Oysters once formed extensive reefs along much of Europe’s coastline—but these complex ecosystems were destroyed over a century ago, new research shows. The paper, published in the journal Nature Sustainability, is titled “Records reveal the vast historical extent of European oyster reef ecosystems.”

Based on documents from the 18th and 19th centuries, the study reveals that European flat oysters formed large reefs of both living and dead shells, providing a habitat supporting rich biodiversity.

Today these oysters are mostly found as scattered individuals—but the researchers found evidence of reefs almost everywhere, from Norway to the Mediterranean, covering at least 1.7 million hectares, an area larger than Northern Ireland.

The research was led by the University of Exeter and The University of Edinburgh.

Native oyster reefs created their own ecosystems, full of a diverse range of underwater life—supporting a greater number of species than surrounding areas.

In addition to creating homes for the almost 200 recorded fish and crustacean species, the oysters also played a vital role in stabilizing shorelines, nutrient cycling and water filtration—with a single adult oyster filtering up to 200 liters of water a day.

Restoration projects are under way across Europe—and small-scale habitat restoration, such as The Wild Oyster Project, led by ZSL and partners, are key stepping stones to the return of these vital ecosystems on an international scale.

However, restoration efforts need to be scaled up with support from governments and other decision makers across the continent.

“Human activities have affected the ocean for centuries,” said Dr. Ruth Thurstan, from the University of Exeter and part of the Convex Seascape Survey, an ambitious five-year project examining ocean carbon storage.

“This makes it difficult to discover what our marine ecosystems used to look like, which in turn hampers conservation and recovery.

“Few people in the UK today will have seen a flat oyster, which is our native species. Oysters still exist in these waters but they’re scattered, and the reefs they built are gone.

“We tend to think of our seafloor as a flat, muddy expanse, but in the past many locations were a three-dimensional landscape of complex living reefs—now completely lost from our collective memory.”

Due to their economic and cultural significance, oysters feature in historical records including newspapers, books, travel writing, landing records, nautical charts, early scientific investigations and interviews with fishermen.

“By combining descriptive accounts from a range of historical sources, we can build a picture of our past seas,” said Dr. Thurstan, who is mapping past ocean changes as part of the Convex Seascape Survey.

“The greatest concentration of oyster reefs we found was in the North Sea.”

Records show extensive reefs existed along the coasts of modern France, Denmark, Germany, the Netherlands, the Republic of Ireland and the UK.

“Oyster reefs are slow to develop, with layers of new oysters building up on the dead shells of their predecessors, but their destruction through overfishing was relatively rapid,” said Dr. Philine zu Ermgassen, honorary researcher at the University of Edinburgh.

“This has caused a fundamental restructuring and ‘flattening’ of our seafloors—removing thriving ecosystems and leaving an expanse of soft sediment behind.

“Thanks to this historical ecology research, we are now able to quantitatively describe what oyster reefs looked like before they were impacted, and the spatial extent of the ecosystems they formed.

“These were huge areas that were thickly crusted with oysters and crawling with other marine life.”

The research team was made up of more than 30 European researchers from the Native Oyster Restoration Alliance.

Ever wish you could stop that fruit fly on your kitchen counter in its tracks? Scientists at Max Planck Florida Institute for Neuroscience have created flies that halt under red light. In doing so, they discovered the precise neural mechanisms involved in stopping.

Their findings, published in Nature, have implications far beyond controlling fly behavior. They demonstrate how the brain engages different neural mechanisms depending on environmental context.

The power of Drosophila to understand complex behaviors

Halting is a critical action essential for almost all animal behaviors. When foraging, an animal must stop when it detects food to eat; when dirty, it must stop to groom itself. The ability to stop, while seemingly simple, has not been well understood as it involves complex interactions with competing behaviors like walking.

Max Planck Florida scientist Dr. Salil Bidaye is an expert at using the powerful research model Drosophila Melanogaster (aka the fruit fly) to understand how neural circuit activity leads to precise and complex behaviors such as navigating through an environment. Having previously identified neurons critical for forward, backward, and turning locomotion, Dr. Bidaye and his team turned to stopping.

“Purposeful movement through the world relies on halting at the correct time as much as walking. It is central to important behaviors like eating, mating, and avoiding harm. We were interested in understanding how the brain controls halting and where halting signals override signals for walking,” said Bidaye.

Taking advantage of the fruit fly’s power as a research model, including the animal’s simplified nervous system, short lifespan, and large offspring numbers, Bidaye and his team used a genetic screen to identify neurons that initiate stopping. Using optogenetics to activate specific neurons by shining a red light, the researchers turned on small groups of neurons to see which caused freely walking flies to stop.

Two mechanisms for stopping

Three unique neuron types, named Foxglove, Bluebell, and Brake, caused the flies to stop when activated. Through careful and precise analysis, the scientists determined that the flies’ stopping mechanisms differed depending on which neuron was active. Foxglove and Bluebell neurons inhibited forward walking and turning, respectively, while Brake neurons overrode all walking commands and enhanced leg-joint resistance.

“Our research team’s diverse expertise was critical in analyzing precise stopping mechanisms. Each team member contributed to our understanding by approaching the question through different methods, including leg movement analysis, imaging of neural activity, and computational modeling,” said Bidaye.

“Further, large research collaborations spanning multiple labs and countries have recently mapped the connections between all the neurons in the fly brain and nerve cord. These wiring diagrams guided our experiments and understanding of the neural circuitry and mechanisms of halting.”

The research team, consisting of scientists from Max Planck Florida, Florida Atlantic University, University of Cambridge, University of California, Berkeley and the MRC Laboratory of Molecular Biology, combined the data from the wiring diagrams and these multiple approaches to gain a holistic understanding of the behavioral, muscular, and neuronal mechanisms that induced the fly’s halting.

They found that activating these different neurons did not stop the flies in the same way but used unique mechanisms, which they named “Walk-OFF” and “Brake.”

As the name implies, the “Walk-OFF” mechanism works by turning off neurons that drive walking, similar to removing your foot from the gas pedal of a car. This mechanism, used by the Foxglove and Bluebell neurons, relies on the inhibitory neurotransmitter GABA to suppress neurons in the brain that induce walking.

The “Brake” mechanism, on the other hand, employed by the excitatory cholinergic Brake neurons in the nerve cord, actively prevents stepping by increasing the resistance at the leg joints and providing postural stability.

This mechanism is similar to stepping on the brake in your car to actively stop the wheels from turning. And just as you would remove your foot from the gas to step on the brake, the “Brake” mechanism also inhibits walking-promotion neurons in addition to preventing stepping.

Lead researcher on the project, Neha Sapkal, describes the team’s excitement at discovering the “Brake” mechanism. “Whereas the ‘Walk-Off’ mechanism was similar to stopping mechanisms identified in other animal models, the ‘Brake’ mechanism was completely new and caused such robust stopping in the fly. We were immediately interested in understanding how and when the fly would use these different mechanisms.”

Context-specific activation of halt mechanisms

To determine when the fly might use the “Walk-OFF” and “Brake” mechanisms, the team again took multiple approaches, including predictive modeling based on the wiring diagram of the fly nervous system, recording the activity of halting neurons in the fly, and disrupting the mechanisms in different behavioral scenarios.

Their findings suggested that the two mechanisms were used mutually exclusively in different behavioral contexts and were activated by relevant environmental cues. The “Walk-OFF” mechanism is engaged in the context of feeding and activated by sugar-sensing neurons. On the other hand, the “Brake” mechanism is used during grooming and is predicted to be activated by the sensory information coming from the bristles of the fly.

During grooming, the fly must lift several legs and maintain balance. The Brake mechanism provides this stability through the active resistance at joints and increased postural stability of the standing legs. Indeed, when the scientists disrupted the “Brake” mechanism, flies often tipped over during grooming attempts.

“The fly brain has provided insight into how contextual information engages specific mechanisms of behaviors such as stopping.”

Bidaye says, “We hope understanding these mechanisms will allow us to identify similar context-specific processes in other animals. In humans, when we stop and lift our foot to adjust our shoe or remove a stone from our tread, we are likely taking advantage of a stabilizing mechanism similar to the Brake mechanism.

“Understanding context-specific neural circuits and how they work together with other sensory and motor circuits is the key to understanding complex behaviors.”

Dolphins are extremely playful, but little is known about how they—and other marine mammals—communicate during playtime. New research published October 2 in the journal iScience shows that bottlenose dolphins (Tursiops truncates) use the “open mouth” facial expression—analogous to a smile—to communicate during social play.

The dolphins almost always use the facial expression when they are in their playmate’s field of view, and when playmates perceived a “smile,” they responded in kind 33% of the time.

“We’ve uncovered the presence of a distinct facial display, the open mouth, in bottlenose dolphins, and we showed that dolphins are also able to mirror others’ facial expression,” says senior author and evolutionary biologist Elisabetta Palagi of the University of Pisa.

“Open-mouth signals and rapid mimicry appear repeatedly across the mammal family tree, which suggests that visual communication has played a crucial role in shaping complex social interactions, not only in dolphins but in many species over time.”

Dolphin play can include acrobatics, surfing, playing with objects, chasing, and playfighting, and it’s important that these activities aren’t misinterpreted as aggression. Other mammals use facial expressions to communicate playfulness, but whether marine mammals also use facial expressions to signal playtime hasn’t been previously explored.

“The open mouth gesture likely evolved from the biting action, breaking down the biting sequence to leave only the ‘intention to bite’ without contact,” says Palagi. “The relaxed open mouth, seen in social carnivores, monkeys’ play faces, and even human laughter, is a universal sign of playfulness, helping animals—and us—signal fun and avoid conflict.”

To investigate whether dolphins visually communicate playfulness, the researchers recorded captive bottlenose dolphins while they were playing in pairs and while they were playing freely with their human trainers.

They showed that dolphins frequently use the open mouth expression when playing with other dolphins, but they don’t seem to use it when playing with humans or when they’re playing by themselves.

While only one open mouth event was recorded during solitary play, the researchers recorded a total of 1,288 open mouth events during social play sessions, and 92% of these events occurred during dolphin-dolphin play sessions.

Dolphins were also more likely to assume the open mouth expression when their faces were in the field of view of their playmate—89% of recorded open mouth expressions were emitted in this context—and when this “smile” was perceived, the playmate smiled back 33% of the time.

“Some may argue that dolphins are merely mimicking each other’s open mouth expressions by chance, given they’re often involved in the same activity or context, but this doesn’t explain why the probability of mimicking another dolphin’s open mouth within 1 second is 13 times higher when the receiver actually sees the original expression,” says Palagi.

“This rate of mimicry in dolphins is consistent with what’s been observed in certain carnivores, such as meerkats and sun bears.”

The researchers didn’t record the dolphins’ acoustic signals during playtime, and they say that future studies should investigate the possible role of vocalizations and tactile signals during playful interactions.

“Future research should dive into eye-tracking to explore how dolphins see their world and utilize acoustic signals in their multimodal communication during play,” says corresponding author and zoologist Livio Favaro.

“Dolphins have developed one of the most intricate vocal systems in the animal world, but sound can also expose them to predators or eavesdroppers. When dolphins play together, a mix of whistling and visual cues helps them cooperate and achieve goals, a strategy particularly useful during social play when they’re less on guard for predators.”