WHat are jellies

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Jellies do not have bones, brains, teeth or blood.  They cannot even flee a predator. Don’t let their simple anatomy fool you. These animals are spectacularly diverse and beautiful and built to survive. Jellyfish can survive without food for extended periods, thrive in chilling and warming oceans and lastly breath in otherwise unoxygenated waters.

 "Jellies" bodies are made up of more than 95 percent water. Both harmful and harmless, from miniscule (<2mm) to gigantic. The lion’s mane jelly is greater than eight feet (25m) across its bell with Its tentacles reaching 100ft long (30m) or more.   Taller than a 9-story building.

A jellyfish's bell is composed of three distinct layers: the epidermis, mesoglea and endoderm. 

Epidermis - Outer Layer

Mesoglea - Middle Layer

Gastrodermis - Inner Layer

Most often the jellyfish body has a radial symmetry, which means that a jelly’s body parts branch out from its center much like the spokes of a bicycle wheel.

Gastrovascular Cavity - Mouth

Oral Arms

Tentacles

Jellies have a variety of vision capabilities, from distinguishing day and night to up and down.  The vision in most jellies include basic nerve nodes called Rhopalia located underneath the bell edges.  The nerves cells sense light and gravity that allows balance and orientation for the jelly. 

The Box jellyfish has a complex eye that includes a retina, cornea and lens much like ours, missing is a central brain. Jellies don't see the in the traditional way but do respond from sensing visual stimuli from their simple eyes.

The pulsation of a jellyfish 

consists of a powerful whoosh of jetted water, propelling the jelly forward. The jelly is not the strongest sea going animal so most of the mobility of the jelly is determined by the prevailing winds and currents.

The synchronized propulsion system pulsing the jellies medusal bell is generated from transparent muscle fibers that are arranged in radial patterns stretched outward from the center of the bell to its edges.

The synchronized squeeze of these muscles are coordinated by the rhopalia below the edge of the outer bell.

Researchers are studying the actions of the jellyfishes' contractions that create doughnut-shaped vortex corkscrews as they push away. The intermittent momentum of the corkscrews creates an opposite reaction that propels the jellyfish forward, similar to an umbrella opening and closing.

The majority of the jellyfish diet is plankton/zooplankton: a mix of krill, amphipods and copepods. To a lesser amount, jellies eat crustaceans, plants, small fish, and 

other jellyfish.

How Do Jellyfish Capture Their Food? 

Most jellies use long tentacles with imbedded nematocysts (stinging cells) that stun or kill their prey. When their ultra-sensitive stinging cells brush up against an object, they discharge thousands of verminous harpoons into its prey. 

Once the venom paralyzes the prey the jellyfish maneuvers the captured prey into its mouth via its oral arms and digestion starts. The digested prey is then circulated throughout the jellyfish body through a series of interconnected channels. 

Beside nematocysts jellies deploy two other strategies to gather food. 

Mucus nets and Colloblasts.

Mucus nets (ranging from 1in to 6ft wide) are secreted from the organ called the endostyle. This net can successfully capture organism too small for the human eye.

The Colloblasts are an adhesive/sticky thread that captures prey but unlike nematocysts, they do not use venom, only the sticky entanglement of its tenacles subdue prey.

Some fish turn the tables, eating the jelly for dinner: blue rockfish, molas, dogfish, anchovies, chum salmon and mackerel have all been recorded eating jellies. The jelly is also a favorite food of sea turtles.

Jellies can reproduce both sexually and asexually. During the adult (and most recognizable) medusa phase of their life cycle, jellies reproduce by broadcasting egg and sperm that develop into free-swimming planula larvae. These larvae float around until conditions are just right and then attach themselves to a substrate. Once attached, they develop into polyps and start to grow and feed.When the time and water conditions are just right, some of these polyps will metamorphose and release ephyrae — infant jellies. These baby jellies grow into the mature medusa phase. Thus, the cycle begins again. 

 There are some fish that spend time swimming amid the tentacles of a jelly. This strange choice of hangout may help them avoid being eaten by bigger fish. They also get the chance to pick at scraps the jelly has caught, or nibble parasites off the jelly.

Some jellies are popular as food in Asia. Worldwide, an estimated 321,000 metric tons of jellies are caught for food every year. Japan alone imports up to 10,000 tons of jellies annually, where they can sell for $10 to $12 per pound. Preparing jellies is a competitive business complete with trade secrets practiced by respected "jellyfish masters."Some jellies sold for human consumption have been known to contain excessive levels of aluminum due to lack of regulation on how jellies are dried and preserved. Consumers have been advised to limit their consumption of products made from jellies.Jellywatch.org is a database created by our sister organization, the Monterey Bay Aquarium Research Institute (MBARI), to monitor jellyfish populations. Report your own jellyfish sightings to help scientists learn more about jelly blooms! 

Groups of jellies are known as “blooms.” Some view the jelly as a problematic animal — or worse, an underwater pest — due to large jelly blooms. These attitudes have led to the intentional destruction or removal of jelly populations. It is important to keep in mind that jellies have been blooming on this planet for over 600 million years and that jelly blooms are not new phenomena.Recent jelly "blooms" are also being studied for their potential as sentinels of ocean change.Most jelly populations are seasonal, but recently some jellies have appeared in areas they've never been seen before. For example, massive blooms of Mediterranean jellies appeared in the Mar Menor coastal lagoon after a regional agricultural boom. The agricultural development caused excessive nutrients to seep into the ground and eventually run into the lagoon through coastal runoff. Scientists are investigating causes for jellyfish blooms like these by studying their life cycles.