Posts Tagged 'South Pacific'

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’

Boron isotope systematics of cultured brachiopods: response to acidification, vital effects and implications for palaeo-pH reconstruction

CO2-induced ocean acidification and associated decrease of seawater carbonate saturation state contributed to multiple environmental crises in Earth’s history, and currently poses a major threat for marine calcifying organisms. Owing to their high abundance and good preservation in the Phanerozoic geological record, brachiopods present an advantageous taxon of marine calcifiers for palaeo-proxy applications as well as studies on biological mechanism to cope with environmental change. To investigate the geochemical and physiological responses of brachiopods to prolonged low-pH conditions we cultured Magellania venosa, Terebratella dorsata and Pajaudina atlantica under controlled experimental settings over a period of more than two years. Our experiments demonstrate that brachiopods form their calcite shells under strong biological control, which enables them to survive and grow under low-pH conditions and even in seawater strongly undersaturated with respect to calcite (pH = 7.35, Ωcal = 0.6). Using boron isotope (δ11B) systematics including MC-ICP-MS as well as SIMS analyses, validated against in vivo microelectrode measurements, we show that this resilience is achieved by strict regulation of the calcifying fluid pH between the epithelial mantle and the shell. We provide a culture-based δ11B−pH calibration, which as a result of the internal pH regulatory mechanisms deviates from the inorganic borate ion to pH relationship, but confirms a clear yet subtle pH dependency for brachiopods. At a micro-scale level, the incorporation of 11B appears to be principally driven by a physiological gradient across the shell, where the δ11B values of the innermost calcite record the internal calcifying fluid pH while the composition of the outermost layers is also influenced by seawater pH. These findings are of consequence to studies on biomineralisation processes, physiological adaptations as well as past climate reconstructions.

Continue reading ‘Boron isotope systematics of cultured brachiopods: response to acidification, vital effects and implications for palaeo-pH reconstruction’

Ecosystem calcification and production in two Great Barrier Reef coral reefs: methodological challenges and environmental drivers

This thesis investigates the drivers of coral reef ecosystem metabolism and the abilities of the different methodologies and analytical approaches to accurately represent reef dynamics. It encompassed tracing natural nutrient additions through bird guano into a coral cay. Developing a new, automated system for measuring carbonate chemistry for coral reef metabolism and the effects of mass coral bleaching on ecosystem functioning were quantified. Overall, it showed that natural nutrient additions and bleaching differentially affect coral reef metabolism and that subtle differences in analytical methods, sampling approaches, and data interpretation techniques can cause significant variation in metabolic estimates.

Continue reading ‘Ecosystem calcification and production in two Great Barrier Reef coral reefs: methodological challenges and environmental drivers’

Carbon outwelling and emissions from two contrasting mangrove creeks during the monsoon storm season in Palau, Micronesia

Mangroves sequester large amounts of carbon in soils but limited information is available on carbon losses from tropical mangrove systems. Here we quantify carbon outwelling, CO2 emissions and pore-water exchange rates from two nearby (∼2 km apart) tropical mangrove creeks located in different geomorphic settings on the island of Palau, Micronesia during the monsoonal storm season. On average, POC and pCO2 were >100% higher and DOC, DIC and TA were 62%, 25%, 16% higher, respectively, from Creek 1 (located within a semi-enclosed bay) than from Creek 2 (located along the coast adjacent to fringing reefs). Both creeks were net exporters of DIC, DOC, POC and emitters of CO2. However, outwelling rates of POC, DIC and DOC and CO2 emissions were 27-fold, 8-fold, 4-fold and 3-fold higher at Creek 1. DIC outwelling (37%) and CO2 emissions (39%) were the major terms contributing to total carbon losses at Creek 1, whilst CO2 emission (61%) was the major contributor at Creek 2. Monsoon storms appeared to explain the organic carbon dynamics whilst tidal pumping appears to drive the inorganic carbon dynamics at both creeks. Our data demonstrates the considerable heterogeneity of mangroves creeks that are in close proximity and subject to similar weather conditions but in differing geomorphological settings.

Continue reading ‘Carbon outwelling and emissions from two contrasting mangrove creeks during the monsoon storm season in Palau, Micronesia’

Elevated CO2 leads to enhanced photosynthesis but decreased growth in early life stages of reef building coralline algae

Crustose coralline algae (CCA) are key organisms in coral reef ecosystems, where they contribute to reef building and substrate stabilization. While ocean acidification due to increasing CO2 can affect the biology, physiology and ecology of fully developed CCA, the impacts of elevated CO2 on the early life stages of CCA are much less explored. We assessed the photosynthetic activity and growth of 10-day-old recruits of the reef-building crustose coralline alga Porolithon cf. onkodes exposed to ambient and enhanced CO2 seawater concentration causing a downward shift in pH of ∼0.3 units. Growth of the CCA was estimated using measurements of crust thickness and marginal expansion, while photosynthetic activity was studied with O2 microsensors. We found that elevated seawater CO2 enhanced gross photosynthesis and respiration, but significantly reduced vertical and marginal growth of the early life stages of P. cf. onkodes. Elevated CO2 stimulated photosynthesis, particularly at high irradiance, likely due to increased availability of CO2, but this increase did not translate into increased algal growth as expected, suggesting a decoupling of these two processes under ocean acidification scenarios. This study confirms the sensitivity of early stages of CCA to elevated CO2 and identifies complexities in the physiological processes underlying the decreased growth and abundance in these important coral reef builders upon ocean acidification.

Continue reading ‘Elevated CO2 leads to enhanced photosynthesis but decreased growth in early life stages of reef building coralline algae’

Phenotypic plasticity at the edge: contrasting population‐level responses at the overlap of the leading and rear edges of the geographical distribution of two Scurria limpets

Aim
To examine the role of ocean temperature and chemistry as drivers of interpopulation differences in multiple phenotypic traits between rear and leading edge populations of two species of limpet.

Location
The coast of north‐central Chile, western South America.

Taxon
Mollusca, Gastropoda (Lottidae).

Methods
We used field and laboratory experiments to study the ecology and physiology of individuals from populations located at the overlap of the rear and leading edges of their respective geographical distributions. At the same time, we characterized local environmental regimes, measuring seawater physical and chemical properties.

Results
Towards the edge of their range, individuals from the leading edge species gradually reduced their shell length, metabolic rate and thermal response capacity, and increased carbonate content in their shells. Individuals of the rear edge species showed dissimilar responses between sites. Contrasting behavioural responses to experimental heating reconciled observations of an unintuitive higher maximal critical temperature and a smaller thermal safety margin for individuals of the rear edge populations. Physical–chemical characterization of seawater properties at the site located on the core of the upwelling centre showed extreme environmental conditions, with low oxygen concentration, high pCO2 and the episodic presence of corrosive seawater. These challenging environmental conditions were reflected in reduced growth for both species.

Main conclusions
We found different spatial patterns of phenotypic plasticity in two sister species around the leading and trailing edges of their distributions. Our results provide evidence that environmental conditions around large upwelling centres can maintain biogeographical breaks through metabolic constraints on the performance of calcifying organisms. Thus, local changes in seawater chemistry associated with coastal upwelling circulation emerge as a previously overlooked driver of marine range edges.

Continue reading ‘Phenotypic plasticity at the edge: contrasting population‐level responses at the overlap of the leading and rear edges of the geographical distribution of two Scurria limpets’

Obligate ectosymbionts increase the physiological resilience of a scleractinian coral to high temperature and elevated pCO2

Invertebrate ectosymbionts within the coralla of scleractinians enhance host fitness through protection from corallivores and nutrient addition. Here, we explore the ectosymbiotic relationship between the coral Pocillopora verrucosa and the crab Trapezia serenei and the shrimp Alpheus spp., to test for effects on coral calcification under contrasts of seawater temperature (27.7 °C and 29.9 °C) and pH (ambient, 8.0 and reduced, 7.7). Regardless of temperature, ectosymbionts depressed calcification by 55% (vs without ectosymbionts) at ambient pH; however, ectosymbionts only depressed calcification under ambient pH but not at reduced pH. These results suggest that P. verrucosa grows fastest at ambient pH without ectosymbionts, but when ectosymbionts are present, colonies are protected from further declines in calcification at reduced pH. This implies that there may be a change from a currently parasitic ectosymbiont–coral relationship to a commensal relationship that could increase fitness advantages for corals hosting crustacean ectosymbionts under ocean acidification conditions.

Continue reading ‘Obligate ectosymbionts increase the physiological resilience of a scleractinian coral to high temperature and elevated pCO2’


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Ocean acidification in the IPCC AR5 WG II

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