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Extinction selectivity among marine fishes during multistressor global change in the end-Permian and end-Triassic crises

Ancient mass extinction events such as the end-Permian and end-Triassic crises provide analogues for multistressor global change of ocean warming, pH reduction, and deoxygenation. Organism physiology is hypothesized to be a key trait influencing vulnerability to these stressors, but it is not certain how physiology predicts survival over evolutionary time scales and when organisms are faced with opposing or synergistic stressors. Fishes (bony fishes and chondrichthyan fishes) are active organisms with high aerobic scope for thermal tolerance and well-developed acid-base regulation, traits that should confer resilience to global change. To test this, we compiled a database of fossil marine fish occurrences to quantify extinction rates during background and mass extinctions from the Permian through Early Jurassic, using maximum likelihood estimation to compare extinction trajectories with marine invertebrates. Our results show that fewer chondrichthyan fishes underwent extinction than marine invertebrates during the end-Permian crisis. End-Triassic chondrichthyan extinction rates also were not elevated above background levels. In contrast, bony fishes underwent an end-Triassic extinction comparable to that of marine invertebrates. The differing responses of these two groups imply that a more active physiology can be advantageous during global change, although not uniformly. Permian–Triassic chondrichthyan fishes may have had broader environmental tolerances, facilitating survival. Alternatively, the larger offspring size of chondrichthyan fishes may provide greater energy reserves to offset the demands of warming and acidification. Although more active organisms have adult adaptations for thermal tolerance and pH regulation, some may nevertheless be susceptible to global change during early life stages.

Continue reading ‘Extinction selectivity among marine fishes during multistressor global change in the end-Permian and end-Triassic crises’

Environmental controls on the growth, photosynthetic and calcification rates of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi

We conducted a series of diagnostic fitness response experiments on the coccolithophore, Emiliania huxleyi, isolated from the Subtropical Convergence east of New Zealand. Dose response curves (i.e., physiological rate vs. environmental driver) were constructed for growth, photosynthetic, and calcification rates of E. huxleyi relative to each of five environmental drivers (nitrate concentration, phosphate concentration, irradiance, temperature, and pCO2). The relative importance of each environmental driver on E. huxleyi rate processes was then ranked using a semi-quantitative approach by comparing the percentage change caused by each environmental driver on the measured physiological metrics under the projected conditions for the year 2100, relative to those for the present day, in the Subtropical Convergence. The results reveal that the projected future decrease in nitrate concentration (33%) played the most important role in controlling the growth, photosynthetic and calcification rates of E. huxleyi, whereas raising pCO2 to 75 Pa (750 ppm) decreased the calcification : photosynthesis ratios to the greatest degree. These findings reveal that other environmental drivers may be equally or more influential than CO2 in regulating the physiological responses of E. huxleyi, and provide new diagnostic information to better understand how this ecologically important species will respond to the projected future changes to multiple environmental drivers.

Continue reading ‘Environmental controls on the growth, photosynthetic and calcification rates of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi’

Ecophysiological responses to elevated CO2 and temperature in Cystoseira tamariscifolia (Phaeophyceae)

Ocean acidification increases the amount of dissolved inorganic carbon (DIC) available in seawater which can benefit photosynthesis in those algae that are currently carbon limited, leading to shifts in the structure and function of seaweed communities. Recent studies have shown that ocean acidification-driven shifts in seaweed community dominance will depend on interactions with other factors such as light and nutrients. The study of interactive effects of ocean acidification and warming can help elucidate the likely effects of climate change on marine primary producers. In this study, we investigated the ecophysiological responses of Cystoseira tamariscifolia (Hudson) Papenfuss. This large brown macroalga plays an important structural role in coastal Mediterranean communities. Algae were collected from both oligotrophic and ultraoligotrophic waters in southern Spain. They were then incubated in tanks at ambient (ca. 400–500 ppm) and high CO2 (ca. 1200–1300 ppm), and at 20 °C (ambient temperature) and 24 °C (ambient temperature +4 °C). Increased CO2 levels benefited the algae from both origins. Biomass increased in elevated CO2 treatments and was similar in algae from both origins. The maximal electron transport rate (ETRmax), used to estimate photosynthetic capacity, increased in ambient temperature/high CO2 treatments. The highest polyphenol content and antioxidant activity were observed in ambient temperature/high CO2 conditions in algae from both origins; phenol content was higher in algae from ultraoligotrophic waters (1.5–3.0%) than that from oligotrophic waters (1.0–2.2%). Our study shows that ongoing ocean acidification can be expected to increase algal productivity (ETRmax), boost antioxidant activity (EC50), and increase production of photoprotective phenols. Cystoseira tamariscifolia collected from oligotrophic and ultraoligotrophic waters were able to benefit from increases in DIC at ambient temperatures. Warming, not acidification, may be the key stressor for this habitat as CO2 levels continue to rise.

Continue reading ‘Ecophysiological responses to elevated CO2 and temperature in Cystoseira tamariscifolia (Phaeophyceae)’

La révolte de l’océan (in French)

Chers Collègues, Chers Parents,

Puissent Splic et Sploc, deux gouttes d’eau attachantes et curieuses, amener les enfants à comprendre que l’excès de rejet de CO2 dans l’atmosphère perturbe l’équilibre de l’océan et de sa vie sous-marine, tel est l’objectif de ce récit.

Confrontés à des coraux qui perdent leurs couleurs, à des coquillages qui ont des problèmes de calcification, les enfants prendront conscience, à travers ce récit, qu’en luttant contre le réchauffement climatique, ils protègent aussi l’océan.

En plus ils découvriront que l’océan global est parcouru d’ un ” grand tapis roulant” (circulation thermohaline) et feront la connaissance des “anges de mer”, petites créatures étranges.

Puisque l’histoire commence et se termine dans les régions polaires, les enfants apprendront aussi la différence entre banquise de mer et calotte glaciaire.

Continue reading ‘La révolte de l’océan (in French)’

Did previous ocean acidification studies underestimate impacts on coastal species?

A new study with scientists from PML says that in order to better understand the impacts of Ocean Acidification (OA) on marine ecosystems, future studies should use more realistic scenarios in experiments.

Ocean acidification is the ongoing decrease in ocean pH caused by human CO2 emissions, such as the burning of fossil fuels. This alteration in basic ocean chemistry is likely to have wide implications for ocean life, especially for those organisms that require calcium carbonate to build shells or skeletons. Scientists have conducted many OA studies over the last 15 years, usually altering the pH (or CO2 concentration) of seawater to simulate future ocean conditions and thereby determine what the impacts on marine organisms might be.

However a study published today in Nature Ecology and Evolution, led by the Universidad de Concepción, Chile, now suggests that many previous OA experiments of this kind did not wholly take into account species’ own natural resilience to changes in their environment; particularly in the highly variable environment of coastal areas where pH/pCO2 levels fluctuate far more dramatically than in the open ocean.

Continue reading ‘Did previous ocean acidification studies underestimate impacts on coastal species?’

University professor advances research on ocean acidification

Wei-Jun Cai, a professor in the School of Marine Science and Policy, discovered his love for marine science when he was in middle school and watched an educational movie about how Mount Everest originated in the ocean. This opened his eyes and immediately attracted him to science. He described his career in marine science as “an accident,” but one he really loves.

Cai has been a professor at the university since 2013, after spending 18 years teaching at the University of Georgia, and was named the Mary A.S. Lighthipe Chair of Earth, Ocean and Environment in 2015. He has been conducting research on marine carbon cycling for 20 years.
His most recent published research is about how the Arctic Ocean has become more acidic in terms of its area and depth.

The paper was a collaborative effort with many other scientists and based off observations of subsurface carbon dioxide in the Arctic Ocean in 2010. They found the water in the Arctic Ocean became much more acidic in comparison to previously recorded observations.

Continue reading ‘University professor advances research on ocean acidification’

Nitrogen nutritional condition affects the response of energy metabolism in diatoms to elevated carbon dioxide

Marine phytoplankton are expected to benefit from enhanced carbon dioxide (CO2), attributable largely to down-regulation of the CO2 concentrating mechanism (CCM) which saves energy resources for other cellular processes. However, the nitrogen (N) nutritional condition (N-replete vs. N-limiting) of phytoplankton may affect the responses of their intracellular metabolic processes to elevated CO2. We cultured the model diatoms Thalassiosira pseudonana, Phaeodactylum tricornutum, and Thalassiosira weissflogii at ambient and elevated CO2 levels under N-replete and N-limiting conditions. Key metabolic processes, including light harvesting, C fixation, photorespiration, respiration, and N assimilation, were assessed systematically and then incorporated into an energy budget to compare the effects of CO2 on the metabolic pathways and the consequent changes in photosynthesis and C fixation as a result of energy reallocation under the different N nutritional conditions. Under the N-replete condition, down-regulation of the CCM at high CO2 was the primary contributor to increased photosynthesis rates of the diatoms. Under N-limiting conditions, elevated CO2 significantly affected the photosynthetic photon flux and respiration, in addition to CCM down-regulation and declines in photorespiration, resulting in an increase of the C:N ratio in all 3 diatom species. In T. pseudonana and T. weissflogii, the elevated C:N ratio was driven largely by an increased cellular C quota, whereas in P. tricornutum it resulted primarily from a decreased cellular N quota. The N-limited diatoms therefore could fix more C per unit of N in response to elevated CO2, which could potentially provide a negative feedback to the ongoing increase in atmospheric CO2.

Continue reading ‘Nitrogen nutritional condition affects the response of energy metabolism in diatoms to elevated carbon dioxide’


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Ocean acidification in the IPCC AR5 WG II

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