Conclusion

The reduction in fish populations in the world has many causes, mostly climate change.  Ocean acidification and temperature rises all reduce the available habitat for many species, especially those who sit on the bottom of the food web.  If the lowest end of the food chain becomes endangered, so do everything else above it.  Considering that plankton count has decreased phenomenally over the past decade, it is expected that everything else as well will follow.  Fishes are also vulnerable to fishing.  With very little international effort to protect the fishing industry, many species are becoming extinct or endangered.  In order to solve the problem of the ocean’s fishes, many preventative measures must be taken.  A good start is to reduce fishing or start using fisheries to meet the demand.  Overfishing can easily change population dynamics and can also alter the entire ecosystem of an ocean habitat.  In order to keep the oceans productive, measures must be taken to reduce carbon emissions in the atmosphere.  Organisms at the bottom of the food chain are very sensitive to pH and temperature, and in order to prevent these species from deteriorating, measures must be taken to reduce climate change.

Overfishing

Overfishing has a very major negative impact on fishes.  In the context of the bluefin tuna, overfishing has almost completely eliminated their population.  However, the bluefin tuna is not a major concern because it resides in the upper parts of the food web.  However, overfishing of smaller fish, such as anchovies, baitfish, and herring has profound impacts.  Many of the smaller fishes are being overharvested.  This in turn affects larger species like sharks and whales who directly or indirectly feed on these smaller fish.  If these fish were to become extinct, many others in the upper tiers of the food chain would also become extinct.

Temperature

Temperature increases is detrimental to many species due to the fact that many of them have a narrow thermal range.  The most alarming scenario from global warming is the disruption of oceanic currents.  If the ocean currents were to cease, the world would end up in another ice age.  However, a more practical and recent scenario is that species are migrating poleward.  The reason is partially because of species’ optimal thermal ranges, but another reason is because food resources are dwindling in tropical oceans.

Warmer waters create less turbulence and become more stratified.  As a result less nutrients are upwelled from the deeper ocean waters.  Because there are less nutrients, the number of phytoplankton also decrease.  This leads to an overall decrease in fish populations.  In cooler waters, the turbulence is much higher and nutrients cycle through the ocean current.  This allows plankton to bloom, which also allows other species to proliferate.  It is easily evident that polar waters are much more productive.  Most of the ocean’s biomass resides in the polar regions of the world, which allows large animals, such as whales, to thrive in the abundance of food.

Ocean Acidification

The acidification of the world's oceans is completely derived from carbon dioxide.  Increased carbon in the atmosphere would lead to a lower pH in the ocean.  At first, it might seem that acidification is quite innocuous.  It is true that the pH does not change by a significant number as to denature proteins and kill organisms directly.  However, the slight changes in pH do affect many crustaceans, copepods, plankton, corals, and mollusks.  Many of these organisms have exoskeletons made of calcium carbonate, but these exoskeletons are very reactive to acid.  If these organisms lose their shells, then they become vulnerable not only to predators, but also parasites and the natural environment.  Most copepods and plankton are at the bottom of the food web.  They provide food for larger organisms, which in turn feed even larger organisms.

The acidification of the ocean causes decreases in these fundamental organisms, which in turn destroys the animals that depend on them.  Crustaceans and mollusks too sit near the bottom of the food web.  If the bottom of the food web declines, it is only natural that everything above would also decline as they rely on these organisms for survival.  Acidification also affects habitat.  Corals provide refuge for many fish and with decreasing pH in the ocean, many of these corals cannot survive.  Because of the acidification of the ocean, not only do food sources dwindle, but also habitable regions.

Introduction

There has been less explorations of the world's oceans than expeditions into space.  Much of our own planet is undiscovered and more importantly, inadequately understood.  It is only natural then that we have very little idea of what happens in the oceans.  What we do know, however, is that the ocean is critical in maintaining homeostasis within our planet.  It is a major heat sink and is partially responsible for keeping the earth warm at night.  In the day the ocean absorbs heat taken from the ground and at night it releases it back. The ocean is also responsible for the balance of atmospheric gases and is the largest current carbon sink.  However, the ocean still has its limits.

Due to fossil fuel emissions, vast quantities of carbon dioxide are released to the atmosphere.  The ocean has a method to cope with this problem.  By spontaneous reaction of carbon dioxide with water, the ocean creates carbonic acid.  However, the ocean can only absorb a finite amount of carbon dioxide.  As the seas become more acidic, it becomes less hospitable to marine life.  All organisms have a fairly narrow window of conditions in which they can survive.  Acidifaction of the oceans would alter the chemical conditions in which many organisms reside, possibly causing mortality.  Many organisms also have narrow temperature windows and the rate of global warming only increases SSTs.

Increases in temperature creates shifts in habitable environments and marine wildlife are forced to migrate into northern latitudes in response to climatic change.  However, climate change is not the only concern to marine wildlife.  Fishing is among the few causes, along with habitat destruction and warming seas, that can destroy marine habitats.  Many of the fish we catch are among the lower end of the food chain.  Reductions in theses populations also means reduced populations of predators, leading to changes in population dynamics.  In order to preserve the natural climate, many measures must be taken in order to prevent further destruction to our ocean and marine wildlife.