Even biologists only capture a glimpse of the lives of whales. There are still many species whose lives are largely a mystery, particularly the deep diving whales.
Authors
- Kirsten Freja Young
Senior Lecturer, Ecology, University of Exeter
- Marion Rossi
Research Fellow in Climate Systems, University of Exeter
But scientists are learning more about the role that whales play in marine ecosystems and the services that they provide. Recent research is showing that even whale urine is important for the planet.
Previous work suggested that whale faeces was important to ecosystems . These giant mammals bring nutrients from the depths where they feed to shallow waters.
This effect is called the "whale pump" and it can enhance the photosynthetic rate of plankton, which is the basis of the food web. Nutrients are not distributed evenly across the ocean and in some areas, phytoplankton populations are limited because there aren't enough of specific elements, such as iron.
Some whale species perform long migrations across the ocean. Humpback whales (Megaptera novaeangliae) perform the longest migration of any mammal at around 10,000 km , moving nutrients across ocean basins as they travel. To some extent the whale pump influences carbon cycling and storage too.
Whales can also help cycle nutrients in the ocean when they disturb the seabed as they feed. Gray whales (Eschrichtius robustus), for example, are known to forage for invertebrates on the seafloor and stir up sediments which release nutrients , such as nitrogen, phosphorus and iron.
Another key area of research describes the oasis ecosystems that whale carcasses provide to deep sea species, from hagfish (Eptatretus deani) and sleeper sharks (Somniosis pacificus) to crustacea, molluscs, nematodes and bacteria. The great whales have large bodies with high amounts of lipids in their bones. These lipids are food for lots of organisms and whale carcasses create mini ecosystems in the deep.
But until now, another benefit that whales provided to ecosystems had not been quantified - that of urine.
A recent study published in Nature Communications indicates that baleen whales' urine could also have a crucial function in oceans. Some whale species can produce up to 950 liters of urine per day, and this means they can relocate nutrients to tropical grounds low in nutrients. Many baleen whales, such as humpback and gray whales, feed in polar and subpolar regions during summer, then migrate to equatorial breeding areas en masse into relatively small areas during the winter.
During migration, the whales carry detritus like placenta, urine, faeces and if they die, carcasses. For example, the paper describes how gray whales tend to winter in several feeding grounds across the north Pacific ocean and aggregate in summer in a few small bays on the coast of California.
The researchers describe how gray, humpback and right whales (Eubalaena glacialis) transport carbon and nitrogen to the tropics, in what they call the "great whale conveyor belt". Globally, for these species, this process results in more than 46,000 tons of biomass (whales' total mass and the nutrients they contain) and almost 4,000 tons of nitrogen per year, transferred to poor nutrient grounds.
Most of this nitrogen transport comes from whale urine, which stimulates phytoplankton growth and photosynthesis. This increase in the rate of photosynthesis could lead to 18,180 tons of carbon being drawn down from the atmosphere. Other large baleen whales probably also contribute to this effect but there is less data on their distributions and ecology.
Sadly, the study estimates that historical whaling has reduced whale related nutrient transportation to almost one third of its previous potential.
Other animals that play a crucial role in nutrient flows have also been suffering from the effect of human-related activities. Seabirds and fish that migrate from the sea into freshwater bodies have a significant effect on phosphorus transfer from sea to land, which is also an important nutrient for photosynthesis.
Bears, otters, eagles and other predators that eat fish which migrate up rivers from the sea, participate in the transport of ocean nutrients to land through their faeces . Moose are also important carriers of nutrients and are known to transfer large amounts from aquatic to land ecosystems as they feed on plants.
Grazing hippopotamus also transfer nutrients in reverse from land to aquatic systems. But these large animals generally don't match whales in quantity, or by geographical scale.
Whales face many threats to their survival today, such as ship strikes, pollution, poorly managed fisheries and climate change. This recent study shows how important it is to protect whales and the ocean they live in.
The contribution that these animals will make to solving our climate crisis through stimulating photosythesis is under debate and their ability to balance the global carbon budget in the face of human-related emissions may be negligible. However, the more we learn about these ocean giants, the more we understand the ways in which whales are vital to marine ecosystems.
Kirsten Freja Young is a Senior Lecturer in Ecology at the University of Exeter and also works as an independent consultant to Greenpeace Research Laboratories.
Marion Rossi does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
