Claude Payri

A comparison of Landsat ETM+, SPOT HRV, Ikonos, ASTER, and airborne MASTER data for coral reef habitat mapping in South Pacific islands

The performances of the Landsat-7 ETM+, ASTER, SPOT HRV, and Ikonos satellite sensors and the airborne MASTER (MODIS‐ASTER simulator) were compared for coral reef habitat mapping in South Pacific reefs. This unique image data set provided different spatial resolution (4 m for Ikonos to 30 m for Landsat-7 ETM+), spectral resolution (two visible bands for SPOT-HRV to five visible bands for MASTER) and digitization (8‐16 bits). We focused on two islands (Tahiti and Moorea, French Polynesia) with barrier and fringing structures representative of reefs of South Pacific volcanic islands. Five levels of benthic habitat complexity were defined (with three, four, five, seven, and nine classes). Using a supervised maximum likelihood algorithm, the comparisons suggested several trends in sensor performances. Overall accuracies of Landsat-7 ETM+ compared well with sensors with higher spatial (Ikonos) or spectral (MASTER) resolution for low or moderate habitat complexity mapping. For high-complexity mapping (nine classes), Ikonos performed best, suggesting that high spatial resolution is important. For low- and moderate-complexity mapping, MASTER performed best, suggesting that spectral resolution and digitization seem more critical. However, these trends must be discussed cautiously in the light of various factors before any generalization can be made. These factors include issues in reconciling-scaling ground-truth data at multiple spatial and thematic scale, reefs specificities, and environmental conditions during image acquisition.

PRIMARY PRODUCTION, CALCIFICATION, AND AIR‐SEA CO2 FLUXES OF A MACROALGAL‐DOMINATED CORAL REEF COMMUNITY (MOOREA, FRENCH POLYNESIA)1

Community metabolism and air‐sea carbon dioxide (CO2) fluxes were investigated in July 1992 on a fringing reef at Moorea (French Polynesia). The benthic community was dominated by macroalgae (85% substratum cover) and comprised of Phaeophyceae Padina tenuis (Bory), Turbinaria ornata (Turner) J. Agardh, and Hydroclathrus clathratus Bory (Howe); Chlorophyta Halimeda incrassata f. ovata J. Agardh (Howe); and Ventricaria ventricosa J. Agardh (Olsen et West), as well as several Rhodophyta (Actinotrichia fragilis Forskál (Børgesen) and several species of encrusting coralline algae). Algal biomass was 171 g dry weight· m−2. Community gross production (Pg), respiration (R), and net calcification (G) were measured in an open‐top enclosure. Pg and R were respectively 248 and 240 mmol Co2·m−2·d−1, and there was a slight net dissolution of CaCO3 (0.8 mmol · m−2·d−1). This site was a sink for atmospheric CO2 (10 ± 4 mmol CO2·m−2·d−1), and the analysis of data from the literature suggests that this is a general feature of algal‐dominated reefs. Measurement of air‐sea CO2 fluxes in open water close to the enclosure demonstrated that changes in small‐scale hydrodynamics can lead to misleading conclusions. Net CO2 evasion to the atmosphere was measured on the fringing reef due to changes in the current pattern that drove water from the barrier reef (a C02 source) to the study site.

Biodegradation of shells of the black pearl oyster, Pinctada margaritifera var. cumingii, by microborers and sponges of French Polynesia

The composition, distribution and infestation sequence of organisms that destroy the commercially valuable shells of the black oyster Pinctada margaritifera var. cumingii Jameson, 1901 were studied. Three ecologically different groups of boring (euendolithic) organisms were identified: (1) phototrophic boring microorganisms (cyanobacteria, Hyella caespitosa, Hyella sp., Mastigocoleus testarum, Plectonema terebrans, and green algae, Phaeophila dendroides, Ostreobium quekettii); (2) heterotrophic boring microorganisms (fungi, Ostracoblabe implexa); (3) filter-feeding boring organisms (sponges, Cliona margaritiferae, C. vastifica). The phototrophic endoliths dominate the external pristmatic region of the shell, whereas the valuable interior nacreous region is attacked mainly by heterotrophs. Boring patterns reflect in part the shape and behaviour of the organisms and in part the structural properties of the shell, and inflict different types of damage. Infestation starts with microbial borers, which prepare the conditions for later invasion by more damaging clionid sponges. The infestation begins always at the apex, the oldest part of the shells, from which the periostracum is often removed by natural attrition or by cleaning procedure. The rate of bioerosion in 1 yr-old hatchery shells is 36 times higher than in natural populations.

Molecular systematics, historical ecology, and phylogeography of Halimeda (Bryopsidales).

Halimeda (Bryopsidales), a genus of calcified, segmented green seaweeds, abounds in reefs and lagoons throughout the tropics. To investigate phylogenetic, phylogeographic, and historic ecological relationships of the genus, the nuclear rDNA including the SSU and both ITS regions were sequenced. A maximum likelihood tree revealed the following: (1) there were anatomical and morphological synapomorphies for five well-supported lineages; (2) the last common ancestor of one lineage invaded sandy substrata; those of two other lineages established in wave-affected habitats, whereas the cenancestor of the remaining two lineages occupied sheltered rocky slopes. Yet, several species adapted to new habitats subsequently, resulting in several cases of convergence; (3) all lineages separated into Atlantic and Indo-Pacific daughters, likely resulting from the rise of the Panamanian Isthmus. Each daughter pair gave rise to additional convergent species in similar habitats in different oceans; (4) Halimeda opuntia, the only monophyletic pantropical species detected so far, dispersed from the Indo-Pacific into the Atlantic well after the closure event; (5) minor SSU-sequence differences across species and phylogeographic patterns of vicariance indicated a relatively recent diversification of the extant diversity. Cretaceous and Early Tertiary fossil look-alikes of modern species must then have resulted from iterative convergence.

Phenolic contents of two brown algae, Turbinaria ornata and Sargassum mangarevense on Tahiti (French Polynesia): interspecific, ontogenic and spatio-temporal variations

Abstract To elucidate the possible implications of phenolic content in survival strategies of two tropical brown fucaleans, Turbinaria ornata and Sargassum mangarevense, we determined total phenolic contents in relation to ontogenic stages, and then followed spatio-temporal variations. Samples were collected at different sites and seasons. Both species exhibited low phenolic contents with, however, some differences: levels were higher in the algae from grazer- and nutrient-rich sites, and during the austral summer. Moreover, adults produced more phenolic compounds than immature stages. In addition, Turbinaria ornata had higher levels than Sargassum mangarevense. Parent thalli may exert an indirect protection of easily-grazed recruits which settle in close vicinity. The differences between species in protection of recruits would, therefore, derive from the respective species morphologies. A mechanical protection can be hypothesized in S. mangarevense because of its soft flexible thallus: plants can sweep around their base and, therefore, would need to produce less phenolics as a repellent than Turbinaria. On the other hand, due to its relatively tough texture, together with its upright-thallus, Turbinaria has a greater need to protect recruits by chemicals. The low phenolic content observed from thalli collected at the outer barrier reef may be explained by an exudation of phenolics after dessication.

Evolutionary history of the Corallinales (Corallinophycidae, Rhodophyta) inferred from nuclear, plastidial and mitochondrial genomes

Systematics of the red algal order Corallinales has a long and convoluted history. In the present study, molecular approaches were used to assess the phylogenetic relationships based on the analyses of two datasets: a large dataset of SSU sequences including mainly sequences from GenBank; and a combined dataset including four molecular markers (two nuclear: SSU, LSU; one plastidial: psbA; and one mitochondrial: COI). Phylogenetic analyses of both datasets re-affirmed the monophyly of the Corallinales as well as the two families (Corallinaceae and Hapalidiaceae) currently recognized within the order. Three of the four subfamilies of the Corallinaceae (Corallinoideae, Lithophylloideae, Metagoniolithoideae) were also resolved as a monophyletic lineage whereas members of the Mastophoroideae were resolved as four distinct lineages. We therefore propose to restrict the Mastophoroideae to the genera Mastophora, Metamastophora, and possibly Lithoporella in the aim of rendering this subfamily monophyletic. In addition, our phylogenies resolved the genus Hydrolithon in two unrelated lineages, one containing the generitype Hydrolithon reinboldii and the second containing Hydrolithon onkodes, which used to be the generitype of the now defunct genus Porolithon. We therefore propose to resurrect the genus Porolithon for the second lineage encompassing those species with primarily monomerous thalli, and trichocyte arrangements in large pustulate horizontal rows. Moreover, our phylogenetic analyses revealed the presence of cryptic diversity in several taxa, shedding light on the need for further studies to better circumscribe species frontiers within the diverse order Corallinales, especially in the genera Mesophyllum and Neogoniolithon.

190 Years of Sargassum Taxonomy, Facing the Advent of DNA Phylogenies

Sargassum C. Agardh is one of the morphologically most complex phaeophyceaen genera and represents the most species-rich genus of the brown algal order Fucales Bory de Saint-Vincent (Phaeophyceae). The genus’ classification system dates back to the 19th century and is based on observed differences in macro-morphological characters. Those morphological characters may display important variation within individual species, and several authors have linked the taxonomic complexity of the genus to its highly polymorphic nature and phenotypic plasticity. Among the large choice of existing species and subspecies epithets (about 1000), identifying taxa accurately is a difficult task, often relying on authors’ interpretation of short Latin diagnoses or descriptions published in local Floras. Recently, the study of individual species’ morphological range and DNA phylogenies underlined inconsistencies within low taxonomic levels (sections, subsections, series and species groups). Results highlighted the weak taxonomic value of traditional characters used to classify species, and pointed out significant taxonomic issues. The four Sargassum subgenera (S. subgen. Arthrophycus, Bactrophycus, Sargassum and Phyllotrichia) are now subdivided into a total of 12 sections and further subdivisions were abandoned. Two possible new sections need to be assessed. In the present paper, we raise the hypothesis that S. subgen. Arthrophycus could be merged to S. subgen. Bactrophycus, and that S. subgen. Phyllotrichia could be transferred to the recently reinstated genus Sargassopsis Trevisan. We also propose that two sections of the S. subgen. Bactrophycus: S. sect. Halochloa and Repentia be merged. A summary of the actual classification is given along with an identification key for Sargassum subdivisions.RésuméSargassum C. Agardh représente le genre le plus complexe et le plus riche de l’ordre des Fucales Bory de Saint-Vincent (Phaeophyceae). La classification du genre remonte au 19ème siècle et se base sur l’observation de plusieurs caractères macromorphologiques, lesquels peuvent montrer des variations importantes au niveau intra-spécifique. Plusieurs auteurs on mis en évidence le lien existant entre la complexité taxonomique du genre et sa nature polymorphique ainsi que sa plasticité phénotypique. Ainsi parmi le large choix d’épithètes d’espèces et de sous-espèces disponible pour Sargassum (près de 1000), identifier un taxon de façon précise est une tâche difficile reposant souvent sur l’interprétation de courtes diagnoses en Latin ou de descriptions disponibles dans des Flores locales. Récemment, l’analyse combinée de la variabilité morphologique et ADN pour des espèces étudiées individuellement, ont permis de mettre en évidence des incohérences au niveau infra-générique (sections, subsections, series et groupes d’espèces). Les résultats ont souligné la faible valeur taxonomique des caractères utilisés pour classer les espèces, et mis en évidence un certain nombre de conséquences taxonomiques. Les quatre sous-genres de Sargassum (S. subgen. Arthrophycus, Bactrophycus, Sargassum et Phyllotrichia) sont dorénavant sous-divisés en 12 sections, et les sous-divisions inférieures ont été abandonnées. Deux nouvelles sections potentielles nécessitent d’être évaluées. Dans ce papier, nous émettons deux hypothèses: (i) la fusion de S. subgen. Arthrophycus avec S. subgen. Bactrophycus, et (ii) le transfert de S. subgen. Phyllotrichia au genre Sargassopsis Trevisan récemment réintégré. Nous proposons la fusion de deux sections de S. subgen. Bactrophycus: S. sect. Halochloa et Repentia. Un résumé de la classification actuelle est donné avec une clef d’identification pour les sous-divisions du genre Sargassum.

Characterization of Exopolysaccharides Produced by Cyanobacteria Isolated from Polynesian Microbial Mats

Six cyanobacterial isolates recovered from Polynesian microbial mats, called “kopara,” were cultured using laboratory-closed photobioreactors and were shown to produce exopolymers as released and capsular exopolysaccharides (EPS). These polymers have been chemically characterized using colorimetric and elemental assays, infrared spectrometry, and gas chromatography. Both capsular and released EPS consisted of 7 to 10 different monosaccharides with neutral sugars predominating. Interestingly, four isolates exhibited sulfate contents ranging from 6% to 19%. On the basis of preliminary data, cyanobacteria from this unusual ecosystem appear to be an important source of novel EPS of a great interest in terms of their biological activities.

Multigene phylogenetic analyses support recognition of the Sporolithales ord. nov.

a Centre for Environmental and Molecular Algal Research, Department of Biology, P.O. Box 4400, University of New Brunswick, Fredericton, NB, Canada E3B 5A3 b UMR 7138/UR R148. ‘‘Systématique, Adaptation, Evolution”, Institut de Recherche pour le Développement, B.P. A5, 98848 Nouméa cedex, Nouvelle-Calédonie, France c UMR 7138 ‘‘Systématique, Adaptation, Evolution”, Département ‘‘Systématique et évolution”, Muséum National d’Histoire Naturelle, CP 39, 75231 Paris cedex 05, France

Halimeda contribution to organic and inorganic production in a Tahitian reef system

Of the seven species of Halimeda inhabiting a lagoon on Moorea island, three representing 10% of the algal covering and averaging 111 g of dry weight m-2, have been studied in the course of a year. The biomass, measured bimonthly, stresses a slight seasonal variability in the species life. The main decrease was reported for H. opuntia after a fruiting event, which happened in October. The primary production was assessed, in situ, periodically over a year, by measuring oxygen variations in enclosures. Either expressed on specific-weight basis or in area units, the highest primary productions were recorded for H. opuntia. Productions and biomasses vary simultaneously during the year. The three species produce all together about 6 g C m-2y-1. The growth rate of the sand-dwelling H. incrassata f. ovata was followed during the year by staining, in the field, individuals with alizarin Red-S. The average rates measured were 3.3 segments ind-1d-1 and 0.17 gdw d-1m-2. The contribution of the three species to the carbonate budget of the reef was estimated by total alkalinity measurements during 24-h cycles. H. opuntia had the highest CaCO3 production. For the three species studied, CaCO3 production of 1.4 kg m-2y-1, which could correspond to a 0.4mm/year accretion of the studied reefal system, was estimated.