So you think barnacles are dull ? Think again , says science correspondent Karen Boswarva
OCEANSCIENCE
Zombie barnacles !
So you think barnacles are dull ? Think again , says science correspondent Karen Boswarva
Barnacles are an often-overlooked group of animals , unless you ’ re gloveless or walking barefoot on a rocky shore – ouch ! They are neither flamboyant or brightly coloured , and rarely scream LOOK AT ME , but have you ever stopped to gaze at their gentle , rhythmic feeding arms ? I urge you to do so . They have quite the hypnotising and calming effect , opening their diamond shaped trap door to rasp for tiny food particles as they float by .
Globally , there are more than 1,400 species of this unassuming member of the crab family . You wouldn ’ t think it , but they are in fact crustaceans and display the same characteristics as crabs , lobsters and prawns . They start life as a small larva drifting in the currents . The big difference
A parasitical barnacle on a female swimming crab
“ Imagine trying to swim with a big bag of rocks stuck to your back !”
is that most will eventually settle on a stationary surface such as a rock or a wreck and secrete a hard protective shell made of calcium .
Those preferring the nomad lifestyle grow long neck-like appendages and wander the world ’ s oceans attached to flotsam and jetsam . Others will grow massive , hitching a ride on the backs of sea turtles and whales , sometimes to the detriment of the animal . Sea turtles can be plagued by the weight of barnacles growing on their shells . The size , shape , and quantity of barnacles causes extra drag that affects their ability to swim properly . Imagine trying to swim with a big bag of rocks stuck to your back ! Sometimes , when the animals are in great distress , humans will intervene to temporarily remove this weighted burden .
Then there are barnacles that have a darker , more sinister side . The crab hacker barnacle Sacculina carcini is a species of parasitic barnacle found throughout the UK . It infects swimming crabs , most commonly the shore crab Carcinus maenas , changing both their behaviour and physiology , rendering the crabs sterile in the process .
This zombie attack occurs in two stages . Stage 1 : the female larvae called kentrogen infects the crabs ’ tissues . Finger-like rootlets form in the crab ’ s body , including the reproductive system . The rootlets absorb nutrients and start to grow . Stage two : up to 36 months later a large creamy-yellow sac will emerge from the underside of the crab . The sac contains developing eggs , which can then be fertilised by male crab hacker larvae called cyprids that are floating around in the water . The cyprids fertilise the eggs and the larvae – called nauplii – develop in the sac until they are ready to be released and start their own search for a host .
Unfortunately , this partnership offers no benefit to the crab . Infected male shore crabs can no longer produce sperm . The abdomen widens , making them look and act like females . Infected female shore crabs will stop producing eggs but behave like they are carrying eggs . The infected crabs are unable to moult , become more prone to infection and are therefore unlikely to survive once the parasitic larvae are released . Crabs that do survive then play host to another cycle of infestation . The old sac will deteriorate and form a scar on the abdomen before a new sac emerges 36 months later .
Infections are thought to be quite common . Fishermen will sometimes find these parasitic barnacles when they check their catch . You may find them too when rock pooling or crabbing .
When you ’ re diving , look out for crab behaviour . Crabs that are ‘ in berry ’ ( with eggs ) will often raise their legs up , lifting their abdomen off the seabed . This allows fresh sea water to flow over their brood and for you to do a quick scan for these creepy stowaways . Bet you ’ ll never look at crabs ( or barnacles ) the same way again . �
20