Whale poo important for ocean ecosystems
Rather than a burden on the marine food chain, whales contribute important nutrients, new research shows.
IT'S LONG BEEN thought that a whale's size and need for huge amounts of food is a burden on ocean ecosystems, but new Australian research shows that its output may offset its intake.
Whales' iron-rich poo actually provides a source of important nutrients for fisheries, says lead researcher Trish Lavery from Flinders University.
Previous scientific models assumed that nutrients from prey consumed by whales is lost to marine ecosystems and that whales take out more nutrients than they give back.
"For a long time it's been speculated that [whales] might be having an effect on marine productivity by eating all this prey," she says.
Whale poo boost ocean nutrients
Whales and other marine mammals are the only species to defecate at surface of the ocean, saving energy for only essential metabolic functions when they dive.
And unlike other marine species, marine mammal faeces are liquid and so linger at the surface rather than sinking. This ensures that nutrients - particularly iron and nitrogen - are available for phytoplankton, the ocean's base on the food chain, to consume.
In the 'iron-limited' Southern Ocean, this is particularly important, Trish says.
The research team had previously examined how the nutrient-rich poo of deep-diving whales helped remove carbon from the atmosphere. Using these results, combined with past studies on the amount of prey consumed by whales, they modelled the blue whales' effect on marine productivity and found that while whales consume huge quantities of food, a large portion of these nutrients are passed back into the ocean and the food chain.
In fact, the whales are having a positive impact and are fertilising their feeding grounds with their poo providing enough nutrients needed to sustain krill population growth.
"We estimate that if blue whale populations returned to their historical abundances, then they would increase the productivity of the whole Southern Ocean by 0.23 per cent."
Whale poo important for marine food chains
The researchers also indicated that past global declines in marine ecosystems occurred about the same time as whale stocks were decreasing during the industrial whaling era, although it's unknown if the decline was caused by the removal of whales.
"I think this study really helps to put a nail in (the) coffin," Trish says. "It really shows that whales are in balance with their environment."
The research is published this month in the journal Marine Mammal Science.