Once upon a time, a bunch of green shore crabs (Hemigrapsus oregonensis) decided to have a race among themselves. Instead of having a simple race where they time how long it takes them to run one meter, they decided to test salinity tolerance.
One of the crabs being adventurous suggested, “hey guys! Let’s see if salt can be our magic potion to make us run faster!”
Another crab said, “That’ll be cool! I remember my parents once told me that we’re osmotic regulator!”
A little baby crab asked, “What does that mean?”
“It means that we can regulate how much salt is in our body independent to the environment!”
The adventurous crab then said, “well if we are not affected by just a little change on salt, then let’s try the extreme concentration of salt!”
With that said, some crabs withdraw from the race because they didn’t think it was a good idea, but some stayed in the race. The rules of the race were that each participant had to spend every second of every day for a in either super salty water or water with low-salinity water. The crabs that wanted to join the race but were hesitant chose to live in the water that they’ve always lived in. three hours later, the fraction of the participants gathered and started their first race. One at a time, the crabs took turn to run one meter; a referee/ score keeper tracked the time that each crab took to finish one meter to calculate their speed. Three days after the first race, a different fraction of the crabs had the same race. Then a week later, the last fraction of the crabs had the same race again.
At the end of the last race, the referee called a meeting and announced the results. “Before I announce the winners, I’d like to take a moment and remember the fellows that passed away because they couldn’t cope with super high amount of salt. It was a tragedy, but they taught us that we suck at regulating when we are hypo-osmotic to the environment. Now, let me announce the results!”
While referee was talking, most of the folks that exposed themselves to a lot of salt were still lethargic and didn’t know what was happening.
“So overall, it turned out that y’all who diluted your water (low salt content) ran faster than everyone! The folks that played it safe and stayed in normal water were second place, and the brave and adventurous bunch who chose lots of salt ran the slowest!”
A grandpa crab just happened to pass by and heard the result, he said, “my generation had the same race when we were young! We had the same result too. Want to know why?”
“I want to know! I want to know!” a crab that lost the race yelled.
“It’s because we are used to the low salt content that happens in the summer, so we are well adapted to low salinity and are fantastic hyper-osmotic regulator. However, we don’t normally experience super salty water, so our body is out of whack and we spend lots of energy trying to restore homeostasis!”
“Wait…why is there less salt in the water in the summer?” a curious crab asked.
“Because snow melts on the top of the mountain, and all the water drains into the ocean and dilute the water,” answered the grandpa. “As a lesson, don’t forget to tell the next generation what you learned from this race so they don’t sacrifice themselves for science again!”
More about osmoregulation of H. oregonensis: https://www.jstor.org/stable/1539589?seq=1#page_scan_tab_contents