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Experimental techniques to assess coral physiology in situ under global and local stressors: current approaches and novel insights

Coral reefs are declining worldwide due to global changes in the marine environment. The increasing frequency of massive bleaching events in the tropics is highlighting the need to better understand the stages of coral physiological responses to extreme conditions. Moreover, like many other coastal regions, coral reef ecosystems are facing additional localized anthropogenic stressors such as nutrient loading, increased turbidity, and coastal development. Different strategies have been developed to measure the health status of a damaged reef, ranging from the resolution of individual polyps to the entire coral community, but techniques for measuring coral physiology in situ are not yet widely implemented. For instance, while there are many studies of the coral holobiont response in single or limited-number multiple stressor experiments, they provide only partial insights into metabolic performance under more complex and temporally and spatially variable natural conditions. Here, we discuss the current status of coral reefs and their global and local stressors in the context of experimental techniques that measure core processes in coral metabolism (respiration, photosynthesis, and biocalcification) in situ, and their role in indicating the health status of colonies and communities. We highlight the need to improve the capability of in situ studies in order to better understand the resilience and stress response of corals under multiple global and local scale stressors.

Continue reading ‘Experimental techniques to assess coral physiology in situ under global and local stressors: current approaches and novel insights’

Planktic foraminiferal and pteropod contributions to carbon dynamics in the Arctic Ocean (North Svalbard Margin)

Planktic foraminifera and shelled pteropods are some of the major producers of calcium carbonate (CaCO3) in the ocean. Their calcitic (foraminifera) and aragonitic (pteropods) shells are particularly sensitive to changes in the carbonate chemistry and play an important role for the inorganic and organic carbon pump of the ocean. Here, we have studied the abundance distribution of planktic foraminifera and pteropods (individuals m–3) and their contribution to the inorganic and organic carbon standing stocks (μg m–3) and export production (mg m–2 day–1) along a longitudinal transect north of Svalbard at 81° N, 22–32° E, in the Arctic Ocean. This transect, sampled in September 2018 consists of seven stations covering different oceanographic regimes, from the shelf to the slope and into the deep Nansen Basin. The sea surface temperature ranged between 1 and 5°C in the upper 300 m. Conditions were supersaturated with respect to CaCO3 (Ω > 1 for both calcite and aragonite). The abundance of planktic foraminifera ranged from 2.3 to 52.6 ind m–3 and pteropods from 0.1 to 21.3 ind m–3. The planktic foraminiferal population was composed mainly of the polar species Neogloboquadrina pachyderma (55.9%) and the subpolar species Turborotalita quinqueloba (21.7%), Neogloboquadrina incompta (13.5%) and Globigerina bulloides (5.2%). The pteropod population was dominated by the polar species Limacina helicina (99.6%). The rather high abundance of subpolar foraminiferal species is likely connected to the West Spitsbergen Current bringing warm Atlantic water to the study area. Pteropods dominated at the surface and subsurface. Below 100 m water depth, foraminifera predominated. Pteropods contribute 66–96% to the inorganic carbon standing stocks compared to 4–34% by the planktic foraminifera. The inorganic export production of planktic foraminifera and pteropods together exceeds their organic contribution by a factor of 3. The overall predominance of pteropods over foraminifera in this high Arctic region during the sampling period suggest that inorganic standing stocks and export production of biogenic carbonate would be reduced under the effects of ocean acidification.

Continue reading ‘Planktic foraminiferal and pteropod contributions to carbon dynamics in the Arctic Ocean (North Svalbard Margin)’

Impacts of seagrass on benthic microalgae and phytoplankton communities in an experimentally warmed coral reef mesocosm

The effects of seagrass on microalgal assemblages under experimentally elevated temperatures (28°C) and CO2 partial pressures (pCO2; 800 μatm) were examined using coral reef mesocosms. Concentrations of nitrate, ammonium, and benthic microalgal chlorophyll a (chl-a) were significantly higher in seagrass mesocosms, whereas phytoplankton chl-a concentrations were similar between seagrass and seagrass-free control mesocosms. In the seagrass group, fewer parasitic dinoflagellate OTUs (e.g., Syndiniales) were found in the benthic microalgal community though more symbiotic dinoflagellates (e.g., Cladocopium spp.) were quantified in the phytoplankton community. Our results suggest that, under ocean acidification conditions, the presence of seagrass nearby coral reefs may (1) enhance benthic primary productivity, (2) decrease parasitic dinoflagellate abundance, and (3) possibly increase the presence of symbiotic dinoflagellates.

Continue reading ‘Impacts of seagrass on benthic microalgae and phytoplankton communities in an experimentally warmed coral reef mesocosm’

A sea of change: Europe’s future in the Atlantic realm


However cold it may seem to some of us in a Scandinavian winter, northern Europe enjoys a relatively mild regional climate for our latitude, thanks to the massive amounts of heat brought up from the subtropics by circulation patterns in the North Atlantic Ocean. So it is no surprise that suggestions that this heat transport may weaken or ‘switch off’ attracts much media attention, with headlines that may refer to ‘tipping points’ or ‘collapse’ of the overturning circulation that brings warm surface waters all the way to the Arctic Circle. Studies of the ocean climate on long timescales have found these processes to have stopped or seriously reduced, generally following large freshwater discharges caused by rapid melting of glacial or multi-year ice in the Arctic. Were this to happen, there could be the paradox that global warming can lead to a colder climate for some of us!

With Greenland and Arctic ice melting at a rapid rate owing to the current rates of global warming, and the evidence from past climates, the future of the Atlantic conveyer has become an important topic for research programmes, and scientific papers are step-by-step improving our understanding of the underlying processes and current trends. The overturning circulation that includes the influx of waters from the subtropics to as far as the Arctic is reported to be weakening, but there is not yet a consensus on trends. At the same time, sea levels are rising and seawater acidification continues, placing additional stresses and uncertainties in safeguarding Europe’s seas and coasts and the resources and ecosystem services that they provide. Europe is also looking to the seas to provide new resources, particularly renewable energy but also a range of activities under the general label of the Blue Economy.

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Ocean acidification: the what, where, how, why and what next on this major ocean issue

In the last 200 years, the ocean has taken up around 30% of all CO2 emissions and this absorption has altered the production of calcium carbonate in oceanic waters, causing the phenomenon known as Ocean Acidification (OA). Our new web story provides a high-level look at all impacts of this problem, where it is happening, and what needs to happen next. 

Ocean Acidification digital web story home page



Mitigation alone is not enough

Mitigation actions by themselves are unable to avoid all consequences associated with OA. There is a need to plan for and implement adaptation measures to alleviate harm. Activities focused on strengthening resilience and enhancing adaptive capacity will provide the greatest opportunities for alleviating the impacts of OA that are not prevented by mitigation. These include the creation of Marine Protected Areas (MPAs) which can directly remediate OA via the preservation of marine vegetation, that, in turn, can buffer against changes in water chemistry. Adaptive capacity in fisheries can be greatly increased by protecting and enhancing fish stock abundance through the reduction of non-acidification related stressors, including overfishing.

The Ocean Acidification International Reference User Group

The web story also goes through the history of OA, including the work of the Ocean Acidification International Reference User Group, an expert group founded in 2005 and funded by the Prince Albert II Foundation. The Group has used the latest findings on ocean acidification to raise awareness of the need to address the issue through targeted policy interventions. 

Continue reading ‘Ocean acidification: the what, where, how, why and what next on this major ocean issue’

TAMU-CC researcher, students to study coral reefs in Hawaii

CORPUS CHRISTI – Changes in the chemistry of the ocean are devastating coral reefs around the world, diminishing their role as a safe haven for marine animals and as a protector of coastal areas from storms and erosion. To more fully understand what is happening to these critically important reefs, Texas A&M University-Corpus Christi Assistant Professor of Marine Biology Keisha Bahr is launching an extensive coral research project thanks to a substantial grant from the National Science Foundation.

Bahr is leading a $1 million NSF grant in collaboration with the University of Hawaii, which includes a unique partnership with the Texas State Aquarium. This grant also will provide an immersive, hands-on opportunity for TAMU-CC undergraduates to study coral reefs in Hawaii for the next three years.  

“The project will study how changes in the chemistry of our ocean impact calcifying organisms, particularly coral reefs,” Bahr said. This project combines the skills of ocean carbon chemists, coral physiologists, and marine technology developers to build a state-of-the-art system that merges new ocean chemistry sensing technologies with cutting-edge methods for studying coral reef health and underlying calcification processes, Bahr said. Most importantly, students will have the opportunity to interact with experts across these fields and be involved in interdisciplinary research.

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Otago takes lead on policy guidance for ocean acidification


Dr Christina McGraw from the Department of Chemistry with Professor Cliff Law, who holds a joint position with NIWA and the University of Otago.

A Policymaker’s Handbook for Addressing the Impacts of Ocean Acidification has recently been launched to help Commonwealth countries tackle the global issue of ocean acidification, a key aspect of climate change.

An initiative of the Commonwealth Blue Charter Action Group on Ocean Acidification, the handbook project was led by Dr Christina McGraw from the Department of Chemistry collaboratively with NIWA, including Professor Cliff Law and Dr Kim Currie, and Marine Science PhD student Jesse Vance.

Dr McGraw says New Zealand stepped forward to lead the Commonwealth’s Blue Charter Action Group on Ocean Acidification in recognition of the role the oceans place in our cultural, social and economic wellbeing.

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Female lobsters are getting smaller, but what about the next generation?

BAR HARBOR — As Maine’s waters are growing warmer and more acidic, lobster researchers are looking at how that’s affecting both the mothers and offspring of the state’s most prized crustacean.   

One thing is known for sure: Mature female lobsters have been shrinking.  

Over the past three years, Jesica Waller, a lobster scientist at the state’s Department of Marine Resources, has collected and analyzed more than 1,200 female lobsters along the coast. She has found that since the 1990s, mature females are getting smaller.  

“DMR research shows that the carapace/shell length at which most females reach maturity has decreased coastwide over the last 25-30 years,” she wrote in an email. “We sampled and analyzed females along Maine’s coast, and we found that the length at which most females reach maturity has decreased between 5.6 mm and 6.7 mm over this period (mid-1990s to today).”  

Continue reading ‘Female lobsters are getting smaller, but what about the next generation?’

Ocean acidification | California Academy of Sciences (text & video)

Join Academy presenter Aya to learn about ocean acidification: what it is; how it might impact coral reefs; and what we can do to help.

The California Academy of Sciences is a renowned scientific and educational institution dedicated to exploring, explaining, and sustaining life on Earth. Based in San Francisco’s Golden Gate Park, it’s the only place in the world to house an aquarium, planetarium, rainforest, and natural history museum—plus cutting-edge research programs—all under one living roof.

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Injecting an alkalinizing agent into the ocean to offset 10 years’ worth of acidification of the Great Barrier Reef

Great Barrier Reef Aerial View

New research has shown that by injecting an alkalinizing agent into the ocean along the length of the Great Barrier Reef, it would be possible, at the present rate of anthropogenic carbon emissions, to offset ten years’ worth of ocean acidification.

The research, by CSIRO Oceans and Atmosphere, Hobart, used a high-resolution model developed for the Great Barrier Reef region to study the impact of artificial ocean alkalinization on the acidity of the waters in the Great Barrier Reef. The study is based on the use of existing shipping infrastructure to inject a source of alkalinity into the ocean, which could also be considered as an acceleration of the chemical weathering of minerals through natural processes. Their results are published today (June 8, 2021) in the IOP Publishing journal Environmental Research Letters.

Continue reading ‘Injecting an alkalinizing agent into the ocean to offset 10 years’ worth of acidification of the Great Barrier Reef’

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Ocean acidification in the IPCC AR5 WG II

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