How eelgrass spread around the world
Seagrasses evolved from freshwater plants and use sunlight and carbon dioxide (CO2) for photosynthesis and are able to thrive in depths down to 50 meters. In contrast to algae, they possess roots and rhizomes that grow in sandy to muddy sediments. The grass-like, leaf-shoots produce flowers and complete their life cycle entirely underwater. Seeds are negatively buoyant but seed-bearing shoots can raft, thus greatly enhancing dispersal distances at oceanic scale. As a foundational species, eelgrass (Zostera marina) provides critical shallow-water habitats for diverse biotas and also provides numerous ecosystem services including carbon uptake. Seagrasses have recently been recognized as one of the important nature-based contributions to store carbon in the ocean. The sediment below seagrass meadows can sequester between 30 and 50 times more carbon annually that the roots of forests on land. Unfortunately, the continuing loss of seagrass beds worldwide—including eelgrass—is of acute concern. An international group of researchers, including Richard Unsworth and coordinated by Professor Thorsten Reusch, Head of the Research Division Marine Ecology at GEOMAR Helmholtz Centre for Ocean Research Kiel, used complete nuclear and chloroplast genomes from 200 individuals and 16 locations to reconstruct and date the colonisation history of the eelgrass Zostera marina from its origin in the Northwest Pacific Ocean to the Pacific, Atlantic and the Mediterranean. The findings described in an article and a Research Briefing published in Nature Plants beg the question, “How well will eelgrass adapt to our new, rapidly changing climate?” Using a phylogenomic approach the scientists were able to determine that Z. marina first arose in the Japanese Archipelago region and then crossed the Pacific from west to east in at least two colonisation events, probably supported by the North Pacific Current. The scientists then applied two DNA “molecular clocks”—one based on the nuclear genome and one based on the chloroplast genome—to deduce the time when eelgrass populations diverged into new ones. The DNA mutation rate was calculated and calibrated against an ancient, whole genome duplication that occurred in eelgrass. Both nuclear and chloroplast genomes revealed that eelgrass dispersed to the Atlantic through the Canadian Arctic about 243 thousand years ago. This arrival is far more recent than expected—thousands of years versus millions of years, as is the case with most Atlantic immigrant species during the Great Arctic Exchange some 3.5 million years ago. Reusch explains, “We thus have to assume that there were no eelgrass-based ecosystems—hotspots of biodiversity and carbon storage—in the Atlantic before that time. Recency was also mirrored in an analysis of the associated faunal community, which features many fewer specialized animals in the Atlantic as compared to the Pacific eelgrass meadows. This suggests that there was less time for animal-plant co-evolution to occur.” Mediterranean populations were founded from the Atlantic about 44 thousand years ago and survived the Last Glacial Maximum. By contrast, today’s populations found along the western and eastern Atlantic shores only (re)expanded from refugia after the Last Glacial Maximum, about 19 thousand years ago—and mainly from the American east coast with help from the Gulf Stream. In addition, the researchers further confirmed the huge difference in genomic diversity between the Pacific and Atlantic, including latitudinal gradients of reduced genetic diversity in northern populations. “Both Atlantic compared to Pacific populations, and northern versus southern ones are less diverse on a genetic level than their ancestors by a factor of 35 among the most and least diverse one,” said postdoctoral scientist Dr. Lei Yu, first author of the publication, which was a chapter in his doctoral thesis. “This is due to bottlenecks arising from past ice ages, which raises concerns as to how well Atlantic eelgrass, will be able to adapt to climate change and other environmental stressors based on its genetic capacity.” “Warming oceans have already caused losses of seagrass meadows at the southern range limits, in particular North Carolina and southern Portugal. In addition, heat waves have also caused losses in shallow waters in some the northern parts of the distribution,” noted Reusch. “This is not good news because seagrass meadows form diverse and productive ecosystems, and no other species is able to take on the role of eelgrass if meadows cannot persist under future conditions.” “One possibility for restoration might be to borrow some genetic diversity from Pacific eelgrass to fortify diversity in the Atlantic. Our next step is to interrogate the eelgrass pangenome. A new reference genome from Pacific eelgrass is currently under development and should tell us more about the adaptive ecotypic capacity across its global range of habitats,” said Prof. Jeanine Olsen, emeritus professor from the University of Groningen who initiated the study and coordinated the work between the Joint Genome Institute (JGI) and the research team. More information: Yu, L. etal, Ocean current patterns drive the worldwide colonization of eelgrass (Zostera marina), Nature Plants (2023). DOI: 10.1038/s41477-023-01464-3 Story provided by Helmholtz Association of German Research Centres
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.
Seagrass meadows key fishing ground globally
Fishing in seagrass occurs around the globe; if there is seagrass (and people) there is fishing. Still, the nature and extent of fisheries in seagrass is poorly understood. It is a prerequisite for natural resource management to understand resource exploitation, therefore we decided to investigate this further. Seagrasses are plants that grow in the shallow ocean. The seagrass attracts many different types of animals, to live, forage, or seek shelter. These animals are collected by humans for subsistence (food), commercial and recreational purposes. Across the globe the reasons for fishing differs, it is more common to fish for recreational purposes in countries where the economic situation is better, while in countries with more challenged economies fishing for subsistence is very important. Interestingly, because seagrasses grow in nearshore environments, almost all types of fishing gears are used. Close to shore in many areas of the world the seagrass gets exposed during spring low tides making it possible to walk in the seagrass meadows. Many people take advantage of the low tide and walk across the seagrass meadows collecting invertebrates, such as mussels and sea cucumbers, often with bare hand or simple fishing gear like sticks. This type of fishery is commonly referred to as gleaning or invertebrate harvesting and is conducted by men, women and children. Gleaning is especially common and important for people with limited resources. Static nets are also used in the intertidal zone, the area where the tides raise and fall, catching fish when the tides come in. It is very common to use hook and line and fishing nets in seagrass. Unfortunately, very destructive fishing gears such as bottom trawls, poison, dynamite, and rakes are also occasionally used. Women and children walk across seagrass meadows at low tide in indonesia collecting resources that they can eat (Photo: Benjamin Jones) On a global scale, anything found in the seagrass that can be eaten, sold, used as bait or sold as a curio is targeted. Globally, the most commonly targeted invertebrates in seagrass appear to be crabs and bivalves (mussels). The most commonly exploited finfish from seagrass are mullet, herring, and snapper. The target species varies greatly across the globe, for example in areas with high biodiversity (many types of species), the number of target species is often higher than in areas with low biodiversity. This pattern often corresponds with colder water fewer species, warmer water more species. Species groups that are least commonly targeted are sea cucumbers, small fish for drying, aquarium trade species, seahorses, and sharks. People access the seagrass fishing grounds by walking, swimming, snorkelling, free diving, use of canoes, scuba diving, use of sailboats and motorboats. Crabs and bivalves appear to be the most commonly targeted invertebrates across the globe (Photo: Benjamin Jones) Seagrass meadows receive limited management attention compared to other nearshore marine habitats. Fisheries management does not yet target seagrass. But seagrass fisheries are diverse and important to people the world over. We, authors, hope that these findings, now systematically and scientifically investigated, will highlight the importance of seagrass for fisheries around the globe. Source: ‘Global significance of seagrass fishery activity’ by Lina Mtwana Nordlund, Richard K.F. Unsworth, Martin Gullström, Leanne C. Cullen-Unsworth. Published in Fish & Fisheries 2017. Arial footage of a nearshore environment with patchy seagrass, in the upper left corner there is a fishing boat and along the right edge there is a long fishing net deployed (blue in color), Tanzania. Drone pilot and photo LM Nordlund.
Registration for the 12th International Seagrass Biology Workshop is Now Open!
The International Seagrass Biology Workshop (ISBW) is the only international meeting specifically tailored to seagrass scientists, professionals and students. Abstract submissions are now open as are proposals for workshops. All payment is via PayPal using credit/debit cards. There is one registration fee. It covers access to all parts of the conference program, including the following: Shuttle bus from Bangor (on Sunday 16th Oct and Monday 17th Oct) and return on 21st and 22nd Oct. Welcome event Field trip (excluding option extra activities e.g. diving) Poster event Conference dinner Tea and coffee Additional local trips Onsite Wifi access Accommodation bookings will include all meals (approx. £95 pppn) and need to be paid directly to Nant Gwrtheyrn. See the Accommodation page here. For more information check out the registration page here.