France: Snorkeling Surveys

2022-11-18

The Bages-Sigean Lagoon is in the south of France – it’s a small, shallow body of salt water that is mostly closed off from the Mediterranean Sea. Each year, two species of jellyfish appear in Bages-Sigean: Moon jellyfish (Aurelia coerulea) and Barrel jellyfish (Rhizostoma pulmo).

The life cycles of both species include a polyp phase, but the polyps in Bages-Sigean have never been located before.

It is known that polyps generally like to live on the underside of different materials near the shore, so in 2015, then-PhD student Valentina Leoni created a map of the different materials found along the shoreline of the lagoon. Our team of snorkellers spent two weeks in November checking each location to look for polyps.

The sites included an ancient roman wall ruin, and plenty of flamingoes.

Polyps are about 1 mm in size, but they typically grow in colonies. They can be tough to find, but it certainly helps to have a well-trained team. In fact, this research group at Montpellier University is one of the few groups in the world that works with wild polyps and I am thrilled to be learning from them!

We found 5 colonies all together and brought them back to the lab for identification. We found that they sometimes grew on mussel shells, which made collections much easier.

Although the medusa stage only lives seasonally and are mostly gone by November, we found a couple of Barrel jellyfish medusae in the lagoon.