Archive for January, 2018

The balance of marine bacteria in the Baltic Sea

Carina Bunse has written a thesis on marine bacteria and how they respond to the changes in their environment. Bacteria affect nutrient turnover in the Baltic Sea and with it the balance of the sea. As they are invisible, our knowledge of marine bacteria is still limited. By studying these microbes and their genes, we can learn more about how the ocean will behave in the future.

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Interactive network configuration maintains bacterioplankton community structure under elevated CO2 in a eutrophic coastal mesocosm experiment (update)

There is increasing concern about the effects of ocean acidification on marine biogeochemical and ecological processes and the organisms that drive them, including marine bacteria. Here, we examine the effects of elevated CO2 on the bacterioplankton community during a mesocosm experiment using an artificial phytoplankton community in subtropical, eutrophic coastal waters of Xiamen, southern China. Through sequencing the bacterial 16S rRNA gene V3-V4 region, we found that the bacterioplankton community in this high-nutrient coastal environment was relatively resilient to changes in seawater carbonate chemistry. Based on comparative ecological network analysis, we found that elevated CO2 hardly altered the network structure of high-abundance bacterioplankton taxa but appeared to reassemble the community network of low abundance taxa. This led to relatively high resilience of the whole bacterioplankton community to the elevated CO2 level and associated chemical changes. We also observed that the Flavobacteria group, which plays an important role in the microbial carbon pump, showed higher relative abundance under the elevated CO2 condition during the early stage of the phytoplankton bloom in the mesocosms. Our results provide new insights into how elevated CO2 may influence bacterioplankton community structure.

Continue reading ‘Interactive network configuration maintains bacterioplankton community structure under elevated CO2 in a eutrophic coastal mesocosm experiment (update)’

Environmental controls on the elemental composition of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi (update)

A series of semi-continuous incubation experiments were conducted with the coccolithophore Emiliania huxleyi strain NIWA1108 (Southern Ocean isolate) to examine the effects of five environmental drivers (nitrate and phosphate concentrations, irradiance, temperature, and partial pressure of CO2 (pCO2)) on both the physiological rates and elemental composition of the coccolithophore. Here, we report the alteration of the elemental composition of E. huxleyi in response to the changes in these environmental drivers. A series of dose–response curves for the cellular elemental composition of E. huxleyi were fitted for each of the five drivers across an environmentally representative gradient. The importance of each driver in regulating the elemental composition of E. huxleyi was ranked using a semi-quantitative approach. The percentage variations in elemental composition arising from the change in each driver between present-day and model-projected conditions for the year 2100 were calculated. Temperature was the most important driver controlling both cellular particulate organic and inorganic carbon content, whereas nutrient concentrations were the most important regulator of cellular particulate nitrogen and phosphorus of E. huxleyi. In contrast, elevated pCO2 had the greatest influence on cellular particulate inorganic carbon to organic carbon ratio, resulting in a decrease in the ratio. Our results indicate that the different environmental drivers play specific roles in regulating the elemental composition of E. huxleyi with wide-reaching implications for coccolithophore-related marine biogeochemical cycles, as a consequence of the regulation of E. huxleyi physiological processes.

Continue reading ‘Environmental controls on the elemental composition of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi (update)’

Unsteady seasons in the sea

Ocean uptake of CO2 slows the rate of anthropogenic climate change but comes at the cost of ocean acidification. Observations now show that the seasonal cycle of CO2 in the ocean also changes, leading to earlier occurrence of detrimental conditions for ocean biota.

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Strengthening seasonal marine CO2 variations due to increasing atmospheric CO2

The increase of atmospheric CO2 (ref. 1) has been predicted to impact the seasonal cycle of inorganic carbon in the global ocean2,3, yet the observational evidence to verify this prediction has been missing. Here, using an observation-based product of the oceanic partial pressure of CO2 (pCO2) covering the past 34 years, we find that the winter-to-summer difference of the pCO2 has increased on average by 2.2 ± 0.4 μatm per decade from 1982 to 2015 poleward of 10° latitude. This is largely in agreement with the trend expected from thermodynamic considerations. Most of the increase stems from the seasonality of the drivers acting on an increasing oceanic pCO2 caused by the uptake of anthropogenic CO2 from the atmosphere. In the high latitudes, the concurrent ocean-acidification-induced changes in the buffer capacity of the ocean enhance this effect. This strengthening of the seasonal winter-to-summer difference pushes the global ocean towards critical thresholds earlier, inducing stress to ocean ecosystems and fisheries4. Our study provides observational evidence for this strengthening seasonal difference in the oceanic carbon cycle on a global scale, illustrating the inevitable consequences of anthropogenic CO2 emissions.

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Scientists pinpoint how ocean acidification weakens coral skeletons

Scientists pinpoint how ocean acidification weakens coral skeletons

Woods Hole Oceanographic Institution scientists Anne Cohen (left) and Nathan Mollica extract core samples from a giant Porites coral in Risong Bay, Palau. They are co-authors of a new study in the Proceedings of the National Academy of Sciences showing how increasing ocean acidifcation will affect coral skeleton growth. Credit: Richard Brooks, Lightning Strike Media Productions, Palau

The rising acidity of the oceans threatens coral reefs by making it harder for corals to build their skeletons. A new study identifies the details of how ocean acidification affects coral skeletons, allowing scientists to predict more precisely where corals will be more vulnerable.

Corals grow their skeletons upward toward sunlight and also thicken them to reinforce them.

The new research, led by scientists at Woods Hole Oceanographic Institution (WHOI), shows that ocean acidification particularly impedes the thickening process—decreasing the skeletons’ density and leaving them more vulnerable to breaking. The study was published today in the Proceedings of the National Academy of Sciences.

Continue reading ‘Scientists pinpoint how ocean acidification weakens coral skeletons’

Ocean acidification affects coral growth by reducing skeletal density

Significance

Ocean acidification (OA) threatens coral reef futures by reducing the concentration of carbonate ions that corals need to construct their skeletons. However, quantitative predictions of reef futures under OA are confounded by mixed responses of corals to OA in experiments and field observations. We modeled the skeletal growth of a dominant reef-building coral, Porites, as a function of seawater chemistry and validated the model against observational data. We show that OA directly and negatively affects one component of the two-step growth process (density) but not the other (linear extension). Combining our growth model with Global Climate Model output, we show that skeletal density of Porites corals could decline by up to 20.3% over the 21st century solely due to OA.

Abstract

Ocean acidification (OA) is considered an important threat to coral reef ecosystems, because it reduces the availability of carbonate ions that reef-building corals need to produce their skeletons. However, while theory predicts that coral calcification rates decline as carbonate ion concentrations decrease, this prediction is not consistently borne out in laboratory manipulation experiments or in studies of corals inhabiting naturally low-pH reefs today. The skeletal growth of corals consists of two distinct processes: extension (upward growth) and densification (lateral thickening). Here, we show that skeletal density is directly sensitive to changes in seawater carbonate ion concentration and thus, to OA, whereas extension is not. We present a numerical model of Porites skeletal growth that links skeletal density with the external seawater environment via its influence on the chemistry of coral calcifying fluid. We validate the model using existing coral skeletal datasets from six Porites species collected across five reef sites and use this framework to project the impact of 21st century OA on Porites skeletal density across the global tropics. Our model predicts that OA alone will drive up to 20.3 ± 5.4% decline in the skeletal density of reef-building Porites corals.

Continue reading ‘Ocean acidification affects coral growth by reducing skeletal density’

Alaskans take to the seas to fight climate change

A new, high-tech traveler is catching a ride on Alaska’s largest passenger ferry. At the end of October, the Columbia, which can carry up to 500 travelers, set off on its two week, nearly 2,000-mile course from Bellingham, Washington to Skagway, Alaska. But for the first time, an onboard system is measuring temperature and levels of salt, oxygen, and carbon dioxide in the seawater every three minutes, giving scientists a detailed look at how climate change could impact the northern Pacific coast.

The main focus of this experiment, which researchers hope will run for at least five years, is ocean acidification. Scientists want to know where acidification is already happening and predict which areas will be at risk in the future. The project is the latest collaborative effort to understand whether ocean acidification, a by-product of climate change, could affect Alaska’s unique coastal ecosystems and, ultimately, its young aquaculture industry. Alaskan officials like Governor Bill Walker hope shellfish and kelp farming can be an area of future economic growth for the state, according to Samuel Rabung, aquaculture section chief at the Alaska Department of Fish and Game in the Division of Commercial Fisheries. But successful aquatic farming depends on healthy marine ecosystems.

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The lowly seagrass that could save your oysters from climate change

The impacts of climate change aren’t a distant threat for the Pacific shellfish industry. Acidifying seawater is already causing problems for oyster farms along the West Coast and it’s only expected to get worse.

That has one Bay Area oyster farm looking for ways to adapt by teaming up with scientists, who are studying how the local ecosystem could lend a helping hand.

Continue reading ‘The lowly seagrass that could save your oysters from climate change’

Growing seasonal extremes in ocean acidity

Scientists have proposed that marine organisms living in regions with large daily or seasonal swings in environmental conditions should more easily acclimate to slow changes over decades such as those caused by climate change. But that optimism might not hold if such short-term variability were also affected. Indeed, a new study published in the journal Nature Climate Change finds that if atmospheric CO2 continues to increase, the differences in extremes in surface-ocean acidity between summer and winter will roughly double by the end of the century.

Continue reading ‘Growing seasonal extremes in ocean acidity’


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