Interactive effects of ocean acidification and temperature on two scleractinian corals from Moorea,French Polynesia

This study tested the hypothesis that the response of corals to temperature and pCO ₂ is consistent between taxa. Juvenile massive Porites spp. and branches of P. rus from the back reef of Moorea were incubated for 1 month under combinations of temperature (29.3 °C and 25.6 °C) and pCO ₂ (41.6 Pa and 81.5 Pa) at an irradiance of 599 μmol quanta m^?2 s^?1. Using microcosms and CO₂ gas mixing technology, treatments were created in a partly nested design (tanks) with two between‐plot factors (temperature and pCO ₂), and one within‐plot factor (taxon); calcification was used as a dependent variable. pCO ₂ and temperature independently affected calcification, but the response differed between taxa. Massive Porites spp. was largely unaffected by the treatments, but P. rus grew 50% faster at 29.3 °C compared with 25.6 °C, and 28% slower at 81.5 Pa vs. 41.6 Pa CO₂. A compilation of studies placed the present results in a broader context and tested the hypothesis that calcification for individual coral genera is independent of pH, [HCO₃ ^?], and [CO₃ ^2?]. Unlike recent reviews, this analysis was restricted to studies reporting calcification in units that could be converted to nmol CaCO₃ cm^?2 h^?1. The compilation revealed a high degree of variation in calcification as a function of pH, [HCO₃ ^?], and [CO₃ ^2?], and supported three conclusions: (1) studies of the effects of ocean acidification on corals need to pay closer attention to reducing variance in experimental outcomes to achieve stronger synthetic capacity, (2) coral genera respond in dissimilar ways to pH, [HCO₃ ^?], and [CO₃ ^2?], and (3) calcification of massive Porites spp. is relatively resistant to short exposures of increased pCO ₂, similar to that expected within 100 y.     

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.     

Small-scale variability in the size structure of scleractinian corals around Moorea, French Polynesia: patterns across depths and locations

The size structure of coral populations is influenced by biotic and physical factors, as well as species-specific demographic rates (recruitment, colony growth, mortality). Coral reefs surrounding Moorea Island are characterized by strong environmental gradients at small spatial scales, and therefore, we expected that the size structure of coral populations would vary greatly at this scale. This study aimed at determining the degree of spatial heterogeneity in the population size structure of two coral taxa, Pocillopora meandrina and massive Porites spp., among depths (6, 12, and 18 m) and among locations (Vaipahu, Tiahura and Haapiti) representing different exposure to hydrodynamic forces. Our results clearly underlined the strong heterogeneity in the size structure of both P. meandrina and massive Porites spp., with marked variation among depths and among locations. However, the lack of any consistent and regular trends in the size structure along depths or among locations, and the lack of correlation between size structure and mean recruitment rates may suggest that other factors (e.g., stochastic life history processes, biotic interactions, and disturbances) further modify the structure of coral populations. We found that the size structure of P. meandrina was fundamentally different to that of massive Porites spp., reflecting the importance of life history characteristics in population dynamics. Handling editor: I. Nagelkerken     

Effects of disturbance on coral communities: bleaching in Moorea,French Polynesia

This study examines patterns of susceptibility and short-term recovery of corals from bleaching. A mass coral bleaching event began in March, 1991 on reefs in Moorea, French Polynesia and affected corals on the shallow barrier reef and to >20 m depth on the outer forereef slope. There were significant differences in the effect of the bleaching among common coral genera, with Acropora, Montastrea, Montipora, and Pocillopora more affected than Porites, Pavona, leptastrea or Millepora. Individual colonies of the common species of Acropora and Pocillopora were marked and their fate assessed on a subsequent survey in August, 1991 to determine rates of recovery and mortality. Ninety-six percent of Acropora spp. showed some degree of bleaching compared to 76% of Pocillopora spp. From March to August mortality of bleached colonies of Pocillopora was 17%, 38% recovered completely, and many suffered some partial mortality of the tissue. In contrast, 63% of the Acropora spp. died, and about 10% recovered completely. Generally, those colonies with less than 50% of the colony area affected by the bleaching recovered at a higher rate than did those with more severe bleaching. Changes in community composition four months after the event began included a significant decrease only in crustose algae and an increase in cover of filamentous algae, much of which occupied plate-like and branching corals that had died in the bleaching event. Total coral cover and cover of susceptible coral genera had declined, but not significantly, after the event.     

Temporal variations of macroborers in massive Porites lobata on Moorea,French Polynesia

Massive colonies of Porites lobata on the barrier reef of Tiahura, Moorea, can be divided into four categories: living colonies, colonies consisting of 50% live coral and 50% dead skeleton, 100% dead coral and colonies which have been reduced to a basal plate. Replicate samples of each of these colony types were collected in the same vicinity of the barrier reef during October 1987. The macroborers were extracted, identified, counted and their volumes determined by displacement. Kruskal-Wallis tests showed that three different boring communities occur within these four categories of Porites colonies. Live colonies are characterised by only 3 species, the bivalve, Lithophaga laevigata; the vermetid Dendropoma maximun; and the non boring serpulid polychaete Spirobranchus. The completely dead colonies contain up to 17 boring species, with five to six individuals per 100 cm. Sipunculans are the dominant bioeroders with the most abundant species being Aspidosiphon elegans, sp A and sp B. Colonies of Porites which have been reduced to basal plates contain up to 18 boring species of which the bivalve Lithophaga hanleyana and the sipunculan Aspidosiphon sp. B are the most abundant.The cumulative volume of CaCO₃ lost by boring activity increases from 0.1 cm³ per 100 cm³ in a completely dead Porites colony to 1.4 cm³ per 100 cm³ in the residual basal plates of Porites. These can be extrapolated to minimum losses of 14.2 kg m^-3. We suggest that rates of boring increase with the time which has elapsed since the death of the colony and the dominant agents of boring also change with increasing age of the coral structure. There are significant additional losses of 5.25 kg m^-3 CaCO₃ caused by grazing echinoids and scarids.     

Recent disturbances augment community shifts in coral assemblages in Moorea, French Polynesia

Coral reefs are often subject to disturbances that can cause enduring changes in community structure and abundance of coral reef organisms. In Moorea, French Polynesia, frequent disturbances between 1979 and 2003 caused marked shifts in taxonomic composition of coral assemblages. This study explores recent changes in live cover and taxonomic structure of coral communities on the north coast of Moorea, French Polynesia, to assess whether coral assemblages are recovering (returning to a previous Acropora-dominated state) or continuing to move towards an alternative community structure. Coral cover declined by 29.7% between July 2003 and March 2009, mostly due to loss of Acropora and Montipora spp. Coral mortality varied among habitats, with highest levels of coral loss on the outer reef slope (7–20 m depth). In contrast, there was limited change in coral cover within the lagoon, and coral cover actually increased on the reef crest. Observed changes in coral cover and composition correspond closely with the known feeding preferences and observed spatial patterns of Acanthaster planci L., though observed coral loss also coincided with at least one episode of coral bleaching, as well as persistent populations of the corallivorous starfish Culcita novaeguineae Muller & Troschel. While climate change poses an important and significant threat to the future structure and dynamics coral reef communities, outbreaks of A. planci remain a significant cause of coral loss in Moorea. More importantly, these recent disturbances have followed long-term shifts in the structure of coral assemblages, and the relative abundance of both Pocillopora and Porites continue to increase due to disproportionate losses of Acropora and Montipora. Moreover, Pocillopora and Porites dominate assemblages of juvenile corals, suggesting that there is limited potential for a return to an Acropora-dominated state, last recorded in 1979.     

Sediment processing by the surgeonfish Ctenochaetus striatus at Moorea, French Polynesia

The sediment-feeding surgeonfish Ctenochaetus striatus was found to reduce the sizes of ingested carbonaceous particles. The mean sizes of particles in stomach samples of the surgeonfish were smaller than those from areas where the fish were observed feeding. The particle sizes in the rectal contents of the fish were smaller than those in the stomach samples. The sediment-feeding activities of this and related surgeonfishes are likely to have a local impact on the particle-size distributions of sediments in reef and lagoon habitats. The assimilation efficiencies of the fish were estimated by the ash-ratio method to be 20% for total organic matter and 37% for nitrogen.     

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     

Spatiotemporal distribution of nocturnal coral reef fish juveniles in Moorea Island,French Polynesia

This study aimed to investigate the spatial structure of nocturnal fish communities at settlement on coral reefs in Moorea Island lagoon, French Polynesia; and the temporal consistency of habitat selection between winter (April to June 2001) and summer (November 2001). The Moorea lagoon was divided into 12 habitat zones (i.e., coral reef zones), which were distinct in terms of depth, wave exposure, and substratum composition. Nocturnal visual censuses among the 12 habitats found that the recently settled juveniles of 25 species recorded were dispatched among three communities spatially distributed according to the distance from the reef crest (reef crest, barrier reef, and fringing reef communities). This spatial communities structure of nocturnal juveniles was consistent in both winter and summer and would be explained primarily by a current gradient in Moorea lagoon (current speed was high near the reef crest and decreased towards the beach) and by the topographic characteristics of reef zones. Among the 25 species, 13 were recorded in both winter and summer. A comparison of the spatial distribution between summer and winter for 13 species that occurred during both seasons found that only 4 differed between the two seasons. For these species, habitat selection would be organized primarily by some stochastic processes such as inter- and intraspecific competition, predation, and food availability. Overall, the present study allowed us to highlight that most nocturnal coral reef fish juveniles at Moorea Island exhibited striking patterns in their distribution and current and topographic characteristics of reef zones might exert considerable influence on the distribution of fishes.     

Distributions of coral reef macroalgae in a back reef habitat in Moorea,French Polynesia

On tropical reefs where macroalgae are subjected to continuous herbivore pressure, spatial refuges typically are identified as large-scale, landscape interfaces that limit foraging behavior. However, algal distributions and community assemblages may also rely on the availability of smaller scale spatial refuges within the reef. The results of this study demonstrate that the patterns of macroalgal distribution across the back reef of Moorea, French Polynesia, are maintained by herbivores interacting with the small-scale structural complexities of the coral reef landscape. Although the majority of space available for colonization is composed of exposed surfaces, macroalgae rarely are found in the open. Instead, macroalgal occurrence is highest in the protected narrow crevices and hole microhabitats provided by massive Porites spp. coral heads. These distributions are determined initially by post-settlement mortality of young algal recruits in exposed habitats. Rates of consumption for two of the most common macroalgal species found in refuges across the back reef, Halimeda minima and Amansia rhodantha, indicate that algal recruits in exposed habitats are limited by herbivory. While algal abundance and community structure are highly dependent upon herbivore grazing, the availability of small-scale spatial refuges ultimately shapes the distinct community patterns and distributional boundaries of coral reef macroalgae in the back reefs of Moorea.     

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.     

Spatio-temporal heterogeneity in coral recruitment around Moorea, French Polynesia: Implications for population maintenance

The spatio-temporal variability of scleractinian coral recruitment was investigated from December 2000 to December 2003 around Moorea Island (French Polynesia). Nine stations, each with 20 terracotta tiles, were placed on the outer reef slope, at 3 sites (Vaipahu, Tiahura, Haapiti), and at 3 depths (6, 12 and 18 m). The relative contribution of the different families of recruits (Pocilloporidae: 60.4%, Poritidae: 18.8%, Acroporidae: 11.2%) and the very low recruitment rates (maximum: 35 recruits per tile, higher mean densities of 10.8 recruits per tile, average 40.77 recruits m^− 2 year^− 1) recorded at Moorea are similar to recruitment patterns recorded on sub-tropical reefs. Over the duration of the study period, we detected a marked seasonal variability in recruitment rates, with the peak recruitment for all families recorded in December-March periods, corresponding to periods of warmest SSTs. However, recruits of Acroporidae were also relatively abundant in the September-December period in some years, which coincides with the known spawning periods of some Acropora species. Total recruitment rate decreased after the first year of the survey, and was probably the result of the bleaching event that occurred in early 2002, which may have reduced fecundity of some coral populations. A lower proportion of recruits were found on the upper surface of the tiles (14.5%), compared to the lower surfaces (57.1%) and sides (28.4%), which is likely the result of intense grazing by herbivorous fish and urchins. We detected a patchy distribution at the station scale, and a significant variation in recruitment patterns among depths and sites. Pocilloporidae recruited more abundantly at 6 and 18 m, whereas Poritidae were generally more abundant at 12 m depth. In contrast, Acroporidae showed no clear depth pattern during the study period. Recruitment was lowest at the most exposed site (Haapiti), especially for Acroporidae, and probably reflects lower settlement rates and/or higher early post-settlement mortality caused by frequent high swells and their associated strong currents. These distinctive characteristics in recruitment patterns of the 3 dominant families of recruits underline the important role of life history strategies in understanding the spatial patterns, dynamics and maintenance processes of coral populations. The relatively low coral recruitment rates recorded from this study indicate that recovery from severe or frequent perturbations will be slow.     

Temporal and Spatial Comparisons of Underwater Sound Signatures of Different Reef Habitats in Moorea Island,French Polynesia

As environmental sounds are used by larval fish and crustaceans to locate and orientate towards habitat during settlement, variations in the acoustic signature produced by habitats could provide valuable information about habitat quality, helping larvae to differentiate between potential settlement sites. However, very little is known about how acoustic signatures differ between proximate habitats. This study described within- and between-site differences in the sound spectra of five contiguous habitats at Moorea Island, French Polynesia: the inner reef crest, the barrier reef, the fringing reef, a pass and a coastal mangrove forest. Habitats with coral (inner, barrier and fringing reefs) were characterized by a similar sound spectrum with average intensities ranging from 70 to 78 dB re 1μPa.Hz^-1. The mangrove forest had a lower sound intensity of 70 dB re 1μPa.Hz^-1 while the pass was characterized by a higher sound level with an average intensity of 91 dB re 1μPa.Hz^-1. Habitats showed significantly different intensities for most frequencies, and a decreasing intensity gradient was observed from the reef to the shore. While habitats close to the shore showed no significant diel variation in sound intensities, sound levels increased at the pass during the night and barrier reef during the day. These two habitats also appeared to be louder in the North than in the West. These findings suggest that daily variations in sound intensity and across-reef sound gradients could be a valuable source of information for settling larvae. They also provide further evidence that closely related habitats, separated by less than 1 km, can differ significantly in their spectral composition and that these signatures might be typical and conserved along the coast of Moorea.     

Changes in Bleaching Susceptibility among Corals Subject to Ocean Warming and Recurrent Bleaching in Moorea,French Polynesia

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.     

Feeding diets and significance of coral feeding among Chaetodontid fishes in Moorea (French Polynesia)

The feeding diets of 18 Chaetodontid fishes from a coral reef of Moorea (French Polynesia) were studied by quantitative analysis of their stomach contents. Three major types of feeding behaviours were distinguished. Sixteen species essentially ingested coral polyps. Among these species, 5 were exclusive coral browsers and the others displayed more heterogeneous diets. One species was a plankton feeder and the other consumed benthic invertebrates other than corals. The importance of coral consumption on the reef by Chaetodontid fishes was estimated knowing the feeding diets and density of species in the various biota. Moreover, the species which were previously observed as quantitatively dominant in the different reef zones, were found to be exclusive coral browsers. Besides, the proportion between obligative and facultative coral feeders was found to be relatively constant on the reef, emphasizing that a balance is established among the Chaetodontid species occupying the same habitat for the resource partitioning.     

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.     

Hormones and reproduction in scleractinian corals

Most broadcast spawning scleractinian corals synchronously release gametes during a brief annual spawning period. In southern Taiwan, the mass spawning of scleractinians occurs in lunar mid-March. The exact cues triggering this annual phenomenon remain unclear. A scleractinian coral, Euphyllia ancora has been selected as a model for the hormones and reproduction studies. Testosterone (T) and estradiol (E2) in free and glucuronided forms were identified and consistently detected in coral polyps throughout the year. Peak levels of free E2, glucuronided E2 and T were obtained in the coral tissue just prior to spawning. The presence of specific aromatase activity was demonstrated in coral tissue. Higher concentrations of free E2 than glucuronided E2 were detected in the coral tissue throughout the year. In contrast, higher levels of glucuronided E2 than free E2 and glucuronided T were found in seawater during mass coral spawning. Furthermore, immunoreactivity and biological activity of immunoreactive gonadotropin-releasing hormone (irGnRH) was detected and quantified in coral tissue. Coral extracts (irGnRH) and mammalian (m)GnRH agonist had a similar dose-dependent effect on luteinizing hormone (LH) release in black porgy fish pituitary cells (in vitro). Peak levels of irGnRH were detected during the spawning period. In in vivo experiments, mGnRH agonist time- and dose-dependently stimulated aromatase activity, as well as the levels of T and E2 in free and glucuronided forms in coral. In conclusion, our data suggest that irGnRH and glucuronided E2 may play important roles in the control of reproduction and mass spawning in corals.     

Spatial distribution and coexistence of monogenean gill parasites inhabiting two damselfishes from Moorea island in French Polynesia

The ectoparasite fauna of two damselfishes, Stegastes nigricans and Dascyllus aruanus, from Moorea Island in French Polynesia was investigated. Gills of these damselfishes were infected with congeneric Monopisthocotylea Monogenea belonging to the genus Haliotrema. Stegastes nigricans were found to harbour a guild of three Haliotrema species whereas only one species inhabited D. aruanus. Microhabitat distribution, inter- and intraspecific competition and interspecific associations on the gill were studied. Observations on site preference revealed no spatial segregation between the three congeneric species inhabiting the gills of S. nigricans. Juvenile and adult monogeneans of that guild occurred on the same microhabitat. The dominant species Haliotrema sp. 1 did not expand on the microhabitat when the intensity of infection increased. Interspecific association tests revealed positive and negative associations. Haliotrema sp. 4 expanded its distribution on the gills of Dascyllus aruanus when the intensity of infection increased suggesting the likelihood of intraspecific competition. Juvenile and adult monogeneans of Haliotrema sp. 4 appeared to segregate as a result of intraspecific competition. This competition may exist to enhance resource availability when the gill habitat is limited. Overlaps between niche breadth and species microhabitat were revealed for monogenean species inhabiting S. nigricans. Interspecific competition did not appear to play an important role in the distribution of S. nigricans congeneric ectoparasites. Reinforcement of reproductive barriers may have led to the avoidance of hybridization.