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| Katrina Refior and Axl the Dog |
A walk around Fort Abercrombie State Historical Park is a chance to observe mutualistic relationships first hand. They turn out to be everywhere. Flowers in the Wildflower Meadow are pollinated by nectar- and pollen-seeking bees and flies. Old Man's Beard, hanging down from the spruce branches, is a lichen-sort of a combination organism formed from the mutualistic relationship between an alga and a fungus.
One of the most interesting and unsung, even obscure, mutualisms I've come across is one we observe in our tidepooling forays along Monashka Bay. The tidepools there have the greatest sea star diversity I've ever encountered. Our sea stars range from the giant sunflower stars to miniature 6-rayed stars to Kodiak's own postcard sea star-the brilliant scarlet blood stars.
Sea stars have hundreds of suction cup-equipped tube feet on the underside of the body. Tube feet are what they use both to move and feed, the suction cups attaching to the prey and manipulating it to the center mouth opening. Feeding consists of indelicately projecting the entire stomach through the mouth, surrounding the unfortunate bivalve or snail with it, digesting the meal outside of the body, and finally bringing the stomach (which surrounds what is now an organic soup) back in through the mouth. Sea stars don't use napkins, so bits of half-digested food swirl around the area where the everted stomach and the tube feet are doing their work.
It doesn't take long for tidepoolers to notice that some of the most common sea stars have segmented scaleworms firmly nestled among the tube feet, or crawling up and down along the underside of the rays. The pattern seems just too consistent to be an accidental encounter between worm and sea star. This relationship turns out to be another example of mutualism. Scaleworms and sea stars of particular species associate together. The advantage to the scaleworm is evident: it gains habitat, protection, and access to those tasty bits of food that the sea star lets cascade out of its mouth and stomach. The sea star gains from the relationship, as well. Scaleworms keep the rows of tube feet free of debris or undigested food, and they even play a protective role. Sea stars are preyed upon by some snails and even by other sea stars. The scaleworm will move over to the area being attacked and nip the predator repeatedly with a pair of sharp jaws.
Where did this relationship come from and where is it going? Was it initially a chance encounter that ended up providing benefits for both participants? Could it have been the beginnings of parasitism that turned out to be even more beneficial to those worms that provided advantages to the host? Will one of the participants become more efficient in this relationship, perhaps at the expense of the other, causing this mutualism to slide into a parasitic or predatory relationship?
Cooperative relationships between different species take many forms. The relationships are also capable of changing. Perhaps a curious and hungry scaleworm will sample a tube foot or two. Maybe our pickup truck dogs will give us that needed companionship, but only if we let them start using our credit cards. Kodiak shows us some fine examples of mutualism, but describing those associations is only the first step in addressing an array of intriguing biological questions.
David A. Evans, Summer Naturalist
Fort Abercrombie State Historical Park.
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