‘There is a great deal of confidence in the future here’
What impact does climate change have on salt marshes? And what role do microbes, plants and crustaceans play in this? If microbial ecologist Joana Falcao Salles knew the answer to that, she would also know which restoration strategy to use to protect the salt marshes.
‘Take a tablespoon of soil. There are more microbes in it than there are people on Earth,’ explains microbial ecologist Joana Falcao Salles. ‘Micro-organisms are hugely important for biodiversity on Earth. They produce nutrients for plants and animals. And they determine how quickly flora and fauna can adapt to changing conditions, for example in the salt marshes.’ Salt marshes are essential as habitats for birds and plants. And not only that: they are also vital for coastal protection, as they can, for example, counteract land subsidence. Because every high tide brings an extra layer of silt, the height of the salt marsh rises in line with the rising sea level. Plants such as sea lavender and glasswort slow down the flow of seawater, allowing the silt to settle and reducing the likelihood of it being washed away.
Sea level
This has been going on for a very long time. And it still is. But what happens to the salt marshes if that balance is disrupted? If, for example, it becomes wetter or, conversely, drier? If climate change continues and the sea level rises too high? Plants and animals will then have to adapt. Microbes in the soil play an essential role in this, explains Falcao Salles. And that is why she is keen to investigate how, in particular, seaweed, the saltmarsh springer (a sand flea-like crustacean) and the microbes influence one another on the saltmarsh soil, during drought and during flooding. What is the interaction between them? How do seaweed, crustaceans and microbes react with and without one another to these changing conditions? What impact does rising sea levels have on the structure of the soil? After all, if the plants die off, the salt marsh will also be washed away. Unless they manage to adapt.
Role of soil bacteria
The role of soil bacteria in adapting to different situations is being investigated in a laboratory-based test: in 48 pots with a diameter of around twenty centimetres, saltmarsh grass and sea lavender are kept submerged or dry for long periods. One hypothesis is that the activity of the microbes changes in different situations. ‘What does this mean for the interaction with the seaweed and the amphipod?’ asks Falcao Salles. The experiment will last two months, after which it will take a further four to six months to analyse all the data.
Disastrous
Falcao Salles: ‘Suppose certain essential functions of the microbes change under constant flooding. It may then be that they make insufficient nutrients available to the salt marsh plants, which subsequently die off, resulting in the salt marsh disappearing permanently during flooding. Disastrous, because then birds will have nowhere left to rest and breed. And, moreover, the salt marsh’s function as a coastal protector will disappear.’ As for the crabs: they dig tunnels in the soil, thereby bringing oxygen to deeper layers. Prolonged flooding leads to reduced oxygen levels in the soil, which can cause crabs and plants to die. Falcao Salles: ‘We hope to find microbes that will help plants and crabs become more resilient to severe drought or flooding. With that knowledge, we can devise recovery strategies.’
