Search

Pollution by heavy metals remains today an important threat to the health of humans and ecosystems, but there is still a paucity of data on the response of early life stages of key organisms. In this context, the present work assessed the fertilization success rate of two Acropora species ( A. cytherea and A. pulchra ) from the French Polynesia reefs exposed to six increasing copper concentrations in seawater. The two species showed a relatively high tolerance to copper (4h30-EC 50 was 69.4 ± 4.8 μg L −1 and 75.4 ± 6.4 μg L −1 for A. cytherea and A. pulchra, respectively). As Cu concentration increases, an increasing proportion of deformed embryos was recorded (67.6% and 58.5% for A. cytherea and A. pulchra , respectively, at 220 μg Cu L −1 ). These results demonstrated thus, that high levels of copper could negatively impair the normal fertilization process of coral gametes and therefore alter the renewal of coral populations. Since the two Acropora species investigated in this study displayed a high resistance to copper, these results should be considered in the context of multiple stressors associated with climate change, where rising temperature or ocean acidification may significantly exacerbate copper toxicity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Mass coral bleaching events are one of the main threats to coral reefs. A severe bleaching event impacted Moorea, French Polynesia, between March and July 2002, causing of colonies to suffer bleaching around the island. However, bleaching varied significantly across coral genera, locations, and as a function of water depth, with a bleaching level as high as 72% at some stations. Corals in deeper water bleached at a higher rate than those in shallow water, and the north coast was more impacted than the west coast. The relatively small scale of variability in bleaching responses probably resulted from the interaction between extrinsic factors, including hydrodynamic condition, and intrinsic factors, such as differential adaptation of the coral/algal association. To cite this article: L. Penin et al., C. R. Biologies 330 (2007). [Copyright &y& Elsevier]