Seagrasses reduce erosion of the coast and protect houses and cities from both the force of the sea and from sea-level rise caused by global warming. [13], The current documented seagrass area is 177,000km2 (68,000sqmi), but is thought to underestimate the total area since many areas with large seagrass meadows have not been thoroughly documented. The grass is eaten by turtles, herbivorous parrotfish, surgeonfish, and sea urchins, while the leaf surface films are a food source for many small invertebrates.[30]. (2019) "Social-ecological drivers and dynamics of seagrass gleaning fisheries". However, the meadows are being threatened by rising temperatures, which slows down its growth, as well as damage from anchors. Simulation of wave attenuation by quasi-flexible, seagrass-like coastal vegetation, Life history of the main habitat-forming taxa in seagrass meadows. On small islands without wastewater treatment facilities in central Indonesia, levels of pathogenic marine bacteria such as Enterococcus that affect humans, fish and invertebrates were reduced by 50 percent when seagrass meadows were present, compared to paired sites without seagrass,[49] although this could be a detriment to their survival. They prefer sheltered places, such as shallow bays, lagoons, and estuaries (sheltered areas where rivers flow in to the sea), where waves are limited and light and nutrient levels are high. [37], Seagrasses prevent erosion of the seafloor to the point that their presence can raise the seafloor. Like all autotrophic plants, seagrasses photosynthesize, in the submerged photic zone. Normally, seagrass sediments must supply oxygen to the below-ground tissue through either photosynthesis or by diffusing oxygen from the water column through leaves to rhizomes and roots. Accumulating evidence also suggests that overfishing of top predators (large predatory fish) could indirectly increase algal growth by reducing grazing control performed by mesograzers, such as crustaceans and gastropods, through a trophic cascade. Carbon sequestration rates in seagrass meadows vary depending on the species, characteristics of the sediment, and depth of the habitats, but on average the carbon burial rate is about 140 g C m2 yr1. They enhance water quality by stabilizing heavy metals and other toxic pollutants, as well as cleansing the water of excess nutrients,[26][2][1] and lowering acidity levels in coastal waters. Seagrass loss has accelerated over the past few decades, from 0.9% per year prior to 1940 to 7% per year in 1990.[72]. [13] The grasses live in areas with soft sediment that are either intertidal (uncovered daily by seawater, as the tide goes in and out) or subtidal (always under the water). [11] These seagrass meadows are highly productive habitats that provide many ecosystem services, including protecting the coast from storms and big waves, stabilising sediment, providing safe habitats for other species and encouraging biodiversity, enhancing water quality, and sequestering carbon and nutrients. [108], Dr. Fred Short of the University of New Hampshire developed a specialized transplant methodology known as "Transplanting Eelgrass Remotely with Frames" (TERF). Therefore, drag forces acting on individuals (proportional to density) are also three orders of magnitude higher, enabling relatively larger-sized propagules to be mobilized. [96] Alternatively, using buoys anchored in place, Z. marina spathes can be suspended over restoration sites in mesh bags; the spathes release and deliver the seeds to the seafloor. According to the study, seagrasses should be recognized and managed to maintain and maximize their role in global fisheries production. "A movement ecology approach to study seed dispersal and plant invasion: an overview and application of seed dispersal by fruit bats". Generally, seagrass is able to combat the sulfides by supplying enough oxygen to the roots. A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Historically, seagrasses were collected as fertilizer for sandy soil. They keep coastal waters healthy by absorbing bacteria and nutrients, and slow the speed of climate change by sequestering carbon dioxide into the sediment of the ocean floor. [26][35], Seagrasses are also ecosystem engineers, which means they alter the ecosystem around them, adjusting their surroundings in both physical and chemical ways. [98][99] Seeds are then extracted from the fruit via vigorous aeration and water movement from pumps at stable temperatures (25C) within tanks. [18][19] Recent estimates from where records exist indicate that at least 20% of the world's seagrass has been lost. Depending on environmental conditions, seagrasses can be either P-limited or N-limited. They argue that: (1) Seagrass meadows provide valuable nursery habitat to over 1/5th of the world's largest 25 fisheries, including walleye pollock, the most landed species on the planet. Landings were of major significance for local food supply and livelihoods at all sites. These include the (re)-colonization of altered or fragmented landscapes, and movement associated with climate change. [58][51], There are a variety of biotic dispersal vectors for seagrasses, as they feed on or live in seagrass habitat. [21][22], The true ecosystem-level consequences of such decline and the benefits that can be afforded through habitat restoration are poorly understood. Typical flow speeds in the ocean are around 0.1 m s1, generally one to two orders of magnitude weaker than typical atmospheric flows (110 m s1), that can limit dispersal. Laffoley, D. & Baxter, J.M. [19] Seagrasses also provide other services in the coastal zone such as preventing coastal erosion, storing and trapping carbon[20] and filtering the water column. [96] Seeds are extracted from spathes after harvesting, but the methods of extraction and delivery vary. The Role of Healthy Oceans in Binding Carbon. Seagrasses evolved from marine algae which colonized land and became land plants, and then returned to the ocean about 100 million years ago. There are four lineages of seagrasses[4] containing relatively few species (all in a single order of monocotyledon). [71], Seagrasses are in global decline, with some 30,000km2 (12,000sqmi) lost during recent decades.

(2019). (2022) "Dependence on seagrass fisheries governed by household income and adaptive capacity". In temperate areas one or a few species usually dominate (like the eelgrass Zostera marina in the North Atlantic), whereas tropical beds are usually more diverse, with up to thirteen species recorded in the Philippines. Tides, wave action, water clarity, and low salinity (low amounts of salt in the water) control where seagrasses can live at their shallow edge nearest the shore;[24] all of these things must be right for seagrass to survive and grow. P availability in Thalassia testudinum is the limiting nutrient. Seagrass meadows are currently being destroyed at a rate of about two football fields every hour.

[6] Seagrasses are habitat-forming species because they are a source of food and shelter for a wide variety of fish and invertebrates, and they perform relevant ecosystem services. This causes insufficient supply of oxygen to the belowground tissues for aerobic respiration, so seagrass must rely on the less-efficient anaerobic respiration. [39][3], Hypothesised links in NE Atlantic coastal seas (1) direct consumption of seagrass (2,3) seagrass-associated fauna(4,5) indirect links from consumption of populations benefitting from seagrass[22], Birds are an often-overlooked part of marine ecosystems, not only are they crucial to the health of marine ecosystems, but their populations are also supported by the productivity and biodiversity of marine and coastal ecosystems. Nitrogen and phosphorus can be acquired from sediment pore water or from the water column, and sea grasses can uptake N in both ammonium (NH4+) and nitrate (NO3) form. [7][8], There are about 60 species of fully marine seagrasses belonging to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the order Alismatales (in the class of monocotyledons). [51], The marine environment acts as an abiotic dispersal vector and its physical properties significantly influence movement, presenting both challenges and opportunities that differ from terrestrial environments. [12][3], Seagrass meadows are sometimes called prairies of the sea. Seagrass meadows provide coastal storm protection by the way their leaves absorb energy from waves as they hit the coast. [16] Given the wide variety of food sources provided by this productive habitat, it is no surprise that seagrass meadows support an equally wide array of grazers and predators. [78], Seagrass propagules are materials that help propagate seagrass. [63][64][51], For example, if a waterbird feeds on a seagrass containing fruit with seeds that are viable after defecation, then the bird has the potential to transport the seeds from one feeding ground to another. They also provide support by promoting the health of fisheries associated with connected habitats, such as coral reefs. [83] Nearly all species are also capable of asexual reproduction through rhizome elongation[84] or the production of asexual fragments (e.g., rhizome fragments, pseudoviviparous plantlets). Continental shelves are underwater areas of land surrounding each continent, creating areas of relatively shallow water known as shelf seas. [36] Seagrasses are not only affected by water in motion; they also affect the currents, waves and turbulence environment. Nordlund, L.M., Unsworth, R.K., Gullstrm, M. and CullenUnsworth, L.C. [87][88] These differences in biology and ecology of propagules strongly influence patterns of recruitment and dispersal, and the way they can be used effectively in restoration. These include dugongs, manatees, turtles, waterfowl, fish and invertebrates. Other methods have been trialed with limited success, including direct planting of seeds by hand, injecting seeds using machinery, or planting and deploying within hessian sandbags. Alternately, seagrasses in environments with higher loading rates and organic matter diagenesis supply more P, leading to N-limitation. (2017) "Seagrass-mediated phosphorus and iron solubilization in tropical sediments". [45], In the oceans, gleaning can be defined as fishing with basic gear, including bare hands, in shallow water not It's estimated that about half of the global fisheries get their start because they are supported by seagrass habitats. In the early 20th century, in France and, to a lesser extent, the Channel Islands, dried seagrasses were used as a mattress (paillasse) filling such mattresses were in high demand by French forces during World War I. For example, seagrasses from meadows fertilized with bird excrement have shown a higher proportion of phosphate than unfertilized meadows. [10], Seagrass meadows are found in depths up to about 50m, depending on water quality and light availability. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. [3], Archaeologists have learned from seagrasses how to protect underwater archaeological sites, like a site in Denmark where dozens of ancient Roman and Viking shipwrecks have been discovered. [32][33], Although seagrass meadows occupy only 0.1% of the area of the ocean floor, they account for 1018% of the total oceanic carbon burial. [9] Seagrasses beds or meadows can be either made up of a single species (monospecific) or mixed. Given the relatively high-per-unit area costs of marine habitat restoration,[23] making the case for such work requires a thorough examination of the ecosystem service benefits of such new habitat creation.[22]. [79] Nevertheless, the diversity of propagules and species used in restoration is increasing and understanding of seagrass seed biology and ecology is advancing. It was also used for bandages and other purposes. This method involves using clusters of plants which are temporarily tied with degradable crepe paper unto a weighted frame of wire mesh. Others produce seeds that are negatively buoyant with limited dispersal potential (e.g., Zostera and Halophila). However, today seagrass meadows are being damaged by human activities such as pollution from land runoff, fishing boats that drag dredges or trawls across the meadows uprooting the grass, and overfishing which unbalances the ecosystem. Nessa, N., Ambo-Rappe, R., Cullen-Unsworth, L.C. [27][28] Further, because seagrasses are underwater plants, they produce significant amounts of oxygen which oxygenate the water column. Tsoar A, Shohami D and Nathan R (2011). [34] Carbon primarily accumulates in marine sediments, which are anoxic and thus continually preserve organic carbon from decadal-millennial time scales. Seagrasses are flowering plants (angiosperms) which grow in marine environments. [53] Within seagrasses, propagules can weakly settle (negatively buoyant), remain effectively suspended in the interior of the water column (neutrally buoyant), or float at the surface (positively buoyant). deeper than that one can stand. [40][41][42] The links of birds to specific habitat types such as seagrass meadows are largely not considered except in the context of direct herbivorous consumption by wildfowl. [2][1] The long blades of seagrasses slow the movement of water which reduces wave energy and offers further protection against coastal erosion and storm surge. According to a 2019 paper by Unsworth et al,[45] the significant role seagrass meadows play in supporting fisheries productivity and food security across the globe is not adequately reflected in the decisions made by authorities with statutory responsibility for their management. and CullenUnsworth, L.C. The seagrass can be damaged from direct mechanical destruction of habitat through fishing methods that rely on heavy nets that are dragged across the sea floor, putting this important ecosystem at serious risk. ", Hemminga, M. A., and Duarte, C. M. (2000), Nellemann, Christian et al. They function as nursery habitats for shrimps, scallops and many commercial fish species. [80] Most others produce seeds, although their characteristics vary widely;[81] some species produce seeds or fruit that are positively buoyant and have potential for long-distance dispersal (e.g., Enhalus, Posidonia, and Thalassia). Seagrass stoichiometry does not follow the Redfield ratio commonly used as an indicator of nutrient availability for phytoplankton growth. High amounts of anthropogenic nitrogen discharge could cause eutrophication in previously N-limited environments, leading to hypoxic conditions in the seagrass meadow and affecting the carrying capacity of that ecosystem. The loss of seagrass also effects the physical characteristics and resilience of seagrass ecosystems. Catches were dominated by bivalves, sea urchins and gastropods. Their root systems also assist in oxygenating the sediment, providing hospitable environments for sediment-dwelling organisms. [76], Seagrass is both a source and a sink for oxygen in the surrounding water column and sediments. [76], Because hypoxia increases the invasion of sulfides in seagrass, this negatively affects seagrass through photosynthesis, metabolism and growth. Nutrient limitation can only occur when photosynthetic energy causes grasses to grow faster than the influx of new nutrients. [70], Nutrient variability in seagrasses can have potential implications for wastewater management in coastal environments. [77], The UNESCO World Heritage Site around the Balearic islands of Mallorca and Formentera includes about 55,000 hectares (140,000 acres) of Posidonia oceanica, which has global significance because of the amount of carbon dioxide it absorbs. They occupy shallow environments on all continents except Antarctica:[5] their distribution also extends to the High Seas, such as on the Mascarene Plateau. Fish and Fisheries". [67], An early study of seagrass stoichiometry suggested that the Redfield balanced ratio between N and P for seagrasses is approximately 30:1. [73][74] When the seagrass does not get enough sunlight, it reduces the photosynthesis that nourishes the seagrass and the primary production results, and then decaying seagrass leaves and algae fuel algal blooms even further, resulting in a positive feedback loop. [79], Seagrass restoration has primarily involved using asexual material (e.g., cuttings, rhizome fragments or cores) collected from donor meadows. Together with colleague Mike Traber (who developed a Knox gelatin matrix to encase the seeds in), they conducted a test planting at Narragansett Bay. Local ecological knowledge suggests seagrass meadows are declining in line with other regional trends. [43] This is despite the fact that both bottom-up and top-down processes have been considered as pathways for the population maintenance of some coastal birds. [48] Invertebrate gleaning (walking) fisheries are common within intertidal seagrass meadows globally, contributing to the food supply of hundreds of millions of people, but understanding of these fisheries and their ecological drivers are extremely limited. In February 2017, researchers found that seagrass meadows may be able to remove various pathogens from seawater. [69], Light availability is another factor that can affect the nutrient stoichiometry of seagrasses. In this way thousands of seedlings can be captured in less than a square meter. floating fruit), ocean surface currents freely move propagules, and dispersal distances are only limited by the viability time of the fruit,[55][56] leading to exceptionally long single dispersal events (more than 100 km),[57] which is rare for passive abiotic movement of terrestrial fruit and seeds. They produce seeds and pollen and have roots and rhizomes which anchor them in seafloor sand. Seagrasses can survive to maximum depths of about 60 metres. Fusi M and Daffonchio D (2019) "How Seagrasses Secure Our Coastlines". Seagrass beds provide nursery grounds and habitat to many harvested commercial, recreational, and subsistence fish and shellfish. Unsworth, R.K., Nordlund, L.M. That excessive input is directly toxic to seagrasses, but most importantly, it stimulates the growth of epiphytic and free-floating macro- and micro-algae. Seagrass meadows are major carbon sinks and highly productive nurseries for many marine species. A 2019 study by Nessa et al. They were able to plant a 400m2 (480sqyd) area in less than two hours. [97][79], For species that release seeds from fruits that float (Posidonia spp., Halophila spp. [44][22], Given the long-term decline in the population of many coastal and seabirds, the known response of many seabird populations to fluctuations in their prey, and the need for compensatory restorative actions to enhance their populations, there is a need for understanding the role of key marine habitats such as seagrass in supporting coastal and seabirds. (2009): Blue Carbon. Per hectare, they hold twice as much carbon dioxide as rain forests and can sequester about 27 million tons of CO2 annually. In addition to the direct blockage of light to the plant, benthic macroalgae have low carbon/nitrogen content, causing their decomposition to stimulate bacterial activity, leading to sediment resuspension, an increase in water turbidity, and further light attenuation. They do this by softening the force of the waves with their leaves, and helping sediment transported in the seawater to accumulate on the seafloor. [66], A number of studies from around the world have found that there is a wide range in the concentrations of C, N, and P in seagrasses depending on their species and environmental factors. [29], As shown in the image above on the left, many epiphytes can grow on the leaf blades of seagrasses, and algae, diatoms and bacterial films can cover the surface. [76], The storage of carbon is an essential ecosystem service as we move into a period of elevated atmospheric carbon levels. [45] In 2022, Jones et al[46] showed seagrass associated small-scale fisheries can provide a safety net for the poor, and are used more commonly than reef-associated fisheries across the Indo-Pacific. (2018) "Global significance of seagrass fishery activity. [96] In Chesapeake Bay several million Zostera marina seeds have been collected each year during the peak reproductive season using a mechanical harvester. For instance, plants collected from high-nutrient environments had lower C:N and C:P ratios than plants collected from low-nutrient environments. [89][90][94][79], Methods for collecting and preparing propagules vary according to their characteristics and typically harness their natural dispersal mechanisms. A major barrier to effective use of seeds in seagrass restoration is knowledge about seed quality. At night, the inner part of seagrass oxygen pressure is linearly related to the oxygen concentration in the water column, so low water column oxygen concentrations often result in hypoxic seagrass tissues, which can eventually kill off the seagrass. If the seagrass habitats are lost, then the fisheries are lost as well. [85][86] Sexually derived propagules of some species lack the ability to be dormant (e.g., Amphibolis and Posidonia), while others can remain dormant for long periods. [15] They contain complex food webs that provide trophic subsidy to species and habitats way beyond the extent of their distribution. The slower current is not able to carry the particles of sediment, so the particles drop down and become part of the seafloor, eventually building it up. However, deoxygenation causes the seagrass to be unable to supply this oxygen, thus killing it off. [59][60][61][62] Each biotic vector has its own internal state, motion capacity, navigation capacity and external factors influencing its movement. They are diverse and productive ecosystems sheltering to and harbouring species from all phyla, such as juvenile and adult fish, epiphytic and free-living macroalgae and microalgae, mollusks, bristle worms, and nematodes. [51], The primary nutrients determining seagrass growth are carbon (C), nitrogen (N), phosphorus (P), and light for photosynthesis. Seagrass leaves act as baffles in turbulent water that slow down water movement and encourage particulate matter to settle out. [11] Compared to terrestrial habitats that lose carbon stocks as CO2 during decomposition or by disturbances like fires or deforestation, marine carbon sinks can retain C for much longer time periods. [79], For species which have seeds contained within spathes (e.g., Zostera spp. High accumulation rates, low oxygen, low sediment conductivity and slower microbial decomposition rates all encourage carbon burial and carbon accumulation in these coastal sediments. ), these can be harvested using divers or mechanical harvesters. [76] Deoxygenation reduces the diversity of organisms inhabiting seagrass beds by eliminating species that cannot tolerate the low oxygen conditions. (2) In complex smallscale fisheries from around the world (poorly represented in fisheries statistics), there is evidence that many of those in proximity to seagrass are supported to a large degree by these habitats. Some fish species that visit or feed on seagrasses raise their young in adjacent mangroves or coral reefs. Hypoxia that leads to eutrophication caused from ocean deoxygenation is one of the main underlying factors of these die-offs. [109], In 2001, Steve Granger, from the University of Rhode Island Graduate School of Oceanography used a boat-pulled sled that is able to deposit seeds below the sediment surface. For example, low light environments tend to have a lower C:N ratio. This can cause the decline and eradication of seagrasses to algal dominance. [82][81] although long-distance dispersal can still occur via transport of detached fragments carrying spathes (modified leaves which enclose the flower cluster; e.g., Zostera spp.