Posts Tagged 'corals'

High pCO2 promotes coral primary production

While research on ocean acidification (OA) impacts on coral reefs has focused on calcification, relatively little is known about effects on coral photosynthesis and respiration, despite these being among the most plastic metabolic processes corals may use to acclimatize to adverse conditions. Here, we present data collected between 2016 and 2018 at three natural CO2 seeps in Papua New Guinea where we measured the metabolic flexibility (i.e. in hospite photosynthesis and dark respiration) of 12 coral species. Despite some species-specific variability, metabolic rates as measured by net oxygen flux tended to be higher at high pCO2 (ca 1200 µatm), with increases in photosynthesis exceeding those of respiration, suggesting greater productivity of Symbiodiniaceae photosynthesis in hospite, and indicating the potential for metabolic flexibility that may enable these species to thrive in environments with high pCO2. However, laboratory and field observations of coral mortality under high CO2 conditions associated with coral bleaching suggests that this metabolic subsidy does not result in coral higher resistance to extreme thermal stress. Therefore, the combined effects of OA and global warming may lead to a strong decrease in coral diversity despite the stimulating effect on coral productivity of OA alone.

Continue reading ‘High pCO2 promotes coral primary production’

Response of corals Acropora pharaonis and Porites lutea to changes in pH and temperature in the Gulf

Coral reefs are harboring a large part of the marine biodiversity and are important ecosystems for the equilibrium of the oceans. As a consequence of anthropogenic CO2 emission, a drop in pH and an increase in seawater temperature is observed in the Gulf coastal waters that potentially threaten coral assemblages. An experimental study was conducted on two species of corals to assess the effect of ocean warming and ocean acidification on the net calcification rate. Two pH conditions 8.2 and 7.5 and three temperatures, 22.5, 27.5 and 32.5 °C, were considered. Net calcification rates were measured using 45Ca radiotracer. Both temperature and pH had a significant effect on net calcification rates following a similar pattern for both species. The highest calcification rate was observed at low temperature and high pH. Increased temperature and decreased pH led to a decrease in net calcification rates. An interactive effect was observed as the effect of pH decreased with increasing temperature. However, the two species of coral were able to calcify in all the tested combination of temperature and pH suggesting that they are adapted to short term changes in temperature and pH. Ability to calcify even at a high temperature of 32.5 °C that is identical to the summertime Gulf seawater temperature under both the ambient and low pH condition with no mortalities, raises a question: are these corals adapted to high seawater temperatures and low pH? More in-depth assessments will be required to confirm if this is an adaptation to higher temperatures in Persian Gulf corals.

Continue reading ‘Response of corals Acropora pharaonis and Porites lutea to changes in pH and temperature in the Gulf’

Mediterranean cold-water corals as paleoclimate archives

Scleractinian cold-water corals preserve in their aragonite skeleton information on the past changes of the physico-chemical properties of the seawater in which they grew. Such information is stored as geochemical signals, such as changes in trace elements concentration (B/Ca, Li/Mg, P/Ca, Sr/Ca, Ba/Ca, U/Ca) or stable and radiogenic isotopes composition (δ11B, δ13C, δ18O, 14C, εNd), that are usually converted into environmental parameters using empirical calibration equations. The aragonite skeleton of cold-water corals is sufficiently uranium-rich to be suitable for U-series dating, providing precise and accurate ages for the last 600–700 kyrs. This opens the possibility to obtain reconstructions of key oceanographic parameters for the intermediate and deep water masses at sub-decadal scale resolution for climatically-relevant time windows in the past. However, part of the geochemical signal incorporated into the coral skeleton is modulated by the physiology of the coral, which complicates the interpretation of the geochemical proxies. This “vital effect” needs to be taken into account and corrected for to obtain reliable reconstructions of past changes in seawater temperature, pH and nutrient content. On the other hand, these biologically-induced geochemical signals can be used to investigate the processes controlling coral biomineralisation and better understand the resilience of cold-water corals to environmental and climate changes.

In the recent years, Mediterranean cold-water corals have been targeted for geochemically-oriented studies and their trace elements and isotopes composition has contributed significantly to developing and understanding new and established coral proxies. Living in an environment characterised by relatively warm seawater temperatures (13–14 °C) and high pH (8.1), the Mediterranean cold-water corals provide the end-member geochemical composition useful to derive empirical calibration equations. In particular, the analysis of several specimens of the cold-water corals species Lophelia pertusa, Madrepora oculata and Desmophyllum dianthus live-collected in the western, central and eastern Mediterranean Sea, has contributed to the development of the Li/Mg thermometer, boron isotopes pH proxy and P/Ca nutrient proxy, as well as a better understanding of the neodymium isotopic composition of cold-water corals as a water mass tracer. A multi-proxy approach has been recently applied to precisely U/Th-dated cold-water corals fragments from coral-bearing sediment cores retrieved in the western and central Mediterranean Sea, showing large changes in the dynamics of the intermediate waters during the Holocene. Further investigations of fossil cold-water corals specimens from different Mediterranean locations will open new perspectives on the reconstruction of past changes in the physico-chemical properties of sub-surface waters and their potential role in modifying the Mediterranean climate.

Continue reading ‘Mediterranean cold-water corals as paleoclimate archives’

A case study: variability in the calcification response of Mediterranean cold-water corals to ocean acidification

The Mediterranean Sea has certain characteristics that make it especially sensitive and vulnerable to changes in atmospheric CO2 and its gradual acidification. Some of the organisms that may be the first to be threatened by this impact are the cold-water corals. The few studies carried out up to date with these organisms by simulating in aquarium the acidified conditions expected for the year 2100 revealed a high variability between and within species. This chapter shows this highly variable response in the calcification of four of the most abundant cold-water coral species in the Mediterranean to low-pH conditions and their potential ecological implications.

Continue reading ‘A case study: variability in the calcification response of Mediterranean cold-water corals to ocean acidification’

The Great Barrier Reef: vulnerabilities and solutions in the face of ocean acidification

As living carbonate-based structures, coral reefs are highly vulnerable to ocean acidification. The Great Barrier Reef (GBR) is the largest continuous coral reef system in the world. Its economic, social, and icon assets are valued at AU$56 billion (Deloitte Access Economics, 2017), owing to its vast biodiversity and services related to commercial and recreational fisheries, shoreline protection, and reef-related tourism and recreation. Ocean acidification poses a significant risk to these ecological and socioeconomic services, threatening not only the structural foundation of the GBR but the livelihoods of reef-dependent sectors of society. To assess the vulnerabilities of the GBR to ocean acidification, we review the characteristics of the GBR and the current valuation and factors affecting potential losses across three major areas of socioeconomic concern: fisheries, shoreline protection, and reef-related tourism and recreation. We then discuss potential solutions, both conventional and unconventional, for mitigating ocean acidification impacts on the GBR and propose a suite of actions that would help assess and increase the region’s preparedness for the effects of ocean acidification.

Continue reading ‘The Great Barrier Reef: vulnerabilities and solutions in the face of ocean acidification’

Fate of Mediterranean Scleractinian cold-water corals as a result of global climate change. A synthesis

This chapter addresses the question as to how Mediterranean cold-water corals might fare in the future under anthropogenically-induced global climate change. The focus on three most prominent scleractinian cold-water corals species, the two branching and habitat-forming forms Madrepora oculata, Lophelia pertusa and the solitary cup coral Desmophyllum dianthus. We provide an introduction to climate change principals, highlight the current status of the marine environment with regard to global climate change, and describe how climate change impacts such as ocean acidification are predicted to affect key calcifiers such as scleractinian cold-water corals in the Mediterranean region. A synthesis of the experimental cold-water coral studies conducted to date on climate change impacts: The present state of knowledge reviewed in this chapter takes into account the number of experiments that have been carried out in the Mediterranean as well as for comparative purposes in other parts of the world, to examine the effects of climate change on the corals. We assess the statistical robustness of these experiments and what challenges the presented experiments. A comprehensive multi-study comparison is provided in order to inform on the present state of knowledge, and knowledge gaps, in understanding the effects of global climate change on cold-water corals. Finally we describe what the fate could be for the important scleractinian coral group in the Mediterranean region.

Continue reading ‘Fate of Mediterranean Scleractinian cold-water corals as a result of global climate change. A synthesis’

Paleobiological traits that determined Scleractinian coral survival and proliferation during the late Paleocene and early Eocene hyperthermals

Coral reefs are particularly sensitive to environmental disturbances, such as rapid shifts in temperature or carbonate saturation. Work on modern reefs has suggested that some corals will fare better than others in times of stress and that their life history traits might correlate with species survival. These same traits can be applied to fossil taxa to assess whether life history traits correspond with coral survival through past intervals of stress similar to future climate predictions. This study aims to identify whether ecological selection (based on physiology, behavior, habitat, etc.) plays a role in the long‐term survival of corals during the late Paleocene and early Eocene. The late Paleocene‐early Eocene interval is associated with multiple hyperthermal events that correspond to rises in atmospheric pCO2 and sea surface temperature, ocean acidification, and increases in weathering and turbidity. Coral reefs are rare during the late Paleocene and early Eocene, but despite the lack of reef habitat, corals do not experience an extinction at the generic level and there is little extinction at the species level. In fact, generic and species richness increases throughout the late Paleocene and early Eocene. We show that corals with certain traits (coloniality, carnivorous, or suspension feeding diet, hermaphroditic brooding reproduction, living in clastic settings) are more likely to survive climate change in the early Eocene. These findings have important implications for modern coral ecology and allow us to make more nuanced predictions about which taxa will have higher extinction risk in present‐day climate change.

Continue reading ‘Paleobiological traits that determined Scleractinian coral survival and proliferation during the late Paleocene and early Eocene hyperthermals’

Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,305,617 hits


Ocean acidification in the IPCC AR5 WG II

OUP book