Clovis Barreira e Castro

Climate change affects key nitrogen-fixing bacterial populations on coral reefs

Coral reefs are at serious risk due to events associated with global climate change. Elevated ocean temperatures have unpredictable consequences for the ocean’s biogeochemical cycles. The nitrogen cycle is driven by complex microbial transformations, including nitrogen fixation. This study investigated the effects of increased seawater temperature on bacteria able to fix nitrogen (diazotrophs) that live in association with the mussid coral Mussismilia harttii. Consistent increases in diazotroph abundances and diversities were found at increased temperatures. Moreover, gradual shifts in the dominance of particular diazotroph populations occurred as temperature increased, indicating a potential future scenario of climate change. The temperature-sensitive diazotrophs may provide useful bioindicators of the effects of thermal stress on coral reef health, allowing the impact of thermal anomalies to be monitored. In addition, our findings support the development of research on different strategies to improve the fitness of corals during events of thermal stress, such as augmentation with specific diazotrophs.

Diversity and pathogenic potential of vibrios isolated from Abrolhos Bank corals.

We performed the first taxonomic characterization of vibrios and other culturable microbiota from apparently healthy and diseased Brazilian-endemic corals at the Abrolhos reef bank. The diseases affecting corals were tissue necrosis in Phyllogorgia dillatata, white plague and bleaching in Mussismilia braziliensis and bleaching in Mussismilia hispida. Bacterial isolates were obtained from mucus of 22 coral specimens originated from the Abrolhos Bank (i.e. Itacolomis reef, Recife de Fora reef and Santa Barbara Island) in 2007. Vibrios counts in the water and coral mucus were approximately 104 cfu ml(-1) and 106 cfu ml(-1) respectively. One hundred and thirty-one representative vibrio isolates were identified. Most vibrio isolates (n = 79) fell into the core group using the pyrH identification marker. According to our analysis, diseased corals did not possess a unique vibrio microbiota. Vibrio species encompassed strains originated from both apparently healthy and diseased corals. The pathogenic potential of representative vibrio isolates (V. alginolyticus 40B, V. harveyi-like 1DA3 and V. coralliilyticus 2DA3) were evaluated in a standardized bioassay using the animal model Drosophila melanogaster and caused 25-88% mortality. This is the first taxonomic characterization of the culturable microbiota from the Brazilian-endemic corals. Endemic Brazilian corals are a reservoir of the vibrio core group. Vibrio alginolyticus, V. harveyi and V. coralliilyticus are dominant in the mucus of these corals and may be a normal component of the holobiont.

Coral community structure and sedimentation at different distances from the coast of the Abrolhos Bank, Brazil

Sedimentation has previously been considered an important source of impact in coral reefs. We compared 3 sites on the Abrolhos Bank, Brazil, regarding sedimentation rates, carbonate sediment composition, coral cover, and colony size for the commonest local coral species (Mussismilia braziliensis, Siderastrea stellata, and Favia gravida). The sites are located at different distances from the mainland: Pedra de Leste (14 km), Pontas Sul (26 km), and Parcel dos Abrolhos (58 km). Sedimentation was higher in winter (p <0.05), but no difference among sites was noted. Sites differed in sediment type (P <0.05), with Parcel dos Abrolhos showing nearly 90% of carbonate in sediment composition, Pontas Sul nearly 65%, and Pedra de Leste only nearly 50%. The farther from the mainland, where the zoanthid cover was smaller, the higher was the coral cover (p <0.01). Differences in colony sizes were found only for M. braziliensis, with smaller colonies occurring at Pedra de Leste (p <0.05). It is suggested that terrigenous sediment distribution and turbidity may be the main factors controlling reef development at the Abrolhos Reefs.

Impact of oil spills on coral reefs can be reduced by bioremediation using probiotic microbiota.

Several anthropogenic factors, including contamination by oil spills, constitute a threat to coral reef health. Current methodologies to remediate polluted marine environments are based on the use of chemical dispersants; however, these can be toxic to the coral holobiont. In this study, a probiotic bacterial consortium was produced from the coral Mussismilia harttii and was trained to degrade water-soluble oil fractions (WSFs). Additionally, we assessed the effect of WSFs on the health of M. harttii in tanks and evaluated the bacterial consortium as a bioremediation agent. The consortium was responsible for the highly efficient degradation of petroleum hydrocarbons, and it minimised the effects of WSFs on coral health, as indicated by raised photosynthetic efficiencies. Moreover, the impact of WSFs on the coral microbiome was diminished by the introduced bacterial consortium. Following introduction, the bacterial consortium thus had a dual function, i.e promoting oil WSF degradation and improving coral health with its probiotic features.

A novel marine mesocosm facility to study global warming, water quality, and ocean acidification

Abstract We describe a completely randomizable flow‐through outdoor mesocosm for climate change and ecotoxicology studies that was built with inexpensive materials. The 16 raceway tanks allow up to 6× water renewal per hour, avoiding changes in natural abiotic seawater conditions. We use an open‐source hardware board (Arduino) that was adapted to control heaters and an innovative CO 2 injection system. This system reduced seawater pH up to −0.9 units and increased temperature up to +6°C in three treatments and a control. Treatments can be continuously compared with the control and vary according to diel fluctuations, thus following the diel range observed in the sea. The mesocosm facility also includes an integrated secondary system of 48 aquaria for ecotoxicology studies. We validated the reproducibility and relevance of our experimental system by analyzing the variation of the total DNA of the microbial community extracted from corals in three elevated temperature scenarios during a 40‐day experiment. We also present data from temperature, acidification, and copper contamination trials, which allowed continuous, reliable, and consistent treatment manipulations.

Comparison of different protocols for the extraction of microbial DNA from reef corals

This study aimed to test different protocols for the extraction of microbial DNA from the coral Mussismilia harttii. Four different commercial kits were tested, three of them based on methods for DNA extraction from soil (FastDNA SPIN Kit for soil, MP Bio, PowerSoil DNA Isolation Kit, MoBio, and ZR Soil Microbe DNA Kit, Zymo Research) and one kit for DNA extraction from plants (UltraClean Plant DNA Isolation Kit, MoBio). Five polyps of the same colony of M. harttii were macerated and aliquots were submitted to DNA extraction by the different kits. After extraction, the DNA was quantified and PCR-DGGE was used to study the molecular fingerprint of Bacteria and Eukarya. Among the four kits tested, the ZR Soil Microbe DNA Kit was the most efficient with respect to the amount of DNA extracted, yielding about three times more DNA than the other kits. Also, we observed a higher number and intensities of DGGE bands for both Bacteria and Eukarya with the same kit. Considering these results, we suggested that the ZR Soil Microbe DNA Kit is the best adapted for the study of the microbial communities of corals.

Broadcast Spawning Coral Mussismilia hispida Can Vertically Transfer its Associated Bacterial Core

The hologenome theory of evolution (HTE), which is under fierce debate, presupposes that parts of the microbiome are transmitted from one generation to the next [vertical transmission (VT)], which may also influence the evolution of the holobiont. Even though bacteria have previously been described in early life stages of corals, these early life stages (larvae) could have been inoculated in the water and not inside the parental colony (through gametes) carrying the parental microbiome. How Symbiodinium is transmitted to offspring is also not clear, as only one study has described this mechanism in spawners. All other studies refer to incubators. To explore the VT hypothesis and the key components being transferred, colonies of the broadcast spawner species Mussismilia hispida were kept in nurseries until spawning. Gamete bundles, larvae and adult corals were analyzed to identify their associated microbiota with respect to composition and location. Symbiodinium and bacteria were detected by sequencing in gametes and coral planula larvae. However, no cells were detected using microscopy at the gamete stage, which could be related to the absence of those cells inside the oocytes/dispersed in the mucus or to a low resolution of our approach. A preliminary survey of Symbiodinium diversity indicated that parental colonies harbored Symbiodinium clades B, C and G, whereas only clade B was found in oocytes and planula larvae [5 days after fertilization (a.f.)]. The core bacterial populations found in the bundles, planula larvae and parental colonies were identified as members of the genera Burkholderia, Pseudomonas, Acinetobacter, Ralstonia, Inquilinus and Bacillus, suggesting that these populations could be vertically transferred through the mucus. The collective data suggest that spawner corals, such as M. hispida, can transmit Symbiodinium cells and the bacterial core to their offspring by a coral gamete (and that this gamete, with its bacterial load, is released into the water), supporting the HTE. However, more data are required to indicate the stability of the transmitted populations to indicate whether the holobiont can be considered a unit of natural selection or a symbiotic assemblage of independently evolving organisms.

Effects of Ocean Acidification and Temperature Increases on the Photosynthesis of Tropical Reef Calcified Macroalgae

Climate change is a global phenomenon that is considered an important threat to marine ecosystems. Ocean acidification and increased seawater temperatures are among the consequences of this phenomenon. The comprehension of the effects of these alterations on marine organisms, in particular on calcified macroalgae, is still modest despite its great importance. There are evidences that macroalgae inhabiting highly variable environments are relatively resilient to such changes. Thus, the aim of this study was to evaluate experimentally the effects of CO2-driven ocean acidification and temperature rises on the photosynthesis of calcified macroalgae inhabiting the intertidal region, a highly variable environment. The experiments were performed in a reef mesocosm in a tropical region on the Brazilian coast, using three species of frondose calcifying macroalgae (Halimeda cuneata, Padina gymnospora, and Tricleocarpa cylindrica) and crustose coralline algae. The acidification experiment consisted of three treatments with pH levels below those occurring in the region (-0.3, -0.6, -0.9). For the temperature experiment, three temperature levels above those occurring naturally in the region (+1, +2, +4°C) were determined. The results of the acidification experiment indicate an increase on the optimum quantum yield by T. cylindrica and a decline of this parameter by coralline algae, although both only occurred at the extreme acidification treatment (-0.9). The energy dissipation mechanisms of these algae were also altered at this extreme condition. Significant effects of the temperature experiment were limited to an enhancement of the photosynthetic performance by H. cuneata although only at a modest temperature increase (+1°C). In general, the results indicate a possible photosynthetic adaptation and/or acclimation of the studied macroalgae to the expected future ocean acidification and temperature rises, as separate factors. Such relative resilience may be a result of the highly variable environment they inhabit.

First record of a reef coral spawning event in the western South Atlantic

Summary The first record of coral spawning in the South Atlantic was observed among Mussismilia hispida colonies at the “Laje de Santos” (24°19′ S, 046°11′ W). Several colonies were observed spawning for about 15 min, early on the night of April 29, 2000. Some colonies did not spawn and no colonies were observed spawning later than circa 20:00 h. The report of M. hispida spawning in Santos came from the southernmost area of occurrence of this species. Data from this record are compared with those from previous studies on the reproduction of this species.

Photosynthetic responses of corals Mussismilia harttii (Verrill, 1867) from turbid waters to changes in temperature and presence/absence of light

Respostas de corais a estresses de mudancas de temperatura sao especificas e dependem tambem da localidade. Como a luz e um componente importante dos estresses induzidos pela temperatura, testamos experimentalmente as respostas de Mussismilia hartii, coral originario de aguas turvas, a mudancas de temperatura, na presenca e ausencia de luz. Parâmetros de fluorescencia da clorofila foram medidos com Diving-PAM. Os experimentos foram mantidos a temperaturas distintas. Os polipos permaneceram no escuro ou foram continuamente expostos a 300 µmol photons m-2.s-1 de irradiância. Nenhum branqueamento visivel foi observado entre as temperaturas de 26,5 a 35,0 oC, mas a maioria dos polipos expostos a temperaturas elevadas mostraram sinais de necrose do tecido. Houve uma reducao de Fv/Fm em resposta ao aumento da temperatura, que foi exacerbada na presenca de luz, indicando um efeito sinergetico desses fatores. Sugerimos que o fotodano sofrido pelos endossimbiontes de M. harttii, desencadeados nas temperaturas de 33,0 e 35,0 oC, resultou de uma diminuicao do processo de reparacao, assim como o efeito da luz sobre o PSII. A recuperacao de polipos mantidos a 31,0 oC indicou que essa temperatura parece ser limitrofe (dependendo do tempo de exposicao); temperaturas acima de 31,0 oC levaram a danos irreversiveis ou morte de M. harttii.