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Book Review

Barnacles as a Forensic Tool

Pirtle D., Magni P.A., Reinecke G.W., Dadour I.R. Barnacle colonization of shoes: Evaluation of a novel approach to estimate the time spent in water of human remains. Forensic Science International 294:1-9. 2019. doi: https://doi.org/10.1016/j.forsciint.2018.10.024

Compared to crabs or lobsters, barnacles are among the more underrated crustaceans in our oceans. They aren’t tasty to eat and often go unnoticed until they’re attached to the sides of your boat. But these small, sessile creatures aren’t only thought of as marine pests. In fact, our law enforcement has begun examining them as evidence for determining the time and location of marine related crimes.

Figure 1. Barnacle remains on a shell. Source: Wikimedia Commons

The life of a bay barnacle

So how does a small harmless barnacle have a run-in with the police? Let’s take a look at their lifestyle. Up to eight months after they are born, juvenile barnacle larvae begin to settle on hard substrates. These include rocks, ships, or sometimes even submerged human remains! After attaching themselves, they begin to grow at rates dependent on their environment (salinity, food, temperature). Their size thus makes it easy to determine their approximate age. One more thing. If there is a suitable place to settle, barnacles will find it quickly. And they’ll tell their friends. So essentially, if you can count and determine the ages of barnacles, you can figure out how long an object has been in the ocean.

Pirtle’s team has begun to use evidence from barnacles in just this way. To figure out how long a human body has been in the ocean, they look at the settled barnacles. To make their study a bit less grim, they simply looked at barnacle settlement on shoes, since recovered bodies are often clothed and accompanied by shoes.

Figure 2. Patent leather shoes (example of what Pirtle et al. placed into the ocean). Source: Wikimedia Commons

Dumping shoes into the Boston Harbor

The method was simple: place 64 sport shoes and 64 patent leather shoes into the Boston Harbor at a depth of 8-10 meters. Every week, the team randomly selected certain shoes and characterized the barnacles that decided to make the shoes their home. After eight months of submersion, the shoes surfaced for good.

Figure 3. Boston Harbor. Source: Wikimedia Commons

Barnacles are picky when it comes to shoes

Thirty days into the study, the scientists noticed barnacle recruitment. Only one type of barnacle settled on the shoes: Amphibalanus improvisus, or the bay barnacle. They settled on nearly every shoe, just in different abundances. It turns out that like humans, barnacles are picky when it comes to the type of shoe. They preferred to congregate on the smooth patent leather instead of the rough sport shoe material. This means that forensics investigators can look at many different types of shoes for barnacle growth.

When the team looked at growth rate, they found that the barnacles grew faster in the warmer summer months than in the colder seasons. With this information, investigators can measure barnacle diameters and infer their ages based on the season. So, with this growth rate and a little bit of math, people can begin to figure out the time of death. Just add about 30 days (time until first settlement) to the age of the oldest barnacle and you’ve got your minimum postmortem interval (PMI).

Without pioneer species like barnacles, investigators would be left guessing how long bodies have been in the ocean. Of course, we hope to never find human remains in the ocean, but in the case that we do, barnacles may be the best indicator of PMI. Or, on a lighter note, if you find a shoe in the ocean and wonder how long it has been there, just count and measure the barnacles to find out!

 

 

 

Constance is a graduate student at the University of Guam studying coral genetics. She also paints murals integrating art and science at various aquariums and scientific institutions (IG: @coco.paints).

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