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Whale and diver. Photo courtesy: NOAA (National Oceanic and Atmospheric Administration)
New research suggests that as the world's oceans become more acidic due to global warming, their acoustic properties may change, allowing low-frequency sounds to travel farther than they do today, similar to how they did in the Cretaceous period.
By 2100 low-frequency sounds, specifically those used by whales for communication, near the ocean surface may travel twice as far as they do today.
Science Daily sums up the work, published by the Acoustical Society of America:Using boron's sound absorption traits and impact on low-frequency transmission, [Rhode Island acoustician David] Browning and his colleagues were able to predict the soundscape of ancient oceans to conclude that 300 million years ago, during the Paleozoic, the low frequency sound transmission in the ocean was similar to conditions today. They also found that transmission improved as the ocean became more acidic, reaching its best transmission value around 110 million years ago.
"This knowledge is important in many ways," notes Browning. "It impacts the design and performance prediction of sonar systems. It affects estimation of low frequency ambient noise levels in the ocean. And it's something we have to consider to improve our understanding of the sound environment of marine mammals and the effects of human activity on that environment."
It's all pretty cold comfort considering it may be brought about because of conditions that devastate the oceans otherwise, but nevertheless it's really a pretty cool discovery.
A specimen of Leptoseris troglodyta, the cave-dwelling coral, photographed near Indonesia in 2003. Photo courtesy: Bert Hoeksema
A new species of coral has been discovered that clings to the ceilings of underwater caves in the western Pacific's Coral Triangle.
Able to tolerate low levels of light, the species lacks the symbiotic algae that most corals need to survive. The newfound species is related to deep-sea corals that survive in dark conditions below depths of 130 feet (40 meters), but so far, this species has been found no deeper than 115 feet (35 m), according to a description of the species published today in the journal ZooKeys.
The coral forms smaller polyps than its relatives and grows quite slowly, said study author Bert Hoeksema, a researcher at the Naturalis Biodiversity Center in Leiden, Netherlands, in a statement.
A close-up of the trumpet of the newly discovered cave-dwelling coral. Photo courtesy: aquaportail.com
Its range overlaps with the Coral Triangle, a region that's well-known for its high diversity of marine organisms. The species has been dubbed Leptoseris troglodyta. The word "troglodyte" is derived from ancient Greek and means "cave dweller." Troglodyte also refers to some of my old boyfriends!
Investigations into how the coral is able to survive without symbiotic bacteria could shed light on the relationship between the two species. This relationship is critical; when water temperatures increase — as is happening in the world's oceans now — many corals may expel their algae, in a process known as coral bleaching. This often leads to the coral's death.
Global warming is likely to shrink the size of fish by as much as a quarter in coming decades, according to a groundbreaking new study of the world's oceans.
The reduction in individual fish size will be matched by a dwindling of overall fish stocks, warned scientists, at a time when the world's growing human population is putting ever greater pressure on fisheries.
"We were surprised as we did not think the effects would be so strong and so widespread," said Prof William Cheung from the University of British Columbia in Canada, who led the research. His team examined the effect of rising ocean temperatures on the growth and distribution of more than 600 species of fish around the world and found that they are expected to shrink in size by 14-24% by 2050, with the biggest effects in tropical regions.
"It could be worse than that," said Prof Callum Roberts, at the University of York, who described the research as the most comprehensive to date. Roberts, who was not one of the study's authors, said additional impacts of climate change such as the acidification of the ocean and reduction of nutrients in surface waters could decrease fish stocks even further, as would continued overfishing.
"We will see dramatic changes in the oceans likely to reduce productivity," said Roberts. "One billion people rely on fish for primary animal protein and that is going to increase, especially in developing countries. We have to get to grips with our dependence on fossil fuels otherwise we are stuffed."
The fish shrinkage predicted by the new research results from two effects: the difficulty of growing in warmer, oxygen-poor waters, and migration.
"The metabolic rate of fish in the warm oceans increases and therefore they need more oxygen," said Cheung, whose work is published in Nature Climate Change. But warm water holds less oxygen and so their growth is limited.
In addition, there are more small-bodied fish in the tropics and these will migrate to temperate or polar regions as the ocean warms, reducing the average fish size.
The two effects are similar in impact, said Cheung, who used computer models to project the effect of warming on fish physiology, distribution, migration and population.
"We are already seeing the effects," he added, pointing to a 2011 study that showed the reduction in the size of haddock in the North Sea correlated closely with increasing temperature. Cheung's team projected temperature rises using data from the Intergovernmental Panel on Climate Change, based on a high-emissions scenario that matches the current trajectory of greenhouse gas emissions.
"Our work shows a very concerning future for the oceans and so it is very important to reduce greenhouse gas emissions and develop better fish management policies to adapt to these changes," said Cheung.
Roberts said the research showed the impact of climate change on the oceans looked set to be greater than previously predicted. The reduction in fish size due to overfishing was well known, he said, as for the last century fish have increasingly "lived fast and died young", preventing them reaching full size. But, if overfishing continues, this effect would be additional to the shrinkage caused by warming, Roberts said.
Furthermore, rising carbon dioxide in the atmosphere leads to more of the gas dissolving in the ocean, increasing its acidity. "That makes life much tougher for animals that make a chalky skeleton," said Roberts. "We need to worry about these tiny animals – such as coccoliths and foraminifera – which are an important part of primary production: the base of the food chain."
Lastly, Roberts said the heating of the oceans means that the warmer layer at the surface mixes less with the colder layer below. As the colder layer contains most of the nutrients, that means less food for fish. "We are already seeing some evidence of this, as oceanic 'deserts' are getting larger."
"All this is yet one more reason to do something to cut greenhouse gases urgently," he said.
Coral cover on Australia's Great Barrier Reef has declined by more than half over the last 27 years according to marine scientists. Storms, coral bleaching and a rise in the number of crown-of-thorn starfish which suck out the coral's nutrients, have led to the alarming decline. Scientists warn that unless action is taken the coral will halve again within a decade. Video courtesy: guardian.co.uk
Coral cover in the Great Barrier Reef has dropped by more than half over the last 27 years, according to scientists, a result of increased storms, bleaching and predation by population explosions of a starfish which sucks away the coral's nutrients.
At present rates of decline, the coral cover will halve again within a decade, though scientists said the reef could recover if the crown-of-thorns starfish can be brought under control and, longer term, global carbon dioxide emissions are reduced.
"This latest study provides compelling evidence that the cumulative impacts of storms, crown-of-thorns starfish (Cots) and two bleaching events have had a devastating effect on the reef over the last three decades," said John Gunn, chief executive of the Australian Institute of Marine Science.
Coral reefs are an important part of the marine ecosystem as sources of food and as protection for young fish. They are under threat around the world from the effects of bleaching, due to rising ocean temperatures, and increasing acidification of the oceans, which reduces the corals' ability to build their calcium carbonate structures.
The Great Barrier Reef is the most iconic coral reef in the world, listed as a Unesco world heritage site and the source of $A5bn (£3.2bn) a year to the Australian economy through tourism. The observations of its decline are based on more than 2,000 surveys of 214 reefs between 1985 and 2012. The results showed a decline in coral cover from 28% to 13.8% – an average of 0.53% a year and a total loss of 50.7% over the 27-year period. The study was published on Monday in the Proceedings of the National Academy of Sciences journal (subscription).
Two-thirds of the coral loss has occurred since 1998 and the rate of decline has increased in recent years, averaging around 1.45% a year since 2006. "If the trend continued, coral cover could halve again by 2022," said Peter Doherty, a research fellow at the institute.
The incredibly beautiful; but, deadly crown-of-thorns starfish is causing the rapid decline of coral reefs. Photo courtesy: shells-of-aquarius.com
Tropical cyclones, predation by Cots, and bleaching accounted for 48%, 42%,and 10% of the respective estimated losses. In the past seven years the reef has been affected by six major cyclones. Cyclone Hamish, for example, ran along the reef, parallel to the coast for almost 930 miles (1,500km), leaving a trail of destruction much greater than the average cyclone, which usually crosses the reef on a path perpendicular to the coast.
The starfish problem was first recorded in 1962 at Green Island off Cairns. "When we say outbreaks, we mean explosions of Cots populations to a level where the numbers are so large that they end up eating upwards of 90% of a reef's coral," Gunn said. "Since 1962 there have been major outbreaks every 13-14 years."
The evidence suggests that outbreaks of Cots start two or three years after major floods in northern rivers.
In September, scientists at the International Union for Conservation of Nature announced that Caribbean coral reefs are on the verge of collapse, with less than 10% of the reef area showing live coral cover. The collapse was due to environmental issues, including over-exploitation, pollution and climate change.
David Curnick, marine and freshwater programme co-ordinator at the Zoological Society of London, said many of the most endangered coral species around the world were also under severe pressure from the aquarium trade.
"Corals are notoriously hard to propagate in captivity and therefore the trade is still heavily dependent on harvesting from the wild."."
He said the results of the Great Barrier Reef survey were not surprising and the challenge for conservationists was to limit the localised threats to give reefs a chance to recover and develop resilience against the effects of climate change. "This is challenging but entirely achievable and there are many community-led projects around the world demonstrating this."
Corals can recover if given the chance. But this is slow – in the absence of cyclones, Cots and bleaching, the Great Barrier Reef can regrow at a rate of 2.85% a year, the scientists wrote. Removing the Cots problem alone would allow coral cover to increase at 0.89% a year.
Reducing Cots means improving water quality around the rivers at the northern end of the reef to reduce agricultural run-off – high levels of nutrients flowing off the land feed and allow high survival of Cots larvae. Another option is some form of biological control of populations – Gunn said there were promising results from research on naturally occurring pathogens that could keep Cots in check, but it was not ready to be applied in the field.
He said the future of the Reef lay partly in human hands. "We can achieve better water quality, we can tackle the challenge of crown-of-thorns, and we can continue to work to ensure the resilience of the reef to climate change is enhanced. However, its future also lies with the global response to reducing carbon dioxide emissions. The coral decline revealed by this study – shocking as it is – has happened before the most severe impacts of ocean warming and acidification associated with climate change have kicked in, so we undoubtedly have more challenges ahead."
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