Hatchery-produced sandfish (Holothuria scabra) show altered genetic diversity in New Caledonia

Facing an alarming continuing decline of wild sea cucumber resources, management strategies were developed over the past three decades to sustainably promote development, maintenance, or regeneration of wild sea cucumber fisheries. In New Caledonia (South Pacific), dedicated management efforts via restocking and sea ranching programs were implemented to cope with the overharvesting of the sandfish Holothuria scabra and the recent loss of known populations. In order to investigate genetic implications of a major H. scabra restocking program, we assessed the genetic diversity and structure of wild stocks and hatchery-produced sandfish and compared the genetic outcomes of consecutive spawning and juvenile production events. For this, 1358 sandfish collected at four sites along the northwestern coasts of New Caledonia, as well as during five different restocking events in the Tiabet Bay, were genotyped using nine polymorphic microsatellite markers. We found that wild H. scabra populations from the northwestern coast of New Caledonia likely belonged to one panmictic population with high level of gene flow observed along the study scale. Further, this panmictic population displayed an effective size of breeders large enough to ensure the feasibility of appropriate breeding programs for restocking. In contrast, hatchery-produced samples did suffer from an important reduction in the effective population size: the effective population size were so small that genetic drift was detectable over one generation, with the presence of inbred individuals, as well as more related dyads than in wild populations. All these results suggest that dedicated efforts in hatcheries are further needed to maintain genetic diversity of hatchery-produced individuals in order to unbalance any negative impact during this artificial selection

Transferts de matière organique et fonctionnement des réseaux trophiques côtiers aux îles Marquises.

The Marquesas archipelago is distinguished from the Polynesian group by many environmental and ecological peculiarities. The hydrodynamic conditions seem to generate local nutrient enrichment process, which contrast with oligotrophic conditions usually encountered around the coral ecosystems. These rich waters seem to favor a high phytoplankton primary production. The Marquesas Islands atypical coral structure, associated with high primary production, suggests particular trophic relationships. In the system, phytoplankton is an important organic matter source, with high nutritional quality, supported by macrophytobenthos. Terrestrial OM sources have only a little influence. Despite the dominance of phytoplankton in OM pools (POM and SOM), macroalgae seem to contribute mainly to the food web functioning, with the support of phytoplankton, especially during phytoplankton bloom (cold season). These observations suggest a benthic-pelagic coupling in OM supply in the food web. The marine primary producers have significantly higher δ15N isotopic signatures than in other parts of the South Pacific. These high isotopic values are also identified for consumers and show seasonal variability, probably reflecting variations in nutrient intakes available to primary producers. These variations would reflect the hydrodynamic processes intensification during the cold season, highlighted in other studies, allowing a rise in nutrients in surface water.However, although Marquesan food webs have high nitrogen isotopic signatures and significant contributions from phytoplankton, the structure and functioning of communities remains similar for other coral ecosystems observed.L’archipel des Marquises se distingue de l’ensemble polynésien par de nombreuses particularités environnementales et écologiques. Ses eaux riches en éléments nutritifs semblent favorables au maintien d’une production primaire phytoplanctonique élevée. La structuration corallienne atypique des îles marquisiennes, associée à cette production primaire élevée, laissent présager des relations trophiques particulières.Dans le système, le phytoplancton représente une source de matière organique importante, supportée par le macrophytobenthos. Les sources de MO d’origine terrestre n’ayant que peu d’influence. Malgré la dominance du phytoplancton dans les réservoirs de MO (MOP et MOS), les macroalgues semblent contribuer majoritairement au fonctionnement du réseau trophique, suggérant un couplage benthique-pélagique dans l’apport de MO dans le réseau trophique. Les producteurs primaires marins de cette étude présentent des signatures isotopiques en δ15N nettement supérieures à d’autres régions du Pacifique Sud. Ces valeurs isotopiques élevées, identifiées également chez les consommateurs, présentent des variabilités saisonnières traduisant probablement des variations dans les apports en éléments nutritifs. Ces variations pourraient être le reflet de l’intensification des processus hydrodynamiques en saison fraîche, favorisant une remontée d’éléments nutritifs dans les eaux de surface. Toutefois, bien que les réseaux trophiques marquisiens présentent des signatures isotopiques en azote élevées et des contributions importantes du phytoplancton, la structure et le fonctionnement des communautés restent similaires à ce qui est observés pour d’autres écosystèmes coralliens

Organic matter transfers and the functioning of coastal food webs in the Marquesas Islands.

L’archipel des Marquises se distingue de l’ensemble polynésien par de nombreuses particularités environnementales et écologiques. Ses eaux riches en éléments nutritifs semblent favorables au maintien d’une production primaire phytoplanctonique élevée. La structuration corallienne atypique des îles marquisiennes, associée à cette production primaire élevée, laissent présager des relations trophiques particulières.Dans le système, le phytoplancton représente une source de matière organique importante, supportée par le macrophytobenthos. Les sources de MO d’origine terrestre n’ayant que peu d’influence. Malgré la dominance du phytoplancton dans les réservoirs de MO (MOP et MOS), les macroalgues semblent contribuer majoritairement au fonctionnement du réseau trophique, suggérant un couplage benthique-pélagique dans l’apport de MO dans le réseau trophique. Les producteurs primaires marins de cette étude présentent des signatures isotopiques en δ15N nettement supérieures à d’autres régions du Pacifique Sud. Ces valeurs isotopiques élevées, identifiées également chez les consommateurs, présentent des variabilités saisonnières traduisant probablement des variations dans les apports en éléments nutritifs. Ces variations pourraient être le reflet de l’intensification des processus hydrodynamiques en saison fraîche, favorisant une remontée d’éléments nutritifs dans les eaux de surface. Toutefois, bien que les réseaux trophiques marquisiens présentent des signatures isotopiques en azote élevées et des contributions importantes du phytoplancton, la structure et le fonctionnement des communautés restent similaires à ce qui est observés pour d’autres écosystèmes coralliens.The Marquesas archipelago is distinguished from the Polynesian group by many environmental and ecological peculiarities. The hydrodynamic conditions seem to generate local nutrient enrichment process, which contrast with oligotrophic conditions usually encountered around the coral ecosystems. These rich waters seem to favor a high phytoplankton primary production. The Marquesas Islands atypical coral structure, associated with high primary production, suggests particular trophic relationships. In the system, phytoplankton is an important organic matter source, with high nutritional quality, supported by macrophytobenthos. Terrestrial OM sources have only a little influence. Despite the dominance of phytoplankton in OM pools (POM and SOM), macroalgae seem to contribute mainly to the food web functioning, with the support of phytoplankton, especially during phytoplankton bloom (cold season). These observations suggest a benthic-pelagic coupling in OM supply in the food web. The marine primary producers have significantly higher δ15N isotopic signatures than in other parts of the South Pacific. These high isotopic values are also identified for consumers and show seasonal variability, probably reflecting variations in nutrient intakes available to primary producers. These variations would reflect the hydrodynamic processes intensification during the cold season, highlighted in other studies, allowing a rise in nutrients in surface water.However, although Marquesan food webs have high nitrogen isotopic signatures and significant contributions from phytoplankton, the structure and functioning of communities remains similar for other coral ecosystems observed

The α-minimum convex polygon as a relevant tool for isotopic niche statistics

Ecological (isotopic) niche refers to a surface in a two-dimensional space, where the axes correspond to environmental variables that reflect values of stable isotopes incorporated in an animal's tissues. Carbon and nitrogen stable isotope ratios (δ13C-δ15N) notably provide precious information about trophic ecology, resource and habitat use, and population dynamics. Various metrics allow for isotopic niche size and overlap assessment. In this paper, we advocate α-minimum convex polygons (MCP) - that have long been used for home range estimation – as a relevant tool for isotopic niche size, overlap, and characteristics. The method allows for outlier rejection while being suited to data that are not Gaussian in the bivariate isotopic (δ13C-δ15N) space. The proposed indicators are compared to other existing approaches and are shown to be complementary. Notably an indicator of divergence within the niche is introduced, and allows for comparisons at low (n > 6) and different sample sizes. The R code is made publicly available and will enable ecologists to perform isotopic niche comparison, contraction and expansion assessment, and overlap, based on various methods

Multi-trophic markers illuminate the understanding of the functioning of a remote, low coral cover Marquesan coral reef food web

We studied the food web structure and functioning of a coral reef ecosystem in the Marquesas Islands, French Polynesia, characterized by low coral cover, high sea surface temperature and meso- to eutrophic waters. The Marquesas constitute a relevant ecosystem to understand the functioning of low diversity reefs that are also subject to global change. A multi-tracer assessment of organic matter pathways was run to delineate ecosystem functioning, using analysis of fatty acids, bulk and compound specific stable isotope analysis and stable isotopes mixing models. Macroalgae and phytoplankton were the two major food sources fueling this food web with, however, some marked seasonal variations. Specifically, zooplankton relied on phytoplankton-derived organic matter and herbivorous fishes on macroalgae-derived organic matter to a much higher extent in summer than in winter (~ 75% vs. ~ 15%, and ~ 70 to 75% vs. ~ 5 to 15%, respectively). Despite remarkably high δ15N values for all trophic compartments, likely due to local dynamics in the nitrogen stock, trophic levels of consumers were similar to those of other coral reef ecosystems. These findings shed light on the functioning of low coral cover systems, which are expected to expand worldwide under global change

Author Correction: Multi-trophic markers illuminate the understanding of the functioning of a remote, low coral cover Marquesan coral reef food web

International audienc

Pempom (volet 1) : polluants émergents, polluants organiques et métaux lours ; sources et devenir dans les écosystèmes récifo-lagonaires

Workshop "Au fil de l'eau", Nouméa, NCL, 17-/09/2019 - 18/09/201

Individual back-calculated size-at-age based on otoliths from Pacific coral reef fish species

International audienceAbstract Somatic growth is a critical biological trait for organismal, population, and ecosystem-level processes. Due to its direct link with energetic demands, growth also represents an important parameter to estimate energy and nutrient fluxes. For marine fishes, growth rate information is most frequently derived from sagittal otoliths, and most of the available data stems from studies on temperate species that are targeted by commercial fisheries. Although the analysis of otoliths is a powerful tool to estimate individual growth, the time-consuming nature of otolith processing is one barrier for collection of comprehensive datasets across multiple species. This is especially true for coral reef fishes, which are extremely diverse. Here, we provide back-calculated size-at-age estimates (including measures of uncertainty) based on sagittal otoliths from 710 individuals belonging to 45 coral reef fish species from French Polynesia. In addition, we provide Von Bertalanffy growth parameters which are useful to predict community level biomass production

Memory but no suppression in low-dimensional symmetric idiotypic networks

We present a new symmetric model of the idiotypic immune network. The model specifies clones of B-lymphocytes and incorporates: (1) influx and decay of cells; (2) symmetric stimulatory and inhibitory idiotypic interactions; (3) an explicit affinity parameter (matrix); (4) external (i.e. non-idiotypic) antigens. Suppression is the dominant interaction, i.e. strong idiotypic interactions are always suppressive. This precludes reciprocal stimulation of large clones and thus infinite proliferation. Idiotypic interactions first evoke proliferation, this enlarges the clones, and may in turn evoke suppression. We investigate the effect of idiotypic interactions on normal proliferative immune responses to antigens (e.g. viruses). A 2-D, i.e. two clone, network has a maximum of three stable equilibria: the virgin state and two asymmetric immune states. The immune states only exist if the affinity of the idiotypic interaction is high enough. Stimulation with antigen leads to a switch from the virgin state to the corresponding immune state. The network therefore remembers antigens, i.e. it accounts for immunity/memory by switching beteen multiple stable states. 3-D systems have, depending on the affinities, 9 qualitatively different states. Most of these also account for memory by state switching. Our idiotypic network however fails to account for the control of proliferation, e.g. suppression of excessive proliferation. In symmetric networks, the proliferating clones suppress their anti-idiotypic suppressors long before the latter can suppress the former. The absence of proliferation control violates the general assumption that idiotypic interactions play an important role in immune regulation. We therefore test the robustness of these results by abandoning our assumption that proliferation occurs before suppression. We thus define an "escape from suppression" model, i.e. in the "virgin" state idiotypic interactions are now suppressive. This system erratically accounts for memory and never for suppression. We conclude that our "absence of suppression from idiotypic interactions" does not hinge upon our "proliferation before suppression" assumption