Anthropogenic Causes of Increasing Jellyfish Populations
Invasive Species
Invasive species of Jellyfish have been reported in numerous locations around the globe. In some cases, there presence has dramatic ecological and economic consequences. In addition, it is likely that far more invasions have occurred than have been documented due to incomplete treatment, and unusual life histories, and species crypsis. The ability of numerous jellyfish to reproduce asexually suggest that successfully invasion could occur from a single benthic organisms. Example taken from invasive jellyfish are all the same sex.
Global Warming
The vast majority of the world's coastal ecosystems and seas have experience and increase in temperature over the last 50 years for example in Berlin 2009, and global temperatures are forecast to continue increasing. A temperature is known to influence jellyfish in many ways, especially during reproductive phases. Warmer temperatures may increase survival. Warmer temperatures may result in the expansion of other jellyfish populations into water that previously inhospitable.
- The sea nettle Chrysaora Quinquecirrha produces more eggs when temperatures are warmer. This species also appears to tolerant of very high temperatures.
-Temperature affects asexual reproduction on Moon jellyfish
-Jellyfish may also persist longer with warmer waters, as the onset of cooler season signals, the signal of Medusae in many temperatures areas.
Not all species of jellies thrive in warmer temperatures. Cold-water species will presumably decrease with warmer waters, and most jellyfish are expected to have upper temperature threshold, but indeed Aurelia polyp mortality increase under continuous high temperatures, and medusae of the tropical declined dramatically in response to warmer temperatures in a marine lake.
- The sea nettle Chrysaora Quinquecirrha produces more eggs when temperatures are warmer. This species also appears to tolerant of very high temperatures.
-Temperature affects asexual reproduction on Moon jellyfish
-Jellyfish may also persist longer with warmer waters, as the onset of cooler season signals, the signal of Medusae in many temperatures areas.
Not all species of jellies thrive in warmer temperatures. Cold-water species will presumably decrease with warmer waters, and most jellyfish are expected to have upper temperature threshold, but indeed Aurelia polyp mortality increase under continuous high temperatures, and medusae of the tropical declined dramatically in response to warmer temperatures in a marine lake.
Eutrophication
Eutrophication is most often described as an increase in the input of nutrients (primarily nitrogen and phosphorus) to a body of water. This results from excess fertilizer from agriculture, dumping of sewage, and effects of logging. The deposition of reactive nitrogen as a result of fossil fuel burning is also a significant contributing factor. If nutrients are limiting, such increased input will in more phytoplankton, often in the form of algal blooms. The subsequent decay of these blooms often leads to reduced concentrations of dissolved oxygen, and in extreme cases, hypoxic and anoxic 'dead zones', There are now over 400 of these regions worldwide, and they have been increasing exponentially since the 1960s.
Eutrophication may benefit jellyfish in a number of ways:
*Increased nutrients can simply create more primary and secondary production, increasing the amount of food available to jellyfish polyps and medusae.
* Rates of asexual reproduction for some species of jellyfish are influenced by nutrition, and therefore increased food availability could lead an increased abundance of jellies.
-Aurelia polyps have been shown to asexually but more polyps at higher food concentrations, possibly leading to larger blooms.
-New populations of large scyphomedusa Rhizostoma pulmo appear to be thriving due to their unusual ability to feed directly on diatoms, and therefore benefit form the increasing eutrophication of the lagoon.
* Jellyfish populations can increase due to higher nutrient input.
* Eutrophication can also decrease water clarity. As jellyfish are mainly tactile predators, they may have an advantage over visual predators (such as fish) in turbid waters.
* Eutrophication can also result in lower concentrations of dissolved oxygen (DO). Many types of jellies are tolerant to low DO concentrations. Such conditions are typically detrimental to other animals, and may reduce survival or impair function, such as the ability to escape from predators.
*Eutrophication appears to be linked to the increase in Aurelia populations observed in the Seto Inland Sea, Japan.
* Hypoxic conditions may explain the success of the ctenophore Mnemiopsis leidyi in Chesapeake Bay, which appears to be much more tolerant of low DO concentrations than the rest of the zooplankton community.
* Jellyfish appear to show an affinity for eutrophic waters.
* Eutrophication can impact the phytoplankton community directly, with potentially significant consequences for the rest of the food chain.
*Jellyfish may benefit from eutrophic waters due to increased availability of production at low trophic levels, increased turbidity, and lower levels of dissolved oxygen.
Eutrophication may benefit jellyfish in a number of ways:
*Increased nutrients can simply create more primary and secondary production, increasing the amount of food available to jellyfish polyps and medusae.
* Rates of asexual reproduction for some species of jellyfish are influenced by nutrition, and therefore increased food availability could lead an increased abundance of jellies.
-Aurelia polyps have been shown to asexually but more polyps at higher food concentrations, possibly leading to larger blooms.
-New populations of large scyphomedusa Rhizostoma pulmo appear to be thriving due to their unusual ability to feed directly on diatoms, and therefore benefit form the increasing eutrophication of the lagoon.
* Jellyfish populations can increase due to higher nutrient input.
* Eutrophication can also decrease water clarity. As jellyfish are mainly tactile predators, they may have an advantage over visual predators (such as fish) in turbid waters.
* Eutrophication can also result in lower concentrations of dissolved oxygen (DO). Many types of jellies are tolerant to low DO concentrations. Such conditions are typically detrimental to other animals, and may reduce survival or impair function, such as the ability to escape from predators.
*Eutrophication appears to be linked to the increase in Aurelia populations observed in the Seto Inland Sea, Japan.
* Hypoxic conditions may explain the success of the ctenophore Mnemiopsis leidyi in Chesapeake Bay, which appears to be much more tolerant of low DO concentrations than the rest of the zooplankton community.
* Jellyfish appear to show an affinity for eutrophic waters.
* Eutrophication can impact the phytoplankton community directly, with potentially significant consequences for the rest of the food chain.
*Jellyfish may benefit from eutrophic waters due to increased availability of production at low trophic levels, increased turbidity, and lower levels of dissolved oxygen.
Overfishing
Fishing and overfishing can cause profound changes in marine ecosystems, including alterations to faunal communities, trophic structure,
production, habitat, biodiversity, as well as ecosystem function and stability. In some cases, it appears that overfishing may also lead to increased jellyfish populations. Many fish are predators and/or competitors of jellyfish, and therefore removing large amounts of fish from a system may release jellyfish from predation and/or competition. Fishing down marine food webs is a phenomenon whereby the largest, high trophic level fish are reduced initially, followed by a gradual shift toward smaller, lower trophic level fish and invertebrates .
Indeed, ‘fishing down’ appears to be widespread , and the mean trophic level of all fisheries catch is considered to be a good indicator of ecosystem health . The extreme result of this process is a near absence of profitable fisheries, and a dominance of planktonic organisms, including jellyfish.
production, habitat, biodiversity, as well as ecosystem function and stability. In some cases, it appears that overfishing may also lead to increased jellyfish populations. Many fish are predators and/or competitors of jellyfish, and therefore removing large amounts of fish from a system may release jellyfish from predation and/or competition. Fishing down marine food webs is a phenomenon whereby the largest, high trophic level fish are reduced initially, followed by a gradual shift toward smaller, lower trophic level fish and invertebrates .
Indeed, ‘fishing down’ appears to be widespread , and the mean trophic level of all fisheries catch is considered to be a good indicator of ecosystem health . The extreme result of this process is a near absence of profitable fisheries, and a dominance of planktonic organisms, including jellyfish.
Bottom-Trawling
Bottom-trawling could lead to increased jellyfish populations. It can destroy benthic communities composed of filter feeders and deposit feeders. These communities tend to keep the water column oligotrophic by suppressing phytoplankton and detritus, as well as preventing re-suspension of sediments. With the loss of these communities, the water column may become increasingly eutrophic and the sediments less consolidated, facilitating the re-suspension of particles and nutrients by storms and by trawling itself, further aggravating the problem.
The coastal waters of Romania, near the productive Danube Delta, were only fished using stationary nets in shallow waters through the 1960s and 1970s. In 1980, bottom-trawling began in this region, and was much more efficient at extracting fish from the sea. Trawl catches increased steadily through the 1980s, but declined drastically after 1990, along with a dramatic change in species composition. Consistent with hypotheses about how bottom-trawling can lead to more jellyfish, some of the many ecological changes observed in the Black Sea include increased episodes of hypoxia and anoxia, increased turbidity, and the decline of benthic species diversity.
The coastal waters of Romania, near the productive Danube Delta, were only fished using stationary nets in shallow waters through the 1960s and 1970s. In 1980, bottom-trawling began in this region, and was much more efficient at extracting fish from the sea. Trawl catches increased steadily through the 1980s, but declined drastically after 1990, along with a dramatic change in species composition. Consistent with hypotheses about how bottom-trawling can lead to more jellyfish, some of the many ecological changes observed in the Black Sea include increased episodes of hypoxia and anoxia, increased turbidity, and the decline of benthic species diversity.
Increased Substrate
Many jellyfish have a sessile polyp phase of their life history which attaches to a hard substrate. In the natural environment, such substrate can include rocks, submerged trees, or the shells of benthic mollusks and other animals. In marine environments that have been developed by humans, the amount of hard substrate increases dramatically, and can include boats, docks, wharfs, marinas, breakwaters, sea walls, platforms, artificial reefs, debris, and many other structures. If habitat for polyps is a limiting factor for jellyfish populations, then increased substrate provided by humans could result in an increase in medusae abundance. Polyps from numerous species appear to show an affinity for anthropogenic materials, such as plastic and glass, over natural materials . Many jellyfish polyps also appear to show a preference for the shaded side of structures, possibly to avoid burial by sedimentation, as well as mortality due to solar irradiation. Natural shaded structures are relatively rare in marine environments, whereas anthropogenic structures are often floating, and therefore provide a multitude of shaded habitat.
One spectacular example comes from a marina in Washington State, U.S.A., where there is an estimated population of 100 million Aurelia
labiata polyps living on the underside of dock floats . As these polyps can produce an average of 10 ephyrae each, this is a potential addition of hundreds of millions of jellyfish to the ecosystem that presumably would not be there otherwise.
In the Gulf of Mexico, both quinquecirrha and aurita have sessile polyp stages that attach to hard substrates. While natural substrates,
such as oyster reefs, are expected to be relatively constant over time, artificial substrates have increased dramatically with the expansion of oil and gas development. There are over 6000 operating and discontinued oil and gas structures in the northern Gulf, with the highest concentrations on the Louisiana shelf . As most of these structures extend throughout the entire water column, they likely provide suitable habitat for thriving polyp colonies, potentially contributing to increases in medusae populations.
In many of these locations, jellyfish are perceived to have increased in abundance.
One spectacular example comes from a marina in Washington State, U.S.A., where there is an estimated population of 100 million Aurelia
labiata polyps living on the underside of dock floats . As these polyps can produce an average of 10 ephyrae each, this is a potential addition of hundreds of millions of jellyfish to the ecosystem that presumably would not be there otherwise.
In the Gulf of Mexico, both quinquecirrha and aurita have sessile polyp stages that attach to hard substrates. While natural substrates,
such as oyster reefs, are expected to be relatively constant over time, artificial substrates have increased dramatically with the expansion of oil and gas development. There are over 6000 operating and discontinued oil and gas structures in the northern Gulf, with the highest concentrations on the Louisiana shelf . As most of these structures extend throughout the entire water column, they likely provide suitable habitat for thriving polyp colonies, potentially contributing to increases in medusae populations.
In many of these locations, jellyfish are perceived to have increased in abundance.
Aquaculture
Aquaculture, or more specifically mariculture, may benefit jellyfish in several ways. Operations typically provide increased
nutrients to the surrounding waters due to excess feed and excrement. \
By far the most convincing example of aquaculture operations affecting jellyfish abundance comes from Tapong Bay in Taiwan. Extensive aquaculture operations over several decades led to increasing eutrophication of this coastal lagoon, with concurrent blooms of Aurelia sp. However, in 2002, the removal of all aquaculture operations resulted in the total absence of jellyfish blooms thereafter, suggesting that aquaculture may be solely responsible for the jellyfish blooms in this bay
There are also aquaculture operations and hatcheries that intentionally attempt to increase jellyfish production for harvesting and human consumption. In Liaodong Bay, China, hundreds of millions of juvenile Rhopilema esculentum are released from hatcheries each year, in the hopes of harvesting them as adults . While some economic success has been achieved with such programs, recent blooms tend to be of less desirable species, and efforts are shifting toward pond culture of jellyfish .
nutrients to the surrounding waters due to excess feed and excrement. \
By far the most convincing example of aquaculture operations affecting jellyfish abundance comes from Tapong Bay in Taiwan. Extensive aquaculture operations over several decades led to increasing eutrophication of this coastal lagoon, with concurrent blooms of Aurelia sp. However, in 2002, the removal of all aquaculture operations resulted in the total absence of jellyfish blooms thereafter, suggesting that aquaculture may be solely responsible for the jellyfish blooms in this bay
There are also aquaculture operations and hatcheries that intentionally attempt to increase jellyfish production for harvesting and human consumption. In Liaodong Bay, China, hundreds of millions of juvenile Rhopilema esculentum are released from hatcheries each year, in the hopes of harvesting them as adults . While some economic success has been achieved with such programs, recent blooms tend to be of less desirable species, and efforts are shifting toward pond culture of jellyfish .
Other Factors and Ocean Acidification
Other factors that can be influenced by human activity are also likely to have important impacts on jellyfish populations, such as salinity and ocean acidification. While many jellyfish species appear to be tolerant of a wide range in salinity, they may also be highly influenced by it. In years of low precipitation, increased salinity may result in large populations of Chrysaora quinquecirrha medusae in Chesapeake Bay.
Based on data collected from 2003-2005, Ding & Cheng (2007) conclude that various water masses in the East China Sea and Yellow Sea, identified by temperature and salinity, may affect the abundance and distribution of Nemopilema nomurai. For some species, such as Aurelia labiata, changes in salinity may have significant influence reproduction, especially when the effects of temperature are also taken into account In addition, evidence suggests that some scyphozoan polyps are able to survive a wide range of salinities. Changes in salinity due to climate change scenarios are expected to be high localized and difficult to predict.
Ocean acidification is occurring as a result of increasing anthropogenic CO2 emissions, with a reduction of ocean pH occurring at a rate not seen in millions of years. This change is likely to portend serious consequences for marine biota, especially organisms that build shells and skeletons of calcium carbonate. If organisms that are competitors of jellyfish are negatively affected by ocean acidification, jellyfish may benefit as a result.
The polyps of some species, including a scyphozoan and a cubozoan, appear to be tolerant of low pH conditions .
Based on data collected from 2003-2005, Ding & Cheng (2007) conclude that various water masses in the East China Sea and Yellow Sea, identified by temperature and salinity, may affect the abundance and distribution of Nemopilema nomurai. For some species, such as Aurelia labiata, changes in salinity may have significant influence reproduction, especially when the effects of temperature are also taken into account In addition, evidence suggests that some scyphozoan polyps are able to survive a wide range of salinities. Changes in salinity due to climate change scenarios are expected to be high localized and difficult to predict.
Ocean acidification is occurring as a result of increasing anthropogenic CO2 emissions, with a reduction of ocean pH occurring at a rate not seen in millions of years. This change is likely to portend serious consequences for marine biota, especially organisms that build shells and skeletons of calcium carbonate. If organisms that are competitors of jellyfish are negatively affected by ocean acidification, jellyfish may benefit as a result.
The polyps of some species, including a scyphozoan and a cubozoan, appear to be tolerant of low pH conditions .