Barnacles – travelling the seas as stowaways

by Heike Pahlow

Text & Illustration: Heike Pahlow, Photos: Mario Müller

While a boisterous Pilot Whale caught our eye during a whale-watching trip – when browsing the photos we became aware of a much smaller but not less interesting creature: a barnacle.

Being responsible for firmm’s website for 20 years, every now and then we aim for our personal encounter with the whales and dolphins in the Strait of Gibraltar. So again this year in June, we travelled to the southern tip of Spain and already on our first trip, we were pampered with sightings of dolphins, a Sperm Whale and a group of Pilot Whales.

One of the Pilot Whales caught everyone’s attention by constantly slapping its tail on the water. Immediately, a lively discussion started among the guests on our boat: Is the whale playful? Are we observing a mating ritual? Do they feel disturbed by us? Due to firmm’s commitment to respectful whale watching, we couldn’t really have been the bother. Our boat had stopped long before the whales came close. They could have given us a wide berth, but instead were heading towards us … with the little “splasher” right in the middle. Even the firmm crew didn’t know how to interpret the whale’s behaviour, though they have been studying these animals for years. “Tail slapping is not a typical Pilot Whale behaviour,“ the foundation’s president Katharina Heyer told us.

What’s dangling from that fluke?

When browsing the photos, we noticed something hanging from the whale’s fluke. Could that have been the reason for its strange behaviour? Jörn Selling, firmm’s marine biologist, identified the “thing” as a barnacle. Was he kidding us? We knew barnacle shells from rocks by the sea and also from Grey Whales and Humpbacks (e.g. Coronula diadema). What we had seen on the Pilot Whale though, did not have shells and looked more like a leech. We got curious …

What are barnacles?

We learned that barnacles are crustaceans (just like crabs and shrimps). They come in many different shapes and sizes. As larvae they float in the water until they attach themselves to a surface. Some species prefer rocks in intertidal zones, others attach to flotsam, ships or even animals. Most species then develop calcareous plates (the carapax) to protect the rest of their bodies, although there are also stalked barnacles with smaller or no shells at all.

Whale barnacles attach to whales. Xenobalanus globicipitis (the one on the Pilot Whale) are typically found on fins and feed on plankton while being chauffeured around. Like most barnacles, they are not parasites, still they can hinder their hosts. Severe infestation with Xenobalanus globicipitis is said to be an indication of a weakened immune system as you can read in firmm’s report "Epidermal conditions, lesions and malformations in cetaceans of the Strait of Gibraltar".

different barnacle species found on whales

Coronula diadema: usually found on baleen whales
Xenobalanus globicipitis: attaches to fins of toothed whales
Conchoderma auritum: specialised on attaching to other barnacles

By the way, there are even barnacles specialised in attaching to other barnacles, for example the rabbit ear barnacle Conchoderma auritum which is often found on Coronula diadema. In 2016, firmm spotted these two species on a Humpback Whale in the Strait of Gibraltar (last two pictures under humpback whale).

Back to our Pilot Whale though. We cannot say for sure whether it was really the barnacles that made him go nuts. But without the fuss we’d probably never taken notice of these strange creatures. Having learned about them, we found even more pictures of those stowaways travelling on whales and dolphins, a detail we’d never payed attention to before.

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