Posts Tagged 'corals'



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’

An assessment of reef coral calcification over the late Cenozoic

Shallow-water reef-building corals have an extensive geological record and many aspects of their evolution, biodiversity, and biogeography are known in great details. In contrast, the adaptive potential and risk of extinction of coral reefs in response to excessive warming and ocean acidification remains largely undocumented. It is well established that anthropogenic CO2 emissions cause global warming and ocean acidification (lowering of pH), which increasingly impede the biomineralization process in many marine calcareous biota. The “light-enhanced” calcification machinery of the shallow-water reef corals is particularly threatened by this development through the combined effect of a lowering of the supersaturation of seawater with CaCO3 (aragonite) and an expulsion of the symbiotic zooxanthellae (bleaching). The bleaching is of prime importance, because it interrupts the supply of DIC and metabolites required for pH upregulation within the calcification fluid. The degree of calcification in scleractinian reef corals may therefore represent a suitable tracer to assess the state of the ocean carbonate system and the photosynthetic performance of the zooxanthellae during past episodes of natural environmental change. This study presents the first comprehensive set of calcification data from corals covering the early Miocene to early Pleistocene interval (20.8 to 1.2 million years, Ma). Various screening procedures ensured that the studied coral skeletons are pristine and suited to yield meaningful stable isotope data (δ18O, δ13C) and calcification records. δ18O and δ13C values document growth environments consistent with current tropical and subtropical settings. To assess fossil calcification rates, we use a reference dataset of recent corals from the Indo-Pacific (Porites) and an independent validation dataset from the Western Atlantic-Caribbean (Orbicella). Almost all fossil corals document very low annual rates of upward growth (“extension rate”) relative to present, and lower skeletal bulk density than predicted by established modern relationships. To allow for a quantitative assessment of coral calcification performance, we use a new approach that we term the calcification anomaly. It is insensitive to sea-surface temperature and well-suited for comparative assessments of calcification performance between reef sites and over time. Based on this approach, the majority of fossil corals in our dataset displays hypo-calcification, while a few show optimal calcification and none display hyper-calcification. Compared to present-day growth conditions, the fossil calcification data show that (1) skeletogenesis responded in a fully compatible way to known environmental stresses (e.g. turbid water, elevated salinity, eutrophy), and that (2) the calcification performance within the reef window (i.e. oligotrophic clear-water settings) remained below that of modern z-corals. Since fossil coral δ13C values are compatible with those of modern reef corals, we infer that the light-enhanced calcification system of symbiotic scleractinian corals was fully established by the beginning of the Neogene and that lower-than-present calcification performance was the likely response to a chronically low pH and/or low carbonate saturation state of the global ocean. If so, the present-day saturation state appears to be rather an exception than the norm and probably not a suitable starting point for predicting future calcification trends. In addition, using trends from the geological past does not include anthropogenic side-effects such as eutrophication and pollution.

Continue reading ‘An assessment of reef coral calcification over the late Cenozoic’

Corals exhibit distinct patterns of microbial reorganisation to thrive in an extreme inshore environment

Climate change threatens the survival of scleractinian coral from exposure to concurrent ocean warming, acidification and deoxygenation; how corals can potentially adapt to this trio of stressors is currently unknown. This study investigates three coral species (Acropora muricata, Acropora pulchra and Porites lutea) dominant in an extreme mangrove lagoon (Bouraké, New Caledonia) where abiotic conditions exceed those predicted for many reef sites over the next 100 years under climate change and compared them to conspecifics from an environmentally more benign reef habitat. We studied holobiont physiology as well as plasticity in coral-associated microorganisms (Symbiodiniaceae and bacteria) through ITS2 and 16S rRNA sequencing, respectively. We hypothesised that differences in coral-associated microorganisms (Symbiodiniaceae and bacteria) between the lagoonal and adjacent reef habitats may support coral host productivity and ultimately the ability of corals to live in extreme environments. In the lagoon, all coral species exhibited a metabolic adjustment of reduced photosynthesis-to-respiration ratios (P/R), but this was accompanied by highly divergent coral host-specific microbial associations. This was substantiated by the absence of shared ITS2-type profiles (proxies for Symbiodiniaceae genotypes). We observed that ITS2 profiles originating from Durusdinium taxa made up < 3% and a novel Symbiodinium ITS2 profile A1-A1v associated with A. pulchra. Bacterial community profiles were also highly divergent in corals from the lagoonal environment, whereas corals from the reef site were consistently dominated by Hahellaceae, Endozoicomonas. As such, differences in host–microorganism associations aligned with different physiologies and habitats. Our results argue that a multitude of host–microorganism associations are required to fulfill the changing nutritional demands of corals persisting into environments that parallel climate change scenarios.

Continue reading ‘Corals exhibit distinct patterns of microbial reorganisation to thrive in an extreme inshore environment’

Impacts of elevated temperature and pCO2 on the brooded larvae of Pocillopora damicornis from Luhuitou Reef, China: evidence for local acclimatization

In this study, we tested whether larvae brooded by the reef coral Pocillopora damicornis from a naturally extreme and highly variable environment are preadapted to cope with predicted increases in temperature and pCO2. We exposed larvae to two temperatures (29 vs. 30.8 °C) crossed with two pCO2 levels (~ 500 vs. ~ 1000 μatm) in a full-factorial experiment for 5 d. Larval performance was assessed as dark respiration (RD), net and gross photosynthesis (PN and PG, respectively), survival, settlement, and the activity of carbonic anhydrase (CA), the central enzyme involved in photosynthesis. The results showed that RD was unaffected by either elevated temperature or pCO2, while elevated temperature and/or pCO2 stimulated PN and PG and increased the ratios of PN to RD, indicating a relatively higher autotrophic capacity. Consequently, larval survivorship under elevated temperature and/or pCO2 was consistently 14% higher than that under the control treatment. Furthermore, elevated temperature and pCO2 did not affect host CA activity, but synergistically enhanced symbiont CA activity, contributing greatly to the stimulated photosynthetic capacity. These results suggest that brooded larvae of P. damicornis larvae from Luhuitou may be preadapted to cope with projected warming and ocean acidification. More generally, it appears that corals from highly variable environments may have increased resilience to the widespread climate change.

Continue reading ‘Impacts of elevated temperature and pCO2 on the brooded larvae of Pocillopora damicornis from Luhuitou Reef, China: evidence for local acclimatization’

Climate‐induced changes in the suitable habitat of cold‐water corals and commercially important deep‐sea fishes in the North Atlantic

The deep sea plays a critical role in global climate regulation through uptake and storage of heat and carbon dioxide. However, this regulating service causes warming, acidification and deoxygenation of deep waters, leading to decreased food availability at the seafloor. These changes and their projections are likely to affect productivity, biodiversity and distributions of deep‐sea fauna, thereby compromising key ecosystem services. Understanding how climate change can lead to shifts in deep‐sea species distributions is critically important in developing management measures. We used environmental niche modelling along with the best available species occurrence data and environmental parameters to model habitat suitability for key cold‐water coral and commercially important deep‐sea fish species under present‐day (1951–2000) environmental conditions and to project changes under severe, high emissions future (2081–2100) climate projections (RCP8.5 scenario) for the North Atlantic Ocean. Our models projected a decrease of 28%–100% in suitable habitat for cold‐water corals and a shift in suitable habitat for deep‐sea fishes of 2.0°–9.9° towards higher latitudes. The largest reductions in suitable habitat were projected for the scleractinian coral Lophelia pertusa and the octocoral Paragorgia arborea, with declines of at least 79% and 99% respectively. We projected the expansion of suitable habitat by 2100 only for the fishes Helicolenus dactylopterus and Sebastes mentella (20%–30%), mostly through northern latitudinal range expansion. Our results projected limited climate refugia locations in the North Atlantic by 2100 for scleractinian corals (30%–42% of present‐day suitable habitat), even smaller refugia locations for the octocorals Acanella arbuscula and Acanthogorgia armata (6%–14%), and almost no refugia for P. arborea. Our results emphasize the need to understand how anticipated climate change will affect the distribution of deep‐sea species including commercially important fishes and foundation species, and highlight the importance of identifying and preserving climate refugia for a range of area‐based planning and management tools.

Continue reading ‘Climate‐induced changes in the suitable habitat of cold‐water corals and commercially important deep‐sea fishes in the North Atlantic’

Meta-analysis reveals reduced coral calcification under projected ocean warming but not under acidification across the Caribbean Sea

Ocean acidification and warming are two of the many threats to coral reefs worldwide, and Caribbean reef-building corals are especially vulnerable. However, even within the Caribbean, experimental acidification and warming studies reveal a wide array of coral calcification responses across reef systems and among species, complicating efforts to predict how corals will respond to these global-scale stressors. We conducted a meta-analysis to investigate the calcification responses of Caribbean corals to experimentally induced seawater ocean acidification, ocean warming, and the combination of both stressors. Calcification rates were reduced for corals reared under warming alone, but acidification and the combination of both stressors did not clearly reduce calcification rates. Calcification responses of corals collected from the Florida Keys and Belize were compared for regional differences since a greater number of studies were performed on corals collected from these two regions. Notably, corals from the Florida Keys did not exhibit reduced calcification under acidification, warming, or the combination of both stressors, while corals from Belize exhibited reduced calcification under warming alone. Further investigation of these regional trends suggests that the warming and acidification treatments employed dictated calcification responses, rather than collection region. Results from this meta-analysis are constrained by the very few studies that have been conducted within the Caribbean to assess ocean acidification and warming and the large variation in experimental procedure among studies. This meta-analysis reveals existing gaps in our understanding of how corals will likely respond to projected acidification and warming and highlights ways to improve comparability among experimental studies conducted on corals within the same region to better predict coral calcification response under global change.

Continue reading ‘Meta-analysis reveals reduced coral calcification under projected ocean warming but not under acidification across the Caribbean Sea’

Year-long effects of high pCO2 on the community structure of a tropical fore reef assembled in outdoor flumes

In this study, fore reef coral communities were exposed to high pCO2 for a year to explore the relationship between net accretion (Gnet) and community structure (planar area growth). Coral reef communities simulating the fore reef at 17-m depth on Mo’orea, French Polynesia, were assembled in three outdoor flumes (each 500 l) that were maintained at ambient (396 µatm), 782 µatm, and 1434 µatm pCO2, supplied with seawater at 300 l h−1, and exposed to light simulating 17-m depth. The communities were constructed using corals from the fore reef, and the responses of massive Porites spp., Acropora spp., and Pocillopora verrucosa were assessed through monthly measurements of Gnet and planar area. High pCO2 depressed Gnet but did not affect colony area by taxon, although the areas of Acropora spp. and P. verrucosa summed to cause multivariate community structure to differ among treatments. These results suggest that skeletal plasticity modulates the effects of reduced Gnet at high pCO2 on planar growth, at least over a year. The low sensitivity of the planar growth of fore reef corals to the effects of ocean acidification (OA) on net calcification supports the counterintuitive conclusion that coral community structure may not be strongly affected by OA.

Continue reading ‘Year-long effects of high pCO2 on the community structure of a tropical fore reef assembled in outdoor flumes’

The effect of seawater environmental factors on the corals of Wailingding Island in the Pearl River Estuary

Highlights

• The seawater environment and corals around Wailingding Island were investigated.

• Increased DIN concentration was an important factor in coral reduction.

• DIN disturbed corals by inducing coral-algal competition and phosphate starvation.

• Coral protection should control Wailingding island’s sewage discharge in dry season.

Abstract

Corals are important marine resources, Wailingding Island is one of the few islands with coral growth in the South China Sea, but the deterioration of seawater environment seriously threatens coral survival. In this study, the coral distribution, temperature, transparency, salinity, pH, dissolved oxygen (DO), chemical oxygen demand (COD), NH4+-N, NO3–N and PO43–P around Wailingding Island were investigated to determine the influential environmental factors affecting coral growth. The results showed that temperature, transparency, salinity, pH, DO and COD were within the ranges required by coral; however, the dissolved inorganic nitrogen (DIN) concentration increased by 200% to approximately 0.33 mg/L from 1990 to 2019, and it was speculated to be an important factor in coral reduction, as DIN can disturb corals by inducing coral-algal competition and phosphate starvation. Pearl River runoff (PRR) and human activity on Wailingding Island were the dominant nutrient sources in the wet season and dry season, respectively, and local coral protection measures should focus on controlling sewage discharge in consideration of this seasonal difference. In addition, the optimum ranges of above environmental factors for local coral were proposed to provide a reference for discharge control. These results will contribute to the coral protection of Wailingding Island.

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Ocean acidification in the IPCC AR5 WG II

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