Mehdi Adjeroud

Patterns of genetic variation do not correlate with geographical distance in the reef‐building coral Pocillopora meandrina in the South Pacific

Dispersal may be a critical factor in the ability of reef‐building corals to recover after major disturbances. We studied patterns of geographical structure using four microsatellite markers in seven South Pacific populations of Pocillopora meandrina, a major coral species from Polynesia. Variation within populations showed evidence of heterozygote deficiency. Genetic differentiation between populations was detected at a large scale (2000 km) between the Tonga and the Society Islands. Within the Society Islands, four of the five studied populations from Bora Bora, Moorea and Tahiti were not significantly different from each other. Unexpectedly, one of the three populations surveyed in Moorea was genetically different from the other two populations of this island (that were 5 and 10 km apart), and from the populations of the other two surveyed islands in this archipelago. We cannot rule out the possibility that this pattern is an equilibrium state, whereby short‐range dispersal is locally more differentiating than long‐range dispersal, as has been suggested by similar patterns reported in other studies. An alternative explanation that is globally consistent with all observations is that this is the signature of a large‐scale destruction event, as for instance a bleaching event, followed by the recent restoration of populations by new colonists.

Factors influencing spatial distribution of fish communities on a fringing reef at Mauritius, S.W. Indian Ocean

This paper analyses the spatial patterns of fish communities on a narrow fringing reef of Mauritius and identifies some controlling factors. Canonical Correspondence Analysis revealed that the location in the reef ecosystem, the living coral coverage, and the proximity to a dredged area were the major factors controlling the distribution and abundance of fish species. Two distinct communities were observed across the fringing reef, representing a land-ocean gradient. The low diversity of fish species, and also of invertebrates such as corals, molluscs, and echinoderms is probably a consequence of the narrowness of the fringing reef and of anthropogenic impacts, notably the high pollution by nutrients.

Zonation des communautés macrobenthiques le long de deux baies d’un écosystème corallien insulaire (Moorea, Polynésie française)

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.

Répartition spatiale des Chaetodontidae dans différents secteurs récifaux de l’ïle de Moorea, Polynésie française

Abstract:Species composition (presence-absence and abundance) of chaetodontid fish assemblages has been investigated at four sites on Moorea Island (French Polynesia), in order to understand the spatial distribution of the butterflyfishes and to establish their relations with some benthic groups. Four fish assemblages were identified, each one typical of a particular geomorphological entity of the reef: (1) the fringing reef of the lagoon and the reef flat of the fringing reef of bays, (2) the barrier reef and the reef crest of the fringing reef of bays, (3) the reef wall of the fringing reef of bays, and (4) the outer slope (coastal oceanic assemblage). Chaetodontid fish assemblages of bays are intermediate between the assemblages of the lagoon and of the ocean. Among the five macrobenthic groups considered (corals, algae, molluscs, echinoderms, sponges), corals seem to be the most important factor affecting the spatial distribution of butterflyfishes. The other groups are also of some importance; this r...

Long-term changes of epibenthic macrofauna communities in a closed lagoon (Taiaro Atoll, french Polynesia) : 1972-1994

Epibenthic macrofauna communities (species composition and densities of the dominant species) were investigated at Taiaro Atoll, Tuamotu Archipelago, 22 years after a previous survey. This small atoll is completely closed, has no permanent functional hoa, and is not affected by direct anthropogenic disturbances since it is a Biosphere Reserve. Ten species were identified in 1994 (5molluscs, 4 corals, and 1 echinoderm). With the 14 species identified in 1972 (12 molluscs, 1 coral, and 1 echinoderm), a total of 17 species (12 molluscs, 4 corals, and 1 echinoderm) has been recorded for the lagoon. There has been a shift in dominance away from the bivalve Crassostrea cucullata (in 1972) to Pinctada maculata (in 1994). A high mortality of the epibenthic macrofauna affected the central part of the lagoon shortly before1972 and reached the inner reef flat afterwards. The distance of Taiaro from sources of colonizers, its small size, and the isolation of its lagoonal waters posing a physical barrier to colonization by organisms and leading to harsh environmental conditions (e.g. very high salinities: 42.5–43 psu), are likely to be the major causes of the exceptionally low diversity observed.

Importance of Recruitment Processes in the Dynamics and Resilience of Coral Reef Assemblages

Recruitment is now widely recognized as a fundamental process governing spatial patterns, dynamics, and maintenance of marine invertebrate communities. Moreover, recruitment is a critical factor for successful recovery following disturbances and thus resilience of ecosystems. Over the last decades, tropical coral reefs, which are one of the most diverse ecosystems on Earth and provide goods and services to ~500 million people, have been confronted with various types of natural and anthropogenic disturbances, causing widespread mortality of reef-building coral species. In this context, understanding processes of coral recruitment and their patterns in time and space is a fundamental step to understand, detect, and predict the effects of climate change on reef ecosystems. Despite major advancements in the last three decades, our understanding of some critical phases of coral recruitment processes remains too limited for their integration into management and conservation actions that are urgently needed for this unique ecosystem. Here, we synthesize and analyze existing literature on coral recruitment to determine the state of knowledge, identify knowledge gaps, and suggest future lines of research. We particularly focus on the spatiotemporal variability of recruitment and its controlling factors, the relative importance of preand post-settlement events and life strategies in the maintenance of adult assemblages, and the critical role of recruitment for the recovery and resilience of disturbed reef communities.