Miss Viola Warter

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Research interests

https://viowarter.wordpress.com/

 

Latest research activities:

Giant Clam (Tridacna) Culture at the Hebrew University of Jerusalem, Israel

Giant clams (family Cardiidae, subfamily Tridacninae, genus Tridacna) are the largest living bivalve molluscs. For some of the species shell growth is so high that it is possible to distinguish microscopically visible daily growth increments (5 - 30 µm) within their aragonite shells. We have most recently used highest resolution LA-ICPMS analysis (laser ablation inductively-coupled-plasma mass spectrometry) to resolve daily cycles in modern and fossil Miocene Tridacna spp., not only for Sr/Ca and Mg/Ca, but also B/Ca and Ba/Ca ratios.

Reliable interpretation of these trace elemental proxy records (Mg/Ca-temperature, Sr/Ca-temperature/light availability, B/Ca-pH, Ba/Ca-primary productivity) is however hampered by the complexity of which environmental  and physiological/biochemical processes (vital effects) exert control over shell growth and/or trace elemental incorporation into the shell structure. In order to interpret daily environmental changes recorded by trace elemental ratios, the various controls such as temperature and light levels need to be disentangled. Control over these external environmental factors is not given under natural conditions, but within the controlled conditions of an aquarium. With this in mind, our idea to culture Tridacna shells was born and we got in contact with Prof Jonathan Erez, the world-leading expert on biomineralization and laboratory culturing, from the Hebrew University in Jerusalem, who fortunately agreed to work with us.

I also was very fortunate and grateful to receive the Kirsty Brown Memorial Fund and funding through the University of London Grants for PGR study, which covered the costs for my five 5 week stay during February and March 2015 in Jerusalem and enabled me to perform the culturing experiments at the Earth Sciences department of the Hebrew University:

Juvenile Tridacna crocea were purchased from an aquarium supplier in Tel Aviv. The original sampling location of the organisms cannot be reconstructed; however we got the information that these clams are derived from a Tridacna culturing site off the coast of Vietnam. Before starting the experiment, the juvenile clams were left to acclimatize at the coral reef aquarium at the Earth Sciences department for several weeks.

The initial experiment focused on calibrating the control of temperature and light over the growth rate. We used an isotopic spike enriched in 135Ba to label the shell parts grown under culture conditions. Each individual was cultured separately in a 700 ml volume flow-through chamber. The chambers were airtight sealed (via an O-ring) and headspace free, to prevent air exchange between chamber seawater and the surrounding atmosphere. A peristaltic pump fed each chamber with the Ba-spiked ‘reservoir seawater’. Each chamber and thus each organism received the same reservoir seawater. The chambers were magnetically stirred and placed into constant (± 0.3 °C) temperature baths. Four different temperature regimes of 23, 25, 27 and 29 °C were created, each organism was exposed to a diurnal light cycles of (12 hours light and 12 hours darkness) using metal halogen light sources. The 27 °C regime was chosen to perform additionally light experiments. Shading was simulated using dark clothes with one of the chambers receiving 45% of the light and another one receiving only 15% of compared to the ‘normal’ light regime. We also performed short-term experiments over a period of three days which included culture under full/permanent light conditions and complete darkness and the labelling of one specimen using Calcein, a fluorescent dye, which is incorporated into the shell structure and visible under fluorescent light.

Seawater samples of the reservoir seawater and the ‘consumed seawater’ were taken each day and the DO, pH and alkalinity were measured. The delta alkalinity (alkalinity of the reservoir seawater minus alkalinity of the consumed seawater) enables to assess the calcification rate of each organism from which it was clear that there is a positive relation between temperature and growth rate and light and growth rate.

All culture experiments were successful; none of the specimen died during the experiment, but all had to be sacrificed after termination of the culture period. The shells were cleaned in sodium hypochloride to remove organic parts and the valves cut in half. At Royal Holloway thin sections of all nine shells were prepared and have been analysed recently via LA-ICPMS. Preliminary results reveal that the labelling with the 135Ba isotopic spike was successful. Detailed evaluation of the data still needs to be carried out.

From the experiment it became clear that Tridacna spp. are ideal culture organisms. They do survive for several weeks without food and can tolerate extreme conditions (e.g. complete darkness, low pHs and solitude). For me the trip to Israel was an unforgettable experience, not only because it was exciting to work on living animals, but also because Jonathan and his research group made me feel sincerely welcome in their beautiful country.


 

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