Fossil Friday #3 – Encrusters!

Today’s Fossil Friday is a sneak peak into the little world of encrusters.  Encrusters, known in the scientific community as epibionts, or sclerobionts, are organisms which attach and live on other organisms.  In modern oceans, the most obvious example of encrusters, or epibionts, are barnacles (see picture below).  Encrusters need a hard surface on which to live, and so other organisms often make great substrates.  The organism acting as the substrate for the encruster is called the host.

Encrusting organisms on a scallop host

Encrustation is a great way to study biotic interactions.  We often think of encrusters as fowling organisms (things that clog up pipes or ruin the sides of ships), and it is true that they can be very detrimental (parasitic) to hosts.  For example, if your mouth parts become clogged or permanently closed from an encruster, you are likely in big-time trouble.  Sometimes the weight and loss of streamlined shape from lots of encrusters can also seriously harm a host.  As a potential solution, some organisms can prevent encrustation by having soft surfaces or a mucus lining to prevent encruster attachment.

A very unhappy host (sea turtle).  Image credit:

However, some hosts, like decorator crabs, actively attract epibionts as a means of camouflage.  Hosts might not be visible to predators if covered in encrusters, and hosts might not even smell like anything tasty to their predators.  A camouflage benefit to the host can lead to strong mutualisms, or even co-evolution of epibionts and hosts.

A very happy host.  Can you see the decorator crab? No? That’s what it wants.  Image credit:

Fossil encrusters (sclerobionts) and their hosts can be used to study how close biotic interactions develop over time.  For example, a lot of the work done in our lab looks for associations between encrusters and hosts that coincide with a decrease in predation rates.  If we are able to find that an increase in encrusters = a decrease in predation, that is pretty good evidence that the encrusters are acting as camouflage for the hosts.  However, I have also seen cases where the encruster clearly killed the host because it encrusted over its feeding parts or openings.  Having encrusters is a bit of a dangerous game.

The Champion 4
Sclerobionts encrusting a brachiopod host

Encrusters will always hold a special place in my heart, as they were my introduction to real research when I was an undergrad, and they were a large part of my MSc thesis.  Even now, I still love popping a fossil under a microscope and discovering complex biology occurring at an entirely different scale.  It’s like a little scavenger hunt.

Plus, there is something very impressive about tiny critters being preserved for hundreds of millions of years…


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