Outreach

Mud-Cake Stories: One process, many services

A delicious way to understand the value of our ecosystems! Dive into the incredible services of mudflats, presented in an engaging and accessible format. 

Explore these fascinating micro-worlds and uncover their unexpected benefits!

Inside every mud-cake - and every mudflat - there’s a little factory capturing CO₂, an essential process for a healthier environment and a more stable climate! 🌍

By now, you probably know that our little mud-cakes, tiny samples of mudflats, host a micro-community of organisms, including microalgae part of the microphytobenthos .. but shhh 🙊, that’s a fancy word!). These microalgae, just like all plants, perform photosynthesis, absorbing CO₂, and releasing oxygen.

By capturing this greenhouse gas and incorporating it into their structure, these microalgae directly contribute to climate regulation, slowing down global warming 🌡️.

This biologically fixed CO₂ goes on to feed local food chains. Did you know that entire food chains rely on the microalgae found in our mud-cakes? They can even end up buried in the sediments… but that’s for another mud-cake story !

On a larger scale, mudflats act as natural carbon sinks, absorbing tons of CO₂ per hectare per year through photosynthesis !

However, mudflat are in danger. We lose thousands of hectares each year, leading to a significant loss of CO₂ absorption and fixation, hence threatening entire food chains that rely on these ecosystems. So, think about supporting the preservation and restoration efforts towards these unique ecosystems.

Just like a treasure chest, every mud-cake - and mudflat - hides a secret beneath the surface: they store carbon, playing a crucial role in climate regulation! 🌍

As we learned in 𝑆𝑡𝑜𝑟𝑦 #1: 𝑝ℎ𝑜𝑡𝑜𝑠𝑦𝑛𝑡ℎ𝑒𝑠𝑖𝑠, microalgae capture CO₂ and incorporate it into their structure. But what happens to this carbon? It becomes part of the food web but can also be stored within the mudflat ecosystem for years, even centuries!

When microalgae and other organisms die in the mudflats, this carbon-rich biomass sinks into the sediment. This, along with other biologically fixed carbon deposited in mudflats, creates layers of organic material beneath the surface in an anoxic environment. Without oxygen, the degradation of this material slows down, effectively trapping carbon! This process, known as carbon storage, burial, or sequestration, is essential for locking carbon away in a safe place, preventing its release into the atmosphere as a greenhouse gas !

In addition to their important role as carbon sinks that continuously absorb CO₂ from the atmosphere, mudflats also serve as vital carbon reservoirs. Recent estimates suggest that carbon accumulates in mudflats at around 130 grams of carbon per m² per year - 10x more than in terrestrial forests 🌲. Despite covering only small areas, mudflats globally store about 1 billion tons of carbon, with approximately 7 million tons being buried each year !

As water flows through the mudflats, it encounters layers of sediment and organic matter, key components of this unique ecosystem (as discussed in Story #2: Carbon Storage). When water passes through these layers, suspended mineral and organic particles are trapped by the fine structure of the mud. This process significantly reduces water turbidity, thereby enhancing light penetration, a critical factor for photosynthesis and growth of our beloved microalgae that form the base of aquatic food webs. Additionally, the trapping of organic matter prevents its degradation within the water column, effectively limiting oxygen consumption and avoiding desoxygenation, which helps maintain healthy oxygen levels. Together, these processes promote a balanced aquatic environment.

But there’s more! Mudflats act as natural barriers, intercepting elements in the water like nitrogen, phosphorus, heavy metals, pesticides, and other contaminants. When these substances come into contact with organic matter and sediment, they are adsorbed through various chemical processes, which prevents their dispersion into rivers, estuaries, and oceans, where they could harm aquatic ecosystems.

Once trapped, many of these elements, including the most harmful pollutants, can be transformed into less toxic forms by the hardworking microorganisms living in the sediment. This transformation is a crucial step in maintaining ecosystem balance and health. But these fascinating processes are for future Mud-Cake Stories! 😉

Have you ever noticed that distinct smell near mudflats, like eggs left out too long? Believe it or not, that’s the smell of life and nature at work !

As we explored in Story #2: Carbon Storage, organic matter in mudflats is primarily trapped in oxygen-poor sediments, limiting its decomposition. However, specific microbes are still capable of decomposing some of this organic material.

The breakdown of organic matter, known as mineralization, involves several processes under anoxic (oxygen-poor) conditions. Unlike aerobic mineralization, where bacteria use oxygen to break down organic compounds, in anoxic environments, bacteria rely on other elements available in the sediment.

One of the most notable processes is sulfate reduction, where bacteria use sulfate (SO42-) to break down organic matter. This process produces hydrogen sulfide (H2S), the gas responsible for the characteristic smell of mud.

Despite this "attractive" smell, this process, along with the other anaerobic mineralization processes, is vital for nutrient cycling. As organic matter is broken down, essential nutrients like nitrogen and phosphorus are released back into the ecosystem. This process, called regenerated production, makes these nutrients available to support the growth of photosynthetic organisms (see Story #1: Photosynthesis), which form the foundation of food webs.

Nitrogen (N) is a vital nutrient that supports growth and various biological processes in living organisms. However, when nitrogen compounds (such as nitrates, nitrites, or ammonium), accumulate excessively in water due to external sources like fertilizers, agricultural runoff, and pollution, they can cause significant environmental issues : 

Excess nitrogen can trigger harmful algal blooms, depleting oxygen levels and deteriorating water quality. This process, known as eutrophication, poses a serious challenge, and the impacts can be particularly severe. Algal blooms can lead to fish kills, reduced biodiversity, and negative effects on recreational activities and local economies. 

Fortunately, our tiny mud-cakes 🧁 offer a natural solution! ✨

As we explored in Stroy #4: Mineralization, beneath the surface of the mudflats, specialized bacteria thrive in the anoxic layers of sediment, breaking down organic matter using the elements present in the sediment. Some of these bacteria use nitrates or nitrites and convert them into harmless nitrogen gas (N₂), which safely returns to the atmosphere. This process, known as denitrification, not only reduces nitrogen levels in the water but also prevents nitrogen overload, protecting both freshwater and marine environments from eutrophication and helping to maintain a balanced ecosystem.

When organic pollutants, heavy metals, or chemicals seep into the sediment, the microorganisms spring into action:

1️⃣ They use specialized enzymes to break down organic pollutants like hydrocarbons from oil spills or industrial waste, turning them into simpler, often non-toxic compounds.

2️⃣ They tackle dangerous heavy metals such as mercury or arsenic, converting them into less bioavailable forms, reducing their toxic impact on marine life.

3️⃣ With the rise of chemicals in our waterways, mudflat microbes have become essential in breaking down emerging contaminants before they enter food webs.

Through biotransformation, mudflats serve as nature’s cleanup crew, maintaining a healthy environment. This process doesn’t just protect local habitats, it contributes to the global health of our ecosystems. This ability to manage pollution helps mitigate human impacts, ensuring that ecosystems remain resilient in the face of growing environmental pressures.

Without this process, contaminants would accumulate in aquatic ecosystems, leading to serious issues like bioaccumulation in fish and shellfish, water quality degradation, or even risks to human health.

However, as with all the incredible services we’ve explored in Mud-Cake Stories, this process is under threat. The global loss of mudflats means fewer microbial communities to detoxify pollutants, underscoring the urgent need to preserve these vital habitats. Protecting mudflats isn’t just about saving muddy landscapes !

Mudflats are nutrient-rich ecosystems that host creatures like aquatic snails, worms, and mollusks. Their activities, including digging, burrowing, and tunneling, actively transform these environments, earning them the title of ecosystem engineers 👷. Through this constant “stirring” of the sediment, they play a crucial role in maintaining the health and functionality of these ecosystems.

From tiny worms to burrowing crabs, these creatures constantly move sediments, mixing oxygen-rich surface layers with deeper, anoxic ones. This natural "ventilation" of sediment regulates the flow of elements and gases within the mud, bossting microbial activity and the essential services they provide (Cf previous stories).

Moreover, bioturbation drives nutrient cycling, releasing locked-up nutrients like nitrogen, phosphorus, and carbon into the ecosystem. These nutrients become available for primary producers such as microalgae 🥰 , which then support food webs from tiny invertebrates to fish 🐟 and birds 🐦.

An example of a bioturbating species would be the famous polychaete worm Nereis diversicolor 🪱. This species is one of those responsible for the little holes you see on intertidal flats, it’s the entrance to their burrow ! 

You already know : many of the species responsible for bioturbation are threatened by habitat loss and pollution. Protecting mudflats means safeguarding these engineers and ensuring that these ecosystems remain balanced and resilient for generations to come.

Mudflats aren’t just muddy ecosystems, they are vital refuges and nurseries for countless species, supporting biodiversity and ensuring the resilience of food webs.

For many species, mudflats are the ultimate sanctuary, a safe haven for their early stages of life. Juvenile fish, crustaceans, and mollusks find shelter here, protected from many predators by the shallow waters. These relatively calm, nutrient-rich areas provide the perfect environment for young marine creatures to feed and develop until they’re strong enough to venture into the open waters. 🌊

Mudflats are also a crucial stopover for migratory birds traveling thousands of kilometers between their breeding and wintering grounds. These birds rely on these ecosystems as feeding grounds, where they can replenish their energy by feasting on the abundant worms, crustaceans, and microorganisms thriving in the mud.

Teeming with life, mudflats are home to an intricate web of microbes, invertebrates, fish, and birds, all interconnected. This biodiversity is essential not only for the species themselves but also for communities that depend on these ecosystems for fisheries and other vital services.

Unfortunately, these nurseries and refuges are under threat. Development, pollution, and climate change are shrinking mudflat habitats, putting the species that depend on them at risk. The loss of these ecosystems has cascading effects on biodiversity and the communities that rely on them. Protecting mudflats isn’t just about saving one ecosystem, it’s about safeguarding the foundation of marine life, migratory routes, and food security.

In mudflats, most of the microorganisms we've explored through previous Mud-Cake Stories, like bacteria and microalgae, secrete exopolymeric susbstances (EPS) for various purposes, including biofilm formation and vertical migration. These EPS are sticky, acting like glue to bind together particles and microorganisms. This "sticky" quality is crucial for holding soil particles together and increasing the stability of the sediment. As a result, mudflats help prevent coastal erosion by acting as a natural buffer against storms and tides.

But it’s not just microorganisms that play a role! Creatures like worms and mollusks also secrete mucus that coats the mud, helping them trap food and support their burrows. This mucus stabilizes the sediment, preventing it from dispersing, and creates a safe environment for species to thrive.

This sticky web of EPS and mucus also plays a vital role in nutrient cycling. It traps organic matter and elements, preventing them from being washed away, and helps with nutrient retention and water filtration (a nice reminder of the previous processes we've explored!).

These sticky substances create the perfect environment for microbial communities, which, in turn, support the entire food web, from tiny invertebrates to larger fish and birds 🐟🐦

Sadly, human activities, coastal development, pollution, and climate change are threatening the "sticky secret" of mudflats, putting the integrity of these habitats at risk. Protecting mudflats is essential for ensuring that our coastlines remain resilient and that biodiversity continues to thrive.

The origin of the name "Mud-Cakes"?

It comes from a lab activity: while studying mudflat microalgae, I work with sediment placed in multi-well plates. I jokingly started calling this process "making mud-cakes," a term that quickly became part of my scientific vocabulary

How did the Mud-Cake Stories come to life? 

When I shared this term with colleagues and friends, I noticed how it sparked curiosity and interest. It became the perfect gateway to explain my research and highlight the richness of mudflats. This inspired me to create an engaging and accessible series to explore these fascinating and often-overlooked ecosystems

Why do mudflats deserve more attention? 

Wetlands are often celebrated, but mudflats remain in the shadows. Yet, they play a vital role in climate change regulation, coastal protection, and much more. With the Mud-Cake Stories, I wanted to give them the attention they deserve, in a accessible and engaging way