Trophic functioning of the Tiahura reef sector, Moorea Island, French Polynesia

 Energy-balanced steady-state models of the fringing and barrier reefs of Tiahura, Moorea Island, French Polynesia, are presented. A total of 43 and 46 trophic groups were identified on the two reef habitats respectively. The models’ outputs indicate that most of the substantial primary productivity is processed and recycled (59–69% of NPP) in the web through detritus based, microbially mediated food webs, with a substantial but secondary flux through grazer-based webs. This mechanism produces long pathways with low trophic efficiencies at the higher trophic levels. The trophic structure of both reef habitats efficiently conserves energy and materials within the reef ecosystem through two forms of internal recycling: a relatively large cycle produced through detritus and a microbial food web, and a relatively short one directly produced through predation. The models outputs suggest that bottom-up and top-down control are each ecologically important in both reef habitats. Accepted: 14 April 1997     

Storms may disrupt top-down control of algal turf on fringing reefs

Coral Reefs - Storms strongly affect coral reefs; one unstudied but potentially important outcome may be a decrease in herbivory, presumably through changes to freshwater, sediment and nutrient...     

Distributional patterns of mobile fauna associated with Halimeda on the Tiahura coral-reef complex (Moorea,French Polynesia)

This study deals with the mobile fauna living associated with the turfs of three Halimeda species [H. incrassata, H. opuntia (three forms) and H. macroloba] from the Tiahura Reef complex. Ten 0.05 m² test areas of each Halimeda form have been randomly sampled from each geomorphological reef unit in order to obtain the specific abundance and biomass of different faunistic groups and species living within Halimeda populations. Then the raw data have been classified using the correspondence factor analysis to highlight the relationships between faunistic groups, or species, and the different Halimeda forms studied. The distributional patterns of the faunal communities seems to be controlled by the morphological features of the host-alga. The complex arborescent structure of the rhyzophytic H. incrassata species shelters fauna three times higher in abundance than other Halimeda heads. This fauna is mostly composed of a highly rich community of microcrustaceans and a very diversified community of Syllidae polychaetes. H. macroloba living on the outer reef flat retains a lot of small Nereidae polychaetes and a rich microgastropod assemblage. Dense H. opuntia tussocks (type A) on the fringing-reef and isolated H. opuntia fronds of pendulous chains (type B) on the barrier reef as well as beds of scattered H. opuntia (type C) on the outer reef flat provide environment for larger animals, and according to their zone of life, they retain very different faunal associations. Some ophiuroids, and some fish, collected in H. opuntia A and C, are newly reported from the Society Islands, French Polynesia, and the Pacific province. One Brachyurid species is presumably undescribed.     

Catastrophic impact of hurricanes on atoll outer reef slopes in the Tuamotu (French Polynesia)

Underwater effects on coral reefs of the six hurricanes which ravaged French Polynesia between December 82 and April 83 were observed by SCUBA diving around high islands and atolls during September and October 1983. Special attention was paid to Tikehau atoll reef formations (Tuamotu archipelago) where quantitative studies on scleractinians, cryptofauna and fishes were conducted in 1982 immediatly prior to the hurricanes. On outer reef slopes coral destruction, varying from 50 to 100%, was a function of depth. Upper slope coral communities composed of small colonies well adapted to high energy level environments, suffered less than deeper formations. However, there is a narrow erosional trough in this zone at a depth of 6 m that was probably the result of storm-wave action (plunge point). Coral destruction was spectacular at depths greater than 12 m: 60 to 80% between 12 m and 30 m and 100% beyond 35 m, whereas earlier living coral coverage ranged from 60 to 75% in these zones. The outer slope was transformed into a scree zone covered with coarse sand and dead coral rubble. Dives on different sites around steep outer slopes (>45°) of the atolls and more gentle slopes (<25°) of some parts of the high islands permitted the formulation of an explanatory hypothesis: direct coral destruction by hurricane-induced waves occurred between the surface and 18–20 m; on low-angle slopes broken colonies were thrown up on reef flats and beaches; on steep slopes avalanches destroyed much of the living corals and left scree slopes of rubble and sand.     

Transformation of algal turf by echinoids and scarid fishes on French Polynesian coral reefs

The respective roles of regular echinoids and scarid fishes in the transformation of turf algae, the main food resource for reef herbivores, were investigated on French Polynesian coral reefs. The role of one species of parrotfish (Scarus sordidus) was compared with that of four species of echinoids. The degree and ways of degradation of the algal matter were determined by the organic matter percentage, the composition of the sugar fraction, and the concentration and composition of chlorophylltype pigments as assayed by HPLC analysis. Chemical analyses were performed on anterior and posterior intestines for scarids, intestinal contents and faeces for echinoids, and on fresh algal turf as a control of initial food quality. A decrease in mean percentage of organic matter in gut content was observed from intestine (9.7%) to faeces (7%) in sea urchins, but not in parrotfishes. The total sugar fraction decreased from fresh algal turf (32% of total organic matter) to echinoid (28%) to scarid (18%) gut contents. The ratio of insoluble to soluble sugars (I/S ratios) was higher in echinoids (2.6) than in scarid gut contents (1.0). A decrease in the total pigment concentration was measured from fresh algal turf to echinoid and it was found to be even lower in scarid gut contents. Chromatograms showed that the composition of chlorophyll-type pigments in scarid intestines was very similar to fresh algal turf, with a dominance of native forms, mainly chlorophyll a and b. On the contrary, degraded pigment forms dominated in echinoids. The main degraded products were pheophorbides in sea urchins, and chlorophyllides in parrotfishes. These results provided evidence for differentiation in digestive processes occurring in the two types of grazers. Echinoids released higher degraded algal material than did scarids. Thus, these two types of grazers play different roles in the recycling of organic matter on coral reefs.     

Spatio-temporal variability in fish recruitment to a coral reef (Moorea,French Polynesia)

Spatial and temporal patterns of recruitment of juvenile coral reef fishes were studied on the reefs of the high island of Moorea (Society Archipelago, French Polynesia) during the wet season (October 1988 to April 1989). Two size-classes of fishes (new-recruits and juveniles) were censused by visual counts within 24 quadrats along a transect across the lagoon. Correspondence analysis was used to calculate the hypothetical movements of the two size classes. Spatial variability was far more important than temporal variability; six main spatial communities were revealed, which could result from differences among habitats. Temporal variability in recuitment occurred only at nearshore stations; stations on the outer fringing reef and inner barrier reef displayed stable recruitment patterns.     

Sexual reproduction of Acropora reef corals at Moorea, French Polynesia

Little information is available on reproductive processes among corals in isolated central Pacific reef regions, including French Polynesia. This study examined the timing and mode of sexual reproduction for Acropora reef corals at Moorea. Spawning was observed and/or inferred in 110 Acropora colonies, representing 12 species, following full moon periods in September through November 2002. Gamete release was observed and inferred in four species of Acropora between 9 and 13 nights after the full moon (nAFM) in September 2002. Twelve Acropora spp. spawned gametes between 5 and 10 nAFM in October 2002, with six species spawning 7 nAFM and four species spawning 9 nAFM. In November 2002, spawning of egg and sperm bundles was observed and inferred in 27 colonies of Acropora austera, 6 nAFM. These are the first detailed records of spawning by Acropora corals in French Polynesia.     

Predation on the urchin Echinometra lucunter (Linnaeus) by migratory shorebirds on a tropical reef flat

Predation on urchins by migratory shorebirds was investigated during tidal exposure of the reef flat at Galeta, Panama. Avian predators, primarily ruddy turnstones Arenaria interpres (Linnaeus) reduced the patchiness of Echinometra lucunter (Linnaeus), the most abundant urchin on the reef flat. No mortality of E. lucunter occurred in quadrats protected from avian predation. No mortality occurred when urchin crowding was increased experimentally in protected areas. Stress-induced mortality could not be determined from the condition of tests alone, since turnstones were capable of removing lantern and internal organs without damage to the test. The importance of shorebird predation in reef communities during aerial exposure can be hard to detect because mortality can occur during brief periods, at night, and without damage to urchin tests.     

Direct measurements of carbon and carbonate export from a coral reef ecosystem (Moorea Island , French Polynesia)

The export of carbon and carbonate from coral reefs was investigated through a multidisciplinary investigation of the hydrological, geochemical, sedimentological and biological features of Tiahura reef on the northwestern coast of Moorea Island (French Polynesia). The hydrology of the fore-reef is characterised by prevailing longshore western currents and a strong thermocline. As revealed by turbidity structures (benthic and intermediate nepheloid layers) and by the amount of particles collected by near-bottom sediment traps, horizontal and downslope advections of particles dominate over offshore vertical transport. The exported material is rich in carbonate (ca. 80%) and poor in organic matter (ca. 4%). Sedimentation rates at 430 m depth, i.e. definitive export, reached 209.6 mg m^-2 d^-1 (dry weight). Estimates of carbon and carbonates export for Tiahura reef also reported here represent respectively 47% and 21% of the organic and inorganic carbon produced within the reef.     

Identical digeneans in coral reef fishes from French Polynesia and the Great Barrier Reef (Australia) demonstrated by morphology and molecules

Three coral reef fish species, Zanclus cornutus, Chaetodon vagabundus and Naso lituratus, were collected in French Polynesia and on the Great Barrier Reef, Queensland. These fish species were each infected by one morphologically similar digenean species in both localities; Schistorchis zancli Hanson, 1953 was found in Zanclus cornutus, Preptetos laguncula Bray and Cribb, 1996 in Naso lituratus and Neohypocreadium dorsoporum Machida and Uchida, 1987 in Chaetodon vagabundus. In addition, on the Great Barrier Reef P. laguncula was also found in Naso unicornis and N. dorsoporum in Chaetodon ephippium and Chaetodon flavirostris. Morphometric differences between the species from the two sites were only slight. Sequences from the second internal transcribed spacer of the ribosomal DNA of each worm revealed total homology or negligible divergence between samples from hosts caught in French Polynesia and on the Great Barrier Reef. These results show that across more than 6000 km these digeneans are similar in morphology and genotype. Some species of fishes and molluscs are considered to have distributions that encompass the entire tropical Indo-West Pacific. These findings suggest that at least some of their parasites have similarly broad distributions.     

Zonation of macrobenthic communities along two bays in an insular coral reef ecosystem (Moorea, French Polynesia)

Zonation of macrobenthic communities (corals, algae, molluscs, sponges and echinoderms) on fringing reefs was investigated in two bays in a coral reef ecosystem (Moorea, French Polynesia). Species richness, abundance and coral cover, and species richness of macroalgae increased from the bayhead to the bay entrance. For molluscs and sponges, no general trend was observed. Species richness and abundance of echinoderms increased from the head to the entrance of Opunohu Bay, but this trend was less pronounced in Cook Bay. The gradients observed for corals, macroalgae and echinoderms were correlated with one or several of the following abiotic factors: salinity, turbidity, concentration of silicates in surface waters, and concentrations of organic carbon, carbohydrates and amino acids in the sediments. These factors are associated with terrestrial run-off via river discharge that occurs at the bayheads, where the major river is located. The high degree of confinement in the bayheads allowed the establishment of only a few tolerant macrobenthic species. Although the low diversity and abundance of corals and echinoderms seem to be a characteristic of Polynesian bays, a high diversity of corals can be found in the vicinity of the bayheads in coral reefs of the western Pacific.     

Two new species of Prosorhynchoides (Digenea: Bucephalidae) from Tylosurus crocodilus (Belonidae) from the great barrier reef and French Polynesia

We surveyed 14 individuals of Tylosurus crocodilus Péron & Lesueur 1821 (Belonidae) collected from the waters around Lizard Island and Heron Island, Great Barrier Reef, Queensland, Australia, and the waters around Moorea, French Polynesia. We describe two new species of bucephaline trematodes from them, Prosorhynchoides galaktionovi n. sp. and P. kohnae n. sp. They are morphologically distinct from existing Prosorhynchoides spp., with molecular data from 28S and ITS-2 ribosomal DNA, as well as cox1 mitochondrial DNA, further supporting our morphological findings. Neither species has been observed in other belonid fishes. The new species fall into the clade of species of Prosorhynchoides from belonids previously identified in Australian waters. These findings strengthen the observation that groups of bucephaline species have radiated, at least in part, in tight association with host taxa. There are now five species of Prosorhynchoides known from two belonid species in Australian waters. We, therefore, predict further richness in the nine other belonid species present.     

Genetic evidence of closed life-cycles for some coral reef fishes within Taiaro Lagoon (Tuamotu Archipelago, French Polynesia)

 Taiaro Lagoon has no permanent or regular connection with the ocean (ingress is restricted to episodes of high sea-level and/or strong wave action) raising the question of how fish populations with normally dispersive larvae are maintained inside this lagoon. We compared the genetic population structures of two coral reef fishes, Acanthurus triostegus and Chaetodon ulietensis, present on both sides of the atoll rim to determine whether there is evidence of reproductive isolation. Genetic surveys showed that the lagoonal and oceanic populations were statistically different at five loci (AAT ^* -3, GDA ^*, HPD ^*, MDH ^* and SDH ^*) in A. triostegus and three loci (PGI-2^*, IDH ^* and PGD ^*) in C. ulietensis, producing high F _st values of 0.055 and 0.021, respectively. Our genetic and demographic data on these species suggest that both may be completing their life-cycles inside the lagoon, which leads us to question the common assumption that coral reef fishes require oceanic conditions for larval development. Accepted: 28 August 1997     

Phytoplankton and its contribution to primary productivity in two coral reef areas of French Polynesia

A study of phytoplankton productivity and related parameters was carried out in two fringing and barrier reef systems around Moorea island (Tiahura lagoon) and Tahiti (Vairao lagoon), Society Islands, during July–August 1974.In Tiahura lagoon, which is the narrower and the shallower, phytoplankton standing crop and production are extremely low; photosynthetic assimilation, as measured in situ by the ¹⁴C method, ranges from 4 to 27 mg C m^?2 day^?1, presumably less than in the impoverished open ocean, but it is surprisingly high at a station just outside the barrier reef (645 mg C m^?2 day^?1) as the result of some island mass effect. As compared to the latter station, the lagoon shows a ten-times increase in particle content and glucose uptake, and a higher percentage of decomposition products of plant pigments. These data support the concept that, in such environments where benthic primary producers prevail, phytoplankton may have lost its ‘usual’ rôle in the aquatic food web.Vairao lagoon, a deeper and wider one, subjected to a greater extent to land fertilization, is more productive (103–420 mg C m^?2 day^?1). Considering this difference, as well as the considerable range of phytoplankton production in coral reef areas of the world, the need for a trophic classification of such ecosystems is emphasized.     

Preliminary insights into the population characteristics and distribution of reef (Mobula alfredi) and oceanic (M. birostris) manta rays in French Polynesia

Coral Reefs - In French Polynesia, both currently recognized manta ray species, Mobula alfredi and M. birostris, are observed. Despite being an important cultural asset and generating significant...     

Revision of Ixora (Rubiaceae) in the Marquesas Islands (French Polynesia)

During the preparation of the Vascular Flora of the Marquesas Islands and Flore de la Polynésie française , four new species of Ixora L. (Rubiaceae) have come to light and are described and illustrated herein: Ixora jourdanii Mouly & J.Florence, Ixora tahuataensis Mouly & J.Florence, Ixora uahukaensis Lorence & W.L.Wagner, and Ixora uapouensis Lorence & W.L.Wagner. In addition to these new taxa, the following three species of Ixora previously described from the Marquesas are recognized: Ixora marquesensis F.Br., Ixora ooumuensis J.Florence, and Ixora spathoidea F.Br. As the Marquesan environment is under serious threat from human impact, feral animals and weeds, the conservation status was estimated for each Ixora species. It is concluded that all Marquesan taxa are in need of inclusion in the IUCN Red List, their status ranging from endangered to critically endangered.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 581–597.     

Coral reefs modify their seawater carbon chemistry – case study from a barrier reef (Moorea,French Polynesia)

Changes in the carbonate chemistry of coral reef waters are driven by carbon fluxes from two sources: concentrations of CO₂ in the atmospheric and source water, and the primary production/respiration and calcification/dissolution of the benthic community. Recent model analyses have shown that, depending on the composition of the reef community, the air‐sea flux of CO₂ driven by benthic community processes can exceed that due to increases in atmospheric CO₂ (ocean acidification). We field test this model and examine the role of three key members of benthic reef communities in modifying the chemistry of the ocean source water: corals, macroalgae, and sand. Building on data from previous carbon flux studies along a reef‐flat transect in Moorea (French Polynesia), we illustrate that the drawdown of total dissolved inorganic carbon (C_T) due to photosynthesis and calcification of reef communities can exceed the draw down of total alkalinity (A_T) due to calcification of corals and calcifying algae, leading to a net increase in aragonite saturation state (Ω_a). We use the model to test how changes in atmospheric CO₂ forcing and benthic community structure affect the overall calcification rates on the reef flat. Results show that between the preindustrial period and 1992, ocean acidification caused reef flat calcification rates to decline by an estimated 15%, but loss of coral cover caused calcification rates to decline by at least three times that amount. The results also show that the upstream–downstream patterns of carbonate chemistry were affected by the spatial patterns of benthic community structure. Changes in the ratio of photosynthesis to calcification can thus partially compensate for ocean acidification, at least on shallow reef flats. With no change in benthic community structure, however, ocean acidification depressed net calcification of the reef flat consistent with findings of previous studies.