She Studies Seashells

G'day! or should I say Bonjour?!

My name's Liza Roger, and I'm a new addition this year to the Ocean Acidification Pteropod Study team. I am currently doing research for my PhD at the University of Western Australia in Perth, under the supervision of Dr Malcolm McCulloch and Dr Julie Trotter at the School of Earth and Environment. I performed part of my undergrad studies in France (I'm French) and finished in Australia. After I graduated, for my Master's degree I studied changes in modern pteropod shells (size, thickness and porosity) collected from regions off the northwest and northeast coasts of Australia over a 45-year-period.

Map of Australia showing my Master's sampling locations (Scott Reef, Rowley Shoals, Browse Island, North West Cape, Lizard Island, Whitsunday Islands, and Heron Island)

My research results suggested that pteropods off Northern Australia (tropical pteropods!) may have been influenced by changes in seawater chemistry over the past few decades, particularly a decrease in the availability of the carbonate ion that pteropods need to produce their aragonitic shells (i.e., a decline in the aragonite saturation state). While most pteropod studies concentrate on polar and sub-polar species I seem to be the 'odd-one' studying tropical pteropods. Pteropods are distributed circumglobally in all the world's oceans though and I strongly belive tropical pteropods should not be over-looked.

Soooo....
 

What am I doing in the Northeast Pacific then?

I met part of the OAPS team in 2011 at a zooplankton conference in Chile and our common interest in pteropods brought us together again when they invited me to join them on this research cruise. The team/lab (ARC Centre of Excellence for Coral Reef Studies) I am part of back in Australia focuses on calcification and concentrates on developing new analytical methods intended to improve the understanding of the impacts of global climate change on the marine environment. Most people in my lab work on corals and calcifying algae so, again, I am the 'odd-one' working on planktonic molluscs!

High magnification images of pteropod shells made with a Scanning Electron Microscope. Top image is of a fracture along the surface of the shell of a specimen of Creseis acicula showing how the shell is made of two crossed lamellae (i.e., layers). Bottom image is of the dorsal surface of the shell of a Diacavolinia longirostris showing the ribbed growth-line patterns.

So, here I am, on the R/V New Horizon, collecting pteropods to study their calcification. Up until now, scientists have studied the dissolution of pteropod shells under different environmental conditions but the actual production of the shells (i.e., calcification) seems to have been a little neglected; I hope to shed some light on the topic...

Here are a few of the questions I am trying to answer:

• What is the chemical composition of pteropod calcium carbonate shells?
• Do pteropods regulate the pH of the fluid  they use to calcify their shells (internal or extra-cellular fluid)?
• If so, do they up-regulate pH? Down-regulate? Or something else?
• In terms of shell calcification, are there differences between species? Ocean basins? Polar vs tropical?

A Limacina helicina shell, dried and ready for analysis back home. Photo L. Roger.

So far we have already caught abundant Limacina helicina in our Reeve net and I have preserved a number of them to analyze once I'm back home in Australia. On that note, I hope to get back to you later in the cruise with some answers and in the mean time we steam towards new horizons...

Liza Roger