Seagrass, a group of aquatic angiosperms, grows in shallow waters in the coastal sea and contributes most of the primary production while participating in many important ecological processes. Heat stress threatens the survival of seagrass, but its damage mechanisms are unclear. Recently, a research team led by Prof. Liu Jianguo
A study of eelgrass meadows planted by researchers from the University of Gothenburg shows that fauna return rapidly once the eelgrass has started to grow. Already after the second summer, the biodiversity in the planted meadow was almost the same as in old established eelgrass meadows. Eelgrass meadows have declined
In Florida alone, thousands of acres of marine seagrass beds have died. Major seagrass die-offs also are occurring around the world. Stressors such as high temperature, hypersalinity and hypoxia or lack of oxygen affect seagrasses’ ability to resist and recover from these stressor-related mortality events or when disturbances lead to
The sea devours large tracts of land when storms wash sand out to sea from the coast. A new study involving a researcher from the University of Gothenburg has shown that seagrass can reduce cliff erosion by up to 70% thanks to its root mats binding the sand. Coastal erosion
“The downward trajectory of the world’s seagrass meadows must be reversed if we are to fight the planetary crisis” say leading seagrass scientists. The United Nations Sustainable Development Goals have recently been described as “the most important to-do list in the history of humankind”. Scientists from Project Seagrass and Swansea
Deep evolution casts a longer shadow than previously thought, scientists report in a new paper published the week of Aug. 1 in the Proceedings of the National Academy of Sciences. Smithsonian scientists and colleagues looked at eelgrass communities—the foundation of many coastal marine food webs along the north Atlantic and
A new study shows that seagrass fisheries provide a reliable safety-net for poor fishermen, since they perceive those habitats to maintain large fish catches over time. Surprisingly, even more so than coral reef fisheries, which people normally associate with small-scale fishery. Seagrass meadows are routinely used as a fishing habitat
Seagrass, a group of aquatic angiosperms, grows in shallow waters in the coastal sea and contributes most of the primary production while participating in many important ecological processes. Heat stress threatens the survival of seagrass, but its damage mechanisms are unclear. Recently, a research team led by Prof. Liu Jianguo from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) primarily explained the physiological and biochemical mechanisms underlying the decline of tropical seagrass meadows caused by heat stress combined with high light at different functional levels. The study was published in Marine Pollution Bulletin. During the lowest tide, intertidal seagrass is frequently faced with the combined stress of exposure to air, direct sunlight, and high temperature, which may have a strongly negative impact on the survival of seagrass, especially in the context of global warming. The researchers found that the largest tropical seagrass Enhalus acoroides can withstand heat below 39°C in the dark. However, under high light, the tolerance to heat stress is greatly reduced. The combined effect of short-term exposure to heat and high light stress destroyed the photosystem II (PSII) and destroyed key components of the photosynthetic system in seagrass leaves. Moreover, high light combined with heat stress caused severe oxidative stress in the seagrass, which led to irreversible damage to the seagrass. These results clearly suggest that heat stress coupled with high light, may be an important cause for the decline of E. acoroides meadows. “Our study reveals that ocean warming, especially when coupled with high light, exacerbates the decline of seagrass meadows and affects the ecological function of intertidal seagrass meadows,” said Dr. Zhang Mengjie, first author of the study. “This serves as a warning that the effects of global warming on seagrass meadows will be even worse than expected,” said Prof. Liu, corresponding author of the study. More information: Mengjie Zhang et al, Heat stress, especially when coupled with high light, accelerates the decline of tropical seagrass (Enhalus acoroides) meadows, Marine Pollution Bulletin (2023). DOI: 10.1016/j.marpolbul.2023.115043
A study of eelgrass meadows planted by researchers from the University of Gothenburg shows that fauna return rapidly once the eelgrass has started to grow. Already after the second summer, the biodiversity in the planted meadow was almost the same as in old established eelgrass meadows. Eelgrass meadows have declined heavily in southern Bohus county in recent decades and in many places have disappeared altogether. Researchers at the University of Gothenburg have been working on the restoration of eelgrass meadows for twelve years. These meadows are important for biodiversity, as the eelgrass serves as habitat or nursery for young cod, crabs and shrimps for example. In a new study, the researchers have evaluated how rapidly replanted eelgrass gets populated by various invertebrates. The study has been going on for over two years in a bay near Gåsö island just west of Skaftö in Bohus county, and the findings are very positive. The researchers counted the abundance of invertebrates that live or burrow in bottom sediments or on the surface of bottom sediments. Size less important “The recolonization has been very rapid. After the first three-month growing season, up to 80 percent of the invertebrates had returned to the newly planted eelgrass,” says Eduardo Infantes, marine biologist at the University of Gothenburg. During the summer in 2019, the researchers planted the eelgrass shoots in four test plots of different sizes on the seabed, and with different spacing between the shoots. According to the researchers’ observations in autumn 2020, size has played less of a role in the recovery of biodiversity in the eelgrass meadows. In fact, even if the eelgrass has not had time to grow to the same density as in an established eelgrass meadow, the biodiversity is similar after only two growing seasons as in a reference area of preserved eelgrass in the same bay. Even smaller patches embedded within larger restoration plots showed good results. Their findings were reported in the journal Restoration Ecology. Can save money “This is good news for future restorations and new plantings of eelgrass meadows. We can plant new smaller plots with fewer shoots and this saves money because this is an expensive method for restoring biodiversity on the seabed,” says Eduardo Infantes. Eelgrass meadows have multiple functions that make it imperative to protect them. In addition to their important role in the coastal ecosystem, eelgrass roots bind the sediment and prevent erosion and limit resuspension of sediment in the water. More information: Karine Gagnon et al, Rapid faunal colonization and recovery of biodiversity and functional diversity following eelgrass restoration, Restoration Ecology (2023). DOI: 10.1111/rec.13887
In Florida alone, thousands of acres of marine seagrass beds have died. Major seagrass die-offs also are occurring around the world. Stressors such as high temperature, hypersalinity and hypoxia or lack of oxygen affect seagrasses’ ability to resist and recover from these stressor-related mortality events or when disturbances lead to seagrass die-off events. Seagrass die-offs also are linked to exposure to sediment-derived hydrogen sulfide, a well-known phytotoxin that accumulates as seagrass ecosystems become more enriched in nutrients. While hydrogen sulfide intrusion into seagrass tissue is considered a leading cause of recurring mortality events, its effects on subsequent recruitment and distribution of new populations is unclear. Moreover, few studies have examined the ability of seagrass meadows‘ resilience to “bounce back” and recolonize in open bare patches. Researchers from Florida Atlantic University, in collaboration with the South Florida Water Management District, Coastal Ecosystems Division, examined if porewater hydrogen sulfide prevents Thalassia testudinum, a dominant tropical Atlantic-Caribbean marine seagrass known as turtlegrass, from recruiting into unvegetated sediment in Florida Bay. The bay is an estuary that covers about 1,100 square miles between the southern tip of Florida and the Florida Keys and is one of the largest global contiguous seagrass systems. Since the 1980s, seagrass meadows in Florida Bay have experienced repeated biomass losses, including massive die-off events of turtlegrass, which typically occur during high temperature and salinity conditions in the northcentral and western bay. The bay provided an excellent case-study site due to high porewater hydrogen sulfide and expansive unvegetated areas adjacent to intact meadows that are recolonized by turtlegrass recruits following morality events. For the study, researchers examined the leaf, stems and root tissue of turtlegrass in Florida Bay to establish tissue exposure to hydrogen sulfide in new recruits and measured internal hydrogen sulfide and oxygen dynamics using cutting-edge microsensors in the field and stable isotope analyses. Results, published in the journal Aquatic Botany, provide evidence that turtlegrass can successfully recruit into open bare sediment following die-off events due to biomass partitioning—a process by which plants divide their energy among their leaves, stems, roots and reproductive parts—during early development, young root structure, and an ability to efficiently oxidize internally, which lowers hydrogen sulfide exposure. However, recovery of seagrass meadows takes time. “Long-term monitoring programs in Florida Bay indicate that the time frame for full recovery of turtlegrass meadows after major die-off events is at least a decade,” said Marguerite Koch, Ph.D., senior author and a professor of biological sciences in FAU’s Charles E. Schmidt College of Science. “Therefore, preventing large-scale seagrass mortality events should be the management goal, particularly as global warming and associated stressors are likely to get more extreme in the future.” Findings of the study indicate that recruiting shoot resistance to hydrogen sulfide exposure is linked to adequate oxidation of internal tissue during the day through late afternoon via photosynthesis and internal plant oxidation promoted by water column oxygen diffusion into the leaves at night, driven at times by tides. Limited belowground root development in new recruits potentially constrains microbial community development and associated sulfate reduction that decrease hydrogen sulfide intrusion into roots and negatively affecting sensitive growing tissue at the base of the seagrass leaves. “Seagrass meadows sustain coastal ecosystems by protecting against erosion, maintaining water quality and providing habitat and food for many marine species and organisms,” said Koch. “Because of their importance in coastal communities, the current decline of seagrass ecosystems on a global scale across geographic regions is a concern.” More information: K. MacLeod et al, Resilience of recruiting seagrass (Thalassia testudinum) to porewater H2S in Florida Bay, Aquatic Botany (2023). DOI: 10.1016/j.aquabot.2023.103650
The sea devours large tracts of land when storms wash sand out to sea from the coast. A new study involving a researcher from the University of Gothenburg has shown that seagrass can reduce cliff erosion by up to 70% thanks to its root mats binding the sand. Coastal erosion is a global problem that is often combated by replenishing the coast and beaches with new sand in locations where storms wreak the greatest havoc. According to a 2016 survey conducted by the Geological Survey of Sweden, 12% of Skåne’s coastline in southern Sweden is vulnerable to increasing rates of coastal erosion. It is an even bigger issue in other countries. In the Netherlands, the coastline is protected through the construction of dikes made from stone and mud. Another solution is to utilize nature’s own defenses against coastal erosion. In this new study, researchers examined the importance of seagrass for preserving the coastline. “We have seen that seagrass meadows in the coast are valuable assets in mitigating erosion. We already know that their long canopies serve as breakwaters, but now we can show that their root mats also bind together the underwater sand dunes, effectively reinforcing them,” says Eduardo Infantes, a marine biologist at the University of Gothenburg and the lead author of the study which has been published in the journal Marine Ecology Progress Series. More powerful storms in the future Common eelgrass is a seagrass species that grows along Sweden’s coasts, and there are areas with large seagrass meadows growing on the bottom sediments, such as in Skåne. In other places, the seagrass has disappeared altogether. This not only represents an ecological loss, it can also mean that the coast becomes more vulnerable to erosion. As the climate changes, storms risk becoming more powerful, which in turn can lead to an increase in coastal erosion. Approximately 8% of the world’s population live in areas at an elevation of fewer than 10 meters above sea level. Rising sea levels may see many people affected by coastal erosion. “This is why it is even more important to preserve those seagrass meadows that still exist today and to replant seagrass in those places where it has disappeared. In our research, we have made successful attempts to restore common eelgrass meadows on the Swedish west coast, but if such replanting efforts are to succeed, there is a need for detailed studies of the current status seabed environment,” says Eduardo Infantes. In this study, the researchers took samples of sandy sediments with and without common eelgrass from a number of sites and placed them in a large tank capable of simulating waves. The experiments demonstrated that the sand is eroded far less by waves when seagrass is growing in it. The researchers also took samples from muddy seabeds but found that the effect of the seagrass there was less. However, this matters less since muddy seabeds are most commonly found in fjords and other areas that are less exposed to waves. More factors in field tests The next step will be to move out of the laboratory environment and take measurements of sand erosion on an exposed shoreline along the coast. Other factors such as currents, traffic on the water, inflows from rivers etc. can then affect the erosion. “It’s more complicated in the field, but we have created realistic storm waves in our experiments and the seagrass has clearly shown a protective effect against erosion. I think we will be able to demonstrate the similar effects in field tests,” says Eduardo Infantes. More information: E Infantes et al, Seagrass roots strongly reduce cliff erosion rates in sandy sediments, Marine Ecology Progress Series (2022). DOI: 10.3354/meps14196
“The downward trajectory of the world’s seagrass meadows must be reversed if we are to fight the planetary crisis” say leading seagrass scientists. The United Nations Sustainable Development Goals have recently been described as “the most important to-do list in the history of humankind”. Scientists from Project Seagrass and Swansea University have this week published a unique review that demonstrates how this “To-Do List” of Sustainable Development Goals provides a blueprint for achieving the net recovery of seagrass ecosystems. Conserving and restoring seagrass meadows contributes to achieving 16 out of the 17 Sustainable Development Goals. Recognising this wide role of seagrass meadows in helping achieve humanity’s ‘to-do list’ and thinking beyond their value in carbon sequestration and storage is critical to achieving the recovery of these degraded ecosystems. The call for urgent action comes after a review into the status of seagrass ecosystems and the major ecological role that they play in the coastal environment published in the leading academic journal Science and written by experts at the marine conservation charity Project Seagrass and Swansea University. Seagrass meadows are being increasingly looked to as a climate solution. However, seagrass ecosystems are sensitive to stressors and remain threatened across the globe. These degraded seagrass ecosystems are less effective at supporting biodiversity and tackling climate change. The authors state “Society needs to create meaningful pathways to net gain at local to global scales. Bold steps are needed through improved legal instruments to halt damaging factors such as bottom trawling, prevent use of damaging boating activities and to apportion responsibility for poor water quality that is causing the slow death of seagrass globally”. By recognising that seagrass meadows contribute to finding solutions to global problems such as food insecurity, water quality, wellbeing and gender equality, as well as the more well known issue such as biodiversity loss and climate change there becomes a more holistic view as to the benefits of taking large cumulative levels of action at local, regional and global scales. We need local and regional authorities to create a baseline of where seagrasses are now, where they used to be and where in the future they could be allowed to recover and be restored to get seagrass on the path to recovery. This needs to occur within the next decade if we are to fight climate change, to fight the biodiversity crisis, protect our coastlines and maintain global food security. Richard Unsworth (lead author) said “The world needs to rethink the management of our coastal environment that includes realistic compensation and mitigation schemes that not only prevent damage, but also drive the restoration, enhancement and creation of seagrass habitat. We also need a major shift in how we perceive the status of our marine environment by examining historical information, not just recent ecological baselines”. Ben Jones, a fellow author of the study added, “It is vital to work collaboratively as it is only through utilising scientific environmental studies and working as cogs in a global partnership for seagrass that meaningful change can happen”. Seagrass conservation faces substantial ecological, social and regulatory barriers and requires strong cross-sectoral partnerships to be put on the path to recovery. Identifying the solutions to seagrass conservation and restoration has never been more urgent and is critical to fight the planetary emergency. This can be achieved by using the Sustainable Development Goals as a blueprint towards recovery. Read the paper here.
Deep evolution casts a longer shadow than previously thought, scientists report in a new paper published the week of Aug. 1 in the Proceedings of the National Academy of Sciences. Smithsonian scientists and colleagues looked at eelgrass communities—the foundation of many coastal marine food webs along the north Atlantic and Pacific coasts—and discovered their ancient genetic history can play a stronger role than the present-day environment in determining their size, structure and who lives in them. And this could have implications for how well eelgrasses adapt to threats like climate change. About a half-million years ago, when the world was warmer, some eelgrass plants made the difficult journey from their homes in the Pacific to the Atlantic. Not all the plants were hardy enough to make the journey across the Arctic. For those that succeeded, a series of ice ages during the Pleistocene Epoch further affected how far they could spread. Those millennia-old struggles left lasting signatures in their DNA: Even today, eelgrass populations in the Atlantic are far less genetically diverse than those in the Pacific. Still, in the classic “nature versus nurture” debate, scientists were stunned to discover that genetic legacy sometimes does more to shape modern eelgrass communities than the current environment. “We already knew that there was big genetic separation between the oceans, but I don’t think any of us ever dreamed that that would be more important than environmental conditions,” said Emmett Duffy, marine biologist with the Smithsonian Environmental Research Center and lead author of the report. “That was a big surprise to everybody.” Eelgrasses in hot water Eelgrass is among the most widespread shallow-water plants in the world. Its range spans from semi-tropical regions like Baja California all the way to Alaska and the Arctic. Besides providing food and habitat for many undersea animals, eelgrass offers a plethora of services to humans. It protects coastlines from storms, soaks up carbon and can even reduce harmful bacteria in the water. But in most places where it grows, eelgrass is the dominant—or only—seagrass species present. That makes its survival critical to the people and animals that live there. And the lower genetic diversity in the Atlantic could make it hard for some populations to adapt to sudden changes. “Diversity is like having different tools in your tool belt,” said Jay Stachowicz, a co-author and ecologist with the University of California, Davis. “And if all you’ve got is a hammer, you can put in nails, but that’s about it. But if you have a full complement of tools, each tool can be used to do different jobs more efficiently.” Ecologists have already seen eelgrass disappearing from some regions as the waters heat up. In Portugal, its southernmost spot in Europe, eelgrass has begun pulling back and moving farther north, into cooler waters. “I don’t think that we’re going to lose [eelgrass] in the sense of an extinction,” said co-author Jeanine Olsen, an emeritus professor at the University of Groningen in the Netherlands. “It’s not going to be like that. It’s got lots of tricks up its sleeve.” But local extinctions, she pointed out, are going to occur in some places. That could leave regions that depend on their local eelgrass in trouble. Reaching a more ZEN worldview Realizing the urgent need to understand—and conserve—eelgrass worldwide, Duffy and his colleagues banded together to form a global network called ZEN, which Project Seagrass was a partner of. The name stands for Zostera Experimental Network, a nod to eelgrass’s scientific name, Zostera marina. The idea was to unite seagrass scientists all over the world, doing the same experiments and surveys, to get a coordinated global picture of seagrass health. For the new study, the team studied eelgrass communities at 50 sites in the Atlantic and Pacific. With 20 plots sampled per site, the team came away with data from 1,000 eelgrass plots. First they collected basic eelgrass data: size, shape, total biomass and the different animals and algae living on and around them. Then they collected genetic data on all the eelgrass populations. They also measured several environmental variables at each site: temperature, the water’s saltiness and nutrient availability, to name just a few. Ultimately, they hoped to discover what shaped eelgrass communities more: the environment or the genetics? After running a series of models, they discovered a host of differences between the Atlantic and Pacific eelgrass ecosystems—differences that closely aligned with the genetic divergence from the Pleistocene migration and subsequent ice ages. While Pacific eelgrasses often grew in “forests” that regularly surpassed 3 feet tall and sometimes reached more than twice that high, the Atlantic hosted more diminutive “meadows” that rarely came close to that height. The genetic differences also aligned with the total biomass of eelgrass. In the Atlantic, evolutionary genetics and the present-day environment played equally strong roles in eelgrass biomass. In the Pacific, genetics had the upper hand. These impacts flowed up to other parts of the ecosystem as well. When it came to small animals that lived in the eelgrass, like invertebrates, the genetic signature from the Pleistocene again played a stronger role than the environment in the Pacific—while the two played equally strong roles in the Atlantic. “The ancient legacy of this Pleistocene migration and bottleneck of eelgrass into the Atlantic has had consequences for the structure of the ecosystem 10,000 years later,” Duffy said. “Probably more than 10,000.” Conserving the future That ancient genetics can play such a strong role—sometimes stronger than the environment—has some ecologists concerned about whether eelgrass can adapt to more rapid changes. “Climate warming—by itself—is probably not the primary threat for eelgrass,” Olsen said. Pollution from cities and farms, which can cloud the water and lead to harmful algal blooms, also endangers seagrasses. That said, the vast array of environments eelgrass can survive in testifies to its hardiness. “I’m hopeful because our results illustrate long-term resiliency to repeated, major changes in thermal tolerances and the wide range of eelgrass habitats over about half the Northern Hemisphere,” Olsen said.
A new study shows that seagrass fisheries provide a reliable safety-net for poor fishermen, since they perceive those habitats to maintain large fish catches over time. Surprisingly, even more so than coral reef fisheries, which people normally associate with small-scale fishery. Seagrass meadows are routinely used as a fishing habitat across the Indo-Pacific region to sustain millions of households by providing fish and other animals for food and income from fishing. A new study in Ocean and Coastal Management investigated how and why households use seagrass meadows across Cambodia, Tanzania, Sri Lanka and Indonesia in the Indo-Pacific region by conducting interviews that asked what habitats they used and which they preferred. Benjamin Jones, director of Project Seagrass and PhD student at the Department of Ecology Environment and Plant Sciences, Stockholm University, says: “Seagrass was the most common habitat used for fishing. Nearly half of all households we talked to preferred fishing in seagrass over other habitats such as coral, mangroves, open ocean, mud and rock for example. This was surprising because most people think of reef fisheries as the key tropical small-scale fishery, but we show that its actually engagement in seagrass fisheries that are much more characteristic of households.” When the researchers asked the fishermen why they preferred seagrass, they expressed a general feeling of reliability: seagrass meadows always provide large catches and fish and invertebrates are always found there. This is likely due to the ecological role that seagrass meadows play for fish. They provide valuable nursery habitats with lots of places for fish to hide and grow which means that there is often a high abundance of fish present. The study also revealed that 3 in 20 people across the region were reliant on seagrass meadows as their fishing ground and did not fish anywhere else. The research from households in 147 villages also revealed that reliance on seagrass meadows was strongly influenced by household income: “Household income had two different effects. On one hand, poorer households were less likely to own motorboats. These were reliant on seagrass as they were unable to fish elsewhere, seagrass is close to shore and easy to access without a motor. On the other hand, wealthier households were more likely to own certain types of fishing gear that incentivized them to use seagrass due to high rewards and low effort requirements. These were static fishing fences that don’t require a fisherman to be present” says Benjamin Jones. Study co-author and fellow Project Seagrass director Leanne Cullen-Unsworth, says “Our results highlight the need for empirical household scale data for management of seagrass meadows. People use and value seagrass for many different reasons so safeguarding seagrass is vital to ensure that all people, all of the time, have equitable and equal access to the resources seagrass provides.” The study was a collaboration between scientists from Stockholm University, Project Seagrass, Swansea University, Uppsala University, Hasanuddin University, among others. Open Access paper: Jones, B.L.H.; Unsworth, R.K.F.; Nordlund, L.M.; Eklöf, J.S.; Ambo-Rappe, R.; Carly, F.; Jiddawi, N.S.; La Nafie, Y.A.; Udagedara, S.; Cullen-Unsworth, L.C. Dependence on seagrass fisheries governed by household income and adaptive capacity. Ocean & Coastal Management 2022, 225, doi:10.1016/j.ocecoaman.2022.106247.
