Transcriptional Activation of c3 and hsp70 as Part of the Immune Response of Acropora millepora to Bacterial Challenges

The impact of disease outbreaks on coral physiology represents an increasing concern for the fitness and resilience of reef ecosystems. Predicting the tolerance of corals to disease relies on an understanding of the coral immune response to pathogenic interactions. This study explored the transcriptional response of two putative immune genes (c3 and c-type lectin) and one stress response gene (hsp70) in the reef building coral, Acropora millepora challenged for 48 hours with bacterial strains, Vibrio coralliilyticus and Alteromonas sp. at concentrations of 106 cells ml-1. Coral fragments challenged with V. coralliilyticus appeared healthy while fragments challenged with Alteromonas sp. showed signs of tissue lesions after 48 hr. Coral-associated bacterial community profiles assessed using denaturing gradient gel electrophoresis changed after challenge by both bacterial strains with the Alteromonas sp. treatment demonstrating the greatest community shift. Transcriptional profiles of c3 and hsp70 increased at 24 hours and correlated with disease signs in the Alteromonas sp. treatment. The expression of hsp70 also showed a significant increase in V. coralliilyticus inoculated corals at 24 h suggesting that even in the absence of disease signs, the microbial inoculum activated a stress response in the coral. C-type lectin did not show a response to any of the bacterial treatments. Increase in gene expression of c3 and hsp70 in corals showing signs of disease indicates their potential involvement in immune and stress response to microbial challenges

Acclimatization of the crustose coralline alga Porolithon onkodes to variable pCO2

Ocean acidification (OA) has important implications for the persistence of coral reef ecosystems, due to potentially negative effects on biomineralization. Many coral reefs are dynamic with respect to carbonate chemistry, and experience fluctuations in pCO2 that exceed OA projections for the near future. To understand the influence of dynamic pCO2 on an important reef calcifier, we tested the response of the crustose coralline alga Porolithon onkodes to oscillating pCO2. Individuals were exposed to ambient (400 ??atm), high (660 ??atm), or variable pCO2 (oscillating between 400/660 ??atm) treatments for 14 days. To explore the potential for coralline acclimatization, we collected individuals from low and high pCO2 variability sites (upstream and downstream respectively) on a back reef characterized by unidirectional water flow in Moorea, French Polynesia. We quantified the effects of treatment on algal calcification by measuring the change in buoyant weight, and on algal metabolism by conducting sealed incubations to measure rates of photosynthesis and respiration. Net photosynthesis was higher in the ambient treatment than the variable treatment, regardless of habitat origin, and there was no effect on respiration or gross photosynthesis. Exposure to high pCO2 decreased P. onkodes calcification by >70%, regardless of the original habitat. In the variable treatment, corallines from the high variability habitat calcified 42% more than corallines from the low variability habitat. The significance of the original habitat for the coralline calcification response to variable, high pCO2 indicates that individuals existing in dynamic pCO2 habitats may be acclimatized to OA within the scope of in situ variability. These results highlight the importance of accounting for natural pCO2 variability in OA manipulations, and provide insight into the potential for plasticity in habitat and species-specific responses to changing ocean chemistry.Funding was provided by grants from the National Science Foundation (OCE-0417412, OCE-10-26852, OCE-1041270) and gifts from the Gordon and Betty Moore Foundation. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript

A novel μCT analysis reveals different responses of bioerosion and secondary accretion to environmental variability

Corals build reefs through accretion of calcium carbonate (CaCO3) skeletons, but net reef growth also depends on bioerosion by grazers and borers and on secondary calcification by crustose coralline algae and other calcifying invertebrates. However, traditional field methods for quantifying secondary accretion and bioerosion confound both processes, do not measure them on the same time-scale, or are restricted to 2D methods. In a prior study, we compared multiple environmental drivers of net erosion using pre- and post-deployment micro-computed tomography scans (μCT; calculated as the % change in volume of experimental CaCO3 blocks) and found a shift from net accretion to net erosion with increasing ocean acidity. Here, we present a novel μCT method and detail a procedure that aligns and digitally subtracts pre- and post-deployment μCT scans and measures the simultaneous response of secondary accretion and bioerosion on blocks exposed to the same environmental variation over the same time-scale. We tested our method on a dataset from a prior study and show that it can be used to uncover information previously unattainable using traditional methods. We demonstrated that secondary accretion and bioerosion are driven by different environmental parameters, bioerosion is more sensitive to ocean acidity than secondary accretion, and net erosion is driven more by changes in bioerosion than secondary accretion

Caractéristiques du feutrage algal des récifs coralliens de Polynésie française soumis à différentes intensités de bioérosion

This study deals with the colonisation of experimental Porites blocks by epilithic and endolithic algal community in two atoll lagoons and two high-island lagoons in French Polynesia, exposed to different environmental conditions during a 5-year period. A qualitative analysis of the community (cyanobacteria and micro-algae) was carried out, and the relationship between the epilithic and endolithic strata observed. HPLC analysis of chlorophyll pigments was used to quantitatively determine the plant biomass, which was then compared to that of the algal turf of neighbouring reefs. The results show that these blocks are colonised according to two factors: the reef structure (atoll or high-island) and the degree of human disturbance. The epilithic and endolithic population dynamics differ. The density of the epilithic algal community and the species diversity increase with the degree of eutrophication and the amount of borers (sea-urchins, parrotfish), while the proportion of endolithic species remains low (34 %-59 %). This is especially marked in the high-island lagoons, where leaching has caused enhanced nutrient levels. An extreme case is the station at Faaa, a highly polluted harbour, where increased sea-urchin levels (44 ind. m(-2)) meant that the blocks disappeared completely in less than five years due to bioerosion. In the oligotrophic waters of the atoll lagoons, the losses of CaCO3 by bioerosion do not exceed 35 % per block, and the algal community is made up mainly of endolithic species (66 %-85 %). The algal biomass is lowest in the Takapoto atolls (10-11 mu g cm(-2)) and maximum in Tikehau atoll (23 and 56 mu g cm(-2)). The first microborers to settle in the ecological succession of the community are the cyanobacteria. These are gradually replaced by Ostreobium (Chlorophyceae borers), which become dominant in the blocks exposed to the lowest bioerosion rate. The richness and the density of the algal turf reflect the convergence of many ecological factors: it seems that the covering of epilithic algae or the richness of endolithic flora could be used as a global indicator of the quality and the health of a reef.Cette étude porte sur la colonisation par du feutrage algal épilithe et endolithe de bloes expérimentaux de Porites, mis en place dans deux atolls et deux îles hautes de Polynésie française et soumis à des contraintes environnementales différentes pendant cinq ans. La composition qualitative des peuplements (cyanobactéries et microalgues) et les relations entre «strateå épilithe et «strateå endolithe ont été observées. La quantification de la biomasse végétale a été effectuée par la mesure des pigments chlorophylliens analysés en HPLC. Des comparaisons ont étéétablies avec le feutrage algal des substrats récifaux avoisinants. Les résultats font apparaître des différences dans l'évolution de la colonisation de ces blocs selon deux facteurs: la structure récifale (atolls ou îles hautes) et le degré d'anthropisation des milieux. Par ailleurs, la dynamique de la colonisation est différente pour les populations épilithes et endolithes. La densité du feutrage algal épilithe et la diversité spécifique augmentent avec le degré d'eutrophisation des eaux et la quantité des organismes brouteurs (oursins, Scaridés), alors que la contribution des espèces endolithes dans ce feutrage reste faible (34 et 59 %). C'est le cas notamment dans les stations des îles hautes, enrichies en nutriments par le lessivage des sols. L'exemple extrême est représenté par la station de Faaa (ville de Papeete) où la forte pollution urbaine et le nombre élevé d'oursins bioérodeurs (> 44 ind. m2) ont entraîné la disparition des blocs en moins de cinq ans. Dans les atolls, les eaux sont oligotrophes, les pertes de CaCO3 par bioérosion ne dépassent pas 35 % par bloc, et le peuplement algal est constitué principalement d'espèces endolithes (66 % à 85 % de l'ensemble du peuplement). Sur les blocs de l'atoll de Takapoto, la biomasse du feutrage algal épilithe et endolithe est la plus faible et n'atteint que 10 à 11 μg chl a cm−2, alors qu'elle est maximale (23 et 56 μg chl a cm−2) aux deux stations de l'atoll de Tikehau. Dans la succession écologique, les premiers microperforants qui s'installent sont les cyanobactéries; celles-ci sont peu à peu remplacées par l'Ostreobium (Chlorophycée perforante) qui devient dominant dans les blocs soumis à la plus faible bioérosion. La richesse et la densité du feutrage algal reflétant l'intégration de nombreux facteurs écologiques, il apparaît que la couverture en épilithes ou la richesse en flore endolithe pourraient servir d'indicateur global de la qualité et de la santé d'un récif

Developmental aspects of biomineralisation in the Polynesian pearl oyster Pinctada margaritifera var. cumingii

The shell biomineralisation with special reference to the nacreous region is observed during the development of the Polynesian pearl oyster. Ultrastructural changes were studied and timed for the first time from planktonic larval shells to two-year-old adult shells. During the first two weeks following fertilization, the prodissoconch-I shell structure is undifferentiated and uniformly granular. The prodissoconch-II stage which develops during the next two weeks acquires a columnar organization. Metamorphosis is characterized by the formation of the dissoconch shell with all the elements of an adult shell and marks the onset of the development of the nacre. Nucleation starts within an organic matrix from point sources forming 'crystal germs' which expand circularly until they fuse. The orientation of the contour lines of scalariform growth margins indicates the direction of shell growth. Five zones of growth (Z) were characterized. One-month-old shells show a homogenous zone, without particular figures (Z0). The contour lines are initially parallel to the growing shell edge (Z1), later becoming labyrinthic (finger prints, Z2) or perpendicular to the edge (Z3). A fourth zone (Z4) characterized by spiral growth and associated with the shell thickening is observed later in the umbo region. This development results from a gradual lowering of the rate of mineralisation over time and from changes in growth pattern from a predominant increase in size, shifting toward an increase in the thickness of the shell. The mineralisation patterns of the shells from larvae reared in hatchery conditions and larvae from the field appear similar. The use of quantified information on shape, density, and distribution of nucleation sites as an indicator of growth conditions is discussed.La biominéralisation de la coquille de l’huître perlière de Polynésie française, en particulier celle de sa partie nacrée, est étudiée au cours du développement du bivalve. Les changements de l’ultrastructure de sa coquille sont suivis, pour la première fois, du stade larvaire planctonique (prodissoconque I et II) au stade adulte de deux ans (dissoconque). Durant les deux premières semaines qui suivent la ponte, la prodissoconque I présente une structure granuleuse, sans aucune organisation apparente. La prodissoconque II qui se développe durant les deux semaines suivantes a une organisation en colonne. Au moment de la métamorphose, une dissoconque s’ajoute à la coquille larvaire. La fixation des larves planctoniques marque ainsi la mise en place de la couche nacrée. La taille, la densité et la distribution des sites de nucléation des carbonates évoluent au cours du temps et dans différentes régions de la coquille. La nucléation prend naissance au sein de la matière organique à partir d’un point formant les ‘germes cristallins’. Ceux-ci, de forme généralement circulaire, croissent, se compriment et finissent par fusionner avec des germes cristallins voisins. L’orientation des fronts de minéralisation près des zones de croissance indique la direction de croissance des coquilles. Cinq zones de croissance (Z) ont été définies en fonction des figures dessinées par ces fronts. La couche nacrée des coquilles d’un mois ne montre aucune figure particulière (Z0) puis les fronts de minéralisation sont parallèles au bord des valves (Z1), ils deviennent sinueux (apparence d’empreintes digitales) (Z2) puis sont perpendiculaires au bord des coquilles (Z3). Une quatrième zone (Z4) caractérisée par des spirales de croissance s’ajoute aux trois autres zones, dans la région du crochet et est associée à un épaississement de la coquille. Ces résultats attestent d’un ralentissement de la minéralisation au cours du temps et d’un changement de la stratégie de croissance des bivalves. Une croissance en longueur est privilégiée chez les jeunes coquilles. Elle est ensuite remplacée par une stratégie d’épaississement chez les coquilles plus âgées. Les figures de minéralisation des coquilles d’écloserie sont similaires à celles du milieu naturel. Les informations sur la forme, la densité et la distribution des sites de nucléation en tant qu’indicateurs de croissance sont ici discutée