Hitchhikers make life difficult for Antarctic sea spiders

Algae, barnacles, and more can grow on sea spiders in Antarctica. How cumbersome can these clingy companions get?

An Antarctic sea spider (Ammothea glacialis) about 6 inches long struggles under the weight of numerous stalked barnacles growing on top of it. These pesky protrusions are not only heavy, but they also increase the chance of the sea spider getting swept off its feet by strong ocean currents.

In the ocean, a wide variety of hitchhikers glom on to other animals. Barnacles are among the most prominent, but there are actually hundreds of creatures that pursue this life strategy. Generally, these freeloaders—which can be seen covering everything from whales to sea turtles to horseshoe crabs—are seen as harmless and even beneficial in some cases.

But what if they become a real drag?

Sea spiders, an enigmatic group of creatures found all over the world, are not immune to such hitchhikers. New research shows that organisms encrusted on or protruding from their surface can affect their movement and interfere with their breathing—since they lack lungs and gills and absorb oxygen through their exoskeleton.

The paper, published in the journal Marine Biology, found that larger hitchhikers such as stalked barnacles did in fact increase the drag experienced by Antarctic sea spiders by two to three times, which increased the energy necessary to walk. The increased surface area also created a Mary Poppins umbrella effect where the sea spiders were more prone to being swept off their feet by ocean currents.

Encrusting organisms such as algae and bryozoans, also known as moss animals, had the potential to greatly reduce breathing locally by up to 50 percent. However, total coverage on most sea spiders was not enough to substantially affect breathing overall.

The study, by a team of scientists led by Steven Lane, a lecturer at Loyola University Maryland, took a look at how three types of sea spiders in Antarctica fare...

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