Posts Tagged 'South Pacific'

Effect of seawater temperature, pH, and nutrients on the distribution and character of low abundance shallow water benthic foraminifera in the Galápagos

In order to help predict the effects of anthropogenic stressors on shallow water carbonate environments, it is important to focus research on regions containing natural oceanographic gradients, particularly with respect to interactions between oceanography and ecologically sensitive carbonate producers. The Galápagos Archipelago, an island chain in the eastern equatorial Pacific, spans a natural nutrient, pH, and temperature gradient due to the interaction of several major ocean currents. Further, the region is heavily impacted by the El Niño—Southern Oscillation (ENSO) and the Galápagos exhibited widespread coral bleaching and degradation following the strong ENSO events of 1982–1983 and 1997–1998. These findings are coupled with reports of unusually low abundances of time-averaged benthic foraminiferal assemblages throughout the region. Foraminifera, shelled single-celled protists, are sensitive to environmental change and rapidly respond to alterations to their surrounding environment, making them ideal indicator species for the study of reef water quality and health. Here, statistical models and analyses were used to compare modern shallow water benthic foraminiferal assemblages from 19 samples spanning the Galápagos Archipelago to predominant oceanographic parameters at each collection site. Fisher α diversity indices, Ternary diagrams, Canonical Correspondence Analysis, regression tree analysis and FORAM-Index (FI; a single metric index for evaluating water quality associated with reef development) implied a combined impact from ENSO and upwelling from Equatorial Undercurrent (EUC) waters to primarily impact foraminiferal abundances and drive assemblage patterns throughout the archipelago. For instance, repeated ENSO temperature anomalies might be responsible for low foraminiferal density, while chronically high nutrients and low aragonite saturation and low pH—induced by EUC upwelling and La Niña anomalies—likely inhibited post-ENSO recovery, and caused foraminiferal assemblages to exhibit a heterotrophic dominance in the southern archipelago. What resulted are low FI values in the southern collection sites, indicating environments not conducive to endosymbiont development and/or recovery.

Continue reading ‘Effect of seawater temperature, pH, and nutrients on the distribution and character of low abundance shallow water benthic foraminifera in the Galápagos’

The effects of nutrient addition and ocean acidification on tropical crustose coralline algae

As the global population increases, the occurrence of multiple anthropogenic
impacts on valuable coastal ecosystems, such as coral reefs, also increases. These
stressors can be global and long-term, like ocean acidification (OA), or local and short term, like nutrient runoff in some areas. The combination of these stressors can  potentially have additive or interactive effects on the organisms in coral reef
communities. Among the most important groups of organisms on coral reefs are crustose coralline algae (CCA), calcifying algae that cement the reef together and contribute to the global carbon cycle. This thesis studied the effects of nutrient addition and OA on Lithophyllum kotschyanum, a common species of CCA on the fringing reefs of Mo’orea, French Polynesia. Two mesocosm experiments tested the individual and interactive effects of OA and short-term nitrate and phosphate addition on L. kotschyanum. These experiments showed that nitrate and phosphate addition together increased photosynthesis, OA had interactive effects with nutrient addition, and after nutrient addition ended, calcification and photosynthetic rates changed in unpredictable ways in different OA and nutrient treatments. Because the results of the first two experiments showed impacts of nutrients even after addition stopped, two more mesocosm experiments were conducted to study the changes in photosynthesis and calcification over hourly time scales more relevant to a single nutrient pulse event. These two experiments revealed the existence of diurnal variation in light-saturated photosynthetic rate, but not calcification rate, under ambient and elevated pCO2. This pattern of increased maximum photosynthesis in the middle of the day can have important implications for how the time of nutrient runoff events during the day impacts CCA physiology. Finally, a field experiment was conducted to determine the effects of short- and long-term nutrient addition on L. kotschyanum. The results showed that a series of short-term nutrient additions did not increase photosynthesis or calcification rates above those in ambient nutrient conditions, but continual nutrient enrichment for 6 weeks increased photosynthetic rates. This increase in photosynthesis under only long-term enrichment shows the need for consideration of specific nutrient addition scenarios on coral reefs when predicting how the community will be affected.

Continue reading ‘The effects of nutrient addition and ocean acidification on tropical crustose coralline algae’

A simple colorimetric method for determining seawater alkalinity using bromophenol blue

The development of small portable USB‐spectrophotometer systems makes monitoring alkalinity and pH possible in the field and remote locations. Here, we present a method utilizing purified bromophenol blue (BPB) as an end‐point indicator for making simple one‐point alkalinity measurements with spectrophotometric detection. The approach utilizes purified BPB dye whose absorbance characteristics have been determined over a range of temperatures and salinities. The end‐point pH for titrated samples was determined using the BPB absorbance ratio (R(t) = 25 A590/A436) for the acid and base forms via the following equation: urn:x-wiley:15415856:media:lom310253:lom310253-math-0001, where, e1 = 0.00533, e2 = 2.232, e3 = 0.0319. A pKa of 3.513 was determined for the dissociation of the second proton from the BPB dye. The temperature (t) dependence of R can be expressed using the following relationship: urn:x-wiley:15415856:media:lom310253:lom310253-math-0002. The dependence of the pKa on salinity (S) was weak and can be expressed as urn:x-wiley:15415856:media:lom310253:lom310253-math-0003. Application of the method for determining the alkalinity of in‐house and certified standards typically produced an uncertainty of ± 1.5 μmol kg−1 for purified BPB dye. When the impure BPB dye was used as an end‐point indicator the uncertainty for alkalinity measured was slightly higher at approximately ± 3–4 μmol kg−1. Hence, if high‐precision alkalinity measurements are not required (≥ 4 μmol kg−1) then utilization of the unpurified BPB maybe suitable. We also compared the use of BPB to two other dyes: bromocresol purple (BCP) and bromocresol green (BCG). The utilization of all three dyes for end‐point determination produced comparable results with an overall precision of ± 4 μmol kg−1. The one‐point titration method using BPB was utilized at a remote field location, One Tree Island, Australia and was found to be suitable for producing accurate and precise alkalinity data in a timely manner; ∼ 10–15 samples can be determined per hour. When combined with seawater pH measurements, the one‐point titration method allows the full marine carbonate system to be fully constrained without the need for high‐tech spectrophotometric equipment and comprehensive laboratory facilities.

Continue reading ‘A simple colorimetric method for determining seawater alkalinity using bromophenol blue’

Resistance of corals and coralline algae to ocean acidification: physiological control of calcification under natural pH variability

Ocean acidification is a threat to the continued accretion of coral reefs, though some undergo daily fluctuations in pH exceeding declines predicted by 2100. We test whether exposure to greater pH variability enhances resistance to ocean acidification for the coral Goniopora sp. and coralline alga Hydrolithon reinboldii from two sites: one with low pH variability (less than 0.15 units daily; Shell Island) and a site with high pH variability (up to 1.4 pH units daily; Tallon Island). We grew populations of both species for more than 100 days under a combination of differing pH variability (high/low) and means (ambient pH 8.05/ocean acidification pH 7.65). Calcification rates of Goniopora sp. were unaffected by the examined variables. Calcification rates of H. reinboldii were significantly faster in Tallon than in Shell Island individuals, and Tallon Island individuals calcified faster in the high variability pH 8.05 treatment compared with all others. Geochemical proxies for carbonate chemistry within the calcifying fluid (cf) of both species indicated that only mean seawater pH influenced pHcf. pH treatments had no effect on proxies for Ωcf. These limited responses to extreme pH treatments demonstrate that some calcifying taxa may be capable of maintaining constant rates of calcification under ocean acidification by actively modifying Ωcf.

Continue reading ‘Resistance of corals and coralline algae to ocean acidification: physiological control of calcification under natural pH variability’

Carbonate system distribution, anthropogenic carbon and acidification in the western tropical South Pacific (OUTPACE 2015 transect) (update)

The western tropical South Pacific was sampled along a longitudinal 4000km transect (OUTPACE cruise, 18 February, 3 April 2015) for the measurement of carbonate parameters (total alkalinity and total inorganic carbon) between the Melanesian Archipelago (MA) and the western part of the South Pacific gyre (WGY). This paper reports this new dataset and derived properties: pH on the total scale (pHT) and the CaCO3 saturation state with respect to aragonite (Ωara). We also estimate anthropogenic carbon (CANT) distribution in the water column using the TrOCA method (Tracer combining Oxygen, inorganic Carbon and total Alkalinity). Along the OUTPACE transect a deeper penetration of CANT in the intermediate waters was observed in the MA, whereas highest CANT concentrations were detected in the subsurface waters of the WGY. By combining our OUTPACE dataset with data available in GLODAPv2 (1974–2009), temporal changes in oceanic inorganic carbon were evaluated. An increase of 1.3 to 1.6µmolkg−1a−1 for total inorganic carbon in the upper thermocline waters is estimated, whereas CANT increases by 1.1 to 1.2µmolkg−1a−1. In the MA intermediate waters (27kgm−3 < σθ < 27.2kgm−3) an increase of 0.4µmolkg−1a−1 CANT is detected. Our results suggest a clear progression of ocean acidification in the western tropical South Pacific with a decrease in the oceanic pHT of up to −0.0027a−1 and a shoaling of the saturation depth for aragonite of up to 200m since the pre-industrial period.

Continue reading ‘Carbonate system distribution, anthropogenic carbon and acidification in the western tropical South Pacific (OUTPACE 2015 transect) (update)’

Coral responses to temperature, irradiance and acidification stress: linking physiology to satellite remote sensing

The success of the symbiosis of scleractinian corals with dinoflagellates of the genus Symbiodinium is highly dependent on the availability of sufficient, but not excess, light for photosynthesis. After decades of fundamental research into the effect of light on the coral-dinoflagellate symbiosis, an important practical application is emerging in remote monitoring of bleaching at coral reefs. Coral bleaching that originates with the dysfunction of photosynthesis can be either photoacclimatory, a controlled adjustment in response to environmental change, or it can be associated with photodamage, an uncontrolled response to environmental change. It is the latter that tends to lead to severe bleaching events that decrease the rate of carbon fixation, generate excessive oxygen radicals and may ultimately lead to coral death if unfavourable conditions persist. Current best practice methods for the prediction of coral bleaching use water temperature as detected via satellite, and predict the onset of coral bleaching accurately, but not the percent of corals bleached at a reef or the extent of the ensuing mortality.

Continue reading ‘Coral responses to temperature, irradiance and acidification stress: linking physiology to satellite remote sensing’

Variation in brachiopod microstructure and isotope geochemistry under low pH–ocean acidification–conditions

Throughout the last few decades and in the near future CO2–induced ocean acidification is potentially a big threat to marine calcite-shelled animals (e.g., brachiopods, bivalves, corals and gastropods). Despite the great number of studies focusing on the effects of acidification on shell growth, metabolism, shell dissolution and shell repair, the consequences on biomineral formation remain poorly understood, and only few studies addressed contemporarily the impact of acidification  on shell microstructure and geochemistry. In this study, a detailed microstructure and stable isotope geochemistry investigation was performed on nine adult brachiopod specimens of Magellania venosa (Dixon, 1789), grown in the natural environment as well as in controlled culturing experiments at different pH conditions (ranging 7.35 to 8.15 ± 0.05) over different time intervals (214 to 335 days). Details of shell microstructural features, such as thickness of the primary layer, density and size of endopunctae and morphology of the basic structural unit of the secondary layer were analysed using scanning electron microscopy (SEM). Stable isotope compositions (δ13C and δ18O) were tested from the secondary shell layer along shell ontogenetic increments in both dorsal and ventral valves. Based on our comprehensive dataset, we observed that, under low pH conditions, M. venosa produced a more organic–rich shell with higher density of and larger endopunctae, and smaller secondary layer fibres, when subjected to about one year of culturing. Also, increasingly negative δ13C and δ18O values are recorded by the shell produced during culturing and are related to the CO2–source in the culture setup. Both the microstructural changes and the stable isotope results are similar to observations on brachiopods from the fossil record and strongly support the value of brachiopods as robust archives of proxies for studying ocean acidification events in the geologic past.
Continue reading ‘Variation in brachiopod microstructure and isotope geochemistry under low pH–ocean acidification–conditions’

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Ocean acidification in the IPCC AR5 WG II

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