Jelly Blubbers in the Georges

The Georges River has become a stage for a fascinating phenomenon – a booming congregation of Jelly Blubbers! Scientifically known as Catostylus mosaicus, these mesmerizing creatures boast a hemispherical or mushroom-shaped bell that can reach an impressive 30 cm in diameter. Their vibrant hues range from warm brownish-yellow which are more common in the Georges River, to a bright blue or creamy white. The colours are controlled by symbiotic algal plant cells! Adorned with eight textured arms dangling beneath the bell, encountering large jelly blubbers is a fascinating sight, but beware – they may look cuddly, but they carry a sting. So, as you revel in the warmth of the water during this time of the year, remember to swim carefully.

These Jellys have a complex life history with five key stages. The adult medusae is the form we often see swimming past our boat. It seems that the presence of Blooms of Jelly Blubbers is quite cryptic. Studies of the Botany Bay population in the 1990s showed no consistent seasonal trends in the pattern of abundance. However, elsewhere it has been shown that their prevalence increased in summer and autumn when water temperatures are warmer and more microscopic food was available. Jelly Blubbers are known to have an important role in inorganic nutrient cycling in estuarine environments, so even though their sting might be a pain, they are a welcome site.