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Every year in eastern Thailand, at the height of the rainy season,
thousands of tourists flock to the edge of the Lamdom river to see a remarkable sight.
All night long, streams of tiny shrimp march out of the water and parade along the river’s edge.
And they’d have to have a really good reason to take a risk this big.
But until recently, no one knew why they did it!
Now, if you’re not familiar with shrimp, walking is a weird way for them to get around.
Shrimp are aquatic animals. Like, they have gills, and if they dry out, they die.
Plus, there’s a slew of predators waiting on land to eat them.
Yet here these less than a centimeter-long shrimps are,
leaving the water for 10 minutes or more and crawling some 20 meters onto land!
The local lore was that it had to do with breeding.
Migrating upstream to breed is pretty common for animals—like salmon,
and even other species of shrimp. So, it’s a pretty good guess.
But when scientists systematically studied the parading shrimp, they found
that they were almost all juveniles. That means they were too young to mate or spawn.
Instead, the reason was much simpler and cuter: it’s to avoid strong currents!
Researchers realized two of the most reliable places to see these
shrimp parades were next to a set of rapids and a small artificial dam.
So, for a 2020 article, they tested this idea in the lab.
They set up tanks where they could vary the current.
And, lo and behold, the smaller shrimp
got out whenever the current was too strong, while the larger ones could still swim.
That’s why, in the wild, these shrimp that walk on land are so teeny.
Bigger ones are also going upstream, but they swim instead.
What we don’t know for sure is why they’re so keen to go up the river.
For clues, we had to look at other shrimp that parade… Because yes, apparently,
other species do this as well! Including ones in India, Australia, and the Americas.
Those species also seem to parade to get around barriers.
And the upstream areas they head for often have fewer predators. So,
the behavior may be a survival tactic.
It may also shed light on how shrimp colonized freshwater habitats in the first place.
Their ancestors most likely came from the ocean. So gaining the ability to walk around
barriers may have been a crucial part of the move into resource-rich freshwater habitats.
But more practically, further research on shrimp
parades could help us take better care of them and their habitats.
On one hand, some freshwater crustaceans are notorious
invaders. So, knowing how and why they move can help us figure out how to keep them in check.
But on the other, many species are struggling, and this sort of knowledge can help with conservation.
These Lamdom shrimp likely fall into that latter category.
It seems like fewer shrimp show up to parade each year.
And if that’s not bad enough,
as of yet unpublished research suggests the animals themselves are getting smaller,
which means rapids and such might pose even more of a problem in the future.
But, if we know what they can and can’t handle, we might be able to help them out.
Like, we could design structures that help these
cute little shrimp get around dams or fast-moving water.
That way, we can ensure these adorable parades continue to amaze and delight us
for many years to come.
It’s pretty amazing that shrimp can tell when they’re big enough to tough out some rapids.
They may have an instinctive understanding of fluid dynamics…
something I definitely do not have. Luckily I can turn to Brilliant!
Fluid dynamics is notoriously complex,
but their differential equations course can help you really understand how fluids flow,
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