Archive for May, 2011

Effects of fishing and acidification-related benthic mortality on the southeast Australian marine ecosystem

Oceanic uptake of anthropogenic carbon dioxide (CO2) is altering the carbonate chemistry of seawater, with potentially negative consequences for many calcifying marine organisms. At the same time, increasing fisheries exploitation is impacting on marine ecosystems. Here, using increased benthic-invertebrate mortality as a proxy for effects of ocean acidification, the potential impact of the two stressors of fishing and acidification on the southeast Australian marine ecosystem to year 2050 was explored. The individual and interaction effects of the two stressors on biomass and diversity were examined for the entire ecosystem and for regional assemblages. For 61 functional groups or species, the cumulative effects of moderate ocean acidification and fishing were additive (30%), synergistic (33%), and antagonistic (37%). Strong ocean acidification resulted in additive (22%), synergistic (40%), and antagonistic (38%) effects. The greatest impact was on the demersal food web, with fishing impacting predation and acidification affecting benthic production. Areas that have been subject to intensive fishing were the most susceptible to acidification effect, although fishing also mitigated some of the decline in biodiversity observed with moderate acidification. The model suggested that ocean acidification and long-term fisheries exploitation could act synergistically with the increasing sensitivity to change from long-term (decades) fisheries exploitation potentially causing unexpected restructuring of the pelagic and demersal food webs. Major regime shifts occur around year 2040. Greater focus is needed on how differential fisheries exploitation of marine resources may exacerbate or accelerate effects of environmental changes such as ocean acidification.
Continue reading ‘Effects of fishing and acidification-related benthic mortality on the southeast Australian marine ecosystem’

Skeletal alterations and polymorphism in a Mediterranean bryozoan at natural CO2 vents

Colonies of the cheilostome bryozoan Schizoporella errata were grown at a site near Ischia Island (Tyrrhenian Sea, Italy) where volcanogenic CO2 emissions lower seawater pH to 7.76, simulating levels of ocean acidification predicted for the end of the present century. Compared with colonies from a control site (mean pH = 8.09), putative defensive polymorphs (avicularia) were significantly fewer, and retarded growth of zooidal basal and lateral walls was evident at the low pH site. The lower proportion of avicularia suggests a switch in resource allocation away from defence to favouring rapid growth. In addition, corrosion of the skeleton was observed in both new and old zooids at the low pH site, and feeding zooids were slightly smaller but had larger orifices for the protrusion of feeding lophophores. These findings corroborate previous studies demonstrating potential dissolution of carbonate skeletons in low pH seawater, while providing new insight into the possible ability of colonial species to respond to ocean acidification by adjusting resource allocation between zooids of different types.
Continue reading ‘Skeletal alterations and polymorphism in a Mediterranean bryozoan at natural CO2 vents’

Live tissue imaging shows reef corals elevate pH under their calcifying tissue relative to seawater

The threat posed to coral reefs by changes in seawater pH and carbonate chemistry (ocean acidification) raises the need for a better mechanistic understanding of physiological processes linked to coral calcification. Current models of coral calcification argue that corals elevate extracellular pH under their calcifying tissue relative to seawater to promote skeleton formation, but pH measurements taken from the calcifying tissue of living, intact corals have not been achieved to date. We performed live tissue imaging of the reef coral Stylophora pistillata to determine extracellular pH under the calcifying tissue and intracellular pH in calicoblastic cells. We worked with actively calcifying corals under flowing seawater and show that extracellular pH (pHe) under the calicoblastic epithelium is elevated by ~0.5 and ~0.2 pH units relative to the surrounding seawater in light and dark conditions respectively. By contrast, the intracellular pH (pHi) of the calicoblastic epithelium remains stable in the light and dark. Estimates of aragonite saturation states derived from our data indicate the elevation in subcalicoblastic pHe favour calcification and may thus be a critical step in the calcification process. However, the observed close association of the calicoblastic epithelium with the underlying crystals suggests that the calicoblastic cells influence the growth of the coral skeleton by other processes in addition to pHe modification. The procedure used in the current study provides a novel, tangible approach for future investigations into these processes and the impact of environmental change on the cellular mechanisms underpinning coral calcification.
Continue reading ‘Live tissue imaging shows reef corals elevate pH under their calcifying tissue relative to seawater’

Physiological and ecological responses of crustaceans to ocean acidification

The sensitivity of marine crustaceans to ocean acidification is poorly understood, but can be assessed by combining data from physiological and ecological studies. The species most at risk are exclusively marine and have limited physiological capacities to adjust to environmental change. They are poor iono- and osmoregulators and have limited abilities to compensate for acid–base disturbances. The problems are compounded in slow-moving, relatively inactive species because they have low circulating protein levels and low buffering capacities. Species living in low-energy environments, such as deep-sea and polar habitats, are particularly vulnerable, because they are metabolically limited with respect to environmental change. Elevated pCO2 levels in seawater, such as those predicted for the year 2300, are known to have diverse effects on calcification rate, little effect on egg production and a negative effect on growth rate and moulting frequency in marine crustacean species. At these levels, embryonic development is negatively impacted, but larval and juvenile stages do not appear to be affected, unless the changes in pCO2 are accompanied by rising temperatures. Overall, marine crustaceans are broadly tolerant to the seawater pCO2 levels expected by 2100 and 2300, but only in the medium-term (weeks) and only in the more adaptable species. The reductions in growth rate are of concern, as these changes could affect species survival, distribution and abundance. Studies are urgently needed to evaluate whether the patterns of vulnerability identified here in crustaceans will still be relevant after long-term (months) exposure to the relevant pCO2 levels, in combination with changes in other environmental factors.
Continue reading ‘Physiological and ecological responses of crustaceans to ocean acidification’

Winners and losers in ocean acidification

A natural experiment in tropical waters off Papua New Guinea suggests that with increasing CO2 emissions and ocean acidification some marine organisms will benefit, but many more will lose out.

Climate scientist, Dr Janice Lough of the Australian Institute of Marine Sciences in Townsville and colleagues report their findings today in the journal Nature Climate Change.

“Even aside from thermal stress and bleaching we’re going to get progressive acidification of the oceans and this study demonstrates that is not good for maintaining healthy coral reef ecosystems,” says Lough.

“Although there are a few winners as you get higher CO2 there are many more losers.”

Increasing atmospheric CO2 levels lead to an increase in ocean acidity as the ocean absorbs some of this CO2.

“About a third of the extra CO2 that we’ve put into the atmosphere has been absorbed by the oceans and that changes the ocean chemistry,” says Lough.

Continue reading ‘Winners and losers in ocean acidification’

Bubbling sea signals severe coral damage this century

Findings from a “natural laboratory” in seas off Papua New Guinea suggest that acidifying oceans will severely hit coral reefs by the end of the century.

Carbon dioxide bubbles into the water from the slopes of a dormant volcano here, making it slightly more acidic.

Coral is badly affected, not growing at all in the most CO2-rich zone.

Writing in journal Nature Climate Change, the scientists say this “lab” mimics conditions that will be widespread if CO2 emissions continue.

The oceans absorb some of the carbon dioxide that human activities are putting into the atmosphere.

This is turning seawater around the world slightly more acidic – or slightly less alkaline.

This reduces the capacity of corals and other marine animals to form hard structures such as shells.

Projections of rising greenhouse gas emissions suggest the process will go further, and accelerate.

“This is the most realistic experiment done to date on this issue,” said Chris Langdon, a coral specialist from the Rosenstiel School of Marine and Atmospheric Science in Miami, US.

“So I don’t have any qualms about believing that what we found will apply in other parts of the world.”

Continue reading ‘Bubbling sea signals severe coral damage this century’

Coral reefs on edge of extinction

Coral reefs around the world could be teetering on the brink of extinction by the end of the century as the oceans become more acidic, scientists have warned.

New evidence from volcanic seeps – fissures in the ocean floor that leak gases and minerals – suggests a bleak future for the reefs that harbour the world’s richest marine ecosystems.

Three natural carbon dioxide (CO2) seeps in Papua New Guinea have given scientists a snapshot of how coral reefs may look in 100 years.

Like man-made sources of carbon dioxide, the seeps are making the water around them more acidic.

The study showed reductions in reef diversity and complexity as pH values fell from 8.1 to 7.8, indicating greater acidity.

At values below 7.7, reef development ceased altogether.

Climate change experts estimate that by the end of the century, ocean acidity worldwide will change in a similar way because of CO2 emissions.

The latest Intergovernmental Panel on Climate Change (IPCC) forecast predicts that rising concentrations of CO2 will reduce worldwide ocean pH from its present level of 8.1 to 7.8.

Authors of the new research, writing in the journal Nature, said the effect of a pH drop below 7.8 would be ”catastrophic” for the coral.
Continue reading ‘Coral reefs on edge of extinction’

Ocean acidification leaves clownfish deaf to predators

Baby clownfish use hearing to detect and avoid predator-rich coral reefs during the daytime, but new research from the University of Bristol demonstrates that ocean acidification could threaten this crucial behaviour within the next few decades.

Since the Industrial Revolution, over half of all the CO2 produced by burning fossil fuels has been absorbed by the ocean, making pH drop faster than any time in the last 650,000 years and resulting in ocean acidification. Recent studies have shown that this causes fish to lose their sense of smell, but a new study published today in Biology Letters shows that fish hearing is also compromised.

Working with Professor Philip Munday at James Cook University, lead author Dr Steve Simpson of the School of Biological Sciences at the University of Bristol reared larvae straight from hatching in different CO2 environments.

“We kept some of the baby clownfish in today’s conditions, bubbling in air, and then had three other treatments where we added extra CO2 based on the predictions from the Intergovernmental Panel on Climate Change for 2050 and 2100,” Dr Simpson said.

After 17-20 days rearing, Dr Simpson monitored the response of his juvenile clownfish to the sounds of a predator-rich coral reef, consisting of noises produced by crustaceans and fish.

“We designed a totally new kind of experimental choice chamber that allowed us to play reef noise through an underwater speaker to fish in the lab, and watch how they responded,” Dr Simpson continued. “Fish reared in today’s conditions swam away from the predator noise, but those reared in the CO2 conditions of 2050 and 2100 showed no response.”
Continue reading ‘Ocean acidification leaves clownfish deaf to predators’

CO2 seeps in PNG give insights to the future of coral reefs in a world of increasing greenhouse gas emissions

Natural carbon dioxide (CO2) seeps in Papua New Guinea have given scientists rare insights into what tropical coral reefs could look like if human-induced atmospheric CO2 concentrations continue to rise unabated.

At present rates of increase, the Intergovernmental Panel on Climate Change (IPCC) forecasts atmospheric CO2 levels of about 750ppm or more by 2100. About a third of this extra atmospheric CO2 is absorbed by the world’s oceans. As a consequence, pH levels will drop from 8.1 to 7.8, resulting in increased ocean acidification which impacts on coral reef ecosystems.

AIMS scientist Dr Katharina Fabricius has led two research expeditions, with researchers from six countries including Papua New Guinea (PNG), to study three natural CO2 seeps in Milne Bay Province, PNG. This unique location is the only presently known cool, CO2 seep site in tropical waters containing coral reef ecosystems. The study has given scientists unprecedented insights into what coral reefs would look like if greenhouse gas emissions and resulting ocean acidification continues to increase at present rates. At the seeps, streams of CO2 bubbles emanate from the ocean floor due to volcanic activity.

A scientific paper on the first results of this study has just been published in the prestigious, international scientific journal Nature Climate Change. It is the first scientific paper to present data on tropical coral reef ecosystems that are naturally adapted and acclimatised to elevated CO2.

“In the past, we have relied on short-term laboratory experiments to tell us what happens to marine organisms exposed to ocean acidification,” Dr Fabricius said. “Those experiments indicated deleterious effects on the performance of many species.”
Continue reading ‘CO2 seeps in PNG give insights to the future of coral reefs in a world of increasing greenhouse gas emissions’

Acid test for corals (video)


Continue reading ‘Acid test for corals (video)’


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