By Eleanor Winston Things are not always what they seem and when it comes to the Asteroidea, or the starfish, they are not the angelic peaceful creatures humans make them out to be. The starfish’s greatest weapon is its feet. They use them to sense their surroundings, eat and capture prey, for transportation, and even reproduction. Starfish are also known to be the “keystone” predators in most of their ecosystems which have kept other species from having outbreaks. However, various species have become detrimental to some coral reefs due to overpopulation. This research paper will explain and expose the starfish species in their daily lives. Asteroidea, or more commonly known as Starfish, are all a part of the phylum Echinodermata. Echinoderms consist of various species of Brittle Stars, Sea Cucumbers, Sea Urchins, and Crinoids. One major characteristic most Echinoderms have in common is that they live in intertidal and subtidal zones and are generally benthic creatures. Benthic meaning creatures that generally live on the ocean floor and do not swim around. Asteroidea generally live on the ocean floor, however, through research, scientists have observed that some starfish have been seen to float up to the surface of the water. (Echinoderm, 2008) The environment of a starfish ranges from soft floors such as mud and sand, to more rocky areas of the ocean. Scientists have estimated there are 2,000 species of starfish and all of them are saltwater organisms, meaning they cannot survive in freshwater. (Whale Facts) Usually, starfish generally live in places where food is easy to come by. This is why scientists may find starfish in giant packs where there is a common food source. (Echinoderms, 2008) The environment of a starfish is very flexible and different species are seen all over the world’s oceans. This is a result of their flexible physical structure, which ties in with the dangerous nature of the starfish. A starfish’s greatest weapon against the harsh environments of the ocean is its feet. Reproduction is arguably the most interesting way a starfish can use its feet. Most starfish reproduce through asexual reproduction and sexual reproduction. When a starfish reproduces sexually, it releases their egg and sperm through its feet into the water. These become fertilized embryos, which are categorized as zooplankton until they undergo metamorphosis. The starfish then settles down on the ocean floor, becoming an adult. The way in which starfish undergo asexual reproduction is through fragmentation. This is where a part of the starfish's limb detaches from its body and then forms into another starfish. (Echinoderms) After asexual reproduction, starfish can regenerate their lost limb and continue on with their lives. This is a great defense mechanism against predators and makes it much harder to kill them off. The ability to regenerate starts with the combination of morphallaxis cells and epimorphosis cells. Regeneration is similar to starfish growing an arm naturally, however it takes a lot of energy to regrow a foot. This limits the organism’s eating habits and requires them to use a lot less energy in their daily lives. (Lawrence, 2013) Most species of Asteroidea have five to forty limbs, which extend from their central body disc, or the center of the organism. Starfish use their limbs to navigate away from danger or towards prey, therefore they are not sessile creatures.(Starfish 2008) Sessile meaning creatures that cannot move on its own, such as a sponge. According to Philip’s encyclopedia, starfish move through their water vascular system. It begins by having water enter through the sieve plate where the water is drawn in by tiny hairs that travel through the five radial canals into their tubed feet. The ampulla will start to contract and water is forced into the foot which allows them to attach to hard rocks. Then, the muscles in the foot shorten which allows water to be forced back into the foot, and thus draw the starfish forward (figure 3). From these steps, it is obvious their methods of transportation are very slow, which is one of their greatest weaknesses. Another characteristic starfish possess is radial symmetry, which allows the organisms to be divided into almost identical halves in every angle of the central axis (Starfish 2008). Another known physical trait starfish are known for is that they do not have a brain. However, that does not make them dumb creatures, like they are portrayed through the famous character Patrick Star in the well-known kid’s TV show Spongebob Squarepants. Instead, they use sensory organs that makes them the perfect predators to bottom feeders. One of the sensory organs they possess is an eyespot, which helps to differentiate between light and dark and gives them the ability to locate any danger or even their next victims. A starfish captures and consumes their prey through grabbing it with their tubed feet. Typically, if the prey has a shell, they have the ability to crack it open, thus making the animal defenseless. Starfish have two stomachs located on the underside of their body. (figure 3) One allows them to capture and the other digests their prey. (figure 2). It can even extend one of its stomachs through its mouth and surround their prey. (Starfish, 2008) As for the food they eat, starfish are carnivores so most of their prey consists of mollusks, crustaceans, sea worms, and plankton. They also feed on bottom debris and most anything they can get their mouths around. This makes them very important species in the ecosystems they live in because they control outbursts of different herbivores. Starfish are the main predator for many intertidal and subtidal environments and have been found to be the keystone predator of the ecosystems they live in. Keystone predators are carnivores that help maintain outbreaks of other species. Though their main diet consists of species from the phylum Mollusca, the starfish is not very picky when it comes to what they consume. On the other hand, starfish can be detrimental to some environments like coral reefs. In 1963, a population of starfish called Acanthaster planci (figure 1) exploded on the great barrier reef. The outbreak of this species killed off a lot of coral and fisherman targeted to kill off this species. Since the first outbreak in Australia, there have been more outbreaks in the southern Pacific. Scientists have yet to understand why these outbreaks happen, but the major hypothesis blames the endangerment of the ‘Pacific Triton,’ the starfish’s biggest predator (Crown of Thorns Starfish, 2017). Starfish are not endangered species but they do have threats just like any other organism. Due to their small size and inability to move fast or defend themselves, they are easy targets to bigger predators such as sharks, various species of crabs, and even humans. Due to their slow nature, they cannot always move fast enough to get back into the water. If the tide does not bring them back, they will become stranded on the shore, drying out and dying, becoming food for birds on the land. (Whale Facts) Starfish are beautiful, yet ruthless organisms. The way they eat, regrow their arms, transport, and capture their prey are just a few interesting characteristics of the species that make them dangerous to other benthic creature. They can live in many diverse ecosystems in which they are the keystone predators, which are essential to the survival of the food chain. On the other hand, starfish have been known to ruthlessly destroy ecosystems like the Great Barrier Reef. Starfish are not endangered mostly because they have a very good defense system. However, due to their inability to move quickly, it can make them defenseless when they are washed up on shore or faced with bigger predators. Overall, starfish are very important to the ecosystem despite their ruthless nature when it comes to coral reefs. It is important society needs to protect this creature, or else many ecosystems will be lost.
Works Cited Starfish. (2008). In Philip's encyclopedia. London, UK: Philip's. Retrieved from https://login.liblink.uncw.edu/login?url=http://search.credoreference.com/content/entry/philipency/starfish/0?institutionId=3329 Crown-of-thorns starfish. (2017). In Encyclopaedia Britannica, Britannica concise encyclopedia. Chicago, IL: Britannica Digital Learning. Retrieved from https://login.liblink.uncw.edu/login?url=http://search.credoreference.com/content/entry/ebconcise/crown_of_thorns_starfish/0?institutionId=3329 Echinoderms. (2008). In C. Love, & C. Stamps (Eds.), Animals: a visual encyclopedia. London, UK: Dorling Kindersley Publishing, Inc. Retrieved from https://login.liblink.uncw.tedu/login?url=http://search.credoreference.com/content/entry/dkanimals/echinoderms/0?institutionId=3329 Echinoderms. (n.d.). Retrieved October 25, 2017, from http://www.mesa.edu.au/echinoderms/echino01.asp Starfish. (n.d.). Retrieved October 25, 2017, from http://www.whalefacts.org/starfish-facts/ Lawrence, J. M. (2013). Starfish: biology and ecology of the Asteroidea. Starfish. (2017). In Encyclopaedia Britannica, Britannica concise encyclopedia. Chicago, IL: Britannica Digital Learning. Retrieved from https://login.liblink.uncw.edu/login?url=http://search.credoreference.com/content/entry/ebconcise/starfish/0?institutionId=3329
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