Lion's Mane Jellyfish, Arctic Cod, and the Great White North
Victoria Vandersommen
It might be difficult to imagine that a gelatinous blob, with no heart, brain, or eyes could possibly have a negative effect on cod, which do have a heart, brain and eyes; but a study published June 2016 in Polar Biology is suggesting just that. While jellyfish and cod are not new to the research scene, this study sought to determine if Lion’s Mane Jellyfish are affecting the distribution of the most abundant, and arguably most important, fish in the Arctic, Arctic cod.
Dr. Richard Crawford and his team from Nunavut, Canada conducted a nine-year study over two periods, 1985-1991 and 2010-2013, in bays around Cornwallis Island in Canada. The island is located at 74* N, only 16*N from the North Pole. The combination of jellyfish, Arctic Cod, and the Arctic Ocean makes for an especially interesting study due to the ongoing warming of the north.
Why is the Arctic of more concern than other regions?
The Arctic is considered especially susceptible to temperature changes due to the Polar Amplification phenomena, which is a result of a change in radiation that then leads to larger temperature changes at the poles compared to the rest of the world, almost twice as large as the rest of the world (Bitz, 2006). This means that the North and South Poles are getting the brunt of the effects of climate change. The changes we are seeing in the Arctic have a cascade effect on wildlife. While oceanic warming has a negative effect on most sea life, jellyfish are actually able to thrive.
Arctic cod (Boreogadis saida) have been classified as a keystone prey species in the Arctic, which means it is an important organism in the function of the Arctic ecosystem. Changes in the distribution of a keystone species can lead to a trophic cascade, similar to a domino effect, by reducing food availability to organisms higher up. Determining if there is a correlation between jellyfish and Arctic Cod presence could help indicate if Arctic cod are at risk if and when jellyfish populations grow as oceanic temperature increases.
While marine life does not breathe the same air we do, they still need oxygen. Oxygen enters the ocean on the surface, and then the oxygen-rich cold water mixes with lower layers, distributing dissolved oxygen. Warmer water interrupts this process in two ways: first, the warmer water cannot hold as much dissolved oxygen; and second, warm water is less dense than cold, and results in less mixing. This warming interrupts nutrient cycling and reduces the number of organisms that can be supported. Jellyfish, unlike most fish, can tolerate low dissolved oxygen quite well, allowing them to colonize dead zones, or areas void of oxygen. This adaptability introduces the importance of determining if Arctic cod are affected by the presence of jellyfish. If jellyfish populations in the Arctic continue growing as water temperature increases, what could this mean for the distribution of Arctic Cod and their predators?
The team of researchers used a series of observations, hydroacoustics systems, and computer software to help answer this question.
Observations were taken on frozen ice from a stationary station, as well as by boat in ice-free water before collection. They decided on three bays around the island to deploy hydroacoustic systems, which is a device that studies the sound in the water column. Acoustic beams were released down a water column, which then echoed off fish based on size restrictions for Lion’s Mane Jellyfish and Arctic cod. This restrictive method allowed the researchers to narrow down the echograms, or the beams that bounced off the organism. The data from the echograms were analyzed with various software to create images of the spatial distribution and abundance. The organisms were not captured nor were they harmed by the beams. Environmental conditions were recorded as well, but because of unforeseen instrument variability, only the temperature readings were considered reliable.
The images from the echograms were telling. A few figures showed a stark boundary between an Arctic cod shoal and a smack of Lion’s Mane, while others showed only jellyfish scattered through the water column. When jellyfish were not present, echograms showed the cod occupying more of the water column. While this suggests the presence of jellyfish may affect the distribution and possibly presence of Arctic Cod, it is important to consider that other factors like weather and presence of other organisms could have had an effect on the results.
The study was able to suggest that Arctic cod were avoiding Lion’s Mane Jellyfish. If the Arctic continues to warm and jellyfish abundance increases, we could see a further change in Arctic cod distribution. This could have a cascade effect on the Arctic food web if cod abundance decreases with increased jellyfish presence.
References
Bitz, C. (2006, January 2). Polar Amplification. Retrieved from http://www.realclimate.org/index.php/archives/2006/01/polar-amplification/
Crawford, R. E. (2015). Occurrence of a gelatinous predator (Cyanea capillata) may affect the distribution of Boreogadus saida, a key Arctic prey fish species. Polar Biology, 39(6), 1049-1055. doi:10.1007/s00300-015-1779-8
Sweetman AK, Smith CR, Dale T, Jones DOB (2014). Rapid scavenging of jellyfish carcasses reveals the importance of gelatinous material to deep-sea food webs. Proceedings of the Royal Society B 281: 20142210. http://dx.doi.org/10.1098/rspb.2014.2210
Dr. Richard Crawford and his team from Nunavut, Canada conducted a nine-year study over two periods, 1985-1991 and 2010-2013, in bays around Cornwallis Island in Canada. The island is located at 74* N, only 16*N from the North Pole. The combination of jellyfish, Arctic Cod, and the Arctic Ocean makes for an especially interesting study due to the ongoing warming of the north.
Why is the Arctic of more concern than other regions?
The Arctic is considered especially susceptible to temperature changes due to the Polar Amplification phenomena, which is a result of a change in radiation that then leads to larger temperature changes at the poles compared to the rest of the world, almost twice as large as the rest of the world (Bitz, 2006). This means that the North and South Poles are getting the brunt of the effects of climate change. The changes we are seeing in the Arctic have a cascade effect on wildlife. While oceanic warming has a negative effect on most sea life, jellyfish are actually able to thrive.
Arctic cod (Boreogadis saida) have been classified as a keystone prey species in the Arctic, which means it is an important organism in the function of the Arctic ecosystem. Changes in the distribution of a keystone species can lead to a trophic cascade, similar to a domino effect, by reducing food availability to organisms higher up. Determining if there is a correlation between jellyfish and Arctic Cod presence could help indicate if Arctic cod are at risk if and when jellyfish populations grow as oceanic temperature increases.
While marine life does not breathe the same air we do, they still need oxygen. Oxygen enters the ocean on the surface, and then the oxygen-rich cold water mixes with lower layers, distributing dissolved oxygen. Warmer water interrupts this process in two ways: first, the warmer water cannot hold as much dissolved oxygen; and second, warm water is less dense than cold, and results in less mixing. This warming interrupts nutrient cycling and reduces the number of organisms that can be supported. Jellyfish, unlike most fish, can tolerate low dissolved oxygen quite well, allowing them to colonize dead zones, or areas void of oxygen. This adaptability introduces the importance of determining if Arctic cod are affected by the presence of jellyfish. If jellyfish populations in the Arctic continue growing as water temperature increases, what could this mean for the distribution of Arctic Cod and their predators?
The team of researchers used a series of observations, hydroacoustics systems, and computer software to help answer this question.
Observations were taken on frozen ice from a stationary station, as well as by boat in ice-free water before collection. They decided on three bays around the island to deploy hydroacoustic systems, which is a device that studies the sound in the water column. Acoustic beams were released down a water column, which then echoed off fish based on size restrictions for Lion’s Mane Jellyfish and Arctic cod. This restrictive method allowed the researchers to narrow down the echograms, or the beams that bounced off the organism. The data from the echograms were analyzed with various software to create images of the spatial distribution and abundance. The organisms were not captured nor were they harmed by the beams. Environmental conditions were recorded as well, but because of unforeseen instrument variability, only the temperature readings were considered reliable.
The images from the echograms were telling. A few figures showed a stark boundary between an Arctic cod shoal and a smack of Lion’s Mane, while others showed only jellyfish scattered through the water column. When jellyfish were not present, echograms showed the cod occupying more of the water column. While this suggests the presence of jellyfish may affect the distribution and possibly presence of Arctic Cod, it is important to consider that other factors like weather and presence of other organisms could have had an effect on the results.
The study was able to suggest that Arctic cod were avoiding Lion’s Mane Jellyfish. If the Arctic continues to warm and jellyfish abundance increases, we could see a further change in Arctic cod distribution. This could have a cascade effect on the Arctic food web if cod abundance decreases with increased jellyfish presence.
References
Bitz, C. (2006, January 2). Polar Amplification. Retrieved from http://www.realclimate.org/index.php/archives/2006/01/polar-amplification/
Crawford, R. E. (2015). Occurrence of a gelatinous predator (Cyanea capillata) may affect the distribution of Boreogadus saida, a key Arctic prey fish species. Polar Biology, 39(6), 1049-1055. doi:10.1007/s00300-015-1779-8
Sweetman AK, Smith CR, Dale T, Jones DOB (2014). Rapid scavenging of jellyfish carcasses reveals the importance of gelatinous material to deep-sea food webs. Proceedings of the Royal Society B 281: 20142210. http://dx.doi.org/10.1098/rspb.2014.2210
Victoria Vandersommen received a Baccalaureate of Environment & Society in 2017.
This piece was selected by Professor Jacqueline Cason.
This piece was selected by Professor Jacqueline Cason.