Tuesday, March 31, 2009

Return to Bouvet Island

From page 264-266, Carroll discuses the potential causes of dwindling numbers of krill, which is used as an important source of food and feed. Among these reasons the most prominent are overfishing and temperature increase in the arctic. Explain how each of these reasons affect the krill population. Also how may these factors play in the population of icefish that were discussed in pages 19-27. Discuss how temperature rise may be catastrophic for these fish and their hemoglobin free blood.

5 comments:

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  2. Krill is, as Carroll puts it, the center of the Antarctic foodweb. As a keystone species, it eats zooplankton and phytoplankton, algae, off of the frozen ice blocks that float around the Antarctic ocean. Thus, it converts the energy of the algae into something that most ocean dwellers depend on-the Euphausia superba has a biomass of over 500 million tons, of which 250 million tons is eaten by whales, seals penguins, squid, octopi, and fishes- like the bloodless fish of Bouvet Island. The entire ecosystem of the ocean is based on these tiny shrimp-like creatures, as they are the primary consumer, much like the cow would be for a particular food chain. The total global harvest is around 200,000 metric tons, which doesn’t seem to be a big part, considering that one particular species, the aforementioned Euphausia superba, has the biomass it does. As Carroll says, the harvest rate is not the current threat to the density of the packs. (265)

    Rather, the current threat to the krill is the fact that average temperatures in the Antarctic Peninsula has risen 4 or so degrees Fahrenheit in the last fifty years- which would be five times more than the average temperature has risen, anywhere else in the world. Obviously, in the Antarctic, this causes the decrease in the mass of the ice blocks that float around the peninsula, and which algae, such as zooplankton and phytoplankton, accumulate on, and live. This could be the start of a domino effect, as less algae means the carrying capacity for krill is diminished, which means eventually some species will die in the competition, due to being unfit, or perhaps not as well suited for survival.

    This leads us to the plight of the ice fish. They rely on a high partial concentration of oxygen to compensate for their hemoglobin free blood, like found in the arctic oceans. However, when climate rises, the partial concentration of oxygen by association decreases. This would be deadly for the icefish- their body, the gills, the heart, the antifreeze, have all been adapted for the cold. The warmer water would mean that oxygen would go down. The gills would take in less oxygen, meaning less in the blood, and the heart would be pushing this lowered oxygen concentration blood around, helping to doom the icefish as it wouldn’t get enough oxygen to its organs in order to survive.

    http://en.wikipedia.org/wiki/Krill
    http://en.wikipedia.org/wiki/Keystone_species

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  4. Due to ovefishing of Krills, the krill population has declined over last few decades. This will affect the primary consumers, secondary consumers and eventually humans. Since most of fish depend on the krill as the food source, it is very crucial for us to stop overfishing the krill. Another reason why krill population has declined is the rise in temperature due to global warming. This causes the ice in the Antartica to melt which will decrease the source of algae which decreased the krill population.
    As Varad had mentioned, amount of dissolved is higher in cold water and as it gets warmer, Icefish will have hard time survive in Antartica due to lack of O2. However, another factor that may reduce Icefish is that we are overfishing Icefish too as Sean Carroll writes in the book “As the whaling industry died, attention turned to toher Antarctic fisheries, including the icefish”(266). The rise in temperature is not only harful to the icefish but also animals live in Antartica such as penguins, polar bears and seals.
    Another interesting fact that resulted from this decrease in krill population is that as Krill disappear, another creature, Salp replaces them. However, the problem is that Salps are not welcome among the marine animals. They don’t like to eat Salps. Here, we see the decline in one species and rise in another species. This will further decrease the abundance of marine animals and eventually affect humans. It almost seems like that humans are creating false natural selection for Krills thus interrupting evolutionary process.

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  5. Krill, located in the far reaches of our planet, are critical to the efficient functioning of its community. According to researchers from the area, the local wildlife are in danger. The catalyst for this potential killer, according to the experts, is the overfishing of krill. Krill are given their name, which means "whale food" in Norweigan, for that exact reason. If the overfishing of krill continues, the future of the whale could be jeopardized. Not only whales, but also seals, penguins, and albatrosses may have trouble feeding their young. This is based on research performed in the 1990's, when the populations of krill were low, causing difficulty for these species in providing for their offspring. Because of the krill's importance as a keystone species, the eventual removal of its entire population from the Antarctic could have catastrophic results, as several other species are dependent upon its presence for food.

    As for the icefish, if the temperature keeps increasing as it has over the years, it will lead to big problems. There is considerable evidence that this will indeed occur. The atmospheric carbon dioxide has increased at a steady rate since the 1960's, when production of automobiles really came into full swing. The result of the buildup of carbon dioxide in the atmosphere is the greenhouse effect, in which infrared radiation from the surface of the earth is reflected back, thereby increasing the temperature of the earth. This is problematic for icefish because the oxygen solubility is much higher in cold water than it is in warm water. Therefore,an increase in temperature would accompany an decrease in oxygen solubility. Because icefish lack hemoglobin and its cooperative-binding property (which allows it to change the amount of oxygen bound to it based upon the pressure of oxygen in the surrounding tissue), this would change would be a disastrous development in the survival of the icefish.

    http://news.nationalgeographic.com/news/2003/08/0805_030805_antarctic_2.html
    http://www.novelguide.com/a/discover/grze_05/grze_05_00316.html
    http://en.wikipedia.org/wiki/Greenhouse_effect

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