A Bermudian mangrove pond, seen from above and under the water.
The Walsingham Pond is an anchialine pond, a type aquatic pool lacking surface connection with the open sea, but one that is permanently connected with the sea waters and thus still subject to tidal flushing. One of the most noticeable features of the pond is the high abundance of the upside down jellyfish. They posess a symbitic algae, which perform photosynthesis. The pond is quite murky in deeper parts and thus the light penetration is limited.
The distribution of jellyfish, their abundance and size should therefore reflect the amount of light reaching the different depths.
Equipped with a sledge with a mounted GoPro camera, depth logger and a GPS we conducted a survey of the whole pond. It took us half a day of constant swimming, duck-diving and filming. But for the survey to be robust you need to put effort into it, even when it means hurting ears the day later.
An ArcGIS plotted track. The only part of the pond not covered (SE) is due to the loss of GPS connection.
an example of a screenshot from the survey video. Shown in the middle are two individuals of Cassiopea sp. jellyfish, upside down, exposing the tentacles with algae. The analysis revealed that both the abundance and bell diameter are dependent on depth, used as a proxy for light.