Despite being known for their rubbery blobs of color and their tendency to squirt water from a headfirst position, sea squirts are actually very advanced animals that have close ties to humans on the evolutionary scale. They are also the source of a powerful anti-tumor drug, and scientists hope to soon make it more available to patients.
Sea squirts are found on almost every continent and in nearly all ocean waters. In addition to being a source of curiosity, these creatures play a vital role in marine ecosystems. They help maintain the health of the ocean by filtering nutrients from the water and then “squirting” them out of their anuses, similar to the way plants do. This process is important in creating a healthy balance between the ocean’s various organisms, as well as maintaining the health of human food chains.
Researchers use sea squirts (also called ascidians) to study how the innate immune system develops in animals, including humans. They have a special property that allows them to rapidly examine what happens in the guts of the animals, which are constantly populated by microbes that settle there from the surrounding seawater. Using this ability, USF scientist Bob Zeller has discovered how a specific group of bacteria affects the production and settlement of an immune molecule that binds to and kills the bacteria responsible for colitis in people. His work has implications for how the body’s innate immune system responds to different strains of intestinal bacteria and could lead to new treatments for inflammatory bowel disease.
Sea squirts have other interesting properties as well, including the ability to fuse with their own species. While this may seem like a negative thing, it actually helps the sea squirts find their way around their habitats in high-density areas such as marinas and intertidal coves. This fusing is accomplished by mobile stem cells that transplant themselves between the two fused individuals and, in the end, one set overpowers the other, essentially taking over the body of the loser.
These amazing animals are also notorious for “eating their own brains.” While this may sound shocking, it is not as dramatic as it sounds. These hermaphrodites, or animals with both male and female functional reproductive organs, are born as free-swimming larvae that look a lot like tadpoles. After the larvae grow into adults, they search for a permanent place to live the rest of their lives. Once they find the right spot, they attach themselves with a sucker located on their heads. The tail, which contains the notochord and nerve cord, is then absorbed and eventually disappears.
These little creatures are hardy, surviving even the coldest waters and deepest depths of the ocean. But they can’t escape the effects of climate change, which is causing nutrient-rich sediment to accumulate in the ocean. This can affect the phytoplankton that are their main food source, as well as clog their gills and slow down their filtering abilities.