Seals’ tolerance of toxic metals offers hope for future

Juan Fernandez fur seals

A new paper by Constanza Toro Valdivieso explores what seals could tell us about exposure to extreme pollution – and the implications for biomedicine.

On a remote island half a world away from Newnham, Constanza Toro Valdivieso is conducting research on a community that is a microcosm of global environmental struggles: communities grappling with sustainable living amid competition for resources, animals exposed to extreme pollution and the tantalising hope that biomedicine can benefit from knowing how they have coped.

Juan Fernandez fur seals only inhabit a tiny group of islands off the coast of Chile, a pristine area so important for marine biodiversity it is UNESCO-protected. Yet even here, miles from any landmass, Constanza has discovered they are ingesting the highest levels of cadmium and mercury found in any living mammal.

In their new paper*, Constanza and colleagues explore what the findings from this sentinel species could mean and key questions for future research.

It’s a timely study given the growing focus on the connections between animal and human health, alongside the impact of environmental change.

Questions with vital implications

“One mystery is the source: is it natural or are these toxic metals leaching from microplastics? At this point, we can’t be sure. Breeding females will forage for food up to 300 miles offshore, which would take the seals through some of the world’s largest areas of microplastic contamination.”

That foraging area includes the massive South Pacific Gyre which scoops up and concentrates plastic pollution out at sea. Plastics can contain cadmium or absorb it from the water and may be eaten by the fur seals or their prey. However there may also be natural ways cadmium can enter the food chain through phytoplankton (small ocean organisms) that form the basis for the food chain.

As an apex predator, examining fur seals’ faeces and carcass bones is a non-invasive way to track indicators of the health of the eco system. They can indicate gut health, interbreeding levels, diet, stress hormones, and toxin levels.

“Consumption of this level of toxic metals would normally have a dramatic effect on the bones of these seals, degrading them severely, but when we analysed them, we found no adverse effects,” Constanza said. The researchers also found a high level of silicon and are keen to understand the possible role it plays in protecting bones from cadmium damage, which would be of significant relevance for biomedical research.

Another possibility is that the seals have been exposed to such high levels of cadmium for long enough to adapt.

“So we are looking for genes in their microbiome that can help in digesting plastics polymers. Which functions are microbiomes playing in adaptation of seals to that changing environment? What generates these functions? It takes many years to really understand what is going on, with people working in fields including immunity, chemistry, and more.”

Competition for resources

Fur seals were hunted almost to extinction in Victorian times but were rediscovered off the west coast of Chile in the 1960s. Chile has a ban on hunting these fur seals which is due to be reassessed in 2025.

Constanza’s research is at the frontline of climate science where communities are already adapting to the changes it brings, amid competition for scarce resources, and are keen to manage the resources they rely on sustainably.

The Juan Fernandez community own those resources and decide what they need to sell or to eat so it’s important for them to get to know their ecosystem and protect it. The local community has backed the creation of the new Marine Protected area around the archipelago to help in this endeavour.

Community support is also important for Constanza logistically, to be able to reach the island to collect samples, with fishing boats the most reliable form of transport. And given their proximity the local community can hugely help with research, logging what they see when they go diving.

“This is what excites me as well as the adventure, it’s working with the local community with respect and collaboration.”

Finding focus at Newnham

She’s also drawn on and been inspired by the dynamic research community at Newnham, with the opportunity to learn from so many women involved in world-class research. There’s a welcome contrast between her lone wolf research and the support she has at Newnham, as well as at the vet school where there are whole groups looking at bioinformatics and pathogens in different systems.

Her PhD supervisor and now collaborator, Dr Barbara Blacklaws, helped Constanza hone and focus her research, which is vital when there are so many interconnected issues. “She gave me space to explore when I was a student, taught me grant writing skills. I couldn’t find funding initially but that made me have to network and this turned into a real positive as I found funding but also a wider network.”

Dr Blacklaws is a virologist whose research focuses on how immune systems affect infectious disease, and, more recently, genetic sequencing of pathogens. There is a growing understanding of the importance of gut health and a wealth of information can be gathered from faeces samples, with no disturbance to the animals.

Dr Blacklaws said: “I’ve learned and benefited from Constanza too and I see huge potential in her work. I’m excited about the conservation element of animal research in this field; little has been done on it but it could be a driver for decision-making.”

* Heavy metal contamination in pristine environments: lessons from the Juan Fernandez fur seal by Constanza Toro-Valdivieso et al.