I recently had a friend ask what it was that could make you so itchy after swimming in the ocean in Maine. Aside from the salt that can dry on your skin and make you feel a bit crusty, there are actually some critters living in the water can irritate your skin. If you’ve ever looked at seawater under a microscope, you’ve likely noticed that there are a lot of things wiggling around in it. Just like the bugs (or bug-like creatures) that irritate us on land, there are little bugs that can irritate us in the water also.
While it is difficult to identify exactly what caused my friend’s itchy reaction, I can identify some likely culprits. The first is a sand flea. These are quite common and live in dead plant material found in wet sand on beaches. Some people call these sand “lice” but they are not lice at all. They are fleas. One difference between these two wingless insects is that fleas can jump from one host to another. There are lice that live in the sea, but these are parasites that live on fish skin. They are crawlers rather than jumpers. Sea lice can cause major problems, as they have in salmon farms where they feed on the mucus-y layer that protects fish skin, leaving them prone to infection. Also, lice can only live a day or two without a host – fleas up to 100 days without host. That’s why sand fleas can live on washed up seaweed or in wet sand.
Sand flea bites can be nasty. The bites are often in clusters and leave small, red bumps, sometimes with a little ring around them – much like a fleabite you might see on your pet. They are concentrated around your feet and ankles – about as high as a flea can jump – unless you’ve been sitting in the sand, or putting seaweed in your hair, as my girls like to do. Sand flea bites are itchy because of the flea’s saliva. The fleas inject their saliva into you to get your blood flowing and the chemical that does this causes a reaction. Not a fun thing to imagine when you are feeling itchy!
Aside from sand fleas, the other marine creatures that can make you itchy don’t seem so nasty. These are tiny larvae – the babies of creatures like jellyfish or crabs that are floating in the water column before settling and growing into adults. To avoid getting eaten, they have chemicals in their bodies that make them irritating to creatures that come in contact with them. These larvae can sometimes be a big problem because they periodically occur in such large numbers. That’s because, when marine animals spawn, they release millions of eggs at a time into the water at one time. Those develop into millions of larvae that can be concentrated in certain areas since they are planktonic (meaning they drift, not swim). So, with ocean currents going just the right way, these larvae can all end up in the same place – an occurrence that can cause waves of reactions among many people all going to the same beach. The reaction to these larvae is sometimes called “bathers eruption”. The reaction usually occurs under a swimsuit or wet clothes where the larvae get trapped and appears as a series of red bumps (different than the more distinct clusters from flea bites). If the reaction is severe, these bumps can all run together into a big red itchy patch.
While it may at first seem icky or uncomfortable to think of all of these creatures sharing the waters that we swim in, I think it is pretty neat to know how much life there is in the water that we can’t even see.
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