Moon jellyfish, scientifically known as Aurelia aurita, are a widely recognized and graceful species found in oceans across the globe. Their translucent, pulsating bells drift through coastal waters, captivating observers with their serene movements. These invertebrates are often seen near shorelines, indicating their preference for temperate and tropical aquatic environments. The question of how large these fascinating creatures can become is natural, given their prevalence and distinctive appearance.
Defining Their Size
Moon jellyfish exhibit a bell diameter ranging from 2 to 15 inches (5 to 38 cm), with an average size around 7 inches (17.8 cm). Some individuals can reach up to 16 inches (40 cm) in diameter. Exceptional cases have noted sizes up to 24 inches (60 cm) in diameter. They possess short, fringe-like tentacles around the bell margin, which do not significantly contribute to their overall length. Four horseshoe-shaped structures, their reproductive organs, are visible through their translucent bells and are a distinguishing feature, not a measure of size.
What Influences Their Growth
Environmental and biological factors influence the growth and ultimate size of moon jellyfish. Food availability plays an important role; when plankton, their food source, is abundant, they can grow rapidly. If food becomes scarce, moon jellyfish can shrink by reabsorbing tissue to conserve energy, returning to their larger size when food is plentiful.
Water temperature also affects their growth rates. Moon jellyfish thrive in temperate waters, with optimal temperatures between 48-66°F (9-19°C). Warmer temperatures promote faster growth. Salinity, or salt content, is another factor. Moon jellyfish prefer specific salinity levels and can be found in waters with relatively low salt content.
Growth Over Their Lifespan
The life cycle of a moon jellyfish involves distinct stages. It begins with a tiny, free-swimming larva called a planula, which settles and develops into a sessile polyp (scyphistoma). This polyp can reproduce asexually, budding off small, star-shaped juvenile jellyfish called ephyrae.
These ephyrae are initially only a few millimeters across. They feed on plankton and grow into the adult medusa form. Moon jellyfish have a relatively short lifespan in the wild, living about 6 to 12 months, which limits their maximum size. Growth is continuous throughout their medusa stage, and their short lifespan means they reach their full size before reproducing and eventually dying.