Baffled at the Beach

Beachwalkers at South Durras were puzzled and amused by the strange things that washed ashore recently.  Carolyn Morey, of Bay and Beyond Kayaks, sent some photos to Nature Coast Marine Group to see if anyone knew what they were.

Despite ribald jokes and suggestions, the things turned out to be fascinating marine creatures, gelatinous colonial animals called Pyrosoma atlanticum.  They can grow to 60cm long and 6cm wide although the ones at Durras were smaller. The name “Pyrosoma” comes from the Greek meaning “fire body” because they often bioluminesce.  As for the “atlanticum” part of the name that is rather misleading as they are found in many temperate oceans as well as the Atlantic, including the seas all around the southern half of Australia. However, as they usually live in deeper water they are not commonly stranded on beaches.

A pyrosome is a colony in the shape of a tube wider at one end and closed at the other and is made up of many cloned individual animals (zooids), each about 8mm long.  They are closely related to animals with backbones because the animals have a notochord as do their solitary relatives the sea squirts like cunjevoi.

These primitive looking organisms could teach us a thing or two.  The individuals all work together in harmony.  Tiny hair-like projections, called cilia, on the inner surface of each zooid beat in unison to draw in sea water through gill slits.  This not only allows them to trap their planktonic food in mucus but also makes a current that propels the colony through the water.

While Pyrosoma spends the day at depths, sometimes as far as 800m down, the colonies are known to come nearer the surface at night.  No mean feat for swimming by cilia action!  It is thought that their bioluminescence could attract plankton when the sun has set.

Nature Coast Marine Group is always interested in the marine life of our region and the ways you and your family are enjoying the Batemans Marine Park.  You can visit their website at www.ncmg.org or email info@ncmg.org.


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