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Overfishing, disease, pollution, poor water quality and dredging have changed the face of our undersea landscape, and brought some species close to extinction. Find out why Dr Joanne Preston is re-introducing the native oyster to British waters - and what will happen if we allow this humble mollusc to take back control of our water quality.

Bringing back the native oyster to save our seas

The air we breathe. The water we drink. The food we eat. All are by-products of a healthy planet with a healthy ecosystem.

Each and every species, no matter how small, plays an important role in our planet's ecosystem. Their rich variety – known as biodiversity – is key. Put simply, the more species there are, the more life on earth can thrive and sustain itself.

But there's been a huge loss in biodiversity over the last 150 years, with marine life hit hard. Although extinctions have always been a fact of life, humans are to blame for this particular loss. Activities such as over-fishing and coastal development have been especially damaging.

There's a lot we can all change in our daily lives to prevent further damage. But scientists have a particularly important contribution to make.

Dr. Joanne Preston is course leader for the Marine Biology degree at the ���ϳԹ�. Joanne's area of research is Marine Ecology and Evolution.

She looks at the way marine organisms function and studies their relationship with the environment. Her aim is to understand how biodiversity is created in the marine environment so that we’re better equipped to protect, maintain and enhance it.

Joanne says:

"Ecosystems provide us with food, oxygenated water, and other things we humans depend on. And ecosystems depend on biodiversity.

"Push an ecosystem too far and you lose biodiversity. This causes the ecosystem to lose resilience, making it less capable of adapting to, say, climate change or pollution.

"Maintaining biodiversity is vital. We hope to do this by learning how different organisms interact and function with each other to create the ecosystem."

Using DNA to predict the future

Molecular evolution is Joanne's other passion. This involves looking at the DNA sequences of various organisms to identify relationships between them.

You can then track evolution patterns, which reveal how marine organisms have evolved, and how diversity is generated. Think Who Do You Think You Are? for sea creatures.

If we know how biodiversity evolved over history, it's possible to project how organisms might evolve into the future.

Joanne says, "Organisms' DNA tells us what's related and what isn't, and we use this to understand true biodiversity. By pinpointing how much genetic variation is out there, you can estimate how likely those organisms can adapt and survive in the future."

We may find the hope of adaptation and survival is worryingly low. Essentially, the less genetic variation, robustness and resilience there is, the higher the chance of extinction.

The unsung heroes of our water quality

Overfishing has caused the gene pool (or genetic diversity) of many different marine species to get smaller and smaller.

This includes oysters, which used to be abundant in the Solent – the strait which runs along the seafront in Portsmouth, and separates the Isle of Wight from mainland England.

In the 1970s, millions of oysters were fished from the Solent. But overfishing, disease, pollution, poor water quality and dredging have taken a toll on the population across Europe, and now the native oyster is extinct in many areas where it once thrived.

There is some concern about the genetic diversity within the remaining population - specifically, whether the population is diverse enough to enable the oysters to survive and adapt to challenges of disease and climate change.

The importance of understanding the genetic identity of marine organisms is clear when you look at the sea sponge, a creature which isn't over-exploited. The difference is staggering, as Joanne explains:

"There's a type of sea sponge with four different species that look identical, yet are genetically distinct. This gives an example of what type of genetic diversity can be lost when you over-exploit a species, but also highlights that molecular ecology can reveal new species we didn’t know existed."

The sea sponge evolved 500 million years ago. It’s probably the earliest multicellular animal – and in evolutionary terms, one of your own ancestors.

"Looking at sponges is like looking back in time. Their skeleton is just glass spicules, like little needles, which can take these amazing, beautiful shapes. They’ve been here since the dawn of multicellularity."

Like sea sponges, oysters are filter feeders, which means they keep the seawater clean and clear, by consuming algae and other bits of organic matter.

In high enough numbers, oysters can have a phenomenal impact on water quality. For example, they reduce the nitrogen and phosphates that cause algal blooms. Such blooms suck oxygen from the water and block out the sunlight that sea grasses need to grow.

One good, healthy oyster can filter an astonishing 200 litres of seawater a day. Oysters do us a service by hoovering up impurities so that our ecosystems, and countless species, can thrive and flourish.

Oysters are also “biogenic”. This means they create a whole ecosystem in the form of oyster reefs. Similar to coral reefs in tropical waters, these reefs are a three-dimensional hard substrate. They’re formed from old oyster shells which mount up as oysters die, and as oysters settle on each other and form oyster “hands”, or clumps of oysters.

Oyster reefs also act like a nursery, supporting a huge amount of marine biodiversity. They’re a habitat for other things to feed from and live in, including crustaceans and juvenile fish.

Yet 85 per cent of global oyster reefs have been wiped out, largely from over-extraction. The 15 per cent that remain are in a poor condition.

Add the problems of poor management and reduced genetic resilience, and our native oysters are all but extinct.

Which means the multiple other species that depend on oyster reefs for food and shelter are also in trouble.

Back from the brink

Joanne is at the heart of a major restoration ecology project to bring native oysters back to the Solent.

It began with a system of cages, suspended in the waters, where oysters could thrive.

"We’ve produced the system in partnership with Ineos, Blue Marine Foundation, UK oyster fisheries and MDL Marinas.

"The system acts like a suspended vertical oyster reef so it’s safe from predators – including humans – and it’s working well. We’re looking to roll it out to marinas across the UK.

"The idea is to eventually have oysters back on the seabed, but as a protected broodstock."

The team discovered 95 different species growing on the oysters – almost as many as if the oysters were on the seabed. These included 30 or 40 juvenile European eels, which are on the critically endangered red list.

To prevent fishing companies from over-extracting again, Joanne is working with the Blue Marine Foundation and the fisheries to drive the project forward together.

Over the next five to ten years, Joanne’s ambition is to see the ecosystem restoration movement gather pace and roll out across both the UK and Europe.

Working with European colleagues, Jo helped set up NORA (European Native Oyster Restoration Alliance) and is collaborating with colleagues in America, observing US oyster reefs for ideas about how to help ours survive.

Joanne will also recruit a UK Oyster Network Coordinator to coordinate the effort and discuss policy with government.

"The idea is to create a restoration management document for Ostrea edulis, the oyster species in question. We need to bring together the best practice across Europe to maximise our chance of success."

For Joanne, success would be seeing a restored and self-sustaining oyster population within the next 20 years or so.

The evidence for success is already in the US. America’s east coast boasts multiple oyster restoration projects.

"The States have reported an increase in biomass of fish stocks with restored reefs. We went all the way around the east coast, looking at different restoration projects, and I probably learned more there in a week than I could have in two years sitting at my desk."

Preserving the Mary Rose

Joanne isn’t just preserving marine life. She has also used her expertise to keep the remains of the Mary Rose in good condition.

King Henry VIII’s warship was raised from the Solent after hundreds of years underwater. The struggle to preserve it has not been easy.

Joanne explains, "The Mary Rose was producing tons of sulphuric acid due to the oxidation of iron and sulphur in the wood and bolts, and also the way it had been buried in the sediment – once it comes up to the air, it projects sulphuric acid."

The acid was eating away at the ship and had to be stopped.

Joanne used her DNA expertise to discover iron-oxidising bacteria in the wood, along with acidophilic bacteria, which live off the iron and sulphur. It was a laborious task:

"I took three months trying to get environmental DNA out of one piece of archeological wood. After amplifying a specific gene of all the microbes that were inside it, I sequenced these to identify what species were living there, as well as growing microbes using classic microbiology culturing techniques. We discovered several species of iron and sulphur organisms present in the Mary Rose, and tested ways of stopping them."

Joanne believes variety is the spice of scientific life, and that testing your knowledge and expertise in different areas is important.

"I always recommend scientists go off-piste and challenge themselves by trying new areas of research and collaborating with people in different fields. The Mary Rose work opened up a whole new world for me in terms of microbiology and microbial ecology, and it feeds into my oyster restoration work."

The bigger picture

Joanne's drive is to help resolve, alleviate and understand the vulnerabilities of ecosystems, through applied marine biology.

She says, "There’s a western idea that you can throw things away, but there is no “away”. It just goes to another place and impacts the planet. My contribution uses marine conservation to understand and protect the marine environment and our natural world."

Molecular Ecology and Evolution is a complex discipline. But in terms of how it helps the planet, it's not so difficult to grasp its importance.

During her PhD studies, Joanne immersed herself in theories of speciation and evolution. And while she values knowledge for knowledge's sake, she also knows the world needs this knowledge put to use. That requires a mind that’s both scientific and creative:

"I like exploring things and making discoveries. And I really love applied marine biology – the creativity of thinking around a problem, doing research that provides answers and helps us make the right decisions in terms of conservation, restoration or policy."

Teamwork is key. Alongside colleagues in her field, Joanne also works with students at Master’s, PhD and undergraduate level to enrich her research.

"Seeing them become passionate and engaged, getting their ideas and perspectives, is brilliant. I love seeing people’s development and progression. Science is pretty much always better done in collaboration."

Being an island, ���ϳԹ�is the ideal place for Joanne's research. "I get to live and work right by the sea and do research on my doorstep that's going to hopefully improve the ecosystems around me."

From the Solent to the seven seas, the voyage of discovery starts in Portsmouth. And it never stops.