Tide pool creatures are not the best at social distancing. One particularly strange species is particularly bad at this practice. They gather in large numbers and like to stick to each other as well as just about everything else. You may not have ever noticed them before because, although they may be there in great numbers, they are perfectly camouflaged among thread-like seaweeds and other tiny plants and animals. Perhaps that’s why they are sometimes called “ghost” shrimp. More commonly, they are known as skeleton shrimp.
I first saw skeleton shrimp on aquaculture cages when I was diving off the coast of New Hampshire in graduate school. What looked like a boring piece of netting suddenly appeared to be moving – and it wasn’t just the water moving or a lack of Oxygen to the brain. There were tiny creatures waving their cartoon-like appendages covering nearly every surface.
These tiny translucent shrimp, or Caprellids, are amphipods. This means that they have bodies that are flattened from side to side versus from top to bottom (think of a beach hopper versus a roly-poly). They are also crustaceans, which means that they have segmented bodies – like lobsters. They have three basic sections like many insects (which are closely related to crustaceans), but in skeleton shrimp, the body section is broken into seven long segments. This reminds me of a giraffe that only has seven neck bones, but each one is so long that the neck can be up to six feet in total. The total length of a skeleton shrimp, however, isn’t more than a single inch.
Somehow, in all the time I have spent tide pooling I had not noticed them there until recently. They really are perfectly disguised. Perhaps that is why they are found throughout the world’s oceans. They also have some amazing adaptations like their ability to capture tiny larvae with their “jaws” like a preying mantis in wait, or to filter-feed plankton from the water with their delicate mouthparts. The fact that they congregate in groups of hundreds provides each one some protection from fishy predators. They also stick to just about anything, so the world is their habitat. If you see one waving around, just put your finger near it and you are likely to have a little inchworm-like friend to examine more closely. You can watch them try to move by bending and straightening their bodies, a motion that helps propel them through the water. To me, they look a bit like those dancing balloons that are used to advertise along the side of the road.
While harmless to us, skeleton shrimp aren’t always nice to each other. The females sometimes inject venom into the males using their sharp jaw part after mating. They can also be harmful to native species. There are many types of skeleton shrimp and they aren’t all supposed to be living in Maine. Because they are so sticky and gather in numbers, they can travel easily from one ocean to another. This can happen through ships or seafood that travels across the world. One species, Caprella mutica, originally lived in the Sea of Japan, but is now an invasive species on our coast.
We are all wary of products coming from far away right now because of the pandemic, but there are plenty of reasons under a variety of conditions to be careful about transporting goods across the ocean, including the introduction of species that are not native to Maine. They can compete for resources like food or habitat and change the balance of the ecosystem. Some are more of a problem than others- skeleton shrimp fall on the less problematic end of the spectrum.
During this time, we all have an opportunity to learn more about how connected we are and about how the ways in which we live can have impacts far overseas. And if you are feeling lonely during this time of isolation, you can make a quick friend by finding one of these odd little creatures that are not afraid of getting close to you.
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