Effects of global warming on marine mammals

The global warming is having severe effects on all wildlife, including the human population. These effects, however, are quite complex. Most consequences involve the interrelation between species (foodweb) but also direct effect are noticed.

The consequences on marine mammals can be resumed as followed:

  • Effects of changes in temperature:

    • Most toothed whales are limited in the range of water temperature that they inhabit. E.g. species of the cold polar regions (like the beluga) are restricted to cold waters and cannot survive in warm water.

    • For other species there will be a shift in geographic ranges (although several species are physically limited to change their ranges e.g. river dolphins).

    • Effects of changes in temperature on prey species (e.g. fish, cephalopods, etc.) have indirect effect on marine mammals like:

      • Distribution, abundance and migration

      • Vulnerability to diseases and contamination

      • Reproductive success

  • A rising sea level has effects on marine mammals that depend on the land for their reproduction (like e.g. sea lions, seals, ice bears, etc.).

  • A change in the ocean currents has effects on

    • the oceanic fronts and consequently on the distribution of marine mammals associated with these fronts.

    • the sustainability, productivity and biodiversity of the whole marine ecosystem, affecting distribution, abundance and migration of plankton, fish, cephalopods, etc. which in turn affect marine mammals.

  • Change in sea-ice cover has a direct effect

    • on the animals depending on the sea-ice for breeding like e.g. seals, ice bears, etc. (habitat loss).

    • biomass, distribution, migration, nutrition, reproduction and abundance of species associated with the sea-ice like phytoplankton, zooplankton, fish, crustaceans and consequently marine mammals (e.g. baleen whales will need to travel greater distances due to the retreat of sea-ice and consequently a change in distribution of their prey).

  • Change in water salinity will alter the distribution and abundance of prey due to their limited salinity tolerance.

  • Increase of El Niño events will have a severe impact on all marine life.

(Source: Learmonth, J.A., Macleod, C.D., Santos, M.B., Pierce, G.J., Crick, H.Q.P., Robinson, R.A., 2006. Potential effects of climate change on marine mammals. Oceanography and Marine Biology: An Annual Review, 44, 431-464)

The most rapid climate change is to  be seen in the polar regions. There is growing evidence that the maximum extend of winter sea ice is declining and several areas of the polar regions are warming at a rate of 2 to 3 times the global average, causing parts to break and melt down, with severe consequences (in the past 50 years, an increase of 2,5°C was measured on the Antarctic Peninsula).

The polar regions contain unique ecosystems. Moreover, the relationship between ice and seawater is the main factor driving the ocean’s currents which pump oxygen and nutrient-rich waters thousands of kilometers into both hemispheres, fertilizing the surface waters.

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