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A Discordant Sea: Global Warming and its Effect on Marine Populations

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Global warming, an increase in the earth's average atmospheric temperature that causes corresponding changes in climate, is a growing environmental issue caused by the influx of human industry and agriculture in the mid-twentieth-century to the present. As greenhouse gases such as CO2 and methane are released into the atmosphere, a shield forms around our Earth, trapping heat inside of our planet and therefore creating a general warming effect. One of the most influenced territories of warming has been our oceans.

Rising air temperatures affect the physical nature of our oceans. As air temperatures rise, water becomes less dense and separates from a nutrient-filled cold layer below. This is the basis for a chain effect that impacts all marine life who count on these nutrients for survival.

There are two general physical effects of ocean warming on marine populations that are crucial to consider:

 

  • Changes in natural habitats and food supply
  • Changing ocean chemistry/acidification

Changes in Natural Habitats and Food Supply

Photosynthesis

Phytoplankton, one-celled plants that live at the ocean surface, and algae use photosynthesis for nutrient fulfillment. Photosynthesis is a process that removes carbon dioxide from the atmosphere and converts it into organic carbon and oxygen that feeds almost every ecosystem. According to a recent NASA study, phytoplankton is more likely to thrive in cooler oceans. Similarly, algae, a plant that produces food for other marine life through photosynthesis, is vanishing due to ocean warming. Since oceans are warmer, nutrients are blocked from traveling upward to these suppliers that are limited to a small surface layer and therefore cannot supplement marine life with necessary organic carbon and oxygen.

Yearly Growth Cycles

Various plants and animals in our oceans need both a temperature and light balance in order to thrive. Temperature-driven creatures, such as Phytoplankton, have started their yearly growth cycle earlier in the season due to warming oceans. Light-driven creatures start their yearly growth cycle around the same time. Since Phytoplankton is thriving in earlier seasons, the entire food chain is affected. Animals that once traveled to the surface for food are now finding an area void of nutrients and light-driven creatures are starting their growth cycles at different times. This creates a non-synchronous natural environment.

Migration

The warming of oceans may also lead to migration of organisms along the east and west coasts. Heat-tolerant species, such as shrimp, will expand northward, while heat-intolerant species, such as clams and flounder, will retreat northward. This migration will lead to a new mix of organisms in an entirely new environment, ultimately causing changes in predatory habits. If some organisms cannot adapt to their new marine environment, they will not flourish and die off.

 

Changing Ocean Chemistry/Acidification

General Acidification

As carbon dioxide is being released into the ocean, the ocean chemistry drastically changes. Greater CO2 concentrations released into our oceans create increased ocean acidity. As ocean acidity increases, Phytoplankton is reduced. This results in less ocean plants able to uptake greenhouse gases. Also, increased ocean acidity threatens marine life, such as corals and shellfish, which may become extinct later this century from the chemical effects of CO2.

Acidification Effect on Coral Reefs

Coral, one of the leading sources for the ocean's food and livelihood, is also changing with the onset of global warming. Naturally, coral secretes tiny shells of calcium carbonate in order to form its skeleton. Yet, as CO2 from global warming is released into the atmosphere, acidification increases and the carbonate ions vanish. This results in lower extension rates or weaker skeletons in most corals.

Coral Bleaching

Coral bleaching, the breakdown in the symbiotic relationship between coral and algae, is also occurring with warmer ocean temperatures. Since Zooxanthellae, or algae, give coral its particular coloration, increased CO2 in our oceans causes coral stress and a release of this algae. This leads to a lighter appearance. When this relationship that is so important for our ecosystem to survive vanishes, corals begin to weaken. Consequently, food and habitats for a great number of marine life are also destroyed.

 

Holocene Climatic Optimum

This drastic climate change and its effect on surrounding wildlife is not news to us. The Holocene Climatic Optimum, a general warming period displayed in our fossil record from 9,000 to 5,000 B.P., proves that climate change can directly impact nature's inhabitants. In 10,500 B.P., younger dryas, a plant that was once spread throughout the world in various cold climates, became near extinct due to this warming period. Towards the end of the warming period, this plant that so much of nature had depended on was only to be found in the few areas that remained cold. Just as younger dryas became scarce in the past, Phytoplankton, coral reefs, and the marine life that depend on them are becoming scarce in the present. Our environment is continuing on a circular path that may soon lead to chaos within a once naturally balanced environment.

 

Future Outlook and Human Effects

The warming of our oceans and its effect on marine life has a direct impact on us. As coral reefs die, we will lose an entire ecological habitat of fish. According to the World Wildlife Fund, a small increase of two degrees Celsius would destroy almost all existing coral reefs. Additionally, ocean circulation changes due to warming would have disastrous impacts on marine fisheries.

This drastic impact is often hard to imagine. It can only be related to a similar historical event. Fifty-five million years ago, ocean acidification led to a mass extinction of ocean creatures. According to our fossil record, it took more than 100,000 years for the oceans to recover. Eliminating the use of greenhouse gases and protecting our oceans will prevent this from reoccurring.

 

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