However, there may be hope for some tropical reefs in the form of feathered friends.

A new study led by researchers at Lancaster University has found that the presence of seabirds on islands adjacent to tropical coral reefs can boost coral growth rates on those reefs by more than double.

And as a result of this faster growth, coral reefs near seabird colonies can bounce-back much quicker from bleaching events — which often cause mass die off of corals when seas become too hot — the international team of researchers also discovered.

The study, published today in Science Advances, focused on Acropora, an important type of coral that provides complex structures supporting fish populations and reef growth, and which is also important for protecting coastal areas from waves and storms. The researchers found that Acropora around islands with seabirds recovered from bleaching events by around 10 months faster (approx. three years eight months) compared to reefs located away from seabird colonies (four years six months).

Researchers say these shorter recovery times could prove the difference between continuing to bounce back for some reefs in the face of a warming planet where damaging bleaching events now occur much more frequently than in earlier decades.

The key to how seabirds can help tropical coral reefs to grow and recover more quickly is through their droppings. Seabirds feed on fish in the open ocean far from islands, and then return to islands to roost — depositing nitrogen- and phosphorus-rich nutrients on the island in the form of guano. Some of the guano is washed off the islands by rain and into the surrounding seas where the nutrients fertilise corals, and other marine species.

“Our results clearly show that seabird-derived nutrients are directly driving faster coral growth rates and faster recovery rates in Acropora coral,” said Dr Casey Benkwitt, research fellow in coral reef ecology at Lancaster University and lead author of the study.

“This faster recovery may be critical as the average time between successive bleaching events was 5.9 years in 2016 — a reduction from 27 years in the 1980s. Even small reductions in recovery times during this window may be key to maintaining coral cover over the short-term,” she added.

The researchers’ study focused on a remote archipelago in the Indian Ocean. They compared reefs next to islands with thriving populations of seabirds, such as red-footed boobies, sooty terns and lesser noddies, against reefs next to islands with few seabirds. The islands with few birds have populations of rats, a very damaging invasive species which is devastating to birdlife as they eat eggs and chicks. It is no coincidence that the islands with thriving bird populations are rat-free.

The reefs in the study area suffered extensive coral bleaching and mortality following marine heatwaves in 2015-16, providing an opportunity to observe, and compare, how coral on different reefs recovered. The researchers surveyed the sites from one year before the bleaching event to six years after the bleaching, and modelled the Acropora recovery for the years between surveys.

The research team sampled nitrogen stable isotope values, a reliable tracer of seabird-derived nutrients, and measured growth rates of the Acropora corals for three years.

The results showed that seabird-derived nutrients taken up by corals next to bird islands boosted coral growth rates — with the rate doubling for each unit of seabird nutrient increase.

In contrast, coral near rat-infested islands had similar nutrient values to coral found distant from islands — showing the supply of these nutrients had been virtually cut off by the lack of birds.

The scientists also undertook an experimental approach to find out if the faster growth was directly due to the nutrients, as opposed to other factors such as genetic differences in corals between different islands. They transplanted some Acropora corals between islands with and without rats.

This experiment confirmed that it was the presence of seabirds that caused the nutrient enrichment.

At an island level, coral colonies transplanted to seabird islands grew twice as fast as those transplanted to rat-infested islands. Natural coral colonies were also found to grow faster near to rat-free islands with an estimated 2.4 times faster growth rate compared to coral around rat infested islands.

Dr Benkwitt said: “We’ve been able to show a clear link between the presence of seabirds and faster coral growth. This is really exciting and encouraging that a natural solution is available to help boost the resilience of coral reefs in the face of a warming planet.

“By restoring seabird populations, corals can quickly take-up and benefit from the supply of new nutrients, and our three-year experiment shows that these benefits are not just a short boost — they can be sustained over the long-term.”

The researchers say their findings add further weight to the growing body of evidence that shows the ecological damage across ecosystems on land and sea from invasive rats on tropical islands.

Professor Nick Graham of Lancaster University and Principal Investigator of the study said: “Combined, these results suggest that eradicating rats and restoring seabird populations could play an important role in re-establishing the natural flows of seabird nutrients to the nearshore marine environment, bolstering rapid coral reef recovery which will be critical as we expect to see more frequent climate disturbances.”

Environmental benefits of seabird nutrients go beyond increased rates of coral recovery. “Growth rates of fish on reefs adjacent to islands with large seabird colonies is also faster and overall biomass of fish is 50% greater than on reefs next to islands with rats,” said Dr Shaun Wilson, a co-author of the study from the Australian Institute of Marine Science. “Consequently, rates of grazing and bioerosion by fishes is three times faster on islands with seabirds, which are key processes helping to maintain a healthy reef.”

The results of the study, which was supported by the Bertarelli Foundation as part of the Bertarelli Programme in Marine Science, are outlined in the paper ‘Seabirds boost coral reef resilience’ published by Science Advances.

The authors of the paper are Cassandra Benkwitt, Samuel Healing and Nicholas Graham of Lancaster University; Ruth Dunn of Lancaster University and Heriot-Watt University; Rachel Gunn of Lancaster University and the University of Tubingen; Cecilia D’Angelo, Maria Loreto Mardones and Joerg Wiedenmann of the University of Southampton; Shaun Wilson of the Australian Institute of Marine Science and the University of Western Australia.

An international research team led by the University of Göttingen have now uncovered clues about the past: they analysed dolomite rocks in a drill core and found an extremely high proportion of the carbon isotope C-13. Further investigations traced this back to a phase of strong methane formation by microorganisms known as archaea in water with a low sulphate content. In contrast, the sediments of the previous, first phase of the crater lake showed clear traces of high sulphate content and bacterial sulphate decomposition. This change reveals that the groundwater pathways to the lake changed as the crater floor cooled. The results have been published in the journal Geochimica et Cosmochimica Acta.

A 250-metre-long drill core taken in 1981 provided information about the chemical processes during the time periods that sediment was being deposited in the crater lake. Combining sedimentological, biogeochemical and isotope geochemical research methods enabled the researchers to identify a distinctive section, which they investigated in more detail using biomarker analyses. They detected organic biomarkers originating from sulphate-reducing bacteria and “normal” dolomite in older rocks from the crater lake. In the younger rocks, they found dolomite enriched with C-13 and a chemical called archaeol which indicates that archaea were present at that time.

The properties of the rocks reflect the conditions in the crater lake during their formation: the decrease in sulphate is due to degradation by bacteria and the C-13 enrichment is due to the formation of methane by archaea. “This chemical development can only be explained by the change in the groundwater supply during the gradual cooling of the crater floor. This led to a change from deep, hydrothermal groundwater (with sulphate) to cooler water without sulphate that must have flowed through limestone rocks near to the surface,” explains study leader Professor Gernot Arp from the Department of Geobiology at the University of Göttingen.

The findings not only provide important information on the development of the crater lake being investigated, but also, as Arp notes: “Our findings show that the conditions in asteroid crater lakes are strongly controlled by internal processes such as crater floor cooling and water supply. In contrast, climatic changes are of secondary importance, unlike in many other lakes. This must be taken into account when deposits in terrestrial and extraterrestrial craters are used as climate archives to deduce past climate conditions from the sediments.”

Mapping Future Abundance

One of the major hurdles in addressing the threat of invasive species is in determining when and where a species crosses the line from being non-native to invasive. A single occurrence of, say, purple loosestrife, does not an invasion make. What invasive plant managers need to know is where a species is likely to take over, outcompeting native plants and altering the ecosystem.

Or, as Bethany Bradley, professor of environmental conservation at UMass Amherst and the senior author of both papers puts it, “managers have very few resources to control invasions, so we don’t want to waste time focusing on species unlikely to become invasive in a given area. But the question of what will become invasive and where has been surprisingly tricky to answer.”

“If we can proactively identify these species and the regions they are most likely to become abundant in as the climate warms, then we can head-off a major ecological threat before it’s too late,” adds Annette Evans, a postdoctoral fellow at UMass Amherst’s Northeast Climate Adaptation Science Center and lead author of the paper on abundance and future invasive hotspots.

To do so, the team combed through 14 current invasive species databases compiled by hundreds of natural resource managers in order to first pinpoint which species are currently abundant and where, geographically, those abundance hotspots occur. They focused on the eastern U.S. (east of the 100^th meridian, which runs from the middle of North Dakota through the center of Texas — a follow-up paper will focus on the western U.S.) and discovered that the hottest hotspots are around the Great Lakes, the mid-Atlantic, and along the northeastern coasts of Florida and Georgia. Each of these regions has the right mix of conditions to currently support abundant populations of more than 30 different invasive plants.

They then ran their data on 144 plants through a series of models that predicted where the hotspots would occur under 2° Celsius of warming.

What they discovered is that most of the species will shift their ranges to the northeast by an average of 213 kilometers, a trend also reflected in shifts to abundance hotspot locations. In some states, warming temperatures will make currently unsuitable areas conducive for abundant infestations of up to 21 new plant species, and the range-shifting could exacerbate the effects of up to 40 currently abundant invasives. On the other hand, 62% of currently abundant invasive species will see a decrease in habitat for large populations in the eastern U.S.

But statistics aren’t enough. “We’ve created something even more user-friendly,” says Evans: a series of publicly available range maps for individual species, which can help plant managers triage which plants most need their attention, as well as state-specific watch lists.

How plant nurseries could seed invasion

“When people think of how invasive plant species spread, they might assume species are moving because of birds or the wind dispersing seeds,” says Evelyn M. Beaury, lead author of the paper on horticulture and invasive species, as well as a postdoctoral researcher at Princeton who completed this research as an extension to her graduate studies at UMass Amherst. “But commercial nurseries that sell hundreds of different invasives are actually the primary pathway of invasive plant introduction.”

Though researchers have long known that invasives are linked to the horticulture trade, Beaury and her co-authors, including Evans and Bradley, wondered how often invasives are sold in the same area in which they are abundant? And how might nurseries be exacerbating the problem of climate-driven invasion?

It turns out that the answer to both questions is: a lot.

Using a case study of 672 nurseries around the U.S. that sell a total of 89 invasive plant species, and then running the results through the same models that the team used to predict future hotspots, Beaury and her co-authors found that nurseries are currently sowing the seeds of invasion for more than 80% of the species studied. If left unchecked, the industry could facilitate the spread of 25 species into areas that become suitable with 2°C of warming.

Furthermore, 55% of the invasive species were sold within 21 kilometers (13 miles) of an observed invasion — the median distance people across the U.S. go to buy landscaping plants. In other words, everyday gardeners who buy plants at their local nurseries could unwittingly help perpetuate invasion and associated ecological harm in their literal backyards.

“But there’s good news here,” says Beaury. “This is the first time that we have real numbers to show the connection between plant nursery sales and the spread of invasive species — including invasions that occur down the street from nurseries, as well as across state borders. Now that we have the data, we have an incredible opportunity to be proactive, to work with the industry, consumers and plant managers to think more critically about how our gardens impact U.S. ecosystems.”

The team has also put together a publicly available list of 24 commonly sold invasive plants that could increase in risk with climate change in the northeast, from butterfly bush to English ivy, to be avoided and native alternatives, such as bottlebrush buckeye and wild blue phlox.

“These two papers together make it pretty clear that not only are we facilitating current invasions through the ornamental plant trade, but we are also facilitating future climate-driven invasion,” says Bradley, “But with these papers, maps and watchlists, we can pinpoint which species are most worrisome where, both now and in the coming decades. These are important new tools in invasive plant managers’ toolboxes.”

The study, recently published in the journal PNAS Nexus, demonstrates how bacteria use mucus to enhance their ability to self-organize and possibly drive infection. The experiments, performed using synthetic pig stomach mucus, natural cow cervical mucus and a water-soluble polymer compound called polyvidone, revealed that bacteria coordinate movement better in thick mucus than in watery substances.

The findings provide insight into how bacteria colonize mucus and mucosal surfaces, researchers said. The findings also show how mucus enhances bacterial collective motion, or swarming, which may increase antibiotic resistance of bacterial colonies.

“To the best of our knowledge, our study is the first demonstration of bacteria collectively swimming in mucus,” said Igor Aronson, Huck Chair Professor of Biomedical Engineering, of Chemistry and of Mathematics at Penn State and corresponding author on the paper. “We have shown that mucus, unlike liquids of similar consistency, enhances the collective behavior.”

Mucus is essential for many biological functions, explained Aronson. It lines the surfaces of cells and tissues and protects against pathogens such as bacteria, fungi and viruses. But it is also the host material for bacteria-born infections, including sexually transmitted and gastric diseases. A better understanding of how bacteria swarm in mucus could pave the way for new strategies to combat infections and the growing problem of antibiotic resistance, according to Aronson.

“Our findings demonstrate how mucus consistency affects random motion of individual bacteria and influences their transition to coordinated, collective motion of large bacterial groups,” Aronson said. “There are studies demonstrating that collective motion or swarming of bacteria enhances the ability of bacterial colonies to fend off the effect of antibiotics. The onset of collective behavior studied in our work is directly related to swarming.”

Mucus is a notoriously challenging substance to study because it exhibits both liquid-like and solid-like properties, Aronson explained. Liquids are typically described by their level of viscosity, how thick or thin the liquid is, and solids are described by their elasticity, how much force it can take before breaking. Mucus, a viscoelastic fluid, behaves as both a liquid and solid.

To better understand how mucus becomes infected, the team used microscopic imaging techniques to observe the collective motion of the concentrated bacteria Bacillus subtilis in synthetic pig stomach mucus and natural cow cervical mucus. They compared those results with observations of Bacillus subtilis moving in a water-soluble polymer polyvidone at a wide range of concentrations, from high to low levels of polyvidone. The researchers also compared their experimental results to a computational model for bacterial collective motion in viscoelastic fluids like mucus.

The team found that the consistency of mucus profoundly affects the collective behavior of bacteria. The results indicated that the thicker the mucus, the more likely the bacteria would exhibit collective movement, forming a coordinated swarm.

“We were able to show how the viscoelasticity in mucus enhances bacterial organization, which in turn leads to coherently moving bacterial groups that cause infection,” Aronson said. “Our results reveal that the levels of elasticity and viscosity in mucus are a main driver in how bacterial communities organize themselves, which can provide insight into how we can control and prevent bacterial invasion in mucus.”

Aronson explained that the team expects human mucus to exhibit similar physical properties, meaning their findings are also relevant for human health.

“The onset of the collective motion of bacteria and their interaction with mucus should be the same as in cow, pig or human mucus since these substances have similar mechanical properties,” Aronson said. “Our results have implications for human and animal health. We’re showing that mucus viscoelasticity can enhance large-scale collective motion of bacteria, which may accelerate how quickly bacteria penetrate mucus protective barrier and infect internal tissues.”

The other co-author on the paper is Wentian Liao, a doctoral candidate in biomedical engineering at Penn State. The National Science Foundation supported the work.