The most recent report published by the Intergovernmental Panel for Climate Change (IPCC) showed there is unequivocal evidence for climate change due to the rise of atmospheric carbon dioxide (CO2). Without a resolution, projected consequences will likely include a further increase of global average temperatures, melting of polar ice caps and ocean acidification. While we are aware of the subsequent impacts on human society, the effects of climate change on marine mammals is lesser-known.
With the rise of ocean temperatures, almost all species will shift their geographic range. Polar-adapted species living in the Arctic and Southern Ocean will especially be impacted as they can lose their cold water habitat while competition with other species for resources may likely increase.
The Arctic has been warming almost twice as fast as the global average. Here, ice-covered areas are quickly disappearing, challenging the adaptive capacity of those species that depend on it, namely: Narwhals, Belugas and Bowhead whales. Ice reduction can have a bottom-up effect on the food web, while the opening of navigable shipping routes can increase the chances of whales being injured, and their communication can be interfered.
Arctic sea ice core studies also revealed that, due to the prevailing ocean currents, microplastic particles have been accumulating in the Arctic ice. However, as sea ice melts, these microplastic pieces can re-disperse in the water column and can become available for accidental ingestion by filter feeding whale species i.e. Minke whales and Humpback whales (see previous blog entries on the effects of plastic ingestion, bioaccumulation and bio magnification).
Whilst the “cold barrier” is disappearing, the increasing risks of infectious diseases and parasites can also impact marine mammal populations. Since 2006, a parasite, which prefers warm-blooded vertebrates and is usually found in cat faeces, has been detected in Beluga whales.
Whale reproductive success can also be affected by the warming ocean temperatures. El Nino Southern Oscillation (ENSO) occurs in every three to seven years, due to the weakening of easterly trade winds in the Western Pacific. As a consequence, unusually warm water appears off the coast of Peru, Chile and in parts of the Southern Ocean. This change in seawater temperature can reduce the availability of krill, with an impact on the Southern Right whale breeding success and calves survival.
Lastly, the issue of ocean acidification (OA) can lead to reduced sound absorption, allowing sound to travel farther under water. Thus, the ocean becomes noisier. On the one hand, this can help cetacean species to communicate over longer distances. On the other hand, the amount of ambient noise can also increase, subsequently leading to stress, higher chances of strandings and ship strikes (see Whalefish.org for more information on strandings). It is estimated that at the current rate of emission, ocean pH will reduce by 0.3 units by mid-century, which will allow sound to travel 70% farther.
Whale species, for example Gray whales, managed to survive climate changes in the past, but today the rate of climate change is much faster than the adaptive ability of many marine species.
By Wanda Bodnar
Image Source: Whalefish