Mediterranean 'Egg Yolk' Jellyfish Fascinates with Unique Biology and Climate Sensitivity

The "egg yolk" jellyfish, scientifically known as Cotylorhiza tuberculata, is a striking and photogenic marine species found in the central and western Mediterranean Sea, including off the coast of Palmachim, Israel. Its name derives from its distinctive appearance, featuring a dark yellow-orange central dome resembling an egg yolk surrounded by white edges like egg whites. A related species, Cotylorhiza erythraea, inhabits the eastern Mediterranean and is less colorful.

Professor Dror Angel from the Recanati Institute for Maritime Studies at the University of Haifa, and CEO of the "Jellyfish Among Us" association, explains that this jellyfish coexists with symbiotic algae living within its tissues. These algae perform photosynthesis, providing organic nutrients to the jellyfish, which in turn offers them protection. This relationship confines the jellyfish to shallow, sunlit waters essential for their life cycle, which includes a complex process from fertilized eggs to polyps and then to mature jellyfish through a stage called strobilation.

Unlike some jellyfish species, the egg yolk jellyfish's sting is mild and generally harmless to humans, as its venom targets small prey like planktonic crustaceans. It is a food source for various marine animals such as turtles, fish, and birds, and plays an integral role in the marine food web. The jellyfish typically appear singly or in small groups, posing less of a nuisance compared to swarming species like the Portuguese man o' war.

Regarding climate change, these jellyfish may initially benefit from warmer, saltier waters, but extreme heat waves threaten their symbiotic algae, potentially causing bleaching similar to coral bleaching, which can halt their growth or cause death. Dr. Angel advises respecting jellyfish in their natural habitat, appreciating their beauty and movement without disturbing them, emphasizing the magical experience of swimming alongside these gelatinous creatures in the sea.

This report was prepared by Zavit, the news agency of the Israeli Society for Ecology and Environmental Sciences.