Discovering some of the tiniest critters on earth

When she left Nebraska, USA, at the beginning of this year, Southern Cross University Masters student Marisa Gibb had no idea that her research would lead to the study of new kinds of microscopic animals.

But after months of painstakingly preparing sea-bed samples from two of Australia’s southern-most coral reefs for imaging by the University’s scanning electron microscope, Marisa has unearthed the exciting world of some of the tiniest critters known on the planet - meiofauna. Meiofauna are animals that are small enough to live in the water that exists in the spaces between grains of sand.

There are weird worms with multiple snake-like tentacles coming out of their mouth, armour-plated shellfish and hairy-legged mites – and they are all hundreds of times smaller than a grain of sand.

The animals have been found in sea-bed samples taken from the two most southern coral atolls in the world, Elizabeth and Middleton Reefs, off Lord Howe Island on Australia’s east coast.

Marisa’s Masters project has been a comparative study of the meiofauna found on these reefs and those found on the nearest northern parts of the Great Barrier Reef 900kms away.

“I have found that there are species common to both geographical areas and species that are unique to both areas,” Marisa said.

“Meiofauna are important because they devour things like bacteria and fungi that live in sediment. They also help to break down organic matter found in pollution from agricultural and stormwater runoff, and sewage. Meiofauna act as environmental monitors and provide food for small or juvenile fish and invertebrates, which supports other life through the food chain.

“Despite their importance, there are few in-depth studies on meiofauna and classification of these organisms is rarely specified further than their ‘class’. Their abundance and dispersal patterns are important to show how other food webs are affected. It may even turn out that some of the animals I have found have not been classified before.”

Marisa was able to look at the small organisms using the scanning electron microscope (SEM) within the School of Environmental Science and Management.

“I had no idea exactly what the SEM would find in my samples,” she said. “While most of the samples I looked at could be viewed using a conventional light microscope, some of the specimens were so small that they required the use of the SEM which can image specimens up to 60,000 times in magnification.

“Once I had the samples under the SEM, I could clearly see the tiny structures that the organisms use to feed with. They have highly adapted structures for feeding and moving about and the SEM allowed me to see the detail of these structures.

“You spend months extracting the organic matter from samples of sand, shellfish and coral and preparing them on special slides for imaging, but you have no idea of exactly what you have captured.

“It is incredibly exciting when you finally get to see the magnified images. It is hard to imagine such perfection in creatures that are so small – they are not even a speck on a slide, being between .4 and .63 micrometres in diameter. Amazing as it seems, we know that there are even smaller critters out there.”

Marisa, who completed her Bachelor of Science at Loyola University of New Orleans, said she chose to undertake her Masters at Southern Cross University within the School of Environmental Science and Management, because of its outstanding reputation in marine and environmental sciences: “and because it was in Australia, near the rainforest and the sea – the three environments I have always wanted to experience.

“I also thought that getting my Masters here would give me access to a broader range of career pathways. My goal is to work on the ecological restoration of the Florida Everglades.”

Marisa said the highlights of her time at Southern Cross have been the numerous field trips associated with her studies and her trips to the region’s many beaches and rainforest areas. She returns to the US later this month.

Photo: A copepod - Order: Harpacticoida. Harpacticoids are often the most abundant components of meiofauna found in coarse sediments. Scanning electron microscope photo by Maxine Dawes.