Running head: JELLYFISH BLOOMS: NATURAL PROCESS OR SIDE-EFFECT OF HUMAN SOCIETY?
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Jellyfish Blooms: Natural Process or Side-Effect of Human Society?
McKenzie Oster
Liberty High School
The Chironex fleckeri Box Jellyfish has the venomous capability to kill a person in less
than five minutes (Centre for Disease Control, 2012, p. 1). Because of this, it is often considered
to be the deadliest creature in the world. Although this jellyfish poses a threat, there is a much
larger menace coming from the gelatinous creatures–phenomena called jellyfish blooms. There is
an ongoing debate throughout researchers of whether these alarming increases in blooms are
natural variations in population density, or if they are a real issue that has come out of human
interference with marine ecosystems. However, many prominent scientists, such as Lisa-Ann
Gershwin–who was awarded a Fulbright in 1998 for her studies on jellyfish blooms and
evolution–are beginning to confidently state that “jellyfish probably are on the increase
worldwide, as human impacted ecosystems change to become less favorable to some species and
more favorable to jellyfish” (2013, p. 15). As more evidence is coming to light it looks as if her,
and other scientist’s, blame of the human species is warranted and the only way to fix things are
to make significant changes and give marine ecosystems a chance to return to balance, before the
damages become irreparable.
A jellyfish bloom appears as a swarm of jellyfish, with so many of the animals that they
are sometimes indistinguishable from each other. While it is natural for populations of all species
to go through increasing and decreasing cycles, these blooms go much deeper than just being a
large group and gradual population increase of the organisms. One of the main characteristics of
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a bloom that distinguishes it from a basic dense gathering is the presence of a “rapid
reproduction and growth rate” (Suchman, Brodeur, Daly, & Emmett, 2012, p. 122). This
population increasing rate can be so rapid that blooms will seem to appear at beaches overnight,
which is occasionally mentioned in news segments in a panicking fashion. Skeptics of the
pressing issue of these blooms initially refused to accept that populations were increasing around
the world as there was no supporting evidence, but a researcher found proof after studying the
oceans that helped in showing just how existent the jellyfish blooms are. “Out of 66 large marine
ecosystems covering the world’s coastal waters and seas, [Lucas] Brote found quantifiable
jellyfish trends in 45, the overwhelming majority of which showed an increase, while only 2
showed a decrease and 12 were stable” (Gershwin, 2013, p. 4). Brote’s study helped to bring
awareness to the issue and show that these increases in population aren’t as normal as was
thought at first. They deserve real attention by scientists, rather than just short TV plugs that
bring more unnecessary panic than solutions.
Jellyfish belong to two invertebrate classifications; some belong to the cnidarian phylum
and others the ctenophore. Most Cnidarian jellyfish have two different stages to their life, the
polyp stage and the medusa stage, which alternate. In the polyp stage the jellyfish remain on the
ocean floor, only becoming mobile when they enter the medusa stage. Cnidarian jellyfish sting,
poison, and stun prey through the presence of nemacysts (stinging cells), in their tentacles and
mouth appendages. Alternatively, Ctenophore jellyfish only have one stage in their life–never
changing from being in the plankton–and use cells called colloblasts to release glue and trap their
prey (Richardson, Bakun, Hays, & Gibbons, 2009, p. 312). Blooms have been occurring
repeatedly in both phyla of jellyfish over the past two centuries (Condon, et al., 2012), and
cnidarians are known to bloom seasonally (Mills, 2001, p. 55), regardless of what humans do.
JELLYFISH BLOOMS: NATURAL PROCESS OR SIDE-EFFECT OF HUMAN SOCIETY?
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Some researchers indicate blooms arise so easily in jellyfish because of their lack of
predators, ease of feeding, and incredible adaptation abilities. One such attribute is their
capability of shrinking when food is unavailable and then resuming regular growth and
reproduction within days of feeding (Richardson et al., 2009, p.317), which allows them to live
on through starvation, and quickly increase their population as the environment permits. Other
researchers contribute blooms to a natural response due to increases in the temperature of the
environment. After a 27 year period of collecting plankton samples in the Ligurian Sea it was
found that, “With the generally warmer waters during the 1980s becoming more extensive until
the early 1990s, the recurrence and strength of gelatinous carnivore outbreaks become more
frequent and the population size increases considerably” (Molinero, Casini, & Buecher, 2008, p.
1463). This same group of researchers discovered that there are small time frames where
jellyfish are more sensitive to environmental conditions and if circumstances are favorable their
annual population spikes are significantly heightened (Molinero et al., 2008, p. 1464), which
may explain why the blooms can appear so rapidly when the climate changes.
Temperature is not always a consistent factor for increasing jellyfish blooms as found in
the North Sea in a study lasting from 1946 to 2007. When analyzing the results of the study,
researchers claimed, “Jellyfish frequency, therefore, is influenced by climate variability across
the main central North Sea, but not in northern or southern regions” (Attrill, Wright, & Edwards,
2007, p. 482). Steven Haddock wrote an article which was published by the same journal,
Limnology and Oceanography, and addressed the flaws that the conclusions drawn from this
study held, but in the end agreed to a more conservative interpretation of the data, saying, “…the
regime shift reported by others has modified the community structure of North Sea planktonic
cnidarians to an extent that merits further detailed study” (Haddock, 2008, p. 2761). His
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impression of the study reflects the overall issue of jellyfish blooms, as researchers tend to draw
too many conclusions from sparse data as there is more speculation on the subject at this point in
time than actual evidence. These various attributes and studies show that jellyfish are naturally
predisposed to blooms; however, they do not explain why the various impacts of the blooms are
becoming magnified and more impactful than if they were naturally occurring, unless human
interference is taken into account.
Many different human factors such as, overfishing, habitat modification, and construction
have been proven to be linked to the increasing number of jellyfish blooms across the world.
Lisa-Ann Gershwin addresses these issues simply, stating, “We are increasingly fishing out their
predators and competitors, and we are altering the physical properties of the seabed and chemical
properties of the oceans to favor jellyfish” (2013, p. 4). Even what are thought of as natural
occurrences of blooms are tainted with human interference, in that pollution from humans has
caused temperatures to rise, and in turn jellyfish bloom occurrences to rise. One of the largest
impacts on the increase in blooms by humans is overfishing. Overfishing weakens the food web
so that it does not support as many fish, marine mammals, turtles and seabirds and in turn makes
an environment with less predators, and more favorable factors for jellyfish (Richardson et al.,
2009, p.314). Fishing carries many indirect consequences to the ecosystem other than just the
direct removal of fish. Trawling along the ocean floor has created areas for jellyfish to hide and
escape predators, and many species of jellyfish are being introduced into new areas and taking
over native populations by either getting into the ballast water of ships or by polyps attaching to
the hull of ships and being transported (National Science Foundation). Although these many
concerns from overfishing sound dismal, this is a human caused problem that is relatively easy to
address as it is a straight forward issue–if fishing continues as it is for too much longer, the
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jellyfish blooms will only worsen and cause more problems. In the coming years, as more
research goes into jellyfish blooms, researchers and the fishing industry will need to come to an
agreement upon what the best way will be to keep up the fishing that the populations in the world
require, but reduce the effects this overfishing is having upon marine ecosystems and jellyfish.
Another large contributor to jellyfish blooms is oceanic eutrophication, which has its
roots in human construction. The creation of coastal power plants and communities has grown,
which increases the amount of sewage and fertilizer run-off entering the ocean. These wastes
carry a large amount of nutrients, which increases primary production and algal biomass in the
ocean, while reducing water transparency and the dissolved oxygen concentration (Richardson et
al., 2009, p.312-314). By introducing this excess of nutrients and cutting off oxygen, heavily
polluted areas called dead zones are made. In these areas–of which Earth has over 400, some of
which cover tens of thousands of square miles–jellyfish are able to thrive and face little to no
competition or predation, as they possess a unique skill that most other marine species lack–the
ability to dissolve oxygen in their tissues (National Science Foundation). This is a side effect of
pollution that is often overshadowed by the global warming aspect, but will demand attention
from researchers as the number of dead zones grows and the ocean ecosystems remain
unbalanced.
When discussing how he viewed peculiarly large or recurrent jellyfish blooms, Monty
Graham, from the Dauphin Island Sea Lab, said they were “a symptom of an ecosystem that has
been tipped off balance by environmental stress” (as cited in National Science Foundation).
Evidence shows that much of this environmental stress has come from human interference such
as overfishing, pollution, and construction, rather than just being a natural cycle as many
researchers suspected initially. Jellyfish, no matter the phylum, are anatomically and
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physiologically equipped to survive in harsh environments and take advantage of what they are
provided with, and the human race has had a catalytic effect on the natural factors that contribute
to blooms. As the human population continues to grow and increase pollution, climate change
and eutrophication along with the continuance of overfishing, will further amplify the growing
jellyfish blooms. An increase in research and evidence, and a plan to reduce human interference
on oceanic ecosystems, must be a focal point of science and society in the near future. With this
intervention the unnatural events that are occurring can be reduced, and the ocean ecosystems
can return to balance–a scenario that humans and all life forms will benefit from.
JELLYFISH BLOOMS: NATURAL PROCESS OR SIDE-EFFECT OF HUMAN SOCIETY?
References
Attrill, M. J., Wright, J., & Edwards, M. (2007, January). Climate-related increases in jellyfish frequency
suggest a more gelatinous future for the North Sea. Limnology and Oceanography, 52(1), 480485. Retrieved from http://www.jstor.org/stable/40006097
Centre for Disease Control. (2012, November). Chironex fleckeri (Box jellyfish). Northern Territory
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Condon, R. H., Graham, W. M., Duarte, C. M., Pitt, K. A., Lucas, C. H., Haddock, S. H., . . . Madin, L. P.
(2012, February). Questioning the rise of gelatinous zooplankton in the world's oceans.
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Retrieved from https://www.nsf.gov/news/special_reports/jellyfish/swarms.jsp
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