Posts Tagged 'calcification'

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’

Species-specific calcification response of Caribbean corals after 2-year transplantation to a low aragonite saturation submarine spring

Coral calcification is expected to decline as atmospheric carbon dioxide concentration increases. We assessed the potential of Porites astreoides, Siderastrea siderea and Porites porites to survive and calcify under acidified conditions in a 2-year field transplant experiment around low pH, low aragonite saturation (Ωarag) submarine springs. Slow-growing S. siderea had the highest post-transplantation survival and showed increases in concentrations of Symbiodiniaceae, chlorophyll a and protein at the low Ωarag site. Nubbins of P. astreoides had 20% lower survival and higher chlorophyll a concentration at the low Ωarag site. Only 33% of P. porites nubbins survived at low Ωarag and their linear extension and calcification rates were reduced. The density of skeletons deposited after transplantation at the low Ωarag spring was 15–30% lower for all species. These results suggest that corals with slow calcification rates and high Symbiodiniaceae, chlorophyll a and protein concentrations may be less susceptible to ocean acidification, albeit with reduced skeletal density. We postulate that corals in the springs are responding to greater energy demands for overcoming larger differences in carbonate chemistry between the calcifying medium and the external environment. The differential mortality, growth rates and physiological changes may impact future coral species assemblages and the reef framework robustness.

Continue reading ‘Species-specific calcification response of Caribbean corals after 2-year transplantation to a low aragonite saturation submarine spring’

Fifty years of sporadic coral reef calcification estimates at One Tree Island, Great Barrier Reef: is it enough to imply long term trends?

Estimates of coral reef ecosystem calcification (Gnet) and productivity (Pnet) provide insight into coral community health and functionality in response to short- and long-term stressors such as ocean warming and acidification. Here, we investigate spatial variability in calcification and organic production at One Tree Island (OTI) and compare our new observations to sporadic metabolic rates reported over the previous 50 years on the same reef flat. Gnet and Pnet estimates at the nearshore site were 50% and 166% lower than an offshore site with a shift in organic production from net productive to net respiratory. Contrary to expectations, calcification rates in 2017 (145.7 ± 20.2 mmol m-2 d-1) were comparable to the 1970s estimate (125.0 ± 12.5 mmol m-2 d-1) and 400% greater than similar observations in 2014. Our results indicate only weak associations between Gnet and aragonite (Ωar). A local increase in coral cover from 18% in 2014 to 31% in 2017 was the likely driver of increased calcification. A steeper TA–DIC slope in 2017 demonstrates a greater control of calcification on seawater carbonate chemistry than prior years. Overall, these results highlight the importance of site selection and replication when comparing metabolic datasets, and demonstrate major short-term variability in metabolic rates. The predictive capabilities of ecosystem metabolism studies may be constrained by using the available short-term datasets to represent long-term calcification trends.

Continue reading ‘Fifty years of sporadic coral reef calcification estimates at One Tree Island, Great Barrier Reef: is it enough to imply long term trends?’

Day length as a key factor moderating the response of coccolithophore growth to elevated pCO2

The fate of coccolithophores in the future oceans remains uncertain, in part due to key factors having not been standardized across experiments. A potentially moderating role for differences in day length (photoperiod) remains largely unexplored. We therefore cultured four different geographical isolates of the species Emiliania huxleyi, as well as two additional species, Gephyrocapsa oceanica (tropical) and Coccolithus braarudii(temperate), to test for interactive effects of pCO2 with the light : dark (L : D) cycle. We confirmed a general regulatory effect of photoperiod on the pCO2 response, whereby growth and particulate inorganic carbon and particulate organic carbon (PIC : POC) ratios were reduced with elevated pCO2 under 14 : 10 h L : D, but these reductions were dampened under continuous (24 h) light. The dynamics underpinning this pattern generally differed for the temperate vs. tropical isolates. Reductions in PIC : POC with elevated pCO2 for tropical taxa were largely through reduced calcification and enhanced photosynthesis under 14 : 10 h L : D, with differences dampened under continuous light. In contrast, reduced PIC : POC for temperate strains reflected increases of photosynthesis that outpaced increases in calcification rates under 14 : 10 h L : D, with both responses again dampened under continuous light. A multivariate analysis of 35 past studies of E. huxleyi further demonstrated that differences in photoperiod account for as much as 40% (strain B11/92) to 55% (strain NZEH) of the variance in reported pCO2‐induced reductions to growth but not PIC : POC. Our study thus highlights a critical role for day length in moderating the effect of ocean acidification on coccolithophore growth and consequently how this response may play out across latitudes and seasons in future oceans.

Continue reading ‘Day length as a key factor moderating the response of coccolithophore growth to elevated pCO2’

Resistance to ocean acidification in coral reef taxa is not gained by acclimatization

Ocean acidification (OA) is a major threat to coral reefs, which are built by calcareous species. However, long-term assessments of the impacts of OA are scarce, limiting the understanding of the capacity of corals and coralline algae to acclimatize to high partial pressure of carbon dioxide (pCO2) levels. Species-specific sensitivities to OA are influenced by its impacts on chemistry within the calcifying fluid (CF). Here, we investigate the capacity of multiple coral and calcifying macroalgal species to acclimatize to elevated pCO2 by determining their chemistry in the CF during a year-long experiment. We found no evidence of acclimatization to elevated pCO2 across any of the tested taxa. The effects of increasing seawater pCO2 on the CF chemistry were rapid and persisted until the end of the experiment. Our results show that acclimatization of the CF chemistry does not occur within one year, which confirms the threat of OA for future reef accretion and ecological function.

Continue reading ‘Resistance to ocean acidification in coral reef taxa is not gained by acclimatization’

Adaptive responses and local stressor mitigation drive coral resilience in warmer, more acidic oceans

Coral reefs have great biological and socioeconomic value, but are threatened by ocean acidification, climate change and local human impacts. The capacity for corals to adapt or acclimatize to novel environmental conditions is unknown but fundamental to projected reef futures. The coral reefs of Kāne‘ohe Bay, Hawai‘i were devastated by anthropogenic insults from the 1930s to 1970s. These reefs experience naturally reduced pH and elevated temperature relative to many other Hawaiian reefs which are not expected to face similar conditions for decades. Despite catastrophic loss in coral cover owing to human disturbance, these reefs recovered under low pH and high temperature within 20 years after sewage input was diverted. We compare the pH and temperature tolerances of three dominant Hawaiian coral species from within Kāne‘ohe Bay to conspecifics from a nearby control site and show that corals from Kāne‘ohe are far more resistant to acidification and warming. These results show that corals can have different pH and temperature tolerances among habitats and understanding the mechanisms by which coral cover rebounded within two decades under projected future ocean conditions will be critical to management. Together these results indicate that reducing human stressors offers hope for reef resilience and effective conservation over coming decades.

Continue reading ‘Adaptive responses and local stressor mitigation drive coral resilience in warmer, more acidic oceans’

Physiological responses of juvenile Chilean scallops (Argopecten purpuratus) to isolated and combined environmental drivers of coastal upwelling

Coastal biota is exposed to continuous environmental variability as a consequence of natural and anthropogenic processes. Responding to heterogeneous conditions requires the presence of physiological strategies to cope with the environment. Ecosystems influenced by upwelling endure naturally cold, acidic and hypoxic conditions, nevertheless they sustain major fisheries worldwide. This suggests that species inhabiting upwelling habitats possess physiological adaptations to handle high environmental variability. Here, we assessed the impact of the main upwelling drivers (temperature, pH and oxygen) in isolation and combined on eco-physiological responses of Chilean scallop Argopecten purpuratus. A. purpuratus responded to hypoxia by increasing their metabolic performance to maintain growth and calcification. Calcification was only affected by pH and increased under acidic conditions. Further, A. purpuratus juveniles prioritized calcification at the expense of growth under upwelling conditions. Increasing temperature had a significant impact by enhancing the physiological performance of A. purpuratus juveniles independently of oxygen and pH conditions, but this was associated with earlier and higher mortalities. Our results suggest that A. purpuratus is acclimated to short-term colder, acidic and hypoxic conditions, and provide important information of how this species responds to the heterogeneous environment of upwelling, which is significantly relevant in the climatic context of upwelling intensification.

Continue reading ‘Physiological responses of juvenile Chilean scallops (Argopecten purpuratus) to isolated and combined environmental drivers of coastal upwelling’


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Ocean acidification in the IPCC AR5 WG II

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