reef:ocean interface. Our results illustrate that the reef is consistently depleted in concentrations of both DOC and bacterioplankton relative to offshore waters (averaging 79 µmol L-1 DOC and 5.5 X 108 cells L-1 offshore and 68 µmol L-1 DOC and 3.1 X 108 cells L-1 over the reef, respectively) across a four year time period. In addition, using a suite of culture-independent measures of bacterial community structure, we found consistent differentiation of reef bacterioplankton communities from those offshore or in a nearby embayment across all taxonomic levels. Reef habitats were enriched in Gamma-, Delta-, and Beta-proteobacteria, Bacteriodetes, Actinobacteria and Firmicutes. Specific bacterial phylotypes, including members of the SAR11, SAR116, Flavobacteria, and Synechococcus clades, exhibited clear gradients in relative abundance among nearshore habitats. Our observations indicate that this reef system removes oceanic DOC and exerts selective pressures on bacterioplankton community structure on timescales approximating reef water residence times, observations which are notable both because fringing reefs do not exhibit long residence times (unlike those characteristic of atoll lagoons) and because oceanic DOC is generally recalcitrant to degradation by ambient microbial assemblages. Our findings thus have interesting implications for the role of oceanic DOM and bacterioplankton in the ecology and metabolism of reef ecosystems.This project was supported by the US National Science Foundation Moorea Coral Reef Long Term Ecological Research project (NSF OCE-0417412) through minigrants to CAC and NSF OCE-0927411 to CAC as well as the MIRADA-LTERs program (NSF DEB-0717390 to LAZ)

Origine, transport et devenir des apports naturels et anthropiques dans le lagon sud-ouest de Nouvelle-Calédonie

L’ird (Institut de recherche pour le développement) conduit depuis dix ans un programme pluridisciplinaire sur les effets des apports naturels et anthropiques sur le fonctionnement du lagon de Nouvelle-Calédonie. Celle-ci connaît actuellement une croissance de sa population et un développement de son industrie minière. Trois grands types d’apports sont pris en compte : les particules entraînées par l’érosion des sols et des sous-sols et dont l'accumulation brutale peut être responsable du dépôt de quantités considérables de sédiments, les métaux potentiellement toxiques pour les organismes vivant dans le lagon et les éléments nutritifs susceptibles de conduire les eaux jusqu'à l’eutrophisation (confinement chimique conduisant à l'élimination de nombreuses espèces vivantes et à la dominance d'un petit nombre d'autres). Le présent article offre trois exemples de problématiques environnementales qui n'ont pu être résolues qu’au moyen de la fédération de différentes approches de recherche complémentaires : l’influence des courants sur la dispersion des particules détritiques en provenance de l'île, le devenir des métaux dans le lagon et leur accumulation dans les organismes, les effets des apports en nutriments sur les communautés planctoniques et les risques d'eutrophisation. Les résultats de ces recherches sont présentés tout en conservant à l’esprit les objectifs nécessairement appliqués d’un programme de recherche pour le développement. Il s’agit principalement de définir les bases scientifiques permettant d’identifier certains outils de diagnostic environnemental et de développer des approches de simulation mathématique susceptibles d'offrir une vision synthétique et prévisionnelle de l’état et du devenir des environnements lagonaires sous influence anthropique.For the past ten years, the ird (Institut de recherche pour le développement) has developed a multidisciplinary programme dealing with the effects of natural and anthropogenic terrigenous inputs on the New Caledonia coral reef lagoon which is currently subjected to environmental pressure due to population increase and development of the mining industry. The ongoing study focused on three main categories of inputs: (i) particles generated by erosion processes and responsible for excessive sediment inputs in the lagoon, (ii) metals exhibiting a potentially lethal effect on the lagoon biota, (iii) nutrients responsible for eutrophication. This article presents three examples of environmental issues that could be addressed through complementary research approaches: (i) the dispersion of terrigenous inputs as commended by currents, (ii) the fate of metals in the lagoon and their accumulation in the biota, (iii) the effects of nutrient enrichment on pelagic communities. Results are presented while keeping in mind the necessary applied outcomes requested from a research programme devoted to development issues. Such outcomes are mainly related to the identification of suited environmental diagnostic tools and to the development of modelling approaches yielding synthetic and predictive information on the status and fate of coral reef lagoons subject to anthropogenic stress

Biomass, production and heterotrophic activity of bacterioplankton in the Great Astrolab Reef lagoon (Fiji

Abstract Biomass, production and heterotrophic activity of bacterioplankton were determined for two weeks in the Great Astrolabe Reef lagoon, Fiji. Bacterial and Bacterial activities were distributed homogeneously throughout the water column (20 to 40m deep) and varied little from site to site inside the lagoon. Bacterioplankton biomass and production also varied little over a diel period with coefficients of variation of 9 and 22%, respectively. On average, over the whole study, bacterial abundance was 0.77 x lo9 cells 1-l and bacterial production averaged 0.36 yg-at. C 1-l d-l. Bacterial abundance and production were greater in the lagoon than in oceanic waters. Attachment to particles seems to provide an advantage for bacterioplankton growth because specific growth rates for attached bacterioplankton were, on average, significantly greater than that of the free community. Growth efficiency, determined by correlating the net increase of bacterial biomass and the net decrease of dissolved organic carbon (DOC) in dilution cultures, was very low (average 6.6%). Using carbon growth efficiency and bacterial production rates, heterotrophic activity was estimated to average 5.4j.i.g-at. C 1-l du'. The turn-over rate of DOC (average 114 yg-at. C 1-I) due to bacterial consumption was estimated to be 0.048d-I during the period of study

Comparing taxonomic and morphological biodiversity of tintinnids (planktonic ciliates) of New Caledonia

Tintinnid ciliates are planktonic grazers of nanoplankton. They have a lorica (or shell) into which the ciliate cell can withdraw. The lorica provides information on both the identity and the ecology of the organism because characteristics of the lorica distinguish species and the diameter of the oral opening is related to the size of prey ingested. We examined the relationship between biodiversity estimates on the basis of classifying specimens as belonging to a species or a simple morphological group defined by lorica oral diameter (LOD) in a presumably species-rich area, a tropical lagoon. Two sites were sampled in the lagoon off Nouméa over an annual cycle. The tintinnid fauna was species-rich (76 species) and represented a relatively even distribution of LOD sizes compared to other tropical and temperate sites. Median LOD varied with the fraction of the chlorophyll concentration by �10 �m. Total chlorophyll concentration was related to tintinnid concentration and, in turn, weakly correlated with numbers of species and LOD size-classes. Numbers of species were closely related to numbers of LOD size-classes as were H � of species and H � (Shannon index) of LOD size-classes. Thus, metrics of a morphological characteristic, related to the ecology of the organisms, can be used to estimate species diversity. With the exception of prokaryotes, organisms are distinguished from each other largely on the basis of morphology

Temporal variations of microbial activity and diversity in marine tropical sediments (New Caledonia Lagoon)

International audienceTemporal variations of oxygen consumption, sensitivity to metal spiking, and microbial diversity were investigated during a one-year survey at the sediment-water interface in the tropical lagoon of New Caledonia. Sediment oxygen consumption (SOC) exhibited strong variations with time with maximum rates during February (Austral summer) and minimum values during July (cold period). SOC was strongly positively correlated with temperature, with an apparent activation energy (E a) of 41 kJ mol-1, corresponding to an apparent Q 10(20-30°C) of 1.75. Strong short-term variations of SOC were also observed with ratios between two consecutive samplings reaching up to twofold of magnitude within one week, whereas the maximum/minimum ratio over the whole year was equal to 2.73. In most cases, metal spiking led to a strong decrease of SOC; however, in a third of sampling dates, spiking did not significantly decrease activity. These periods of apparent metal tolerance were not characterized by a particular bacterial community structure. Bacterial community structure estimated from terminal restriction fragment length polymorphism (T-RFLP) analysis exhibited strong variations over the one-year survey, and no seasonality was observed for bacterial richness. However, on average, the Whittaker similarity index between two consecutive T-RFLP profiles was above 60% suggesting a relative stability of the bacterial community structure on the short timescale with prominent T-RFs representing on average more than 67% of relative abundance occurring over most of the year, whereas other T-RFs only occurred during some periods

Effect of Ni and black carbon addition on bacterial production, respiration and community composition on aggregates in the barrier reef Lagoon of Noumea (New Caledonia)

International audienceThe barrier reef lagoon of Noumea (New Caledonia) is potentially influenced by Ni and black carbon (BC) rich aerosols (the two latter originating from a Ni power plant). Experiments were performed with lagoon water collected close to the reef crest to assess the effect of anthropogenic influences on bacterial abundance (BA), production (BP), respiration (BR), growth efficiency (BGE) and community composition (BCC) in artificial produced aggregates. In both treatments, BA and VA were not affected or enhanced compared to the unamended control (up to 40% for BA and 180% for VA). BP was not or negatively affected (up to70%). No clear trend was found for BR in the Ni treatment; in the BC treatment BR was enhanced by 63-69%. BGE was reduced in both treatments. The strongest effects on BCC profiles as determined by 16S rDNA denaturing gradient gel electrophoresis were due to incubation time treatment particularly for BC. BP was not or negatively (-38-70%) influenced. A phylotype corresponding to a specific BC band was closely related to Acinetobacter oleivorans DR1. Thus, this experimental study confirms potential anthropogenic influences for the bacterial and viral community on aggregates in the Bay of Noumea

Chlorophylls and Phycoerythrins as Markers of Environmental Forcings Including Cyclone Erica Effect (March 2003) on Phytoplankton in the Southwest Lagoon of New Caledonia and Oceanic Adjacent Area

Spatio-temporal variations of chlorophylls and phycoerythrins, inferred by spectrofluorometric methods, were studied from April 2002 to June 2003 in the southwest lagoon and oceanic waters of New Caledonia. Trade winds blew 75% of the time and appeared as the main factor influencing surface Tchla (sum of monovinyl- and divinyl-chlorophyll a) variations in the ocean, near the barrier reef. Lagoon and oceanic waters differed in the composition of picoplanktonic cyanobacteria with a relative dominance of Prochlorococcus and high-phycourobilin Synechococcus in the ocean, and a relative dominance of high-phycoerythrobilin Synechococcus in the lagoon. Main pigment variations in the lagoon were associated with cyclone Erica in March 2003 and showed a 5-6 fold Tchla increase around Nouméa. The cyclone stimulated mainly diatom growth as indicated by the high chlorophyll (c1+c2)/chlorophyll a ratio and by the lowest values for the other pigment ratios. The relative importance of divinyl-chlorophyll a concentration and fluorescence excitation spectra of phycoerythrins appeared as useful tools for characterizing lagoon-ocean exchanges