Marine mammals disturbed by warming waters

From the polar bears of the Arctic to the Irrawaddy dolphins of the Tropics, climate change is bearing down on marine mammals, leading  to loss of habitat, changes in distribution and migration patterns and threats to the availability of prey.

The warming of the oceans could also mean diminished reproductive success and increased susceptibility to diseases, according to a Silliman Journal article by Dr. Ma. Louella L. Dolar, a foremost authority on Philippine marine mammals, and Edna S. Sabater, a doctoral candidate at Silliman University.

Dolar now works at the San Diego, California, Tropical Marine Research for Conservation, but she began her scientific career at the Silliman University Marine Laboratory, where she continues to do collaborative research and teaching.

The researchers wrote that the most vulnerable marine mammals are those with limited distributions, such as those found in the rivers, estuaries and coastal areas, many of which are in Southeast Asia.

Southeast Asia comprises only 3% of the earth’s area but harbors 20% of all known species of plants and animals. “The mountains, jungles and seas of the countries found in it form one of the biggest biodiversity pools in the world.”

“Southeast Asia has the most extensive coastline in the world, the most diverse coral reefs and the richest marine biodiversity. It is also the most ecologically threatened.”

Dolar and Sabater reviewed research studies on the subject using as framework the reports of the Intergovernmental Panel on Climate Change (IPCC), the scientific body composed of hundreds of scientists under the auspieces of the United Nations  to study climate change and its political and socioeconomic impacts.

According to those reports, land and sea surface temperatures have been significantly and steadily increasing in the last 50 years and human activities involving the burning of fossil fuel have contributed much to it.

“Over the 20th century, the global average surface temperature has increased by 0.6±0.2°C, with an increase of 0.4-0.7°C  in air temperature over the oceans and a 0.4-0.8°C in sea-surface temperature.

“The increase in global temperature in 1956 to 2005 is nearly twice that of the 100 years from 1906 to 2005…It is projected that globally, land and sea surface temperatures will increase by 1.1-6.4°C by 2100.  

“The ocean absorbs 80% of the heat being added to the climate system, and 60% of that heat is being absorbed in the upper 700 meters of the oceans,” they wrote.

This is significant because water temperature “appears to be the main factor that influences the geographic ranges of most marine mammals…Latitudinal zones (tropical, sub-tropical, temperate, Antarctic or Arctic) define the distribution of many marine mammals.

The scientists said climate change affects land and water ecosystems by altering their physical and geochemical characteristics, such as “increase in temperature, decrease in sea-ice cover, rise in sea level, increases in CO2  concentrations, and changes in salinity, pH oxygen solubility, rainfall patterns, storm frequency and intensity, wind speed, wave conditions and climate patterns.”

“These changes, in turn, affect the biological components of the ecosystems such as the abundance and distribution of plants and animals, composition and abundance of competitors and predators, timing and range of migration, vulnerability to diseases and pollutants, timing of breeding, and reproductive success and survival.”

One study said as the sea surface warms, “the tropical zones will expand into higher altitudes, the temperate zones will shift toward the poles and polar zones will contract. Mobile organisms will react by also shifting their distribution in order to remain in their preferred environmental envelope, as had been observed with the white beaked dolphin of Scotland and the Pacific white-sided dolphin in northeastern Pacific.”

It is predicted that “the geographic range of 88% of all cetacean species may be affected by changes in water temperature. Of these, 47% may have unfavorable implications for their conservation and 21% may be put at risk of extinction.”

Shifts in temperature have more serious implications for polar species, such as the bowhead whales and polar bears, “because climate change in the polar zones are among the most rapid of any regions on earth and these species have less time to cope with changes in their shrinking habitat.”

Availability and distribution of prey are also “linked to water currents, upwelling, eddies and primary productivity, all of which can be affected by water temperature.”

“Reproductive success and calf survival are also tied to prey abundance. There appears to be a close relationship between food abundance, body fat and fecundity. The female fin whales, for example, may produce a calf in two consecutive years if food is abundant but only one in three years if prey supply is poor.”

The timing of migration coincides with maximum prey abundance in their feeding grounds.  This timing is important for the lactating mother and the calves being weaned.  Observations made in the last 40 years of the migration patterns of grey whales showed that in response to the El Niño event of 1998/1999, there had been a delay of one week (January 8 to January 15),” the scientists wrote.

Changes in migration patterns could result in the mixing of populations and species not previously associated with each other, which could lead to the introduction of novel pathogens and parasites into the native population.  Increased water temperature could also increase infection rates and growth of pathogens and increase the marine mammals’ susceptibility to pollutants such as mercury.

Additional made-made pressures  are overharvesting, pollution, and habitat fragmentation and destruction, leading to local extirpations or even species extinctions.

Marine mammals found in Southeast Asia that are already threatened are the Irrawaddy dolphin (Orcaella brevirostris), finless porpoise (Neophocaena phocaenoides), Indo-Pacific humpback dolphin (Sousa chinensis), and dugong (Dugong dugon). The Irrawaddy are critically endangered.

Climate changes have been noted in the past, such as in the Pleistocene almost 2 million years ago, when temperature and precipitation fluctuated. But these happened in a much slower rate, giving the plants and animals enough time to adapt and survive. And the environment was not as stressed then as it has been in this century, the scientists noted. – Celia E. Acedo, SU Research and Environment News Service