Archive for February, 2016

Applying organized scepticism to ocean acidification research

“Ocean acidification” (OA), a change in seawater chemistry driven by increased uptake of atmospheric CO2 by the oceans, has probably been the most-studied single topic in marine science in recent times. The majority of the literature on OA report negative effects of CO2 on organisms and conclude that OA will be detrimental to marine ecosystems. As is true across all of science, studies that report no effect of OA are typically more difficult to publish. Further, the mechanisms underlying the biological and ecological effects of OA have received little attention in most organismal groups, and some of the key mechanisms (e.g. calcification) are still incompletely understood. For these reasons, the ICES Journal of Marine Science solicited contributions to this special issue. In this introduction, I present a brief overview of the history of research on OA, call for a heightened level of organized (academic) scepticism to be applied to the body of work on OA, and briefly present the 44 contributions that appear in this theme issue. OA research has clearly matured, and is continuing to do so. We hope that our readership will find that, when taken together, the articles that appear herein do indeed move us “Towards a broader perspective on ocean acidification research”.

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How ocean acidification and warming could affect the culturing of pearls

“Interactive effects of seawater acidification and elevated temperature on the transcriptome and biomineralization in the pearl oyster Pinctada fucata”, Environmental Science & Technology

Pearls have adorned the necklines of women throughout history, but some evidence suggests that the gems’ future could be uncertain. Increasingly acidic seawater causes oyster shells to weaken, which doesn’t bode well for the pearls forming within. But, as scientists report in ACS’ journal Environmental Science & Technology, the mollusks might be more resilient to changing conditions than previously thought.

Pearl aquaculture is big business, particularly in Asia and Australia. But much of it takes place in oceans, which are susceptible to the increasing amounts of carbon dioxide human activity releases into the atmosphere. CO2 from the air gets absorbed by the oceans, which become more acidic as a result. Research has found that pearl oysters produce weaker shells under these conditions, and this could hurt their chances of survival. But in addition to acidity, rising water temperature could also play a role in oyster health. Rongqing Zhang, Liping Xie and colleagues wanted to see how combining acidity and water temperature would affect pearl oysters.

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Ocean acidification slowing coral reef growth, study confirms

First scientific study on a natural coral reef shows the effect of acidification caused by global warming, rather than common factors in reef decline

Coral reefs are having their growth stunted by ocean acidification caused by global warming, new research has confirmed.

For the first time, scientists conducted an experiment on a natural coral reef which involved altering sea water chemistry to mimic the effect of excess carbon dioxide in the atmosphere.

The results provide strong evidence that ocean acidification linked to greenhouse gas emissions is already slowing coral reef growth, the team claims.

Without “deep cuts” in greenhouse gas emissions, the world’s coral reefs may not survive into the next century, scientists say.

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Environmental drivers of the coral reef accretion-erosion balance in present and future ocean conditions

Worldwide, declines in coral cover and shifts in coral reef community composition have raised concerns about whether reef accretion will continue to exceed reef erosion. Reef persistence is influenced by global and local anthropogenic factors, such as ocean warming, acidification, eutrophication, and overfishing, as well as natural environmental variability. Predicting reef response to environmental stress requires an understanding of both natural and anthropogenic environmental drivers of reef accretion and erosion, and how these drivers interact at different spatiotemporal scales. In Chapters 2 and 3, I measured the variation in accretion, erosion, and net change rates along a natural gradient to determine the dominant environmental drivers of accretion-erosion rates at small spatial scales (tens of meters). In Chapter 4, I expanded the geographic range to 1000s of kilometers, measuring variation in accretion and erosion rates, as well as bioeroder community composition, across the Hawaiian Archipelago. In Chapter 5, I used a controlled mesocosm experiment to directly examine the effects of global anthropogenic drivers (i.e., temperature and ocean acidification) on the coral reef accretion-erosion balance. The results of my dissertation research highlight the significance of spatial scale in understanding reef dynamics and the differential responses of reef accretion and erosion to environmental drivers, which will change our predictions of net coral reef response to future environmental change. Further, my results suggest that increases in reef erosion, combined with expected decreases in calcification, could accelerate the shift of coral reefs to an erosion-dominated system in a high CO2 world.

Continue reading ‘Environmental drivers of the coral reef accretion-erosion balance in present and future ocean conditions’

Synergistic effect of elevated temperature, pCO2 and nutrients on marine biofilm

Natural marine biofilms provide signatures of the events that occur over a period of time and can be used as bioindicators of environmental changes. Hence, the effects of temperature (30 and 34 °C), pCO2 (400 and 1500 μatm) and nutrients (unenriched and enriched f/2 media) on the marine biofilm were evaluated using a 2 × 2 × 2 factorial design. In unenriched condition, acidification significantly increased the abundance of phytoperiphytes whereas reduced that of bacteria and it was vice versa in the enriched condition. Warming had significant negative effect on the abundance of both phytoperiphytes and bacteria, except in unenriched condition wherein it favoured bacterial growth. Synergistically, acidification and warming had deleterious effects resulting in further reduction in the abundance of both phytoperiphytes and bacteria, except in enriched condition wherein bacterial abundance increased. Such changes in biofilm communities in response to warming and acidification can have cascading effect on the subsequent build-up of macrofouling community.

Continue reading ‘Synergistic effect of elevated temperature, pCO2 and nutrients on marine biofilm’

Seawater acidification affects the physiological energetics and spawning capacity of the Manila clam Ruditapes philippinarum during gonadal maturation

Ocean acidification is predicted to have widespread implications for marine bivalve mollusks. While our understanding of its impact on their physiological and behavioral responses is increasing, little is known about their reproductive responses under future scenarios of anthropogenic climate change. In this study, we examined the physiological energetics of the Manila clam Ruditapes philippinarum exposed to CO2-induced seawater acidification during gonadal maturation. Three recirculating systems filled with 600 L of seawater were manipulated to three pH levels (8.0, 7.7, and 7.4) corresponding to control and projected pH levels for 2100 and 2300. In each system, temperature was gradually increased ca. 0.3 °C per day from 10 to 20 °C for 30 days and maintained at 20 °C for the following 40 days. Irrespective of seawater pH levels, clearance rate (CR), respiration rate (RR), ammonia excretion rate (ER), and scope for growth (SFG) increased after a 30-day stepwise warming protocol. When seawater pH was reduced, CR, ratio of oxygen to nitrogen, and SFG significantly decreased concurrently, whereas ammonia ER increased. RR was virtually unaffected under acidified conditions. Neither temperature nor acidification showed a significant effect on food absorption efficiency. Our findings indicate that energy is allocated away from reproduction under reduced seawater pH, potentially resulting in an impaired or suppressed reproductive function. This interpretation is based on the fact that spawning was induced in only 56% of the clams grown at pH 7.4. Seawater acidification can therefore potentially impair the physiological energetics and spawning capacity of R. philippinarum.

Continue reading ‘Seawater acidification affects the physiological energetics and spawning capacity of the Manila clam Ruditapes philippinarum during gonadal maturation’

Ocean acidification is already damaging coral reefs

A large proportion of the carbon dioxide dumped in the atmosphere by humans ends up in the oceans, and when this CO2 interacts with ocean water, it turns the ocean more acidic in a process known as ocean acidification. Even though this is one of the greatest environmental challenges facing our planet today, measuring its effects is extremely difficult because of the sheer volume of the ocean and the slow speed at which the process is happening. A common criticism of studies that attempt to do so is that most experiments are done in small tanks, and that conditions in these tanks might be vastly different from those in actual ocean habitats. Ideally, a study about the impacts of ocean acidification would need to measure variables like reef coral growth from 100 years ago and compare them with growth rates today. Scientists don’t have time machines, but we do have the next best thing: changing the pH of a natural reef to what it was 100 years ago.

To change the pH in a natural reef, scientists would have to pump a chemical like sodium hydroxide to the water “upstream” and wait for it to flow over the reef. This was exactly the strategy of a group led by Drs. Rebecca Albright and Ken Caldeira, scientists at Stanford University’s Carnegie Institution for Science. The researchers manipulated the chemistry of seawater flowing over a natural coral reef (not in an aquarium) and observed the coral’s response.

Continue reading ‘Ocean acidification is already damaging coral reefs’

Reversal of ocean acidification enhances coral reef calcification (video)

Rebecca Albright talks about Abright et al, “Reversal of ocean acidification enhances net coral reef calcification” in Nature 2016.

Carnegie Global Ecology, via Youtube, 24 February 2016. Video.

Coral reefs: Turning back time

An in situ experiment finds that reducing the acidity of the seawater surrounding a natural coral reef significantly increases reef calcification, suggesting that ocean acidification may already be slowing coral growth.

Continue reading ‘Coral reefs: Turning back time’

Reversal of ocean acidification enhances net coral reef calcification

Approximately one-quarter of the anthropogenic carbon dioxide released into the atmosphere each year is absorbed by the global oceans, causing measurable declines in surface ocean pH, carbonate ion concentration ([CO32−]), and saturation state of carbonate minerals (Ω)1. This process, referred to as ocean acidification, represents a major threat to marine ecosystems, in particular marine calcifiers such as oysters, crabs, and corals. Laboratory and field studies2, 3 have shown that calcification rates of many organisms decrease with declining pH, [CO32−], and Ω. Coral reefs are widely regarded as one of the most vulnerable marine ecosystems to ocean acidification, in part because the very architecture of the ecosystem is reliant on carbonate-secreting organisms4. Acidification-induced reductions in calcification are projected to shift coral reefs from a state of net accretion to one of net dissolution this century5. While retrospective studies show large-scale declines in coral, and community, calcification over recent decades, determining the contribution of ocean acidification to these changes is difficult, if not impossible, owing to the confounding effects of other environmental factors such as temperature. Here we quantify the net calcification response of a coral reef flat to alkalinity enrichment, and show that, when ocean chemistry is restored closer to pre-industrial conditions, net community calcification increases. In providing results from the first seawater chemistry manipulation experiment of a natural coral reef community, we provide evidence that net community calcification is depressed compared with values expected for pre-industrial conditions, indicating that ocean acidification may already be impairing coral reef growth.

Continue reading ‘Reversal of ocean acidification enhances net coral reef calcification’


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