Human pathogen can cause coral disease

Despite the resilience of corals as a taxonomic group through geologic time, warming oceans, shifting seawater chemistry, overfishing, pollution, and disease currently threaten these habitat-building invertebrates with many coral reef ecosystems in a state of decline.  Researchers have identified a bacterium, Serratia marcescens as the cause of a disease called white pox in elkhorn coral (Acropora palmata).  White pox, more formally known as acroporid serratiosis, can lead to tissue loss and potentially the death of the coral colony.  What makes this especially interesting is that S. marcescens normally causes health troubles in humans–this is the first evidence of a human pathogen to a marine invertebrate.  Acropora palmata was once the dominant coral in the Caribbean, especially in the forereef and reef crest, shallow spots with high wave action.  Today, populations of this coral species has been decimated, reduced by up to 95% in abundance since 1980, and is now considered critically endangered by the IUCN.  Much of this decline is attributable to disease, along with other factors that compound this plight–for example, this species is particularly vulnerable to bleaching.

Previous work done in 2003 noted that S. marcescens was found in both untreated human waster and within A. palmata suffering from white pox, suggesting a relationship between the two.  In a new paper published this week in PLoS ONE, Dr Katheryn Sutherland and colleagues used Koch’s postulates, a standard method for showing disease causation, to  investigate the relationship between the two.  In short, fulfilling these postulates requires researchers to be able to isolate the suspected pathogen (S. marcescens) from the host coral and grown up in culture, the disease to manifest itself when a pure culture of the pathogen is introduced to the host, and isolated yet again from the experimentally-infected host (more on Koch’s postulates here).  The results show that S. marcescens is capable of causing white pox in this coral species speedily, with the coral losing tissue in as little as four days (see figure below).

While this disease is specific to this particular coral, the researchers also found that other coral species could possibly be acting as reservoirs for this pathogen while in seawater, given that the pathogen itself is not adapted well for life in the ocean.  Additionally, a coral predator, a snail, may act as a disease vector or reserve.

Improving wastewater containment and treatment in areas such as the Florida Keys can reduce this pathogen’s transmission, and efforts are ongoing in Florida to improve wastewater management, though this issue is occurring in the wider Caribbean as well.  This study shows an exception to the usual animal-to-human transmission model, but also that this pathogen, found in land-based mammals (us), can cause a disease in a marine invertebrate, jumping not only into a profoundly different environment but also into a much different animal, a colonial invertebrate rather than a vertebrate.  Responding to this issue would be obviously beneficial to corals themselves, but also to human health and for the economies that depend on reef habitats for tourism and resources.  The dynamics of this disease are yet another example that illustrate the interconnectivity of society, ecosystems, and economics.

 Figure:  Sutherland et al. 2011 (CC 2.5)

Sutherland, K., Shaban, S., Joyner, J., Porter, J., & Lipp, E. (2011). Human Pathogen Shown to Cause Disease in the Threatened Eklhorn Coral Acropora palmata PLoS ONE, 6 (8) DOI: 10.1371/journal.pone.0023468

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Economically, live sharks > dead sharks

1 live reef shark in Palau = 179,000 USD in the ecotourism industry.  Or killed and sold once for 108 USD.  Just economically, not even considering the ecosystem services involved, sharks are worth much more alive.  This has been in the news for a bit but worth pointing out especially in the wake of Shark Week.

Video: Pew Environment Group. Press release here.

Beautiful intruders: the misplaced lionfish

Lionfish (Pterois volitans and P. miles) populations have drastically exploded in the western Atlantic and the Caribbean in the past decade, and not without attracting some attention. The trouble is that these gorgeous fish sporting an array of venomous spines are invasive species.  They naturally occur in the Indo-Pacific but have been introduced to Florida via aquarium releases and are now potentially causing significant changes to marine ecosystems, the inhabitats of which have not evolved with this fish.  They can now be found from Costa Rica and Venezuela up the US eastern seaboard to Rhode Island, a truly impressive extent considering the first individual was found offshore of Florida in 1985.  Recently, I was fortunate enough to dive in Roatan, Honduras on my honeymoon and lionfish were a relatively common sight, despite their efforts to hide among the barrel sponges on the benthos.  They could potentially spread well into the southern hemisphere, along the the coast of South America, based on the lethal minimum water temperature [pdf] for this fish (10 C).  Lionfish feed upon the larvae of reef fishes, undercutting the next generation of fishes.  They can spawn year-round and release buoyant egg masses that can float in the currents for weeks, ensuring a wide distribution.

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Fish stocks: Good news is a drop in the ocean | Editorial | Comment is free | The Guardian

There is an interesting editorial in the Guardian regarding the recent news of the beginnings of a fishery recovery off the Canadian coast.  (For those outside the paywalls of Nature, Hannah over at Culturing Science has nicely reviewed the paper here).

The gist is that despite this bit of sunlight within global overfishing, the situation is still alarming.  For example, the editors point out that:

In the North Sea, 93% of cod are fished before they can breed

The article’s worth a read.

Fish stocks: Good news is a drop in the ocean | Editorial | Comment is free | The Guardian.

Shark week and some numbers

The Discovery Channel’s annual Shark Week, a week of television programs devoted to these toothy ocean residents, began yesterday.  Shark Week has introduced many people to the wonder of these unique predators, the likes of which help to keep ocean ecosystems balanced, and usually includes bits on shark conservation and other scientific content.  If you head over to their website there’s a nifty interactive map where you can click on different regions and learn about what species of sharks frequent those areas and even what their conservation statuses are.  There’s also a shark facts page with shark conservation information and states that you are more likely to get bitten by another person than a shark.

However, in regards to the high-profile television programs themselves, many of the titles  evoke images of attacks, such as ‘Rogue Sharks’ and ‘Killer Sharks.’

Over the years, the media in general has not been kind to these animals, giving disproportionate attention to, as John Bruno over at SeaMonster puts it, “sharks behaving badly, i.e. eating stuff.”  However, the reality is that tens of millions of sharks are being killed every year, and the populations of these ecologically important creatures are declining globally.

Six fatal shark attacks were reported last year globally, according to the International Shark Attack File.  73 non-fatal attacks were also recorded.  Loss of life is tragic, and I am certainly not attempting to play down any individuals’ experiences who were harmed by sharks, but these sorts of numbers do not justify an all-out fear of these animals.  For example, in 2008 (the latest year data seems to be available), 39,000 people in the United States were killed in car accidents, and most of us view traveling by car as a reasonable risk.  For some other comparisons, you can see the Florida Museum of Natural History’s ‘Relative Risk’ page.

I’m not trying to pick on Discovery, which over the years, has gotten many people more interested in science.  Nor am I implying that you should rub seal innards on yourself and try to give one of these big fish a peck on the cheek.  But sharks need our help—that is, we need to stop decimating them.  And that does include considering the economics and motivations of the fin trade and presenting people with an alternative.

Be sure to check out SeaMonster, Deep Sea News, and Southern Fried Science for more on Sharks and Shark Week.

Image 1:  Caribean reef shark, Alfonso Gonzàlez on Flickr (CC). Image 2: Windell Oskay on Flickr (CC).  

Dr Jason Hall-Spencer at the Guardian

Dr Jason Hall-Spencer has written an excellent essay on the urgency of oceanic action, fueled by the recent findings of the International Programme on the State of the Ocean (IPSO).  Make sure to check it out.

The crux of the problem is that the rate of changes in ocean systems is accelerating and outstripping what was expected just a few years ago. Destructive fishing practices, pollution, biodiversity loss, spreading low-oxygen “dead zones” and ocean acidification are having synergistic effects across the board – from coastal areas to the open ocean, from the tropics to the poles.

via A steward for our oceans | Jason Hall-Spencer | Comment is free | The Guardian.

See also:  The State of the Ocean’s site and the original full report (PDF) Dr Hall-Spencer refers to.

Teaching sharks that lionfish are tasty?

Some gutsy local divers have been teaching sharks just how good lionfish are to eat in Roatan Marine Park off the coast of Honduras [The Seamonster].

Dr John Bruno, over at the excellent new ocean-science blog, Seamonster, points out some new efforts in the fight against a particularly troubling invasive species, the lionfish.  Lionfish are native to the Indo-Pacific but have invaded waters along the US eastern seaboard, all the way down to South America, and represent an enormous ecological change, as pretty much nothing is left to eat them.  But apparently there are efforts afoot to change that, by working with sharks, and by attempting to convince a largely land-based bunch of bipeds that they’re yummy as well.

Is the Earth’s sixth mass extinction looming near and large?

Fossil fish sculpture. Rae Allen. CC BY 2.0.
Ideally, your expenses are offset by your paycheck, so as you spend money for say, rent and food, you have cash coming in.  On the surface at least, this is similar to the dovetailing of extinction and speciation.  The vast majority (~99%) of all the species ever to have existed on Earth are extinct, never to be seen alive again.  However, this process is balanced by new species evolving, a process known as speciation.  So what happens when species extinctions far outpace species creation?  Mass extinctions, timeframes during which 75% of species are lost in a relatively short period (usually less than two million years and sometimes significantly less), have occurred five times (the Big Five) in the past 540 million years.  They are unique, singular events that stand out above the background level of extinction that is constantly ongoing.  However, more and more modern extinctions are being observed, amidst the myriad of human-derived disturbances, such as rapid climate change, invasive species introductions, habitat fragmentation, directly killing species, among others.

It is not a straightforward task to ascertain whether or not we are on track to another mass extinction—data from the fossil record must be comparable to historic and modern species assessments.  In a paper recently published in Nature, Dr Anthony Barnosky and colleagues point out why data comparisons of this type are difficult and proceed to broadly get around them by looking at the global picture.

The fossil record is not evenly distributed across taxa or geographies.  Fossils are particularly meager in some broad swathes of Earth, such as the tropics.  On the other hand, distributions are known for many modern species.  In terms of taxa, or groups of species, usually only animals with hard bits fossilize well.  Studying modern species is easier, because they’re still around, but less than 2.7% of known species have been assessed for risks (e.g. endangered, extinct in the wild, etc.) by the International Union for the Conservation of Nature (IUCN).  There’s also trouble with the species concept.  Fossils are usually identified at the genus, rather than species, level; modern work frequently uses genetic approaches to identify individuals to species.  Fossils are also not distributed evenly through time.  Fossil extinctions are recorded when a certain group of animals vanishes from the fossil record, the extinctions known are likely underestimates since most species have no fossil record.

In spite of these caveats, the researchers evaluated the existing data and show that it is possible to circumvent these various data comparison issues by taking a ‘big-picture’ global approach.  Conservatively, mass extinctions occur when the extinction to speciation ratio becomes so unbalanced that three quarters of species disappear, usually within less than two million years.  If two million years sounds like a leisurely long time, bear in mind that the Earth is ~4.54 billion years old. Most living things forever blinking of out existence in roughly 0.04% of that time is a colossally unique situation indeed.

Using a rate-based method, the researchers compared extinctions per million species-years (E/MSY)1 from throughout the fossil record and modern time.  By using various paleontology databases and accounting for data biases, they were able to establish a background rate of extinction.  Through this approach, it is clear that the maximum extinction rates since about 1,000 years ago are much higher than the average fossil rate and the recent average extinction rates are also significantly higher when compared to pre-anthropogenic (that’s pre-us, mind you) averages.

Another way to consider this is by splitting up the fossil record into 500-year intervals and calculating the likelihood that extinction rates were as high in many of these 500-year intervals as they were in the most recent 500 years. In the case of mammals, which have an average of 1.8 extinctions per million species-years, only 6.3% of these 500-year segments could have extinction rates comparable to the current 500-year interval in order to preserve the background E/MSY.  So no, it is supremely unlikely that many of these past 500-year bins had extinction rates that were as high as they are today.

But would these current rates produce a large magnitude extinction event?  By using modern species assessments of very well-surveyed groups coupled with fossil data, Dr Barnoksy and his team calculate that extinction rates for mammals, birds, amphibians, and reptiles are as quick or quicker than all rates that would have been responsible for the previous five mass extinctions.  If all threatened species (defined by IUCN criteria) are lost within a century, and the current extinction rate continue, land-based amphibians, birds, and mammals would reach mass extinction thresholds in ~240 -540 years.  This slows down a bit if ‘only’ critically endangered species disappear within the next 100 years to ~890 – 2,265 years for those same groups of animals. Current extinction rates are higher or as high as those that preceded and caused the previous mass extinctions.  The researchers point out that while a pressing need for new research exists, the 75% species loss threshold could occur within the next three centuries.

Modern species losses are serious but does not pass the threshold for a mass extinction event yet.  Relatively small numbers of species surveyed historically have been lost, although scores of species have yet to be discovered and/or evaluated.  However, the researchers point out that losing critically endangered species would put us on the fast track to mass extinction, and losing endangered and vulnerable species would achieve the sixth extinction even faster, within a few hundred years. Sobering commonalities between the present-day and the past mass extinctions exist:

It may be of particular concern that this extinction trajectory would play out under conditions that resemble the ‘perfect storm’ that coincided with past mass extinctions: multiple, atypical high-intensity ecological stressors, including rapid, unusual climate change and highly elevated atmospheric CO2. [Barnosky et al.]

The diversity of life should be preserved while it’s still here.

 

1  Think of this as man-hours (or really person-hours).  On a purely mathematical basis, if you had one million species and an extinction rate of 1 per million species-years, one species would go extinct a year.

Barnosky AD, Matzke N, Tomiya S, Wogan GO, Swartz B, Quental TB, Marshall C, McGuire JL, Lindsey EL, Maguire KC, Mersey B, & Ferrer EA (2011). Has the Earth’s sixth mass extinction already arrived? Nature, 471 (7336), 51-7 PMID: 21368823

Image:  Rae Allen on Flickr (cc).

This article is also posted at The Urban Times.

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Careening towards the sixth mass extinction

Even taking into account the difficulties of comparing the fossil and modern records, and applying conservative comparative methods that favour minimizing the differences between fossil and modern extinction metrics, there are clear indications that losing species now in the ‘critically endangered’ category would propel the world to a state of mass extinction that has previously been seen only five times in about 540 million years. Additional losses of species in the ‘endangered’ and ‘vulnerable’ categories could accomplish the sixth mass extinction in just a few centuries.

More thoughts to come.  In the meantime, please consider doing something about it.

From:  Barnosky AD, et al. Has the Earth’s sixth mass extinction already arrived? Nature 471: 51-57 doi:10.1038/nature09678