As the largest animals on Earth, great whales play a role in maintaining Hawaii’s ecosystems by bringing in nutrients from their migrations.

"They are nutrient pumps," said Craig Smith, an oceanography professor at the University of Hawaii at Manoa. "For example, humpback whales, they’re migrating from Alaska and are productive in bringing nutrients."

These nutrients are nitrate and dissolved iron, which stimulate the growth of primary producers, such as phytoplankton, providing food at the base of the food web, Smith said.

A paper co-authored by Smith and a group of researchers from around the world found that the decline in populations of these great whales, also known as baleen and sperm whales, has altered the ocean’s ecosystems.

The paper, "Whales as Marine Ecosystem Engineers," appears in the July issue of the journal Frontiers in Ecology and the Environment.

Across the oceans, great whales act as transporters carrying nutrients vertically and horizontally.

After the whales feed on krill deep in the ocean, they come toward the surface to defecate, which releases nutrients such as iron and nitrogen to primary producers near the ocean’s surface.

Like the humpbacks in Hawaii, many great whales feed in high-latitude areas in the summer and migrate to warmer waters in the winter to breed and calve. This movement carries nutrients from one region to another.

Whales also contribute to the ecosystem when they die. Their carcasses sink to the bottom of the ocean — an occurrence referred to as a "whale fall" — where they provide homes and nutrients for various organisms.

"These whale fall species enhance biodiversity, help to recycle large carcasses, and provide ‘raw material’ for the evolution of new species and biodiversity in the deep ocean," Smith said.

But with the decline of great whale populations, marine ecosystems have changed.

Smith’s paper estimates that, due to commercial whaling, the great whale population has decreased between 66 percent and 90 percent, leaving about 1.2 million to 1.5 million great whales left.

He notes that some species, like blue whales, are only at about 1 percent of their original abundance.

"The abundance of whale falls, the availability of that special kind of habitat has dramatically decreased," said Smith, who has been studying whale graveyard communities since 1989. "We think there’s a good possibility that there’s been a significant number of species going extinct."

The species he talks about are invertebrates, such as mussels, limpets and worms.

He thinks his paper will increase the public’s awareness of the importance of whales in their marine ecosystems.

"I’m really amazed at the potential role of whales to restore marine ecosystems to their pre-whaling role," Smith said.