A research team in California uses a hormone mixture to induce male and female sunflower sea stars to release their sperm and eggs. - PHOTO: BIRCH AQUARIUM AT SCRIPPS INSTITUTION OF OCEANOGRAPHY via The Straits Times/ANN
SINGAPORE (The Straits Times/ANN): With its arms fanned wide open, the solitary creature sits regally on the Pacific Ocean floor, some 450m deep.
One of the largest and fastest sea stars in the world, the sunflower sea star has up to 24 arms – the most of its kind – can reach a diameter of 1m and can move as quickly as 3m per minute across the seabed, thanks to more than 15,000 tube feet beneath its arms which draw in water and move it through internal canals of its body.
But it cannot outrun an underwater pandemic that has devastated sea star populations by the billions in the past decade. Scientists are racing to turn the tide on this decline through breeding programmes.
With colours ranging from orange to yellow to purple to brown, the majestic creatures have, heartbreakingly, been turning into piles of white goo due to an unknown waterborne virus that has been attacking sea stars up and down the US West Coast, from Alaska to Mexico.
When the sea star wasting disease strikes, white lesions form on the creature’s arms as connective tissue start to break down, causing the arms to fall off.
While sunflower sea stars (Pycnopodia helianthoides) typically regenerate missing or damaged arms, the disease causes the body to dissolve into a jelly-like puddle and they die within days. Since the outbreak of the sea star wasting disease in 2013, an estimated 5.75 billion sunflower sea stars have died, decimating the global population by 94 per cent, the US-based global environmental organisation The Nature Conservancy says.
A researcher collecting eggs from a female sunflower sea star. - PHOTO: BIRCH AQUARIUM AT SCRIPPS INSTITUTION OF OCEANOGRAPHY via The Straits Times/ANN
The disease has spread among numerous sea star species, both through direct contact and via waterborne transmission.
The sunflower sea star has suffered the most severe impact, and was listed as critically endangered in 2020 by the International Union for the Conservation of Nature, the global authority on the status of the natural world.
While higher sea temperatures speed up the progression of the wasting disease, there is no clear link between climate change and the pandemic.
Efforts are taking off globally to help the sunflower sea star – as well as other marine species threatened by climate change and overharvesting – reproduce, to ensure the long-term survival of the species.
Sunflower sea stars are typically found in rocky reefs, kelp forests and sand flats in the eastern Pacific Ocean, from the Aleutian Islands in Alaska to Baja California in Mexico.
They feed on vegetation-eating sea urchins. When sea star numbers decline, the surging urchin populations devour kelp forests that are both habitats and food sources for all kinds of marine life, including fish, seals, sea lions, sea otters and whales.
In February, a research team at the Birch Aquarium at the Scripps Institution of Oceanography at the University of California in San Diego succeeded in breeding the sunflower sea star.
The team used a hormone mixture to induce male and female sunflower sea stars to release their sperm and eggs by the millions, which were collected for fertilisation in a controlled environment.
The team, made up of researchers from Birch Aquarium, Aquarium of the Pacific, California Academy of Sciences, San Diego Zoo Wildlife Alliance and Sunflower Star Laboratory, is part of a larger collaborative effort among researchers, marine conservation professionals and environmental educators to accelerate the recovery of the species along the US West Coast.
Another team in Washington, led by research scientist Jason Hodin, in 2023 reintroduced 48 juvenile sea stars aged between one and two years old into the ocean.
They were released in cages to closely track their progress. One of the cages – containing 10 sea stars – was lost. It was believed to be due to recreational fishing activity nearby, but Dr Hodin said the other 38, which have been brought back to the lab for further study, are “healthy and growing a lot”, with other juveniles being reared.
The team is also planning its first small-scale release of lab-reared juvenile stars into the wild by July or August – these will be tracked regularly to monitor their growth.
Tiger cowries feed voraciously on invasive sponges that can overtake live corals, which allow other native creatures in reef habitats to have enough space and resources. - PHOTO: NUS TROPICAL MARINE SCIENCE INSTITUTE via The Straits Times/ANN
Dr Hodin said a group of researchers led by marine ecologists Drew Harvell and Alyssa Gehman, including microbiologists from the University of British Columbia, could be close to finding the cause of the disease – which may be a bacterium.
A genomics team at the University of California, Merced, led by Professor Mike Dawson and research scientist Lauren Schiebelhut, is studying the genetic make-up of the sunflower sea stars that have survived the pandemic. It hopes to find the gene that helps the sea stars to fight the disease, so as to replicate it in a new generation.
Meanwhile, in Singapore, the National University of Singapore’s Tropical Marine Science Institute has been assisting the boring giant clam (Tridacna crocea) and the tiger cowrie (Cypraea tigris) in boosting their numbers.
Overharvested for their attractive shells and popular with aquarium hobbyists, both shellfish are found in shallow reef waters and are deemed endangered here, although they have healthy populations elsewhere in the world.
The boring giant clam is an important food source for a wide array of predators and scavengers. Dense clusters of giant clams serve as shelters and nurseries for fishes.
Tiger cowries feed voraciously on invasive sponges that can overtake live corals, which allow other native creatures in reef habitats to have enough space and resources.
A three-year project led by principal investigator Neo Mei Lin was started in 2021 to study the breeding and culturing of boring giant clams and tiger cowries to develop the cultivation, management and harvesting of these shellfish.
Giant clams have both male and female reproductive organs.
Dr Neo’s research team first injects the hormone serotonin into the clams’ reproductive parts, which causes them to release sperm and eggs into the water. The sperm and eggs are collected separately before they are mixed in various tanks for fertilisation.
The researchers monitor the clam larvae closely and culture them for about a month as they develop into juvenile clams, and another two years before they reach adulthood.
Dr Neo’s team reported in 2023 that they had succeeded in getting larvae of endangered tiger and Arabian cowries to develop and settle into juveniles by keeping them in optimal environmental conditions in the lab, where other previous reproduction studies had not succeeded.
With the tiger cowries, the researchers focused on providing the sea snails with optimal living conditions in the lab, but did not intervene directly to induce breeding.
“The bulk of work comes from upkeeping and feeding the broodstock, monitoring the status of the brooding females, collecting the larvae and keeping them in the lab for culturing, as well as growing out the larvae into juveniles,” said Dr Neo.
Dr Neo’s research team hopes to boost the production of both endangered marine species – for research and conservation. It has been able to produce juvenile boring giant clams about once every three months.
She said: “Assisted reproduction of marine species is akin to buying insurance, where we can withdraw this knowledge to help species recover their numbers in the event of challenges such as disease outbreaks and global warming.” - The Straits Times/ANN
