Posts Tagged 'dissolution'

Ecological and physiological constraints of deep-sea corals in a changing environment

Deep-water or cold-water corals are abundant and highly diverse, greatly increase habitat heterogeneity and species richness, thereby forming one of the most significant ecosystems in the deep sea. Despite this remote location, they are not removed from the different anthropogenic disturbances that commonly impact their shallow-water counterparts. The global decrease in seawater pH due to increases in atmospheric CO2 are changing the chemical properties of the seawater, decreasing the concentration of carbonate ions that are important elements for different physiological and ecological processes. Predictive models forecast a shoaling of the carbonate saturation in the water column due to OA, and suggest that cold-water corals are at high risk, since large areas of suitable habitat will experience suboptimal conditions by the end of the century. The main objective of this study was to explore the fate of the deep-water coral community in time of environmental change. To better understand the impact of climate change this study focused in two of the most important elements of dee-sea coral habitat, the reef forming coral Lophelia pertusa and the octocoral community, particularly the gorgonian Callogorgia delta. By means of controlled experiments, I examined the effects of long and short-term exposures to seawater simulating future scenarios of ocean acidification on calcification and feeding efficiency. Finally In order to understand how the environment influences the community assembly, and ultimately how species cope with particular ecological filters, I integrated different aspects of biology such functional diversity and ecology into a more evolutionary context in the face of changing environment. My results suggest that I) deep-water corals responds negatively to future OA by lowering the calcification rates, II) not all individuals respond in the same way to OA with high intra-specific variability providing a potential for adaptation in the longterm III) there is a disruption in the balance between accretion and dissolution that in the long term can shift from net accretion to net dissolution, and IV) there is an evolutionary implication for certain morphological features in the coral community that can give an advantage under stresfull conditions. Nevertheless, the suboptimal conditions that deepwater corals will experience by the end of the century could potentially threaten their persistence, with potentially negative consequences for the future stability of this already fragile ecosystem.

Continue reading ‘Ecological and physiological constraints of deep-sea corals in a changing environment’

Evaluation of autonomously measured alkalinity, pH, and pCO2 variability on a coral reef

Currently, our understanding of alkalinity (AT) variability in highly dynamic
environments such as coral reefs is limited by the dearth of AT measurements. In order to better characterize these environments, high temporal resolution AT data are needed. This work employed the newly developed Submersible Autonomous Moored Instrument for Alkalinity (SAMI-alk), a fully autonomous in situ AT analyzer, to study seawater AT variability. The main goals of this research were to evaluate the utility of combining the SAMI-alk data with currently available in situ measurements of pH and partial pressure of carbon dioxide (pCO2) to characterize the inorganic carbon cycle, and to measure AT variability and determine what drives it on a coral reef. Autonomous AT and pH sensors (SAMI-alk and SAMI-pH) were deployed along with existing pCO2 (MAPCO2) and pH (SeaFET) sensors in Kanoehe Bay, HI from June 4 – 21, 2013. The results show that the pH – AT combination can provide important information about autonomously measured in situ data quality, and that it can be used to fully characterize the inorganic CO2 system in seawater. The SAMI-alk data were also used to examine AT variability and thereby calcification rates on coral reefs in Kaneohe Bay. AT varied by more than 100 µmol kg-1 on a diel basis due to CaCO3 production and dissolution. Dissolved inorganic carbon (DIC), calculated from the pH – AT sensor pair, varied by more than 200 µmol kg-1 , due primarily to biological metabolism on the reef. Reef calcification and metabolism dramatically alter the seawater chemistry from the open ocean source water and drive the large diel changes in all measured inorganic carbon parameters (i.e. aragonite saturation state (Ωarag), pH, pCO2, AT, DIC). This data set demonstrates the value of a high-quality in situ AT analyzer in a coral reef environment; making it possible to determine combined CO2 system variability with unprecedented temporal resolution. These data show that NEC can be consistently sustained (net CaCO3 production) until a threshold level of net respiration (NEP) is reached, around -50 (mmol m-2 h-1), which corresponds to an AT : DIC ratio of about 1:1.

Continue reading ‘Evaluation of autonomously measured alkalinity, pH, and pCO2 variability on a coral reef’

pH regulation and tissue coordination pathways promote calcium carbonate bioerosion by excavating sponges

Coral reefs are threatened by a multitude of environmental and biotic influences. Among these, excavating sponges raise particular concern since they bore into coral skeleton forming extensive cavities which lead to weakening and loss of reef structures. Sponge bioerosion is achieved by a combination of chemical dissolution and mechanical chip removal and ocean acidification has been shown to accelerate bioerosion rates. However, despite the ecological relevance of sponge bioerosion, the exact chemical conditions in which dissolution takes place and how chips are removed remain elusive. Using fluorescence microscopy, we show that intracellular pH is lower at etching sites compared to ambient seawater and the sponge’s tissue. This is realised through the extension of filopodia filled with low intracellular pH vesicles suggesting that protons are actively transported into this microenvironment to promote CaCO3 dissolution. Furthermore, fusiform myocyte-like cells forming reticulated pathways were localised at the interface between calcite and sponge. Such cells may be used by sponges to contract a conductive pathway to remove chips possibly instigated by excess Ca2+ at the boring site. The mechanism underlying CaCO3 dissolution by sponges provides new insight into how environmental conditions can enhance dissolution and improves predictions of future rates of coral dissolution due to sponge activity.

Continue reading ‘pH regulation and tissue coordination pathways promote calcium carbonate bioerosion by excavating sponges’

Carbonate dissolution by reef microbial borers: a biogeological process producing alkalinity under different pCO2 conditions

Rising atmospheric CO2 is acidifying the world’s oceans, affecting both calcification and dissolution processes in coral reefs. Among processes, carbonate dissolution by bioeroding microflora has been overlooked, and especially its impact on seawater alkalinity. To date, this biogeological process has only been studied using microscopy or buoyant weight techniques. To better understand its possible effect on seawater alkalinity, and thus on reef carbonate budget, an experiment was conducted under various seawater chemistry conditions (2 ≤ Ωarag ≤ 3.5 corresponding to 440 ≤ pCO2 (µatm) ≤ 940) at 25 °C under night and daylight (200 µmol photons m−2 s−1) with natural microboring communities colonizing dead coral blocks (New Caledonia). Both the alkalinity anomaly technique and microscopy methods were used to study the activity of those communities dominated by the chlorophyte Ostreobium sp. Results show that (1) the amount of alkalinity released in seawater by such communities is significant and varies between 12.8 ± 0.7 at ΩArag ~ 2 and 5.6 ± 0.4 mmol CaCO3 m−2 day−1 at ΩArag ~ 3–3.5 considering a 12:12 photoperiod; (2) although dissolution is higher at night (~ 80 vs. 20% during daylight), the process can occur under significant photosynthetic activity; and (3) the process is greatly stimulated when an acidity threshold is reached (pCO2 ≥ 920 µatm vs. current conditions at constant light intensity). We show that carbonate dissolution by microborers is a major biogeochemical process that could dissolve a large part of the carbonates deposited by calcifying organisms under ocean acidification.

Continue reading ‘Carbonate dissolution by reef microbial borers: a biogeological process producing alkalinity under different pCO2 conditions’

In-situ incubation of a coral patch for community-scale assessment of metabolic and chemical processes on a reef slope

Anthropogenic pressures threaten the health of coral reefs globally. Some of these pressures directly affect coral functioning, while others are indirect, for example by promoting the capacity of bioeroders to dissolve coral aragonite. To assess the coral reef status, it is necessary to validate community-scale measurements of metabolic and geochemical processes in the field, by determining fluxes from enclosed coral reef patches. Here, we investigate diurnal trends of carbonate chemistry, dissolved organic carbon, oxygen, and nutrients on a 20 m deep coral reef patch offshore from the island of Saba, Dutch Caribbean by means of tent incubations. The obtained trends are related to benthic carbon fluxes by quantifying net community calcification (NCC) and net community production (NCP). The relatively strong currents and swell-induced near-bottom surge at this location caused minor seawater exchange between the incubated reef and ambient water. Employing a compensating interpretive model, the exchange is used to our advantage as it maintains reasonably ventilated conditions, which conceivably prevents metabolic arrest during incubation periods of multiple hours. No diurnal trends in carbonate chemistry were detected and all net diurnal rates of production were strongly skewed towards respiration suggesting net heterotrophy in all incubations. The NCC inferred from our incubations ranges from −0.2 to 1.4 mmol CaCO3 m−2 h−1 (−0.2 to 1.2 kg CaCO3 m−2 year−1) and NCP varies from −9 to −21.7 mmol m−2 h−1 (net respiration). When comparing to the consensus-based ReefBudget approach, the estimated NCC rate for the incubated full planar area (0.36 kg CaCO3 m−2 year−1) was lower, but still within range of the different NCC inferred from our incubations. Field trials indicate that the tent-based incubation as presented here, coupled with an appropriate interpretive model, is an effective tool to investigate, in situ, the state of coral reef patches even when located in a relatively hydrodynamic environment.

Continue reading ‘In-situ incubation of a coral patch for community-scale assessment of metabolic and chemical processes on a reef slope’

Ocean acidification reduces hardness and stiffness of the Portuguese oyster shell with impaired microstructure: a hierarchical analysis

The rapidly intensifying process of ocean acidification (OA) due to anthropogenic CO2 is not only depleting carbonate ions necessary for calcification but also causing acidosis and disrupting internal pH homeostasis in several marine organisms. These negative consequences of OA on marine calcifiers, i.e. oyster species, have been very well documented in recent studies; however, the consequences of reduced or impaired calcification on the end-product, shells or skeletons, still remain one of the major research gaps. Shells produced by marine organisms under OA are expected to show signs of dissolution, disorganized microstructure and reduced mechanical properties. To bridge this knowledge gap and to test the above hypothesis, we investigated the effect of OA on juvenile shells of the commercially important oyster species, Magallana angulata, at ecologically and climatically relevant OA levels (using pH 8.1, 7.8, 7.5, 7.2). In lower pH conditions, a drop of shell hardness and stiffness was revealed by nanoindentation tests, while an evident porous internal microstructure was detected by scanning electron microscopy. Crystallographic orientation, on the other hand, showed no significant difference with decreasing pH using electron back-scattered diffraction (EBSD). These results indicate the porous internal microstructure may be the cause of the reduction in shell hardness and stiffness. The overall decrease of shell density observed from micro-computed tomography analysis indicates the porous internal microstructure may run through the shell, thus inevitably limiting the effectiveness of the shell’s defensive function. This study shows the potential deterioration of oyster shells induced by OA, especially in their early life stage. This knowledge is critical to estimate the survival and production of edible oysters in the future ocean.

Continue reading ‘Ocean acidification reduces hardness and stiffness of the Portuguese oyster shell with impaired microstructure: a hierarchical analysis’

Condition of pteropod shells near a volcanic CO2 vent region

Highlights

 • in situ shell dissolution and change in shell biomass were the predominant features observed in the live pteropods collected within and nearby CO2 vent regions.

• Low pteropod biomass shells (collected nearby the CO2 vents) were more fragile and therefore more prone to fracture than the more robust, high biomass shells (collected in the control stations).

• In the Gulf of Naples, intermittent shifts away from optimum Ωar values can significantly affect pteropod calcification despite waters remaining oversaturated.

Abstract

Natural gradients of pH in the ocean are useful analogues for studying the projected impacts of Ocean Acidification (OA) on marine ecosystems. Here we document the in situ impact of submarine CO2 volcanic emissions (CO2 vents) on live shelled-pteropods (planktonic gastropods) species Creseis conica in the Gulf of Naples (Tyrrhenian Sea, Mediterranean). Since the currents inside the Gulf will likely drive those pelagic calcifying organisms into and out of the CO2 vent zones, we assume that pteropods will be occasionally exposed to the vents during their life cycle. Shell degradation and biomass were investigated in the stations located within and nearby the CO2 vent emission in relation to the variability of sea water carbonate chemistry. A relative decrease in shell biomass (22%), increase in incidence of shell fractures (38%) and extent of dissolution were observed in Creseis conica collected in the Gulf of Naples compared to those from the Northern Tyrrhenian Sea (control stations). These results suggest that discontinuous but recurrent exposure to highly variable carbonate chemistry could consistently affect the characteristic of the pteropod shells.

Continue reading ‘Condition of pteropod shells near a volcanic CO2 vent region’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book