Jellyfish

In this episode of the I Can't Sleep Podcast, fall asleep learning about Jellyfish. They sound so cuddly and kind, but they are more boring than that--don't be deceived. They just float along, waiting to eat food that comes near them. That's pretty boring. Happy sleeping!

Transcript

Welcome to the I Can't Sleep Podcast,

Where I read random articles from across the web to bore you to sleep with my soothing voice.

I'm your host,

Benjamin Boster.

Today's episode is from a Wikipedia article titled,

Jellyfish.

Jellyfish and sea jellies are the informal common names given to the medusa phase of certain gelatinous members of the subphylum Medusazua.

A major part of the phylum Cnidaria.

Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles,

Although a few are anchored to the seabed by stalks rather than being mobile.

The bell can pulsate to provide propulsion for highly efficient locomotion.

The tentacles are armed with stinging cells and may be used to capture prey and defend against predators.

Jellyfish have a complex life cycle.

The medusa is normally the sexual phase,

Which produces planula larvae that disperse widely and enter a sedentary polyp phase before reaching sexual maturity.

Jellyfish are found all over the world,

From surface waters to the deep sea.

Schiphozoans,

The true jellyfish,

Are exclusively marine,

But some hydrozoans with a similar appearance live in freshwater.

Large,

Often colorful jellyfish are common in coastal zones worldwide.

The medusae of most species are fast-growing and mature within a few months,

Then die soon after breeding,

But the polyp stage attached to the seabed may be much more long-lived.

Jellyfish have been in existence for at least 500 million years,

And possibly 700 million years or more,

Making them the oldest multi-organ animal group.

Jellyfish are eaten by humans in certain cultures.

They are considered a delicacy in some Asian countries,

Where species in the Rhizostomae order are pressed and salted to remove excess water.

Australian researchers have described them as a perfect food,

Sustainable and protein-rich,

But relatively low in food energy.

They are also used in research,

Where the green fluorescent protein used by some species to cause bioluminescence has been adapted as a fluorescent marker for genes inserted into other cells or organisms.

The stinging cells used by jellyfish to subdue their prey can injure humans.

Thousands of swimmers worldwide are stung every year,

With effects ranging from mild discomfort to serious injury or even death.

When conditions are favorable,

Jellyfish can form vast swarms,

Which can be responsible for damage to fishing gear by filling fishing nets,

And sometimes clog the cooling systems of power and desalination plants which draw their water from the sea.

Names The term jellyfish,

In use since 1796,

Has traditionally been applied to Medusae and all similar animals,

Including the comb jellies.

The term jellies or sea jellies is more recent,

Having been introduced by public aquaria in an effort to avoid use of the word fish,

With its modern connotation of an animal with a backbone,

Though shellfish,

Cuttlefish,

And starfish are not vertebrates either.

In scientific literature,

Jelly and jellyfish have been used interchangeably.

Many sources refer to only cypozoans as true jellyfish.

A group of jellyfish is called a smac.

Mapping to taxonomic groups Phylogeny Definition The term jellyfish broadly corresponds to Medusae,

That is,

A life cycle stage in the Medusazoa.

The American evolutionary biologist Paulin Cartwright gives the following general definition.

Typically,

Medusazoan cnidarians have a pelagic predatory jellyfish stage in their life cycle.

Starozoans are the exceptions,

As they are stalked.

The Merriam-Webster dictionary defines jellyfish as follows.

The free-swimming marine coelenterate that is the sexually reproducing form of a hydrazoan or cyphozoan and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells.

Given that jellyfish is a common name,

Its mapping to biological groups is inexact.

Some authorities have called the comb jellies and certain salps jellyfish,

Though other authorities state that neither of these are jellyfish,

Which they consider should be limited to certain groups within the Medusazoa.

Taxonomy The subphylum Medusazoa includes all cnidarians,

With a Medusa stage in their life cycle.

The basic cycle is egg,

Planula larva,

Polyp,

Medusa,

With the Medusa being the sexual stage.

The polyp stage is sometimes secondarily lost.

The subphylum include the major taxa,

Cyphozoa,

Large jellyfish,

Cubizoa,

Box jellyfish,

And Hydrazoa,

Small jellyfish,

And excludes Anthozoa,

Corals,

And sea anemones.

This suggests that the Medusa form evolved after the polyps.

Medusazoans have tetramera symmetry,

With parts in fours or multiples of four.

The four major classes of Medusazoa cnidaria are Cyphozoa are sometimes called true jellyfish,

Though they are no more truly jellyfish than the others listed here.

They have tetraradial symmetry.

Most have tentacles around the outer margin of the bowl-shaped bell and long oral arms around the mouth in the center of the sub-umbrella.

Cubizoa,

Box jellyfish,

Have a rounded box-shaped bell and their valerium assists them to swim more quickly.

Box jellyfish may be related more closely to Cyphozoan jellyfish than either are to the Hydrazoa.

Hydrazoa medusae also have tetraradial symmetry,

Nearly always have a vellum,

Diaphragm used in swimming,

Attached just inside the bell margin,

Do not have oral arms,

But a much smaller central stalk-like structure,

The manubrium,

The terminal mouth opening,

And are distinguished by the absence of cells in the mesoglia.

Hydrazoa show great diversity of lifestyle.

Some species maintain the polyp form for their entire life and do not form medusae at all,

Such as Hydra,

Which is hence not considered a jellyfish,

And a few are entirely medusal and have no polyp form.

Starazoa,

Stalked jellyfish,

Are characterized by a medusa form that is generally sessile,

Oriented upside down and with a stalk emerging from the apex of the calyx bell,

Which attaches to the substrate.

At least some Starazoa also have a polyp form that alternates with the medusoid portion of the life cycle.

Until recently,

Starazoa were classified within the Cyphozoa.

There are over 200 species of Cyphozoa,

About 50 species of Starazoa,

About 20 species of Kubozoa,

And the Hydrazoa includes about 1,

000 to 1,

500 species that produce medusae,

But many more species that do not.

Fossil History Since jellyfish have no hard parts,

Fossils are rare.

The oldest Conillariid Cyphozoans appeared between 635 and 577 million years ago in the Neoproterozoic of the Lantian Formation in China.

Others are found in the youngest Ediacaran rocks of the Tamango Formation of Brazil,

Circa 505 million years ago through the Triassic.

Kubozoans and Hydrazoans appeared in the Cambrian of the Margem Formation in Utah,

USA,

Circa 540 million years ago.

Anatomy The main feature of a true jellyfish is the umbrella-shaped bell.

This is a hollow structure consisting of a mass of transparent jelly-like matter known as mesoglia,

Which forms the hydrostatic skeleton of the animal.

95% or more of the mesoglia consists of water,

But it also contains collagen and other fibrous proteins,

As well as wandering amoebocytes which can engulf debris and bacteria.

The mesoglia is bordered by the epidermis on the outside and the gastrodermis on the inside.

The edge of the bell is often divided into rounded lobes known as lapids,

Which allow the bell to flex.

In the gaps or niches between the lapids are dangling rudimentary sense organs known as ropalia,

And the margin of the bell often bears tentacles.

On the underside of the bell is the manubrium,

A stalk-like structure hanging down from the center with the mouth,

Which also functions as the anus at its tip.

There are often four oral arms connected to the manubrium,

Streaming away into the water below.

The mouth opens into the gastrovascular cavity where digestion takes place and nutrients are absorbed.

This is subdivided by four thick septa into a central stomach and four gastric pockets.

Near the free edges of the septa,

Gastric filaments extend into the gastric cavity.

These are armed with nematocytes and enzyme-producing cells,

And play a role in subduing and digesting the prey.

In some cyphozoans,

The gastric cavity is joined to radial canals,

Which branch extensively and may join a marginal ring canal.

Cilia in these canals circulate the fluid in a regular direction.

The box jellyfish is largely similar in structure.

It has a squarish,

Box-like bell.

A short pedallium or stalk hangs from each of the four lower corners.

One or more long,

Slender tentacles are attached to each pedallium.

The rim of the bell is folded inward to form a shelf known as a valarium,

Which restricts the bell's aperture and creates a powerful jet when the bell pulsates,

Allowing box jellyfish to swim faster than true jellyfish.

Hydrozoans are also similar,

Usually with just four tentacles at the edge of the bell.

Although many hydrozoans are colonial and may not have a free-living medusal stage,

Stalked jellyfish are attached to a solid surface by a basal disc and resemble a polyp,

The oral end of which has partially developed into a medusa with tentacle-bearing lobes and a central manubrium with four-sided mouth.

Most jellyfish do not have specialized systems for osmoregulation,

Respiration,

And circulation and do not have a central nervous system.

Nematocytes,

Which deliver the sting,

Are located mostly on the tentacles.

True jellyfish also have them around the mouth and stomach.

Jellyfish do not need a respiratory system because sufficient oxygen diffuses through the epidermis.

They have limited control over their movement but can navigate with the pulsations of the bell-like body.

Some species are active swimmers most of the time,

While others largely drift.

The ropalia contain rudimentary sense organs which are able to detect light,

Waterborne vibrations,

Odor,

And orientation.

A loose network of nerves called a nerve net is located in the epidermis.

Although traditionally thought not to have a central nervous system,

Nerve net concentration in ganglion-like structures could be considered to constitute one in most species.

A jellyfish detects stimuli and transmits impulses both throughout the nerve net and around a circular nerve ring to other nerve cells.

The ropalia ganglia contain pacemaker neurons which control swimming rate and direction.

In many species of jellyfish,

The ropalia include ocelli,

Light-sensitive organs able to tell light from dark.

These are generally pigment-spot ocelli which have some of their cells pigmented.

The ropalia are suspended on stalks with heavy crystals at one end,

Acting like gyroscopes to orient the eyes skyward.

Certain jellyfish look upward at the mangrove canopy while making a daily migration from mangrove swamps into the open lagoon where they feed and back again.

Box jellyfish have more advanced vision than other groups.

Each individual has 24 eyes,

Two of which are capable of seeing color,

And four parallel information processing areas that act in competition,

Supposedly making them one of the few kinds of animals to have a 360-degree view of its environment.

Box jellyfish eye.

The study of jellyfish eye evolution is an intermediary to a better understanding of how visual systems evolved on Earth.

Jellyfish exhibit immense variation in visual systems,

Ranging from photoreceptive cell patches seen in simple photoreceptive systems to more derived complex eyes seen in box jellyfish.

Major topics of jellyfish visual system research with an emphasis on box jellyfish include the evolution of jellyfish vision from simple to complex visual systems,

The eye morphology and molecular structures of box jellyfish,

Including comparisons to vertebrate eyes,

And various uses of vision including tax-guided behaviors and niche specialization.

Experimental evidence for photosensitivity and photoreception in Cnidarians antecedes the mid-1900s,

And a rich body of research has since covered evolution of visual systems in jellyfish.

Jellyfish visual systems range from simple photoreceptive cells to complex image-forming eyes.

More ancestral visual systems incorporate extraocular vision,

Vision without eyes,

That encompass numerous receptors dedicated to single-function behaviors.

More derived visual systems comprise perception that is capable of multiple task-guided behaviors.

Although they lack a true brain,

Cnidarian jellyfish have a ring nervous system that plays a significant role in motor and sensory activity.

This net of nerves is responsible for muscle contraction and movement,

And culminates the emergence of photosensitive structures.

Across Cnidaria,

There is a large variation in the systems that underlie photosensitivity.

Photosensitive structures range from non-specialized groups of cells to more conventional eyes similar to those of vertebrates.

The general evolutionary steps to develop complex vision include,

From more ancestral to more derived states,

Non-directional photoreception,

Directional photoreception,

Low-resolution vision,

And high-resolution vision.

Increased habitat and task complexity has favored the high-resolution visual systems common in derived Cnidarians such as box jellyfish.

Basal visual systems observed in various Cnidarians exhibit photosensitivity representative of a single task or behavior.

Extraocular photoreception,

A form of non-directional photoreception,

Is the most basic form of light sensitivity and guides a variety of behaviors among Cnidarians.

It can function to regulate circadian rhythm,

As seen in eyeless hydrazoans,

And other light-guided behaviors responsive to the intensity and spectrum of light.

Extraocular photoreception can function additionally in positive phototaxis and planula larvae of hydrazoans,

As well as in avoiding harmful amounts of UV radiation via negative phototaxis.

Directional photoreception,

The ability to perceive direction of incoming light,

Allows for more complex phototactic responses to light,

And likely evolved by means of membrane stacking.

The resulting behavioral responses can range from guided spawning events,

Timed by moonlight,

To shadow responses for potential predator avoidance.

Light-guided behaviors are observed in numerous cyphozoans,

Including the common moon jelly,

Aurelia aurita,

Which migrates in response to changes in ambient light and solar position,

Even though they lack proper eyes.

The low-resolution visual system of box jellyfish is more derived than directional photoreception,

And thus box jellyfish vision represents the most basic form of true vision,

In which multiple directional photoreceptors combine to create the first imaging and spatial resolution.

This is different from the high-resolution vision that is observed in camera or compound eyes of vertebrates and cephalopods that rely on focusing optics.

Critically,

The visual systems of box jellyfish are responsible for guiding multiple tasks or behaviors,

In contrast to less derived visual systems in other jellyfish that guide single behavioral functions.

These behaviors include phototaxis based on sunlight positive or shadows negative,

Obstacle avoidance,

And control of swim pulse rate.

Box jellyfish possess proper eyes similar to vertebrates that allow them to inhabit environments that lesser derived medusa cannot.

In fact,

They are considered the only class in the clade medusazoa that have behaviors necessitating spatial resolution and genuine vision.

However,

The lens in their eyes are more functionally similar to cup eyes exhibited in low-resolution organisms and have very little to no focusing capability.

The lack of the ability to focus is due to the focal length exceeding the distance to the retina,

Thus generating unfocused images and limiting spatial resolution.

The visual system is still sufficient for box jellyfish to produce an image to help with tasks such as object avoidance.

Utility as a model organism.

Box jellyfish eyes are a visual system that is sophisticated in numerous ways.

These intricacies include the considerable variation within the morphology of box jellyfish's eyes,

Including their task behavior specification,

And the molecular makeup of their eyes,

Including photoreceptors,

Opsins,

Lenses,

And synapses.

The comparison of these attributes to more derived visual systems can allow for a further understanding of how the evolution of more derived visual systems may have occurred,

And puts into perspective how box jellyfish can play the role as an evolutionary developmental model for all visual systems.

Characteristics.

Box jellyfish visual systems are both diverse and complex,

Comprising multiple photosystems.

There is likely considerable variation in visual properties between species of box jellyfish,

Given the significant interspecies morphological and physiological variation.

Eyes tend to differ in size and shape,

Along with number of receptors,

Including opsins,

And physiology across species of box jellyfish.

Box jellyfish have a series of intricate lensed eyes that are similar to those of more derived multicellular organisms,

Such as vertebrates.

Their 24 eyes fit into four different morphological categories.

These categories consist of two large morphologically different medial eyes,

A lower and upper lensed eye containing spherical lenses,

A lateral pair of pigment slit eyes,

And a lateral pair of pigment pit eyes.

The eyes are situated on Rapalia,

Small sensory structures,

Which serve sensory functions of the box jellyfish,

And arise from the cavities of the X-umbrella,

The surface of the body,

On the side of the bells of the jellyfish.

The two large eyes are located in the midline of the club,

And are considered complex because they contain lenses.

The four remaining eyes lie laterally on either side of each Rapalia,

And are considered simple.

The simple eyes are observed as small invaginated cups of epithelium that have developed pigmentation.

The larger of the complex eyes contains a cellular cornea created by a monociliated epithelium,

Cellular lens,

Homogenous capsule to the lens,

Vitreous body with prismatic elements,

And a retina of pigmented cells.

This smaller of the complex eyes is said to be slightly less complex,

Given that it lacks a capsule,

But otherwise contains the same structure as the larger eye.

Box jellyfish have multiple photosystems that comprise different sets of eyes.

Evidence includes immuno-cytochemical and molecular data that show photopigment differences among the different morphological eye types,

And physiological experiments done on box jellyfish to suggest behavioral differences among photosystems.

Each individual eye type constitutes photosystems that work collectively to control visually guided behaviors.

Box jellyfish eyes primarily use cPRCs,

Ciliary photoreceptor cells,

Similar to that of vertebrate eyes.

These cells undergo phototransduction cascades,

Process of light absorption by photoreceptors,

That are triggered by C-opsins.

Available opsin sequences suggest there are two types of opsins possessed by all cnidarians,

Including an ancient phylogenetic opsin and a sister ciliary opsin to the C-opsins group.

Box jellyfish could have both ciliary and cnidops,

Cnidarian opsins,

Which is something not previously believed to appear in the same retina.

Nevertheless,

It is not entirely evident whether cnidarians possess multiple opsins that are capable of having distinctive spectral sensitivities.

Comparison with other organisms.

Relative research on genetic and molecular makeup of box jellyfish's eyes vs more derived eyes seen in vertebrates and cephalopods focuses on lenses and crystalline composition,

Synapses,

And PAX genes and their implied evidence for shared primordial ancestral genes in eye evolution.

Box jellyfish eyes are said to be an evolutionary developmental model of all eyes,

Based on their evolutionary recruitment of crystallines and PAX genes.

The lens structure of box jellyfish appears very similar to those of other organisms,

But the crystallines are distinct in both function and appearance.

Weak reactions were seen within the sera and there were very weak sequence similarities within the crystallines among vertebrate and invertebrate lenses.

This is likely due to differences in lower molecular weight proteins and the subsequent lack of immunological reactions with antisera that other organisms' lenses exhibit.

All four of the visual systems of box jellyfish species investigated with detail have invaginated synapses but only in the upper and lower lensed eyes.

Different densities were found between the upper and lower lenses and between species.

Four types of chemical synapses have been discovered within the Vripalia which could help in understanding neural organization including clear unidirectional,

Dense core unidirectional,

Clear bidirectional,

And clear and dense core bidirectional.

The synapses of the lensed eyes could be used as markers to learn more about the neural circuit in box jellyfish retinal areas.

Evolution as a response to natural stimuli.

The primary adaptive responses to environmental variation observed in box jellyfish eyes include pupillary constriction speeds in response to light environments,

As well as photoreceptor tuning and lens adaptations to better respond to shifts between light environments and darkness.

Interestingly,

Some box jellyfish species' eyes appear to have evolved more focused vision in response to their habitat.

Pupillary contraction appears to have evolved in response to variation in the light environment across ecological niches across three species of box jellyfish.

Behavioral studies suggest that faster pupil contraction rates allow for greater object avoidance and in fact species with more complex habitats exhibit faster rates.

Light-dark adaptation via pupillary light reflexes is an additional form of an evolutionary response to the light environment.

This relates to the pupil's response to shifts between light intensity,

Generally from sunlight to darkness.

In the process of light-dark adaptation,

The upper and lower lens eyes of different box jellyfish species vary in specific function.

The lower lens eyes contain pigmented photoreceptors and long pigment cells with dark pigments that migrate on light-dark adaptation,

While the upper lens eyes play a concentrated role in light direction in phototaxis given that they face upward towards the water surface,

Towards the sun or moon.

Largest and smallest.

Jellyfish range from about 1 mm in bell height and diameter to nearly 2 m in bell height and diameter.

The tentacles and mouth parts usually extend beyond this bell dimension.

The smallest jellyfish are the peculiar creeping jellyfish in the genera Staurocladia and Eleutheria,

Which have bell discs from 0.

5 mm to a few mm in diameter,

With short tentacles that extend out beyond this,

Which these jellyfish use to move across the surface of seaweed or the bottoms of rocky pools.

Many of these tiny creeping jellyfish cannot be seen in the field without a hand lens or microscope.

They can reproduce asexually by fission,

Splitting in half.

Other very small jellyfish,

Which have bells about 1 mm,

Are the Hydromedusae of many species that have just been released from their parent polyps.

Some of these live only a few minutes before shedding their gametes in the plankton and then dying,

While others will grow in the plankton for weeks or months.

The lion's mane jellyfish,

Cyanea capillata,

Was long cited as the largest jellyfish and arguably the longest animal in the world,

With fine thread-like tentacles that may extend up to 36.

5 m long,

Though most are nowhere near that large.

They have a moderately painful but rarely fatal sting.

The increasingly common giant Nomuras jellyfish,

Found in some but not all years in the waters of Japan,

Korea,

And China in summer and autumn,

Is another candidate for largest jellyfish in terms of diameter and weight,

Since the largest Nomuras jellyfish in late autumn can reach 2 m in bell body diameter and about 200 kg in weight,

With average specimens frequently reaching 0.

9 m in bell diameter and about 150 kg in weight.

The large bell mass of the giant Nomuras jellyfish can dwarf a diver and is nearly always much greater than the lion's mane,

Whose bell diameter can reach 1 m.

The rarely encountered deep-sea jellyfish is another candidate for largest jellyfish,

With its thick,

Massive bell up to 100 cm wide and four thick,

Strap-like oral arms extending up to 6 m in length,

Very different from the typical fine thread-like tentacles that rim the umbrella of more typical-looking jellyfish,

Including the lion's mane.

Life History and Behavior Lifespan Little is known of the life history of many jellyfish,

As the places on the seabed where the benthic forms of those species live have not been found.

However,

An asexually reproducing strobila form can sometimes live for several years,

Producing new medusae each year.

An unusual species might be effectively immortal because of its ability under certain circumstances to transform from medusa back to the polyp stage,

Thereby escaping the death that typically awaits medusae post-reproduction,

If they have not otherwise been eaten by some other organism.

So far,

This reversal has been observed only in the laboratory.

Locomotion Using the moon jelly Aurelia aurita as an example,

Jellyfish have been shown to be the most energy-efficient swimmers of all animals.

They move through the water by radially expanding and contracting their bell-shaped bodies to push water behind them.

They pause between the contraction and expansion phases to create two vortex rings.

Muscles are used for the contraction of the body,

Which creates the first vortex and pushes the animal forward.

But the mesoglia is so elastic that the expansion is powered exclusively by relaxing the bell,

Which releases the energy stored from the contraction.

Meanwhile,

The second vortex ring starts to spin faster,

Sucking water into the bell and pushing against the center of the body,

Giving a secondary and free boost forward.

The mechanism called passive energy recapture only works in relatively small jellyfish moving at low speeds,

Allowing the animal to travel 30% farther on each swimming cycle.

Jellyfish achieved a 48% lower cost of transport,

Food and oxygen intake vs energy spent in movement than other animals in similar studies.

One reason for this is that most of the gelatinous tissue of the bell is inactive,

Using no energy during swimming.

Ecology Diet Jellyfish are like other cnidarians,

Generally carnivorous or parasitic,

Feeding on planktonic organisms,

Crustaceans,

Small fish,

Fish eggs and larvae,

And other jellyfish,

Ingesting food and voiding undigested waste through the mouth.

They hunt passively using their tentacles as drift lines,

Or sink through the water with their tentacles spread widely.

The tentacles,

Which contain nematocytes to stun or kill the prey,

May then flex to help bring it to the mouth.

Their swimming technique also helps them to capture prey.

When their bell expands,

It sucks in water,

Which brings more potential prey within the reach of the tentacles.

Predation Other species of jellyfish are among the most common and important jellyfish predators.

Sea anemones may eat jellyfish that drift into their range.

Other predators include tunas,

Sharks,

Swordfish,

Sea turtles,

And penguins.

Jellyfish washed up on the beach are consumed by foxes,

Other terrestrial mammals,

And birds.

In general,

However,

Few animals prey on jellyfish.

They can broadly be considered to be top predators in the food chain.

Once jellyfish have become dominant in an ecosystem,

For example,

Through overfishing,

Which removes predators of jellyfish larvae,

There may be no obvious way for the previous balance to be restored.

They eat fish eggs and juvenile fish,

And compete with fish for food,

Preventing fish stocks from recovering.

Symbiosis Some small fish are immune to the stings of the jellyfish and live among the tentacles,

Serving as bait in a fish trap.

They are safe from potential predators and are able to share the fish caught by the jellyfish.

The cannonball jellyfish has a symbiotic relationship with 10 different species of fish,

And with the long-nosed spider crab,

Which lives inside the bell,

Sharing the jellyfish's food and nibbling its tissues.

Blooms Jellyfish form large masses or blooms in certain environmental conditions of ocean currents,

Nutrients,

Sunshine,

Temperature,

Season,

Prey availability,

Reduced predation,

And oxygen concentration.

Humans collect jellyfish together,

Especially in years with unusually high populations.

Jellyfish can detect marine currents and swim against the current to congregate in blooms.

Jellyfish are better able to survive in nutrient-rich oxygen-poor water than competitors,

And thus can feast on plankton without competition.

Jellyfish may also benefit from saltier waters,

As saltier waters contain more iodine,

Which is necessary for polyps to turn into jellyfish.

Rising sea temperatures caused by climate change may also contribute to jellyfish blooms,

Because many species of jellyfish are able to survive in warmer waters.

Increased nutrients from agricultural or urban runoff with nutrients including nitrogen and phosphorus compounds increase the growth of phytoplankton,

Causing eutrophication and algal bloom.

When the phytoplankton die,

They may create dead zones,

So-called because they are hypoxic,

Low in oxygen.

This in turn kills fish and other animals,

But not jellyfish,

Allowing them to bloom.

Jellyfish populations may be expanding globally as a result of land runoff and overfishing of their natural predators.

Jellyfish are well-placed to benefit from disturbance of marine ecosystems.

They reproduce rapidly,

Prey upon many species,

While few species prey on them,

And feed via touch rather than visually so they can feed effectively at night and in turbid waters.

It may be difficult for fish stocks to re-establish themselves in marine ecosystems once they have become dominated by jellyfish,

Because jellyfish feed on plankton,

Which includes fish eggs and larvae.

As suspected at the turn of this century,

Jellyfish blooms are increasing in frequency.

Between 2013 and 2020,

The Mediterranean Science Commission monitored on a weekly basis the frequency of such outbreaks in coastal waters from Morocco to the Black Sea,

Revealing a relatively high frequency of these blooms nearly all year round,

With peaks observed from March to July,

And often again in the autumn.

The blooms are caused by different jellyfish species,

Depending on their localization within the basin.

Some jellyfish populations that have shown clear increase in the past few decades are invasive species,

Newly arrived from other habitats.

Examples include the Black Sea,

Caspian Sea,

Baltic Sea,

Central and Eastern Mediterranean,

Hawaii and tropical and subtropical parts of the West Atlantic,

Including the Caribbean,

Gulf of Mexico,

And Brazil.

Jellyfish blooms can have significant impact on community structure.

Some carnivorous jellyfish species prey on zooplankton,

While others graze on primary producers.

Reductions in zooplankton and axioplankton due to a jellyfish bloom can ripple through the tropic levels.

High-density jellyfish populations can out-compete other predators and reduce fish recruitment.

Increased grazing on primary producers by jellyfish can also interrupt energy transfer to higher tropic levels.

During blooms,

Jellyfish significantly alter the nutrient availability in their environment.

Blooms require large amounts of available organic nutrients in the water column to grow,

Limiting availability for other organisms.

Some jellyfish have a symbiotic relationship with single-celled dinoflagellates,

Allowing them to assimilate inorganic carbon,

Phosphorus,

And nitrogen,

Creating competition for phytoplankton.

Their large biomass makes them an important source of dissolved and particulate organic matter for microbial communities through excretion,

Mucus production,

And decomposition.

The microbes break down the organic matter into inorganic ammonium and phosphate.

However,

The low carbon availability shifts the process from production to respiration,

Creating low oxygen areas,

Making the dissolved inorganic nitrogen and phosphorus largely unavailable for primary production.

These blooms have very real impacts on industries.

Jellyfish can out-compete fish by utilizing open niches in overfished fisheries.

Much of jellyfish can strain fishing gear and lead to expenses relating to damaged gear.

Power plants have been shut down due to jellyfish blocking the flow of cooling water.

Blooms have also been harmful for tourism,

Causing a rise in stings and sometimes the closure of beaches.

Jellyfish form a component of jellyfalls,

Events where gelatinous zooplankton fall to the seafloor,

Providing food for the benthic organisms there.

In temperate and subpolar regions,

Jellyfalls usually follow immediately after a bloom.

Habitats Most jellyfish are marine animals,

Although a few hydromedusae inhabit fresh water.

The best known freshwater example is the cosmopolitan hydrazoan jellyfish.

It is less than an inch in diameter,

Colorless,

And does not sting.

Some jellyfish populations have become restricted to coastal saltwater lakes,

Such as Jellyfish Lake in Palau.

Jellyfish Lake is a marine lake where millions of golden jellyfish migrate horizontally across the lake daily.

Although most jellyfish live well off the ocean floor and form part of the plankton,

A few species are closely associated with the bottom for much of their lives and can be considered benthic.

The upside-down jellyfish typically lie on the bottom of the shallow lagoons,

Where they sometimes pulsate gently with their umbrella top facing down.

Even some deep-sea species of hydromedusae and siphomedusae are usually collected on or near the bottom.

All the staromedusae are found attached to either seaweed or rocky or other firm material on the bottom.

Some species explicitly adapt to tidal flux.

In Roscoe Bay,

Jellyfish ride the current at ebb tide until they hit a gravel bar and then descend below the current.

They remain in still waters until the tide rises,

Ascending and allowing it to sweep them back into the bay.

They also actively avoid fresh water from mountain snowmelt,

Diving until they find enough salt.

Reviews

This works and I now know a few facts about 🪼 jellies.

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A smack of jellyfish wound up in my dreams.
Thank you Sir.

I didn't make it past something about Medusa! I thought it'd be more interesting but not at all, thanks!'

I was wide awake at 3:00 AM and was happy to see this! Thank you for your soothing voice and the boring subject of jellyfish! 🤗🥰🤗🥰