In this series, we showcase the diversity of rare, peculiar, and fascinating native flora and fauna in Singapore. We enthusiastically invite you to explore our nature reserves and gardens, urging you to pause and observe your surroundings—whether by looking up or down—to see if you can catch a glimpse of these unique wonders.
Sea Stars
Sea Stars, commonly called Starfish, are not fish. They don’t have gills, fins, scales, and no backbone. These star-shaped invertebrates are related to sea urchins and sea cucumbers, which all belong to the group Echinodermata––meaning spiny skin. Echinoderms have hard calcified skin that helps them protect them from most predators.
Image courtesy of Profmauri
Sea stars can be found in every ocean of the world. Most species have five long arms that join a central disk, although some may have more like the Eight-armed Sea Star!
Common name: Eight-armed Sea Star
Scientific name: Luidia maculate
The Eight-armed Sea Star is native to the Indo-Pacific region. It is one of the largest species of sea stars in Singapore and can grow up to 60cm across in diameter. The number of arms can range from five to nine, but it is commonly observed that they have eight arms. It is often spotted in sub-tidal waters or near areas with seagrass or coral rubble in Northern shores. It feeds on both algae, rotting plants, mussels, clams, snails, worms, and other small creatures.
Image courtesy of Walaa
Sea stars are known for their five-point radial symmetry. Some sea stars have arms so short and stubby that they resemble a pentagon, like the Cushion Star.
Common name: Cushion Star
Scientific name: Culcita novaeguineae
The Cushion Star is a small sea star that grows up to 5cm. It has very short, broad arms and a puffy appearance, resembling a pentagonal pin cushion. It varies in colour and can be found in tropical waters in the Indo-Pacific. It feeds on algae, barnacles, and other invertebrates. To catch its food, the cushion star inflates its “cushion”, and deflates on top of its prey.
Image courtesy of Shizhao
Sea stars have hundreds of suction-bottomed tube feet on the underside of their arms. These tube feet serve various functions such as helping sea stars move, attach to surfaces, and collect food.
Most sea stars are carnivores, feeding on sea urchins, clams, oysters, crabs, and snails. They display a scavenging behaviour, devouring nearly anything they can grasp with their arms. Certain species are omnivores, also incorporating algae and decaying plant matter in their diet.
Image courtesy of California Sea Grant
In numerous ecosystems, sea stars play a vital role as keystone species, contributing to the maintenance of a healthy marine ecosystem. Their position as natural predators of sea urchins enables them to effectively control the population of sea urchins. Sea urchins have a voracious appetite for kelp and other vegetation, which serve as critical habitat and a food source for a wide variety of species. If sea stars were to decline or die off, the sea urchin population would multiply unchecked, leaving them to consume kelp uncontrollably. In Northern California, for example, the sunflower sea star’s disappearance has turned kelp forests into “urchin barrens”.
In any ecosystem, including marine ecosystems, a keystone species plays a vital role in maintaining the overall structure and function of the system. Without their presence, ecosystems would experience significant alterations and may struggle to adapt to environmental changes. The disappearance of a keystone species can have far-reaching consequences, potentially disrupting the intricate balance and stability of the entire ecosystem.
Sea stars face a range of threats, including habitat loss in reef flats and seagrass habitats due to human activities such as coastal development, land reclamation, and dredging. In addition to these localized threats, the broader issue of global warming and rising temperatures poses a significant risk to sea stars as well.
Sea stars have a unique respiratory system as they do not rely on gills or lungs to breathe. Instead, they absorb oxygen through specialized structures called papulae, or skin gills, which are distributed all across their outer surface. These papulae enable the sea stars to facilitate the process of oxygen diffusion. However, a recent study conducted by Cornell University highlights that current ocean conditions have created an environment favourable for increased bacterial growth. Unfortunately, this excessive bacterial growth has led to a depletion of oxygen in the surrounding water––essentially depriving sea stars of the oxygen they need to survive.
Image courtesy o: Joi Ito
That being said, sea stars are incredibly resilient. They possess an incredible ability to regenerate parts of their body. Even if they lose an arm or a significant portion of their body, they have the remarkable capacity to regrow those sections. As long as at least one-fifth of the central disk and one arm remain intact, the sea star can fully recover. The process of regeneration may take up to a year.
There are at least 31 species of sea stars on the shores of Singapore. Here are two more remarkable species you might be fortunate enough to spot!
Common name: Knobbly Sea Star
Scientific name: Protoreaster nodosus
The Knobbly Sea Star, also referred to as the Chocolate Chip Sea Star, stands out as one of the largest sea stars found in Singapore, growing up to an impressive 30cm in diameter. It has distinctive brown knobs that look like chocolate chips on its body and arms. These sea stars are commonly observed in areas abundant in coral rubble. Their diet consists of a diverse range of food sources such as clams, snails, sponges, as well as organic matter such as dead plants and animals.
Image courtesy of Rob
Common name: Common Sea Star
Scientific name: Archaster typicus
The Common Sea Star, which is also known as the Sand Star, is typically found in the shallow waters of the Indo-Pacific region. Despite its name, this sea star has become increasingly rare on the shores of Singapore. With a maximum diameter of around 15cm, these sea stars usually exhibit gray or brownish colors. They prefer habitats in shallow, sheltered areas with silty or sandy substrates, often in proximity to seagrass beds and mangroves. Their diet consists of decaying plant matter as well as small creatures. One fascinating aspect about them is their ability to swiftly move using their tube feet, accomplishing speeds of up to 70cm per minute.
Image courtesy of Ria Tan
A key consideration when you spot a sea star: don’t pick it up!
You may have heard of the Starfish Story, where a man throws sea stars back into the ocean to save them. Contrary to this tale, picking up sea stars is not encouraged. Sea stars have soft and thin tissues and can become contaminated with bacteria passed on through human touch. The sunscreen or oils on our hands may also harm them.
Sea stars have a crucial dependence on seawater and have limited survival capabilities outside of their watery habitat. Notably, according to Ria Tan from Wild Singapore, if you happen to come across sea stars outside of water, they are likely alive and belong to intertidal species accustomed to enduring periods without water during low tide.
All sea stars that you see are probably alive, [since] dead sea stars disintegrate quickly and don’t leave behind whole skeletons.
Ria Tan, Wild Singapore
If you come across sea stars in the wild, we encourage you to (safely and respectfully) capture photos and document your observations. We especially recommend using the local SGBioAtlas app, or the iNaturalist app, which enables you to share and validate your findings within the community.
Discover the wonders of nature, observe the intricacies of the world around you, and let curiosity be your guide. Happy exploring!
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