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Report on the Health of the World's Oceans (7)

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Whatever the cause, whether it is a switch in the ocean currents, excess CO2, or other factors, rising temperatures do have an effect on the oceans.

Even small changes in the temperature of the oceans can affect the marine life dramatically. Interactions between species that are sensitive to temperature changes could lead to great changes within the oceans (26). An example of this is the sea star Pisaster ochraceus. Amazingly, temperatures varying by only 3 degrees C caused extreme variation in the sea star's feeding habits. Sea stars in tanks at 9 degrees C ate an average of 29% fewer mussels than those in tanks at 12 degrees C (26). Sea stars that were held in tanks where the temperature alternated between 12 degrees C and 9 degrees C, heavily consumed mussels at 12 degrees, ate more slowly at 9 degrees, and ate faster again at 12 degrees (26). A warming in ocean temperatures would lead to sea stars continually consuming mussels at a faster rate.

An effect of warmer temperatures that most of us did not count on was a decrease in ocean salinity. Across the Indian and Pacific oceans, researchers found that water 500 to 1000 meters below the surface has become much less salty in the past 20 years (27). In conjunction with this, surface water around the equator has increased in salinity (27). Presumably, warmer temperatures cause more rain and snowfall towards the poles, which dilute surface waters, cool and sink (27). The waters then sink and move toward the equator (27). Some fish, like salmon, can move between salt and fresh waters, but most saltwater fish do not tolerate fresh water conditions. This could mean that we'll see a movement of fish away from the areas of fresher water if the salinity decreases too much. Warmer water temperatures may have a negative impact on krill in the Antarctic (19), (30).

Not just the warmer temperatures, but also a decrease in sea ice due to the warmer temperatures affect the krill throughout its life cycle (30). Because krill are such an important species in this region, the effects of decreasing numbers will have a broad impact on many species of marine life in the Arctic. Penguins, seals and baleen whales, all feed on krill. Toothed whales feed on penguins and seals. The impact of a loss of krill due to warmer temperatures, coupled with an increase in commercial fishing of krill could have a devastating consequence on Antarctic marine life (19). Not only will the krill, penguins, seals, and whales be affected, but other fish species will also take a hit. Penguins and seals will increase predation on other fish to offset the loss of the krill as a food source.

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