Seagrass Seedlings Research Articles

Impact of microplastic exposure on the health of tropical seagrass (Enhalus acoroides) seedlings.

The early stages of seagrass life are marked by the development of seagrass seedlings. Enhalus acoroides is a persistent seagrass species with a high prevalence in tropical waters. The decline in water quality caused by human activities, such as microplastic contamination, is suspected to affect the growth and development of seagrass seedlings. This study examines the impact of microplastic exposure on the growth, chlorophyll content, and anatomical structure of Enhalus acoroides seedlings. This experimental research included four treatments: Treatment A (no microplastics), Treatment B (0.5g/L microplastics), Treatment C (1.0g/L microplastics), and Treatment D (1.5g/L microplastics). The results show that increasing microplastic concentrations disrupt photosynthesis in seagrass seedlings, indicated by a decrease in chlorophyll content, which leads to reduced growth and lower survival rates in seedlings (Treatment D). Based on this study, it is suggested that higher microplastic exposure may prevent seedlings from developing into mature seagrass individuals.

The root of influence: root-associated bacterial communities alter resource allocation in seagrass seedlings

IntroductionSeagrass roots harbour diverse assemblages of microorganisms that likely benefit the growth and survival of meadows. Yet, restoration efforts rarely consider their effect on developing seagrass seedlings. Sediment origin should determine the types of rhizosphere and root-colonising (rhizoplane) microorganisms and thus the performance of seedlings during restoration, particularly for slow growing climax species like Posidonia. Recent Posidonia restoration attempts in South Australia used commercially sourced 'play pit sand' for seedling propagation and planting, but have been impacted by high mortality. More natural substrates like seagrass meadow sediment have not been previously investigated for suitability over conventional substrates with regard to seedling growth and survival.MethodsTo assess the relevance of seagrass associated microorganisms in the growth of Posidonia angustifolia seedlings, we investigated the bacterial communities from tank-raised seedlings propagated in autoclave treated and untreated 'play pit sand' and meadow mix (comprising a 1:3 ratio of natural meadow sediment and beach sand) over a 12-week period. Autoclave treatment was adopted in order to diminish the bacterial load prior to planting and thus inform their contribution (if any) on early seedling growth. Samples for bacterial community analysis and seedling growth measurements (numbers and total length of roots/leaves, root diameter, seedling weight, starch reserves) were taken at 4 and 12 weeks. Bacterial assemblages were surveyed from DNA extracts from bulk and rhizosphere sediments and root tissues, as well as from swabs of P. angustifolia fruit, established meadow sediment and water samples prior to seedling propagation, by constructing Illumina 16S rRNA gene libraries.ResultsWhile most growth measurements did not vary significantly between sediment type or treatment, proportional growth of roots versus leaves (as expressed as a pseudo root:shoot ratio) was significantly related to treatment, sediment type and seed length. Seedlings from meadow mix invested more in leaves, regardless of treatment, when compared to play sand. Autoclave treatment increased investment in roots for play sand but increased the investment in leaves for meadow mix. Bacterial communities differed significantly between sediments and between sample types (bulk, rhizosphere and roots), with the roots from meadow mix seedlings containing an increased abundance of various potentially beneficial bacterial taxa.DiscussionWhile such changes appear to affect the early development of seedlings, bacterial community dynamics are also likely coupled to changes in nutrient availability. Further research is thus required to disentangle host seedling growth-nutrient-bacterial community dynamics with the view to identifying microbes that may support the growth and vigour of seedlings under different nutrient conditions as part of future restoration efforts.

Effect of Temperature on the Physiological Response of Enhalus acoroides Seedlings

Increasing sea surface temperatures as an effect of global warming can affect the survival of marine organism, among these marine organisms is seagrass. Temperature is one factor that can determine seagrass's physiological response in maintaining its life, including in the early stages of life in seagrass seedlings. This research aims to study the effect of temperature on the physiological response of Enhalus acoroides seedlings such as growth rate, leaf tissue anatomy, and chlorophyll content. The method used was an experiment in the laboratory. The seagrass seedlings were grown in an aquarium with three sea water temperature treatments (28°C, 31°C and 35°C) for 8 weeks of maintenance. The choice of sea water temperature treatment of 28°C (A) as a control is the optimal temperature range for seagrass, the treatment temperature of 31°C (B) refers to previous study, i.e. the temperature in the area of origin of the seagrass meadow, and the treatment temperature of 35°C (C) is considered as an estimate of temperature under the scenario of. The growth rate and the average leaf length were more optimal with a high chlorophyll content found at a temperature treatment of 28°C. The highest anatomical size of leaf tissue in the upper and lower epidermis was observed at 31°C, while the most extensive mesophyll tissue was observed at 35°C. In this study, temperature significantly affected the growth rate, average leaf length, anatomical structure of mesophyll tissue, and chlorophyll content of the Enhalus acoroides seedlings.

Seagrass (<I>Enhalus acoroides</I>) Restoration Performance with Two Different Methods (Anchor and Seed) in Panjang Island, Jepara, Indonesia

Highlight Research Seeds can grow into seagrass seedlings for an optimal period of five weeks Seed sowing can be optimized by supplementing nutrients with fertilizers The seedling transplant method, which utilizes seed seedlings, is not significantly different in daily growth from the anchor transplant method, which utilizes donors/seeds transport The biomass content of seagrass leaves can be used to determine the growth rate of the leaves Abstract Globally, the area of seagrass beds important to the ecosystems in coastal environment is decreasing due to environmental pressures, both natural and artificial. Transplantation is one way to restore the condition of damaged seagrass beds, the anchor transplant method uses the transfer of donor seagrass to the transplant area, while the seed transplant method uses seed sowed from seagrass. This study aimed to investigate the survival and growth rates of seagrass transplants and the biomass and chlorophyll content of transplanted Enhalus acoroides in the waters of Panjang Island Jepara utilizing anchor and seedling methods. The research was conducted in the waters around Panjang Island, Jepara, between September and December 2021. The results indicated that transplantation of seagrass E. acoroides using the anchor method resulted in the highest average growth rate of 0.25 cm/day and a survival rate of 96.67%, while transplantation using the seedling method resulted in a growth rate of 0.18 cm/day and a survival rate of 83.33%. The results showed that the anchor method scored better than the seedling transplantation method in terms of growth rate and survival rate. However, seedling is a feasible method to meet the availability of seeds that will later be transplanted, considering that the anchor method still has shortcomings in terms of the availability of seeds and the use of pegs which are still not environmentally friendly. so that the seedling method can be recommended for the restoration process of seagrass ecosystems by taking into account the season, weather and other important indices.

Cable bacteria at oxygen‐releasing roots of aquatic plants: a widespread and diverse plant–microbe association

Summary Cable bacteria are sulfide‐oxidising, filamentous bacteria that reduce toxic sulfide levels, suppress methane emissions and drive nutrient and carbon cycling in sediments. Recently, cable bacteria have been found associated with roots of aquatic plants and rice (Oryza sativa). However, the extent to which cable bacteria are associated with aquatic plants in nature remains unexplored.Using newly generated and public 16S rRNA gene sequence datasets combined with fluorescence in situ hybridisation, we investigated the distribution of cable bacteria around the roots of aquatic plants, encompassing seagrass (including seagrass seedlings), rice, freshwater and saltmarsh plants.Diverse cable bacteria were found associated with roots of 16 out of 28 plant species and at 36 out of 55 investigated sites, across four continents. Plant‐associated cable bacteria were confirmed across a variety of ecosystems, including marine coastal environments, estuaries, freshwater streams, isolated pristine lakes and intensive agricultural systems. This pattern indicates that this plant–microbe relationship is globally widespread and neither obligate nor species specific.The occurrence of cable bacteria in plant rhizospheres may be of general importance to vegetation vitality, primary productivity, coastal restoration practices and greenhouse gas balance of rice fields and wetlands.

Substrate Type Influences the Structure of Epiphyte Communities and the Growth of Posidonia oceanica Seedlings.

Epiphytes colonizing adult seagrasses highly contribute to seagrass ecosystem functioning and plant growth. Yet, little information exists on epiphytic communities developing on seagrass seedlings. Moreover, for some species our knowledge about seedling performance is limited to early establishment phases, and the role of substrate type in affecting their growth is still unclear. These are considerable knowledge gaps, as seedlings play an important role in meadow expansion and recovery from disturbance. In this study, seedlings of Posidonia oceanica, a keystone species of the Mediterranean, were grown in a shallow (1.5 m deep) coastal area along the Tuscany coast (Italy). After five years of growth (July 2009), seedlings were collected and, through multivariate analysis, we examined whether the epiphytic communities of leaves (both internal and external side) and rhizomes, as well as the growth characteristics differed between rock and sand substrate. The epiphytic communities of seedlings largely reflected those found on adult shoots. Epiphyte cover was similar between the two leaf sides, and it was higher on seedlings grown on rock than on sand, with encrusting algae dominating the community. No differences in epiphyte cover and community structure on rhizomes were found between substrates. Seedling growth characteristics did not differ between substrates, apart from the number of standing leaves being higher on rock than on sand. No correlation was found among epiphyte communities and seedling growth variables (i.e., leaf area, maximum leaf length, number of leaves, total number of leaves produced, rhizome length, total biomass, and root to shoot biomass ratio). Results indicate that epiphytes successfully colonize P. oceanica seedlings, and the surrounding micro-environment (i.e., substrate type) can influence the leaf epiphytic community. This study provides new valuable insights on the biological interactions occurring in seagrass ecosystems and highlights the need for better understanding the effects of seedling epiphytes and substrate on the formation of new meadows.

Rising Temperature Is a More Important Driver Than Increasing Carbon Dioxide Concentrations in the Trait Responses of Enhalus acoroides Seedlings

Increasing temperature and CO2 concentration are among the most important factors affecting marine ecosystems under climate change. We investigated the morphological, biochemical, and physiological trait responses of seedlings of the tropical seagrass Enhalus acoroides under experimental conditions. Trait responses were greater under temperature effects than increasing CO2 concentration. Seedlings under rising temperatures showed enhanced leaf growth, lower leaf nutrient content, and stimulated down-regulating mechanisms in terms of photo-physiology. Increasing CO2 concentrations did not show any significant effects independently. There was a significant interaction for some of the trait responses considered, such as leaf number and carbon content in the roots, and trends of higher starch concentrations in the leaves and lower rETRmax under combined enriched CO2 and high temperature, even though none of these interactions were synergistic. Understanding the single and interactive trait responses of seagrass seedlings to increasing temperature and CO2 concentration is of importance to determine the relative responses of early life stages of seagrasses, which may differ from adult plants, in order to form a more holistic view of seagrass ecosystem health under climate change.

Stage-dependent effects of a non-native invasive saltmarsh plant on the seedling establishment of a native seagrass

Concerns on the environmental disruption and ecosystem degradation due to the biological invasions are growing, with far-reaching consequences for the resilience of recipient ecosystems. While numerous studies mostly emphasized the negative impacts of invasive species on native species at a single time point, there is a lack of knowledge whether and how the invasion impacts vary with time. Here, we provide an empirical study on stage-dependent invasive impacts in an intertidal seagrass habitat (Zostera japonica), which is undergoing invasion of an invasive cordgrass (Spartina. alterniflora). Combining results from field surveys and experiments suggested that, impacts of cordgrass on seedling establishment of native seagrass species shift from facilitation at the initial stage of invasion to inhibition at the later stage when the invasive cordgrass become densely vegetated, causing density-dependent effects. In addition, at the later stage, patch expansion of cordgrass triggered degradation of seagrass-dominant habitats, showing the remnant patches of seagrass-dominant habitat have a strong patch-size dependent effect, with an optimal patch size of ~8 m2 and ~1.5 cm detritus to the establishment of seagrass seedlings. These stage-dependent effects strongly linked to water movement and sedimentation rate. Both of them are modified by the abundance of the invasive cordgrass and patch formation through transforming native seagrass habitat with invasion. Our findings highlight the importance of unraveling stage-dependent impacts for assessing the consequences of biological invasion on native ecosystems degradation.

Short Communication: Restoration of seagrass Enhalus acoroides using a combination of generative and vegetative techniques

Abstract. Ambo-Rappe R, La Nafie YA, Syafiuddin, Limbong SR, Asriani N, Handayani NT, Lisdayanti E. 2019. Short Communication: Restoration of seagrass Enhalus acoroides using a combination of generative and vegetative techniques. Biodiversitas 20: 3358-3363. Seagrass areas have been declining in extent worldwide, with associated loss in seagrass ecosystem functions and services. Seagrass restoration is important to mitigate, halt and reverse such declines and their consequences. Generative propagation has benefits in terms of genetic biodiversity, however, survival of seagrass seedlings has often been poor especially in high energy environments. Terrestrial restoration often uses shade trees to protect vulnerable seedlings. This study aimed to evaluate the feasibility of a similar approach in the marine environment, using adult plants to protect seedlings of the tropical seagrass Enhalus acoroides (L.f.) Royle. Enhalus seeds taken from a donor bed were germinated and grown into seedlings, then planted in a location with high hydrodynamic exposure at three different densities (high, medium, and low). Adult Enhalus transplants were co-planted to provide three levels of protection: fifty (high), ten (medium), and none (no protection). Results showed that high-density seedling co-planting with high protection from adult transplants had significantly (p< 0.05) higher six-month survival rate compared to the other treatments. Our results indicate that, even in high energy environments, co-planting seedlings with adult transplants may combine the advantages of generative and vegetative propagation methods, promoting greater short-term effectiveness in terms of seedlings survival and growth in the restored seagrass meadows.

Negative effects of warming on seagrass seedlings are not exacerbated by invasive algae

The observed and projected rise in sea surface temperature challenges marine biodiversity worldwide, and particularly in temperate ecosystems dealing with the arrival of novel species of tropical provenance. When the impacted biota are early life stages of ecosystem engineers, the effects of those impacts are of major concern for ecologists and coastal managers. We experimentally examined the individual and potential additive effects of seawater warming and the presence of the invasive algae on the development of seedlings of the seagrass Posidonia oceanica in a three-month mesocosm experiment. Whereas the presence of the invasive algae (Caulerpa cylindracea and Lophocladia lallemandii) did not result in detrimental effects on seedlings, warming negatively affected seedling development. Interestingly, the presence of both invasive algae may ameliorate the negative effects of warming.

Physiological responses of Enhalus acoroides to osmotic stress

AbstractThis study aims to examine photophysiological and osmotic responses in seedlings of the seagrassEnhalus acoroidesafter exposure to different salinity levels. Seagrass seedlings were grown for 20 days in control (salinity 30), hyposaline (salinity 10 and 20) and hypersaline (salinity 40 and 50) conditions. The present study showed that both hypo- and hypersaline conditions affected the photophysiology ofE. acoroidesseedlings, reducing the maximum quantum yield of photosystem II (Fv/Fm) and total chlorophyll content. The photosynthetic system appeared to be more sensitive to hyposaline than to hypersaline conditions as shown by immediate declines inFv/Fmand total chlorophyll content. Hyposaline conditions increased the water content in roots. The increase in tissue Na+content induced by hypersalinity did not affect photosynthetic integrity and was more pronounced in leaves than in roots. It is concluded that the ionic homeostasis ofE. acoroidesseedlings is less affected by short-term hypersalinity than by hyposalinity. The K+/Na+ratios in leaves with hypersalinity decreased by 20 days after treatment. Additionally, the photosynthetic efficiency (Fv/Fmand total chlorophyll content) is highly sensitive to salinity shifts and can be used as a marker for short-term acclimation to salinity stress in this seagrass species.

Future warmer seas: increased stress and susceptibility to grazing in seedlings of a marine habitat-forming species.

Increases in seawater temperature are expected to have negative consequences for marine organisms. Beyond individual effects, species-specific differences in thermal tolerance are predicted to modify species interactions and increase the strength of top-down effects, particularly in plant-herbivore interactions. Shifts in trophic interactions will be especially important when affecting habitat-forming species such as seagrasses, as the consequences on their abundance will cascade throughout the food web. Seagrasses are a major component of coastal ecosystems offering important ecosystem services, but are threatened by multiple anthropogenic stressors, including warming. The mechanistic understanding of seagrass responses to warming at multiple scales of organization remains largely unexplored, especially in early-life stages such as seedlings. Yet, these early-life stages are critical for seagrass expansion processes and adaptation to climate change. In this study, we determined the effects of a 3 month experimental exposure to present and predicted mean summer SST of the Mediterranean Sea (25°C, 27°C, and 29°C) on the photophysiology, size, and ecology (i.e., plant-herbivore interactions) of seedlings of the seagrass Posidonia oceanica. Warming resulted in increased mortality, leaf necrosis, and respiration as well as lower carbohydrate reserves in the seed, the main storage organ in seedlings. Aboveground biomass and root growth were also limited with warming, which could hamper seedling establishment success. Furthermore, warming increased the susceptibility to consumption by grazers, likely due to lower leaf fiber content and thickness. Our results indicate that warming will negatively affect seagrass seedlings through multiple direct and indirect pathways: increased stress, reduced establishment potential, lower storage of carbohydrate reserves, and increased susceptibly to consumption. This work provides a significant step forward in understanding the major mechanisms that will drive the capacity of seagrass seedlings to adapt and survive to warming, highlighting the potential additive effects that herbivory will have on ultimately determining seedling success.

Artificial seagrass leaves shield transplanted seagrass seedlings and increase their survivorship

Seagrass meadows provide important ecosystem functions and services. The progressive global deterioration of seagrass meadows requires management strategies to stop and recover seagrass losses. Seagrass restoration can be promoted using seagrass seedlings germinated in vitro, but early mortality of seedlings is a severe bottleneck for successful restoration programs. In this study, we tested a technique to promote in situ survivorship of in vitro germinated seedlings of the seagrass Cymodocea nodosa. In particular, we predicted that artificial seagrass leaves (plastic green raffia, i.e. ‘Artificial Seagrass Shields', ASSs) surrounding seagrass seedlings would increase the long-term survivorship of seedlings by decreasing herbivory-induced mortality. After 2 years, the survivorship of seagrass seedlings in plots without the ASSs was nil, whereas one third of plots containing ASSs developed small-sized seagrass patches, including a one order of magnitude exponential increase in shoot density. Herbivory intensity on seagrass leaves significantly decreased when surrounded with ASSs. This study demonstrates how ASSs facilitate the establishment of transplanted seagrass seedlings and suggests ASSs could be a cheap, easy-to-use, restoration element to promote the survivorship of seagrass seedlings by decreasing the magnitude of herbivory.

Seagrass derived organic matter influences biogeochemistry, microbial communities, and seedling biomass partitioning in seagrass sediments

Seedling establishment is a crucial life history stage in seagrasses, yet factors that affect seedling health are poorly characterized. We investigated if organic matter (OM) additions to sediments provided nutritional benefits for seagrass seedlings through microbial degradation. We tested the effects of sedimentary OM additions on Posidonia australis seedlings growing in tank cultures. We focussed on sediment biogeochemical processes and microbial communities that may impact seedling growth and physiology. Enrichment of sediments with OM changed microbial community composition (DNA-ARISA) and a significant increase in hydrolytic enzyme expression. Total seedling biomass did not differ between OM treatments, but above:belowground biomass increased with OM enrichment. Nitrogen and phosphorus concentration of seagrass leaves was lower with increasing OM. Seagrass derived OM has been considered a refractory store of carbon, yet here we show its deposition into sediments significantly alters belowground conditions. Remineralization of the OM changes both physical and chemical nature of sediments that leads to greater biochemical activity, change in microbial communities and greater investment into above ground photosynthetic biomass. The presence of OM may assist seagrass seedling survival during early development by enhancing root branching and stability in sediments, but is unlikely to provide nutritional benefits.

Inorganic Nutrient Supplements Constrain Restoration Potential of Seedlings of the Seagrass, Posidonia australis

AbstractSeed represents a potentially ecologically sustainable source of planting units for restoring seagrasses, particularly for seagrasses where transplanting negatively impacts donor beds. However, newly germinated seeds may be nutrient limited as their underdeveloped root systems may constrain capacity to access sediment‐based resources. We conducted a study in land‐based aquaculture tanks to determine whether early growth of newly germinated Posidonia australis seedlings could be enhanced by adding inorganic nutrients to the sediment. Sediments were supplemented with nitrogen and phosphorus in a factorial design (no nutrients, N, P, N + P). Shoot survival, whole shoot biomass, root morphology, root architecture, and nutrient concentration of seedlings were assessed monthly for the first 4 months after germination. More than 90% of seedlings survived during the 4 months of the experiment, irrespective of nutrient treatment. Growth of P. australis seedlings was not enhanced by addition of N or P to the sediment despite nutrient uptake occurring. Seedling growth was found to be more dependent on seed nutrient reserves rather than external nutrient sources for at least the first 4 months after germination. Adding inorganic nutrients to the sediment also significantly reduced the development of the seedling root system in terms of biomass, length, and density of lateral root branches. This study demonstrated that inorganic nutrient supplements constrain root development and therefore capacity for successful anchorage of seagrass seedlings, and pose a significant limitation on seedling establishment when transferred to the field, as well as potentially limiting natural and transplanted seedling establishment in eutrophic sediments.

Posidonia oceanica and Cymodocea nodosa seedling tolerance to wave exposure

We studied the role of hydrodynamics in the establishment of sea grass seedlings for two Mediterranean sea grass species, Posidonia oceanica and Cymodocea nodosa, by combining flume and field studies. Flume measurements under both unidirectional and oscillatory flow showed that P. oceanica seedlings experienced higher drag forces than C. nodosa, which could be related to the larger total leaf area. Drag coefficients were between 0.01 and 0.1 for Reynolds numbers of 103 and 105. As a result, P. oceanica seedlings required 40‐50% of root length anchored to the sediment before being dislodged, whereas C. nodosa required ≈ 20%. To validate the flume results, seedling survival in sandy beds was evaluated for two depths (12 and 18 m) at two field locations. To calculate near‐bottom orbital velocities at the planting sites, deep‐water waves were propagated to shallow water using a numerical model. Our results showed that P. oceanica seedlings experienced high losses after the first autumn storms when near‐bottom orbital velocities exceeded 18 cm s‐1. The loss of C. nodosa seedlings was much lower and some seedlings survived velocities as high as 39 cm s‐1. Thus, flume and field results are consistent in explaining relative higher losses of P. oceanica seedlings than for C. nodosa.

Responses of eelgrass Zostera marina seedlings to reduced light

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 223:133-141 (2001) - doi:10.3354/meps223133 Responses of eelgrass Zostera marina seedlings to reduced light Joanne C. Bintz1,*, Scott W. Nixon2 1Ocean Studies Board, National Academy of Sciences, 2101 Consitution Av. NW, HA 470, Washington, DC 2041, USA 2Graduate School of Oceanography, University of Rhode Island, PO Box 200, South Ferry Road, Narragansett, Rhode Island 02882, USA *E-mail: jbintz@nas.edu ABSTRACT: We subjected seedlings of Zostera marina L. to High (72%), Medium (23%), and Low (10%) daily irradiance (mean daily PAR of 24.4, 7.9, and 3.3 E m-2 d-1 respectively) over 12 wk. We measured plant response in terms of survivorship, lateral shoot production, morphology, growth rate, photosynthesis and respiration, and leaf pigment concentration. Decreasing the light available to eelgrass seedlings from 72 to 23% resulted in a reduction of lateral shoot formation, lower plant biomass, and longer and wider leaves. Shoot area, growth rate, and pigment concentrations remained similar. A reduction of incident light to 10% decreased survival to 74% and had a negative effect on shoot growth, size, and above- and belowground biomass. Pigment concentrations increased with respect to seedlings raised at medium light. In general, the responses of seedlings to reduced light are similar to those reported for mature Z. marina. Rapid expansion of seedling patches can only occur at irradiance levels greater than 7.9 E m-2 d-1. Morphological changes resulting from exposure to mean daily PAR levels of less than 8 E m-2 d-1 such as thinner leaves and low belowground biomass, have serious implications for decreased seedling survival in the field. KEY WORDS: Eelgrass · Seagrass seedlings · Light · Zostera marina · Shade adaptation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 223. Online publication date: November 28, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.