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Outbreaks of Acanthaster planci (COTS) in French Polynesia were observed in 1969 and between 1980-1984 where concentrations as high as 110 ind/hectare were observed at Tahiti and Moorea in 1984. Subsequently, outer reef slopes have recovered their preoutbreak percentage coral cover. According to a general survey carried out at the end of 2006, COTS have increased in abundance on islands of both the Society (Tahiti, Moorea, Bora Bora, Raiatea, Huahine) and the Austral archipelagos (Rurutu), but not for the Tuamotu atolls (Manihi, Rangiroa, Tikehau, Fakarava). In order to evaluate the distribution and abundance of COTS at an island scale, a « manta tow » was developed to survey the outer reef slope along the 95 km perimeter of Moorea. This method consists of evaluating feeding marks and after establishing the correlation between feeding marks and COTS abundance, the density of COTS is calculated. Results from 2006-2007 show a mosaic distribution of COTS around Moorea. The outer slope of Moorea, between 10 and 30 m in depth was divided into sectors 250 m long, parallel with the reef crest. Only a few sectors (10 out of 395), mainly on the North and East coasts, show COTS concentrations above 17 ind, which is lower than in 1984. Other sectors show lower concentrations, of which 117 sectors had less than 2 COTS. A comparison of COTS densities between November 2006 and April 2007 does not indicate that the COTS outbreak is progressing. Nevertheless on some sectors with COTS, coral cover, mainly Acropora and Pocillopora, has been reduced by up to 50 %. Future surveys are planned to monitor this event and its consequences more...

This study provides the first detailed quantitative data on the sexual reproduction, larval development and settlement competency periods of broadcast spawning Acropora reef corals at Moorea, French Polynesia. From 2002 to 2004 the timing and mode of sexual reproduction for Acropora reef corals was examined at four sites on the outer reef slope and reef lagoon. To determine extent of spawning synchrony within and among species, colonies of Acropora spp. were tagged and repeatedly sampled, or collected for spawning in flow through outdoor aquaria, during September through November. Spawning was observed in aquaria and inferred in the field from the disappearance of mature gametes for 13 species of Acropora, between 6-9 nights after the full moon in September, October and November. Following spawning in November 2004, post fertilisation samples were taken from A. nasuta, A. striata and A. lutkeni to compare the morphological stages of embryo and larval development from early cleavage to ciliated planula larvae. Larval development and settlement competency periods were studied using A. retusa and A. striata planulae. Larval attachment onto settlement tiles occurred within 3-4 DAS (days after spawning) in both species. Peak periods of larval metamorphosis and permanent settlement occurred between 4-10 DAS for A. retusa and 5-10 DAS for A. striata. The early development and initial rapid attachment patterns of A. retusa and A. striata larvae indicate that some planulae may be retained close to their natal reef. However, the extended settlement competency periods observed in A. striata (31 DAS) and A. retusa (26 DAS) suggest that some planulae also have the potential for dispersal away from their natal reef before settling. This information is important for understanding and predicting the likely sources of larval supply to Moorea, and examining the potential likelihood of reef interconnectivity via larval dispersal in French Polynesia more...

Bleaching in corals can be attributed to loss of endosymbiotic zooxanthellae and/or loss of photosynthetic pigments within zooxanthellae. This major disturbance of the reef ecosystem is principally induced by increases in water temperature. Since the beginning of the 80's and the onset of global climate change, this phenomenon has been occurring at increasing rates and scales, and with increasing severity. In this study, we focused on finding early regulated genes involved in bleaching. In aquaria, one set of Pocillopora damicornis nubbins was subjected to a gradual seawater temperature increase from 28°C to 32°C over 15 days, and a second control set remained at constant temperature (28°C). Bleaching was monitored by measuring zooxanthellae density. The mRNA differentially expressed between the stressed state (sampled just before the onset of bleaching) and the non stressed state (control) were isolated from the nubbins by Suppression Subtractive Hybridization. The corresponding cDNA were sequenced and confronted to sequence databases to obtain gene similarities. Finally, transcription rates of the most interesting genes were conducted by Q-PCR. Two particularly interesting candidate genes showed an important decrease in their transcription rates following thermal stress and before zooxanthellae loss. These two genes show similarities with genes involved in host/symbiont and host/parasite models. The implication of these molecular actors suggests a possible role of recognition mechanisms between the host and its symbiont, in the breakdown of the symbiosis during the bleaching phenomenon. Experiments such as RACE-PCR, in situ hybridization and immunohistochemistry are currently underway to confirm our hypotheses more...

At a fundamental level, spatial variation in the abundance and community structure of scleractinian corals must be influenced by patterns of larval settlement. However, spatial variation in early post-settlement mortality has the potential to greatly distort patterns established at settlement, and the relative influence of variation in settlement rates and post-settlement processes on spatial dynamics of coral assemblages remains largely unknown. In this study, spatial variation in mortality of recruits (< 3 months of age) and juvenile corals (< 5 cm in diameter; ~1-4 years of age) was quantified in three depth zones at each of three locations and round Moorea, French Polynesia. Mortality of coral recruits was extremely variable and particularly high (50 % in 7 days), and is associated with the abundance of parrotfishes (Fam. Scaridae). Juvenile mortality was less intense (up to 40 % in 14 months), but also shows strong spatial variability, corresponding with variation in abundance of butterflyfishes (Fam. Chaetodontidae). Spatial variability in early post-settlement mortality partly accounts for apparent differences in the abundance of coral recruits versus juveniles corals, highlighting the potential importance of post-settlement processes as a driver of spatial variation in the dynamics of coral assemblages. Moreover, variation in early-post settlement mortality of corals appears to be influenced mainly by local densities of Scaridae and Chaetodontidae, which each affect a different stage in the life-cycle (recruits versus juvenile corals, respectively). more...

Temporal variability in coral community structure on the outer reef at Tiahura, Moorea (French Polynesia) was investigated between 1991 and 2006 to test for the effects of major disturbances. During the study, the reef was impacted by one cyclone (1991) and four bleaching events (1991, 1994, 2002, 2003). The cyclone and bleaching of 1991 had the greatest impact, and caused a rapid decline in coral cover from 51.0 % in 1991 to 24.2 % in 1992. In contrast, the three successive bleaching events had little effect on coral cover, even though the thermal anomalies causing these events were similar to the conditions leading to the 1991 bleaching. By 2001, coral cover returned to the 'pre-disturbance' levels of early 1991, but the trajectories of change differed among genera. Acropora was affected by the disturbances of 1991, but subsequently showed a high rate of recovery; Montipora was affected by most disturbances and showed no sign of recovery; Pocillopora was affected by the disturbances of 1991, and showed a partial recovery by 1995; and Porites was not affected by any disturbances, but increased in cover throughout the study. Our results demonstrate that large-scale disturbances are not always associated with a phase-shift from coral- to algal-dominated communities, but instead show that coral cover can recover rapidly after dramatic declines. To our knowledge, our study is the first contemporary analysis to demonstrate rapid recovery of coral cover, despite the effects of ongoing disturbances, although importantly this trend was achieved through a shift in the relative abundance of coral genera. Thus, coral communities at Tiahura appear to be characterized by ecological resilience to disturbances in terms of coral cover, but fragility in terms of generic composition more...