What dolphin teeth can tell us about ocean pollution

Crucial clues about the contamination of our coasts could be found - of all places - inside the teeth of bottlenose dolphins.

Metal contaminants in marine environments are a particular health risk for humans and other animals as they get absorbed into teeth and bones.

Now, Dr Carolina Loch, of Otago University's Faculty of Dentistry, is leading a study to track metal exposure in marine species to help determine pollution in the ocean.

Similar to humans, bottlenose dolphin teeth are made up of enamel and dentine which grows in layers like the rings in a tree.

Each layer corresponded to one year of the life of the animal and using laser spectroscopy, Loch hoped to be able to reveal the toxic metal bioaccumulation.

Dolphin teeth reliably recorded contamination because toxic metals and trace elements from diet were incorporated into enamel and dentine throughout life.

As dolphins fed from fish and other animals in the ocean, they were potentially susceptible to metals like lead or mercury – just as humans are.

Humans, too, ate some of the same seafood as dolphins.

"One of the key issues is that the wastewater from mining and city pollution goes back into the marine environment and it comes back to us when we consume seafood," Loch said.

"The idea is about using a species living in that environment with teeth that record contamination throughout the animal's life."

Water or seaweed samples could reveal information about contaminants at a certain point in time, but the dolphin's teeth enables the researchers to look at what happened in past times.

Loch was particulary interested to see whether there was any correlation to a reduction in pollution when leaded-fuel bans for road vehicles came into effect in New Zealand in 1996.

She and colleagues from Otago University are collaborating on the project with Massey University's Dr Karen Stockin, Dr Cath Kemper from the South Australian Museum and Professor Mark Taylor from Australia's Macquarie University.

The team will compare metal exposure in dolphin teeth from supposedly low-polluted areas in New Zealand to a high-metal-exposure area in South Australia.

The bottlenose species had been specifically chosen as they did not migrate.

Loch expected that high concentrations of toxic metals in teeth would be correlated with increased industrial contamination, while decreased levels would be expected where there was improved environmental practices.

As long-term exposure data for anthropogenic marine contaminants was lacking, the pilot study offered an opportunity to understand historical coastal contamination to generate baseline datasets for New Zealand, benchmarked against known Australian high exposure data.

If successful, the Otago researchers want to roll the research out on a larger scale and are applying for further funding.

To date, little use has been made of animal teeth as a model to study coastal contamination, although Loch was aware of studies being carried out in Europe with teeth of rats investigating contamination on the land.

Storms wash up epic travellers

Meanwhile, scientists have also revealed how some sea creatures are able to hitch rides on kelp for hundreds of kilometres across the wild Southern Ocean, thanks to extreme weather events.

An Otago University team used DNA and geological evidence to establish the origins of kelp rafts that were driven on to the beaches of Dunedin by cyclonic winds in April and July last year.

Macquarie Island kelp rafts reached mainland New Zealand in the storm of July 2017. Image / Supplied

They found that one July 21 storm had been powerful enough to take some of the rafts all the way from the remote sub-antarctic Macquarie Island - some 1200km away.

The unusually strong southerly winds drove these rafts north, across the Subtropical Front - a major ocean barrier, allowing them to reach mainland New Zealand.

"While we have long suspected that kelp rafts can drift for long distances, these findings represent some of the longest natural rafting events ever documented anywhere," study leader Professor Jon Waters said.

Some of the key evidence for long-distance rafting came from exotic rocks found attached to some of the kelp rafts.

"These rocks clearly show that many of the rafts have come a long way, from very distant geological sources," said co-author Professor Dave Craw, of Otago's Department of Geology.

The study also found several rocky-shore animal species such as limpets and chitons were able to raft with kelp to reach Dunedin.

"We've often wondered how some coastal species come to be distributed so widely across the Southern Hemisphere," Waters said.

"It's now becoming clear that storms might play a really big part in this."

The study, just published in the British interdisciplinary Journal of the Royal Society Interface, could ultimately help to explain how some rocky shore species come to be widely spread across remote parts of the Southern Ocean.