In coastal areas around the world, seagrass meadows play a crucial ecological and economic role. A large amount of seagrass beds dominates primary production and contributes to the high secondary productivity of this ecosystem. The microbial loop (consuming bacterial biomass by grazers and using seagrass-derived detritus by bacteria) may be an important mechanism for transferring seagrass-derived organic matter to the aquatic food chain. This study aims to improve our understanding of how bacterial growth and mortality (grazing and viral lysis rates) differ in seagrass and adjacent unvegetated meadow habitats. We found that viral lysis and grazing caused similar mortality rates of bacteria in a seagrass environment during the summer. It has been found, however, that bacterial production is controlled by the availability of resources (bottom-up control) and is cycled within the bacteria-virus-DOC loop in adjacent unvegetated waters. Our study region may be affected by this shift in organic matter fate and cycling.

Approximately 20% of the world's population resides in coastal areas at risk of rising sea levels due to climate change. This could lead to severe weather events and ecological impact on critical infrastructure. To combat the effects of water-based environmental forces on the land, hard engineering methods such as seawalls have been utilized. However, a more sustainable solution is emerging in nature-based engineering, which involves growing vegetation. This approach can help extend the lifespan of existing technology and provide climate change adaptation and resilience for coastal and riverine communities. The following paper will review seaweed farms as an advanced nature-based mitigation approach. The paper also outlines the findings of experiments at RWTH Aachen University's hydraulic laboratory. These tests involved using seaweed as a natural solution to dampen waves in a model system to test a hypothesis. One result involving a system with two lines of seaweed revealed 15 percent wave damping. Using seaweed as a nature-based solution, a gentle engineering approach to designing future vegetated protection systems can extend the design life of existing coastal infrastructure. This can also provide protection against climate-induced sea level rise, promote coastal risk mitigation, restore ecosystems, and foster blue bio-economic development.

Due to the expansion of applications of rare earth elements (REE) in various technological pro-cesses, increasing amounts of these metals pollute the environment, including the marine one. Very little is known about the bioaccumulation and toxicity of REE in marine organisms. In the present work, we assessed the contents of these metals, including yttrium and scandium, in rhizomes and leaves of the widespread seagrass Zostera noltei and in the nearby sediments from the Black Sea coast. The total REE content in the sediments was found to be much higher than in Z. noltei. The order of decrease in the major REE contents in the sediments and the seagrass rhizomes was identical, except for La and Y: La was the most abundant in the sediments and Y in the rhizomes. The contents of all REE in rhizomes of Z. noltei were 1.5–10 times higher than in leaves. The greatest difference in the REE contents was found for the minor heavy elements (Sm–Lu). Translocation coefficients for Sc and the minor elements (excluding Tb) from sediments to rhizomes and from rhizomes to leaves turned out to be pairwise equal, which indicate the similarity of the REE translocation mechanisms. Comparing our results with the literature data, it is possible to conclude that the seagrass Z. noltei does not have an advantage in the REE accu-mulation over marine macroalgae. However, large coastal deposits of this seagrass after storms allow it to consider as a possible resource of REE.

One-fifth of the world’s population and critical infrastructures are near the coast and regions at high risk of sea level elevation. Climate change is expected to increase coastal extreme events, rising sea levels, and impact on ecosystem. This paper reviews coastal physical processes, wave and impacts, and the introduction of nature-based models for the mitigation of flooding, erosion, and recovery. Hard engineering like seawalls has been used to prevent, protect, and control water-based environmental forces with an extended impact on the land. A nature-based engineering solution, such as growing vegetation, is being adopted as a sustainable solution to help make existing technology live its design life and provide climate change adaptation and resilience for coastal and riverine communities. This paper presents applications of seaweed farms as an advanced nature-based mitigation approach. The result of the experiments conducted at RWTH Aachen University on wave damping of seaweed types and farming structures to validate the hypothesis will be presented in part B. A soft engineering approach to designing future vegetated protection systems using seaweed as a nature-based solution can help existing coastal infrastructure design life and protect against climate-induced SLR rise and adaptation, coastal risk mitigation, ecosystem restoration, and blue bio-economic development.

Seagrasses are considered as efficient bioindicators of coastal trace element contamination. This chapter provides an overview on the trace element accumulation, tolerance and biomonitoring capacity of the various seagrass species distributed along the coast of India. A total of 10 trace elements are reported in seagrasses, 11 in sediment and nine in the water column from India. From the 11 seagrass species studied, 60% of research have focused on Syringodium isoetifolium, Cymodocea serrulata, Cymodocea rotundata and Halophila ovalis. 78% of seagrass trace element research in India is from Palk bay and Gulf of Mannar (GOM), Tamil Nadu and 16% from Lakshadweep Islands. Out of the 10 trace elements, Cd, Cu, Pb and Zn are the most studied in seagrass, Fe, Mn, Ni and Pb in sediment and Cu, Fe, Mg, Ni and Zn in the water column. Accumulation capacity of various trace elements in seagrass were species-specific. S. isoetifolium have the highest concentration of Cd and Mg at Palk bay and Lakshadweep Islands respectively. The concentration of Cu was higher in C. serrulata at GOM. Halodule uninervis and Halophila decipens have the highest concentration of Co, and Cr, Ni, Pb and Zn from Lakshadweep Islands. The highest concentration of Fe and Mn were highest in Halophila beccarii and H. ovalis from the coast of Goa and Palk bay respectively. Threshold levels (>10 mg L^-1) of Cd, Cu, Pb and Zn were observed for C. serrulata, H. ovalis, H. uninervis and T. hemprichii, that can affect the Photo System -II of these seagrasses and exert cellular stress leading to seagrass loss and die-off. High concentration of these elements can exert negative impacts on seagrass associated trophic assemblages and ecosystem functioning. Seagrasses of India can be utilized as bioindicators of coastal trace element contamination but the associated toxicity and human health risks needs further investigation.

There is no doubt that seagrass beds constitute one of the most productive ecosystems in shallow coastal waters. Despite this, picoplankton in seagrass ecosystems has received relatively little attention. The purpose of this study was to compare picoplankton growth and mortality rates between seagrass and unvegetated habitats using chamber incubations. We tested two main hypotheses: (i) incubation with seagrass would result in higher bacterial growth rates due to increased DOM release from seagrass photosynthesis, and (ii) Synechococcus spp. would be lower in the presence of seagrass due to competition for inorganic nutrients. Our results showed bacterial growth rates of 2.31 and 2.44 d–1 without and with seagrass, respectively. In seagrass chambers, bacterial growth was higher than that in non-seagrass chambers, suggesting that organic carbon coming from the seagrass community may support bacterial production. Furthermore, we observed a negative Synechococcus spp. growth rate (-0.9 d–1) in the seagrass treatment, likely reflecting nutrient competition with the seagrass. Small-scale chambers proved to be a useful tool for studying the factors controlling spatial and temporal patterns of picoplankton across different habitats. Furthermore, future studies should examine picoplankton growth over a wider range of spatial scales in seagrass beds and adjacent unvegetated sediment.

Macrophytes and seagrasses play a crucial role with a variety of the functions in the marine ecosystem and respond synchronized-promptly to the changing climate, followed by ecological status. Monitoring of the seagrasses was one of the paramount topics at the marine environment. One of the fast monitoring techniques is the vegetation acoustics with the advantages compared to the other remote sensing techniques. The acoustic method alone is ambitious to sea-truth identities of the backscatterers at the sea. Therefore, a package of computer programs was developed to identify, estimate leaf biometrics (leaf length and biomass) of one of the common seagrasses, Posidonia oceanica. Some troubleshooting in the acoustical data were fixed and then solved to reach the estimates regarding to the matters encountered for the vegetation as well as fisheries and plankton acoustics. One of the trouble was the “Lost” bottom which occurred during the data collection and post-processing due to occurrence of the acoustical noises, reverberations, interferences and intense scatterers suchlike fish schools. Another problem to remove was the occurrence as studying the near-bottom echoes belonging to submerged vegetations such as seagrasses, followed by spurious echoes. Last one was recognition of the seagrass to estimate leaf length and biomass calibrating the sheaths/vertical rhizome of the seagrass and establishing relationships between acoustical units and biometrics, respectively. As a consequence, an autonomous package of the code written in language MatLab was developed to perform all processes, and the name of the package was abbreviated as POSIBIOM, POSIdonia BIOMass. This study presented the algorithms, methodology, acoustics-biometrics relation, and mapping of the biometrics for the first time, and discussed advantages and disadvantages of the package compared to the software purposed for the bottom types, habitat and vegetation acoustic. The future studies were recommended to improve the package.

A Mamdani-type fuzzy-logic model has been developed to link Mediterranean seagrass abundance to the prevailing environmental conditions. Big Databases, as UNEP-WCMC (seagrass abundance), CMEMS and EMODnet (oceanographic/environmental) and human-impact parameters were utilized for this expert system. Model structure and input parameters were tested according to their capacity to accurately predict seagrass families at specific locations. The optimum FIS comprised of four input variables: water depth, sea surface temperature and nitrates and bottom chlorophyll-a concentration, exhibiting fair accuracy (76%). Results illustrated that Posidoniaceae prefers cool (16-18oC) and low chlorophyll-a presence (< 0.2 mg/m3); Zosteraceae favors cool (16-18oC) and mesotrophic waters (Chl-a > 0.2 mg/m3), but also slightly warmer (18-19.5 oC) with lower Chl-a levels (< 0.2 mg/m3); Cymodoceaceae lives from warm, oligotrophic (19.5-21.0oC and Chl-a < 0.3 mg/m3) to moderately warm mesotrophic sites (18-21.3oC and 0.3 – 0.4 mg/m3 Chl-a). Finally, Hydrocharitaceae thrives in warm Mediterranaean waters (21-23oC) of low chlorophyll-a content (< 0.25 mg/m3). Climate change scenarios showed that Posidoniaceae and Zosteraceae tolerate bathymetric changes, Posidoniaceae and Zosteraceae are mostly affected by sea temperature rise, while Hydrocharitaceae exhibits tolerance in higher sea temperature rise. This FIS could be used by national and regional policy-makers and public authorities.

The present study documented the presence of seagrass Halodule uninervis for the first time along with previously documented Halophila ovalis at Haripur creek. The population structure of both these seagrass species is assessed. The physico-chemical parameters were similar for both seagrass species except for the sediment grain size fractions. The sand content of H. ovalis patches was 1.2-fold higher than H. uninervis beds, whereas the silt content of H. uninervis beds was 2-fold higher than H. ovalis patches. The pH levels were lower than the standard oceanic pH of 8.2. Macroalgae like Ceramium sp. and Gracilaria verrucosa were growing on the leaves of H. uninervis due to high nitrate and phosphate levels of the creek waters. Leaf reddening was only observed in the leaves of H. ovalis. Under similar environmental conditions, H. ovalis (5004 ± 114.51 ind. m-²) had a 2-fold lower shoot density than that of the H. uninervis (11598 ± 187.52 ind. m-²). Both above- and below-ground biomass of H. ovalis (96.34 ± 10.18 and 197.5 ± 18.30 g DW m^-2) was 2-fold lower than that of H. uninervis (198 ±7.45 and 456 ± 9.59 g DW m^-2). H. uninervis leaves were 9-fold longer than that of H. ovalis, whereas H. ovalis leaves were 5-fold wider than H. uninervis. The leaf plastochrone interval is 2.3 days for H. ovalis and 9.6 days for H. uninervis. Consequently, the leaf growth rate of H. ovalis is 2-fold lower than that of H. uninervis. H. ovalis had 2.6-fold longer internodes than H. uninervis. The root length of H. uninervis was longer than H. ovalis. Consequently, the shorter root length of H. ovalis led to higher branching frequency than H. uninervis. The total C and N content were higher in the leaves of H. ovalis than H. uninervis.

The present work was performed to evaluate the levels of phytochemical constituents and the antioxidant and antibacterial properties of marine red seaweed (Kappaphycus alvarezii) and seagrass (Cymodocea serrulata). Quantitative phytochemical analysis, antioxidant activity and antimicrobial activity against 5 potential pathogenic bacteria was investigated. In both cases were found presence of flavonoids, tannins, phenolic compounds, glycosides, steroids, carbohydrates and ashes. Alkaloids were only found in K. alvarezii, buy not in C. serrulata. The antimicrobial properties of both K. alvarezii and C. serrulata chloroform extracts were found to be antagonis-tically effective against the gram-positive bacterium Bacillus subtilis and the gram-negative bacterium Vibrio parahaemolyticus, Vibrio alginolyticus, Vibrio harveyi and Klebsiella pneu-moniae. GC‒MS analysis revealed the presence of 94 bioactive compounds in K. alvarezii and 104 C. serrulata, including phenol, decane, dodecane, hexadecane, vanillin, heptadecane, diphenyla-mine, benzophenone, octadecanoic acid, dotriaconate, benzene, phytol, butanoic acid, and 2-hydroxyl-ethyl ether, which played a vital role in antioxidant and antibacterial activities. Thus, in view of the results, both K. alvarezii and C. serrulata could be considered as sources of ingre-dients with appreciable nutritional and medicinal value.

Seagrass ecosystems are lost due to habitat disturbance, coastal development and human pressure. We assessed the impact of boat anchors from traditional fishing and recreational activities on the seagrass Halophila ovalis from the Andaman and Nicobar Isalnds of India. The plant density, biomass, morphometrics, canopy height and percentage cover were estimated from two sites of Govind Nagar beach of Andaman and Nicobar Islands. The shoot density of H. ovalis was reduced by physical damage caused by boat anchors. The morphometrics of H. ovalis, such as number of leaves per ramet, leaf length, width and horizontal rhizome length were significantly reduced when impacted by boat anchors. Seagrass canopy height and percentage cover were reduced by 41% and 47% respectively. Though the impact of boat anchors reported here is on small-scale, it may impact feeding grounds of locally endangered dugongs. Therefore, proper management and preventive measures should be implemented to prevent the loss of dugong grass habitats from tourism, recreational and fishing activities.

Decapod assemblages in Zostera marina beds from two bays adjacent to unvegetated habitats were investigated to assess their influence on decapod assemblages. Thirty-eight decapod species belonging to 4 taxa were collected using a small beam trawl at four habitat types from two different locations off the coast of Namhae Island, southern Korea. Dominant decapod taxon at all habitats was the caridean shrimps, with Eualus leptognathus, Heptacarpus pandaloides, Latreutes anoplonyx, La. laminirostris and Palaemon macrodactylus being the most abundant caridean species. Crabs were characterized by the highest biomass, but moderate species richness and abundance. Penaeoids and sergestoids shrimps only accounted for <1% of the total decapod abundance. The number of species, their abundance, and the diversity of decapod assemblages varied greatly by habitat type, season, and diel patterns. Species number and abundance peaked in seagrass beds of southern exposed bays during the autumn, and were lowest in unvegetated habitats during the summer months. Diel decapod species and catch rates were higher at night. Dense seagrass vegetation and nighttime supported greater decapod species richness and higher mean densities, but not diversity. Multivariate analyses revealed that habitat type and season significantly affected the structure of decapod assemblages, but diel patterns had a minor influence. Among decapod species, Pa. macrodactylus and Pugettia quadridens characterized the decapod assemblages in seagrass beds at the northern semi-closed bay, while Telmessus acutidens, Crangon affinis, Cr. hakodatei, Charybdis japonica and Portunus sanguinolentus were significantly associated with both vegetated and unvegetated habitats at the southern exposed bay, with the former two species more abundant during winter and spring.

The bioindicator potential of seagrass ecosystems in coastal trace metal monitoring is low for tropical island ecosystems. This study evaluated the bioindicator potential of six seagrass species exposed to anthropogenic trace metal pollution in the Andaman and Nicobar Islands (ANI) of India. Sediment and seagrass biomass, samples were analyzed for trace metals (Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Zn) from four locations of ANI exposed to anthropogenic contamination. Geo accumulation Index values indicated moderate trace metal contamination in seagrass sediment. Seagrass trace metal accumulation from sediment was both species-specific and location- specific for ANI. Small seagrass species such as H. ovalis, H. beccarii and H. uninervis accumulated the maximum concentration of six trace metals (Cr, Cu, Fe, Ni, Pb, Zn) in their tissues compared to big seagrass species like T. hemprichii and E. acoroides of ANI. This study indicates leaves of small seagrass and roots of big seagrass species can serve as short- and long-term bioindicators respectively, of coastal trace metal contamination in tropical islands of ANI.

We used population reconstruction techniques to assess for the first time the population dynamics of a seagrass, Cymodocea nodosa, exposed to long-term elevated CO₂ near three volcanic seeps and compare them with reference sites away from the seeps. Under high CO₂, the density of shoots and of individuals (apical shoots), and the vertical and horizontal elongation and production rates, were higher. Nitrogen effects on rhizome elongation and production rates and on biomass, were stronger than CO₂ as these were highest at the location where the availability of nitrogen was highest. At the seep where the availability of CO₂ was highest and nitrogen lowest, density of shoots and individuals were highest, probably due to CO₂ effects on shoot differentiation and induced reproductive output, respectively. In all three seeps there was higher short- and long-term recruitment and growth rates around zero, indicating that elevated CO₂ increases the turnover of C. nodosa shoots.

Intertidal seagrass plays a vital role in estimating the overall health and dynamics of coastal environments due to its interaction with tidal changes. However, most seagrass habitats around the globe have been in steady decline due to human impacts, disturbing the already delicate balance in environmental conditions that sustain seagrass. Miniaturization of multi-spectral sensors has facilitated very high resolution mapping of seagrass meadows, which significantly improve the potential for ecologists to monitor changes. In this study, two analytical approaches used for classifying intertidal seagrass habitats are compared: Object-based Image Analysis (OBIA) and Fully Convolutional Neural Networks (FCNNs). Both methods produce pixel-wise classifications in order to create segmented maps, however FCNNs are an emerging set of algorithms within Deep Learning with sparse application towards seagrass mapping. Conversely, OBIA has been a prominent solution within this field, with many studies leveraging in-situ data and multiscale segmentation to create habitat maps. This work demonstrates the utility of FCNNs in a semi-supervised setting to map seagrass and other coastal features from an optical drone survey conducted at Budle Bay, Northumberland, England. Semi-supervision is also an emerging field within Deep Learning that has practical benefits of achieving state of the art results using only subsets of labelled data. This is especially beneficial for remote sensing applications where in-situ data is an expensive commodity. For our results, we show that FCNNs have comparable performance with standard OBIA method used by ecologists, while also noting an increase in performance for mapping ecological features that are sparsely labelled across the study site.

We reviewed the current status of a Vulnerable seagrass, Halophila beccarii from the coast of India using the published data from 1977-2020. We found that the seagrass, H. beccarii has a pan India distribution on both east and west coast. It is abundant in the intertidal silty-muddy region on the west coast, while on the east coast it is found on sandy habitats, with few exceptions of muddy habitat. H. beccarii was found to be associated with mangroves or smaller seagrass species within a depth limit of 1.7m. Low salinity and high nitrate levels were observed for the H. beccarii meadows of the west coast due to its association with mangroves. The nutrient levels in H. beccarii meadows of India were comparatively lower than other seagrass meadows. Most of the research on H. beccarii has focoused on its morphometrics (41%), reproductive (33%) and distribution (29%) along the coast of India. Reproductive traits such as flowering and fruiting varying according to the seasons of each coast due to the influence of monsoon and its associated temperature, salinity and nutrient influx. H. beccarii has a great potential of various bioactive compounds, which needs further investigation. Habitat disturbance, anthropogenic pollution and coastal development are the major cause of declining H. beccarii ecosystems in India. Significant loss of the seagrass was observed from the west coast of India due to increased coastal development activities. There is a significant need in quantifying H. beccarii population trends, impact of climate and anthropogenic stressors, economic values of ecosystem services and the role of ecological connectivity for better conservation and management of H. beccarii seascapes across India. There is a need for integration of research outcomes in policy framing for preventing the decline and further loss of this vulnerable seagrass ecosystem.

Globally, seagrass meadows provide critical ecosystem services. However, seagrasses are globally degraded at an accelerated rate. The lack of information on seagrass spatial distribution and seagrass health status seriously hinders seagrass conservation and management. Therefore, this study proposes to combine remote sensing big data with a new hybrid machine learning model (RF-SWOA) to predict potential seagrass habitats. The multivariate remote sensing data is used to train the machine learning model, which can improve the prediction accuracy of the model. This study shows that a hybrid machine learning model (RF-SWOA) can predict potential seagrass habitats more accurately and effectively than traditional models. At the same time, it has been shown that the most important factors influencing the potential habitat of seagrass in the Hainan region were the distance from land (38.2%) and the depth of the ocean (25.9%). This paper provides a more accurate machine learning model approach for predicting the distribution of marine species, which can help develop seagrass conservation strategies to restore healthy seagrass ecosystems.