A small glass-like creature drifts through the ocean. One of the most delicate creatures in the world, it gently pulses through the bay. However, these seemingly gentle creatures can be deadly. In order to better understand jellyfish, one must understand how their bodies work, how climate change affects them, and the threat they pose to humans.

I truly love jellies and the way their bodies work. After reading a book on Irukandjis, I became truly fascinated by these creatures. These jellyfish have no brain, yet they move with ease, no hearts, but they still live. I hope by the end of this presentation you are able to understand why I am so fascinated by these animals.

A jellyfish body is one of the most simple structures in the animal kingdom. Most jellyfish start as a larva. The larva then latches onto a solid structure, such as a rock. On the solid structure, it grows into a polyp, which is a coral-like structure. Many polyps detach from the rocks they grew on and become free swimming medusae.

The medusae use their bell to contract and expel water, pushing the water out of their bodies to jet forward. Jellies have eyes pores to see. Some jellies, such as the box jelly, have a 360 degree view of its surroundings because they have eyes all over their bell. It is still a mystery how the eyes work without a brain. They also have tentacles that sting prey and oral arms which bring it to the mouth.

Perhaps the most dangerous part of its body is the stinger cells. Their tentacles are lined with millions of stinger cells. When the tubular part of the cell is triggered, they pierce human flesh and inject venom into the body. Some jellies, like Moon Jellyfish, have stings that are relatively harmless, one victim said it was an “Undetectable or a warm sensation.”

However, not all jellies are that peaceful. The Irukandji, a 3/8 inch monster of the sea, can cause an illness known as “Irukandji Syndrome” which causes nausea, vomiting, difficulty breathing, sweating, brain hemorrhage, and in rare cases, heart failure.

A box jellyfish, while not as venomous as the Irukandji, has an even higher fatality rate. Those who are lucky will be scarred for life, the others will die of its deadly sting within two to five minutes because their hearts stop.

Only one animal on Earth is truly immortal. The Turritopisis, or Immortal Jellyfish, can revert back into a larval stage and come back to life, essentially throwing itself back in time. The genetics of this miraculous jellyfish are not yet understood, but scientists are studying these jellies in hopes to find out their secret.

Some jellies, like the Beroe, do not even have tentacles. Instead, they catch their prey with jaws full of teeth, taking cookie shaped bites out of prey. They engulf small prey or use their jaws to bite off chunks of larger victims.

Another odd jelly is the Comb Jelly. Comb Jellies are not actually jellyfish, but are closely related to coeloplanas, a type of floating tissue that looks like a flatworm. Now, while most people think of jellies as free-swimming or drifting medusae, these Comb Jellies are latched onto a specific host, becoming two volcano-shaped structures.

Warming waters are significantly changing these jellies. Most dangerous jellies, like the Irukandji, live in warmer waters, such as Australia. However, as oceans warm, jellies with presumably fatal stings are being found much further north than they used to. Irukandjis, once thought to live in only the southern hemisphere, have been found as far north as Wales and Great Britain.

Box jellyfish, a mainly tropical species, have been slowly creeping up to the northern hemisphere. However, not all jellies like the heat. The Giant Siphonophore is a deep-dwelling creature, meaning it likes the cold. As ocean temperatures rise, this jelly may be forced to go deeper and deeper to reach the cold it needs.

Polluted oceans are also a problem. A predator of jellies, such as a sea turtle, will eat plastic bags thinking it is their favorite snack of sea jelly. This causes jellyfish populations to rise, as their predators die due to pollution consumption. Most jellies are 95% water, and as acid levels rise, some jellyfish become sick and die. Humans are mostly to blame for the new problems facing the oceans.

Overfishing is another reason jelly populations are growing. The Nomura’s Jelly has a six foot long bell and long tentacles. It lives on the coast of China. However, as overfishing becomes more popular, the Normura’s Jellyfish have fewer natural predators. In addition, their potentially deadly sting has led fishers away from those ports.

Jellyfish populations are a huge threat to humans as they grow. Stings from the Box Jelly are usually fatal if not treated properly, and Box Jelly populations have been estimated to double every year. Stings from the Irukandji have been spreading farther from their homeland of northern Australia, and have been seen further south into Queensland. Blooms of stinging jellies are becoming more populous.

Some jellies, like the Blue Blubber Jelly, have nonfatal stings but can swim into nuclear power plants and ruin the systems, putting places near it at risk. Moon Jellies, a usually harmless species, can drift into fish farms and kill the fish with their stings, ruining the income for that year. The crowned jelly, living in India, collaborates with eleven other jelly species to create an endless bloom in India. This creates a huge hazard for people and industries.

Some huge jellies, like the Bitey Whitey, have nasty stings and have many human fatalities blamed on them. Sea lizards, a jelly-eating species in the class Glaucus, eat jellies and take their stinging cells to use as its own. The painted box jelly is nearly invisible in the Great Barrier Reef, but like all box jellies, has a potentially fatal sting.

After learning more about jellyfish, one can better understand why they kill over 150 people a year, and sting approximately 150 million more. Jellies may be delicate, but they have one of the best defenses in the animal kingdom.