A fascinating transformation is happening in Norway’s Sognefjord. A barnacle called Anelasma squalicola has made a dramatic leap from filter feeding to parasitism, latching onto deep-sea sharks. Instead of sifting plankton from the water, these barnacles now insert modified stalks into their shark hosts, drawing nutrition directly from their flesh. This shift shows that even ordinary sea creatures can undergo extraordinary changes.
Henrik Glenner from the University of Bergen studied these barnacles closely. The unusual growths he found attached to lantern sharks revealed that the barnacles had transformed their anatomy. They still have the feathery appendages typical of their kind, but these no longer capture food. Instead, the embedded stalk provides all the nutrition they need, marking a significant break from their previous way of life. This is a rare example of evolutionary change witnessed in real time, rather than inferred from fossils.
Evidence gathered through DNA analysis shows that Anelasma squalicola evolved from traditional barnacles, not from pre-existing parasites. This insight reveals how a free-living creature can adapt to a parasitic lifestyle, offering a glimpse into nature’s adaptability.
In Sognefjord, lantern sharks like Etmopterus spinax live a few hundred to over three thousand feet below the surface. Researchers found a surprising concentration of sharks bearing these barnacles. The unique conditions in this deep-water habitat may support the barnacle’s survival and spread.
While barnacles have been around for millions of years, significant shifts in their feeding strategies are rarely seen. Glenner notes that past fossil evidence suggests that major lifestyle changes can happen quickly in evolutionary terms, often leaving little trace.
Once attached to a shark, the barnacle’s root-like structure absorbs nutrients from the shark’s tissues, rather than from the water. Microscopic studies indicate that while they still possess a digestive tract, it often remains empty as they rely on blood for sustenance. This adaptation allows them to thrive even in turbulent water.
While black lantern sharks seem to tolerate parasites, the barnacle’s presence could be detrimental, diverting energy away from growth and reproduction. Interestingly, sharks have coexisted with various parasites for hundreds of millions of years, making this barnacle-host relationship a recent development.
Looking ahead, researchers see two potential futures for this unusual barnacle. It may either fade away or expand its range to other oceans. Limited reports from regions like Greenland suggest it remains rare outside Norway, but continued monitoring will shed light on its future.
This case offers an incredible opportunity to witness evolution in action. The barnacle’s switch from a plankton-filtering past to a blood-feeding future showcases how life can adapt in surprising ways.
The full study can be found in the Zoological Journal of the Linnean Society here.
