Marine microbes—the good, the bad, and the ugly.
Maybe, like us, you’ve spun a globe in a library or school and realised that there’s one viewpoint that shows pretty much all ocean.
Not surprising, really, when you recall that oceans cover 71% of our planet’s surface.
And with rising sea levels, perhaps even more than 71% of the earth’s surface will be covered in water in the future.
Oceans contain a vast amount of life, the huge majority of which is microbial.
In fact, some estimates suggest that 98% of marine biomass is made up of microorganisms.
That’s 98% microbes, and 2% whales, whelks, whiting, and weed—and everything else in between.
Scientists say a single milliliter of seawater can contain up to a million microbes, or, to put it another way, just 6 liters (1.5 gallons) of seawater contains more microorganisms than there are people on Earth.
Mind you, in recent years, estimates of the total marine biomass have changed on a scale that is rather more than what you might call a rounding error.
In 2012, scientists based at the University of Rhode Island’s Graduate School of Oceanography concluded that estimates of the mass of all life on earth should be reduced by around one third.
They explained that this was necessary because of past overestimates of microbes living under the seabed, mainly because the figures had been extrapolated from historical surveys conducted in nutrient-rich parts of the world, whereas about half of the planet’s oceans are, in fact, extremely nutrient-poor.
So, we used to believe that the oceans contained 300 billion tons of microbes, whereas it is now thought the mass is more like 4 billion tons.
A rather different figure, as you may agree.
Just as your own personal collection of bacteria (the average human microbiome consists of trillions of bacterial cells) includes both helpful and harmful microbes, the oceans contain some bacterial species that are vital for our existence and others that are actually pretty life-threatening.
Before moving on to the bad and ugly, let’s begin with the good.
Microorganisms in the oceans supply more than half of the world’s oxygen, and half of that comes from bacteria.
Cyanobacteria, for example, carry out photosynthesis, taking carbon dioxide from the air, turning it into organic parts of their own cells, and releasing oxygen—just like plants.
In fact, this process delivers a double benefit, as carbon dioxide is of course one of several greenhouse gases, meaning that Cyanobacteria in the ocean have the potential to mitigate the effects of climate change.
But wait, there’s more, and it’s definitely not all good news on the marine bacteria front.
You see, a trend for rising sea surface temperatures is strongly associated with the spread of a potentially dangerous genus of bacteria named Vibrio.
Vibrio bacteria are rod-shaped, and got their name because they appear to vibrate.
Some Vibrio species are seriously dangerous.
Vibrio cholerae, for example, causes cholera, a disease responsible for up to 142,000 deaths around the world annually, according to the World Health Organisation.
Less prevalent, but equally concerning, is Vibrio vulnificus, which can infect humans often through uncooked/undercooked seafood or when wounds come into contact with contaminated seawater.
In the US, Vibrio bacteria are responsible for about 80,000 illnesses and 100 deaths per year, but records show that in the 15 years between 1996 and 2010, the annual incidence rate of environmentally-acquired Vibrio infections has increased almost fivefold. And we’re talking potentially serious — in some cases “flesh-eating” — infections here, particularly dangerous for people with compromised immune systems.
This makes work published just a few months ago (June 2016) in the Proceedings of the National Academy of Scientists of particular interest.
A team of researchers from the University of Maryland and the Johns Hopkins Bloomberg School of Public Health examined samples of plankton that had been collected every year for 50 years, from the North Atlantic and North Sea, and preserved in formalin.
Along with the plankton came bacteria, so the researchers specifically looked for the presence and abundance of Vibrio bacteria.
They also had records of the ocean’s surface temperature over the same period, 1958-2011.
As the temperature rose, so did the population of Vibrio bacteria.
There was a 1.5 degrees Celsius increase, coinciding pretty ominously with greater numbers of Vibrio infections.
Humankind’s interactions with the world are complex, as is our relationship with the bacteria with which we share both the planet and our lives.
We would do well to treat them with respect.