Posts Tagged 'corals'



Investigating marine bio‐calcification mechanisms in a changing ocean with in vivo and high‐resolution ex vivo Raman spectroscopy

Ocean acidification poses a serious threat to marine calcifying organisms, yet experimental and field studies have found highly diverse responses among species and environments. Our understanding of the underlying drivers of differential responses to ocean acidification is currently limited by difficulties in directly observing and quantifying the mechanisms of bio‐calcification. Here, we present Raman spectroscopy techniques for characterizing the skeletal mineralogy and calcifying fluid chemistry of marine calcifying organisms such as corals, coralline algae, foraminifera, and fish (carbonate otoliths). First, our in vivo Raman technique is the ideal tool for investigating non‐classical mineralization pathways. This includes calcification by amorphous particle attachment, which has recently been controversially suggested as a mechanism by which corals resist the negative effects of ocean acidification. Second, high‐resolution ex vivo Raman mapping reveals complex banding structures in the mineralogy of marine calcifiers, and provides a tool to quantify calcification responses to environmental variability on various timescales from days to years. We describe the new insights into marine bio‐calcification that our techniques have already uncovered, and we consider the wide range of questions regarding calcifier responses to global change that can now be proposed and addressed with these new Raman spectroscopy tools.

Continue reading ‘Investigating marine bio‐calcification mechanisms in a changing ocean with in vivo and high‐resolution ex vivo Raman spectroscopy’

Sponge bioerosion versus aqueous pCO2: morphometric assessment of chips and etching fissures

Bioeroding sponges are important macroborers that chemically cut out substrate particles (chips) and mechanically remove them, thereby contributing to reef-associated sediment. These chemical and mechanical proportions vary with elevated levels of partial pressure of carbon dioxide (pCO2). To assess related impacts, the morphometric parameters “chip diameter” and “etching fissure width” were analyzed for Cliona orientalis Thiele, 1900, hypothesizing that their dimensions would differ with different pCO2 exposures (72 h at ca. 400, 750 and 1700 μatm). Under ambient conditions, we obtained a mean chip diameter of 21.6 ± 0.7 μm and a mean fissure width of 0.29 ± 0.01 μm. Chips were evenly distributed across the medium and coarse silt fractions regardless of treatment. We could not find a reliable pCO2 treatment effect for chip diameter and fissure width, but we observed strong data variability not related to our key questions. A hierarchical data design further reduced the test power. Fissure width was the more sensitive, but also more variable parameter. Sample size analyses nevertheless indicated that we had processed enough data. Thus, we reject our scenario of an increase in fissure width and consequent reduction in chip size to explain why chemical sponge bioerosion increases more strongly than the mechanical counterpart. Instead, we propose that a lowered ambient pH may favor respiratory acid build-up in the sponge tissue, possibly leading to a less localized bioerosion, causing bias towards more chemical bioerosion. Overall, this does not seem to affect the morphometry of sponge chips and the quality of sponge-generated sediment.

Continue reading ‘Sponge bioerosion versus aqueous pCO2: morphometric assessment of chips and etching fissures’

Anthropogenic ocean warming and acidification recorded by Sr/Ca, Li/Mg, δ11B and B/Ca in Porites coral from the Kimberley region of northwestern Australia

Highlights

• Ocean warming has accelerated since the 1970s in the nearshore Kimberley.

• Coral calcification remains less affected and ‘normal’ seasonal coral internal carbonate chemistry is observed.

• Under intensified warming, coral’s ability to concentrate metabolic DIC has been reduced.

• Ocean acidification has led to the secular reduction of pHcf.

Abstract

The impact of climate changes on corals living in naturally extreme environments is poorly understood but crucial to longer-term sustainability of coral reefs. Here we report century-long temperature (Sr/Ca and Li/Mg) and calcifying fluid (CF) carbonate chemistry (δ11B and B/Ca) records for a long-lived (1919 to 2016) Porites coral from the high thermally variable Kimberley region of northwestern Australia. We investigate how increasing temperatures and ocean acidification are manifested in the carbonate chemistry of coral’s CF and impacts of climate change on calcification. Using Sr/Ca and Li/Mg multiproxy we show that annual temperature in the nearshore Kimberley exhibited a gradual increase (0.009 ± 0.003 °C/yr) from the 1920s onward. However for the most recent years (2000–2015) more rapid summer warming (0.05 ± 0.01 °C/yr) are registered, indicative of intensified warming. Despite that, we find no significant trend for calcification rate of this coral over the past century, as well as ‘normal’ seasonal variability in coral’s CF carbonate chemistry. Importantly, the coral’s ability to concentrate inorganic carbon seems to be affected by recent warming, with reduced DICcf observed during 2008 to 2015, while the minimally-affected pHcf acts to compensate the decreases of DICcf with the calcification rate showing only slight decrease. Additionally, we also find that ocean acidification has clearly led to the long-term reduction in the pH of the CF.

Continue reading ‘Anthropogenic ocean warming and acidification recorded by Sr/Ca, Li/Mg, δ11B and B/Ca in Porites coral from the Kimberley region of northwestern Australia’

Corallivory in the Anthropocene: interactive effects of anthropogenic stressors and corallivory on coral reefs

Corallivory is the predation of coral mucus, tissue, and skeleton by fishes and invertebrates, and a source of chronic stress for many reef-building coral species. Corallivores often prey on corals repeatedly, and this predation induces wounds that require extensive cellular resources to heal. The effects of corallivory on coral growth, reproduction, and community dynamics are well-documented, and often result in reduced growth rates and fitness. Given the degree of anthropogenic pressures that threaten coral reefs, it is now imperative to focus on understanding how corallivory interacts with anthropogenic forces to alter coral health and community dynamics. For example, coral bleaching events that stem from global climate change often reduce preferred corals species for many corallivorous fishes. These reductions in preferred prey may result in declines in populations of more specialized corallivores while more generalist corallivores may increase. Corallivory may also make corals more susceptible to thermal stress and exacerbate bleaching. At local scales, overfishing depletes corallivorous fish stocks, reducing fish corallivory and bioerosion, whilst removing invertivorous fishes and allowing population increases in invertebrate corallivores (e.g., urchins, Drupella spp.). Interactive effects of local stressors, such as overfishing and nutrient pollution, can alter the effect of corallivory by increasing coral-algal competition and destabilizing the coral microbiome, subsequently leading to coral disease and mortality. Here, we synthesize recent literature of how global climate change and local stressors affect corallivore populations and shape the patterns and effect of corallivory. Our review indicates that the combined effects of corallivory and anthropogenic pressures may be underappreciated and that these interactions often drive changes in coral reefs on scales from ecosystems to microbes. Understanding the ecology of coral reefs in the Anthropocene will require an increased focus on how anthropogenic forcing alters biotic interactions, such as corallivory, and the resulting cascading effects on corals and reef ecosystems.

Continue reading ‘Corallivory in the Anthropocene: interactive effects of anthropogenic stressors and corallivory on coral reefs’

Temporal effects of ocean warming and acidification on coral–algal competition

While there is an ever-expanding list of impacts on coral reefs as a result of ocean warming and acidification, there is little information on how these global changes influence coral–algal competition. The present study assessed the impact of business-as-usual ocean warming and acidification conditions on the survivorship, calcification, photosynthesis and respiration of the coral–algal interaction between the macroalga Halimeda heteromorpha and the coral Acropora intermedia over 8 weeks in two seasons. The physiological responses of A. intermedia and H. heteromorpha were highly dependent on season, with both organisms demonstrating optimal rates of calcification and photosynthesis under present-day conditions in summer. Contact with H. heteromorpha did not influence A. intermedia survivorship, however did reduce long-term calcification rates. Photosynthetic rates of A. intermedia were influenced by algal contact temporally in opposing directions, with rates reduced in winter and increased in summer. Enhanced photosynthetic rates as a result of algal contact were not enough to offset the combined effects of ocean warming and acidification, which regardless of coral–algal contact, reduced survivorship, calcification and photosynthesis of A. intermedia and the calcification rates of H. heteromorpha. These findings provide experimental support for the idea that the effects of coral–algal competition are temporally variable, and help improve our understanding of how future ocean warming and acidification may alter the dynamics of coral–algal interactions.

Continue reading ‘Temporal effects of ocean warming and acidification on coral–algal competition’

The combined effects of pH and temperature on the physiology of the temperate coral Oculina arbuscula

The purpose of this investigation was to investigate the impact of ocean acidification and warming sea temperature on Oculina arbuscula, a temperate scleractinian coral found in Gray’s Reef National Marine Sanctuary (GRNMS) off the coast of Sapelo Island, GA. GRNMS experiences seasonal fluctuations in temperatures that reach 30°C and concurrent decreases in pH to approximately 8.0, thus naturally modelling the projected effects of anthropogenic climate change on an annual basis. Oculina arbuscula colonies in GRNMS are exposed to these natural fluctuations in temperature and pH, therefore I hypothesized that this species is resistant to the combined effects of high temperature and low pH. Specifically, I predicted that there would be no effects on calcification rates, symbiont densities, or chlorophyll a concentrations. To test these predictions, O. arbuscula colonies were collected from GRNMS, divided into three treatments and a control, and maintained for 75 days. Ambient temperature was applied at 26°C while high temperature was 31°C, and the ambient pH was 7.9 with a low pH of 7.65. The ambient values were applied to the control aquaria, and the three treatments experienced ocean acidification (ambient temperature, low pH), ocean warming (high temperature, ambient pH), and combined ocean warming and acidification (high temperature, low pH). Results showed that calcification rates were significantly reduced by the combined stressors and symbiont densities and chlorophyll concentrations were significantly reduced by high temperature treatments. These results indicated that with continued ocean acidification and warming, the success of Oculina arbsucula within the spatially competitive benthic communities in GRNMS may be compromised.

Continue reading ‘The combined effects of pH and temperature on the physiology of the temperate coral Oculina arbuscula’

Coral reef calcification and production after the 2016 bleaching event at Lizard Island, Great Barrier Reef

Severe coral bleaching events have affected the Great Barrier Reef (GBR) causing massive losses of hard coral cover. Here, we use flow respirometry approaches to assess coral reef net ecosystem calcification (NEC) and net ecosystem production (NEP) following the 2015/2016 bleaching event at Lizard Island in the northern GBR, a heavily impacted area. Previous studies conducted in 2008 and 2009 [Silverman et al., 2014] were used as pre‐impact data. Lagrangian and Eulerian approaches provided varied results. Estimated NEC (29.1 – 137.7 mmol m‐2 day‐1) and NEP (‐876.7 – 50.5 mmol m‐2 day‐1) rates in 2016 were highly sensitive to assumptions about reef water residence times and oceanic endmember concentrations. Replicating the methodology used for the 2008 and 2009 study resulted in post‐bleaching NEC in 2016 at 32 ± 10.8 mmol m‐2 day‐1, 40 – 46% lower than pre‐bleaching estimates in 2008 (61 ± 12 mmol m‐2 day‐1) and 2009 (54 ± 13 mmol m‐2 day‐1). The slopes of a total alkalinity vs. dissolved inorganic carbon (TA – DIC) plot decreased from ~ 0.3 in 2008 and 2009 to 0.1 in 2016, indicating elevated organic production and a shift in community function. Changes in NEC relative to the previous study were not driven by changing Ω arag. Coral cover shifted from 8.3% and 7.1% in 2008 and 2009 to 3.0% in 2016. We demonstrate a clear decrease in coral reef NEC following bleaching and highlight that subtle assumptions/methodological differences may create bias in the interpretation of results. Therefore, comparing coral reef metabolism datasets and predicting long‐term coral reef calcification based on existing short‐term datasets needs to be done with care.

Continue reading ‘Coral reef calcification and production after the 2016 bleaching event at Lizard Island, Great Barrier Reef’


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Ocean acidification in the IPCC AR5 WG II

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