Academic literature on the topic 'Seagrass loss'

SummaryMany natural and human-induced events create disturbances in seagrasses throughout the world, but quantifying losses of habitat is only beginning. Over the last decade, 90000 ha of seagrass loss have been documented although the actual area lost is certainly greater. Seagrasses, an assemblage of marine flowering plant species, are valuable structural and functional components of coastal ecosystems and are currently experiencing worldwide decline. This group of plants is known to support a complex trophic food web and a detritus-based food chain, as well as to provide sediment and nutrient filtration, sediment stabilization, and breeding and nursery areas for finfish and shellfish.We define disturbance, natural or human-induced, as any event that measurably alters resources available to seagrasses so that a plant response is induced that results in degradation or loss. Applying this definition, we find a common thread in many seemingly unrelated seagrass investigations. We review reports of seagrass loss from both published and ‘grey’ literature and evaluate the types of disturbances that have caused seagrass decline and disappearance. Almost certainly more seagrass has been lost globally than has been documented or even observed, but the lack of comprehensive monitoring and seagrass. mapping makes an assessment of true loss of this resource impossible to determine.Natural disturbances that are most commonly responsible for seagrass loss include hurricanes, earthquakes, disease, and grazing by herbivores. Human activities most affecting seagrasses are those which alter water quality or clarity: nutrient and sediment loading from runoff and sewage disposal, dredging and filling, pollution, upland development, and certain fishing practices. Seagrasses depend on an adequate degree of water clarity to sustain productivity in their submerged environment. Although natural events have been responsible for both large-scale and local losses of seagrass habitat, our evaluation suggests that human population expansion is now the most serious cause of seagrass habitat loss, and specifically that increasing anthropogenic inputs to the coastal oceans are primarily responsible for the world-wide decline in seagrasses.

Seagrasses are unique marine flowering plants that play an important ecological role by yielding primary production and carbon sequestration to the marine environment. Seagrass ecosystems are rich in organic matter, supporting the growth of bio-medically important epi and endophytic microorganisms and harbor rich marine biodiversity. They are an essential food source for endangered Andaman state animal Dugongs. Seagrasses are very sensitive to water quality changes, and therefore they serve as ecological bio-indicators for environmental changes. The benthic components in and around the seagrass beds support a significant food chain for other Micro and organisms apart from fishery resources. The epiphytic bacterial communities of the leaf blades support the sustenance against the diseases. Recent reports have shown that the loss of seagrass beds in tropical and temperate regions emphasizes the depletion of these resources, and proper management of seagrass is urgent. The decline of seagrass will impact primary production, biodiversity, and adjacent ecosystems, such as reefs. Therefore, restoring the seagrass meadows could be possible with effective implementing management programs, including seagrass meadows in marine protected areas, restoration projects, seagrass transplantation, implementation of legislative rules, monitoring coastal water quality and human activities in the coastal zone. Lacunas on the seagrass ecosystem management in Andaman & Nicobar Islands are addressed.

Coastal, reef-associated and deepwater (> 15 m) seagrass habitats form a large and ecologically important community on the Queensland continental shelf. Broad-scale resource inventories of coastal seagrasses were completed in the 1980s and were used in marine park and fisheries zoning to protect some seagrasses. At least eleven of the fifteen known species in the region reach their latitudinal limits of distribution in Queensland and at least two Halophila species may be endemic to Queensland or northeastern Australia. The importance of seagrasses to Dugongs Dugong dugon, Green Turtles Chelonia mydas and commercially valuable prawn fisheries, will continue to strongly influence directions in seagrass research and conservation management in Queensland. Widespread loss of seagrasses following natural cyclone and flood events in some locations has had serious consequences to regional populations of Dugong. However, the impacts to Queensland fisheries are little studied. Agricultural land use practices may exacerbate the effects of natural catastrophic events, but the long-term impacts of nutrients, pesticides and sediment loads on Queensland seagrasses are also unknown. Most areas studied are nutrient limited and human impacts on seagrasses in Queensland are low to moderate, and could include increases in habitat since modern settlement. Most impacts are in southern, populated localities where shelter and water conditions ideal for productive seagrass habitat are often targets for port development, and are at the downstream end of heavily modified catchments. For Queensland to avoid losses experienced by other states, incremental increases in impacts associated with population and development pressure must be managed. Seagrass areas receive priority consideration in oil spill management within the Great Barrier Reef and coastal ports. Present fisheries legislation for marine plant protection, marine parks and area closures to trawl fishing help protect inshore seagrass prawn nursery and Dugong feeding habitat, but seagrasses in deep water do not yet receive any special zoning protection. Efficacy of the various Local, State and Commonwealth Acts and planning programmes for seagrass conservation is limited by the expanse and remoteness of Queensland's northern coast, but is improving through broad-based education programmes. Institutional support is sought to enable community groups to augment limited research and monitoring programmes with local "habitat watch" programmes. Research is helping to describe the responses of seagrass to natural and human impacts and to determine acceptable levels of changes in seagrass meadows and water quality conditions that may cause those changes. The management of loss and regeneration of sea grass is benefiting from new information collected on life histories and mechanisms of natural recovery in Queensland species. Maintenance of Queensland's seagrasses systems will depend on improved community awareness, regional and long-term planning and active changes in coastal land use to contain overall downstream impacts and stresses.

Seagrasses cover about 0.1–0.2% of the global ocean, and develop highly productive ecosystems which fulfil a key role in the coastal ecosystem. Widespread seagrass loss results from direct human impacts, including mechanical damage (by dredging, fishing, and anchoring), eutrophication, aquaculture, siltation, effects of coastal constructions, and food web alterations; and indirect human impacts, including negative effects of climate change (erosion by rising sea level, increased storms, increased ultraviolet irradiance), as well as from natural causes, such as cyclones and floods. The present review summarizes such threats and trends and considers likely changes to the 2025 time horizon. Present losses are expected to accelerate, particularly in South-east Asia and the Caribbean, as human pressure on the coastal zone grows. Positive human effects include increased legislation to protect seagrass, increased protection of coastal ecosystems, and enhanced efforts to monitor and restore the marine ecosystem. However, these positive effects are unlikely to balance the negative impacts, which are expected to be particularly prominent in developing tropical regions, where the capacity to implement conservation policies is limited. Uncertainties as to the present loss rate, derived from the paucity of coherent monitoring programmes, and the present inability to formulate reliable predictions as to the future rate of loss, represent a major barrier to the formulation of global conservation policies. Three key actions are needed to ensure the effective conservation of seagrass ecosystems: (1) the development of a coherent worldwide monitoring network, (2) the development of quantitative models predicting the responses of seagrasses to disturbance, and (3) the education of the public on the functions of seagrass meadows and the impacts of human activity.

Due to climate change and human activities, seagrass is in crisis as the coverage of seagrass declines at an accelerated rate globally. In this paper, the severe challenges of seagrass ecosystem were briefly reviewed, including adverse effects of natural factors and human activities on seagrass beds. The research status of pollutants and pollution in seagrass bed ecosystem was reviewed, the future research directions in related fields were proposed as well. The eutrophication in coastal waters and discharge of pollutants such as sulfide, heavy metals, organic matter and microplastics caused by human activities are important reasons for seagrass loss. In addition, environmental stressors lead to reduced immunity and decreased resistance of seagrass to various pathogens, leading to seagrass wasting diseases. Future studies concerning the influence of novel pollutants, i.e., plastic waste on non-native algae, microorganisms and seagrasses, as well as their interrelationships, will be of vital importance. In addition, researches on seagrass wasting diseases and their pathogens should be much accounted in China, to fill in gaps in related fields and improve the response ability to emergent seagrass diseases. In conclusion, this review was proposed to arouse the concern about the seagrass bed pollution, and provide possible enlightening information for the protection and restoration of this significant ecosystem.

The seagrass community are angiosperm plant communities that mostly grow in shallow marine waters. The community has an ecological role and function, both as a habitat for various types of biota and as a carbon sink. The purpose of this study was to determine the type and condition of the seagrass ecosystem in Kelapa Island based on the percentage of cover; and to determine the estimated carbon stocks of seagrasses contained. Seagrass community data collection was carried out in September-October 2020 in the waters of Kelapa Island, Bima Regency, West Nusa Tenggara Province. A quadratic transect was used for data collection of seagrass cover, and analysis of seagrass community cover using the PhotoQuad application, followed by determining the condition of the seagrass community ecosystem, and analysis of estimated carbon storage using the Loss On Ignition (LOI) method. The results showed that there were 4 types of seagrass found, consisting of: Thalassia hemprichii, Halophila ovalis, Cymodocea rotundata, and Halodule pinifolia. The percentage of seagrass cover is 52.31%, because it is less than 60%, the health status of seagrass beds is unhealthy based on the Decree of the Minister of the Environment Number 200 of 2004. Total carbon storage is 16.1 gr.Cm-2. Thalassia hemprichii as the highest carbon storage species was 8.27 gr.Cm-2.

This study was conducted to determine the types of seagrasses and calculate biomass and calculate how much carbon absorption in seagrasses was found in the location of Tongkaina Beach, Bunaken District, Manado City, North Sulawesi. The sampling procedure in the field is the method of cruising surveys. A cruising survey is a sample collection method that is carried out by walking through the coastal area of all seagrasses found. After the sampling at the site is completed, the sample in the inventory is then photographed. The samples that have been obtained are analyzed in the laboratory using the loss on ignition (LOI) method. The results of the study on Tongkaina coastal waters covering an area of 25,000 meters with a coastal length of ±500 meters, in an area parallel to the coastline as wide as ±50 meters towards the sea and six types of seagrasses were obtained, namely: Enhalus acoroides, Thalassia hemprichii, Syringodium isoetifolium, Cymodocea rotundata, Halodule uninervis, and Halodule pinifolia. The biomass in seagrasses found had an average value of 78.10% with the highest individual seagrass biomass found in seagrass type Enhalus acoroides with a biomass value of 87.23grams of dry weight (gbk)/individual and the lowest type of seagrass individual biomass value was found in seagrass type seagrass with a biomass value of 66.67grams of dry weight (gbk)/individual. The total carbon content calculated in the entire seagrass obtained was 46,0941gCKeywords: Tongkaina Beach; seagrasses; biomass; carbon absorptionAbstrakPenelitian ini dilakukan untuk mengetahui jenis-jenis lamun dan menghitung biomassa serta menghitung berapa serapan karbon pada lamun yang ditemukan dilokasi Perairan Pantai Tongkaina Kecamatan Bunaken Kota Manado Provinsi Sulawesi Utara. Prosedur pengambilan sampel di lapangan menggunakan metode survei jelajah. Survei jelajah adalah metode pengumpulan sampel yang di lakukan dengan cara menyusuri daerah pantai terhadap semua lamun yang ditemukan. Setelah pengambilan sampel di lokasi selesai, sampel di inventarisir kemudian difoto. Sampel yang telah diperoleh dianalisa di laboratorium dengan menggunakann metode loss on ignition (LOI). Hasil penelitian pada perairan pantai Tongkaina seluas 25.000 meter dengan panjang pantai ±500 meter sejajar garis pantai dan lebar ±50 meter ke arah laut. Ditemukan enam jenis lamun yaitu: Enhalus acoroides, Thalassia hemprichii, Syringodium isoetifolium, Cymodocea rotundata, Halodule uninervis dan Halodule pinifolia. Biomassa pada lamun yang ditemukan memiliki nilai rata-rata 78,53% dengan biomassa individu lamun tertinggi terdapat pada lamun jenis Enhalus acoroides dengan nilai biomassa mencapai 87,23gram berat kering (gbk)/individu dan nilai biomassa individu jenis lamun terendah terdapat pada lamun jenis Syringodium isoetifolium dengan nilai biomassa 66,67gram berat kering (gbk)/individu. Untuk total kandungan karbon yang dihitung pada keseluruhan lamun yang didapat sebesar 46,0941gC.Kata kunci: Pantai Tongkaina; Lamun; biomasa, serapan carbon

Macroherbivory is an important process in seagrass meadows worldwide; however, the impact of macroherbivores on seagrasses in the Great Barrier Reef (GBR) has received little attention. We used exclusion cages and seagrass tethering assays to understand how the intensity of macroherbivory varies over space and time in the seagrass meadows around Green Island (Queensland), and what impact this has on overall meadow structure. Rates of macroherbivory were comparatively low, between 0.25–44% of daily seagrass productivity; however, rates were highly variable over a one-year period, and among sites. Loss of seagrass material to macroherbivory was predominantly due to fish; however, urchin herbivory was also taking place. Macroherbivory rates were of insufficient intensity to impact overall meadow structure. No macroherbivory events were identified on video cameras that filmed in the day, indicating that feeding may be occurring infrequently in large shoals, or at night. While relatively low compared to some meadows, seagrass macroherbivory was still an important process at this site. We suggest that in this highly protected area of the GBR, where the ecosystem and food webs remain largely intact, macroherbivory was maintained at a low level and was unlikely to cause the large-scale meadow structuring influence that can be seen in more modified seagrass systems.

Abstract Seagrass ecosystem is natural objects that can be used to adapt and mitigate climate change through blue carbon sequestration. There are 16 seagrass species in Indonesia and the high diversity of these species supports the high potential of carbon that can be absorbed and stored. This study aimed to develop a general equation to estimate seagrass aboveground carbon stock (AGC) from the percent cover (PC), and to map seagrass AGC using PlanetScope imagery in Nemberala, Rote Island. Nemberala has very diverse seagrass species such as Enhalus acoroides (Ea), Cymodocea rotundata (Cr), Halophila ovalis (Ho), Syringodium isoetifolium (Si), Thalassodendron ciliatum (Tc) and Thalassia hemprichii (Th). The results of laboratory analysis to obtain the value of carbon stocks using the Loss on Ignition method from each species were 0.016, 0.004, 0.001, 0.002, 0.001, and 0.0001 (gC/leaf) for Ea, Th, Cr, Si, Tc, and Ho, respectively. The general equation for predicting AGC from PC is SeagrassAGC = (0.051*SeagrassPC) – 0.635 with r of 0.61 and R2 of 0.36. This formula will be applied to convert field seagrass PC data to AGC, which will then be used to train and test the accuracy of seagrass AGC mapping based on PlanetScope SuperDove 8 bands image.

Experiments were undertaken to differentiate between abiotic and biotic factors affecting seagrass growth. Monospecific patches of both Zostera marina and Zostera japonica were transplanted into one shallow subtidal and three intertidal sites at Roberts Bank, British Columbia. In transplanted patches, initiated in 1988, neither Z. marina nor Z. japonica showed any consistent differences in either population growth or mean shoot length among the sites. Abiotic environmental conditions could therefore not be considered responsible for the differences observed between the natural vegetation of the respective monospecific zones and the zone of naturally mixed seagrass vegetation. In a manipulation experiment, opaque and clear plastic seagrass canopies were imposed on Z. japonica vegetation and the resulting growth was compared with treatments of a natural Z. marina canopy and removal of the natural canopy. The artificial seagrasses combined with the patch layout of the experiment did not create the shade conditions intended and may have facilitated the loss of shoots. The results were not conclusive, but there were consistently higher densities of Z. japonica in the treatment where Z. marina had been removed. Interactions between these two seagrasses in their vegetative phase may contribute to the observed differences in population and morphological characters, but the dispersal and establishment phases remain to be studied. Key words: Zostera marina, Zostera japonica, seagrass, competition, transplants, artificial seagrass.

As climate change continues, climactic extremes are predicted to become more frequent and intense, in some cases resulting in dramatic changes to ecosystems. The effects of climate change on ecosystems will be mediated, in part, by biotic interactions in those ecosystems. However, there is still considerable uncertainty about where and how such biotic interactions will be important in the context of ecosystem disturbance and climactic extremes. Here, I review the role of consumers in seagrass ecosystems and investigate the ecological impacts of an extreme climactic event (marine heat wave) and subsequent widespread seagrass die-off in Shark Bay, Western Australia. Specifically, I compare seagrass cover, shark catch rates, and encounter rates of air breathing fauna in multiple habitat types before and after the seagrass die-off to describe post-disturbance dynamics of the seagrass community, shifts in consumer abundances, and changes in risk-sensitive habitat use patterns by a variety of mesoconsumers at risk of predation from tiger sharks (Galeocerdo cuvier). Finally, I conducted a 16 month field experiment to assess whether xi loss of top predators, and predicted shifts in dugong foraging, could destabilize remaining seagrass. I found that the previously dominant temperate seagrass Amphibolis antarctica is stable, but not increasing. Conversely, an early-successional tropical seagrass, Halodule uninervis, is expanding. Following the die-off, the densities of several consumer species (cormorants, green turtles, sea snakes, and dugongs) declined, while others (Indo-Pacific bottlenose dolphins, loggerhead sea turtles, tiger sharks) remained stable. Stable tiger shark abundances following the seagrass die-off suggest that the seascape of fear remains intact in this system. However, several consumers (dolphins, cormorants) began to use dangerous but profitable seagrass banks more often following seagrass decline, suggesting a relaxation of anti-predator behavior. Experimental results suggest that a loss of tiger sharks would result in a behaviorally mediated trophic cascade (BMTC) in degraded seagrass beds, further destabilizing them and potentially resulting in a phase shift. My work shows that climactic extremes can have strong but variable impacts on ecosystems mediated in part by species identity, and that maintenance of top predator populations may by important to ecological resilience in the face of climate change.

Estuaries are dynamic environments that are strongly affected by natural variability, as well as direct and indirect anthropogenic impacts. A better understanding of the drivers of carbon fluxes and biogeochemical variability in estuarine systems is needed, particularly with the increasing threat of ocean acidification. Morro Bay in Central California is a small nationally protected estuary, with seasonally low freshwater inputs. Since 2007, the bay has experienced a significant loss of native seagrass, Zostera marina, which is an important component of the marine ecosystem. Because seagrass photosynthesis decreases carbon dioxide and increases oxygen in the water column, the loss of seagrass has the potential to substantially change short-term carbonate chemistry and long-term carbon fluxes of an estuary. The spatial variability of carbonate chemistry was measured in Morro Bay using ship-board surveys during the low-inflow summer season and measured the temporal variability by collecting samples close to the shore from July to November. Discrete samples show an increase in total alkalinity and dissolved inorganic carbon in the mid and back bay regions, historically dominated by seagrass. Slightly lower total alkalinity and dissolved inorganic carbon were observed in the Fall season compared to the low-inflow Summer season. Analysis of the relative modification of alkalinity and dissolved inorganic carbon, paired with salinity and temperature data, contributes to an understanding of the drivers of the observed carbonate variability. This understanding may provide clues to the causes and effects of observed changes to the bay with seagrass loss. More broadly, it will inform the vulnerability of other low-inflow estuaries to future acidification and highlight the role seagrasses play in mitigating local acidification.

The study documents seagrass patch dynamics over large spatial extents in Tampa Bay, Florida. Using GIS techniques a set of fine scale seagrass maps was created within locations previously identified as "patchy" seagrass or areas of seagrass loss. Thirty randomly selected landscape windows of various extents were mapped for the years 2004, 2006, and 2008 by visualizing 0.3 m resolution color imagery on-screen at a digitizing scale of 1:500 using a minimum mapping unit of 1 m2. Characteristics of seagrass patches and patterns of seagrass change were quantified using area-based and time interval metrics including total seagrass area, percent change in seagrass area, seagrass percent cover, and number of patches. Patterns of change were then reviewed at multiple levels of spatial organization and multiple temporal scales. Results from seagrass mapping generated from the fine scale (1 m2 resolution) and previously-reported broad scale (2.02 ha resolution) mapping approaches were also compared. The study documented seagrass patches ranging in size from 1 m2 to greater than 10,000 m2. The fine scale mapping data reported a net increase in seagrass cover from 2004 to 2008. However, only 19 landscape windows were either stable in cover or contributed to the gains in seagrass documented during the study. The remaining 11 landscape windows exhibited various temporal patterns in seagrass loss where patch contraction, complete patch mortality, seagrass fragmentation, and seagrass gap formation were all documented. Results from fine scale mapping indicate that the amount of total seagrass patch area represented by locations categorized as "patchy" in broad scale mapping were, on average, 44 percent less than estimated by the broad scale maps. Together these findings provide new information on how different mapping techniques may produce variable views of seagrass dynamics.

Biology
Ph.D.
Examining how ecological processes are influenced by spatial variation can provide valuable insights into how communities are formed and how they may change in dynamic landscapes. In this thesis I address three objectives surrounding the spatial and temporal variation in species’ recruitment and predation, the influence of habitat isolation on consumer-resource relationships, and the influence of habitat fragmentation on a multi-trophic system. I used marine invertebrates, specifically crustaceans, bivalves, and sessile species as a model system. First, I address the spatial and temporal variation in local and regional processes in a multispecies assemblage of marine sessile invertebrates. Using diverse communities of marine sessile invertebrates as a model system I tested the hypothesis that spatial and temporal variation in recruitment and predation would shape local communities, and that both recruitment and predation would have significant effects on the abundance and structure of adult communities. I found that both recruitment and predation vary through time and space leading to the emergence of regional community divergence. I also address how habitat isolation interacts with top-down and bottom-up processes in seagrass ecosystems. Spatial structure of the habitat may mediate top-down and bottom-up controls of species abundances through decreased habitat connectivity and increased habitat isolation. I manipulated top down and bottom up processes by excluding mesograzers, adding resources, or altering both factors in isolated and contiguous patches of artificial seagrass. I then measured epiphyte recruitment, epiphyte abundances, and macroalgae abundance. I paired this with epiphyte sampling from isolated natural seagrass patches. I found that habitat isolation significantly decreased the abundance of epiphytes settling on seagrass blades due to dispersal limitation for epiphytic invertebrates. I found that consumers had strong effects on epiphyte biomass in continuous habitats, but not isolated habitats. Resource additions increased macroalgae cover and epiphyte biomass only in isolated habitats. The results suggest that isolated habitats may be nutrient limited and that top-down effects are stronger in continuous habitats, while bottom-up effects may dominate in isolated habitats. In my third objective, I address how habitat fragmentation may alter marine food webs. I examined whether predation rates, prey, and predator behavior differed between continuous and fragmented seagrass habitat in a multi-trophic context at two sites in Barnegat Bay, NJ. I hypothesized that blue crab predation rates and foraging would decrease in fragmented seascapes, due to a reduction in adult blue crab densities, increasing survival rates of juvenile blue crabs and hard clams. I expected hard clams to exhibit weaker predator avoidance behavior in fragmented habitats because of decreased predation. I found that species’ responses to fragmentation were different based on trophic level. Clams experienced higher predation and burrowed deeper in continuous habitats at both sites. Densities of blue crabs, the primary predator of hard clams, were higher in continuous habitats at both sites. Predation on juvenile blue crabs was significantly higher in fragmented seagrass at one site. Our results suggest that in fragmented seascapes, the impact of fragmentation on higher trophic level predators may drive predation rates and prey responses across the seascape, which may lead to trophic cascades in fragmented habitats.
Temple University--Theses

Les phanérogames marines sont un compartiment biologique fondamental au bon maintien des environnements côtiers grâce aux nombreux services écosystémiques qu’elles fournissent. Au cours des dernières décennies, leur surface a été considérablement réduite à l’échelle mondiale, entraînant la perte de leurs fonctions régulatrices, notamment des conditions hydrodynamiques et des flux sédimentaires. Dans ce contexte, cette thèse s’attache à mieux comprendre la réponse des processus hydro-sédimentaires des lagunes côtières peu profondes au déclin d’espèces intertidales, à travers l’étude régionale de l’effet de la régression des herbiers de zostères (Zostera noltei et Zostera marina) du Bassin d’Arcachon. Cette analyse a été menée grâce à de la modélisation numérique, qui a nécessité de développer et mettre en place une plateforme de modélisation bio-hydro-sédimentaire, constituée de quatre modèles couplés (modèle hydrodynamique, modèle de vagues, modèle de transport sédimentaire et modèle de croissance des zostères), prenant tous en compte l’influence de la végétation. Une attention particulière a été portée à l’implémentation de la végétation dans le modèle de vague et le modèle de transport, en utilisant des approches combinant expériences en laboratoire, de terrain et de la modélisation numérique. Dans un premier temps, l’influence de la régression des herbiers de zostères a été étudiée sur les conditions hydrodynamiques et a révélé d’importantes modifications de l’hydrodynamique tidale et des conditions de vagues, notamment l’intensification des vitesses sur le fond de l’ordre de 100 % et de la hauteur de vagues de 50 % sur les estrans où les herbiers ont le plus décliné. Ensuite, la contribution de la régression des herbiers sur la modification de l’hydrodynamique tidale a été comparée à celle induite par la reconfiguration des Passes, montrant que le déclin des herbiers a été le principal responsable de la modification des vitesses sur les estrans et chenaux à l’intérieur du Bassin. En réponse au déclin de Zostera spp., ainsi qu’à l’intensification des conditions hydrodynamiques qui en a résulté, cet environnement a subi d’importantes modifications de la dynamique sédimentaire. Les flux d’érosion et de dépôt ont été particulièrement impactés par le déclin, générant des concentrations en matières en suspension de 2 à 6 fois plus importantes. La régression des herbiers a également perturbé les échanges sédimentaires entre la lagune et l’océan ouvert, ainsi qu’entre les différentes zones du Bassin, donnant lieu à une redistribution des différentes classes sédimentaires et à la modification de la composition du sédiment superficiel. Les estrans situés le long des côtes ont eu tendance à s’accréter et à s’envaser, alors que les estrans plus centraux ont eu tendance à s’éroder et devenir plus sableux. En particulier, nous avons montré que la régression des herbiers est le principal responsable des évolutions bathymétriques observées à l’intérieur du Bassin. Enfin, l’évolution potentielle des herbiers de zostères a été étudiée à travers différentes conséquences du changement climatique que sont la hausse du niveau marin et l’évolution des températures de l’air et de l’eau. Une attention particulière a été portée à la génération de forçages environnementaux futurs, reproduisant les éventuelles températures et le niveau marin à l’horizon 2050. La biomasse des herbiers a témoigné de réponses contrastées à ces deux processus, très dépendantes de plusieurs facteurs environnementaux (profondeur, exposition à l’hydrodynamique, temps de renouvellement). Nous avons également montré que, plus que l’augmentation des températures moyennes, c’est l’augmentation de la fréquence et de l’intensité des événements extrêmes de température qui devrait être le principal facteur de contrôle des évolutions de biomasse dans le Bassin d’Arcachon
Seagrass meadows provide numerous ecosystem services and constitute a fundamental biological component for the sustainability of coastal environments. Over the past decades, the surface colonized by seagrasses has drastically declined globally, reducing their capacity to regulate hydrodynamic conditions and sediment fluxes. In this context, this work aims to better understand the response of hydro-sedimentary processes to the decline of intertidal seagrass in a shallow coastal lagoon. For this purpose, the Arcachon lagoon (France), extensively colonized by seagrass meadows (Zostera noltei and Zostera marina), was used as a study area. This analysis was conducted through a numerical modeling approach that required the preliminary development and implementation of a hydro-bio-sedimentary modeling platform, consisting of four coupled models (flow model, wave model, sediment transport model, and seagrass growth model), all accounting for the effect of vegetation. Specific attention was paid to the implementation of vegetation in the wave and sediment models, utilizing combined numerical, field, and laboratory experiments. The impact of seagrass decline was first studied on hydrodynamics, revealing significant changes in tidal hydrodynamics and the wave regime, especially an intensification in bottom current velocities by 100% and wave height by 50% on the tidal flats. Further investigation into the relative influence of seagrass decline and morphological evolutions of the inlet on tidal hydrodynamics showed that vegetation loss was the main factor influencing the modification of current velocities inside the lagoon. In response to the decline of Zostera spp. and the subsequent intensification of hydrodynamic conditions, this environment underwent significant changes in sediment dynamics. Modification of erosion and deposition fluxes resulted in suspended sediment concentrations 3 to 6 times higher in the areas where vegetation decreased the most. Seagrass decline also impacted sediment transport between the lagoon and the open ocean, as well as among different areas of the lagoon, leading to the redistribution of the different sediment classes and altering the composition of the seabed sediment. The tidal flats located along the coastlines accreted and became siltier, while those in the center of the lagoon eroded and became sandier. In particular, our results demonstrated that seagrass decline was the primary contributor to the observed bathymetric changes in the lagoon. Finally, potential evolutions of marine phanerogams were investigated, considering various consequences of climate change such as sea level rise and increase of temperature. For this analysis, special consideration was given to generating environmental forcing that reproduces potential temperature and water level conditions by 2050. Seagrass biomass exhibited contrasting responses to these processes, clearly dependent on multiple environmental factors (depth, hydrodynamic exposure, renewal time). We also showed that, beyond global warming, it is the increase in frequency and intensity of extreme temperature events that are expected to induce the most significant changes in seagrass biomass

AbstractSeaweeds, Cyanobacteria, seagrasses and mangroves are the principal inshore primary producers in the southern basin of the Arabian Gulf. Of these the seaweeds are by far the most diverse with about 120 species recorded from those Emirates bordering the region. Little is still known of the seaweed floras of the two Emirates within the Gulf of Oman (Fujairah, Sharjah). Briefly discussed are the very extensive cyanobacterial mats association with inshore sedimentary environments. Described are the bands of seaweeds, cyanobacteria and sessile animals that are a feature of the intertidal of rocky shores. Much consideration is given to the striking forest-like community that develops seasonally on shallow and often seaward sloping rocky platforms. Large foliose brown seaweeds are the canopy dominants of this community that develops rapidly over the months of lowest sea temperature (‘winter’). Many of these seaweeds decay and are lost during the early summer resulting in a striking transformation of the seascape when the understory of smaller mat/turf-forming and crustose coralline seaweeds becomes evident. Since the late 1990s there has been a ‘phase shift’ with seaweeds replacing stony corals as the spatial dominants on many rocky platforms. The ecological significance of the large biomass of dead and decaying seaweed produced in early summer is discussed. Briefly mentioned are seaweeds as providers of ecosystem services.

Restoration of ecosystems is becoming an increasingly essential aspect of tropical and subtropical marine conservation. Seagrass and coral reefs provide a variety of ecological facilities, including nursery habitat, better water quality condition, coastline protection, and carbon sequestration. Ecological restoration is receiving more attention as a conservation tactic, hence methods to improve restoration success must be explored. Impacts of human activity pose a danger to seagrass, coral reef and the vital ecological services they provide worldwide. To create an environment in which restoration activities are likely to be successful, proper conservation management is necessary before the start of restoration operations. In order to address the fast changes and loss brought on due to climate change and numerous directly human-related impacts, restoration must be seen as a crucial element of our ecosystems long-term viability.

Abstract Anthropogenic threats to shallow-water coastal ecosystems such as coral reefs, seagrass beds, mangroves, intertidal mud flats, rocky shores, and beaches (among others) are numerous. Addressing the serious issue of marine and coastal degradation in Indonesia will require development and implementation of new management plans for the coastal and marine sector, and integrated marine and coastal zone management is the key process. “What is evident from, a number of case studies, such as Kepulauan Seribu (Brown 1986), Jakarta Bay (Tomascik et al. 1994; Suharsono and Tuti 1994) and the inner Ambon Bay, is that side-stepping current environmental issues and spending limited resources to speculate about issues such as the upcoming climate change is questionable, since many shallowwater ecosystems will be lost even before any significant changes in sea level rise are manifested.

The great majority of marine ecosystems in Qatar are in fast decline and nearing collapse, where most ecosystem has lost the biological and economic functionality. Aiming to support the decision makers in the management and restoration strategies for recovering the biological and economic functionality of the ecosystems/natural resources of Qatar, we conducted 1) a typology mapping of the main components of the ecosystem of two islands, 2) a sensitivity and vulnerability assessment according to the known guidelines and standards. Highlighting the potential ecological risk and required recommendations for sustainable management plans, within the frame of Qatar National Vision 2030 (QNV 2030). The Islands present different anthropogenic pressure. As expected, Al Alyia the coastal Island is under real risk, with critical areas of sensibility but still presenting a potential for recovering its economy and ecological functionality, highlighting the collapsed stage of the very sensitive coral reefs, the vulnerability of oyster beds and seagrass and the functionality of the mangrove (expanding) and Sabha with massive birds nesting. The offshore Island Halul presented in the typology mapping the coral reefs as the main ecosystem but with the presence of seagrass, algae bed, sandy beach, and Sabha. The coral reef still presents a certain functionality, with corals covering several hard substrates, however with high sensitivity and high vulnerability, especially the coral in the shallow areas with scattered colonies, and the vulnerable nesting of marine turtles on beaches. As the management, we recommend increasing the restoration effort of targeted ecosystems, mainly involving coral reefs for increasing the marine biodiversity in general and restoring the oyster beds for recovering the filtration service. Strategies must be made for recovering the ecosystems’ functionality and restore the productivity of the Qatari fishing stock. We recommend applying this mapping method and sensitivity classification for all marine areas around Qatar for supporting the management plans.