Killer whales (Orcinus orca) form the last link in a long food chain and are among the mammals with the highest level of PCBs (polychlorinated biphenyls) in their tissue. Researchers have measured values as high as 1300 milligrams per kilo in the fatty tissue (blubber) of killer whales. For comparison, a large number of studies show that animals with PCB levels as low as 50 milligrams per kilo of tissue may show signs of infertility and severe impacts on the immune system.

Together with colleagues from a wide range of international universities and research institutions, researchers from Aarhus University have documented that the number of killer whales is rapidly declining in 10 out of the 19 killer whale populations investigated and that the species may disappear entirely from several areas within a few decades.

Killer whales are particularly threatened in heavily contaminated areas like the waters near Brazil, the Strait of Gibraltar and around the UK. Around the British Isles, the researchers estimate that the remaining population counts less than 10 killer whales. Also along the east coast of Greenland, killer whales are effected due to the high consumption of sea mammals like seals.

PCBs accumulate in the food chain

The killer whale is one of the most widespread mammals on Earth and is found in all of the world’s oceans from pole to pole. But today, only the populations living in the least polluted areas possess a large number of individuals.

Overfishing and man-made noise may also affect the health of the animals, but PCBs particularly can have a dramatic effect on the reproduction and immune system of the killer whales.

Killer whales whose diet includes, among other items, seals and large fish such as tuna and sharks critical accumulate PCBs and other pollutants stored at successive levels of the food chain. It is these populations of killer whales that have the highest PCB concentrations and it is these populations that are at the highest risk of population collapse. Killer whales that primarily feed on small-sized fish such as herring and mackerel have a significantly lower content of PCBs and are thus at lower risk of effects.

PCBs have been used around the world since the 1930s. More than one million tonnes of PCBs were produced and used in, among other things, electrical components and plastics. Together with DDT and other organic pesticides — PCBs have spread around the global oceans.

Through the 1970s and 1980s, PCBs were banned in several countries and in 2004, through the Stockholm Convention, more than 90 countries have committed themselves to phase out and dispose of the large stocks of PCBs.

PCBs are only slowly decomposed in the environment. Moreover, PCBs are passed down from the mother orca to its offspring through the mother’s fat-rich milk. This means that the hazardous substances remain in the bodies of the animals, instead of being released into the environment where they eventually deposit or degrade.

Global investigation of killer whales

“We know that PCBs deform the reproductive organs of animals such as polar bears. It was therefore only natural to examine the impact of PCBs on the scarce populations of killer whales around the world,” says Professor Rune Dietz from the Department of Bioscience and Arctic Research Centre, Aarhus University, who initiated the killer whale studies and is co-author of the article.

The research group, which includes participants from the United States, Canada, England, Greenland, Iceland and Denmark, reviewed all the existing literature and compared all data with their own most recent results. This provided information about PCB levels in more than 350 individual killer whales around the globe — the largest number of killer whales ever studied.

Applying models, the researchers then predicted the effects of PCBs on the number of offspring as well as on the immune system and mortality of the killer whale over a period of 100 years.

More than 50% of the populations under threat

“The findings are surprising. We see that over half of the studied killer whales populations around the globe are severely affected by PCBs” says postdoc Jean-Pierre Desforges from Aarhus University, who led the investigations.

The effects result in fewer and fewer animals over time in these populations. The situation is worst in the oceans around Brazil, the Strait of Gibraltar, the northeast Pacific and around the UK. Here, the models show that the populations have virtually been halved during the half century where PCBs have been present.

“In these areas, we rarely observe newborn killer whales,” says Ailsa Hall, who together with Bernie McConnell developed the models used by Sea Mammal Research Unit in Scotland.

“As the effects have been recognized for more than 50 years, it is frightening to see that the models predict a high risk of population collapse in these areas within a period of 30-40 years,” says Jean-Pierre Desforges.

A female killer whale may live for 60-70 years, and although the world took its first steps to phase out PCBs more than 40 years ago, killer whales still have high levels of PCBs in their bodies.

“This suggests that the efforts have not been effective enough to avoid the accumulation of PCBs in high trophic level species that live as long as the killer whale does. There is therefore an urgent need for further initiatives than those under the Stockholm Convention,” concludes Paul D. Jepson, Institute of Zoology, Zoological Society of London, England, who is another killer whale expert and co-author of the article.

In the oceans around the Faroe Islands, Iceland, Norway, Alaska and the Antarctic, the prospects are not so gloomy. Here, killer whale populations grow and the models predict that they will continue to do so throughout the next century.

For the study, published this week in the journal Restoration Ecology, researchers installed 11,000 small, hexagonal structures called “spiders” across 5 acres of reef in the center of Indonesia’s Coral Triangle. Coral diversity is the highest on Earth in that region but is threatened by human activity, including overfishing, pollution and climate change.

Between 2013 and 2015, researchers attached coral fragments to the structures, which also stabilized rubble and allowed for water to flow through freely.

A CORAL SUCCESS STORY

Live coral cover on the structures increased from less than 10 percent to more than 60 percent. This was more than what was reported for reefs in many other areas of the Coral Triangle, at a cost of about $25 per square meter.

“Coral reef rehabilitation and restoration efforts are rapidly increasing around the world, but there are few large-scale examples of successful projects,” said corresponding author Christine Sur, who was a UC Davis graduate student at the time of the study. “Our study demonstrates a cost-effective, scalable method that can inform other coral reef restoration efforts aimed at reducing the global decline of these valuable and unique ecosystems.”

Of particular surprise, while massive coral bleaching decimated other parts of the world between 2014 and 2016, bleaching in the rehabilitation area was less than 5 percent, despite warm water conditions known to stress corals.

A SCIENTIST’S LEGACY

The study is one of the last publications led by Susan Williams, a professor and marine biologist with the UC Davis Bodega Marine Laboratory and Department of Evolution and Ecology who passed away in April 2018.

“Collaboration played a key role in the study’s outcome,” said corresponding author Jordan Hollarsmith, a doctoral candidate in the UC Davis Graduate Group in Ecology at Bodega Marine Laboratory. “Dr. Williams’ dedication to building true partnerships between industry, local scientists and the people who live by the reefs she worked to rebuild was critical to this project’s success.”

Mars Symbioscience, a business segment of Mars, Incorporated, initiated the project in 2013 in collaboration with local residents on the islands.

“This research is an important step in demonstrating how coral can be restored to a higher degree of cover quite quickly and at a relatively low cost,” said Frank Mars, vice president of Mars Sustainable Solutions. “Healthy coral reef ecosystems provide natural coastal protection and are the foundation for many local fisheries, as well as jobs for tourism. They also play a critical role in the Mars supply chain as they provide food security and work for the families and communities we rely on to grow the raw materials we use in our brands around the world. For Mars, helping restore coral reefs is not only a business issue, it’s also the right thing to do to ensure the planet, people, and communities that rely on them are healthy and thriving.”

BUYING TIME TO REVERSE THE DECLINE

Coral reefs are declining worldwide. Reversing their decline will require fully addressing climate change and other human impacts, the study said. For instance, illegal fishing, lack of island sanitation systems, threatened seagrass communities and marine debris such as plastic pollution are common issues in Indonesia and many tropical environments. People living in small island communities in this region also have few alternatives to fishing livelihoods and often lack access to education about the ocean environment.

In the meantime, the “spider” technique and restoration projects offer a way to rehabilitate large swaths of coral reefs and the communities that depend on them, giving the reefs a chance to adapt or acclimate to worsening ocean conditions.

A team of international scientists, led by University of the Witwatersrand (Wits) palaeontologist Professor Jonah Choiniere, described the new species in the journal Current Biology today.

The dinosaur’s name is Sesotho for “a giant thunderclap at dawn” (Sesotho is one of South Africa’s 11 official languages and an indigenous language in the area where the dinosaur was found).

“The name reflects the great size of the animal as well as the fact that its lineage appeared at the origins of sauropod dinosaurs,” said Choiniere. “It honours both the recent and ancient heritage of southern Africa.”

Ledumahadi mafube is one of the closest relatives of sauropod dinosaurs. Sauropods, weighing up to 60 tonnes, include well-known species like Brontosaurus. All sauropods ate plants and stood on four legs, with a posture like modern elephants. Ledumahadi evolved its giant size independently from sauropods, and although it stood on four legs, its forelimbs would have been more crouched. This caused the scientific team to consider Ledumahadi an evolutionary “experiment” with giant body size.

Ledumahadi‘s fossil tells a fascinating story not only of its individual life history, but also the geographic history of where it lived, and of the evolutionary history of sauropod dinosaurs.

“The first thing that struck me about this animal is the incredible robustness of the limb bones,” says lead author, Dr Blair McPhee. “It was of similar size to the gigantic sauropod dinosaurs, but whereas the arms and legs of those animals are typically quite slender, Ledumahadi‘s are incredibly thick. To me this indicated that the path towards gigantism in sauropodomorphs was far from straightforward, and that the way that these animals solved the usual problems of life, such as eating and moving, was much more dynamic within the group than previously thought.”

The research team developed a new method, using measurements from the “arms” and “legs” to show that Ledumahadi walked on all fours, like the later sauropod dinosaurs, but unlike many other members of its own group alive at its time such as Massospondylus. The team also showed that many earlier relatives of sauropods stood on all fours, that this body posture evolved more than once, and that it appeared earlier than scientists previously thought.

“Many giant dinosaurs walked on four legs but had ancestors that walked on two legs. Scientists want to know about this evolutionary change, but amazingly, no-one came up with a simple method to tell how each dinosaur walked, until now,” says Dr Roger Benson.

By analysing the fossil’s bone tissue through osteohistological analysis, Dr Jennifer Botha-Brink from the South African National Museum in Bloemfontein established the animal’s age.

“We can tell by looking at the fossilised bone microstructure that the animal grew rapidly to adulthood. Closely-spaced, annually deposited growth rings at the periphery show that the growth rate had decreased substantially by the time it died,” says Botha-Brink. This indicates that the animal had reached adulthood.

“It was also interesting to see that the bone tissues display aspects of both basal sauropodomorphs and the more derived sauropods, showing that Ledumahadi represents a transitional stage between these two major groups of dinosaurs.”

Ledumahadi lived in the area around Clarens in South Africa’s Free State Province. This is currently a scenic mountainous area, but looked much different at that time, with a flat, semi-arid landscape and shallow, intermittently dry streambeds.

“We can tell from the properties of the sedimentary rock layers in which the bone fossils are preserved that 200 million years ago most of South Africa looked a lot more like the current region around Musina in the Limpopo Province of South Africa, or South Africa’s central Karoo,” says Dr Emese Bordy.

Ledumahadi is closely related to other gigantic dinosaurs from Argentina that lived at a similar time, which reinforces that the supercontinent of Pangaea was still assembled in the Early Jurassic. “It shows how easily dinosaurs could have walked from Johannesburg to Buenos Aires at that time,” says Choiniere.

South Africa’s Minister of Science and Technology Mmamoloko Kubayi-Ngubane says the discovery of this dinosaur underscores just how important South African palaeontology is to the world.

“Not only does our country hold the Cradle of Humankind, but we also have fossils that help us understand the rise of the gigantic dinosaurs. This is another example of South Africa taking the high road and making scientific breakthroughs of international significance on the basis of its geographic advantage, as it does in astronomy, marine and polar research, indigenous knowledge, and biodiversity,” says Kubayi-Ngubane.

The research team behind Ledumahadi includes South African-based palaeoscientists, Dr Emese Bordy and Dr Jennifer Botha-Brink, from the University of Cape Town and the South African National Museum in Bloemfontein, respectively.

The project also had a strong international component with the collaboration of Professor Roger BJ Benson of Oxford University and Dr Blair McPhee, currently residing in Brazil.

“South Africa employs some of the world’s top palaeontologists and it was a privilege to be able to build a working group with them and leading researchers in the UK,” says Choiniere, who recently emigrated from the USA to South Africa. “Dinosaurs didn’t observe international boundaries and it’s important that our research groups don’t either.”

Video: https://www.youtube.com/watch?v=Q8FHxPocwDM