Posts Tagged 'dissolution'

Natural ocean acidification at Papagayo upwelling system (north Pacific Costa Rica): implications for reef development

Numerous experiments have shown that ocean acidification impedes coral calcification, but knowledge about in situ reef ecosystem response to ocean acidification is still scarce. Bahía Culebra, situated at the northern Pacific coast of Costa Rica, is a location naturally exposed to acidic conditions due to the Papagayo seasonal upwelling. We measured pH and pCO2 in situ during two non-upwelling seasons (June 2012, May–June 2013), with a high temporal resolution of every 15 and 30 min, respectively, using two Submersible Autonomous Moored Instruments (SAMI-pH, SAMI-CO2). These results were compared with published data from the 2009 upwelling season. Findings revealed that the carbonate system in Bahía Culebra shows a high temporal variability. Incoming offshore waters drive intra- and interseasonal changes. Lowest pH (7.8) and highest pCO2 (658.3 µatm) values measured during a cold-water intrusion event in the non-upwelling season were similar to those minimum values reported from upwelling season (pH  =  7.8, pCO2  =  643.5 µatm), unveiling that natural acidification also occurs sporadically in the non-upwelling season. This affects the interaction of photosynthesis, respiration, calcification and carbonate dissolution and the resulting diel cycle of pH and pCO2 in the reefs of Bahía Culebra. During the non-upwelling season, the aragonite saturation state (Ωa) rises to values of  >  3.3 and during the upwelling season falls below 2.5. The Ωa threshold values for coral growth were derived from the correlation between measured Ωa and coral linear extension rates which were obtained from the literature and suggest that future ocean acidification will threaten the continued growth of reefs in Bahía Culebra. These data contribute to building a better understanding of the carbonate system dynamics and coral reefs’ key response (e.g., coral growth) to natural low-pH conditions, in upwelling areas in the eastern tropical Pacific and beyond. Continue reading ‘Natural ocean acidification at Papagayo upwelling system (north Pacific Costa Rica): implications for reef development’

Bivalves in the face of ocean acidification

Anthropogenic CO2 emissions are leading to a gradual decrease in ocean pH and changes in seawater carbonate chemistry, a process known as ocean acidification (OA). Such changes in oceanic environmental conditions will have negative consequences for marine life and organisms producing calcium carbonate (CaCO3) structures are amongst the most vulnerable due to the additional costs associated with calcification and maintenance of calcified structures under more acidic conditions. As calcifying animals of particular commercial and ecological relevance, bivalve molluscs have frequently been the object of OA research. In this thesis, responses to changes in seawater acidity in commercially important bivalve species were investigated with the aim of understanding their adaptation potential to OA. As the main focus was on blue mussels, the first part of the thesis provided an introduction to blue musselspecies complex in Europe which is characterized by the three species Mytilus edulis, M. galloprovincialis and M. trossulus. An analysis of potential consequences of interspecies hybridization for the aquaculture industry, especially in the context of changing environmental conditions, was provided. Possible positive and negative effects of hybridization were identified, the complexity of the blue mussel-species complex was highlighted and the implications of hybridization for adaptation were discussed. In the following section of the thesis, responses of Mytilus edulis larvae from a Swedish west coast population to elevated seawater acidity were investigated. By exposing larvae to a wide range of seawater acidity, the physiological tolerance threshold for normal shell development was identified and corresponded to pHT (pH on the total scale) ~ 7.8 which approximates the lower extremes of the local pH range naturally experienced by the larvae. This suggests that these mussels are well adapted to their local environment characterized by considerable fluctuations in seawater pH. Additionally, this result allowed selecting an appropriate pH level (pHT ~ 7.5, beyond the present range of natural variability), representing a realistic OA scenario for the investigated population and driving enough biological response to further investigate adaptation potential. This was achieved by measuring genetic variance and heritability of larval fitness-related traits (i.e. size and malformation of shell) through a crossbreeding experimental design and quantitative genetic techniques. Results showed high trait heritability under elevated seawater acidity, an indication of the potential of adapting to OA. Finally, in order to understand what functions and genes may be targeted by natural selection in the context of OA, genes involved in the initial phases of shell formation in Pacific oyster (Crassostrea gigas) larvae were identified. With a genome available, the Pacific oyster was an ideal candidate for this task. The identified genes were attributed to four categories (metabolic genes, transmembrane proteins, shell matrix proteins and protease inhibitors) and are candidates for genes under selection in the context of an acidifying ocean. Altogether the results of this thesis contribute to a better understanding of bivalve adaptation potential to global changes and provide critical information for future work (e.g. investigation of allelespecific associated tolerance to changes in environmental parameters).

Continue reading ‘Bivalves in the face of ocean acidification’

Decalcification and survival of benthic foraminifera under the combined impacts of varying pH and salinity

Highlights

  • Coastal ocean acidification did not enhance apparent test dissolution or affect survival in the short term of the benthic foraminifera species Ammonia sp. and Elphidium crispum.
  • Ωcalc <1 caused by low salinity decreases resistance to dissolution of the foraminifera.
  • The response of foraminifera to the combined impact of low pH and desalination was species-specific.
  • Living, decalcified juvenile specimens of Ammonia sp. were observed after one month at salinity 5.

Abstract

Coastal areas display natural large environmental variability such as frequent changes in salinity, pH, and carbonate chemistry. Anthropogenic impacts – especially ocean acidification – increase this variability, which may affect the living conditions of coastal species, particularly, calcifiers. We performed culture experiments on living benthic foraminifera to study the combined effects of lowered pH and salinity on the calcification abilities and survival of the coastal, calcitic species Ammonia sp. and Elphidium crispum. We found that in open ocean conditions (salinity ∼35) and lower pH than usual values for these species, the specimens displayed resistance to shell (test) dissolution for a longer time than in brackish conditions (salinity ∼5 to 20). However, the response was species specific as Ammonia sp. specimens survived longer than E. crispum specimens when placed in the same conditions of salinity and pH. Living, decalcified juveniles of Ammonia sp. were observed and we show that desalination is one cause for the decalcification. Finally, we highlight the ability of foraminifera to survive under Ωcalc < 1, and that high salinity and [Ca2+] as building blocks are crucial for the foraminiferal calcification process.

Continue reading ‘Decalcification and survival of benthic foraminifera under the combined impacts of varying pH and salinity’

Influence of acidification on carbonate sediments of Majuro Atoll, Marshall Islands

Influence of acidification on carbonate sediments in Majuro Atoll, Marshall Islands was studied by chemical and mineralogical methods coupled with synchrotron-based X-ray µ-CT. We found that the lowering of soil pH near the surface layer caused decrease of Mg concentration and increase of porosity of foraminifera (Calcarina spp.) due to the selective dissolution of magnesian calcite in Calcarina spp.test.

Continue reading ‘Influence of acidification on carbonate sediments of Majuro Atoll, Marshall Islands’

Cidaroids spines facing ocean acidification

When facing seawater undersaturated towards calcium carbonates, spines of classical sea urchins (euechinoids) show traces of corrosion although they are covered by an epidermis. Cidaroids (a sister clade of euechinoids) are provided with mature spines devoid of epidermis, which makes them, at first sight, more sensitive to dissolution when facing undersaturated seawater. A recent study showed that spines of a tropical cidaroid are resistant to dissolution due to the high density and the low magnesium concentration of the peculiar external spine layer, the cortex. The biofilm and epibionts covering the spines was also suggested to take part in the spine protection. Here, we investigate the protective role of these factors in different cidaroid species from a broad range of latitude, temperature and depth. The high density of the cortical layer and the cover of biofilm and epibionts were confirmed as key protection against dissolution. The low magnesium concentration of cidaroid spines compared to that of euechinoid ones makes them less soluble in general.

Continue reading ‘Cidaroids spines facing ocean acidification’

Bleaching and mortality of a photosymbiotic bioeroding sponge under future carbon dioxide emission scenarios

The bioeroding sponge Cliona orientalis is photosymbiotic with dinoflagellates of the genus Symbiodinium and is pervasive on the Great Barrier Reef. We investigated how C. orientalis responded to past and future ocean conditions in a simulated community setting. The experiment lasted over an Austral summer under four carbon dioxide emission scenarios: a pre-industrial scenario (PI), a present-day scenario (PD; control), and two future scenarios of combined ocean acidification and ocean warming, i.e., B1 (intermediate) and A1FI (extreme). The four scenarios also simulated natural variability of carbon dioxide partial pressure and temperature in seawater. Responses of C. orientalis generally remained similar between the PI and PD treatments. C. orientalis under B1 displayed a dramatic increase in lateral tissue extension, but bleached and displayed reduced rates of respiration and photosynthesis. Some B1 sponge replicates died by the end of the experiment. Under A1FI, strong bleaching and subsequent mortality of all C. orientalis replicates occurred at an early stage of the experiment. Mortality arrested bioerosion by C. orientalis under B1 and A1FI. Overall, the absolute amount of calcium carbonate eroded by C. orientalis under B1 or A1FI was similar to that under PI or PD at the end of the experiment. Although bioerosion rates were raised by short-term experimental acidification in previous studies, our findings from the photosymbiotic C. orientalis imply that the effects of bioerosion on reef carbonate budgets may only be temporary if the bioeroders cannot survive long-term in the future oceans.

Continue reading ‘Bleaching and mortality of a photosymbiotic bioeroding sponge under future carbon dioxide emission scenarios’

Bioerosion in a changing world: a conceptual framework

Bioerosion, the breakdown of hard substrata by organisms, is a fundamental and widespread ecological process that can alter habitat structure, biodiversity and biogeochemical cycling. Bioerosion occurs in all biomes of the world from the ocean floor to arid deserts, and involves a wide diversity of taxa and mechanisms with varying ecological effects. Many abiotic and biotic factors affect bioerosion by acting on the bioeroder, substratum, or both. Bioerosion also has socio‐economic impacts when objects of economic or cultural value such as coastal defences or monuments are damaged. We present a unifying definition and advance a conceptual framework for (a) examining the effects of bioerosion on natural systems and human infrastructure and (b) identifying and predicting the impacts of anthropogenic factors (e.g. climate change, eutrophication) on bioerosion. Bioerosion is responding to anthropogenic changes in multiple, complex ways with significant and wide‐ranging effects across systems. Emerging data further underscore the importance of bioerosion, and need for mitigating its impacts, especially at the dynamic land–sea boundary. Generalised predictions remain challenging, due to context‐dependent effects and nonlinear relationships that are poorly resolved. An integrative and interdisciplinary approach is needed to understand how future changes will alter bioerosion dynamics across biomes and taxa.

Continue reading ‘Bioerosion in a changing world: a conceptual framework’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book