The stars of Villefranche-Sur-Mer

29 November 2018

Joost Mansour and Andreas Norlin, MixITiN ESRs, report from the French Riviera

After weeks of drafting up experiments and planning for all possibilities, we found ourselves on the brink of autumn when the heat of an extraordinarily hot summer in Europe had started to fade. That is when our ‘mission’ and search for endosymbiotic Radiolaria in the bay of Villefranche-sur-mer, Côte d’Azur, began. These Radiolaria were to be the stars of our stable isotope experiments; we wanted to find out how these organisms take up carbon and nitrogen.

Enjoying a quick tour of Villefranche-sur-mer

On Sunday, September 16, four of us from Team MixITiN arrive in town, we were finally ready to start our first Radiolaria-mission. We start with a “lift” on the laboratory boat to the Observatoire Océanologique de Villefranche Sur Mer. After the necessary ‘corridor sessions’ of introductions and coffee (of course), we unpacked and set up our equipment for the experiments before venturing out to sea to find our Radiolarian stars. Armed with different sized plankton nets we were prepared for the unpredictable. Collodarian colonies can be seen by the naked eye. Right from the first tow we were thankful that Lady Luck was with us, offering us a good amount of Collodaria for our experimental set up.

Getting ready to set sail

Eager to get the experiments started, we sorted the Collodarian colonies into individual containers. We continued to check under stereomicroscopes what we had from our plankton sampling tows. We saw a plethora of different shapes but one shape dominated; small star shaped Acantharia with 20 thin spicules extruding from an often spherical cell-centre. You can see them here:

The sampling of the first day seemed to be a success. The Collodaria just needed some rest; after 24 hours we would be ready to set up our first experiment with these Radiolaria. In the meantime there were plenty of Acantharia for us to isolate; with great eagerness we started sorting and isolating the tiny stars of the sea.

Happy with our success on the first day we could not wait to start the next day. Unfortunately, this time Collodaria were very sparse. We shifted our focus to the smaller sized nets. We checked the new water samples to see what we had brought back – did we have the same Acantharia species as the previous day?! We did find some and so with some hope we went to check our cells from the previous day. Here again we met with disappointment – nearly all the acantharian cells were in bad shape. Fortunately, on the bright side, most of the Collodaria were still in great shape so we could begin our first experiment!

The first few days taught us a lot; we realised that we would not necessarily be able to “shop” for our preferred Collodarian species during our daily sampling in the bay. We learnt to identify the robust acantharian cells that could survive being handled versus the “delicate” acantharians which could not survive a night in the laboratory and which deteriorated overnight.

Our daily routine became very clear: (i) sampling on the boat; (ii) sorting and isolating the Collodaria (if any) into individual containers; (iii) identifying and sorting the smaller Acantharia until we had about 150 cells to set up our experiments. All our days went by like this.

Radiolaria are beautiful, single-celled protists, which occur in various fascinating shapes, it is very easy to get distracted from the sorting task. Some Acantharia look like small twinkling stars while others like little windows to the Milky Way or even small hovercrafts! But words cannot do justice to these fascinating oceanic greenhouses. Have a look at our photos – a picture can often say more than words:

The weekends gave us a tiny window of opportunity to explore the French riviera with diving, hiking and just enjoying the warm weather. We went hiking through the neighbouring area, and climbed up to the fortification that make up the old town of Éze.

The rewarding sights of some diving and climbing

By the end of our two weeks we had completed four experiments on two groups of Radiolaria. After our first successful ‘mission’, we packed up for the return trip, back to the grey and cloudy shores of Brittany. We left Villefranch sur Mer with hope that each of our experimental sample contained enough biomass for a CN signal…

Joost Mansour

Andreas Norlin