The Moon Jellyfish (Aurelia aurita) is one of the most recognizable and widespread species of jellyfish, known for its translucent, saucer-shaped bell and four horseshoe-shaped gonads. Its delicate appearance often leads people to wonder about its vulnerability, especially given the general decline of many marine populations. However, the answer is straightforward: Moon Jellyfish are highly abundant and are not considered an endangered species. They thrive in coastal environments across the globe, often becoming so numerous that their populations dominate local ecosystems.
Current Conservation Status
The species is so widespread and plentiful that it does not appear on any national or international threatened species lists. The International Union for Conservation of Nature (IUCN) Red List, the global authority on species conservation status, has officially classified the Moon Jellyfish as “Not Evaluated” (NE). This designation reflects that the species has not been formally assessed against threat criteria, largely because its population stability is not a concern.
Moon Jellyfish are a cosmopolitan species, meaning their geographic range is vast, spanning nearly all the world’s oceans. They inhabit the coastal waters of the Atlantic, Pacific, and Indian Oceans, avoiding only the most extreme polar regions. Their presence is recorded in both temperate and tropical zones, demonstrating remarkable adaptability. Far from declining, many populations of Aurelia are stable or increasing in abundance globally.
Biological Factors Driving Their Abundance
The success of the Moon Jellyfish population stems from a complex life cycle that allows for rapid growth under changing environmental conditions. Their life history alternates between sexual reproduction in the free-swimming medusa stage and asexual reproduction in a stationary polyp stage. The polyp stage is responsible for their high abundance; this small, sessile organism attaches to surfaces on the seafloor and can live for up to 25 years.
When environmental conditions become favorable, these polyps reproduce asexually through strobilation. The polyp segments itself, releasing dozens of tiny, juvenile jellyfish called ephyrae into the water column. This rapid, non-sexual cloning mechanism allows local populations to explode quickly when food is plentiful or temperatures rise.
Moon Jellyfish exhibit exceptional resilience to environmental stresses often associated with human activity. They can tolerate a wide range of water temperatures, from 6°C to 31°C. They are also highly tolerant of variable salinity, thriving in brackish estuaries where salt content is lower than in the open ocean. This adaptability allows them to flourish in coastal areas that may experience low oxygen levels (hypoxia) or high nutrient loads, which stress other marine life.
Ecological Role and Consequences of Blooms
The high population density of Moon Jellyfish often results in a “jellyfish bloom,” where millions of individuals aggregate in a specific area. These blooms significantly impact the marine food web, mainly through intense competition for resources. Moon Jellyfish are voracious predators of zooplankton, including copepods and fish larvae, which are primary food sources for many commercial fish species.
By consuming vast amounts of zooplankton, the jellies interrupt the typical flow of energy up the food chain. This sometimes leads to a trophic cascade where zooplankton reduction causes an increase in phytoplankton, fundamentally changing the ecosystem’s composition. Despite their abundance, Moon Jellyfish are a prey item for a few specialized predators, such as leatherback sea turtles.
Impacts on Human Infrastructure and Industry
Jellyfish blooms frequently interfere with the fishing industry by clogging nets and reducing the catch of commercial fish. They also cause economic damage by blocking cooling water intake pipes at coastal power plants and desalination facilities. For aquaculture and tourism, the presence of these blooms can lead to losses due to fish farm mortality and beach closures.