Posts Tagged 'corals'



Prior exposure to elevated pCO2 does not affect calcification of a tropical scleractinian when returned to ambient pCO2

Highlights

•Coral reefs experience biologically-driven pCO2 oscillations

•Calcification of A. retusa with two pCO2 exposure histories differed.

•When subsequently placed in common pCO2 environment, calcification was similar.

•Some corals are capable of a reversible plastic response of calcification.

Abstract

Coral reefs experience biologically-driven pCO2 oscillations that are predicted to become more extreme in magnitude and duration under ocean acidification (OA) regimes. Understanding the plasticity of responses in common reef-building corals to oscillations in pCO2 will allow for better predictions of their function in future seawater conditions. This study explored the effects of variation in seawater pCO2 on coral calcification using experiments conducted over one month between 9 April 2018 and 18 May 2018. Branches (~4-cm long) of Acropora retusa were sampled from colonies at 10-m depth on the fore reef of Mo’orea, French Polynesia (17° 28′ 53.9004″ S, 149° 49′ 50.5992″ W). We tested the hypothesis that depressed calcification caused by elevated pCO2 (~1000 μatm) is relaxed (i.e., calcification increases) upon return to ambient pCO2 (~400 μatm). Corals first were incubated in ambient or elevated pCO2 for 19 days, with the result that calcification integrated over this period was reduced by 31% under elevated pCO2. The same corals were then incubated at ambient pCO2 for 11 days, during which calcification was independent of the experimental pCO2 exposure history. Our results suggest that a quick relaxation of pCO2-depressed calcification in A. retusa following cessation of high pCO2 indicates that corals are capable of a reversible plastic response of calcification when confronted by pCO2 oscillations.

Continue reading ‘Prior exposure to elevated pCO2 does not affect calcification of a tropical scleractinian when returned to ambient pCO2’

How does the sexual reproduction of marine life respond to ocean acidification?

Recent research indicates that synchronicity of sexual reproduction in coral spawning events is breaking down, leading to aging populations and decreased recruitment success. In this perspective, we develop a hypothesis that this phenomenon could be caused by ongoing ocean acidification (OA). We hypothesize, that the underlying physiological machinery could be the carbon concentrating mechanism (CCM). The endosymbiotic zooxanthellae of corals could use this mechanism to sense calm water motion states in a comparable way to that known from macroalgae. In macroalgae, it is well-established that dissolved inorganic carbon (DIC) acts as the trigger for signaling low water motion. Hence, evolutionarily developed signals of low water motion, suited for gamete-release, may be misleading in the future, potentially favoring opportunistic species in a broad range of marine organisms.

Continue reading ‘How does the sexual reproduction of marine life respond to ocean acidification?’

Pacific-wide pH snapshots reveal that high coral cover correlates with low, but variable pH

Ocean acidification (OA) is impairing the construction of coral reefs while simultaneously accelerating their breakdown. The metabolism of different reef organism assemblages alters seawater pH in different ways, possibly buffering or exacerbating OA impacts. In spite of this, field data relating benthic community structure and seawater pH are sparse. We collected pH time-series data snapshots at 10 m depth from 28 different reefs (n = 13 lagoon, n = 15 fore reef) across 22 Pacific islands, spanning 31° latitude and 90° longitude. Coincident with all deployments, we measured percent cover of the benthic community. On fore reefs, high coral cover (CC) negatively correlated with mean and minimum pH, but positively correlated with pH variability. Conversely, pH minima were positively correlated to coverage of coralline and turf algae. Benthic cover did not correlate with pH in lagoonal reefs. From 0%–100% CC, mean pH and aragonite saturation state (Ωarag ) declined −0.081 and −0.51, respectively, while declines in minimum values were greater (Δmin pH = −0.164, Δmin Ωarag = −0.96). Based upon previously published relationships, the mean pH decline from 0%–100% CC would depress coral calcification 7.7%–18.0% and increase biologically-mediated dissolution 13.5%–27.9%, with pH minima depressing dark coral calcification 14.4%–35.2% and increasing biologically-mediated dissolution 31.0%–62.2%. This spatially expansive dataset provides evidence that coral reefs with the highest coral cover may experience the lowest and most extreme pH values with OA.

Continue reading ‘Pacific-wide pH snapshots reveal that high coral cover correlates with low, but variable pH’

Influence of water masses on the biodiversity and biogeography of deep-sea benthic ecosystems in the North Atlantic

Circulation patterns in the North Atlantic Ocean have changed and re-organized multiple times over millions of years, influencing the biodiversity, distribution, and connectivity patterns of deep-sea species and ecosystems. In this study, we review the effects of the water mass properties (temperature, salinity, food supply, carbonate chemistry, and oxygen) on deep-sea benthic megafauna (from species to community level) and discussed in future scenarios of climate change. We focus on the key oceanic controls on deep-sea megafauna biodiversity and biogeography patterns. We place particular attention on cold-water corals and sponges, as these are ecosystem-engineering organisms that constitute vulnerable marine ecosystems (VME) with high associated biodiversity. Besides documenting the current state of the knowledge on this topic, a future scenario for water mass properties in the deep North Atlantic basin was predicted. The pace and severity of climate change in the deep-sea will vary across regions. However, predicted water mass properties showed that all regions in the North Atlantic will be exposed to multiple stressors by 2100, experiencing at least one critical change in water temperature (+2°C), organic carbon fluxes (reduced up to 50%), ocean acidification (pH reduced up to 0.3), aragonite saturation horizon (shoaling above 1000 m) and/or reduction in dissolved oxygen (>5%). The northernmost regions of the North Atlantic will suffer the greatest impacts. Warmer and more acidic oceans will drastically reduce the suitable habitat for ecosystem-engineers, with severe consequences such as declines in population densities, even compromising their long-term survival, loss of biodiversity and reduced biogeographic distribution that might compromise connectivity at large scales. These effects can be aggravated by reductions in carbon fluxes, particularly in areas where food availability is already limited. Declines in benthic biomass and biodiversity will diminish ecosystem services such as habitat provision, nutrient cycling, etc. This study shows that the deep-sea VME affected by contemporary anthropogenic impacts and with the ongoing climate change impacts are unlikely to withstand additional pressures from more intrusive human activities. This study serves also as a warning to protect these ecosystems through regulations and by tempering the ongoing socio-political drivers for increasing exploitation of marine resources.

Continue reading ‘Influence of water masses on the biodiversity and biogeography of deep-sea benthic ecosystems in the North Atlantic’

Regulation of ion transport and energy metabolism enables certain coral genotypes to maintain calcification under experimental ocean acidification

Cold‐water corals (CWCs) are important foundation species in the world’s largest ecosystem, the deep sea. They support a rich faunal diversity but are threatened by climate change and increased ocean acidification. As part of this study, fragments from three genetically distinct Lophelia pertusa colonies were subjected to ambient pH (pH = 7.9) and low pH (pH = 7.6) for 6 months. RNA was sampled at 2, 4.5, and 8.5 weeks and sequenced. The colony from which the fragments were sampled explained most of the variance in expression patterns, but a general pattern emerged where up‐regulation of ion transport, required to maintain normal function and calcification, was coincident with lowered expression of genes involved in metabolic processes; RNA regulation and processing in particular. Furthermore, there was no differential expression of carbonic anhydrase detected in any analyses, which agrees with a previously described lack of response in enzyme activity in the same corals. However, one colony was able to maintain calcification longer than the other colonies when exposed to low pH and showed increased expression of ion transport genes including proton transport and expression of genes associated with formation of microtubules and the organic matrix, suggesting that certain genotypes may be better equipped to cope with ocean acidification in the future. While these genotypes exist in the contemporary gene pool, further stresses would reduce the genetic variability of the species, which would have repercussions for the maintenance of existing populations and the ecosystem as a whole.

Continue reading ‘Regulation of ion transport and energy metabolism enables certain coral genotypes to maintain calcification under experimental ocean acidification’

Pore water conditions driving calcium carbonate dissolution in reef sands

Due to decreases in seawater pH resulting from ocean acidification, permeable calcium carbonate reef sands are predicted to be net dissolving by 2050. However, the rate of dissolution and factors that control this rate remain poorly understood. Experiments performed in benthic chambers predict that reefs will become net dissolving when the aragonite saturation state (Ωa) in sea water falls below ∼ 3, as underlying reef sediments start net dissolution due to lower saturation states in the pore water. We used flow-through reactors to investigate the rate of dissolution at various Ωa at the pore scale. The sediment became net dissolving at Ωa = 1.68 – 2.25, which is significantly greater than 1. This indicates that the bulk pore water does not represent conditions at the site of dissolution, and dissolution probably occurs in microniches inside porous sand grains. Measured dissolution rates were much higher under oxic conditions than anoxic conditions, but were not affected by the addition of carbonic anhydrase. Analysis of δ13C-CO2 produced in the flow-through reactors revealed a bias in the conventional alkalinity anomaly method under anoxic conditions, showing that some of the CO2 attributed to metabolism by may actually be derived from carbonate dissolution. This deviation likely originates from alkalinity consumption by fermentation, which masks the alkalinity generated by dissolution. Therefore, dissolution rates determined by alkalinity changes in reef sands with anaerobic metabolisms may underestimate actual values.

Continue reading ‘Pore water conditions driving calcium carbonate dissolution in reef sands’

Coral persistence despite extreme periodic pH fluctuations at a volcanically acidified Caribbean reef

Naturally acidified environments, such as those caused by volcanic CO2 venting, reveal how complex coral reef ecosystems may respond to future ocean acidification conditions. Few of these sites have been described worldwide, and only a single such site is known from the Caribbean. Herein, we have characterized an area of volcanic acidification at Mayreau Island, St. Vincent and the Grenadines. Despite localized CO2 enrichment and gas venting, the surrounding area has high hard and soft coral cover, as well as extensive carbonate frameworks. Twice daily extremes in acidification, in some cases leading to undersaturation of aragonite, are correlated with tidal fluctuations and are likely related to water flow. Corals persisting despite this periodic acidification can provide insights into mechanisms of resilience and the importance of natural pH variability on coral reefs.

Continue reading ‘Coral persistence despite extreme periodic pH fluctuations at a volcanically acidified Caribbean reef’

Ocean acidification: calcifying marine organisms

This document is one in a series on ocean acidification (OA). The series Introduction, Ocean Acidification: An Introduction, contains a general overview and information on the causes and chemistry of OA. Because OA is very large-scale and complex, each document in the series addresses a specific aspect of this issue. Florida, with an extensive coastline and deep cultural and economic ties to marine resources, will be directly affected by changes in seawater chemistry. Thus, each topic in the series also highlights information of specific relevance for Florida.

Continue reading ‘Ocean acidification: calcifying marine organisms’

Patterns in microbiome composition differ with ocean acidification in anatomic compartments of the Mediterranean coral Astroides calycularis living at CO2 vents

Highlights

• Coral microbiomes contribute to host acclimatization to environmental change.

• Natural CO2 gradients are a model of global change-induced ocean acidification.

• Non-symbiotic coral Astroides calycularis survives in a natural acidified site.

• Calycularis mucus microbiome is the most affected by low pH conditions.

• Low pH conditions induce changes in microbiome supporting nitrogen cycling.

Abstract

Coral microbiomes, the complex microbial communities associated with the different anatomic compartments of the coral, provide important functions for the host’s survival, such as nutrient cycling at the host’s surface, prevention of pathogens colonization, and promotion of nutrient uptake. Microbiomes are generally referred to as plastic entities, able to adapt their composition and functionality in response to environmental change, with a possible impact on coral acclimatization to phenomena related to climate change, such as ocean acidification. Ocean sites characterized by natural gradients of pCO2 provide models for investigating the ability of marine organisms to acclimatize to decreasing seawater pH. Here we compared the microbiome of the temperate, shallow water, non-symbiotic solitary coral Astroides calycularis that naturally lives at a volcanic CO2 vent in Ischia Island (Naples, Italy), with that of corals living in non-acidified sites at the same island. Bacterial DNA associated with the different anatomic compartments (mucus, tissue and skeleton) of A. calycularis was differentially extracted and a total of 68 samples were analyzed by 16S rRNA gene sequencing. In terms of phylogenetic composition, the microbiomes associated with the different coral anatomic compartments were different from each other and from the microbial communities of the surrounding seawater. Of all the anatomic compartments, the mucus-associated microbiome differed the most between the control and acidified sites. The differences detected in the microbial communities associated to the three anatomic compartments included a general increase in subdominant bacterial groups, some of which are known to be involved in different stages of the nitrogen cycle, such as potential nitrogen fixing bacteria and bacteria able to degrade organic nitrogen. Our data therefore suggests a potential increase of nitrogen fixation and recycling in A. calycularis living close to the CO2 vent system.

Continue reading ‘Patterns in microbiome composition differ with ocean acidification in anatomic compartments of the Mediterranean coral Astroides calycularis living at CO2 vents’

Evaluation of heterotrophic bacteria associated with healthy and bleached corals of Gulf of Kutch, Gujarat, India for siderophore production and their response to climate change factors

Highlights

• Comparison of siderophore production by healthy and bleached coral associated microbes.

• Catecholate type of siderophore is mainly produced by coral associated microbes.

• Adapting ability of healthy and bleached coral isolates in changing climate.

• Significant effect of lowering pH and increasing temperature on growths and siderophore production of coral associated bacteria.

Abstract

Bacteria are known to play a crucial role in coral health but their mechanisms are unclear. Siderophore production could be one of the mechanisms by which they benefit or harm the corals. Bacteria produce siderophore to adapt in harsh conditions, such as nutrient limiting and competing environments such as coral surface. In the present study, siderophore producing ability of microbes associated with healthy and bleached corals is evaluated as both healthy and bleached coral surface provide a different environment concerning nutrients and competitions. Total of 129 siderophore-producing bacteria associated with two healthy (n = 66 isolates) and bleached coral (n = 63) species (Porites spp. and Turbinaria spp.) from the Gulf of Kutch (GoK), Gujarat (India) are screened and compared. No relation between coral health status and siderophore producing ability of microbes is observed (one-way ANOVA, p = 0.67). All the isolates are positive to catecholate type of siderophore which has the strongest affinity for limiting iron. The study also explores the growth and siderophore production behavior of healthy and bleached coral isolates at decreasing pH and temperature rise as they are the important factors that affects the solubility of nutrients and thus, the structure and functioning of the microbes. Isolates from bleached corals showed an increase in growth even at pH 6, whereas the growth of healthy coral isolates reduces at pH 6. Temperature rise is negatively correlated to growth and siderophore production by all isolates except Bacillus sp. PH26. Combined low pH and temperature rise stress, negatively affect growth and siderophore production of coral-associated microbes with Bacillus sp. PH26 as exception. General correlation trend of bacterial growth and siderophore production is positive. The isolates showing exceptional behavior might be possibly beneficial or harmful to the coral health. Thus, growth and siderophore production of microbes under changing climate conditions might be used as preliminary tools to screen beneficial and pathogenic microbes of corals from opportunistic microbes. This screening would reduce the number of possible candidates for in-situ and in-vitro microcosm experiments to understand the role of siderophore producing microbes in coral health. Overall, pH and temperature have a significant impact on coral-associated microbial growth and siderophore production, which ultimately impact the coral health and disease as the microbes form an integral part of coral holobiont. The study laid the foundation for future studies to understand the role of siderophore producing bacteria in coral health in the global climate-changing era.

Continue reading ‘Evaluation of heterotrophic bacteria associated with healthy and bleached corals of Gulf of Kutch, Gujarat, India for siderophore production and their response to climate change factors’


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Ocean acidification in the IPCC AR5 WG II

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