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Tales of crustacean and human development

pumice2-wp

Story & photo Mary Gardner

Our recent storms have origins in tropic seas far away. In their passing, they leave on the beach nuggets of news. Nature being as it is, the news is in code. I scrutinise the pumice stones. Some are as small as fingernails and others as large as the palm of my hand (8cm). Although most pumice eventually takes on water and sinks, these ones still hold enough gas in some pockets so they float. Likely, they rafted across the Pacific from Fiji to Vanuatu to New Caledonia and came south from the Coral Sea. Along the way, they picked up marine hitchhikers. The ones in my hand carry goose barnacles (Lepas species). They’re sized by the length of the outer edges of their shells. With the longest at 2–3cm, I guess these could be at least a year old. Anyone can figure this by considering the rate of their development. That’s development in the original sense of the word as ‘unfolding’. This meaning is still used by biologists to describe the expected stages of growth experienced by living beings from birth to maturity.

The development of goose barnacles from egg to adult is now well known. In the 1830s, zoologists Thompson and Burmeister traced the pathway from the free-floating larvae to the fixed adult. They showed that barnacles were most similar to crabs and lobsters. This led to its reclassification from Molluscs (clams and snails) to Crustaceans.

My prof used to describe them as shrimps with their heads glued to rocks. Their exoskeletons are reshaped, with hinged joints. They open these and wave their hairy legs around in the water to catch a meal of particles. They are hermaphrodites who use a long penis to cross-fertilise. A partner must be physically close enough for this to be successful. The eggs are incubated inside a pouch for a week. The young are released as swimmers who hunt out a place to settle down and develop into adults.

Two months is the time hatchlings need to grow to 10mm in size. Imagine being so small, full of life, hunting food and deciding where to go within the immense opportunity of the open ocean. Taking advantage of the by-products of volcanoes. Making use of immense weather systems and currents. Growing through six or seven stages.

From the 13th to the 17th century in Europe, their development was understood very differently. The drifting sea creatures were known as the embryo stage of a species of goose called a ‘barnacle’. No one ever saw these birds nest or grow up. But every year, they flew away over the unknown sea, so development must happen somewhere over there. As a barnacle goose was a special type of fish, Christians were permitted to eat it on Fridays and during Lent.

Understanding the course of biological development is hard won knowledge. In the late 19th–early 20th century, this concept was co-opted to illustrate changes over time in real estate and human societies. But now in the 21st century, such changes are clearly seen as quite unlike the growth of juveniles to adults. The changes of land or civilisation do not follow inevitably from ‘primitive’ to ‘rural’ to ‘urban’ or ‘urbane’. A town like Byron or Mullumbimby is not fated to become a copy of Surfers Paradise, nor has it an innate drive to become like Sydney or Brisbane. This realisation is also hard won but gives power to community choice. How about a new word for what human enterprise creates as it follows human desires? Leave ‘development’ alone, to gasp in wonder about barnacles and other species.


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