In another section of the lab, some work on cultivating phytoplankton and zooplankton to feed the sea jellies and other marine animals in the aquarium.

Others in the aquatic nursery concentrate on the breeding of sea animals like clownfish (of near-threatened status in Singapore) and banggai cardinalfish (of endangered status globally), among others.

Aquarists tending to sea animals in the lab’s aquatic nursery.

Before the aquarium is opened to the public at 10am, the team will have wrapped up the first round of cleaning and feeding of the medusae, or mature jellies. The babies, or ephyrae, would also have had their first meal of the day.

Opened in 2023, the Aquarist Lab is a showcase of the aquarium’s breeding programmes and live cultures. Of these, 70 per cent are focused on sea jellies.

Aquarist Jessie Boey surveying a moon jelly habitat to choose suitable ones for public viewing in the main display habitat.

Four of the sea jelly species bred – moon jellies, white-spotted sea jellies, Atlantic sea nettles and Pacific sea nettles – are on display in the aquarium.

A batch of moon jellies, a crowd favourite, being released into a display habitat.

The public can watch how the lab works through a window, while those wanting a close-up view of its inner workings can buy a ticket for a special behind-the-scenes tour.

Senior aquarist Vivian Cavan (left), 36, checking on the health of the lab’s zooplankton first thing in the morning before the aquarium opened, while other aquarists worked on the nursery section.

Sea jellies – as they are called at the aquarium, instead of jellyfish – are invertebrates that have been around for 500 million years, and there are at least 2,000 species of them. According to the aquarium’s education guide, Mr Bryan Ang, 30: “A sea jelly is not a fish as it does not have fins, gills or scales, which are characteristics of most fish; hence, ‘sea jelly’ is more appropriate.”

A fried egg sea jelly and its reflection in a habitat in the lab. The sea jelly is named for its bell, which looks like a fried egg yolk. Fried egg sea jellies can currently be observed only in the lab.

“It is a term being used more now in the aquarium industry,” he adds.

The process of breeding sea jellies is complicated, with each species having different needs. Veering from these conditions, no matter how slightly, can affect their survival and breeding.

Ms Boey measuring the temperature of the water in a grow-out habitat for juvenile medusae during a water change. Different species of sea jellies need water of different temperatures to survive.

Sea jellies need controlled water quality with precise temperature, salinity and pH levels. Being weak swimmers with soft, gelatinous bodies that can be easily damaged, they are bred in special rounded tanks called kreisel (German for “roundabout”) aquariums, which create a gentle, cyclic water flow so that the sea jellies are not injured from getting stuck in corners or against walls.

Education guide Arthur Liu, 20, with visitors to the aquarium’s Behind The Scenes: Aquarist Lab tour.

To support its breeding programme, the lab keeps live cultures of zooplankton and phytoplankton in sterile and exact conditions. Zooplankton serves as a food source for the jellies. The zooplankton eat phytoplankton, which are given nutrient boosts and controlled lighting for photosynthesis.

A row of phytoplankton (right). They are key food for zooplankton and other marine animals.
A jug of zooplankton, which the lab breeds for the sea jellies and other aquatic animals.

Aquarist Benjamin Pang, 27, who has a degree in aquaculture and has been at the lab for four months, says: “Most people don’t realise it, but the job can be physically demanding – we’re always standing and moving. During the first two months, I lost 6kg!”

Mr Pang pouring disinfectant onto a mat at one of the lab’s entrances. This helps to keep the lab as sanitised and clean as possible for the sea jellies and other animals in the lab.

Each day, usually in the morning, an aquarist scrutinises a sample of zooplankton under a microscope.

PRIME CONDITION

Cell counts are done to ensure the zooplankton are in prime condition for harvesting and ready to serve as a mother culture for the next batch.

A sample of rotifer, a type of zooplankton, under a microscope. The aquarists study samples of zooplankton under microscopes daily to monitor the health of the population. ST PHOTO: NG SOR LUAN

The grow-out habitats of the medusae are cleaned four times daily. Debris, such as tentacles that have fallen off the sea jellies, food waste and excrement, is siphoned out.

Tentacles that have fallen off are among debris that the aquarists siphon out of the habitats several times a day to keep the water clean.

Ammonia build-up from excrement is toxic to sea jellies. Food waste and tentacles that have fallen off can decay over time and cause bacterial growth. A clean habitat helps aquarists monitor the sea jellies’ health and behaviour better.

Ms Boey cleaning a grow-out habitat. The water in the habitats is cleaned four times a day.
This includes siphoning out tentacles that may have fallen off, food waste and excrement.

The jellies are fed on a precise schedule that varies according to their different life stages, from the polyp, which reproduces asexually to produce the ephyra, to the mature medusa.

The sea jellies are fed through two processes: broadcast feeding and target feeding.

With broadcast feeding, food is dispersed throughout the habitat, allowing animals to feed freely.

Aquarist Clarice Ong, 21, broadcast feeding a black sea nettle after the grow-out habitats have been cleaned.

Target feeding is used on juvenile jellies, as well as those that did not get enough food during the broadcast feed.

Ms Ong target feeding an Atlantic sea nettle, with a black sea nettle drifting in the foreground.

During feeding, the aquarists also observe the sea jellies to monitor their health, ensure that they have received enough sustenance and understand their behaviour.

Ms Ong observing the moon sea jellies after feeding, to monitor their health and ensure they are feeding well.

With feeding done, the aquarists turn their attention to cleaning the grow-out habitats of the juvenile jellies.

Ephyrae are typically less than 5mm in size, with many smaller than that, while juvenile medusae are 1mm to 2cm in size. Because they are so tiny, changing the water of their grow-out habitats – jars or smaller kreisel tanks – requires infinite patience, focus, tenacity and stamina.

Purple-striped sea nettle ephyrae in a dish before being returned to a grow-out habitat during a daily water change. They measure about less than 1mm in size.

Aquarists first scoop water containing the ephyrae and juvenile medusae into white picking bowls, from which they are siphoned through a pipette into a holding container.

Atlantic sea nettle ephyrae being poured into holding containers.
Atlantic sea nettle ephyrae seen in a holding container in the Aquarist Lab.

This process is repeated until the jars or kreisels are sifted through, with each taking up to 30 minutes of work. The habitats are then cleaned before being filled with treated seawater of an appropriate temperature.

Ms Boey pouring water out of a kreisel aquarium during a water change. The aquarists spend at least two hours a day changing water for ephyrae and juvenile medusae.

Bubbles that have formed on the wall of the grow-out habitats are removed with a pipette, before the ephyrae and juvenile medusae are released back into them and fed again.

Ms Ong checking on jars of ephyrae and juvenile medusae. The lights of the grow-out habitats are switched off whenever possible to conserve energy.
Ms Ong rubbing her eyes after two hours of water change for polyps.

A similar process is carried out for polyps, which are kept in containers in industrial refrigerators.

Containers of polyps kept in an industrial fridge, seen in the background.

Polyps grow on substrates such as acrylic plates. Different sea jelly species require different substrates.

Ms Boey checking on polyps in the fridge.

The polyps are first basted to clean them and help them release uneaten food and ephyrae produced. The aquarists check the health of the polyps by looking at the “fluffiness” of the tentacles as well as their size and shape, and if they are reproducing.

Ms Ong (left) picking out loose polyps and newly found ephyrae from water from a holding container of polyps, while Ms Boey checked on the health of a batch of polyps attached to a substrate before conducting water change.

Algae that has formed on the substrates is scraped off before the plates of polyps are placed in a holding container.

A close-up of polyps on a substrate in a jar. The aquarists have to remove algae that forms on the substrate and sometimes in the polyps themselves.
Some polyps that have attached themselves to the walls of the habitats are not removed during cleaning to serve as backups, in case other polyps die.

The aquarists then pick through water in the picking bowls, poured from the polyps containers, hunching over them for as long as it takes to pick out loose polyps and ephyrae.

Ms Ong picking out loose polyps and newly found ephyrae from a picking bowl of polyps.

The polyp container is then cleaned and filled with treated seawater. The polyp plates and loose polyps are returned to it and put back in the fridge, while the newly collected ephyrae are moved to grow-out habitats.

Ms Boey creating flow within a dish of black sea nettle ephyrae so that they do not fall and settle at the bottom of the dish, as they acclimatise to the temperature of the water in their grow-out habitat.
Freshly found black sea nettle ephyrae, measuring about 1mm each, being transferred to a grow-out habitat that contains fresh water after it has acclimatised to the water.

As the ephyrae mature into jellies, they are moved into increasingly bigger habitats, and eventually, perhaps, into display habitats to be enjoyed by the public.

The cannonball sea jelly has more structured and intricate tentacles than other sea jellies at the aquarium. It is also harvested or cultured for human consumption in some parts of China.

Sea jellies have an average lifespan of a year.

SELF-SUSTAINABLE

Breeding sea jellies and cultivating plankton allows the aquarium to be assured of their state of health as well as self-sustainable, so it can avoid taking jellies from the wild.

Purple-striped sea jellies drifting among artemia (a type of zooplankton) that is being fed to them. The purple-striped sea jellies can currently be observed only in the lab.  ST PHOTO: NG SOR LUAN

The aquarium carries out exchanges of jellies and polyps with other aquariums. A spokesperson for the aquarium says: “Sharing surplus sea jellies and their polyps with other aquariums is a more sustainable approach to resource management. This practice supports conservation by reducing the need to collect additional animals from the wild and fosters the spirit of collaboration within the aquarium community.”

A visitor taking photos with white spotted sea jellies at one of four display habitats at the aquarium.

Although caring for sea jellies can be tedious, Mr Benjamin Pang finds it worthwhile. “I have interned at a lot of different sea farms… I found farms quite depressing because at the core of it, I love animals, but we were raising them to be killed. I find this more enjoyable than farms.”