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Asteroidea (Sea Stars)

Asteroidea

(Sea stars)

Phylum Echinodermata

Class Asteroidea

Number of families 35

Thumbnail description
Conspicuous and successful bottom-dwelling animals that can survive without food for months and feed on almost every type of marine organism encountered on the seabed; they range in size from 0.4 in (1 cm) in diameter to more than 3 ft (91 cm) across and inhabit virtually every latitude and ocean depths


Evolution and systematics

The class Asteroidea is a highly diverse group comprised of seven orders, 35 families, and an estimated 1,600 known living species, although their precise phylogenetic relationship and hence classification still proves challenging to taxonomists.

Asteroids belong to a major group of other bottom-dwelling animals called echinoderms. Collectively this group includes echinoids (sea urchins), holothurians (sea cucumbers), crinoids (feather stars), and ophiuriods (brittle stars), the latter group closely resembling sea stars. All echinoderms share similar pentamerous radial symmetry and spiny skin characteristics, although sea stars differ slightly because they have five or more arms large enough to contain space for digestive and reproductive glands. Another group of animals thought to belong to echinoderms are concentricycloids, or sea daisies. These small disc-shaped animals discovered in the abyssal seas off New Zealand and Bahamas in the late 1980s are considered an evolutionary forerunner to asteroids.

Sea stars have an ancient linage that shows embryologically they are not too distantly related to the phylum Chordata (back-boned animals). The fossil record places a form of asteroid over 300 millions years before the dinosaurs, sharing a common ancestry with ophiuroids, yet within 50 million years of their appearance they became clearly differentiated. Their evolutionary path has included some bizarre taxa that have been hard to classify, yet this successful group has persisted and remain ecologically important to many marine communities worldwide.

Physical characteristics

Sea stars vary considerably in size, shape, and color, even within the same populations. Their diverse forms reflect evolutionary adaptation to the cosmopolitan habitats they occupy. Despite this diversity they all share similar physical characteristics. All are star-shaped (stellate) with a central body or disc that has symmetrically projecting arms with rows of tube feet running along the lower surface of a V-shaped furrow called the ambulacral groove. Typically, the number of arms is five, but some species such as the coral-eating crown-of-thorns Acanthaster planci can have up to 30. Their size ranges from the 0.4 in (1 cm) arms of the cushion star Patiriella parvivipara, which gives the appearance of a nearly spherical body, to the long skinny arms of Novodinia antillensis, which span almost 3 ft (91 cm) in diameter. In most species, the arm tips carry an optic cushion of red-pigmented and light-sensitive cells that sense changes in the prevailing environment.

The skeleton of a sea star consists of small calcium carbonate plates called ossicles. These are often studded and spiny, and provide a firm but flexible skeleton of connective tissue. Flexibility enables a variety of postures to be adopted without muscular effort, thus providing an effective means to capture and handle prey and allow individuals to closely follow irregular substrates in search of food. Alternatively, their flexibility can enable sea stars to upright themselves if over-turned.

The surface of a sea star looks and feels rough because of the numerous small and transparent sacs called papulae that cover the body, which provide a respiratory surface for exchanging oxygen. The upper and lower body surfaces also contain pincer-like structures called pedicellariae, which come in a variety of forms from simple modified spines to highly specialized opposing hooks. Their function is to rid areas around the papulae of small organisms and debris, and in some species capture prey by detecting their presence. These are

usually small fish or shrimp-like crustaceans on which the sea star feeds. The shape of pedicellariae is an important characteristic for asteroid taxonomy.

Sea stars have an unusual way of moving. Water is taken in through the madreportite, a small, perforated plate on the upper surface of the disc, and into the water vascular system, a canal of tubes connected to the tube feet. Following muscular contraction water is directed under pressure to the tube feet, which then extend under its force. Movement is achieved through a coordinated stepping motion where, on muscle contraction, the feet adhere to the sediment surface, pushing the individual forward. Depending on the species, tube feet have suckers that help stick the sea star to hard surfaces or assist in prying open the shells of its mollusk prey. Besides involvement in prey capture; tube feet also have a respiratory function. Species with more than five arms and reproduce asexually will have numerous madreportites.

Distribution

The greatest diversity of sea stars occur in coastal regions, although as a group, they are well represented globally from the Antarctic, Pacific, Atlantic, and Indian Oceans. They inhabit wave-exposed inter-tidal zones of coastal waters to the calm sandy pavements of the deepest oceans. The Benthopectinidae family of sea stars, for example, lives exclusively in the deep-sea of the Atlantic and Pacific Oceans, whereas the species Odontaster validus, which belongs to the family Ganeriidae, are found only in the Antarctic Ocean. Perhaps the most well-known and ubiquitous group of sea stars belongs to the order Forcipulatida. This group includes the genus Asterias, a veracious predator of mussels and oysters in many coastal waters around the world. In the Far East, the species Asterias amurensis has extended its normal range into New Zealand and Australia, where as a non-native species it has caused extensive economical and ecological damage to the shellfish industry.

Habitat

As a group, sea stars live in virtually every habitat found in the sea, ranging from tidal pools, rocky shores, sea grass and kelp beds, beneath rock rubble, on coral reefs, sand, and mud. In some species a broad and flattened body may act as a snowshoe when foraging on very soft mud. In the upper shore, they are periodically exposed by the retreating tide, resulting in extended periods of desiccation. The only refuge is cover in moist crevices beneath rocks. By contrast, in the deep sea at depth greater than 29,530 ft (9,000 m) they are found inhabiting sandy bottoms and steep cliffs.

They are prominent seafloor predators. Perhaps their success and influence comes from a unique combination of attributes. These include indeterminate growth, a morphology and digestive system generalized enough to capture, handle, and ingest many different prey types and sizes, and a sensory ability sophisticated enough to respond quickly to the presence of prey and changes in the prevailing environment. Moreover, their flexible bodies and suckered tube feet enable them to adhere firmly to the seabed whilst manipulating prey, thus enabling them to survive in high stress environments by withstanding the full force of crashing waves.

Behavior

Sea stars have a "central nervous system," or diffuse nerve net, but lack anything identified as a brain. Despite this, they are sophisticated enough to adapt to change based on previous experiences (conditioning), whereby behavior that is persistently unsuccessful, usually a feeding one, is stopped.

They are not considered social animals, yet many species tend to aggregate or swarm in large numbers during certain times of the year. These events tend to be triggered during spawning periods, feeding frenzies, or seasonal migrations to deeper waters offshore. Some sea stars show avoidance behavior to other species or attraction towards members of the opposite sex. Feeding is perhaps the most common cause of aggregation, where sea stars can appear in thousands to prey on mussels, oysters, or coral.

The daily activity patterns in many sea stars are synchronized to changes in light intensity, usually around dawn and dusk. Such activity may help to avoid predators and coincide sea star foraging activity with the activity of their preferred prey. In others such as Astropecten irregularis, daily activity patterns are synchronized to periods of slack water on a high and low tide when velocities are low enough to optimize foraging success.

Feeding ecology and diet

Sea stars are carnivorous, preying on sponges, shellfish, crabs, corals, worms, and even on other echinoderms. Most are generalists, feeding on anything that is too slow to escape, such as mussels and clams, whilst others are specialized feeders preying exclusively on sponges, corals, bivalves, or algae. Prey is located by the chemical odors emanating from its waste products or by small movements that betray its presence when detected by a sea star. Food preferences can change depending on availability of prey, which change geographically and seasonally. Even weather conditions in temperate species and reproductive state (usually during gonad growth) affects dietary requirements.

Feeding strategies can be divided into those that are scavengers, feeding mainly on decaying fish and invertebrates; those that are deposit feeders, filling their stomachs with mud from which they extract microscopic organisms and organic matter; and those that are suspension feeders, filtering prey and food particles from the water (e.g., Novodinia antillensis).

Depending on the species, sea stars have two different feeding methods. Intra-oral feeders ingest their prey into their stomach alive, sometimes distending or rupturing their disc in the process. The burrowing sand star Astropecten irregularis, for example, can swallow hundreds of live juvenile mollusks during one foraging period. In some cases prey such as clams

and snails resist digestion by keeping their valves or operculum plate tightly closed, forcing sea stars to take weeks to digest them. Extra-oral feeders devour their prey (usually oysters and mussels) by pulling the shells apart using their tube feet and arms. Digestion occurs once the sea star's stomach is everted through its mouth and brought into direct contact with soft tissue. Often they take advantage of imperfections in the seal of the prey's shell and squeeze their stomach into 0.1 mm-wide gaps. Some animals such as clams, worms, and crustaceans avoid predation by co-existing as commensals. The worm Acholoë astericola, for example, lives within the arm grooves of its host, the burrowing starfish Astropecten irregularis, but when threatened the worm seeks refuge inside the sea star's stomach. In coral eaters, such as the crown-of-thorns Acanthaster planci, the stomach is applied directly to the coral and a patch digested. Sea stars can go without food for months. Pisaster ochraceus, for example, can survive for 18 months without eating, losing an estimate 35% of its body weight.

They have few predators as adults due to their armored spiny skeleton and rigid nature. In less heavily armored and juvenile sea stars, protection from predators comes from having a cryptic coloration. Other defensives include toxic spines or skin (e.g., Crossaster papposus and Acanthaster planci) and predator avoidance by burrowing beneath the sediment surface (e.g., Astropecten irregularis and Anseropoda placenta). Some crabs, fish, birds, and other echinoderms are known to prey on sea stars. Usually, they feed on arm tips, as their calcified bodies are difficult to eat and not very nutritious.

Reproductive biology

Most sea stars have separate sexes with no visible differences between them. Internally, each arm contains a pair of gonads that become almost filled with eggs or sperm, depending on the sex, at the time of breeding. The majority of species are broadcast spawners where eggs and sperm are released into the water column to be fertilized. To increase the chances of fertilization, sea stars aggregate when they are ready to spawn. These events usually rely on environmental cues, such as day length, to coordinate timing and may use chemical signals to indicate readiness. The crown-of-thorns sea star, for example, releases a potent chemical into the water column to attract the opposite sex. Fertilized eggs rapidly develop into free-living bipinnaria and later brachiolaria larvae that are planktonic. Eventually, they undergo metamorphosis and settle on the seabed to grow into adults. This type of reproductive strategy is known as indirect-development.

Some sea stars brood their young, where females hold their fertilized eggs in a brood space under the arm (e.g., Asterina phylactica), in the stomach (e.g., Leptasterias hexactis), or incubate them in the gonads (e.g., Patiriella parvivipara). In the last two cases, young develop internally and escape through small openings the female's body wall called gonopores. Many brooding sea stars inhabit polar and deep-sea regions. Some brooding sea stars, however, produce unguarded egg masses that they attach to the seabed (Asterina gibbosa).

Asexual reproduction is another method of development that involves either fission or regeneration of entire animal from arm parts. Almost a dozen species divide through their disc, producing clones with identical genetic makeup (e.g., Linckia laevigata). Seven species are known to voluntarily pinch off one or more arms (autotomous asexual reproduction) that subsequently regenerate a complete new disc and arms; these species tend to be very small. Even sexually reproducing animals can show asexual characteristics at different stages of their life cycle. For example, larvae can pinch off body structures capable of growing into another independent feeding larvae.

Conservation status

No asteroid is listed in the IUCN Red List of Threatened Species. Some species are protected, however, at local levels, particularly in tropical destinations where souvenir hunters have lead to a decline in numbers. In the Caribbean, for example, the sea star Oreaster reticulatus has protection.

Significance to humans

Various sea stars cause significant ecological and commercial impact, particularly to harvested shellfish throughout the world. On the North Atlantic coasts, Asterias forbesi feed intensely on oysters, mussels, and scallops, with sea star aggregations causing massive damage to shell fisheries. In New Zealand and Australia the accidental introduction of Asterias amurensis has caused extensive damage to both commercial fisheries and endemic communities. Their arrival is thought to be from ballast water discharged before docking by visiting ships and has triggered a nationwide strategy to halt their progress. Coral reefs often fall victim to the destructive feeding power of some sea stars that invade these globally important habitats. In Indo-Pacific regions Acanthaster planci is an infamous coralivore of coral reefs, causing devastating infestations and major management problems.

However, sea stars do have some commercial value. In Denmark, Asterias are used as an ingredient in fish meal, which is fed to poultry. The ancient Indians of British Columbia and the Egyptians used them as fertilizer. Some companies collect sea stars for biological supplies to schools and collectors. Their multi-rayed image is emblematic of the sea, making their dried bodies a valuable commodity to the souvenir trade.

Species accounts

List of Species

Velcro sea star
Northern Pacific sea star
Ocher star
Sunflower star
Sand star
Crown-of-thorns
Cushion star
Odontaster validus
Blue starfish
Oreaster reticulatus

Velcro sea star

Novodinia antillensis

order

Brisingida

family

Brisingidae

taxonomy

Novodinia antillensis Rowe, 1989.

other common names

None known.

physical characteristics

The sea star has between 10 and 14 arms with rows of spines and teeth-like pedicellaria. Arms are long and thin. Red brick coloration.

distribution

Atlantic Ocean, West Indies down to depths of 1,970–2,625 ft (600–800 m).

habitat

Found attached to hard substratum with steeply sloping rocky surfaces; under cliffs. Prefers areas where current speeds are relatively strong. Often associated with large semi-sedentary filter-feeding animals such as large sponges, sea fans, and stony corals.

behavior

Semi-sedentary. Spiny arms and pedicellaria act like Velcro® by sticking the sea star to virtually any surface.

feeding ecology and diet

An opportunistic suspension-feeder. Characteristic arm posture creates a basket-like appearance as arms extend into the water column and their tips curl inwards over its mouth, providing maximum exposure to currents. Food is captured as it becomes impinged on the array of arm spines and hook-like structures adapted to piercing and gripping objects. Feeds on planktonic crustaceans such as copepods, mysids, and amphipods. Remain relatively inactive whilst in the feeding posture, but slowly bend their arms to envelope captured prey.

reproductive biology

Little known about its life-history. Sexual reproduction.

conservation status

Not listed by the IUCN.

significance to humans

None known.


Northern Pacific sea star

Asterias amurensis

order

Forcipulatida

family

Asteriidae

taxonomy

Asterias amurensis Lutken, 1871.

other common names

English: Flatbottom sea star, Amur sea star.

physical characteristics

Diameter of 16–20 in (40–50 cm), with five arms that are distinctly turned up at the tips. Colors can include rosy brown, ochre and yellowish brown, red, and purple. The underside is very flat. Skin covered with numerous unevenly arranged small spines with jagged ends.

distribution

Far East, Russia, Korea, Japan, China, Alaska (north and south of the Alaska Peninsula), and ranges from British Columbia, Canada, and the northern Pacific down to a depth below 820 ft (250 m).

habitat

Found in shallow water on sheltered coasts. It can tolerate a range of temperatures (45°F [7°C] and 72°F [22°C]) and salinities, which is unusual in many sea stars; hence is also found living in estuaries. Found on sandy, mud and rock sediments, among stones and algae thickets.

behavior

Forms dense spawning aggregations, where the females have been observed lifting themselves above ground on their rays and release the eggs between the arms while the male sea star crawls beneath. Polychaete Actonoe has a symbiotic relationship with the sea stars and serves to clean its surface of unwanted microorganisms.

feeding ecology and diet

A generalist feeder. Diet includes scallops, oysters, mussels, shrimp, and even other echinoderms. Juvenile king crab Paralithodes shelter between its arms, presumably for protection against predators. Feeds by using its tube feet and arms to pull apart the shells of its prey before everting its stomach.

reproductive biology

Sexual reproduction. Spawning geographically variable; in Russia, June–July and September, and in Australia, July–October. Estimated 20 million eggs are released, and develop into free-living larvae.

conservation status

Not listed by the IUCN.

significance to humans

Accidentally introduced into southeastern Australia and Tasmania, causing extensive commercial and ecological damage.


Ocher star

Pisaster ochraceus

order

Forcipulatida

family

Asteriidae

taxonomy

Pisaster ochraceus Brandt, 1835.

other common names

English: Purple sea star.

physical characteristics

Large central disc with stout tapering arms, varying from four to seven, but usually five. Size variable but can reach 11 in (28 cm). Commonly yellow, orange, brown, and purple in color. Body covered with numerous small white spines.

distribution

Pacific coast from Alaska to California and down to a depth of 328 ft (100 m).

habitat

Intertidal rocky shores exposed to strong wave action; predator of kelp forests. Also found inhabiting tide pools at low tide.

behavior

Keystone predator because it has impact on its marine community that is disproportionately large. Can withstand 50 hours exposed to air if among moist algae.

feeding ecology and diet

Feeds mainly on the mussel Mytilus californinus, although can feed on other bivalves, snails, limpets, and chitons. Uses tube feet to pull apart shells and everts stomach to digest soft tissue. Few predators, but some are eaten by sea otters and gulls.

reproductive biology

Sexual reproduction, shedding eggs and sperm into water column. Spawn between April and May. Free-swimming larvae that feed on small planktonic organisms until they settle out on rocks. Can regenerate arms.

conservation status

Not listed by the IUCN.

significance to humans

None known.


Sunflower star

Pycnopodia helianthoides

order

Forcipulatida

family

Asteriidae

taxonomy

Pycnopodia helianthoides Brandt, 1835.

other common names

English: Sun star, twenty-rayed star.

physical characteristics

Adults usually have between 10 and 24 arms, while juveniles have only 5. One of the largest and heaviest sea stars; sizes can range between a radius of 16 in (40 cm) and 35 in (90 cm). Color variable from pink, purple, brown, red, orange, or yellow. A broad central disc and armed with over 15,000 tube feet. Skeleton has few ossicles, so the species has a soft and flexible body wall ideal for stretching mouth to accommodate large prey.

distribution

Northeast Pacific coastal waters. Found inhabiting the intertidal and subtidal zones from Alaska to California down to a depth of 1,640 ft (500 m).

habitat

Commonly found in dense seaweeds in low intertidal zones on rocky shores because their fragile bodies need the support of surrounding water.

behavior

Solitary. A fast-moving predator that can reach speeds of 5 ft (1.6 m) per minute. When two individuals meet, they display aggressive or combative behavior.

feeding ecology and diet

Feeds on bivalves, polychaetes, chitons, snails, crabs, sea cucumbers, sea urchins (e.g., Strongylocentrotus purpuratus), sand dollars, sea stars (e.g., Leptasterias), and dead or dying squid when seasonally available. Uses sucker feet when capturing prey and swallows whole, although has the ability to partly evert stomach. Main predator is the king crab Paralithodes.

reproductive biology

Sexual reproduction. Shed eggs and sperm into water column. Spawn from March to July, peaking in May and June. Planktonic larvae stage lasts between 2 and 10 weeks. Have the ability to regenerate arms.

conservation status

Not listed by the IUCN.

significance to humans

None known.


Sand star

Astropecten irregularis

order

Paxillosida

family

Astropectinidae

taxonomy

Asterias irregularis Pennant, 1777.

other common names

English: Burrowing starfish.

physical characteristics

Varies in size, but commonly between 2 in (5 cm) and 4 in (10 cm), but up to 8 in (20 cm) in deep waters. Pale violet to yellowish color with five relatively short and tapering arms that form stiff and distinct angles. It has well-developed upper and lower marginal plates fringed with small spines. The tube feet are pointed and sucker-less.

distribution

Geographical range extends from Norway to Morocco and found sub-tidally between 16 ft (5 m) and 3,281 ft (1,000 m).

habitat

Inhabits a variety of different substratum ranging from coarse gravel to fine mud, although it is more commonly found in sandy substrata. Usually buried either partially or completely within the sediment.

behavior

Migrates offshore into deeper water during the winter months to avoid cooling seawater temperatures and being dislodged by strong onshore storm surges. They show quadri-diurnal pattern of locomotory activity that coincide with periods of slack water during high and low tidal cycles, enabling prey buried in sediment to be detected more easily. It has a commensal worm Acholoe squamosa, which freely enters the stomach and lives in the ambulacral grooves.

feeding ecology and diet

Intra-oral feeder, prey are excavated from the sediment and swallowed whole. Voracious predators of mollusks, particularly the clam Spisula subtruncata, polychaetes, crustaceans, and other echinoderms. It has a limited olfactory ability and relies on detecting prey by touch.

reproductive biology

Sexual reproduction. Spawning occurs between May and July following a rise in seawater temperature. Prior to spawning sea stars aggregate together to reproduce.

conservation status

Not listed by the IUCN.

significance to humans

Arm damage is used as an indicator of bottom trawling impact.


Crown-of-thorns

Acanthaster planci

order

Valvatida

family

Acanthasteridae

taxonomy

Acanthaster planci Linnaeus, 1758.

other common names

None known.

physical characteristics

Size over 16 in (40 cm) in diameter with between 10 and 30 arms covered in dense thorn-like spines, which are mildly venomous; can inflict painful wounds that are slow to heal. Red and green coloration with reddish tips to spines. Juveniles are cryptic in color. Tube feet can function in gas exchange and feeding.

distribution

Pacific and Indian coral reefs, particularly associated with reefs in Hawaii, Australia, the Red Sea, India, and South Africa.

habitat

Adults found on open sand and feed among coral, whilst juveniles tend to hide among the coral, under rocks, and coral rubble.

behavior

Sedentary dwellers of reef habitats. Large numbers may suddenly appear feeding on coral and then disappear.

feeding ecology and diet

Solitarily, generally feeds at night. A voracious predator of hard corals. Digests food by everting its stomach over coral, releasing a digestive enzyme and then absorbing liquefied tissue. Can survive without food for six months and feed on an estimated 3.1 mi2 (8 km2) of coral per year, leaving behind dead coral skeletons.

reproductive biology

Sexual reproduction. Planktonic larvae undergo bipinnaria and brachiolaria development. Regenerates broken arms to form another individual.

conservation status

Not listed by the IUCN.

significance to humans

Have caused widespread damage to coral reefs in the Indo-Pacific Ocean, Red Sea, and Australia's Great Barrier Reef. Toxic spines capable of stinging humans, inflicting pain at site of sting and causing nausea.


Cushion star

Patiriella parvivipara

order

Valvatida

family

Asterinidae

taxonomy

Patiriella parvivipara Dartnall, 1972.

other common names

None known.

physical characteristics

One of the world's smallest known sea stars, measuring up to 0.4 in (1 cm) in diameter with stout arms. They are conspicuous yellow-orange color. Morphologically, they are similar to a co-occurring species Patiriella exigua.

distribution

Among sea stars, this species has the most restricted distribution. Currently found only within the coastal waters of southern Australia.

habitat

In either sheltered or exposed shores, usually under small boulders. At low tide, they remain covered with a few centimeters of water, although occasionally they are completely exposed.

behavior

Slow-moving and spends most of their time beneath the underside of boulders to avoid predators and desiccation at low tide.

feeding ecology and diet

Opportunistic feeder, consuming essentially algal growth and detritus, although small epifaunal organisms and decaying animals are also eaten.

reproductive biology

Unusual life-history. It is simultaneous hermaphrodite (self-fertilizing), has intragonadal fertilization, and incubates its young in the gonads. The strategy is to produce few eggs and small amounts of sperm at any one time. The advantage is a higher survival rate of offspring compared to the more usual strategy of broadcasting species. Cannibalism by juveniles feeding on other juveniles is common in this species. Most juveniles crawl away from the parent when sufficient size is reached. Emergence of juveniles appears to be influenced by temperature increases during the summer months.

conservation status

Not listed by the IUCN.

significance to humans

None known.


Cushion star

Odontaster validus

order

Valvatida

family

Odontasteridae

taxonomy

Odontaster validus Koehler, 1906.

other common names

None known.

physical characteristics

Broad central disc with five short arms tapering to a blunt tip. Can reach a size of 5.5 in (14 cm) in diameter and adopts a characteristic position with arm tips slightly raised. Colors variable, ranging from dark brown, purple, purple-red, orange, red-orange, red, brick red, dark carmine, and pink. It may have light-colored arm tips with yellowish white under surface.

distribution

Found throughout Antarctica and the Antarctic Peninsula, South Shetland Islands, South Orkney Islands, South Sandwich Islands, South Georgia Island, Shag Rocks, Marion and Prince Edward Islands, and Bouvet Island at depths down to 2,950 ft (900 m).

habitat

Commonly found inhabiting the shallow shelf waters of Antarctica, usually occurring between 49 ft (15 m) and 660 ft (200 m) depths.

behavior

Attack large prey in gangs (e.g., the sea urchin Sterechinus neumayeri and sea star Acodontaster conspicuus). Recognizes chemical odor of individuals from the same species during feeding, minimizing the risk of cannibalism.

feeding ecology and diet

An omnivore, capable of filter-feeding and eating a varied diet, including detritus, Weddell seal feces, diatoms, algae, crustaceans, mollusks, hydroids, bryozoans, sponges, polychaetes, and sea urchins. Everts stomach to feed. Predator is another sea star Macroptychaster accrescens and anemone Urticinopsis antarcticus.

reproductive biology

Sexual reproduction. Broadcast spawning. Larvae feed on bacteria and algae, and have exceptionally low metabolic rates, which are ideal for long-term survival. Slow-growing, taking up to nine years to reach normal adult size.

conservation status

Not listed by the IUCN.

significance to humans

None known.


Blue starfish

Linckia laevigata

order

Valvatida

family

Ophidiasteridae

taxonomy

Asterias laevigata (Linnaeus, 1758).

other common names

None known.

physical characteristics

Usually five arms with a body diameter that can reach 12 in (30 cm). Adults have brilliant blue coloration. Juveniles are blue-green, purplish with dark spots. The genus Linckia has many color morphs, making it difficult to identify species.

distribution

Common in shallow waters of Indo-Pacific Oceans. In particular, eastern Africa to Hawaii and the South Pacific Islands to Japan.

habitat

Adults found along coral gravel substrates of reef terraces in direct sunlight, sandy sediments, and under rocks.

behavior

Adults characteristically knock over coral when foraging. Hides during the day in coral and rocky crevices. Juveniles may sometimes aggregate in large numbers under coral and rock. Has a commensal shrimp Periclimenes cornutus.

feeding ecology and diet

Non-selective grazer, feeding on detritus, debris, and small organisms. Everts stomach to feed on prey. Predator is the Triton trumpet snail Charonia tritonis.

reproductive biology

Little known about their natural history. Asexual reproduction.

conservation status

Not listed by the IUCN.

significance to humans

Used in home aquaria and are the most commonly imported sea star.


Cushion star

Oreaster reticulatus

order

Valvatida

family

Oreasteridae

taxonomy

Asterias reticulata (Linnaeus, 1758).

other common names

English: West Indian sea star.

physical characteristics

A robust animal that can reach 20 in (50 cm) in radius. A massive inflated central disc that supports five short, slightly tapering arms. Highly variable in color from juveniles, which are mottled green, brown, tan, and gray, to adults, which are yellow, brown, or orange. All have a beige or cream lower surface. Upper surface has thick, heavy plates forming a reticulate pattern. The plates carry numerous prominent tubercles with bluntly rounded tips.

distribution

Found on both sides of the Atlantic, ranging from North Carolina, Bermuda, south to Florida, the Bahamas, Brazil, and the Cape Verde Islands off western Africa.

habitat

Prefers shallow, quiet waters of reef flats, sea grass, lagoons, and mangrove channels. Often found among sea grass beds (e.g., Thalassia testudinum and Halodule wrightii) and on sand flats associated with these sea grasses.

behavior

Solitary. Visible during day on sand and sea grass patches. Sluggish and large sea star with an estimated speed of 5–13 in (12–33 cm) per minute.

feeding ecology and diet

Feeds mainly on microorganisms and particulate matter associated with sand, sea grass, and algal substrates. Stomach everted for feeding.

reproductive biology

Sexual reproduction. Broadcast fertilized eggs into the water column. Larvae undergo planktonic stage before settling to the seafloor. Can regenerate arms.

conservation status

Not listed by the IUCN, but considered rare. Vulnerable to humans. Locally protected in the Caribbean.

significance to humans

Exploited for its ornamental value and sold as souvenirs as dried or garishly painted objects.


Resources

Books

Birkeland, C. "The Influence of Echinoderms on Coral-reef Communities." In Echinoderm Studies, edited by Michael Jangoux and John Lawrence. Rotterdam, The Netherlands: A. A. Balkema, 1989.

Blake, B. D. "Asteroidea: Functional Morphology, Classification and Phylogeny." In Echinoderm Studies, edited by Michael Jangoux and John Lawrence. Rotterdam, The Netherlands: A. A. Balkema, 1989.

Clark, A. M., and M. E. Downey. Starfish of the Atlantic. London: Chapman and Hall, 1992.

Ebert, T. A. "Recruitment in Echinoderms." In Echinoderm Studies, edited by Michael Jangoux and John Lawrence. Rotterdam, The Netherlands: A. A. Balkema, 1983.

Eugene, N. K. Marine Invertebrates of the Pacific Northwest. Seattle: University of Washington Press, 1996.

Feder, H., and A. M. Christensen. "Aspects of Asteroid Biology." In Echinoderm Studies, edited by Michael Jangoux and John Lawrence. Rotterdam, The Netherlands: A. A. Balkema, 1983.

Freeman, S. M., C. A. Richardson, and R. Seed. "Seasonal Abundance, Prey Selection and Locomotory Activity Patterns of Astropecten irregularis." In Echinoderm Research. Proceedings of the 5th European Conference on Echinoderms, edited by Maria D.C. Carnevali and Francesco Bonasoro. Rotterdam, The Netherlands: A. A. Balkema, 1999.

Hendler, G., J. E. Miller, D. L. Pawson, and P. M. Kier. Sea Stars, Sea Urchins, and Allies: Echinoderms of Florida and the Caribbean. Washington, DC, and London: The Smithsonian Institution Press, 1995.

Jangoux, M. "Digestive Systems: Asteroidea." In Echinoderm Nutrition, edited by Michael Jangoux and John Lawrence. Rotterdam, The Netherlands: A. A. Balkema, 1982.

——. "Food and Feeding Mechanism: Asteroidea." In Echinoderm Nutrition, edited by Michael Jangoux and John Lawrence. Rotterdam, The Netherlands: A. A. Balkema, 1982.

Janies, D., and R. Mooi. "Xyloplax Is an Asteroid." In Echinoderm Research. Proceedings of the 5th European Conference on Echinoderms, edited by Maria D.C. Carnevali and Francesco Bonasoro. Rotterdam, The Netherlands: A.A. Balkema, 1999.

Kozloff, E. N. Seashore Life of the Northern Pacific Coast. Seattle: University of Washington Press, 1993.

Lerman, M. Marine Biology: Environment, Diversity, and Ecology. Redwood City, CA: Cummings Publishing Company, 1986.

Menge, B. "Effects of Feeding on the Environment: Asteoidea." In Echinoderm Nutrition, edited by Michael Jangoux and John Lawrence. Rotterdam, The Netherlands: A. A. Balkema, 1982.

O'Clair, R. M., and E. O. O'Clair. Southeast Alaska's Rocky Shores, Animals. Auke Bay, AK: Plant Press, 1998.

Picton, B. E. EA Field Guide to the Shallow-water Echinoderms of the British Isles. London: Immel Publishing Ltd., 1993.

Sloan, N. A., and A. C. Campbell. "Perception of Food." In Echinoderm Nutrition, edited by Michael Jangoux and John Lawrence. Rotterdam, Netherlands: A. A. Balkema, 1982.

Periodicals

Blake, B. D. "Adaptive Zones of the Class Asteroidea (Echinodermata)." Bulletin of Marine Science 46 (1990): 701–718.

——. "A Classification and Phylogeny of Post-Paleozoic Sea Stars (Asteroidea: Echinodermata)." Journal of Natural History 21 (1987): 481–528.

Bryne, M. "Reproduction of Sympatric Populations of Patiriella guunii, P. calcar and P. exigua in New South Wales, Asterinid Sea Stars with Direct Development." Marine Biology 114 (1992): 297–316.

——. "Viviparity and Intragonadal Cannibalism in the Diminutive Sea Stars Patiriella vivipara and P. parvivipara (family Asterinidae)." Marine Biology 125 (1996): 551–567.

Bryne, M., and A. Cerra. "Evolution of Intragonadal Development in the Diminutive Asterinid Sea Star Patiriella vivipara and P. parvivipara with an Overview of Development in the Asterinidae." Biological Bulletin 191 (1996): 17–26.

Bryne, M., M. G. Morrice, and B. Wolf. "Introduction of the Northern Pacific Asteroid Asterias amurenis to Tasmania: Reproduction and Current Distribution." Marine Biology 127 (1997): 73–685.

Ebert, T. A. "The Consequences of Broadcasting, Brooding, and Asexual Reproduction in Echinoderm Metapopulations." Oceanologica Acta 19 (1996): 217–226.

Emson, R. H., and I. C. Wilkie. "Fission and Autotomy in Echinoderms." Oceanography Biological Annual Review 18 (1973): 389–438.

Emson, R. H., and C. M. Young. "Feeding Mechanism of the Brisingid Starfish Novodinia antillensis." Marine Biology 118 (1994): 433–442.

Freeman, S. M., C. A. Richardson, and R. Seed. "The Distribution and Occurrence of Acholoe squamosa (Polychaeta: Polynoidae), a Commensal with the Burrowing Starfish Astropecten irregularis (Echinodermata: Asteroidea)." Estuarine, Coastal and Shelf Science 47 (1998): 107–118.

——. "Seasonal Abundance, Spatial Distribution, Spawning and Growth of Astropecten irregularis (Echinodermata: Asteroidea)." Estuarine, Coastal Shelf Science 53 (2001): 39–49.

Kaiser, M. J. "Starfish Damage as Indicator of Trawling Intensity." Marine Ecology Progress Series 134 (1996): 303–307.

Keesing, J. K., and J. S. Lucas. "Field Measurement of Feeding and Movement Rates of the Crown-of-thorns Starfish Acanthaster planci." Journal of Experimental Marine Biology and Ecology 156 (1992): 89–104.

Kidawa, A. "Antarctic Starfish, Odontaster validus, Distinguish Between Fed and Starved Conspecifics." Polar Biology 24 (2001): 408–410.

Lawrence, J. M., M. Byrne, L. Harris, B. Keegan, S. M. Freeman, and B. C. Cowell. "Sublethal Arm Loss in Asterias amurensis, A. rubens, A. vulgaris and A. forbesi (Echinodermata: Asteroidea)." Vie et Milieu 49 (1999): 69–73.

Lawrence, J. M., and J. Herrera. "Stress and Deviant Reproduction in Echinoderms." Zoological Studies 39 (2000): 151–171.

Laxton, J. H. "A Preliminary Study of the Biology and Ecology of the Blue Starfish Linckia laevigata on the Australian Great Barrier Reef and an Interpretation of Its Role in the Coral Reef Ecosystem." Biological Journal of the Linnean Society 6 (1974): 47–64.

Littlewood, D. T. J. "Echinoderm Class Relationships Revisited." In Echinoderm Research, edited by R. H. Emson, A. B. Smith, and A. C. Cambell. Rotterdam, Netherlands: A.A. Balkema, 1995.

McClintock, J. B. "Trophic Biology of Antarctic Shallow-water Echinoderms." Marine Ecology Progress Series 111 (1994): 191–202.

Menge, B. A., E. L. Berlow, S. A. Blanchette, S. A. Navarrete, and S. B. Yamada. "The Keystone Species Concept: Variation in Interaction Strength in a Rocky Intertidal Habitat." Ecological Monographs 64 (1994): 249–286.

Mosig, J. "Pacific Sea Star Looms as Threat to Aquaculture." Austasia Aquaculture 4 (1998): 57–58.

Paine, R. T. "A Note on Trophic Complexity and Community Stability." American Naturalist 103 (1969): 91–93.

Pawson, D. L. "Some Aspects of the Biology of Deep-sea Echinoderms." Thalassia Jugoslavica 12 (1976): 287–293.

Pearse, J. S. "Reproductive Periodicities in Several Contrasting Populations of Odontaster validus Koehler, a Common Antarctic Asteroid." Biology of the Antarctic Seas 2, Antarctic Research Series 5 (1965): 39–85.

Scheibling, R. E. "Dynamics and Feeding Activity of High Density Aggregations of Oreaster reticulatus (L.) (Echnodermata: Asteroidea) in a Sand Patch Habitat." Marine Ecology Progress Series 2 (1980): 321–327.

——. "Feeding Habits of Oreaster reticulatus (Echnodermata: Asteroidea)." Bulletin of Marine Science 32 (1982): 504–510.

Sloan, N. A. "Aspects of the Feeding Biology of Asteroids." Marine Biology Annual Review 18 (1980): 57–124.

Tyler, P. A., S. L. Pain, and J. D. Gage. "The Reproductive Biology of the Deep-sea Asteroid Bathybiaster vexillifer." Journal of the Marine Biological Association of the United Kingdom 62 (1982): 57–69.

Zann, L., J. Brodie, C. Berryman, and M. Naqasima. "Recruitment, Ecology, Growth and Behavior of Juvenile Acanthaster planci (L.) (Echinodermata: Asteroidea)." Bulletin of Marine Science 41 (1987): 56–575.

Other

Freeman, S. M. "The Ecology of Astropecten irregularis and Its Potential Role as a Benthic Predator in Structuring a Soft-sediment Community." PhD Thesis. School of Ocean Sciences, University of North Wales, Bangor, UK, 1999.

Steven Mark Freeman, PhD

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