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Decoding the science of jellyfish

Maude Delap is celebrated within the scientific community worldwide. She is known as the Victorian woman who studied jellyfish on Valentia Island. Delap was a self-taught marine biologist with no formal education and little resources. But what exactly was she studying?

black and white image of Maude Delap, an old woman with glasses looking into the camera.

Maude Delap [Wikimedia]

It’s common knowledge among many that Maude Delap used to capture jellyfish from the shores of Iveragh and bring them back to her home-made laboratory (fondly referred to as “The Department”). However, the full details of her research are rarely talked about and often the enormous significance of this work is not made clear. To truly understand the significance of Maude Delap’s work, it requires an understanding of just how difficult it is to raise jellyfish.

Jellyfish exhibits are often most visited sites within aquariums. People love to gaze mesmerised into the glass and watch the jellyfish elegantly pulsate and turn in the water. Yet it’s not really known just how hard it is to produce and maintain the jellyfish that you’re looking at in the tank. Even in today’s world the process is tricky and requires a lot of trial and error. Jellyfish can be sensitive to many different variables, and this means the scientists must constantly be regulating their environment.

photo of an unusual large blue glass container filled with jellyfish

Moon jellyfish (Aurelia aurita) exhibit in Dingle Oceanworld Aquarium

The process begins before you even put your jellyfish into a tank. The tank requires an optimal environment containing the right balance of salts, acidity and minerals. Certain species of jellyfish have different temperature requirements too and the water inside the aquarium will likewise need a good circulation system. Getting this balance right can be nerve-wrecking alone as one slight error may lead to you having to start over. After several weeks of routine check-ups and testing, jellyfish planulae can finally be inserted into the tank. Just when you think the trials have ended – they have only just begun.

Jellyfish have a very complex life cycle which can vary in stages depending on species. The adult jellyfish, either male or female, will produce eggs or sperm which combine to produce a larva known as a planula. The planulae are found on the tentacles of the adult jellyfish and are often numerous. These planulae will float about in the water and eventually settle down to the bottom of an aquarium (or the ocean) and develop into a hydroid or polyp. All going well, the polyp will feed and grow.

illustration describing the complex life cycle of a jellyfish

The complex jellyfish life cycle (Illustration by Jane Sheehan)

When conditions are right, the polyp will begin to reproduce. It does this by budding clones of itself called the ephyrae. These ephyrae are about two millimetres in diameter and look almost like flower heads with petals. Under the right conditions, this ephyrae will grow into a full-sized jellyfish with the classic bell shape that we are familiar with. Finally, the full cycle is completed, and you have successfully reared a jellyfish. A nice video showing how polyps bud off ephyrae can be seen below.

Born of Baby Jellyfish: budding Polyp release Ephyra - Super Sea Monkey

In some oceanic species of jellyfish there is no polyp stage of the jellyfish life cycle. Instead, they reproduce by direct development. Here, the adult medusa will produce a planulae which will develop into a full sized adult medusae without any fixed polyp stage. As you can gather, raising jellyfish is quite complex. Your jellies might only grow and develop for a while and then begin to shrink and die due to water conditions, bringing your life cycle to a halt. Sometimes, try all you might, your jellyfish will not want to eat, swim, or grow.

 beautifully intricate jellyfish drawings  in greens and pinks by Ernst Haeckel

The beautifully intricate jellyfish drawings of Ernst Haeckel (Source: Public Domain Review)

photo of a glass model of a type of jellyfish

Attempts to raise jellyfish have been carried out for centuries. Jellyfish became popular at the end of the 19th century through the influence of the European Art Nouveau period. A German zoologist, Ernst Haeckel, created wonderfully intricate drawings of jellyfish which ignited an interest in gelatinous species. They inspired Leopold and Rudolph Blaschka to make their famous scientific glass models of jellyfish. The Blaschka models, which are still viewable today, were popular with museums and universities worldwide because they allowed people to observe and study the anatomy of jellyfish. At the time, studying jellyfish was quite difficult, as nobody could successfully sustain jellies in captivity. Often the jellyfish would live for a few weeks and die or would only develop to a certain life stage.

Glass model of cnidarian medusae (Hydractiniaproboscidea) by Blaschka of Dresden, late 19th century. National Museum of Ireland.

detailed drawing of Edward T. Browne, a middle aged man with moustache and blading hair

When Edward T. Browne came in 1895 to Valentia to study the plankton and jellyfish of Valentia Harbour, he became a mentor to Maude Delap. She was already an avid naturalist with an interest in the marine environment, but with him she learned much about plankton and jellyfish. Maude, along with her sister Constance, helped his study by collecting plankton and identifying them, recording the sea temperatures, and logging their records.

A portrait of Edward T. Browne (Obituary published by Marine Biological Association)

After Browne’s scientific study finished, he returned to the Marine Biological Association laboratory in Plymouth and began experimenting with maintaining jellyfish in captivity. He had little success with this and after the death of many jellyfish specimens in the laboratory, Browne realised what was missing from his aquarium was the tidal movement in the ocean. In 1899, he introduced his “plunger jar”, which helped circulate the water by mimicking the tide. This helped prolong the lifespan of some jellyfish from as little as 24 hours to days and weeks. This was the first time that anyone had considered the importance of circulating the water in the tank. Still, it was not perfect.

black and white antique photo of an elaborate scientific set up, bell jars with water, levers etc.

Edward Browne's Plunger Jar (On keeping Medusae alive in an Aquarium)

Maude continued to work on jellyfish and plankton within the harbour after Browne left. She began to carry out her own experiments into jellyfish culturing. Eventually, through dedication, passion, or sheer perseverance, Maude did something Edward Browne and other marine scientists could only have dreamed of at the time – she successfully raised jellyfish through their different life cycles.

In 1899, Maude collected a damaged Compass jellyfish (Chrysaora isosceles) on the shore of Valentia and placed it within a 10-inch bell jar. It began to produce a number of planulae. These planulae developed into many hydroids and in turn into many ephyrae. She made extensive notes and sketches on each of these life cycles. There were several different individuals of different life stages alive within the bell jars of various sizes. Over the next year, she began to observe and tend to each of them. At the time, there were no articles on how to culture jellyfish, therefore everything she did was of her own instinct and trial.

beautiful pale yellow and brown jellyfish in a very blue sea

Compass jellyfish (Chrysaora isosceles)

Providing a suitable diet for many forms of the jellyfish meant trialling it with different species of plankton as food. Delap made sure that fresh supplies of plankton were always kept available within the bell jar. She would row her boat, a grey punt, out into the harbour and cast off a tow net. The plankton were collected in the tow net and brought back to the laboratory and placed within the bell jars. Through the process of elimination, she noted that the jellyfish preferred different species during different parts of its lifecycle and often fed upon copepods and small jellyfish species. At this time, it was believed that invertebrates mainly fed on copepods and other plankton, and Delap’s observation of the jellyfish feeding on other jellyfish changed this. She also concluded that the jellyfish required a large abundance of food, which was not always available, due to the changes in weather and the inability of Maude to go out in her boat and collect them in these conditions.

Delap kept the bell jars on a window with an eastern aspect and was sheltered from the sun. Temperatures of the bell-jar were taken and compared to the surface temperature of the sea. The water in the large bell jar was changed daily with one gallon removed and a fresh supply added. There are accounts from Maude’s nephew, Peter Delap, on how whenever Maude was asked, later in life how she had managed to keep the seawater circulating in the glass jars she would grin and proceed to make a circular movement with her hand. Maude wasn’t in possession of a circulatory system so instead she improvised and stirred the water every so often by dipping her fingers in.

By the 8th of July 1900, Maude had successfully raised a full-sized adult jellyfish from the planulae of the original Compass which had been collected on shore in 1899. It was 13 weeks old and reached its maximum growth of 9 inches in diameter. This accomplishment made Maude Delap the first person in the world to successfully rear jellyfish in captivity and observe their full life cycle. Where others had difficulty keeping jellyfish and their offspring alive for days and weeks at a time, she had successfully reared them for an entire year. Her hard work was recognised, and she published her findings in The Irish Naturalist in 1901, under the title “Notes on the Rearing of Chrysaora Isosceles in an Aquarium”.

Despite having just conquered the impossible, Delap continued to further her studies on rearing jellyfish in aquaria and published two more articles; “Notes on the rearing, in an aquarium, of Cyanea lamarackii, Peron et Lesuer.” her final paper on jellyfish “Notes on the rearing, in an aquarium, of Aurelia aurita, L. and Pelagia perla*(Slabber)” were both submitted to Sea and Inland Fisheries Scientific Investigations in 1905. Additionally, all her publications were authored with her own name which was very unusual for the time as women were still discouraged from science. These articles investigated the culturing of other species of jellyfish – the Blue jellyfish (Cyanea lamarackii), the Moon jellyfish (Aurelia aurita) and the Mauve stinger (Pelagia perla, now classified as (Pelagia noctiluca). Like the first article, these describe the various life cycles and the process involved in rearing each of the three species of jellyfish.

photo of an almost transparent pale whie and pink jellyfish that looks like a decorative lampshade

Moon jellyfish, (Aurelia aurita)

Throughout her studies, Maude Delap was able to recognise that certain life stages belonged to different species, which at the time was not known. The different stages of the life cycle of a jellyfish were often mistaken for a whole new species. In fact, the complete lifecycle of many species of jelly is still unknown and the work to understand them continues today. Delap was the first person to realise the correlation between jellyfish diet and jellyfish growth and mortality. Diet had often been overlooked in other studies on rearing jellyfish.

photo of a blue almost purply round blob of a jellyfish on wet sand

Blue Jellyfish (Cyanea lamarackii),

Jellyfish husbandry is still difficult today but could not be accomplished without the findings of Delap’s work. Her research is still cited in various laboratory manuals on how to rear jellyfish. It’s clear, concise and includes all the various reasonings behind her decisions. Her full description of diet, temperature and aquarium placement allows any future scientist to be able to replicate her experiment. Maude Delap’s ability to raise jellyfish was an extraordinary feat considering she had no formal education, was self-taught, lived on a remote-island and worked with little resources and a home-made laboratory.

speckled pick and brown jellyfish, round top with think string tentacles flowing in light blue sea

Mauve Stinger (Pelagia noctiluca)

At the time, there was no literature available to her on culturing jellyfish as no one had successfully done it. Without a handbook to refer to, she continually battled against the many variables and difficult needs of the jellyfish. She used her own instinct and a process of trial and error. It’s possible Delap may have spent hours observing the jellyfish within the tanks, figuring out what needed to be done next. Her observations on the importance of diet were incredibly important to further studies on rearing jellyfish, as at the time, diet was not taken wholly into account. Marie Lebour was a biologist with the Marine Biological Association in Plymouth who was interested in culturing many different types of marine animals. She combined Edward Browne’s plunger jar and Delap’s understanding of diet to successfully raise and study jellyfish in an aquarium.

photo of a modern bell jar, round on top, flat on bottom, with tiny jellyfish in it.

Modern day jellyfish bell jar “The Darwin Tank” (Kickstarter)

Of course, Maude continued to try many different rearing experiments. From her sketches that have been observed in the Valentia Heritage Centre and the Natural History Museum in London, we can see that Maude brought many things in from the sea and placed in her aquariums to observe and rear. Often these descriptive sketches were sent to Edward T. Browne for observation and examination. Some other successful rearing experiments of Maude’s concerned the hydromedusae, which are the smaller species of jellyfish which inhabit the water. These can either be a few millimetres in scale and only visible under a microscope or can be large enough to observe by eye in the water. Rearing these species would have involved a lot of meticulous lab work and micrcroscopy.

In 1906, Browne received a letter with drawings from Delap saying that she had kept a group of a microscopic jellyfish species known as Cuspidellacostata in an aquarium. Before this, the reproduction process of Cuspidella was unknown. Examination of these medusae led Browne to the conclusion that they were Laodicea undulata (which is now it’s accepted scientific name).

slightly blured photo of a microscopic plankton, white blob with tentacles

Laodicea undulata. Source:

In 1936, Fredrick Stratten Russell, a famous English marine biologist who specialized in plankton, published a paper “On the hydroid of Laodicea undulata” which confirmed what was detailed in Maude’s sketches; that the hydroid of L. undulata is a species of Cuspidella. In his paper, which was published in the Journal of the Marine Biological Association of the United Kingdom, he acknowledged Maude’s work in detailing and recording this species and included her original sketches which were sent to Browne.

pen illustration of plankton

Proof 1 JMBA

pen illustration of plankton

Proof 2 JMBA

Additionally, Maude continued to rear other hydroids resembling Cuspidella­ from species known as Cosmetira pilosella and Dipleurosoma typicum. These life-history studies are still referred to today in modern literature.

detailed photo of very pale white and purple plankton blog with speckles and lines

Cosmetira pilosella

detailed photo of very pale white and peach plankton blog with speckles and lines

Dipleurosoma typicum

In 1904, Maude found a hydroid of a species called Stauridiosarsia ophiogaster off Valentia Island which had never been found at the time. The hydroid and the medusae she reared from this species were sent to Browne, and it was confirmed to be S. ophiogaster by Russell.

detailed photo of very pale white and yellow plankton shape with speckles and lines

Stauridiosarsia species. Source: Peter Schuchert

The fact that Maude Delap was able to successfully rear jellyfish, both large and microscopic, with such limited resources is astounding when today even with all our emerging technology, culturing jellyfish is still a difficult task. Therefore, the successful growth of jellyfish must have required extreme perseverance patience and dedication. Maude succeeded where others couldn’t and was a true icon in the history of marine biology research in Ireland.


You can read more about Maude Delap here.

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