Moon jellyfish, scientifically known as Aurelia aurita, are a species of jellyfish found across the globe. They are characterized by their translucent, bell-shaped bodies. These organisms inhabit coastal and temperate waters throughout the Atlantic, Indian, and Pacific Oceans.
Understanding Moon Jellyfish Size
The size of a moon jellyfish is determined by its bell diameter. Adult moon jellyfish typically measure between 10 to 40 centimeters (approximately 4 to 16 inches) across their bell. While this range represents a common size, some individuals can grow larger, with maximum observed diameters reaching up to 50 centimeters (about 20 inches) or even 60 centimeters (24 inches).
The bell is largely translucent. Visible through the bell are four horseshoe-shaped gonads. The color of these gonads, and sometimes the bell itself, can vary, appearing white, pink, blue, purple, or orange, often influenced by the jellyfish’s diet. Short, fringe-like tentacles surround the bell margin.
Factors Affecting Growth
Moon jellyfish size can vary significantly due to several environmental and biological factors. Food availability is a primary influence; these animals are carnivores that consume zooplankton. When prey is abundant, moon jellyfish experience faster growth, and conversely, they can shrink in size if food becomes scarce, regaining size when resources are plentiful.
Water temperature also plays a role in their growth rate. While Aurelia aurita can endure a wide thermal range, optimal temperatures typically fall between 9 and 19 degrees Celsius (48-66°F). Warmer waters often correlate with accelerated growth, influencing their final size.
Salinity, or the salt content of the water, is another factor. Moon jellyfish exhibit a tolerance for varying salinity levels, thriving even in low salt concentrations. However, rapid or extreme shifts in salinity can cause physiological stress, impacting their health and growth.
Water quality, encompassing levels of substances like ammonia, nitrite, and nitrate, directly affects a moon jellyfish’s well-being and growth. Poor water quality can lead to effects such as shrinking or weakened bell pulsations. Maintaining clean water is important for their health and development, allowing them to reach full size.
Size Across Their Life Cycle
Moon jellyfish undergo a life cycle with distinct stages and sizes. The journey begins with a small, ciliated planula larva, typically less than one millimeter long. This larva seeks a suitable surface to attach itself.
Upon finding a substrate, the planula transforms into a sessile polyp, a scyphistoma. These tiny, stalk-like organisms are usually a few millimeters tall and remain anchored. Polyps can also reproduce asexually through budding.
Under environmental cues, the polyp undergoes strobilation, segmenting into disc-shaped units. Each segment detaches to become a free-swimming ephyra, the juvenile jellyfish. Ephyrae are small, about one centimeter in diameter, and grow by feeding on plankton.
The ephyra then develops into the medusa, the familiar adult moon jellyfish. This is the largest stage in their life cycle, reaching 10 to 40 centimeters in bell diameter.