The General Assembly of the United Nations has stated that “Changes to the climate, brought about by increasing levels of greenhouse gases in the atmosphere, will thus lead to changes in the oceans, including sea-level rise and ocean acidification, which will put marine ecosystems and coastal communities at risk. Most of these changes can be attributed to human activities and will negatively affect the animal inhabitants of the marine environment. Some effects of global warming on marine animals include changes in distribution, reduction of habitats and reductions in diversity and sex ratios.
In the last hundred years, the rate of global warming experienced by the earth is unparalleled in human history. Crowley (2000) has found that almost seventy five percent of temperature variability in the Northern Hemisphere can be attributed to increases in greenhouse gas emissions, driven by human activities. The burning of fossil fuels such as oil, coal and natural gas produces atmospheric gases such as methane, nitrous oxide, ozone and carbon dioxide. These gases, which build up in the atmosphere, contribute to an intensification of the Greenhouse Effect.
The naturally occurring phenomenon known as the Greenhouse Effect occurs when solar radiation is trapped against the earth’s surface. This effect allows the earth’s temperature to remain constant and warm enough to sustain life. However, a large increase in greenhouse gases in the last century, caused mostly by industrialization, has increased the earth’s temperature. This is due to increased greenhouse gases trapping more infrared energy and not allowing the excess to escape into the .
Th destruction of large swathes of the earth’s forests also contributes to climate change. Productive ecosystems such as savannahs and tropical rainforests are the sink for a large amount of the earth’s carbon and the active interface for the exchange of carbon between the earth and the atmosphere .
Increases in ocean temperatures caused by global warming, to which marine species are particularly vulnerable, are affecting the animals and plants of the marine environment.
Global warming can influence marine species in a number of ways. Species may shift their ranges closer to the poles or to higher elevations in response to the range of temperatures that they are able to tolerate. Many species respond to temperature-related cues to time such events as migration or egg laying, and changes to the temperature of their habitats will alter the timing of these events . Changes to shape, structure or form of many species, as evidenced by changes in behavior or body size, together with changes in the genetic frequencies, may also occur..
Studies have found that the Northern Hemisphere is most affected by rises in temperature, because temperatures have risen faster at higher global latitudes. In the last thirty years, Arctic temperatures have risen much more rapidly than in other regions of the globe, and have incurred changes in the behavior of whales in the region (Vikingsson et al., 2014). A reduction in Arctic sea ice has reduced areas for breeding and resting, and sites for suitable feeding habitats (Vikingsson et al., 2014). Studies have also found that loss of sea ice is responsible for changes in whale breeding seasons and migration routes and that sightings of particular whales have occurred far outside their normal ranges .
As is the case with other marine animals, fish and invertebrates react to increases in temperature by moving to deeper waters and into higher latitudes, which are cooler . This has negative implications for the sustainability of global fisheries and for the food security of many developing nations
Until they reach maturity, sea turtles endure substantial losses of offspring from the time they hatch but they face additional threats incurred by climate change.
. Turtles, which nest on sandy beaches and lay their eggs in deep depressions, later covered in sand, return every year to nest in the same site. Global warming is causing rises in seal levels, which will destroy existing turtle nesting sites, leaving turtles nowhere to lay their eggs. The sex of turtles is determined by nest temperature: warmer sites produce females while cooler sites produce males. As turtles move to cooler regions in response to global warming, this will result in the production of more males than females, which will seriously affect turtle populations.
Coral reefs survive only within a very narrow range of temperatures and thus are particularly vulnerable to ocean warming.(Pockley, 1999). Recent coral “bleaching” events in Puerto Rico, the Caribbean and on Australia’s Great Barrier Reef have occurred in response to increases in ocean temperatures. Coral is not actually “bleached”: the loss of its color is caused by the coral ejecting the symbiotic photosynthetic algae (zooxanthellae), which live in the tissues of coral and provide it with food . When zooxanthellae get too hot, they stop producing food and are ejected from the coral. Corals can also only survive within a limited range of water depths because they need light to survive, thus most corals are limited to the area of maximum light penetration – the euphotic zone . Any rise in sea level will mean that the amount of light available for coral to function will be reduced.
Intergovernmental government consensus to reduce the rate and degree of climate change was achieved in Paris at the end of 2015 . One hundred and seventy seven nations agreed that the preservation of the marine environment was a priority and vowed to work towards reducing their emissions of greenhouse gases into the environment. One effect of emissions reduction will be to halt or reduce the increase in ocean temperatures, which will subsequently reduce the negative impacts on marine animals. By so doing, the productivity and usefulness of the marine environment to all humans will be preserved.
References
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