Study reveals our European ancestors ate seaweed and freshwater plants

For many people seaweed holds a reputation as a superfood, heralded for its health benefits and sustainability, but it appears our European ancestors were ahead of the game and were consuming the nutrient-rich plant for thousands of years.

Researchers say they have found "definitive" archaeological evidence that seaweeds and other local freshwater plants were eaten in the mesolithic, through the Neolithic transition to farming and into the Early Middle Ages, suggesting that these resources, now rarely eaten in Europe, only became marginal much more recently.

The study, published in Nature Communications, reveals that while aquatic resources were exploited, the archaeological evidence for seaweed is only rarely recorded and is almost always considered in terms of non-edible uses like fuel, food wrappings or fertilisers.

Historical accounts report laws related to collection of seaweed in Iceland, Brittany and Ireland dating to the 10th Century, while sea kale is mentioned by Pliny as a sailor's anti-scurvy remedy.

By the 18th Century seaweed was considered as famine food, and although seaweed and freshwater aquatic plants continue to be economically important in parts of Asia, both nutritionally and medicinally, there is little consumption in Europe.

The team, led by archaeologists from the universities of Glasgow and York, examined biomarkers extracted from dental calculus from 74 individuals from 28 archaeological sites across Europe, from north Scotland to southern Spain, which revealed "direct evidence for widespread consumption of seaweed and submerged aquatic and freshwater plants."

Samples where biomolecular evidence survived revealed consumption of red, green or brown seaweeds, or freshwater aquatic plants, with one sample from Orkney also containing evidence for a Brassica, most likely sea kale.

There are approximately 10,000 different species of seaweeds in the world, however only 145 species are eaten today, principally in Asia.

The researchers hope that their study will highlight the potential for including more seaweeds and other local freshwater plants in our diets today -- helping Europeans to become healthier and more sustainable.

Karen Hardy, Professor of Prehistoric Archaeology at the University of Glasgow and Principal Investigator of the Powerful Plants project, said: "Today, seaweed and freshwater aquatic plants are virtually absent from traditional, western diets and their marginalisation as they gradually changed from food to famine resources and animal fodder, probably occurred over a long period of time, as has also been detected elsewhere with some plants.

"Our study also highlights the potential for rediscovery of alternative, local, sustainable food resources that may contribute to addressing the negative health and environmental effects of over-dependence on a small number of mass-produced agricultural products that is a dominant feature of much of today's western diet, and indeed the global long-distance food supply more generally."

"It is very exciting to be able to show definitively that seaweeds and other local freshwater plants were eaten across a long period in our European past."

Co author on the paper, Dr Stephen Buckley, from the Department of Archaeology at the University of York, said "The biomolecular evidence in this study is over three thousand years earlier than historical evidence in the Far East.

"Not only does this new evidence show that seaweed was being consumed in Europe during the Mesolithic Period around 8,000 years ago when marine resources were known to have been exploited, but that it continued into the Neolithic when it is usually assumed that the introduction of farming led to the abandonment of marine dietary resources.

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One billion-year-old green seaweed fossils identified, relative of modern land plants

Virginia Tech paleontologists have made a remarkable discovery in China: 1 billion-year-old micro-fossils of green seaweeds that could be related to the ancestor of the earliest land plants and trees that first developed 450 million years ago.

The micro-fossil seaweeds -- a form of algae known as Proterocladus antiquus -- are barely visible to the naked eyed at 2 millimeters in length, or roughly the size of a typical flea. Professor Shuhai Xiao said the fossils are the oldest green seaweeds ever found. They were imprinted in rock taken from an area of dry land -- formerly ocean -- near the city of Dalian in the Liaoning Province of northern China. Previously, the earliest convincing fossil record of green seaweeds were found in rock dated at roughly 800 million years old.

The findings -- led by Xiao and Qing Tang, a post-doctoral researcher, both in the Department of Geosciences, part of the Virginia Tech College of Science -- are featured in the latest issue of Nature Ecology & Evolution.

"These new fossils suggest that green seaweeds were important players in the ocean long before their land-plant descendants moved and took control of dry land," Xiao said.

"The entire biosphere is largely dependent on plants and algae for food and oxygen, yet land plants did not evolve until about 450 million years ago," Xiao said. "Our study shows that green seaweeds evolved no later than 1 billion years ago, pushing back the record of green seaweeds by about 200 million years. What kind of seaweeds supplied food to the marine ecosystem?"

Shuhai said the current hypothesis is that land plants -- the trees, grasses, food crops, bushes, even kudzu -- evolved from green seaweeds, which were aquatic plants. Through geological time -- millions upon millions of years -- they moved out of the water and became adapted to and prospered on dry land, their new natural environment. "These fossils are related to the ancestors of all the modern land plants we see today."

However, Xiao added the caveat that not all geobiologists are on the same page -- that debate on the origins of green plants remains debated. "Not everyone agrees with us; some scientists think that green plants started in rivers and lakes, and then conquered the ocean and land later," added Xiao, a member of the Virginia Tech Global Change Center.

There are three main types of seaweed: brown (Phaeophyceae), green (Chlorophyta), and red (Rhodophyta), and thousands of species of each kind. Fossils of red seaweed, which are now common on ocean floors, have been dated as far back as 1.047 billion years old.

"There are some modern green seaweeds that look very similar to the fossils that we found," Xiao said. "A group of modern green seaweeds, known as siphonocladaleans, are particularly similar in shape and size to the fossils we found."

Photosynthetic plants are, of course, vital to the ecological balance of the planet because they produce organic carbon and oxygen through photosynthesis, and they provide food and the basis of shelter for untold numbers of mammals, fish, and more. Yet, going back 2 billion years, Earth had no green plants at all in oceans, Xiao said.

It was Tang who discovered the micro-fossils of the seaweeds using an electronic microscope at Virginia Tech's campus and brought it to Xiao's attention. To more easily see the fossils, mineral oil was dripped onto the fossil to create a strong contrast.

"These seaweeds display multiple branches, upright growths, and specialized cells known as akinetes that are very common in this type of fossil," he said. "Taken together, these features strongly suggest that the fossil is a green seaweed with complex multicellularity that is circa 1 billion years old. These likely represent the earliest fossil of green seaweeds. In short, our study tells us that the ubiquitous green plants we see today can be traced back to at least 1 billion years."

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