Jellyfish

Jellyfish

Biology

Jellyfish may be an interesting and potentially dangerous underwater creature, but in actuality they are 95% water . What's left is divided into three main layers: the epidermis–outer layer–mesoglea, which makes up the middle layer, and gastrodermis, or inner layer . Jellyfish have many parts, but none of them is a brain. Instead, they have a network of neurons, i.e. a "nerve net." It's not just their brains either, their entire body is made up of these neural networks, from the epidermis (outer layer) to the gastrodermis (inner layer) . This inner layer is where the stomach and anus lie, allowing a jellyfish to take in nutrients . This network provides jellyfish with the ability to sense the environment around them so as to determine food sources or the presence of another animal . Part of the reason they're so simple is because they belong to the invertebrates in the Phylum Cnidaria, which includes other creatures like sea anemones, sea whips, and corals . As a member of this phylum, all parts of their body are centered around a central axis and this symmetry allows them to respond to food, or alternatively danger, from any direction . Within the ecosystem, jellyfish play an important role protecting certain species, balancing food chains, and helping ensure nutrients are available to species in the ocean. As jellyfish drift through the water, they are able to protect certain species of baby fish, who will swim with or under the jellyfish to hide from potential predators. As jellyfish travel along, they can sting and kill some prey that the fish can eat as food while traveling, allowing the number of fish species to recover and increase their populations. Not only do they protect these fish, but they themselves work to control species populations through their own consumption of fish larvae and eggs. However, they are not at the top of the food chain, so they are susceptible to being eaten–even by other jellyfish. One such example of this is the Lion's Mane jellyfish, which will consume smaller Moon species of jellyfish. Some other species that will eat them include sunfish, spadefish, crabs, marine turtles, and deep-sea creatures that will eat their remains from the ocean floor. Finally, jellyfish are involved in the nutrient cycling process. As a species that wanders from the sea floor up to the surface of the ocean, they transport nitrogen and phosphorus that can then be used by other organisms .

A jellyfish is born through sexual reproduction. From the union of a jellyfish egg and sperm, a larva is produced. These larva attach to hard surfaces like rocks at the bottom of the ocean floor. From there, they exist as a polyp (a ring of tentacles surrounding a central body) in the polyp stage until conditions are favorable, at which point they bud off into many young jellyfish through asexual reproduction that will grow up to repeat the cycle . Sometimes conditions are favorable after mere days, but it can take decades for the temperature and food conditions to appear. Typically these polyps are not alone, and therefore when the time is right, a whole swarm of tens of thousands of jellyfish will rise from the ocean floor and quickly develop into adult jellyfish , otherwise known as the medusa stage. After it has transitioned to this phase, the jellyfish normally lasts no longer than a year .

Although jellyfish have gained a reputation of being immortal due to their regenerative abilities, this is only true for one species - Turritopsis dohrnii. It is through transdifferentiation that they can regress back into a younger version of themselves by telling their specialized medusa cells to become specialized polyp cells. Instead of dying, these jellyfish will shrink in on themselves, reabsorbing their tentacles, and losing their ability to swim. From there, they return to polyp stage, as they develop from a tentacle-less blob into a new polyp . Jellyfish in general are known to live all different lengths of time depending on the species. A moon jellyfish may live only 8-12 months, while a Flame jellyfish can live in an aquarium for up to 25 years! A typical life span is said to be between one and three years, although they are much more likely to have lower lifespans in the wild due to predators.

Distribution Around the Globe

The habitat of jellyfish is vast with over 2,000 species inhabiting the world. They range from Arctic waters to tropical waters, on the surface of oceans to the seafloor, far out in water to being close to the shore. Each species is different and prefers varying areas, following ocean currents. Jellyfish can be seen alone or in small groups as well as in what is known as a jellyfish bloom . These are substantial growths in populations of jellyfish that are caused naturally by ocean and wind patterns, ecosystem shifts, and behaviors. But coastal habitat modifications, global warming, translocation, and overfishing have caused more frequent outbreaks. These blooms are most common in Japan, Denmark, the Mediterranean, the Barents Sea, and the North Atlantic Shelf. Jellyfish are located in both seawater and freshwater around the world. Scyphozoans, also known as the "true jellyfish" are exclusively marine but some similar looking hydrozoans live in freshwater. The best known freshwater species is the Cosmopolitan Hydrozoan Jellyfish, Craspedacusta sowerbii . This species is 2.5 cm in diameter, colorless, and does not sting. C. sowerbii is native to the Yangtze basin in China but has been introduced on every continent excluding Antarctica. They can be found in calm, freshwater reservoirs, lakes, impoundments, gravel pits or quarries, as well as slow moving rivers, such as the Ohio River.

Saltwater, or marine, jellyfish are common in coastal zones around the world . Most species live off of the ocean floor and are considered plankton but some are considered benthic as they associate with the bottom for much of their lives. The Upside-Down Jellyfish likes to lie on the bottom of shallow lagoons and some deep-sea hydromedusae and scyphomedusae become collected on or near the bottom. All of the scyphomedusae are attached to firm material on the bottom such as seaweed or rocks.

The number of jellyfish around the world has been on a rise since 1950 in a lot of different areas , but there has been a decrease off the coast of Chile, Greenland, and the eastern coast of Russia near the Bering Sea. Larger populations of jellyfish are located in/near Antarctica, the Hawaii Islands, Japan, Angola, and Turkey. Locations with medium high populations include the Pacific USA, Mexico/Central America, the coasts of Brazil and Argentina, Australia, near the UK and Nordic countries, the Mediterranean, the southwest coast of Africa, and on the coast of India spanning east and west .

Impact/Role on Coral Reefs

Ocean Food Chains

Jellyfish have an essential part in food chains throughout the ocean. As a carnivore, having a diet consisting of fish larvae and eggs, jellyfish help control other species populations and maintain balance of the ecosystem. Jellyfish also consume phytoplankton, small crustaceans, small fish, and even other jellyfish. They also play a role in the diets of other ocean species such as sunfish, spadefish, crabs, and marine turtles . Leatherback turtle diets are almost completely made up of jellyfish. Jellyfish are essential to the survival of these animals, helping to sustain life in coral reefs and throughout the oceans. Jellyfish can also provide habitat and space for juvenile fish as a means of protection and for feeding opportunities. This helps reduce fish mortality and increase recruitment .

Nutrient Transfer

In addition to being a nutrient source to other marine animals, jellyfish also help with nutrient cycling . As they drift and follow ocean currents, they help transport nutrients such as nitrogen and phosphorus through the sea and the different water column layers. This helps other organisms grow and survive. When swimming, jellyfish displace water mixing the different layers and transferring nutrients through the sea. Jellyfish also release nutrients when feeding or through excretion that help organisms such as phytoplankton grow. The mucus and feces that jellyfish release are used by bacteria for respiration. All in all, it is "estimated that between 3.7-3.8 billion tonnes of organic carbon can be traced back to jellies each year" rivaling the USA’s annual carbon emissions.

Carbon Transfer

A large role of jellyfish in coral reefs and in their own ecosystems has to do with the carbon cycle. As jellyfish feed on phytoplankton that transfer carbon dioxide from the atmosphere to the ocean, they consume that carbon and become a source or sink of carbon . Carbon is then cycled to the seabed by the excrement of jellyfish or when their remains sink to the floor. This allows for more carbon dioxide to be dissolved in the oceans as well as helping calcifying organisms such as corals or molluscs to incorporate the inorganic carbon into their shells directly.

Ecosystem Services and Benefits to Humans

Ecosystem services are the invaluable benefits that ecosystems provide to humans, including provisioning (food source), regulation (carbon cycle), support (nutrient transfer), and cultural (aquariums and tourism) services . Like all creatures in the coral reef ecosystem, jellyfish offer various services and benefits to humans.

Firstly, by serving as important links in the ocean carbon cycle, they offer regulating services. Salps, a marine invertebrate, as well as jellyfish consume phytoplankton and transport carbon to the ocean floor through their faecal pellets. In addition, the accumulation of jellyfish carcasses also facilitates the transfer of carbon from surface waters to the benthos. Jellyfish offer a diverse array of supporting services: their sloppy feeding habits provide vital nutrients for primary production, their movements through water contribute to oceanic mixing, and they serve as prey for numerous marine species while also acting as important predators in pelagic ecosystems . Furthermore, jellyfish provide habitats and refuges for a diverse array of marine life. Lastly, they offer cultural services through citizen science programs that engage the public in counting and identifying stranded jellyfish on beaches, and their presence in aquariums captures the imagination of children, promoting an appreciation for marine life and conservation efforts.

Facts

1. Jellyfish can learn! A study found that jellyfish could learn despite not having a brain. They do this through a process called associative learning, where jellies form mental connections between sensory stimulations and behaviors. In the study, scientists observed jellyfish learning to avoid obstacles through visual stimuli and from bumping into the objects.

2. Jellyfish can get wrinkles! When they are scared, they become wrinkled as a warning to their predators.

3. Regeneration Ability Jellyfish in the adult medusa stage have a surprisingly high regenerative ability that allows them to regenerate organs and body parts. It involves processes like wound healing, blastema formation, and systemic patterning.

4. Ability to wait in the polyp stage Jellyfish can live in the polyp stage for many years. This is so they can wait for the appropriate conditions to arrive before becoming an adult. Once they transition to the adult stage and start reproducing though, they do not normally live longer than a year.

5. Some Jellyfish are safe to eat Jellyfish are commonly consumed in Southeastern Asia and are believed to offer health benefits such as being high in nutrients and a good source of collagen . There are at least 11 species that have been identified as safe for human consumption. As jellyfish are often caught as by-catch in commercial fishing, some believe this by-catch could be utilized as food instead of being wasted .

6. Potential for being used as bioindicators Jellyfish can be used as bioindicators for plastic pollution, as they are able to internalize macro- and microplastics. As they are widespread in food webs worldwide, they could be a very good option for future bioindicator surveys .

7. Stinging Ability The Lion's Mane jellyfish, one of the largest species of jellyfish in the world, can sting at 5 million Gs, or approximately 110000000 mph/s, which is the fastest on earth. While many jellyfish can sting, not all jellyfish possess stinging cells.