No wonder cubozoans or box jellyfish received little attention from biologists—in its reproductive biology at least. In the recent years scientists have learned about the box jellyfish life cycle but they were not successful (as much) in studying how do box jellyfish reproduce in their natural habitat and whether the reproduction involves sexual or asexual process.
Studies have confirmed that cubozoans produce both sexually and asexually. Asexual reproduction is a mode in which offspring are born from a single parent. That is to say it doesn’t involve sex. In the asexual mode the offspring, perhaps understandably, are identical to the parent (clone). Let’s study the reproductive biology of box jellyfish in detail.
How Do Box Jellyfish Reproduce?
- Box jellyfish are thought to reproduce in the spring season. During spring cubozoans travel to freshwater habitats to find partner. In the freshwater rivers adult box jellyfish lays eggs and sperms after which they die. Box jellyfish gather in large number in spring every year and soon after spawning they are as dead as a doornail.
- Box jellyfish are oviparous.
- Cubozoans breed only once every year.
- The breeding season mostly begins in late summer and ends in early fall.
- Male and female box jellyfish attains maturity at 2 months age.
- Adult parents do not contribute in rearing the young because the female dies soon after spawning.
- The average lifespan of box jellyfish is only 8 – 9 months.
Box Jellyfish Lifecycle (Metamorphosis)
Box jellyfish (cubozoans) have the ability to reproduce sexually as well as asexually. This indeed makes cubozoans’ life cycle little complex. Cubozoans also undergo gametic meiosis. They go through different life stages namely;
- Non-pigmented Larva
- Pigmented Larva
- Vegetative Polyp
- Three polyp-to-medusa metamorphosing stages
- Juvenile Medusa
- Adult Female
- Adult Male
The ciliated larva of cubozoans is formed by the combination of sperm and eggs. The larva of a box jellyfish is known as planula. Planulae are recognized by their pigment spots and they are fairly responsive to light. The pear-shaped planulae are likely to swim for few days (maybe a week). When the planula settles it develops into a polyp.
Polyp (Benthic Stage)
A poly in cubozoans is a stage that substitutes a medusoid stage. The planula turns into a polyp and the latter begins to crawl much like an inchworm. Polyp grows up to 1 – 2 mm in length. More polyps bud off the first polyp through an asexual reproduction. However unlike scyphozoan polyps, cubozoan polyps do not go through strobilation. Strobilation in scyphozoans (true jellyfish) takes place as and when polyp divides itself into body segments. On the contrary, in box jellyfish the entire polyp grows into a juvenile medusa.
In cnidarians polyps are cylindrical in shape but they seem like a ball having tentacles. They use these two tentacles to grab any object or other animals. In order to avoid any danger polyps mostly hide themselves in a crevice or an underside rock. They do this because they are highly vulnerable during this phase of the lifecycle. So far as diet is concerned polyps feed on plankton. The polyps of cubozoans do not in any way resemble polyps of true jellyfish (scyphozoans).
Medusa (Pelagic Stage)
Polyps will soon enter into the final stages of a lifecycle. During this phase polyps begin to develop into a small medusa. This happens in spring before the monsoon rain sets in. As the polyp grows into a medusa (completely) it probably leaves the freshwater for the sea. Here in sea the box jellyfish will continue to grow into adulthood until it attains the full size. Box jellyfish typically reaches a length of about 16 to 24 cm. You might like to know how big do box jellyfish get?