Sea monkeys, or brine shrimp, are invertebrates that can tolerate intense conditions like no other. They may seem like simple novelty pets, but their calm demeanor hides their extreme side. Brine shrimp are particularly good at living in water with high salt concentrations, surviving in water where the salinity can be as high as 300 parts per thousand (for a reference, the ocean is generally around 30 ppt!). They can produce cysts that lay dormant for years until conditions are favorable for hatching, making them ideal survivalists, and pets. I became interested in these robust little shrimp and decided to study how they respond to quick changes in salt concentrations.
Salt is a major limiting factor for aquatic species, which makes the durability of brine shrimp so intriguing. One explanation for their high tolerance is that it helps them avoid predators: nothing can eat you if your enemies die when they step foot in your home. But this evasion may come with a cost, as the brine shrimp need to expend more energy to maintain their health when exposed to high concentrations of salt. Salt also seems to affect young shrimp more than adults. Scientists have studied the effects of long-term exposure to high salinity but know less about how brine shrimp respond to fast salinity changes.
I wanted to see if quickly changing salinity altered brine shrimp behavior. I collected some brine shrimp from a toy store and hatched them in my room, raising them in 30 ppt water. They breathe through their feet, so I measured how fast they beat them in response to changing salt concentrations. I found that younger shrimp (one-week old) increased their beating activity when exposed to higher salinities, but that juveniles (two-week old) had no response. This shows how there may be costs associated with extreme lifestyles, as young shrimp need to expend more energy to tolerate high salt concentrations.
This highlights the powerful rule in nature that there are no free lunches. Brine shrimp are just one example of the tradeoffs often found in biology. While being able to live at high salinities is beneficial for predator avoidance it is not so simple as just hopping pools; salt tolerance requires energy and appears to put stress on young brine shrimp (many studies have found that baby brine shrimp aren’t as good at tolerating salt as adults).
Brine shrimp are by no means the only extremophiles out there. There are species that live in such intense environments they are used as models for organisms we may find on other plants! Some organisms can only live in areas without oxygen, while some can live at pressures over 1000x that on the surface of the Earth. Studying these extreme creatures is a useful way to understand just how flexible, and resilient, life can be.
Check out this site if you are interested in learning more about brine shrimp: http://learn.genetics.utah.edu/content/gsl/artemia/
Cover picture from http://www.warrenphotographic.co.uk/16391-brine-shrimp