Elkhorn Coral + Human Sewage = Disease

Henry Wolcott 2005 / Marine Photobank 

I noted yesterday that I was under intellectual duress.  The other half of the story from Thursday that I didnt highlight was a lecture I attended by Dr. Katie Sutherland from Rollins College, which is right here in Winter Park, FL. 

Dr. Sutherland’s work focuses on coral disease and especially white pox disease of elkhorn and staghorn coral, the two species of Acropora in the Caribbean.  Elkhorn is now federally listed as threatened.  In the Caribbean white band disease and white pox are just two forces that are pushing this species to the edge. We also have illegal harvest, destruction by otherwise-well-meaning tourists, and natural predators and storm knockdowns working on the populations.

Originally coral disease was looked at as a result of increased nutrient runoff from land sources (ie. fertilizer for lawns and crops).  Turns out that nutrient sources may stress corals so that they are prone to infection from bacteria, fungi, and viruses which may – or may not – ultimately be the source of disease. 

Between 1996 and 2000, 85-90% of Elkhorn coral in the Florida Keys died triggering a lot of interest in disease and the cause of white pox.  By sampling affected coral’s mucus layer (which acts as a barrier between them and the ocean) Sutherland found one commonality, the presence of a little bacteria known as Serratia marcescens.  When she went to find information about Serratia she discovered it is a very common land-based bacteria that is often as a fecal enteric bacteria in humans.  Yep, you can find it in human waste.  Nice.

Earlier studies have found some shocking things about the Florida Keys.  Most toilets on the islands empty into septic systems.  The trouble is that the Keys are built up on extremely porous limestone which can cause septic systems to leak.  A 2000 study from the Univ. South Florida found that when tracers were flushed down toilets on land the tracers could be detected in nearby downstream ocean water in just over three hours.  That is quite a serious leak!

Incredibly, 95% of the canals in the Keys are contaminated with human viruses associated with human waste.  And a 2007 study found that 64% of reefs sampled in the Keys were likewise contaminated with human waste viruses.  Grossssssss.

Sutherland’s work will continue to study the association between white pox, Serratia, and elkhorn in an attempt to fully confirm the link and to find a way to combat the disease.  She also wants to confirm as fact that human waste is the source of the bacteria.  Interestingly, she found sources for the bacteria also in snail predators of Acropora and in nearby corals that are non-Acropora.  But, she didnt find any of the bacteria in other predators of Acropora or other marine organisms.  And, moreover, the presence of Serratia in human waste was several times that of the bacterial count from snails and other corals.  Human waste as the source seems the most likely.

Even if human waste ultimately is not found to be the cause for elkhorn coral losses, we still need better waste treatment and regulation in the Keys.  Beaches are now being regularly closed due to high fecal coliform counts from nearby waters.  You just can’t convince me that any amount of human sewage in the ocean is a good thing. 

And since nearshore coastal water is the home of my favorite thing – seagrass – I’ll be keeping track of this interesting conservation puzzle.  It also has me wondering what other communities in Florida make use of septic systems which are slowly leaking into coastal ecosystems.  Perhaps we need to take a closer look at the barrier island communities even. 

Now if we can just regulate bilge pumping from people (and tourists) living on boats we will be really getting somewhere. 

In fact, if there were ever a case to be made for composting toilets, I think this potential link between human sewage and coral disease would be it!


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