Download Hwang 1 The Effects of Acanthaster planci Species on

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The Effects of Acanthaster planci Species on Humans and Marine Life
Christina Hwang
Abstract
Acanthaster planci, a predatory species that feed off of the algae and coral polyps are
found mainly in the Indian and Pacific Ocean. They start off as eggs that hatch into larvae and
feed on plankton as they make their way onto coral reefs, where they settle down and grow into
juveniles and start to feed on algae, mature completely and then feed on the coral. This
predatory species of starfish have already done some damage to the coral reefs because of their
diet; however, within the last decade or so, there has been a boom of “Crown of Thorns” starfish
that have appeared in many islands’ coral reefs, which can be due to human influence on the
marine population and environment; this then has an effect on the overall marine populations that
rely on the coral reefs for shelter and food (Randall). Their feeding habits, reproduction and
development records, predation, as well as the explosion of their appearance throughout the
Indo-Pacific Oceans can be explained by the environment as well as human influence on those
environments.
Figure 1. Thai Crown of Thorns Starfish
http://www.richardseaman.com/Wallpaper/Nature/Underwater/Invertebrates/SeaStars/ThaiCrownOfThorns.jpg
Introduction
Acanthaster planci, also known as the “Crown-of-thorns” starfish, is one the many
various organisms living in the marine environment. Like all living organisms, Acanthaster
planci relies on a source of nutrition to sustain its life in the competitive world of the ocean, and
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it thrives depending on where it resides and gains its nutrients. In the case of the “Crown of
Thorns” starfish, it derives its food from coral polyps and the algae growing on the corals of
shallow reefs. Considered as a ravenous creature that feeds on large quantities of coral polyps,
Acanthaster planci is a fast-growing organism that has the potential to negatively affect the
ecosystems surrounding coral reefs. Because of their large size and their voracious appetites,
with few predators to worry about, Acanthaster planci are fairly well adapted and their survival
rate is fairly successful, which then affects their population size, which, in large numbers has
detrimental effects on other marine organisms, especially the coral on which they live and feed
on.
This species thrive while others are at a larger risk of becoming endangered because of
the feeding and mating habits, as well as the evolutionary adaptations that have allowed this
organism to have fewer predators that can penetrate the thick and toxic thorns that are used to
protect the starfish from the majority of predators. The ability for this species to thrive does have
something to do with human actions and influence that have affected the marine environment,
which then had a major effect on the species of Acanthaster planci.
Discussion
Habitat:
Acanthaster planci usually live on coral reefs because they feed on the coral polyps that
develop. However, these starfish do not originate from one area and one coral reef; they float
and feed on plankton as larvae and then swim to a coral reef, and then develop and grow into
mature starfish, which then feed on the coral polyps. However, this habitation is not symbiotic
like other organisms that have symbiotic relationships with the coral they live in and on. This
relationship is detrimental to the coral that these Acanthaster planci live and develop on because
these “Crown of Thorns” starfish just feed off of the coral polyps, which then kill and destroy the
corals that are continuously developing and have been developing for hundreds to thousands of
years. These starfish have a variety of preferences for their habitation; however, some coral
reefs have a somewhat symbiotic relationship with Acanthaster planci because these specific
coral reefs produce coral polyps that specifically attract these starfish (Pratchett); however, it
becomes detrimental to them when the starfish attach and feed off of the coral.
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Figure 2. Acanthaster planci feeding on coral reef near Pigeon Island.
http://www.sundaytimes.lk/120610/images/Crown-of-thorns.jpg
Predation:
As explained earlier, the main source of food for Acanthaster planci is coral polyp, but
when it is has just hatched from the egg, it swims up to the surface and feeds on plankton. It was
studied that the main food source for larval Acanthaster planci were ultraplankton or
cyanobacteria that were between 1 and 1.8µm; however, the larvae of Acanthaster planci were
able to derive more nutrition from the plankton than the bacteria (Ayukai). It then uses its cilia
and swims to a coral reef that it is attracted to, either because of the food available on the coral or
the environment around it. When it grows into a juvenile, it feeds on the coralline algae for four
to six months until it is grown enough to switch its diet to coral polyps (Crown of thorns starfish
(Acanthaster planci)). The mature adult starfish then devour the coral polyps by turning the
gastric sac inside out, spreading its membranes over the coral and digesting the soft membrane of
the coral polyps (Chesher). Acanthaster planci usually feeds at night, making it a nocturnal
feeder; however, there have been some instances when the marine organism is seen eating during
daylight (Chesher). The starfish, in moderation, is a normal part of the ecosystem; however,
when over-population occurs, there is a harmful effect to the coral cover along the shallow reefs
that line the islands oceans.
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Figure 3. Coral polyp, taken by Darwin’s Reef Exploration Team
http://darwinsreef.pbworks.com/f/1370700455/SunnyDelightzoa2.jpg
Although Acanthaster planci are considered a ravenous predator of corals, there are also
predators that eat the starfish, especially when it is in its juvenile form, and its defensive spikes
have not formed yet. These predators include crab, shrimps, fish, as well as some annelid worms.
Because these ancestors do not have a shell around them to protect them the number of predators
that are readily available to attack increase, but as time goes on and Acanthaster planci start to
develop further and become an actual adult with spikes and thorns, it is then just the carnivorous
fish such as the humphead wrasse and the starry puffer fish (Crown of thorns starfish
(Acanthaster planci)) are the predators; however, even this is very infrequent, which is why
Acanthaster planci species are able to flourish.
Reproduction:
The reproductive habits of Acanthaster planci species reproduces sexually, unlike some
marine organisms that are able to reproduce asexually, usually between December and April
(Crown of thorns (Acanthaster planci)). They reproduce by releasing eggs and sperm into the
water through the pores present on the top of the central disk, and while the eggs and sperm are
in the water, they then fertilize. Acanthaster planci female can produce up to 60 million eggs to
be fertilized by the male sperm. Because of this, Acanthaster planci species has one of the
highest rates of fertilization for invertebrate species because even if the majority of the eggs did
not hatch, quite a few would still become fertilized and hatch (Crown of thorns (Acanthaster
planci)), which can then have quite a few Acanthaster planci that would add to the additional
population present in the Indo-Pacific waters.
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Figure 4. Larval stages of Crown of Thorns Starfish
http://eatlas.org.au/sites/default/files/resize/eatlas/articles/Larval%20cycle%20of%20crown-ofthorns-480x392.png
The fertilized eggs are developed fairly quickly, usually within a day into swimming
larvae that rely on cilia as transportation so that the dispersal of the species is fairly high, that
feed on plankton. Then in about a month, the larva becomes a juvenile, in waters that are about
25°C, about room temperature, with five arms. As the juvenile becomes a young adult, more
arms are added and they become like small adults and keep growing and maturing until two
years later, when they become sexually mature (Branham) and usually live about fifteen to
seventeen years (Ault et.al).
Usually, the reproductive habits of Acanthaster planci are fairly well regulated (Crown of
thorns (Acanthaster planci)); however, due to temperature fluctuations and an increase in
temperature in the past decade, the number of Acanthaster planci that were able to reproduce and
create more offspring increased, causing a boom in the population size, which then has a
detrimental effect on the overall marine environment of the coral reefs and the living areas of
Acanthaster planci species (Randall).
Effect of Temperature:
Temperature greatly affects any environment, whether it is on land or under the sea;
however, there are many effects that can occur because of the temperature, whether it has
fluctuated greatly, or showed signs of even the slightest fluctuation. Temperature changes have,
in this case, affected the population growth of Acanthaster planci species, in which Acanthaster
planci species were able to flourish and multiply in numbers over the past decade, populating the
coral reefs of so many more islands than in the past (Randall). This explosion of the population
is worrisome because since Acanthaster planci feed on coral polyps and are already causing so
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much damage with just a handful of them, the fact that there is an explosion of this species and
the number is still growing, populating and feeding off of so many coral reefs, it then becomes
an arduous task in finding the solution to preserve the coral reefs, that are being destroyed faster
than they are being created, and not hunting the starfish species to extinction just to create a form
of balance between the two species.
The difference in temperature, probably due to climate change, has an effect on the flow
of the currents, which can then bring larvae into these areas of coral reefs, creating the sudden
appearance of Acanthaster planci into areas where this species was not discovered and because
of the fluctuations in the ocean temperatures, the different temperatures in these ocean currents,
can then confuse and trick the larvae into believing that one area of the Indo-Pacific Ocean is
more favorable than another area, where the species has been going to for generations, causing
the introduction of the species into that newfound area (Johnson and Babcock). This can be the
cause of the “population outbreak” that many researchers have been noting. Another reason why
there has been a population outbreak and a “boom” of the species, Acanthaster planci, in
different areas and islands that have not had Acanthaster planci sighting before, because of the
different temperatures. Because Acanthaster planci do not develop when the water temperature
is above room temperature, 25°C (Johnson and Babcock), the larvae could be searching for
cooler waters to feed and settle so that they would thrive. In Johnson and Babcock’s research
regarding temperature and larval development, they noted that in lower temperatures such as
10°C and 13°C, the larval development was normal, but Acanthaster planci cannot develop in
warmer temperature, coming to the conclusion that the increase in water temperatures of the
ocean have shifted Acanthaster planci’s habitat, from its former places of residence to cooler
waters.
Effect of Acanthaster planci on its habitats:
The species of Acanthaster planci are voracious and ravenous predators that feed off of
coral polyp as a mature adult. In small numbers, this species can be maintained and can live
somewhat harmoniously with its surroundings because it can feed in small numbers, providing
the food source to develop enough so that it is not completely killed off. In large numbers;
however, it can prove to be quite a destructive force of nature. In many instances, the population
explosion of the species, Acanthaster planci, has caused many researchers to become startled and
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worried for the coral species and habitats where the “Crown of Thorns” starfish reside. Because
the feeding rate of the species is faster than the rate at which the coral polyps develop, it was
shown that the coral along the Great Barrier Reef in Australia were being destroyed, due to
Acanthaster planci (Chesher). Acanthaster planci were then discovered on the reefs of the U.S.
Territory of Guam, causing this infestation of the species to be monitored and controlled. By
monitoring the species, it was seen that the infestation of the species was seen as simultaneous
throughout the Indo-Pacific Ocean and that this infestation has not occurred on a short-term basis
(Chesher).
The predation by Acanthaster planci species on the coral reefs had an effect on coral
species diversity. Predation, in general, does affect species diversity, killing off the species that
is less physically fit and allowing for the species that are physically fit to excel and reproduce;
however, this is not the case for the coral species that have fallen victim to Acanthaster planci.
Because Acanthaster planci do not have specific preferences to which coral polyp they develop,
all living coral are put at risk whenever an Acanthaster planci appear and make the coral its
home and source of sustenance. However, because of this competition, these living coral adapt
to the surrounding environment in an attempt to survive. This then results in a greater diversity
in areas where Acanthaster planci are more prevalent, compared to the areas where Acanthaster
planci are less diverse and abundant (Porter).
The damage that Acanthaster planci can do is extraordinary. Although coral reefs do
undergo a lot of destruction, from human interaction, to animals feeding and living within the
reefs, Acanthaster planci have had a big impact on the destruction of the coral found on the reefs
of many islands. It was found that since 1967, Acanthaster planci have killed over ninety
percent of the living coral on the coastline of Guam, which caused an overgrowth of coralline
algae because a large number of the polyps that usually filter feed the algae have been devoured
by Acanthaster planci. Because of this overgrowth of algae, the juveniles that feed on the
coralline algae are then attracted to the coral reefs, which then cause a bigger population of
Acanthaster planci adults to develop on the coral reef as well as the adjoining reefs, causing a
population explosion in that area. Acanthaster planci were not seen anywhere near Guam before
1967; however, when the species became more abundant and the number of starfish increased,
the majority of the coral reefs were stripped of living corals; when this occurred, Acanthaster
planci moved to the adjacent areas that had more coral polyps for the species to feed on.
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In order to somewhat control this outbreak, researchers have found that the prevention of
overfishing and protection of fish, especially in areas that have a high outbreak of Acanthaster
planci species, can help to control the population growth. They found that when enforcing no
fishing zones, the population of Acanthaster planci was 3.75 times less likely to have an
explosion of the species available in the area, but when fishing took place, the opposite was more
likely to happen (Sweatman). Zoning areas from fishing really helped to limit the explosion of
the species from overtaking the area (Sweatman). Even through these precautions; however, the
overdevelopment of the species, Acanthaster planci, is still a problem, due to their low predation
and high reproductive rates. Although precautions can be taken, because they develop so quickly,
within one week of the eggs hatching and becoming a larva, it is difficult to fully prevent
Acanthaster planci from overtaking coral populations.
Human Influence on Acanthaster planci:
Humans are one of the major causes found for the overgrowth and population boom of
Acanthaster planci. One of the major reasons why humans are to blame is chemical spills. The
concentration of Acanthaster planci has increased significantly within the last decade. The
chemical sewage and toxic runoff affected the population of the trumpet shell, Charonia tritonis,
which then started to die off because of the lethal levels of toxins that accumulated in this
organism, which affected its ability to reproduce, then affected the population “boom”
Acanthaster planci because of the reduction of this predator (Randall). Another effect of
chemical spills or introduction of additional chemicals such as thyroxine, on Acanthaster planci
demonstrated that an acceleration of adult development occurred (Johnson and Cartwright). This
then demonstrates that introduction of chemicals positively affects the growth and development
of Acanthaster planci, which then negatively affects the development of corals and coral species.
Figure 5. The BP Deepwater Horizon oil spill
http://oceanservice.noaa.gov/hazards/spills/spill.jpg
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Acanthaster planci effect on humans:
Acanthaster planci have is not only a predatory marine organism, but a venomous one as
well. Acanthaster planci species is composed of a soft membrane, but is covered in thick and
venomous thorns to ward off predators and competition for the same food source. The spines of
this organism can inflict an extremely painful wound. It is believed that the venom is in the
epidermal cell layer of the spines, where the acidophilic glandular cells produce the venom,
when making contact with another organism, can have hemolytic and lethal results in a rodent,
which is what was used to test the effects of the toxin produced by Acanthaster planci organism,
as well as the ability to induce skeletal muscle myonecrosis, necrosis of the skeletal muscle
(Hayes and Kruger). Not only does the venom from Acanthaster planci cause skeletal muscle
myonecrosis, it provokes strong cytotoxicity by reducing cellular enzymes, SOD and CAT, as
well as a significant decrease in total thiol level, while enhancing lipid peroxidation. In
conclusion, to the study, the venom, plancitoxin I, inhibited the proliferation of A375.S2,
mitochondrial dysfunction and ER stress associated apoptosis; however, although the venom can
be extremely toxic, it was found that the toxin that had cytotoxic activity inhibited the growth in
cancer cells (Lee et. al).
Conclusion
The marine organism, Acanthaster planci, also known as the “Crown of Thorns” Starfish,
is a thriving species that has detrimental effects on other marine organisms, such as living corals.
Because of the habitation of this marine organism, especially its feeding patterns, it negatively
affects the marine environment around it. Since Acanthaster planci relies on coralline algae as a
juvenile and then coral polyps as an adult, it then devours and kills living coral; once that coral is
devoid of anymore food to provide for the starfish, the starfish then travels to the next coral reef.
The significant increase in population regarding Acanthaster planci can be due to human
influences, such as chemical spills, as well as increased carbon dioxide output, resulting in
warmer temperatures. Because of the chemical spills, Acanthaster planci are able to develop at a
heightened rate, developing even faster from juveniles to adults, quickening the rate at which the
coral polyp is devoured. Warmer temperatures also have affected the population growth of
Acanthaster planci in coral areas in new areas. Because Acanthaster planci cannot develop as
efficiently in warmer climates, the starfish species then travel to cooler water temperatures, thus
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introducing the species to new areas. However, as much as human influence affects Acanthaster
planci, the starfish species affects humans and other mammals that come into contact with this
species. Acanthaster planci produce venom on its thorns, used to ward off predators and
competition, Plancitoxin I, which causes extreme pain as well as skeletal muscle myonecrosis.
Acanthaster planci is not an endangered species because of its ability to thrive in almost all
forms of coral reefs, since this species of starfish is not particular in its meal preferences.
References
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