The ecosystem engineers of the deep
Cape Town - It’s well established that large terrestrial animals like elephants are “ecosystem engineers”, influencing and altering their habitats both to the benefit and sometimes the cost of fellow creatures sharing these spaces with them.
But researchers are now saying we’ve been ignoring the similar function that great whales perform in the oceans.
And they point out that the global slaughter of these creatures that may have reduced their numbers by up to 90 percent, was so severe it probably altered the biological structure and ecological functioning of the oceans.
This is the conclusion of a new research paper by University of Vermont conservation biologist Joe Roman and a global team of collaborators, just published in the online edition of the scientific journal Frontiers in Ecology and the Environment.
“For a long time, whales have been considered too rare to make much of a difference in the oceans,” Roman notes, and says this was a mistake.
He and his colleagues analysed several decades of research on great whales – baleen whales like blue, right, bowhead, sei, fin and humpback whales, and the toothed sperm whale – from around the world.
This showed that the animals in fact made a huge difference, having a “powerful and positive influence” on the function of oceans, global carbon storage and – notably – on the health of commercial fisheries.
“The decline in great whale numbers, estimated to be at least 66 percent and perhaps as high as 90 percent, has likely altered the structure and function of the oceans,” they say.
But the good news is that recovery is possible “and in many cases is already under way”.
“The continued recovery of great whales may help to buffer marine ecosystems from destabilising stresses”.
The great whales – the blue whale is the largest known creature on Earth – can be called the ocean’s ecosystem engineers for several reasons. They eat many fish and marine invertebrates and are themselves prey to other predators like killer whales.
They also distribute nutrients through the water and enhance primary productivity when they poo. They do this by feeding at depth and then releasing nutrient-rich faecal plumes near the surface which in turn support plankton growth – a process described as a “whale pump”, the researchers say.
In death, whale carcasses drop to the seafloor, providing a habitat for many species that only exist on these “whale falls”.
“Dozens, possibly hundreds, of species depend on these whale falls in the deep sea,” Roman notes.
“Our models show that the earliest human-caused extinctions in the sea may have been whale fall invertebrates. These would have disappeared before we had a chance to discover them.”
Commercial fishermen sometimes view whales as competition. But Roman’s paper shows strong evidence that the opposite is true: whale recovery could lead to higher productivity in locations where whales aggregate to feed and give birth, supporting more robust fisheries, it suggests.
The great whales’ recovery may be especially important as climate change threatens ocean ecosystems.
l Southern right whales, critically endangered until quite recently, should start arriving in the Cape waters this month during their annual migrations from deep Southern Ocean waters to calve and mate. - Cape Argus