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Life in the ocean is a little different than it is up here.
For one thing, water holds onto heat a lot better than air, so temperatures tend to
stay the same from day to day rather than fluctuating with the sun.
But this doesn’t mean that ocean-dwelling organisms are less susceptible to rising
temperatures brought about by the climate crisis.
In fact, most marine critters are adapted to live at a
very narrow temperature range, so even a tiny change can quickly spell trouble.
And we might not have understood just how much trouble
without the help of an unassuming little snail.
The threeline mud snail is a small, spiral-shelled snail commonly found
crawling around beneath the waves on the North Atlantic seafloor.
While the adults spend their lives on the bottom of the ocean,
their larvae start out life swimming around up in the water.
These babies are so small that they are at the
mercy of the waves and ocean currents.
This snail species typically spawns in the summer, when the water
temperatures warm up enough to signal to their bodies that it’s baby-making time.
And the summertime ocean currents in the North Atlantic gently tow the freshly
hatched larvae out to cooler, deeper waters found at the edge of the continental
shelf, where the babies can then feed, grow and
eventually settle onto the seafloor as adult snails.
However, in a 2020 study, researchers from Rutgers University uncovered
a disturbing trend happening with the threeline mudsnail, along with
potentially dozens of other bottom-dwelling species living in the North Atlantic.
They found that this little snail was missing from the deeper,
colder waters of the North Atlantic outer shelf.
They expected to see increasing populations of these creatures
in the deeper waters because the deep waters are places of refuge.
They’re cooler than the shallow waters,
whose temperatures have risen dramatically in recent years.
Instead, the researchers found higher populations of
these snails in the warmer waters close to shore.
Which is not good, because remember, most marine
creatures are adapted to survive at narrow temperature ranges.
And the baby mud snails are particularly fragile.
They’re less likely to make it to adulthood in warm waters than colder waters.
The researchers believe that this shift in habitat is an
unexpected consequence of climate change.
But this is not something the snail is choosing to do.
See, in response to changing temperatures,
some organisms choose to travel north or south
toward the poles to seek refuge in cooler waters.
But these snails are too small to travel that far.
Instead, the snail’s physiology makes them easily influenced by changes in the
ocean’s physics, and it’s making them migrate in the completely wrong direction.
First, their spawning behavior is temperature dependent, so when the ocean
waters warm earlier in the year, they trigger an earlier spawning event.
This means those little baby snails are floating around in the water in
the springtime instead of in the summer.
And the currents in the North Atlantic vary throughout the year, changing directions
depending on the prevailing winds,
as well as the amount of water running into the ocean from the rivers on land.
Which leads to the second issue:
the baby snails are being pushed around by springtime ocean currents,
which are different from summertime currents.
The spring currents funnel these babies towards the shore
instead of away from it, as they do in the summer.
And the waters closer to shore are shallower and warmer
than the deeper edge of the shelf waters.
That means fewer babies will survive to adulthood,
and the survivors will spend the rest of their lives at those higher temperatures.
Which means that those adults will spawn even earlier in the year than past
generations, trapping the threeline mud snail in a feedback loop
that they cannot escape from.
This unfortunate circumstance could spell the beginning of the end for
the threeline mud snail, and potentially several other
bottom-dwelling North Atlantic species.
That’s because other seafloor-dwellers, like sea stars, clams, and worms,
have similar spawning and larval behavior to the threeline mud snail.
In fact, researchers have found that since the 1960’s,
around 80% of bottom-dwelling species have disappeared from
the deep waters of North Atlantic,
potentially all unwilling victims of this wrong-way migration phenomenon.
And it may not be just a North Atlantic occurrence.
This could be happening in other locations around the world.
Through no fault or choice of their own, bottom-dwelling species
are being pushed to the limits of their survival, thanks to the climate crisis.
But at least this is helping us to understand the many unexpected ways the climate
crisis can affect the creatures who share the planet with us.
And maybe help us understand how to help them.
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