Study reveals widgeongrass has replaced eelgrass as the dominant seagrass species in Chesapeake Bay
Mangroves are growing in areas historically dominated by salt marshes and oyster reefs. Invasive pacific oysters are replacing native blue mussels in the Wadden Sea. Macroalgae are exhibiting dominance over hard corals in the Caribbean and Indo-Pacific. Climate change-driven shifts in dominant, habitat-forming species such as these can have significant implications for conservation, and this is a phenomenon that seems to be particularly prevalent for seagrass systems around the world. In research published today in the Proceedings of the National Academy of Sciences, VIMS researchers and their collaborators evaluate the causes and consequences of a new dominant seagrass species rising in the Chesapeake Bay, demonstrating both new threats and management opportunities. For this study, the authors combined 38 years of data on nutrient and sediment pollution from runoff, temperature, plankton blooms, and river flow with aerial seagrass surveys to describe the causes and consequences of shifting seagrass foundation species across 26,000 hectares of habitat in Chesapeake Bay. Demonstrated shifts in seagrass create faster recovery but larger die-offs across Chesapeake Bay Marine heatwaves and poor water clarity in Chesapeake Bay over the last few decades have cut the area occupied by the previously dominant seagrass, eelgrass, in half. At the same time, successfully implemented nutrient reductions throughout the bay have encouraged the rapid expansion of another seagrass, the cosmopolitan widgeongrass. Confined to a fringing area of shallow brackish waters until the mid 1990s, widgeongrass has now replaced eelgrass as the most abundant seagrass in Chesapeake Bay by expanding over 150% due to both high temperature-tolerance and long-lasting seeds that allow for rapid recovery after disturbance. “Widgeongrass’ recovery and expansion ability is so strong,” explains lead author Hensel, “that ideal widgeongrass conditions have fueled two record-setting peaks for Chesapeake Bay seagrass cover. In fact, much of the nearly 300% increase in Bay plants since the mid 1990s has been widgeongrass expansion into areas that eelgrass has vacated.” However, some negative consequences from the shift have concerned habitat managers. “We’ve seen periods of rapid widgeongrass expansion and retraction for decades now, far beyond what we’ve documented for eelgrass,” says Landry, co-author and leader of the Chesapeake Bay Program’s Submerged Aquatic Vegetation (SAV) Workgroup. “But now that widgeongrass has become so widespread in the bay, its fluctuating abundance can have a big impact on our overall acreage trends and on our Bay-wide restoration goal attainment. That’s the management concern. The ecological concern is the impact those fluctuations are having on the animals that have grown to depend on widgeongrass for habitat in the absence of eelgrass.” The causes of these fluctuations have been difficult to understand because widgeongrass and eelgrass appear to respond differently to climate change and nutrient pollution stressors. Yet when the authors examined long-term, large-scale data on climate stressors and watershed pollution from agriculture and development in tandem with year-to-year aerial survey imagery of seagrass meadows, they recognized an important shift in the dominant climate stressor for Chesapeake Bay seagrass: while widgeongrass is resistant to heatwaves and high temperatures, it is highly vulnerable to periods in spring when high rains can bring huge influxes of nutrient- and sediment-loaded water into the bay, reducing water clarity. “This study is an important step forward in building our knowledge of human-ecosystem interactions along the coast and how they are changing over time,” says author Lefcheck. “Our past work showed a record-setting resurgence of underwater grasses in response to nutrient management, but now we are seeing that the story is vastly more complex and in fact, is still being written. Understanding, adapting to, and communicating this shifting narrative is a challenge, but not an insurmountable one by any stretch.” Conserving species with different needs simultaneously is necessary, complex The team’s modeling contributes to a greater understanding of both human and climate drivers of annual changes in widgeongrass and highlights a crucial difference in management compared to an eelgrass-dominated bay. “Heatwave stress is uncontrollable on a local and regional level,” explains Patrick, Director of the SAV Monitoring Program at VIMS, “but managing the amount of nutrients that enter the bay from the watershed during a rainy spring is something that we can actually control.” This study underscores that, because species differ in their traits and stressor sensitivities, managing for conservation of living habitats requires more community- or species-focused research, monitoring, and actions under climate change. Climate change is shifting the landscape of species composition, creating new winners in these novel environments, and management needs to shift alongside them. Detailed monitoring data allow agencies to focus on each species and encourages them to manage for community or individual habitat requirements, adapting strategies as species composition changes. This study also demonstrates pitfalls that can occur if habitat forming species are lumped together into single “stocks,” such as “hectares of seagrass” or “acres of marsh.” In fact, differences between the seagrass species in this study explain many of the shifts in Chesapeake Bay seagrass meadow dynamics. “Widgeongrass has shorter, thinner blades than eelgrass,” says Hensel, “which makes it more vulnerable to springtime run-off events because sunlight can’t reach the short blades through the clouded, nutrient-loaded water. Also, widgeongrass’ shallower root system may not sequester carbon as well and its tendency to wildly fluctuate in cover means that it may not provide consistent habitat for key seagrass-dependent species like Blue Crabs and Black Sea Bass.” The authors call for a parallel shift in coastal monitoring and evaluation of management successes and failures, using the Chesapeake Bay as an example. They cite the necessity of long-term monitoring programs with coordinated and standardized on-the-ground and detail-oriented surveys, as well as the importance of community or species-specific recovery goals across coastlines where multiple seagrass species co-occur and respond to climate differently. “This is a compelling example of the how climate change is unfolding across the globe,” said Patrick. “As regional climates shift, the emergence of novel ecosystems is fundamentally challenging everything we think we know from analysis of historical data. The rules governing the dynamics of the world’s ecosystems are changing and
What causes decline of tropical seagrass meadows?
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
Seagrass meadows show resilience to ‘bounce back’ after die-offs
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
It’s an ill bird that fouls its own nest
[vc_row type=”in_container” full_screen_row_position=”middle” scene_position=”center” text_color=”dark” text_align=”left” overlay_strength=”0.3″ shape_divider_position=”bottom” bg_image_animation=”none”][vc_column column_padding=”no-extra-padding” column_padding_position=”all” background_color_opacity=”1″ background_hover_color_opacity=”1″ column_link_target=”_self” column_shadow=”none” column_border_radius=”none” width=”1/1″ tablet_width_inherit=”default” tablet_text_alignment=”default” phone_text_alignment=”default” column_border_width=”none” column_border_style=”solid” bg_image_animation=”none”][vc_column_text] Nearly 30,000 tonnes of sewage containing human waste is to enter the UK despite potential problems for human health. Yet, what stinks for me is that sewage and livestock waste are driving seagrass loss across the UK – we already have a problem, and we don’t need to exacerbate this. Back in 2018, we released a study documenting this problem and called on the government to make changes – but water companies, some farmers and the Government have not, and it would appear are still not, doing enough to address theses risks. While the EU’s landmark legislation to improve bathing water quality has been a success in many places, much of what we do in the UK is woefully insufficient. Many seagrass meadows around the UK are in areas with designated EU protection. Protection on paper, but not in practice. Many seagrass meadows around the UK are polluted with nutrients derived from human sewage and livestock waste. Adding excessive amounts of nutrients to the environment, like spreading sewage liberally over fields, leads to those nutrients leeching out and into our rivers. Transported downstream to our coasts, these nutrients are a nightmare for seagrass leading to excessive growth of tiny algae called epiphytes which smother seagrass, leading to its death. Dead seagrass means no carbon sequestration, and in many cases dead seagrass means carbon emissions. Dead seagrass also means a loss of habitat for juvenile fish such as cod, herring and plaice, and dead seagrass means no coastal protection. Sewage puts all the benefits that seagrass provide to humans at risk. Farming is likely the UK’s leading cause of water pollution. Inefficiencies in the storage and disposal of sewage slurry mean that it ends up in rivers and coastal waters. Dr Andrew Singer, a senior scientist at the world-renowned Centre for Ecology and Hydrology, has said that there are no rivers in the UK that is safe to be swimming in. It’s clear then that there are some pretty systematic issues in the way we deal with sewage and livestock waste across the UK. Add on top of this the health issues that even the Environment Agency themselves acknowledge and you have a recipe for something that stinks. At the moment, we really don’t know whether spreading human sewage is safe or not for our food, according Alistair Boxall, a professor in environmental science at the University of York. It’s an ill bird that fouls its own nest.[/vc_column_text][/vc_column][/vc_row]
Global fisheries threatened by loss of seagrass
Seafood consumption is both a love and a necessity for hundreds of millions of people all across the world. And the supply of seafood is a key part of maintaining food security for the whole planet. But as demand for seafood is increasing, stocks of wild fish and invertebrates (such as mussels and prawns) are declining. A major problem is that policies and plans designed to ensure the sustainability of our fisheries almost exclusively target fishing activity. But we also need to protect the critical habitats that these fisheries also depend on. Most species that are fished require more than one habitat to complete their lifecycles. For example Atlantic cod (Gadus morhua) spends its adult life shoaling in deep water, but juveniles require more stable habitat where they can hide such as seagrass meadows. So, if we want to manage stocks for sustainability, it is essential to protect the supporting habitats of targeted species. Seagrass meadows are a critical habitat supporting biodiversity and in turn the productivity of the world’s fisheries. Seagrass meadows are not only suitable for juvenile fish but also for larger fish of different species. As seagrass meadows occur in shallow, clear waters, they are an easily exploitable fishing habitat. Today, we published the first quantitative global evidence on the significant roles that seagrasses play in world fisheries . Seagrass as nursery grounds: provide a safer, less exposed, environment for eggs to be laid and young animals to find food and protection from predators as they grow. This includes commercial species such as tiger prawns, conch, Atlantic cod and white spotted spinefoot. In fact, one-fifth of the world’s most landed fish — including Atlantic Cod and Walleye Pollock benefit from the persistence of extensive seagrass meadows. Seagrass as a fishing area: it is not just large scale fishing industries that benefit from the presence of seagrass meadows. They are an easily accessible fishing ground used by small scale artisanal and subsistence fisheries around the world. Seagrass gleaning: seagrass is also essential habitat for gleaning activity, fishing for invertebrates such as sea cucumbers in water that is shallow enough to walk in. This is often done by women and children, and provides a source of essential protein and income for some of the most vulnerable people in tropical coastal communities. It is a common and increasingly visible activity, but it is not usually included in fishery statistics and rarely considered in resource management strategies. Seagrass supports other fisheries: seagrass also provides trophic support to other fisheries. They do this by creating expansive areas rich in fauna, from which there are vast quantities of living material, organic matter and associated animal biomass that supports other fisheries. Seagrasses also promote the health of connected habitats (like coral reefs), and have the capacity to support whole food webs in deep sea fisheries. Threats to seagrass, fisheries and food security: the coastal distribution of seagrass means that it is vulnerable to a multitude of land and sea derived threats. These include land runoff, coastal development, boating activity and trawling. On a global scale, seagrass is rapidly declining and when seagrass is lost associated fisheries and their stocks are likely to become compromised with profound and negative economic consequences. Seagrass meadows support global fisheries production Pdf Supporting policy and action is needed now! The importance of seagrass meadows for fisheries productivity and hence food security is not reflected by the policies currently in place. Urgent action is needed if we want to continue enjoying the benefits that healthy and productive seagrass meadows provide. Fisheries management must be broadened from just targeting fishing activity to also targeting the habitats on which fisheries depend. Awareness of the role of seagrass in global fisheries production, and associated food security, must be central to policy, and major manageable threats to seagrass, such as declining water quality, must be dealt with. Action is urgently needed to protect the worlds seagrass meadows if we are to continue to enjoy the benefits they provide.
Sewage and livestock waste is killing Britain’s seagrass meadows
Britain’s seagrass is a refuge for numerous species of fish, stabilises sandy beaches, and helps to lock away the carbon which humans produce. The meadows that surround the country’s coast have been called the “canaries of the sea”, due to their sensitivity to a changing environment. And like a canary in a coal mine, their health can be used as an indicator of the condition of coastal areas. We know that the seagrass meadows surrounding the UK are in a perilous state of decline, and our recently published research has now uncovered one of the biggest causes. Our study suggests that a major driver of seagrass decline is nutrient pollution from sewage and livestock waste. Though a new finding, it sadly comes as no surprise, given that about 40% of rivers in England and Wales are polluted with sewage. This nutrient pollution puts the long term viability of seagrass meadows in doubt. Over-enrichment results in the suffocation of seagrass. The nutrients cause microscopic algae – called epiphytes – to smother the seagrass leaves, decreasing their ability to capture light, ultimately killing them, and destroying the habitat for fish and other marine animals. Â The seagrass, Zostera marina, covered in epiphytes. In addition to this environmental impact, we found that several areas, including the Thames waterway seagrass, and a meadow in Studland Bay, Dorset – which are popular with swimmers and boaters – were considerably enriched in nutrients from sewage, livestock effluent and/or human waste. Despite this, neither location, nor any other we identified with the same problem, were classed as unsuitable for swimmers. Outdated treatment Clearly, we have a massive problem at hand – but water companies, farmers and the government have not done and are still not doing enough to prevent it. Though efforts have been made to develop a British marine protected area network, and EU legislation has improved water quality in the last few decades, we have found these initiatives to be insufficient. Ten of the 11 sites we studied were in areas with designated EU protection, but most of these seagrass meadows were still polluted with nutrients derived from urban sewage and livestock waste. So how has this happened? Analysis of the seagrass tissues points to constant sewage exposure. Old and outdated water treatment facilities are one of the likely culprits, resulting in discharges of untreated sewage during times of heavy rainfall. These are legal, but evidently the capacity of these facilities is insufficient to handle the country’s needs, and waterways are suffering because of it. There is also the problem of livestock waste. Farming is now one of the UK’s leading causes of water pollution, and inefficiencies in storage and disposal of slurry mean that it ends up in rivers and coastal waters. Local and national Evidently, in addition to national and international initiatives, we need to start quickly identifying and understanding all local threats to seagrass. Especially if we are going to harmonise conservation goals with sustainable economic development. Only by finding out specifically where the nutrients affecting seagrass areas have come from can we really start to think about a targeted solution for each meadow. Unfortunately, to date, the conservation of specific seagrass meadows is rarely based on the explicit consideration of local threats and drivers. Instead, projects focus on conserving seagrass as part of a broader plan, incorporating other specific habitats or species. While this may be effective at dealing with problems such as fisheries impacts, and is certainly a step forward for the marine environment, it doesn’t deal with the persistent and chronic problem of pollution – which can go largely unnoticed. Poor water quality isn’t just a problem for seagrass in the British Isles, it’s a global concern. But if we want to solve it, we must look beyond “protecting” seagrasses with legislation, and challenge the way we think about marine protection overall. Serious infrastructure changes and better management of river catchments – for example, restoration of riverbanks – are vital if we are going to develop long term waste water management plans that span both land and sea. You can read the study, Tracking Nitrogen Source Using δ15N Reveals Human and Agricultural Drivers of Seagrass Degradation across the British Isles, here. This article was originally published on The Conversation. Read the original article.
How hurricanes such as Irma and Maria can devastate the Caribbean marine environment
 Hurricane Irma – one of the strongest on record to hit the Caribbean – recently scoured the islands leaving catastrophic damage in its wake. And just as we began to piece together the devastating and potentially long–term impacts of Irma, Hurricane Maria has now left another path of destruction. Puerto Rico, the British dependency of the Turks and Caicos, and many other Caribbean islands have suffered what have been described as “apocalyptic conditions”. When the world talks of the tragic and devastating consequences of severe hurricanes, the focus tends to be on the land, and the people who live in affected communities. Indeed, nearly 30 people have been reported killed, while Puerto Rico Resident Commissioner Jenniffer Gonzalez has said that the hurricane has set the country back by “20 to 30 years”. We see images of toppled trees, torn off roofs and severe flooding. But marine environments can be also badly affected by hurricanes, with potential long-term effects. The force of hurricane winds, and the resultant tides and waves are so strong that both plants and animals are ripped from the sea floor leaving lifeless rubble and sediment behind. Hurricanes have a washing machine effect: they mix up coastal sediments with knock-on effects for marine life. Suspended matter left floating in the water column limits the amount of sunlight that reaches marine habitats and so reduces growth and recovery. Meanwhile in shallow coastal environments, debris, sewage and run-off continue to flow in to the sea long after the hurricane has passed. Human dependency on the sea  The fishery for Queen Conch (Strombus gigas) is a major source of income to many around the Caribbean. The devastation of coastal environments, particularly seagrass meadows, can also result in long-term losses of the benefits that humans receive from them, such as fisheries support or coastal protection. Damage to these ecosystem services consequently impacts human well-being, because people can no longer rely on them for their livelihood and food supply. Some of the most severely affected areas of the recent hurricanes in the Caribbean – Florida, Turks and Caicos, Puerto Rico, Cuba and the British Virgin Islands – all house extensive seagrass meadows. These shallow water marine habitats support valuable lobster fisheries, as well as shrimp, conch, and finfish fisheries. Seagrass also stabilises sediments and protects the white sand beaches that attract so many tourists to the region. Previous hurricanes, cyclones, and typhoons (weather events which are essentially the same but have different names depending on where the storm happens) across the globe have shown the severe negative effects they can have on these vital seagrass meadows. The seagrass plants are ripped up or buried under sediments, leading to their suffocation. The extensive associated murky water leads to widespread loss of seagrass, as was seen in the years that followed hurricane Katrina hitting the US. Initial indications from the Everglades in Florida show that seagrass destruction in the wake of Irma is extensive, with large piles already being washed far onshore. This should ring alarm bells for Caribbean fisheries, as hurricanes Katrina and Rita led to losses in the seafood industry that reached billions of dollars. The Caribbean spiny lobster fishery business alone is worth more than US$450m, and directly employs 50,000 people. Healthy seagrass provides the best fishing grounds with the greatest revenue, and the recent hurricanes have the potential to decimate this. Environmental impact But this is not just about money. Seagrass loss also threatens marine biodiversity and the health of charismatic species. After a severe cyclone in Australia in 2011, turtles and dugong starved due to the damaged meadows. In addition, seagrass is a marine powerhouse, which stores vast amounts of carbon in meadow sediments. When the seagrass is removed, this carbon is released back into the environment.  Caribbean spiny lobsters depend on clams they find in seagrass. Hurricanes have always been a part of life in tropical seas. The destruction they cause and their recovery have been observed throughout human history. What is alarming now, however, is the apparent increased frequency and intensity. The already poor state of the Caribbean marine environment restricts the ability of habitats such as seagrass meadows and coral reefs to recover from the effects of severe storms. Poor water quality and over-fishing, for example, promotes the overgrowth of algae, preventing recovery. With repeated hurricanes occurring over time periods that are insufficient for recovery to occur, this will only get worse. The severity of hurricanes Irma and Maria are a wake up call. We need a fundamental shift in how marine environments are protected to enable long-term sustainability for the food and income they provide. Many locations in the Caribbean, for example Puerto Rico, have ineffective marine protection rules and so destructive practices continue unchecked, meaning that when a disaster does occur, the environment is unable to recover. Although local actions against climate change are difficult to achieve, it is possible to manage river catchments to improve water quality, and focus on small scale immediate actions, such as implementation of marine protected areas to limit immediate and direct damage to coastal resources. Coordinated small scale actions will ultimately help enhance the resilience of the Caribbean Sea, and make sure that the environment can better recover from any future extreme events. Richard K.F. Unsworth, Research Officer (Marine Ecology), Swansea University; Benjamin L. Jones, Research Assistant at the Sustainable Places Research Institute, Cardiff University; Leanne Cullen-Unsworth, Research Fellow, Cardiff University, and Lina Mtwana Nordlund, Researcher in coastal environmental sciences, Stockholm University This article was originally published on The Conversation. Read the original article.