Paper: Deutsch, C., Ferrel, A., Seibel, B., Pörtner, H. O., & Huey, R. B. (2015). Climate change tightens a metabolic constraint on marine habitats. Science,348(6239), 1132-1135.
Wooooowee is it hot out lately.
Every time I go outside…
This hot weather is not only bad for Chris Pratt’s and my boob sweat (he could rock boob sweat anyway), but also terrible for breathing in the sea. Let me explain.
Aquatic life needs more than just water to live.
They also need air. And by air, I mean oxygen.
But how do they get air? They live underwater. If there was air down there, couldn’t we live there, too?
As you probably already know, but I’m gonna say it anyway, fish don’t actually breathe water.
Fish and other aquatic life breathe the little bits of oxygen that dissolved in the water, referred to as “dissolved oxygen,” DO.
You don’t need to read this whole diagram, but I just wanted to show what that means, kinda.
Basically, oxygen from the atmosphere mixes into the surface waters of the sea and critters can bring this oxygen.
Colder water can dissolve more oxygen than warmer water. But there’s enough oxygen – at present – in tropical waters for the sea life there to breathe.
Just look at all of those bubbles.
Anywho, the researchers of this week’s paper looked at how the reduction of dissolved oxygen in the sea (due to warming temperatures via climate change and overall loss of O2) will impact where different organisms can live based on their oxygen demands.
This was a pretty math-based paper, but don’t worry. We’ll get through this together.
(Leo is not only beautiful, he is also super passionate about the environment. Leonardo DiCaprio Foundation)
The scientists figured out how much oxygen each species they studied needed for their resting metabolism. Aka how much oxygen they breathe just exist.
Like this guy.
Obviously, these animals do more than watch cartoons all day and need more oxygen to catch dinner, avoid predators, and make babies.
Here’s where math starts to come into play.
The scientists defined “metabolic index” as the ratio of the amount of oxygen available in the environment, the supply, to the amount of oxygen the organism needs for its resting metabolism.
If this ratio is equal to 1: the animal can do no more than watch Netflix all day and just breathe
If this ratio is more than 1: the animal can hit the gym and catch tonight’s dinner and do lots of stuff
If this ratio is less than 1: the animal can’t even breathe and must do anaerobic respiration (aka breathing without oxygen) which they can’t do for very long before dying. they basically suffocate
The ratio across the globe did not vary much seasonally or longitudinally, but did vary a bit with latitude. Also, the ratio didn’t increase significantly in deeper water.
In the low-latitude tropical water, the ratios were pretty low:
1. there’s less oxygen in tropical water since it’s warmer there
2. organisms in warm environments have higher metabolic rates – aka need more oxygen for their resting metabolism
The tropical seas suffocate in their own beauty.
Meanwhile, closer to the poles, the ratio was much higher because the water holds more oxygen since the water temperature is colder and organisms there have lower metabolic rates.
As the average sea temperature increases due to climate change, the amount of oxygen in the water will decrease.
So the ratio of habitats close to the equator will decrease. For some critters, this means their ratio (oxygen supply:demand) in these locations could drop below 1 and they won’t be able to live there anymore.
Breathing issues, that is.
This study looked at how the ocean temperature projected for the end of the century – a bit warmer than today’s – will affect where certain species can live based on metabolic index ratios.
The animals examined spanned a variety of habitats.
Mid-latitude open ocean: Atlantic Cod
Mid-latitude benthic (bottom-dwelling): Atlantic Rock Crab
Subtropical latitude: Seabream
What they found:
In 100 years:
– cods will have to dive deeper in the summer to escape the warmed surface waters — they will have to take deep breaths – get it? breaths at deeper depths. The title of this post!
I’m so funny.
– rock crabs will have to move roughly 10 deg latitude north for more oxygen
– depth zones of organisms will shrink
– habitable zone of organisms will move toward the poles
However, not all of this will happen for sure.
Many factors affect how much oxygen is in the water.
Primary production (algae growth, etc) will affect the concentration of oxygen in the water. Algae and plants of the sea produce oxygen. When they die, they’re eaten by bacteria who use oxygen. So this relationship of primary production and oxygen concentration is a bit complicated.
The acidity of the ocean, which is projected to increase, could also affect dissolved oxygen concentrations. Additionally, pollution can impact oxygen levels.
From a biological perspective, some of these organisms will be able to adapt or the species could evolve over many generations to decreasing oxygen conditions. But that often takes many, many years depending on the species generation time and is unlikely to keep most organisms’ habitable range the same.
The only thing we do know for certain is that increasing temperatures have a negative impact on oxygen supply for organisms. So we should do our best to reduce our release of GHGs (green house gases – like carbon dioxide) and slow the warming of the seas!