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Climate Change And Dolphins

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We don’t think of heatwaves as something that affects the ocean, but increasingly, as the planet warms, there have been instances where ocean water temperatures become much higher than normal for extended periods of time.  There has been much discussion of this phenomenon with regard to coral reefs where the catastrophic rise in coral bleaching events has been the result.

Recently, a study at the University of Zurich looked at the effects of ocean heatwaves on marine life higher in the food chain.  They studied the well-known dolphin population in Shark Bay, Western Australia.

In early 2011, a heatwave caused water temperatures in Shark Bay to rise more than 4 degrees above the annual average for an extended period.  This led to a substantial loss of seagrass, which is a driving factor in the Shark Bay ecosystem.

The researchers investigated how this environmental damage affected survival and reproduction of dolphins, using long-term data on hundreds of animals collected over a ten-year period from 2007 to 2017.

Their analysis showed that dolphins’ survival rate dropped by 12% and female dolphins were giving birth to fewer calves.  That phenomenon that began in 2011 lasted at least until 2017.

The researchers were surprised by the extent and the duration of the influence of the heatwave, especially the fact that the reproductive rate of dolphins had not returned to normal even after 6 years.

This study shows for the first time that marine heatwaves not only affect organisms at the lower levels of the food chain, but also might have considerable long-term consequences for the animals at the top, such as dolphins.

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Climate change is a threat to dolphins’ survival

Photo, posted December 14, 2014, courtesy of Ed Dunens via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

How Much CO2 Can The Oceans Hold?

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The carbon dioxide that enters the atmosphere doesn’t necessarily stay there.  As part of the natural carbon cycle, much of it goes into plants, soil and, very significantly, the ocean.  In fact, the world’s oceans are a sink for human-generated carbon dioxide without which the extent of global climate change would be far worse.

Oceans takes up CO2 in two steps: first the CO2 dissolves in the surface water.  Then, the ocean’s overturning circulation distributes it.  Currents and mixing processes transport the dissolved CO2 from the surface deep into the ocean’s interior, where it accumulates over time.

A long-standing priority for climate researchers is to determine how much of the CO2 we produce is being absorbed by the oceans and, ultimately, how much can they hold?

An international team of scientists has recently provided some answers.  As reported in Science, the researchers have determined that the oceans have taken up from the atmosphere as much as 37 billion tons of human-made carbon between 1994 and 2007.  This figure corresponds to nearly a third of all the anthropogenic CO2 emitted during that time.

Furthermore, they found that the percentage of CO2 taken up by the oceans has remained relatively stable compared to the preceding 200 years even as the absolute quantity has increased.  So, evidently, the oceans’ capacity for carbon dioxide has not yet been saturated.

That’s the good news.  The bad news is that putting all that CO2 into the oceans has a steep price:  the dissolved CO2 acidifies the water.  The consequences for a wide range of marine life including coral reefs are serious and getting worse.  We need to drastically reduce carbon emissions.

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Ocean sink for human-made carbon dioxide measured

Photo, posted November 5, 2018, courtesy of Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Disease On Coral Reefs

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The warming oceans have led to bleaching events in coral reefs around the world, but bleaching is not the only problem corals face.  Disease outbreaks are also becoming more frequent, severe, and widespread.

Many factors are contributing to the problem, including pollution and nitrogen runoff from fertilizers and coastal sewer and septic systems.  However, the key culprit is likely the steadily increasing ocean temperatures, which are the cause of coral bleaching.  Elevated water temperatures can cause coral polyps to expel the algae that sustains them and gives them color. 

According to scientists, bleaching makes corals more susceptible to illness.  In the Caribbean, a coral disease hotspot, about 80% of coral cover has disappeared, largely from outbreaks of “white band disease”, so called because of a white band of dead tissue that forms in affected corals.  Two crucial reef-building species, elkhorn and staghorn coral, are now nearing extinction in the regions.  The reef extending along the Florida coastline is the third largest reef ecosystem in the world and nearly 35% of it has been lost to disease.

Estimates are that disease outbreaks have wiped out at least 6% of the corals on the Great Barrier Reef in Australia.  In that region, diseases are more prevalent in areas where corals were damaged by fishing and other human activity because wounded coral provides an entry point for pathogens and bacteria.

In the face of climate change and mounting disease outbreaks, scientists are scrambling for solutions to stave off catastrophe.  Assisting the migration of hardier coral species and breeding so-called “super corals” are among the strategies being pursued.  It is unknown whether these and other forms of intervention can be used on a wide enough scale to really make a difference.

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As Disease Ravages Coral Reefs, Scientists Scramble for Solutions

Photo, posted November 29, 2012, courtesy of Robert Linsdell via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Is There Hope For Coral Reefs?

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News about the world’s coral reefs has been relentlessly bad for a number of years.  Warming, acidifying oceans have wreaked havoc with coral reefs leading to enormous losses.  Nowhere have things been more dire than in Australia’s Great Barrier Reef.  Coral bleaching events have been increasingly common and severe over the past two decades.  In fact, only 7% of the Great Barrier Reef has escaped bleaching entirely since 1998.

While the future of the world’s coral reefs is very much uncertain as global heating continues, there is a recent bit of hopeful news.   According to a study published in Nature Climate Change, the response of the Great Barrier Reef to the extreme temperatures in 2017 was quite different from that of the previous year in the aftermath of back-to-back bouts of coral bleaching.

Surprisingly, corals that bleached in 2016 but managed to survive were more resistant to the recurrence of hot conditions in 2017.

Many corals don’t survive bleaching events at all and, of course,those corals don’t bleach for a second time. But the surviving corals from the 2016 bleaching event were tougher species.   As a result of bleaching, the mix of coral species on the reef is changing very rapidly.  The net result was that there was less bleaching in 2017 even though the temperatures that year were even more extreme than in 2016.

There have now been four mass bleaching events on the Great Barrier Reef over the past 20 years and it is only a matter of time before another one occurs triggered by the next marine heatwave. Almost half of the corals on the northern two-thirds of the reef have been killed.  But at least some of the reef is showing impressive survival skills.

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A glimmer of hope for the world’s coral reefs

Photo, posted November 29, 2012, courtesy of Robert Linsdell via Flickr. 

Earth Wise is a production of WAMC Northeast Public Radio.

Rapid Response To Climate Change More Important Than Ever

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The Intergovernmental Panel on Climate Change has issued a new report emphasizing the importance of taking rapid action to limit global warming to 1.5 degrees Celsius and examining the consequences of allowing temperatures to rise 2 degrees instead.

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Heat-Resistant Corals

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All over the world, coral reefs are being wiped out by rising sea temperatures brought about by climate change.  When sea temperatures get too high, the symbiotic relationship between coral polyps and microscopic algae living within the coral breaks down and the coral either digests or expels the algae.   The result is coral bleaching which weakens, and if it persists, kills the coral.

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Protecting Reefs Of Hope

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One of the most harmful effects of the changing climate is what is happening to coral reefs.  Warmer ocean temperatures and acidification are causing widespread bleaching of coral.  Stressed corals expel the algae living in their tissue, turning the corals white and robbing them of nutrients.  When bleaching events persist, the corals starve and die.   Reefs everywhere have been experiencing mass bleaching events in recent years with over 70% of the coral reefs around the world being damaged.

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Fewer Snowbird Sharks

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Blacktip sharks are snowbirds, to use a cross-species metaphor.   At least, they usually are.  The males of the species swim south to southern Florida during the coldest months of the year and head back north to North Carolina in the spring to mate with females.

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Looking For “Super Coral”

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Coral reefs are essential for much of marine life and are the basis of many commercial fisheries.  In places from Florida to Australia, they are major tourist attractions.  Estimates are that the economic impact of coral reefs is more than $375 billion a year.  And apart from all of that, they are some of the most beautiful places on the planet.

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Breeding Dory

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The regal blue tang is one of the most common and most popular marine aquarium fish in the world.  In the U.S., they have been ranked as high as the 10th most imported fish species out of over 2,000 that enter the country.  Apart from aquarium hobbyists, millions of people now associate blue tangs with the character Dory in a couple of popular animated films.

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Some Good News For Coral Reefs

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Most recent news about coral reefs around the world has been bad news.  There has been unprecedented coral bleaching in places like Australia’s Great Barrier Reef.   The effects of climate change – including warming temperatures and rising seas – as well as the recent El Niño event have led to damaged reefs across the globe.

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