Seagrass Habitats Research Articles

A multi-year study of acoustic propagation and ambient sound in a Thalassia testudinum seagrass meadow in a shallow sub-tropical lagoona).

Seagrasses provide a multitude of ecosystem services and act as important carbon sinks. However, seagrass habitats are declining globally, and they are among the most threatened ecosystems on earth. For these reasons, long-term and continuous measurements of seagrass parameters are of primary importance for ecosystem health assessment and sustainable management. This paper presents results from both active and passive acoustical methods for ecosystem monitoring in seagrass meadows. From a propagation perspective, gas bodies contained within the seagrass tissue as well as photosynthetic-driven bubble production result in attenuation, dispersion, and scattering of sound that produce increased transmission loss. For the passive approach, the detachment of gas bubbles from the plants is an important component of the ambient soundscape. Examples of both techniques will be presented based on data collected as part of a two-year continuous deployment of an acoustical measurement system operating in a moderately dense seagrass bed dominated by Thalassia testudinum (turtle grass) in Corpus Christi Bay, Texas. The data show annual trends related to the seasonal growth pattern of Thalassia as well as diurnal trends correlated with photosynthetically active radiation.

Using a natural capital risk register to support the funding of seagrass habitat enhancement in Plymouth Sound.

By assessing the risk to the status of seagrass assets through this approach, it is possible to determine the complementary governance actions needed to underpin investment in seagrass habitat enhancement. The methods are transferable to other locations where data exists to define the asset status. These specific findings are relevant nationally where similar vectors of risk (pressures) are identified.

Rise Up: Ecological and Social Responses to the Use of Advanced Mooring Systems to Recover Seagrass Habitat at Cawsand, England

UK recreational boating infrastructure in UK ports and harbors consistently coincides with Marine Protected Area designation. Under UK Marine Protected Area designations, vulnerable seabed habitats such as seagrass beds require protection and/or restoration. Mooring and anchoring activity has coincided with increasing concerns over the conservation status of the climate-buffering properties of seagrass beds in the literature and from empirical studies. Up until this study, there has yet to be a significant UK based trial of a number of modified moorings to see their impact on the reduction in pressure on vulnerable benthic habitats. In May 2019, we installed and tested five Advanced Mooring Systems (AMS) in Cawsand Bay, Plymouth Sound, UK. A further 10 such devices were installed in 2021 after the COVID 19 pandemic. The original five devices tested were ‘Stirling’ systems, whereby the rode is raised above the seabed by use of several submerged floats set at 1.5–2 m intervals along the chain, leading to a top mark that secures the vessel. Each AMS were attached to the seabed using helical screwpiles by commercial divers using a waterproof hydraulic wrench. The devices have held securely since May 2019, and monitoring of seagrass around these five moorings has occurred regularly (at approximately 6 monthly intervals) between May 2019 and May 2023. No seeding or transplantation to prime seagrass recovery has taken place around the base of the moorings during this period. Nevertheless, during the sixth dive survey in May 2023, 4 years after installation, a 212% increase in seagrass density was recorded within the zone previously abraded by the moorings and riser chains. Blade length of the longest seagrass shoots has also increased over the test period. Semi-structured interviews were held with participants in the trial from boat users, NGOs and government agencies to ascertain attitudes and responses to seagrass conservation and the use of AMS. Interaction with stakeholders are important to securing positive community buy-in to such interventions. We recommend that for small sailing craft and powerboats these systems provide a fit-for-purpose engineering and ecological solution to support the restoration of seagrass beds, but that such initiatives must be accompanied by significant understanding and interaction with local stakeholders.

Identifying Gaps in the Protection of Mediterranean Seagrass Habitats Using Network‐Based Prioritisation

ABSTRACTAimSeagrass meadows represent a key marine ecosystem owing to the significant biodiversity they host. Protection actions are often implemented without considering connectivity between habitats. In this article, we project and prioritise Mediterranean seagrass habitats (Posidonia oceanica and Cymodocea nodosa) based on their potential as sources/retention and stepping stones for dispersal propagules of the associated biotic communities. We use this information to identify gaps in the protection of highly ranked habitats.LocationMediterranean Sea.MethodsWe related seagrass observations with marine environmental predictors to run species distribution models and infer the distribution of Mediterranean seagrasses. We then used a network‐based approach (CONEFOR) to rank patches of seagrass suitable areas based on their contribution to the seascape in terms of patch area, potential as source/retention of propagules and stepping stone. Finally, by overlaying our ranking with the spatial distribution of marine protected areas (MPAs), we identified potential gaps in the protection of important seagrass habitats across the Mediterranean and its basins.ResultsMost of the identified patches of seagrass suitable areas are not included in MPAs, only reaching a maximum protection coverage of ~50% in the Northwestern Mediterranean. Relatively few patches contribute disproportionately to connectivity, but top‐ranked habitat patches are not included within the existing MPAs network, both at the Mediterranean scale and for most basins. The largest gaps for the source/sink role are in the Aegean and Ionian Sea, and largest gaps for the stepping stone role are in the Adriatic, Ionian and Tyrrhenian Sea.Main ConclusionsOur results suggest that the current MPAs network fails to protect highly relevant patches of seagrass suitable areas in most of the Mediterranean basins. However, this gap could be filled by a few well‐placed MPAs. Overall, we provide novel insights for the identification of key habitats and planning novel coastal MPAs in the region.

Specialists regulate microbial network and community assembly in subtropical seagrass sediments under differing land use conditions

Microorganisms in the sediment play a pivotal role in the functioning and stability of seagrass ecosystems and their dynamics are influenced by the nutrient acquisition strategies of host plants. While the distinct impacts of microbial generalists and specialists on community dynamics are recognized, their distribution patterns and ecological roles within seagrass ecosystems remain largely unexplored. To address this issue, we conducted an analysis of community assembly processes and co-occurrence relationships of both microbial generalists and specialists within sediment profiles (0–100 cm) from seagrass habitats subjected to differing land use conditions. The results revealed that seagrasses in Yifeng Estuary experienced the large proportion of cultivated land and exhibited higher organic carbon content in the 0–20 cm surface sediment layer. Nitrogen-cycling bacteria were predominantly associated with seagrasses from Yifeng Estuary, whereas Vibrio spp. was more prevalent in seagrasses from Liusha Bay. Notably, seagrass Halophia beccarii (YHB) in Yifeng Estuary harbored higher niche breadths for both microbial generalist and specialist compared to Halodule uninervis (LHU) and Halophia ovalis (LHO) from Liusha Bay. Stochastic processes were pivotal in shaping seagrass sediment microbial communities, with a higher immigration rate observed in YHB, suggesting greater microbial turnover in this area. Additionally, YHB sediment presented lower drift and higher dispersal limitation among generalists compared to LHU and LHO, whereas the pattern was reversed among specialists. Specialists were found to play a crucial role in shaping microbial interactions within YHB sediment, with genera Halioglobus identified as keystone species in the network. The specialists were further found to significantly influence microbial β-diversity in seagrass sediment directly. Overall, our findings illustrated how microbial generalists and specialists were distributed in seagrass sediments in response to land use changes and provided new insights into the potential roles of microbial regulation in degraded seagrass ecosystems.

Early seedling development and survival of seagrasses Posidonia australis and P. sinuosa using different seed‐based restoration methods

Seagrass seed‐based restoration has been developed in several places worldwide, but disturbance at the vulnerable initial stages of seedling recruitment has proved to be a major bottleneck to successful restoration. A detailed investigation of seagrass seedling survival and growth at the earliest stages of seedling development is an important contribution to developing techniques to improve seedling establishment and survival. Here, we investigated the early seedling development of Posidonia australis and P. sinuosa as well as quantifying the variation in seedling survival and development under different seed‐based restoration methods. Early seedling development was documented in indoor aquaria during the first month after fruit dehiscence. In the second ex situ experiment, we determined the effects of three different restoration methods (surface sowing, seedling planting, and planting inside a hessian bag) on seedling survival and development over the first 2 months of life. In the first experiment, a primary root with the first root hairs developed after 7 days. After 1 month, roots were 20–60 mm in length, firmly establishing the seedling into the sediment. Compared to surface sowing, seedling planting and hessian bag restoration treatments did not significantly affect survival for P. australis but increased seedling mortality in P. sinuosa, although growth was greater (shoot and root lengths were approximately 50 and 40% longer, respectively). These aquarium‐scale experiments suggest that planting methods would enhance seedling establishment at larger scales in some species, promoting restoration of damaged seagrass habitats.

Comparative analysis of seagrass habitat structure: distinct patterns at semi-enclosed and open sites in South Sulawesi, Indonesia

Habitat structure in the seagrass ecosystems are crucial for coastal biodiversity and substrate stability. The purpose of this research conducted from June to December 2021 in South Sulawesi Province, Indonesia was to examine the habitat structure of seagrass beds at two sites with different levels of exposure: Puntondo (semi-enclosed bay) and Batu Kalasi (exposed). Species identification, non-metric multidimensional scaling (nMDS), Bray Curtis cluster analysis, similarity percentage (SIMPER), Particle Size Analysis (PSA), and satellite imagery were used to evaluate complexity, heterogeneity, sediment particle size, and extent. The presence of macroalgae and coral species at Batu Kalasi, likely related to substrate condition, contributed to significant differences in seagrass community composition. The nMDS and Bray Curtis cluster analyses revealed patterns of complexity, while satellite imagery revealed habitat heterogeneity. Seagrass meadow tracking showed a larger and more patchy area in Puntondo Village, measuring 164,318 m², while in Batu Kalasi Island, it only reached 136,901 m². The findings underscore the need for tailored conservation strategies for seagrass ecosystems, in particular to address the specific challenges observed at each site, emphasizing the importance of understanding and preserving diverse coastal environments.

Evaluating UAV‐based multispectral imagery for mapping an intertidal seagrass environment

Abstract Worldwide seagrass habitats are under severe anthropogenic threat. In the United Kingdom (UK), the health of habitats of the widely distributed Zostera species is particularly threatened by eutrophication that can lead to detrimental macroalgae overgrowth. To manage and conserve seagrass habitats, effective monitoring tools are required. We use an off‐the‐shelf consumer‐grade multispectral (RGB, red edge, and near‐infrared) camera mounted on an unoccupied aerial vehicle (UAV) to map an intertidal multispecies seagrass environment in Lindisfarne National Nature Reserve, Northumberland, UK. Field surveys were undertaken of three seagrass areas, including those dominated by Zostera noltii, Zostera marina and macroalgae. Using the Maximum Likelihood Classifier (MLC), results indicated an overall accuracy (OA) between 84% and 91% across classified habitat maps. As expected, the red edge and near‐infrared bands offered an advantage beyond RGB imagery to discriminate between the vegetation types for accurate habitat mapping. Our research provides a foundation for accurately mapping a complex intertidal seagrass environment through the utilisation of an off‐the‐shelf multispectral UAV. The study may aid the implementation and development of effective monitoring programmes for the management of Zostera spp. decline and macroalgae proliferation to prevent seagrass degradation and conserve these valuable yet fragile ecosystems.

Spatial and temporal variability of fouling communities on oyster spat collectors at Inhaca Island Southern Mozambique: Exploring the influence on recruitment of the oysters Pinctada capensis and Saccostrea cucullata

In the transition from pelagic larva to benthic adult, larvae likely encounter a diverse assemblage of resident invertebrates in their habitat, which may also compete for space during post-settlement periods. Fouling fauna in rocky and seagrass habitats on Inhaca Island, southern Mozambique, was evaluated over 4 months in each of two seasons on oyster collectors fixed at 2 cm above the bottom. As expected, two species of oysters recruited to tiles: the rock oyster Saccostrea cucullata in rocky habitats and the pearl oyster, Pinctada capensis in seagrass habitats. The composition and density of other fouling fauna varied among habitats, location, seasons and surfaces and depending on the duration of the deployment. In seagrass habitats, oysters and barnacles were generally less abundant, allowing other taxa to have higher relative abundance, while higher density of individuals was recorded in rocky habitat. Barnacles dominate among fouling fauna on collectors in both habitats. Despite evidence consistent with negative interactions between oysters and barnacles, the effects of other fouling fauna on oyster abundance appear modest up to 4 months after tiles are placed. Overall, the results help improve our general understanding of the environmental processes that affect the colonisation of intertidal invertebrates, particularly in the southwestern Indian Ocean.

The Effect of Sediment Mud Content on Primary Production in Seagrass and Unvegetated Intertidal Flats

As a consequence of anthropogenic activities and climate change, accelerated terrestrial sediment runoff is causing the gradual mudification of soft sediment estuarine habitats worldwide. Increased sediment mud content (< 63 µm) has been recognised to alter seagrass morphology and cause declines in primary production in unvegetated habitats. However, the effect of increased mud content on primary production in seagrass meadows remains largely unknown. To address this, primary production in intertidal seagrass meadows (Zostera muelleri) and adjacent unvegetated habitats was measured in situ using benthic incubation chambers across an existing sedimentary gradient (nine sites spanning 5–33% mud content). An additional two unvegetated mudflat sites (39–49% mud content) were also sampled to expand the gradient. Seagrass net (NPP) and gross primary production (GPP) was greater than in the adjacent unvegetated habitat and did not vary with mud content, even after standardising GPP by photosynthesising biomass (i.e. photosynthetic efficiency). In contrast, in the adjacent unvegetated habitat, photosynthetic efficiency declined with increasing mud content. Inclusion of the additional mudflat sites negatively impacted NPP, GPP, and photosynthetic efficiency in the unvegetated habitat. Thus, while primary production in seagrass meadows may have some resilience to future increases in mud content (up to ~33%), further degradation and loss of seagrass habitats could result in the expansion of unvegetated habitats and ultimately lead to production losses, likely to be most acute in areas with high mud content (≥ 39%).

Contrast in larval sensitivity to low pH in sea urchins from neighbouring seagrass meadows at Inhaca Island, Mozambique

Ocean acidification presents a major threat to marine life, and a large body of evidence has documented its negative effects on various marine species and ecosystems. Recent meta-analyses highlight the key role of local adaptation and have linked species’ sensitivity to extremes of the present range of pH variability. More specifically, ‘physiological tipping points’ can be correlated with the lowest experienced pH where the organisms live. We verified this hypothesis by comparing the responses of larvae of the collector urchin Tripneustes gratilla originating from two neighbouring seagrass meadows at Inhaca Island in southern Mozambique. The two seagrass meadows experience different conditions: the site at the Inhaca Marine Biology Research Station (Estação de Biologia Marítima de Inhaca, EBMI) is subtidal, and the site at Banguá is intertidal. Larvae of adults collected from the two sites were cultured in the laboratory under four different target pH treatments (8.04, 7.67, 7.46 and 7.29) for 7 days. The results showed an overall negative effect of lower pH on survival and growth as well as on an index of symmetry. Larvae originating from the intertidal seagrass habitat at Banguá which experiences large pH fluctuations were more sensitive to a lower pH than those from the subtidal seagrass habitat at EBMI. This finding suggests that different mechanisms for pH tolerance and local adaptation may apply in subtidal versus intertidal environments. Consequently, the unifying principle that physiological tipping points are correlated with the extreme low pH in the present range of variability, may reach its limit in increasingly extreme environments under natural conditions.

Seagrass recovery trajectories and recovery potential in relation to nutrient reduction

Abstract Seagrass recovery has been reported across the globe where previously eutrophied waters have become less nutrient‐rich. In the European Wadden Sea, different recovery trajectories were found after riverine nutrient loads decreased, namely full, temporary and no recovery. We compiled intertidal seagrass presence (Zostera noltei and Z. marina) and eutrophication data for 1930–2020, to relate the seagrass trajectories and regional eutrophication differences to riverine nutrient loads, and inferred prospects for seagrass recovery. Seagrass fully recovered in the less eutrophic North Frisian region. The recovery trajectory was tightly coupled to riverine nutrient load reduction. Relative seagrass area (meadow area/region area) dropped from 10% prior to eutrophication to 2% during the eutrophication peak, increased to 7% during the nutrient reduction period and subsequently expanded to 13%. Colonization of marginal habitats was observed, indicating propagule spillover from neighbouring meadows. The more eutrophic southern regions showed no or only temporary seagrass recovery. Prospects for (limited) recovery are good in only two out of four southern regions, provided that riverine nutrient loads are further reduced by ~40% (reference: 2010–2017). Without this reduction, seagrasses may only temporarily recover and will remain vulnerable to erratic disturbances like macroalgae accumulation or storms. Historical evidence and application of habitat suitability models suggest that the potential relative seagrass area in the southern regions is low: less than 0.2% in the western Dutch region and maximum 2.4% in the Ems‐Jade region. Synthesis and applications. Within a large seascape (15,000 km2) the least eutrophicated region showed seagrass recovery upon nutrient reduction. We translated the critical riverine nutrient loads for this recovery, via regional eutrophication indicators, to loads that may enable a sustained recovery in the other regions. This technique is applicable in other complex systems, provided sufficient historical data are available. Propagule spillover exerts a positive feedback at metapopulation scale leading to acceleration of recovery. Occupied and potential seagrass habitat (e.g. assessed by the maximum recorded area in the past) are thus important landscape selection criteria for restoration, particularly when eutrophication is not yet sufficiently reduced.

High-resolution, precision mapping of seagrass blue carbon habitat using multi-spectral imaging and aerial LiDAR

Blue carbon ecosystems, particularly seagrass meadows, provide a myriad of critical ecosystem services through their role in supporting biodiversity, protecting shorelines, and sequestering and storing carbon. Despite their increased recognition for advancing global marine conservation efforts, our knowledge of the location and spatial extent of seagrass ecosystems globally remains relatively poor, due to the logistical and operational challenges of accurately mapping seafloor habitat using remote sensing techniques. Here we develop and validate an aerial LiDAR approach for mapping tropical seagrass blue carbon habitat in The Bahamas, by integrating full waveform bathymetric LiDAR with multi-spectral imaging. The results demonstrate accuracies between 92 and 98% for predicting seagrass types, over an extensive (e.g., >1000 km2) study area whilst utilizing robust ground-truthing techniques. These findings demonstrate the value of the aerial LiDAR approach used here for ongoing bathymetric surveys of seagrass habitat in The Bahamas and throughout similar ecosystems in the wider Caribbean, which should provide key insights for coastal management and conservation efforts.

Insights on Evaluating Commercially Important Macroinvertebrate Species in Danjugan Island Marine Reserve, Philippines

The commercial importance of benthic macroinvertebrates like echinoderms and molluscs has led to the overexploitation of wild stocks in many areas around the Philippines. Despite their ecological and economic importance, studies on the status of wild populations of commercial macroinvertebrates in unexploited habitats such as marine protected areas (MPAs) are very scarce. The diversity and abundance of commercially valuable echinoderms and molluscs in the seagrass and reefs of Danjugan Island Marine Reserve were assessed. Shallow areas (1-3 m depth) around the island were surveyed both during the day and after dusk using belt transects. A total of 226 individuals belonging to 21 different taxa were recorded during the surveys, of which 71% were molluscs and 29% were echinoderms. In the seagrass habitat, Cypraeidae, Toxopneustidae, and Conidae were the dominant families, while molluscs from the Cardiidae family comprised more than half of the total assemblage in the reef flat. The most diverse commercial macroinvertebrate group was Holothuriidae with five different species. The densities of the families were higher during dusk than during the day in both habitats, except for Cardiidae in the seagrass. The highest values of species richness and H´ index were observed during dusk surveys in the reef habitat (H´= 1.57), while the lowest was observed in seagrass areas during morning surveys (H´= 1.37). This is the first study that assessed commercially valuable macroinvertebrates during day and night in two connected habitats within a protected area. The differences in diversity and abundance in each habitat depending on the time of day highlight the importance of considering these factors when evaluating macroinvertebrate populations in unexploited areas.

Impact of Hurricane Irma on coral reef sediment redistribution at Looe Key Reef, Florida, USA

Abstract. Understanding event-driven sediment transport in coral reef environments is essential to assessing impacts on reef species, habitats, restoration, and mitigation, yet a global knowledge gap remains due to limited quantitative studies. Hurricane Irma made landfall in the Lower Florida Keys with sustained 209 km h−1 winds and waves greater than 8 m on 10 September 2017, directly impacting the Florida Reef Tract (FRT) and providing an opportunity to perform a unique comprehensive, quantitative assessment of its impact on coral reef structure and sediment redistribution. We used lidar and multibeam derived digital elevation models (DEMs) collected before and after the passing of Hurricane Irma over a 15.98 km2 area along the lower FRT including Looe Key Reef to quantify changes in seafloor elevation, volume, and structure due to storm impacts. Elevation change was calculated at over 4 million point locations across 10 habitat types within this study area for two time periods using data collected (1) approximately 1 year before the passing of Irma and 3 to 6 months following the storm's impact as well as (2) 3 to 6 months after and up to 16.5 months after the storm. Elevation change data were then used to generate triangulated irregular network (TIN) models in ArcMap to calculate changes in seafloor volume during each time period. Our results indicate that Hurricane Irma was primarily a depositional event that increased mean seafloor elevation and volume at this study site by 0.34 m and up to 5.4 Mm3, respectively. Sediment was transported primarily west-southwest (WSW) and downslope, modifying geomorphic seafloor features including the migration of sand waves and rubble fields, formation of scour marks in shallow seagrass habitats, and burial of seagrass and coral-dominated habitats. Approximately 16.5 months after Hurricane Irma (during a 13-month period between 2017 and 2019), net erosion was observed across all habitats with mean elevation change of −0.15 m and net volume change up to −2.46 Mm3. Rates of elevation change during this post-storm period were 1 to 2 orders of magnitude greater than decadal and multi-decadal rates of change in the same location, and changes showed erosion of approximately 50 % of sediment deposited during the storm event as seafloor sediment distribution began to re-equilibrate to non-storm sea-state conditions. Our results suggest that higher-resolution elevation change data collected over seasonal and annual time periods could enhance characterization and understanding of short-term and long-term rates and processes of seafloor change.

Seasonal fish larvae abundance and composition in seagrass habitats of coastal East Africa.

Seagrass habitats play a major role in fisheries productivity through nursery functions and feeding grounds for diverse fish species. However, little is known about the seasonal distribution of fish larvae at large spatial scales in coastal East Africa. We investigated drivers of the seasonal fish larvae abundance and composition in seagrass habitats in Kenya and Tanzania. We found a high diversity of fish larvae (54 families) inhabiting seagrass habitats that differed between sites and seasons. Fish larvae abundance were highest in Kenya, particularly during the northeast monsoon season. Overall, total larval abundances per site were low, reaching less than 190 individuals/100m3 in Kenya and less than 40 individuals/100m3 in Tanzania, likely related to the low productivity and strong hydrodynamic processes in this region. Our data suggests that most of the fish spawn year-round in these tropical waters as we did not find strong seasonal patterns. All sites had a high relative abundance of larvae from demersal spawning fishes, indicating that many fish species move to coastal sites for spawning. Primary productivity and dissolved oxygen, driven by hydrodynamics conditions are positively related to fish larvae productivity both in Kenya and Tanzania. These findings indicate that the occurrence of both resident and transient fish larvae in seagrass meadows is driven by strong hydrodynamic and tidal processes that transport fish larvae across adjacent habitats.

Local Variation in Feeding Ground Utilization of Dugongs (Dugong dugon) Across Two Intertidal Seagrass Beds in Talibong Island, Thailand

In this study, we describe the population characteristics and residency patterns of dugongs (Dugong dugon) across two intertidal seagrass beds in Talibong Island, Thailand: Site A, covering an area of 2.0 × 105 m2, and Site B, covering an area of 2.8 × 105 m2. Transect and individual identification surveys were conducted under clear water conditions using drones: 16 separate days over 11 months at Site A and 10 separate days over 3 months at Site B. Sixty-four individuals were identified from 180 videography sessions. The results confirmed at least two distinct patterns of seagrass habitat utilization among sites located approximately 5 km apart. Site A was characterized by a lower population density, higher year-round site fidelity, occupancy by relatively large individuals, and an absence of feeding aggregations. In contrast, Site B was characterized by a higher population density, lower site fidelity, occupancy by individuals with a wider range of body lengths, and the presence of feeding aggregations. The average population density at Site B was three to five times higher than that at Site A. Site A had a median nearest neighbor distance of 320 m with no significant bias in its distribution, whereas Site B had a median of 20 m with a significant bias. The mean site fidelity index for Site A (0.62 ± 0.08; n = 16) was significantly higher than that for Site B (0.39 ± 0.14; n = 10). Dugongs at Site A might have monopolized this site to some extent, while those at Site B might have benefited from increased opportunities for social interaction provided by aggregations. These findings highlight the importance of fine-scale monitoring of feeding ground utilization by dugongs, taking into consideration individual-specific details such as body lengths and resighting rates for a better understanding of their spatial distribution.

Vegetation Hydrodynamics To Inform Climate Mitigation And Adaptation

Coastal ecosystems, such as seagrass, provide many ecosystem services, including coastal protection and carbon sequestration, which make them an integral part of climate mitigation and adaptation (e.g., Fourqurean et al. 2012). Predicting the value of these ecosystem services requires an understanding of the interaction of fluid motion with vegetation. While seagrass meadows are recognized as global hotspots for carbon storage, the verification of seagrass carbon is complicated by significant heterogeneity. For example, Lavery et al. (2013) reported an 18-fold range in carbon stock across 17 different seagrass habitats (260 to 4800 g C m-2). This variability is a major source of uncertainty in assessing carbon stocks, motivating work to understand what drives it. Recent studies have highlighted how hydrodynamic conditions can be an important factor (e.g., Oreska et al. 2017, Novak et al, 2020). In this talk, we consider a combination of modeling and field measurement that explores the influence of wave and current conditions on carbon accretion in seagrass meadows.

Impact of Microplastic (MP) Pollution in Seagrass Ecosystem

Seagrass ecosystems are one of the vital coastal habitats that claim numerous ecological, economic, and social benefits. However, this unique underwater ecosystem is facing threats from MP (MP) pollution which is an emerging global concern. MPs are tiny, fragmented plastic bits (5mm) found all over the world. Plastics, used in daily life are frequently blindly discarded into the ocean by humans, causing harm to the marine ecosystem by lowering its quality. Since MPs can persist in the environment for a prolonged period, they can harm the environment and are difficult to eradicate. They are used by marine species, which results in their assimilation, biomagnification, and bioaccumulation in the trophic levels. The existing documentation and research on MP accumulation in seagrass habitats is remarkably limited. Additionally, taking into account more than a decade of research (from 2000 to 2023), none of the research that came out before 2017, demonstrated the severity of the issue and devoted efforts to address and manage the problem. India, is one among the nations having significant seagrass habitats. If prompt attention isn’t paid to tackling MP pollution in marine systems, it will eventually result in the disruption of seagrass beds. This review paper synthesizes current knowledge on the biological and chemical impact of MP pollution in seagrass ecosystems. This review article gives a brief idea about the seagrass ecosystems and their global as well as Indian distribution. It also explores the sources, distribution, and destiny of microplastics in various ecosystems, together with their potential ecological and biological consequences on seagrass and their associated organisms. Additionally, the paper discusses mitigation strategies and identifies critical research gaps, emphasizing the need for comprehensive studies to understand and mitigate the continuing effect of MPs on seagrass ecosystems.

Environmental DNA highlights the influence of salinity and agricultural run-off on coastal fish assemblages in the Great Barrier Reef region

Agricultural run-off in Australia's Mackay-Whitsunday region is a major source of nutrient and pesticide pollution to coastal and inshore ecosystems of the Great Barrier Reef. While the effects of run-off are well documented for the region's coral and seagrass habitats, the ecological impacts on estuaries, the direct recipients of run-off, are less known. This is particularly true for fish communities, which are shaped by the physico-chemical properties of coastal waterways that vary greatly in tropical regions. To address this knowledge gap, we used environmental DNA (eDNA) metabarcoding to examine fish assemblages at four locations (three estuaries and a harbour) subjected to varying levels of agricultural run-off during a wet and dry season. Pesticide and nutrient concentrations were markedly elevated during the sampled wet season with the influx of freshwater and agricultural run-off. Fish taxa richness significantly decreased in all three estuaries (F = 164.73, P = <0.001), along with pronounced changes in community composition (F = 46.68, P = 0.001) associated with environmental variables (largely salinity: 27.48% contribution to total variance). In contrast, the nearby Mackay Harbour exhibited a far more stable community structure, with no marked changes in fish assemblages observed between the sampled seasons. Among the four sampled locations, variation in fish community composition was more pronounced within the wet season (F = 2.5, P = 0.001). Notably, variation in the wet season was significantly correlated with agricultural contaminants (phosphorus: 6.25%, pesticides: 5.22%) alongside environmental variables (salinity: 5.61%, DOC: 5.57%). Historically contaminated and relatively unimpacted estuaries each demonstrated distinct fish communities, reflecting their associated catchment use. Our findings emphasise that while seasonal effects play a key role in shaping the community structure of fish in this region, agricultural contaminants are also important contributors in estuarine systems.