Éditeur(s) : HAL CCSD
Résumé : International audience
Sharks International
Durban, South Africa

hal-01487162
http://hal.univ-reunion.fr/hal-01487162

Éditeur(s) : HAL CCSD
Résumé : International audience
The active selection of recent volcanic habitats by juvenile fish following a cyclone could explain the unusual mass-settlement of the Indian Ocean blacktip grouper Epinephelus oceanicus observed on 25 May 2006, few weeks after tropical storm Diwa on the latest lava flows of the Piton de la Fournaise volcano at Reunion Island. Following a cyclonic depression, shallow underwater habitats are devoid of resident fishes, including predators, favouring juvenile fish survival. Otherwise, the recent origin of the volcanic habitats, which vary in age, could facilitate the spatial segregation of adult and juvenile fish on the lava flows, reducing intraspecific competition and adult aggression toward juveniles. Regional characteristics of larval recruitment could also contribute to the infrequency of the described event; the isolated situation of the island would be expected to result in an average density of fish postlarvae 0.25 % to 1 % of that seen on some reefs in the Pacific. The supposed origin of juvenile groupers in the neighbouring island of Mauritius should encourage Reunionese managers to look beyond their own jurisdictions to adopt a collaborative approach to conservation of the entire connected network.
Environmental Biology of Fishes

hal-01306707
http://hal.univ-reunion.fr/hal-01306707
http://hal.univ-reunion.fr/hal-01306707/document
http://hal.univ-reunion.fr/hal-01306707/file/Mass-settlement%20of%20the%20Indian%20ocean%20black-tip%20grouper_hal.pdf
DOI : 10.1007/s10641-014-0303-2

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Introduction The Latitudinal Gradient Hypothesis (LGH) foresees that specialized metabolites are overexpressed under low latitudes, where organisms are subjected to higher herbivory pressure. The widespread macroalga Asparagopsis taxiformis is composed of six distinct genetic lineages, some of them being introduced in many regions. Objectives To study (i) metabolic fingerprints of the macroalga and (ii) its bioactivity in space and time, both as proxies of its investment in defensive traits, in order to assess links between bioactivities and metabotypes with macroalgal invasiveness. Methods 289 macroalgal individuals, from four tropical and three temperate regions, were analyzed using untargeted metabolomics and the standardized Microtox (R) assay. Results Metabotypes showed a low divergence between tropical and temperate populations, while bioactivities were higher in temperate populations. However, these phenotypes varied significantly in time, with a higher variability in tropical regions. Bioactivities were high and stable in temperate regions, whereas they were low and much variable in tropical regions. Although the introduced lineage two exhibited the highest bioactivities, this lineage could also present variable proliferation fates. Conclusion The metabolomic approach partly discriminates macroalgal populations from various geographic origins. The production of chemical defenses assessed by the bioactivity assay does not match the macroalgal genetic lineage and seems more driven by the environment. The higher content of chemical defenses in temperate versus tropical populations is not in accordance with the LGH and cannot be related to the invasiveness of the macroalgae.
ISSN: 1573-3882

hal-01681538
https://hal.archives-ouvertes.fr/hal-01681538
DOI : 10.1007/s11306-017-1169-z

Éditeur(s) : HAL CCSD
http://hal.univ-reunion.fr/hal-01487167

hal-01487167
http://hal.univ-reunion.fr/hal-01487167

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study constitutes one of the few works conducted on the colonization of recent lava flows by fish communities in coral reef environment. It attempted to describe the mechanisms of colonization and environmental variables infuencing the structure of communities on the lava flows of the Piton de la Fournaise volcano at Reunion Island. It also proposed some hypotheses on the mechanisms of selection and speciation of endemic species of thesouthwestern Indian Ocean region, particularly diversified on the most recent lava flows of the Piton de la Fournaise, and provided a model of distribution of environmental and fish assemblage variables in four homogeneous patterns of colonization (landscapes) retained within the study area. The results showed fish community structure strongly related to measured environmental variables, of which depth, width of the island shelf, age of the lava flow and distance to the most recent lava flow were the most influential. It also appeared that the maximum endemic species richness was measured on the shallower stations, with narrow insular shelf, located on recent lava flows, near the lava flow from the eruption of 2007 (latest volcanic event). These characteristics define a harsh environment, to which endemic species seem well-adapted due in particular to their strong demographic and dietary flexibility. Finally, the patterns of colonization were characterized by significantly different environmental variables. The four homogeneous areas, defined by two geomorphological features, basalt blocks and drop-offs, nested within two locations, inside and outside the volcanic enclosure (current caldera), hosted fish communities whose dominant diets mainly depend on the nature, the abundance and the accessibility of available food resources. Overall, the study highlights that during early stages of ecological succession, site selection by fish communities is highly dependent on environmental constraints, specially of volcanic origin, but the physical habitat selection (geomorphology, substrate rugosity, percentage of soft substrate) seems to have littleimportance, while at least on the trophic structure and the distribution of endemic species.
ISSN: 0022-0981

hal-01253768
https://hal.archives-ouvertes.fr/hal-01253768
https://hal.archives-ouvertes.fr/hal-01253768/document
https://hal.archives-ouvertes.fr/hal-01253768/file/Pinault%20et%20al.%20-%202014%20-%20Fish%20community%20structure%20in%20relation%20to%20environmen_hal.pdf
DOI : 10.1016/j.jembe.2014.06.005