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Scientists led by the University of South Florida College of Marine Science used NASA satellite observations to discover the largest bloom of macroalgae in the world called the Great Atlantic Sargassum Belt (GASB), as reported in Science.

They confirmed that the belt of brown macroalgae called Sargassum forms its shape in response to ocean currents, based on numerical simulations. It can grow so large that it blankets the surface of the tropical Atlantic Ocean from the west coast of Africa to the Gulf of Mexico. This happened last year when more than 20 million tons of it – heavier than 200 fully loaded aircraft carriers – floated in surface waters and some of which wreaked havoc on shorelines lining the tropical Atlantic, Caribbean Sea, Gulf of Mexico, and east coast of Florida.

The team also used environmental and field data to suggest that the belt forms seasonally in response to two key nutrient inputs: one human-derived, and one natural.

In the spring and summer, Amazon River discharge adds nutrients to the ocean, and such discharged nutrients may have increased in recent years due to increased deforestation and fertilizer use. In the winter, upwelling off the West African coast delivers nutrients from deep waters to the ocean surface where the Sargassum grows.

“The evidence for nutrient enrichment is preliminary and based on limited field data and other environmental data, and we need more research to confirm this hypothesis,” said Dr. Chuanmin Hu of the USF College of Marine Science, who led the study and has studied Sargassum using satellites since 2006. “On the other hand, based on the last 20 years of data, I can say that the belt is very likely to be a new normal,” said Hu.

Hu spearheaded the work with first author Dr. Mengqiu Wang, a postdoctoral scholar in his Optical Oceanography Lab at USF. The team included others from USF, Florida Atlantic University, and Georgia Institute of Technology. The data they analyzed from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) between 2000-2018 indicates a possible regime shift in Sargassum blooms since 2011.

“The scale of these blooms is truly enormous, making global satellite imagery a good tool for detecting and tracking their dynamics through time,” said Woody Turner, manager of the Ecological Forecasting Program at NASA Headquarters in Washington.

In patchy doses in the open ocean, Sargassum contributes to ocean health by providing habitat for turtles, crabs, fish, and birds and producing oxygen via photosynthesis like other plants. “In the open ocean, Sargassum provides great ecological values, serving as a habitat and refuge for various marine animals. I often saw fish and dolphins around these floating mats,” Wang said.

But too much of this seaweed makes it hard for certain marine species to move and breathe, especially when the mats crowd the coast. When it dies and sinks to the ocean bottom at large quantities it can smother corals and seagrasses. On the beach, rotten Sargassum releases hydrogen sulfide gas and smells like rotten eggs, potentially presenting health challenges for people on beaches who have asthma, for example.

2011: A Tipping Point

Before 2011, most of the pelagic Sargassum in the ocean was primarily found floating in patches around the Gulf of Mexico and Sargasso Sea. The Sargasso Sea is located on the western edge of the central Atlantic Ocean and named after its popular algal resident. Christopher Columbus first reported Sargassum from this crystal-clear ocean in the 15th century, and many boaters of the Sargasso Sea are familiar with this seaweed.

In 2011, Sargassum populations started to explode in places it hadn’t been before, like the central Atlantic Ocean, and it arrived in gargantuan gobs that suffocated shorelines and introduced a new nuisance for local environments and economies. Some countries, such as Barbados, declared a national emergency last year because of the toll this once-healthy seaweed took on tourism.

“The ocean’s chemistry must have changed in order for the blooms to get so out of hand,” Hu said. Sargassum reproduces vegetatively, and it probably has several initiation zones around the Atlantic Ocean. It grows faster when nutrient conditions are favorable and when its internal clock ticks in favor of reproduction.

To unravel the mystery, the team analyzed fertilizer consumption patterns in Brazil, Amazon deforestation rates, Amazon River discharge, two years of nitrogen and phosphorus measurements taken from the central western parts of the Atlantic Ocean, among other ocean properties.

While the data are preliminary, the pattern seems clear: the explosion in Sargassum correlates to increases in deforestation and fertilizer use, both of which have increased since 2010.

A Recipe for a Doom and Gloom Bloom

The team identified key factors that are critical to bloom formation: a large seed population in the winter left over from a previous bloom, nutrient input from West Africa upwelling in winter, and nutrient input in the spring or summer from the Amazon River. In addition, Sargassum only grows well when salinity is normal and surface temperatures are normal or cooler.

The 2011 bloom was likely caused by Amazon River discharge in previous years, Wang said, but was driven to even larger proportions by the double whammy of upwelling in the eastern Atlantic and river discharge on the western Atlantic.

As noted in the satellite imagery, major blooms occurred in every year between 2011 and 2018 except 2013 – and the cocktail of ingredients necessary explains why. No bloom occurred in 2013 because the seed populations measured during winter of 2012 were unusually low, Wang said.

Hu also explained why the tipping point started in 2011 instead of 2010, even on the heels of significant Amazon discharge in 2009. Significant rain in 2009 introduced freshwater to the ocean, which reduced salinity. Plus, in 2010 the sea surface temperature was higher than normal. Sargassum didn’t bloom in either 2009 or 2010 because these conditions do not favor Sargassum growth.

“This is all ultimately related to climate change because it affects precipitation and ocean circulation and even human activities, but what we’ve shown is that these blooms do not occur because of increased water temperature,” Hu said. “They are probably here to stay.”

The team reports that a more detailed seasonal pattern likely to be recurring looks like this:

• January: Sargassum in Central Atlantic provides the seeds for the subsequent spring-summer blooms
• Jan-April: Sargassum develops into a bloom extending to the tropical Atlantic (some may reach Caribbean)
• Apr – July: Blooms continue to develop into a Great Atlantic Sargassum Belt (extends northwestward by the North Brazil Current and North Equatorial Current, and eastward to the West Africa coast by the North Equatorial Counter Current)
• After July: Bloom continues to the eastern Atlantic while overall abundance begins to decrease
• Sept-Oct: Bloom gradually dissipates
• Winter: Either the mats dissipate (as in 2012) or contribute to new blooms in the coming year

No Crystal Ball and More Work Needed

The Sargassum bloom in the Caribbean during the early parts of this year was even worse than last year, Hu said, and it’s likely to impact holiday vacations in the northern Caribbean and south Florida, including Dominican Republic, Puerto Rico, Jamaica, Quintana Roo, Florida Keys, Miami Beach, and Palm Beach.

In general, predicting future blooms is difficult, Hu said, because the blooms depend on a wide-ranging spectrum of factors that are hard to predict. There’s a lot left to understand, too, such as whether and how the Sargassum belt affects fisheries.

“We hope this provides a framework for improved understanding and response to this emerging phenomenon,” Hu said. “We need a lot more follow-on work.”

Read the paper: Science

Article source: University of South FLorida

Image: Brian Cousin, Florida Atlantic University’s Harbor Branch Oceanographic Institute

Researchers in Japan have edited plant mitochondrial DNA for the first time, which could lead to a more secure food supply.

Nuclear DNA was first edited in the early 1970s, chloroplast DNA was first edited in 1988, and animal mitochondrial DNA was edited in 2008. However, no tool previously successfully edited plant mitochondrial DNA.

Researchers used their technique to create four new lines of rice and three new lines of rapeseed (canola).

“We knew we were successful when we saw that the rice plant was more polite – it had a deep bow,” said Associate Professor Shin-ichi Arimura, joking about how a fertile rice plant bends under the weight of heavy seeds.

Arimura is an expert in plant molecular genetics at the University of Tokyo and led the research team, whose results were published in Nature Plants. Collaborators at Tohoku University and Tamagawa University also contributed to the research.

Genetic diversity for the food supply

Researchers hope to use the technique to address the current lack of mitochondrial genetic diversity in crops, a potentially devastating weak point in our food supply.

In 1970, a fungal infection arrived on Texas corn farms and was exacerbated by a gene in the corn’s mitochondria. All corn on the farms had the same gene, so none were resistant to the infection. Fifteen percent of the entire American corn crop was killed that year. Corn with that specific mitochondrial gene has not been planted since.

“We still have a big risk now because there are so few plant mitochondrial genomes used in the world. I would like to use our ability to manipulate plant mitochondrial DNA to add diversity,” said Arimura.

Plants without pollen

Most farmers do not save seeds from their harvest to replant next year. Hybrid plants, the first-generation offspring of two genetically different parent subspecies, are usually hardier and more productive.

To ensure farmers have fresh, first-generation hybrid seeds each season, agricultural supply companies produce seeds through a separate breeding process using two different parent subspecies. One of those parents is male infertile – it cannot make pollen.

Researchers refer to a common type of plant male infertility as cytoplasmic male sterility (CMS). CMS is a rare but naturally occurring phenomenon caused primarily by genes not in the nucleus of the cells, but rather the mitochondria.

Green beans, beets, carrots, corn, onions, petunia, rapeseed (canola) oil, rice, rye, sorghum, and sunflowers can be grown commercially using parent subspecies with CMS-type male infertility.

Beyond green

Plants use sunlight to produce most of their energy, through photosynthesis in green-pigmented chloroplasts. However, chloroplasts’ fame is overrated, according to Arimura.

“Most of a plant isn’t green, only the leaves above the ground. And many plants don’t have leaves for half the year,” said Arimura.

Plants get a significant portion of their energy through the same “powerhouse of the cell” that produces energy in animal cells: the mitochondria.

“No plant mitochondria, no life,” said Arimura.

Mitochondria contain DNA completely separate from the cell’s main DNA, which is stored in the nucleus. Nuclear DNA is the long double-helix genetic material inherited from both parents. The mitochondrial genome is circular, contains far fewer genes, and is primarily inherited only from mothers.

The animal mitochondrial genome is a relatively small molecule contained in a single circular structure with remarkable conservation between species.

“Even a fish’s mitochondrial genome is similar to a human’s,” said Arimura.

Plant mitochondrial genomes are a different story.

“The plant mitochondrial genome is huge in comparison, the structure is much more complicated, the genes are sometimes duplicated, the gene expression mechanisms are not well-understood, and some mitochondria have no genomes at all – in our previous studies, we observed that they fuse with other mitochondria to exchange protein products and then separate again,” said Arimura.

Manipulating plant mitochondrial DNA

To find a way to manipulate the complex plant mitochondrial genome, Arimura turned to collaborators familiar with the CMS systems in rice and rapeseed (canola). Prior research strongly suggested that in both plants, the cause of CMS was a single, evolutionarily unrelated mitochondrial gene in rice and in rapeseed (canola): clear targets in the perplexing maze of plant mitochondrial genomes.

Arimura‘s team adapted a technique that had previously edited mitochondrial genomes of animal cells growing in a dish. The technique, called mitoTALENs, uses a single protein to locate the mitochondrial genome, cut the DNA at the desired gene, and delete it.

“While deleting most genes creates problems, deleting a CMS gene solves a problem for plants. Without the CMS gene, plants are fertile again,” said Arimura.

The fully fertile four new lines of rice and three new lines of rapeseed (canola) that researchers created are a proof of concept that the mitoTALENs system can successfully manipulate even the complex plant mitochondrial genome.

“This is an important first step for plant mitochondrial research,” said Arimura.

Researchers will study the mitochondrial genes responsible for plant male infertility in more detail and identify potential mutations that could add much-needed diversity.

Read the paper: Nature Plants

Article source: University of Tokyo

Image: Tomohiko Kazama

High in the Andes Mountains, dagger-shaped ice spires house thriving microbial communities, offering an oasis for life in one of Earth’s harshest environments as well as a possible analogue for life on other planets.

The distinctive icy blade formations known as nieves penitentes (or, “penitent ones”) are named for their resemblance to praying monks in white robes and form in cold, dry conditions at elevations above 13,000 feet. The penitentes, which can range from a few inches to 15 feet high, are found in some of the most hostile conditions on Earth, with extreme winds, temperature fluctuations and high UV radiation exposure due to the thin atmosphere.

And yet, as a recently published study led by CU Boulder student researchers finds, these spires offer shelter for microbes by providing a water source in an otherwise arid, nutrient-poor environment.

In March 2016, CU Boulder students and faculty members traveled to Volcán Llullaillaco in Chile, the world’s second-highest volcano. The two-week expedition into the arid landscape, planned in collaboration with their Chilean colleagues, was no easy feat.

“This is a very remote area that’s difficult to access,” said Steve Schmidt, a professor in CU Boulder’s Department of Ecology and Evolutionary Biology (EBIO) and a co-author of the study. “The entire back of one of our pickup trucks had to be filled with barrels of drinking water. It’s no trivial thing to go out there, and that’s one of the reasons these formations haven’t been studied much.”

After reaching the penitente fields at 16,000 feet above sea level, the scientists noticed patches of red coloration, a telltale sign of microbial activity that has been previously observed in other snow and ice formations around the world.

Upon bringing back samples for analysis, the researchers confirmed the presence of algal species Chlamydomonas and Chloromonas in the ice, the first documentation of snow algae or any other life forms in the penitentes.

“Snow algae have been commonly found throughout the cryosphere on both ice and snow patches, but our finding demonstrated their presence for the first time at the extreme elevation of a hyper-arid site,” said Lara Vimercati, lead author of the study and a doctoral researcher in EBIO. “Interestingly, most of the snow algae found at this site are closely related to other known snow algae from alpine and polar environments.”

The new findings add to scientists’ understanding of the limits of life on Earth, says Alexandra Krinsky, a co-author of the study and an undergraduate in the Department of Molecular, Cellular and Developmental Biology who helped analyze the samples.

“From looking at the extreme environments of the dry Andes to the aquatic life roaming the sea floor, we have broken the original ideas of where life can and has been found,” she said.

The study may also have implications for the search for alien life. Penitente-like formations have recently been discovered on Pluto and are speculated to exist on Europa, one of Jupiter’s moons. The Atacama region in Chile is also considered to be the best Earth analogue for the soils of Mars.

“We’re generally interested in the adaptations of organisms to extreme environments,” Schmidt said. “This could be a good place to look for upper limits of life.”

“Our study shows how no matter how challenging the environmental conditions, life finds a way when there is availability of liquid water,” Vimercati said.

Additional co-authors of the research include Adam Solon of CU Boulder; John Darcy of the University of Colorado Denver; Dorota Porazinska of the University of Florida; and Pablo Arán and Cristina Dorador of the Universidad de Antofagasta (Chile).

Read the paper: Arctic, Antarctic, and Alpine Research

Article source: University of Colorado at Boulder

Image: Steve Schmidt/CU Boulder