Uptake of dissolved free amino acids by four cold-water coral species from the Mediterranean Sea

Dissolved organic matter, which contains many compounds such as lipids, sugars and amino acids, is an important source of carbon and nitrogen for several symbiotic and asymbiotic tropical coral species. However, there is still no information on its possible uptake by cold-water coral species. In this study, we demonstrated that dissolved organic matter, in the form of dissolved free amino acids (DFAA), is actively absorbed by four cold-water coral species from the Mediterranean Sea. Although the uptake rates observed with 3mM DFAA concentration were one order of magnitude lower than those observed in tropical species, they corresponded to 12–50% of the daily excreted-nitrogen, and 16–89% of the daily respired-carbon of the cold-water corals. Consequently, DFAA, even at in situ concentrations lower than those tested in this study, can supply a significant amount of carbon and nitrogen to the corals, especially during periods when particulate food is scarce. Versión del editor

Tissue and skeletal changes in the scleractinian coral Stylophora pistillata Esper 1797 under phosphate enrichment

Long-term phosphate enrichments (0, 0.5, and 2.5 μmol L− 1; 4 to 11 weeks) were used to assess a possible limitation in phosphorus of zooxanthellae and to complement data on the effect of phosphate enrichment on calcification and elemental composition of the tissue in the scleractinian coral Stylophora pistillata. Phosphate addition mainly affected the coral symbionts. Indeed, at 2.5 μmol L− 1 P-enriched, zooxanthellae had a greater photosynthetic efficiency, their intracellular carbon and nitrogen contents increased by 70% and their phosphorus content by 190%, while their specific growth rate increased by 18%. C:P and N:P ratios in zooxanthellae were much higher than the Redfield ratios advocated for nutrient-repleted phytoplankton, and decreased with phosphate enrichment. Collectively, these results suggest a phosphorus limitation of the zooxanthellae growth in hospite. However, the increase in zooxanthellae specific growth rate did not lead to the building of a higher symbiont density, as zooxanthellae growth just matched the tissue and skeletal growth of the enriched corals. Benefits of phosphate supplementation were thus not substantial enough to lead to the building of higher zooxanthellae density and to their balanced growth, which suggests that symbiont growth was likely limited by another nutrient as well, probably nitrogen. At the host level, there were no changes in the elemental composition or in the protein levels, while skeletal growth rate increased by 31% between unenriched and 2.5 μmol L− 1 P-enriched corals. Phosphate-enriched corals also incorporated 1.7 times more phosphorus into their skeleton than did unenriched corals. These results evidenced that zooxanthellae and the skeleton are the two accumulation sites of inorganic phosphorus within the symbiotic association

Coral bleaching under thermal stress: putative involvement of host/symbiont recognition mechanisms

<p>Abstract</p> <p>Background</p> <p>Coral bleaching can be defined as the loss of symbiotic zooxanthellae and/or their photosynthetic pigments from their cnidarian host. This major disturbance of reef ecosystems is principally induced by increases in water temperature. Since the beginning of the 1980s and the onset of global climate change, this phenomenon has been occurring at increasing rates and scales, and with increasing severity. Several studies have been undertaken in the last few years to better understand the cellular and molecular mechanisms of coral bleaching but the jigsaw puzzle is far from being complete, especially concerning the early events leading to symbiosis breakdown. The aim of the present study was to find molecular actors involved early in the mechanism leading to symbiosis collapse.</p> <p>Results</p> <p>In our experimental procedure, one set of <it>Pocillopora damicornis </it>nubbins was subjected to a gradual increase of water temperature from 28°C to 32°C over 15 days. A second control set kept at constant temperature (28°C). The differentially expressed mRNA between the stressed states (sampled just before the onset of bleaching) and the non stressed states (control) were isolated by Suppression Subtractive Hybridization. Transcription rates of the most interesting genes (considering their putative function) were quantified by Q-RT-PCR, which revealed a significant decrease in transcription of two candidates six days before bleaching. RACE-PCR experiments showed that one of them (<it>PdC-Lectin</it>) contained a C-Type-Lectin domain specific for mannose. Immunolocalisation demonstrated that this host gene mediates molecular interactions between the host and the symbionts suggesting a putative role in zooxanthellae acquisition and/or sequestration. The second gene corresponds to a gene putatively involved in calcification processes (<it>Pdcyst-rich</it>). Its down-regulation could reflect a trade-off mechanism leading to the arrest of the mineralization process under stress.</p> <p>Conclusion</p> <p>Under thermal stress zooxanthellae photosynthesis leads to intense oxidative stress in the two partners. This endogenous stress can lead to the perception of the symbiont as a toxic partner for the host. Consequently, we propose that the bleaching process is due in part to a decrease in zooxanthellae acquisition and/or sequestration. In addition to a new hypothesis in coral bleaching mechanisms, this study provides promising biomarkers for monitoring coral health.</p

Effects of Light, Food Availability and Temperature Stress on the Function of Photosystem II and Photosystem I of Coral Symbionts

Background: Reef corals are heterotrophic coelenterates that achieve high productivity through their photosynthetic dinoflagellate symbionts. Excessive seawater temperature destabilises this symbiosis and causes corals to "bleach," lowering their photosynthetic capacity. Bleaching poses a serious threat to the persistence of coral reefs on a global scale. Despite expanding research on the causes of bleaching, the mechanisms remain a subject of debate.\ud \ud Methodology/Principal Findings: This study determined how light and food availability modulate the effects of temperature stress on photosynthesis in two reef coral species. We quantified the activities of Photosystem II, Photosystem I and whole chain electron transport under combinations of normal and stressful growth temperatures, moderate and high light levels and the presence or absence of feeding of the coral hosts. Our results show that PS1 function is comparatively robust against temperature stress in both species, whereas PS2 and whole chain electron transport are susceptible to temperature stress. In the symbiotic dinoflagellates of Stylophora pistillata the contents of chlorophyll and major photosynthetic complexes were primarily affected by food availability. In Turbinaria reniformis growth temperature was the dominant influence on the contents of the photosynthetic complexes. In both species feeding the host significantly protected photosynthetic function from high temperature stress.\ud \ud Conclusions/Significance: Our findings support the photoinhibition model of coral bleaching and demonstrate that PS1 is not a major site for thermal damage during bleaching events. Feeding mitigates bleaching in two scleractinian corals, so that reef responses to temperature stresses will likely be influenced by the coinciding availabilities of prey for the host

Correction: The Minderoo-Monaco Commission on Plastics and Human Health

This article details a correction to: Landrigan PJ, Raps H, Cropper M, et al. The Minderoo-Monaco Commission on Plastics and Human Health. Annals of Global Health. 2023; 89(1): 23. DOI: https://doi.org/10.5334/aogh.4056

Etude de la nutrition hétérotrophe des coraux scléractiniaires

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Etude de la physiologie de deux coraux méditerranéens

Cette thèse présente la réponse de deux coraux symbiotiques Méditerranéens Cladocora caespitosa and Oculina patagonica aux variations des paramètres environnementaux. L effet de variations saisonnières ainsi que d une élévation anormale de la température a été testé sur les deux coraux. Par contre, les effets de l éclairement, d un apport en nourriture, ou d une élévation de pCO2 n ont été testés que sur l espèce modèle, C. caespitosa. J ai montré que la température était le paramètre ayant le plus fort impact sur le métabolisme des coraux. En effet, des températures basses, couplées à un apport de nourriture (conditions hivernales), augmentent les concentrations en chlorophylle et zooxanthelles, permettant ainsi une meilleure efficacité photosynthétique au cours de conditions défavorables. Au contraire, les taux de photosynthèse et de calcification sont augmentés l été, pour des températures comprises entre 18 et 23C. Des températures plus élevées (entre 24 et 28C) ont un effet négatif sur le métabolisme des coraux. Cependant, alors que C. caespitosa résiste pendant 5 semaines à des températures égales ou supérieures à 24C, avant de s effondrer et mourir, O. patagonica diminue immédiatement sa densité en zooxanthelles et son taux de croissance, mais conserve une vitalité élevée. Ces résultats, couplés aux observations in situ de mortalité massive de C. caespitosa pendant les récentes périodes estivales, montrent que ce corail vit à sa limite supérieure de température. Nous avons également montré, en utilisant C. caespitosa, que la nourriture constitue le deuxième facteur le plus important pour le métabolisme de ces coraux tempérés. Par contre, une augmentation d un facteur 8 d éclairement ne produit aucun changement dans les concentrations en chlorophylle et zooxanthelles ou dans les taux de croissance, suggérant que l éclairement n est pas un facteur important chez ces coraux. Finalement, un doublement de pCO2, comme il est prévu suite aux changements climatiques, n a aucun effet sur le métabolisme de C. caespitosa, suggérant que la température reste le paramètre le plus important.This thesis explores the physiology of two symbiotic Mediterranean corals, Cladocora caespitosa and Oculina patagonica to changes in their environmental parameters. The effect of temperature was investigated both under the normal seasonal range as well as in the perspective of climate change on the two coral species. The effects of irradiance, food supply, and pCO2 level were only investigated with C. caespitosa taken as a model. Temperature was one of the main environmental factors affecting corals metabolism. Increased concentrations of zooxanthellae and chlorophyll were observed at low temperatures and high food supply, allowing an increase in the photosynthetic efficiency during unfavorable conditions. Conversely, photosynthetic and growth rates were maximal under summer conditions, at temperatures ranging from 18 to 23C. Higher temperatures (from 24 to 28C) negatively affected the photosynthesis, growth and symbiosis in both corals. While C. caespitosa resisted 5 weeks at temperatures equal or above 24C before decreasing its metabolic functions and dying, O. patagonica reduced its symbiont density and growth rates as soon as temperature increased, but showed a low mortality rate. These results, together with the observations of mass mortalities of C. caespitosa during the last summers suggest that this coral is living near its upper thermal limits. We also demonstrated, using C. caespitosa, that food supply was the second most important parameter for these two temperate corals. Conversely, a 8-fold increase in the light level did not change zooxanthellae and chlorophyll concentrations, or growth rates, suggesting that this factor is not important for the coral metabolism. Finally, a doubling in the pCO2 level, as expected by the end of the century, did not either affect C. caespitosa metabolism, leading temperature as the most important parameter.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

On the use of 31P NMR for the quantification of hydrosoluble phosphorus-containing compounds in coral host tissues and cultured zooxanthellae

31P Nuclear Magnetic Resonance (NMR) was assessed to investigate the phosphorus-containing compounds present in the tissues of the scleractinian coral Stylophora pistillata as well as of cultured zooxanthellae (CZ). Results showed that phosphorus-containing compounds observed in CZ were mainly phosphate and phosphate esters. Phosphate accounted for 19 ± 2% of the total phosphorus compounds observed in CZ maintained under low P-levels (0.02 μM). Adding 5 mM of dissolved inorganic phosphorus (KH2PO4) to the CZ culture medium led to a 3.1-fold increase in intracellular phosphate, while adding 5 mM of dissolved organic phosphorus led to a reduction in the concentration of phosphorus compounds, including a 2.5-fold intracellular phosphate decrease. In sharp contrast to zooxanthellae, the host mainly contained phosphonates, and to a lesser extent, phosphate esters and phosphate. Two-months of host starvation decreased the phosphate content by 2.4 fold, while bleaching of fed corals did not modify this content. Based on 31P NMR analyses, this study highlights the importance of phosphonates in the composition of coral host tissues, and illustrates the impact of phosphorus availability on the phosphorus composition of host tissues and CZ, both through feeding of the host and inorganic phosphorus enrichment of the CZ.This research was supported by the government of the Principality of Monaco. Financial support to C.G. was provided by the École Normale Supérieure and the Centre Scientifique de Monaco.peer-reviewe

Similar thermal breadth of two temperate coral species from the Mediterranean Sea and two tropical coral species from the Great Barrier Reef

Temperate organisms are generally exposed to a more variable and cooler climate than tropical organisms, and are therefore expected to have broader thermal tolerance and a different thermal performance curve. This study investigated these hypotheses by comparing the thermal performance of two common tropical coral species found in the Great Barrier Reef with the two most common temperate coral species from the Mediterranean Sea. Photosynthesis rates, dark respiration rates, maximum PSII quantum yield (Fv/Fm) and electron transport rates (rETRm) were measured on coral fragments exposed to an acute temperature increase and decrease up to 5 °C above and below the average environmental seawater temperature. Dark respiration rates and Fv/Fm increased linearly with temperature, suggesting broad thermal tolerance. For photosynthesis and rETRm, the performance breadths were surprisingly similar between the tropical and temperate species. However, the thermal optimum for performance was generally below the local average temperature, and only coincided with the prevailing environmental temperature for one of the tropical species. The broad thermal tolerance for photosynthesis displayed in this study supports previous observations that corals can survive short periods of abnormally warm temperatures and suggests that corals adopt thermal generalist strategies to cope with temperature variation in the environment. Nevertheless, current mean temperatures are 10–30% above the thermal optimum for the species studied here, demonstrating that conditions are already pushing the boundaries of coral thermal tolerance

New insights into carbon acquisition and exchanges within the coral - dinoflagellate symbiosis under NH4+ and NO3- supply

WOS:000362305500017International audienceAnthropogenic nutrient enrichment affects the biogeochemical cycles and nutrient stoichiometry of coastal ecosystems and is often associated with coral reef decline. However, the mechanisms by which dissolved inorganic nutrients, and especially nitrogen forms (ammonium versus nitrate) can disturb the association between corals and their symbiotic algae are subject to controversial debate. Here, we investigated the coral response to varying N:P ratios, with nitrate or ammonium as a nitrogen source. We showed significant differences in the carbon acquisition by the symbionts and its allocation within the symbiosis according to nutrient abundance, type and stoichiometry. In particular, under low phosphate concentration (0.05 mu M), a 3 mu M nitrate enrichment induced a significant decrease in carbon fixation rate and low values of carbon translocation, compared with control conditions (N : P = 0.5 : 0.05), while these processes were significantly enhanced when nitrate was replaced by ammonium. A combined enrichment in ammonium and phosphorus (N: P = 3 : 1) induced a shift in nutrient allocation to the symbionts, at the detriment of the host. Altogether, these results shed light into the effect of nutrient enrichment on reef corals. More broadly, they improve our understanding of the consequences of nutrient loading on reef ecosystems, which is urgently required to refine risk management strategies