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The ongoing environmental crisis, driven by biodiversity loss and climate change, raises concerns about the impacts on marine systems and human well-being. These environments provide crucial ecosystem services valued at approximately USD 74.5 trillion·year−1 globally. Seagrasses support fisheries, protect coasts, help mitigate climate change, maintain biodiversity, provide food security, and enhance water quality. However, comprehensive assessments of seagrass ecosystem services (SESs) and their impacts are lacking. Focusing on the Brazilian southwest Atlantic, our aim is to bridge this gap and identify key research areas for improved management decisions. Our literature search employed n = 19 paired terms for seagrass in Brazil. We screened 30,351 search returns for 394 relevant documents. Research on SESs has grown over time, and most research has focused on provisioning and supporting ecosystem services: 79.7% of documents mentioned at least one SES, while 24.5% of the documents provided evidence of observed SESs; 31.5% only provided information on expected SESs. Provisioning services were the most observed and expected. Coastal urbanization (54%) and marine food provisioning (17%) were the main drivers impacting SESs. Terrestrial food and material provision (9%) and climate change (8%) were also significant drivers. This study provides key recommendations aimed at fostering further research and management strategies to consider the complete ensemble of ecosystem services for a range of seagrass bioregions, to better understand the provision of and impacts to seagrass services and human well-being at the global scale. [ABSTRACT FROM AUTHOR]

Plant species usually have either annual or perennial life cycles, but facultative annual species have annual or perennial populations depending on their environment. In terrestrial angiosperms, facultative annual species are rare, with wild rice being one of the few examples. Our review shows that in marine angiosperms (seagrasses) facultative annual species are more common: six (of 63) seagrass species are facultative annual. It concerns Zostera marina, Z. japonica, Halophila decipiens, H. beccarii, Ruppia maritima, and R. spiralis. The annual populations generally produce five times more seeds than their conspecific perennial populations. Facultative annual seagrass species occur worldwide. Populations of seagrasses are commonly perennial, but the facultative annual species had annual populations when exposed to desiccation, anoxia-related factors, shading, or heat stress. A system-wide 'experiment' (closure of two out of three connected estuaries for large-scale coastal protection works) showed that the initial annual Z. marina population could shift to a perennial life cycle within 5 years, depending on environmental circumstances. We discuss potential mechanisms and implications for plant culture. Further exploration of flexible life histories in plant species, and seagrasses in particular, may aid in answering questions about trade-offs between vegetative and sexual reproduction, and preprogrammed senescence. [ABSTRACT FROM AUTHOR]

The seagrass species in Halodule and Halophila may for several reasons be considered as taxonomic complexes. They show close evolutionary relationships, morphological plasticity and share similar features making misidentifications likely when morphological identification is applied. In Tanzanian coastal waters, there is some uncertainty about the identity of members of Halodule, particularly the existence of Halodule wrightii and the species composition of the Halophila ovalis complex. This study used morphology as well as internal transcribed spacer (ITS1 and ITS2) and ribulose‐bisphosphate carboxylase (rbcL) DNA barcoding to identify species of Halodule and Halophila. Seagrass samples were collected during low spring tides, from Tanzania's coastal waters of Tanga, Dar es Salaam, Mtwara, Mafia Island and Unguja Island, from August 2020 to February 2022. Morphological diagnosis, phylogenetic analysis and evolutionary divergences inferred from the ITS gene supported the identification of five species, namely Halophila ovalis, H. minor and H. stipulacea, with the first two forming the H. ovalis complex; as well as Halodule uninervis and H. pinifolia. It is the first time that H. pinifolia is reported in Tanzania. This is the first study reporting the delineation of seagrass species in East African coastal waters using DNA barcoding coupled with morphology. [ABSTRACT FROM AUTHOR]

Seagrass habitats are recognised as providing essential ecosystem services and being indicators of estuarine health, and are under increasing threat globally. This study examined the spatial and temporal variability of four dominant seagrass genera (Posidonia, Zostera, Halophila and Ruppia) among five geomorphic estuary types and four levels of estuarine maturity in New South Wales (NSW), Australia, over a 40-year period. While there was a decline in total seagrass area across NSW over the last 40 years, this was mostly attributed to Ruppia, the genus with the greatest temporal variability. The composition of seagrasses differed among estuary types and with the maturity of Barrier estuaries. Posidonia was found to be the least temporally variable genus over the last 40 years. The greatest overall annual rate of decline was 1.85% year−1 for Ruppia which is considerably less than the global estimated rate of 5% year−1 over the same time period. Average annual rates of decline were greater over the last 18 years than the last 40 years, but only for the most transient genera and only in some estuary types. Recent declines in Posidonia were greater than those over the last 40 years in two of the most heavily urbanised estuaries. The temporal variability of Zostera differed significantly among estuary types and decreased with increasing water depth across all estuaries. No relationships were found between catchment disturbances, measured as land use or population density, and seagrass change or temporal variability at the estuary scale. Our results highlight the importance of distinguishing among seagrass genera when interpreting changes over time and considering factors such as estuary type, which is effectively a surrogate for environmental conditions. [ABSTRACT FROM AUTHOR]

The Gulf of Kachchh (GoK) is diversified with various marine habitats, influenced by semi-diurnal tidal amplitude and heavy sedimentation. Seagrass is one of the key habitats in GoK with the predominant diversity of Halophila ovalis, Halodule uninervis, and Thalassia hemprichii. The seagrass is subjected to be at risk than any other habitats due to natural and human impacts. Strategies need to be developed to conserve seagrass patches of inhospitable environments like GoK, which demands the present feasibility study on seagrass restoration. In the present study, the seagrass habitats of the GoK were assessed in Pirotan, Narara, and Mithapur reef areas. Halophila ovalis showed the most extensive coverage in all the studied sites during the study period (62.11 ± 5.60/m2 in Pirotan; 60.70 ± 7.24/m2 in Mithapur and 59.32 ± 5.45/m2 in Narara sites). Likewise, Thalassia hemprichii showed the least cover in all the three studied sites (25 ± 6.28/m2 at Narara; 28.93 ± 3.54/m2 in Pirotan and 31.78 ± 4.16/m2 in Mithapur sites). Site-specific strategies have been attempted to develop a successful seagrass restoration nursery for Ha. ovalis and H. uninervis in the GoK region. To restore the seagrass species, vegetative sprigs were planted using the staple method. To increase the stability, the sprigs were later planted by attaching them within the iron frame (1 m x 1 m size) with the support of metallic mesh. The water quality and physical property of the restoration sites were documented. Two potential seagrass meadows were also identified along the Marine National Park (MNP) which can act as donor sites for restoration along the GoK in future. [ABSTRACT FROM AUTHOR]

Plant species usually have either annual or perennial life cycles, but facultative annual species have annual or perennial populations depending on their environment. In terrestrial angiosperms, facultative annual species are rare, with wild rice being one of the few examples. Our review shows that in marine angiosperms (seagrasses) facultative annual species are more common: six (of 63) seagrass species are facultative annual. It concerns Zostera marina, Z. japonica, Halophila decipiens, H. beccarii, Ruppia maritima, and R. spiralis. The annual populations generally produce five times more seeds than their conspecific perennial populations. Facultative annual seagrass species occur worldwide. Populations of seagrasses are commonly perennial, but the facultative annual species had annual populations when exposed to desiccation, anoxia-related factors, shading, or heat stress. A system-wide ‘experiment’ (closure of two out of three connected estuaries for large-scale coastal protection works) showed that the initial annual Z. marina population could shift to a perennial life cycle within 5 years, depending on environmental circumstances. We discuss potential mechanisms and implications for plant culture. Further exploration of flexible life histories in plant species, and seagrasses in particular, may aid in answering questions about trade-offs between vegetative and sexual reproduction, and preprogrammed senescence.

The sea cucumber Holothuria atra is an ecologically and economically important benthic animal. However, biological and ecological data on growth of H. atra in Thai waters are non-existent. Therefore, the present study aimed to obtain and compare growth parameters from length-frequency data of H. atra collected from two habitats. Specimens were collected above ground on intertidal seagrass and seaweed beds along the Andaman coast of Thailand in Satun Province. Theoretical von Bertalanffy growth parameters were analyzed using the ELEFAN I program in the FiSAT II software package. Asymptotic length was smaller and growth coefficient was higher in the seagrass habitat than in the seaweed habitat (L∞ = 32 cm; K = 0.65 year-1 and L∞ = 40 cm; K = 0.55 year-1, respectively). It might be that sea cucumbers in the seagrass habitat survived in the less favorable environment by reaching asymptotic length more rapidly. The more complex structure of the seaweed habitat provides protection and shelter from water movement and low tide stresses. These conditions might be more suitable for growth. The theoretical age at length zero was -0.24 year in the seagrass habitat and -0.27 year in the seaweed habitat. In both habitats, length at birth was around 5 cm. Growth was rapid from age 0-2 years, but slow thereafter, until asymptotic length was reached at around 4 years in the seagrass habitat and 5 years in the seaweed habitat. These findings suggest that different habitats influence the growth of H. atra. [ABSTRACT FROM AUTHOR]

Seagrass has important ecological functions, namely as a nursery-grown, spawning and protection areas for marine biota. In the world, there are 60 species of seagrasses, and in Indonesia, there are 14 species from 7 genera. The waters of North Sulawesi store a high potential of seagrass ecosystems. This study aimed to observe the distribution of seagrass from the Bahoi, Manembo-Nembo, and Tandurusa coast, North Sulawesi, Indonesia. Sampling carried out at the lowest ebb at the lunar or full moon phase. The method used for sampling is random, both for transect and squared lines. The results showed that from the Bahoi, Menembo-Nembo and Tandurusa coast, ten seagrass species from 7 genera and two families were found, namely Enhallus acoroides, Cymodocea rotundata, Cymodocea serrulata, Halodule uninervis, Halodule pinifolia, Halophila minor, Halophla ovalis, Syringodium isoetifolium, Thalassia hemprichii, dan Thalassodendron ciliatum. Information on seagrass distribution in an area can be taken into consideration for the government and related agencies in drafting a regulation in the management of seagrass ecosystem resources.

Seven species of seagrass have been found in the Indian River Lagoon (IRL), making it an unusually diverse location at the global scale. From 1994 to 2019, the lagoon-wide distribution of these species reflected variations in temperature, salinity, and the availability of light at depth, which were related to latitudinal differences in hydrology and hydrodynamics along the IRL. In general, species richness was higher near the four southern inlets, and fewer species were found in areas with longer residence times for water. At a finer scale, the distribution of species varied among depths, with the greatest number of species found at mid-depths (~0.4-0.9 m). Prior to 2011, these patterns remained relatively consistent for ~ 40 years, but several, intense and prolonged phytoplankton blooms disrupted them. The areal extent of all seagrasses decreased by over 50%, the offshore ends of canopies moved shoreward and shallower, distributions of species along gradients of latitude and depth were disrupted, and mean percent cover decreased. Major changes in distribution and abundance of seagrasses arose when salinity, temperature, and availability of light at depth exceeded limits derived for each species. These substantial and widespread changes engendered concerns for recovery or rehabilitation of seagrasses in the lagoon. [ABSTRACT FROM AUTHOR]

The interaction between wave and submerged vegetation is the primary cause of wave-induced attenuation. Studies on wave vegetation interactions mostly considered aquatic monotypic plant meadows and limited work have been reported on heterospecific plant meadows, common in tropical shores of southern India. An attempt was made to understand the heterospecific vegetation meadow-wave interactions through a two-level, four factors, full factorial experimental design-based laboratory flume study under controlled conditions. Simulated vegetation mimics were used as a simplified representation of heterospecific seagrass species, Halophila spinulosa, Halophila ovalis to develop a linear empirical model. Four input variables viz., water depth (h), wave period (T), plant density (N) and bed roughness factor (f), were considered for the study with the wave attenuation (E %) as a response. The developed model was tested for adequacy by using the analysis of variance (ANOVA) technique. Main and interaction effects of the input variables were analyzed, compared, and validated. The results show that all the four input variables are statistically significant with the T has the highest significant individual effect on wave attenuation followed by f, h, and N. Evidential two-way interaction effects, mainly between h with the rest of the parameters were also observed. [ABSTRACT FROM AUTHOR]

Estimates of organic carbon (Corg) storage by seagrass meadows which consider inter-habitat variability are essential to understand their potential to sequester carbon dioxide (CO2) and derive robust global and regional estimates of blue carbon storage. In this study, we provide baseline estimates of seagrass extent, and soil Corg stocks and accumulation rates from different seagrass habitats at Rottnest Island (in Amphibolis spp., Posidonia spp., Halophila ovalis, and mixed Posidonia/Amphibolis spp. meadows). The Corg stocks in 0.5 m thick seagrass soil deposits, derived from 24 cores, were 5.1 ± 0.7 kg Corg m–2 (mean ± SE, ranging from 0.05 to 12.9 kg Corg m–2), accumulating at 23.2 ± 3.2 g Corg m–2 year–1 (ranging from 0.22 to 58.9 g Corg m–2 year–1) over the last decades. There were significant differences in Corg content (%) and stocks (mg Corg cm–3), stable carbon isotope composition of the soil organic matter (δ13C), and soil grain size among the seagrass meadows studied, highlighting that biotic and abiotic factors influence seagrass soil Corg storage. Mixed meadows of Posidonia/Amphibolis spp. and monospecific meadows of Posidonia spp. and Amphibolis spp. had the highest Corg stocks (ranging from 6.2 to 6.4 kg Corg m–2), while Halophila spp. meadows had the lowest Corg stocks (1.2 ± 0.6 kg Corg m–2). We estimated a total soil Corg stock of 48.1 ± 8.5 Gg Corg beneath the 755 ha of Rottnest Island’s seagrasses, and a Corg sequestration capacity of 0.81 ± 0.06 Gg Corg year–1, which is equivalent to the sequestration of ∼22% of the island’s current annual CO2 emissions. Our results contribute to the existing global dataset on seagrass soil Corg storage and show a significant potential of seagrass to sequester CO2, which are particularly relevant in the context of achieving carbon neutrality through conservation actions in environmentally-marketed, tourist destinations such as Rottnest Island.

Highlights • T. testudinum and H. johnsonii use external carbonic anhydrase to facilitate dehydration of HCO 3 −. • T. testudinum also utilizes an active proton pump to create localized H+ gradients. • Isotope ratios suggest T. testudinum is more C-limited under high-light conditions. • Ocean acidification may have greater benefits for H. johnsonii compared to T. testudinum. Abstract Mechanisms for carbon uptake in the small-bodied Halophila johnsonii and large-bodied Thalassia testudinum were compared using photosynthesis measurements (oxygen flux) with, and without, the extracellular carbonic anhydrase inhibitor acetazolamide (AZ) and TRIS buffer. Our results indicated T. testudinum and H. johnsonii both utilize external membrane-bound carbonic anhydrase to facilitate dehydration of HCO 3 − into CO 2(aq). T. testudinum also utilizes an active proton (H+) pump to create localized H+ gradients within the boundary layer and it derives a larger portion of photosynthetic carbon from bicarbonate than H. johnsonii. Stable carbon isotope composition (δ13C) of T. testudinum and H. johnsonii leaves under high and reduced irradiance were also compared to evaluate photosynthetic carbon use. Isotope ratios of H. johnsonii were significantly more negative than T. testudinum at a high-light field site (−10.44 ± 0.26‰ vs −9.25 ± 0.25‰). In contrast, there was no significant difference in isotope ratios between species for plants maintained in a greenhouse under reduced photosynthetically active radiation. This suggests photosynthesis of T. testudinum is more carbon limited or more reliant on bicarbonate for photosynthesis than H. johnsonii under high-light conditions. Although photosynthesis of both species is expected to increase in response to greater CO 2(aq) availability, ocean acidification and its CO 2(aq) enrichment of seawater may have greater benefits for H. johnsonii compared to T. testudinum , whose photosynthesis relies more heavily on HCO 3 − use. [ABSTRACT FROM AUTHOR]

Abstract The remediation and subsequent use of saline-alkaline land are of great significance to ecological environment construction and sustainable agricultural development. Iris halophila Pall. is a salt-tolerant medicinal and ornamental plant, which has good application prospects in the ecological construction of saline-alkaline land; therefore, study of the molecular mechanisms of salt tolerance in I. halophila has important theoretical and practical value. To evaluate the molecular mechanism of the response of I. halophila to salt toxicity, I. halophila seedlings were treated with salt (300 mM NaCl) and subjected to deep RNA sequencing. The clean reads were obtained and assembled into 297,188 unigenes. Among them, 1120 and 100 salt-responsive genes were identified in I. halophila shoots and roots, respectively. Among them, the key flavonoid and lignin biosynthetic genes, hormone signaling genes, sodium/potassium ion transporter genes, and transcription factors were analyzed and summarized. Quantitative reverse-transcription PCR analysis strengthened the reliability of the RNA sequencing results. This work provides an overview of the transcriptomic responses to salt toxicity in I. halophila and identifies the responsive genes that may contribute to its reduced salt toxicity. These results lay an important foundation for further study of the molecular mechanisms of salt tolerance in I. halophila and related species. Highlights • The transcriptome of Iris halophila Pall. was investigated under salt stress. • 1215 salt-regulated genes were identified by RNA-Seq in I. halophila. • Provides an overview of transcriptomic responses to salt toxicity in I. halophila. [ABSTRACT FROM AUTHOR]

Highlights • Seagrasses in the Eastern Tropical Pacific are difficult to locate and may be ephemeral. • We report seagrasses at a new location on the northern Pacific coast of Costa Rica. • Species found were Halophila baillonis and Halodule beaudettei. • Biomass at Bahía Potrero was lower than further south in Golfo Dulce. Abstract Seagrass meadows provide a multitude of ecosystem services, yet they are currently threatened and declining worldwide due to anthropogenic impacts. Current knowledge of seagrass presence in the Eastern Tropical Pacific (ETP) is scarce, in part due to challenges in finding the small seagrass species found and their dynamic and possibly ephemeral nature, with only very limited reports of currently extant meadows. Here, we characterize seagrasses at a new location, Bahía Potrero, on the northern Pacific coast of Costa Rica. Seagrasses were sighted at this location on four occasions between 2015 and 2017. Two seagrass species were found, Halophila baillonis and Halodule beaudettei. Seagrasses were present at ∼ 3–6 m depth at mean sea level (local tidal range ∼ 3 m). Biomass and sediment cores were collected in 2017, total biomass was 3.9 ± 4.0 g DW m−2 and density 569 ± 493 shoots m−2. Leaf length was 1.1 ± 0.29 cm, width 0.5 ± 0.08 cm, and area 1.4 ± 0.67 cm2. Above ground biomass δ 13C was -11.7 ± 0.8‰ and δ 15N 5.4 ± 0.8‰, while below ground was -11.7 ± 1.3‰ and 5.3 ± 0.8‰. Sediment δ 13C was -21.2 ± 0.6‰ and δ 15N was 8.6 ± 0.4‰. Sediments were dominated by very fine sand, with 1.6 ± 0.3% organic carbon content and 23.0 ± 7.9% inorganic carbon. Carbon content standardized to 10 cm sediment depth was 20.5 ± 5.1 Mg OC ha-1 and 295.1 ± 109.8 Mg IC ha-1. Given the numerous threats that seagrasses are under and the lack of information on seagrasses in the ETP it is critical to increase our knowledge on seagrasses in this region for adequate management and conservation initiatives. [ABSTRACT FROM AUTHOR]

Natural populations of a Rivularia-like cyanobacterium were collected from the carbonate deposits of the temporarily flooded littoral zone of a hypersaline, high elevation lake, The Laguna Negra, Andes, Argentina. Subsequently, the cyanobacterial strain PUNA-NP3, named after its origin (Puna Volcanic Plateau) was isolated from these Rivularia-like rounded, pillow-like, black microbial mats. None of the previously described species of the genus Rivularia occupy inland, hypersaline aquatic environments. After morphological examination of this strain, we found clear morphological autapomorphies, such as mucilaginous pads at the bases of the young trichomes, wide trichomes and filaments, and uniquely branched trichomes. Furthermore, based on results from 16S rRNA phylogeny and analysis of the 16S-23S ITS region, PUNA-NP3 was found to be an independent lineage of the evolutionary tree. Based on the combination of ecological, morphological and molecular evidence, we name strain PUNA-NP3 Rivularia halophila sp. nov. a new species under requirements of the International Code of Nomenclature for Algae, Fungi and Plants. [ABSTRACT FROM AUTHOR]

The effects of opening the Suez Canal as a connection between the Red Sea and the Mediterranean Sea were reported for a number of marine species. However, the evolutionary origin of the seagrasses in the Red Sea and the linking population genetics of seagrasses between the Arabian Sea, the Gulf of Aden, the Red Sea and the Mediterranean Sea have not yet been investigated in detail. The invasion of Halophila stipulacea Asch. from the Red Sea into the Mediterranean Sea after the opening of the Suez Canal was already recorded. We hypothesize that Halophila ovalis populations in the Red Sea developed through long-term historical processes such as vicariant evolutionary diversification. Seagrass samples were collected along the Egyptian coastline of the Red Sea and analysed by the molecular marker ITS. The sequences were compared with published ITS sequences from seagrasses collected in the whole area of interest. In this study, we reveal the linking population genetics, phylogeography and phylogenetics of two dominant seagrass species, Halophila stipulacea and Halophila ovalis, among species collected in the Red Sea and worldwide. The results indicate that the Red Sea Halophila ovalis populations do not group to Halophila ovalis worldwide, and Halophila major, Halophila ovalis collected worldwide and Halophila ovalis collected at the Red Sea are sister clades. Hence, vicariant evolutionary diversification for Halophila ovalis may occur in the Red Sea. [ABSTRACT FROM AUTHOR]

This study aimed to shed further light on the capacity of the seagrass Halophila stipulacea to accumulate and biomonitor the elements As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn, present in water and sediments. Results showed that the organs of H . stipulacea accumulate different levels of trace elements, whose concentrations decrease mainly in the order of roots > rhizomes > leaves. The seagrass H . stipulacea showed levels of trace elements similar to those found in other Mediterranean seagrasses, e.g. Posidonia oceanica and Cymodocea nodosa . This study showed that H . stipulacea could act as a promising bioindicator of several elements, present in sediments, including As, Cd, Cu, Mn, Ni and Zn. [ABSTRACT FROM AUTHOR]

Deviations from the 1:1 sex ratio are common in dioecious plants. The tropical seagrass Halophila stipulacea is among an extremely rare group of dioecious plants that are widely recognized as female-biased. Here we report on differences in sex ratios between native (Eilat, northern Red Sea) and invasive (Cyprus, Mediterranean Sea) populations. While H. stipulacea populations were female-biased in their native region, invasive populations were either male- or female-biased. The existence of both sexes simultaneously in the Mediterranean invasive populations might help its ongoing expansion in the Mediterranean, thereby threatening local seagrasses species. [ABSTRACT FROM AUTHOR]

Cytogenetic studies for systematic and evolutionary purposes are lacking on marine phanerogams. Halophila stipulacea is a tropical seagrass that invaded the Mediterranean from the Red Sea through the Suez Canal. In this study, we report, for the first time, the karyotype features and genome size of H. stipulacea populations from different localities. Also, an attempt to compare our data with those reported in literature on other Halophila species is discussed. To determine the karyological relationships among taxa, we used basic karyotypic features such as chromosome number, size and symmetry, and position of chromosomal landmarks. To estimate karyotype asymmetry, the Coefficient of Variation of Chromosome Length (CV CL ) and the Mean Centromeric Asymmetry (M CA ) values were calculated. The estimations of DNA amounts were carried out by Image Cytometry (IC) using the interphase-peak method. All the taxa, including those reported in literature, present a uniform and slightly bimodal karyotype, but significant differences are found in nuclear DNA content among species. Each taxa had a karyotype formula 2 n  = 18 = 10 m  + 2 sm  + 6 st . Aneuploidy and polyploidy seemed to not be involved in the speciation of this genus. The conserved karyotype in these taxa suggests the presence of mechanisms selecting for constancy, or against changes, in karyotype number and morphology. [ABSTRACT FROM AUTHOR]

Seagrasses inhabit environments where light varies at different timescales, nonetheless are acutely sensitive to reductions in light beyond some conditional bounds. Two tropical deep-water seagrasses, Halophila decipiens and Halophila spinulosa , from the Great Barrier Reef were tested for their response to defined light and temperature regimes to identify their growth requirements and potential thresholds of mortality. Species were exposed to two light intensities, saturating (75 μmol photons m −2 s −1 ) and limiting (25 μmol photons m −2 s −1 ) light and two temperature treatments (26 °C and 30 °C) over a four-week period. Wavelength-specific parameters of PSII photochemistry were evaluated for seagrass leaves, as well as shoot density, gas exchange, and pigment content. Both species were sustained under saturating light levels (3.2 mol photons m −2 d −1 ) while limiting light led to decreased shoot density for H. decipiens and H. spinulosa after two and four weeks, respectively. Wavelength-specific photochemistry was also affected under light-limiting treatments for both species while the functional absorption cross section was highly conserved. Photoacclimation and physiological adjustments by either species was not adequate to compensate for reduced irradiance suggesting these plants reside at the margins of their functional limits. As such, relatively short periods of light attenuating events, like dredging or flood plumes, may be detrimental to deep-water seagrass populations. [ABSTRACT FROM AUTHOR]

Background and Aims Ephemeral seagrasses that respond rapidly to environmental changes are important marine habitats. However, they are under threat due to human activity and are logistically difficult and expensive to study. This study aimed to develop a new functional--structural environmentally dependent model of ephemeral seagrass, able to integrate our understanding of ephemeral seagrass growth dynamics and assess options for potential management interventions, such as seagrass transplantation. Methods A functional--structural plant model was developed in which growth and senescence rates are mechanistically linked to environmental variables. The model was parameterized and validated for a population of Halophila stipulacea in the Persian Gulf. Key Results There was a good match between empirical and simulated results for the number of apices, net rhizome length or net number of internodes using a 330 d simulation. Simulated data were more variable than empirical data. Simulated structural patterns of seagrass rhizome growth qualitatively matched empirical observations. Conclusions This new model successfully simulates the environmentally dependent growth and senescence rates of our case-study ephemeral seagrass species. It produces numerical and visual outputs that help synthesize our understanding of how the influence of environmental variables on plant functional processes affects overall growth patterns. The model can also be used to assess the potential outcomes of management interventions like seagrass transplantation, thus providing a useful management tool. It is freely available and easily adapted for new species and locations, although validation with more species and environments is required. [ABSTRACT FROM AUTHOR]

Summary: The influence of soil temperature on rhizome depths of four intertidal seagrass species was investigated in central Queensland, Australia. We postulated that certain intertidal seagrass species are soil temperature‐sensitive and vertically stratify rhizome depths. Below‐ground vertical stratification of intertidal seagrass rhizome depths was analysed based upon microclimate (soil temperature) and microhabitat (soil type). Soil temperature profiles exhibited heat transfer from surface layers to depth that varied by microhabitat, with vertical stratification of rhizome depths between species. Halodule uninervis rhizomes maintain a narrow median soil temperature envelope; compensating for high surface temperatures by occupying deeper, cooler soil substrates. Halophila decipiens, Halophila ovalis and Zostera muelleri rhizomes are shallow‐rooted and exposed to fluctuating temperatures, with broader median temperature envelopes. Halodule uninervis appears to be a niche specialist, with the two Halophila species considered as generalist niche usage species. The implications of niche use based upon soil temperature profiles and rhizome rooting depths are discussed in the context of species’ thermal tolerances and below‐ground biomass O2 demand associated with respiration and maintenance of oxic microshields. This preliminary evidence suggests that soil temperature interaction with rhizome rooting depths may be a factor that influences the distribution of intertidal seagrasses. [ABSTRACT FROM AUTHOR]

The effect of citric acid (CA) and EDTA on the growth, root and leaf anatomical structure, photosynthetic properties and lead (Pb) accumulation in Iris halophila seedlings cultivated in Pb mine tailings for 30 days were studied. Results showed that the dry weights of above-ground parts and underground parts of I. halophila under the treatments of 2 mmol kg −1 CA increased significantly and the tolerant index (IT) value treated with 2 mmol kg −1 EDTA was 19% lower than the control. The contents of photosynthetic pigments increased and decreased significantly with 0.5 mmol kg −1 CA and 2.0 mmol kg −1 EDTA, respectively. The leaf anatomic structure was negatively impacted by 2.0 mmol kg −1 EDTA. Treatment of 2 mmol kg −1 CA enhanced Cd and Zn accumulation in the above-ground parts, and Pb, Cu, Cd and Zn accumulation in the underground parts. EDTA treatments promoted Pb and Cd accumulation in both parts of I. halophila . The results indicated that the addition of organic acids could promote Pb and Cd accumulation and I. halophila could serve as pioneer species to be used in remediation of Pb mine tailings to improve the harsh environment. [ABSTRACT FROM AUTHOR]

Abstract: The tropical seagrass Halophila stipulacea exhibits a limited capacity to use nitrate, but has a high uptake capacity and efficiency for ammonium. Consequently, N2 fixation by associated diazotrophic epiphytes may be important in providing ammonium needed for seagrass photosynthesis and growth. When exposed to seasonality, this association could provide a competitive advantage for H. stipulacea in relation to other seagrass species, but related knowledge is scarce. Here, we thus report measurements of net photosynthesis (O2 fluxes) and N2 fixation (acetylene reduction) associated with H. stipulacea from the Northern Red Sea over all four seasons of 2013. In parallel, we characterized the seagrass meadow areal extent, shoot and leaves density, and the leaf area index. Using this data, we quantified meadow net primary production and N2 fixation and estimated the photo‐metabolic N demand met by N2 fixation at the community level. Results revealed a marked seasonality of meadow N2 fixation, with rates ranging from 0.06 in winter to 4.60 mmol N m−2 d−1 in summer, i.e., an increase by two orders of magnitude. In summer, when nutrient concentrations in the water column were lowest and light intensity and temperature highest, there was a significant positive linear relationship between meadow net primary production and N2 fixation, with the latter accounting for ca. 20% of the photo‐metabolic N demand. These findings suggest that N2 fixation by associated diazotrophic epiphytes can mitigate N limitation of H. stipulacea meadows under N scarcity. This trait may also favor the ongoing geographical expansion of H. stipulacea. [ABSTRACT FROM AUTHOR]

The invasive seagrass Halophila stipulacea has spread throughout the eastern Caribbean since it was first recorded in Grenada in 2002. We quantified the distribution and abundance of H. stipulacea , and its associated macroinvertebrate fauna, in sampling stations and transects around the island of Carriacou (a nearby dependency of Grenada) in early 2016. Halophila stipulacea occurred in extensive monospecific stands (average bottom cover, 62%), or smaller mixed stands with native seagrass ( Thalassia testudinum , Syringodium filiforme , Halodule wrightii ), at 1–5 m depth in large bays along the leeward (west) coast. It was sparsely distributed on the more wave-exposed east and south coasts, usually in mixed patches with native seagrass. In leeward bays, H. stipulacea has largely replaced the native seagrass H. wrightii , providing a novel biogenic habitat for various filter-feeding invertebrates living within the turf-like leaf canopy (e.g., sponges, ascidians, bivalves, ophiuroids), and sea urchins (mainly Tripneustes ventricousus ) and a microphagous sea star ( Oreaster reticulatus ) that graze upon it. Populations of the sea star consisted mainly of juveniles indicating the seagrass may serve as a nursery habitat for this endangered species. The spread of H. stipulacea along the leeward coast of Carriacou in recent years represents a community-level shift in the shallow subtidal zone, with attendant changes in habitat structure, species composition, and trophic interactions. [ABSTRACT FROM AUTHOR]

Caribbean seagrass habitats provide food and protection for reef-associated juvenile fish. The invasive seagrass Halophila stipulacea is rapidly altering these seascapes. Since its arrival in the Caribbean in 2002, H. stipulacea has colonized and displaced native seagrasses, but the function of this invasive seagrass as a juvenile fish habitat remains unknown. To compare diversity, community structure, and abundance of juvenile fish between H. stipulacea and native seagrass beds, fish traps were deployed in four nearshore bays around St. Thomas, U.S. Virgin Islands. Traps were deployed in Frenchman, Lindbergh, and Sprat Bays for 24 h intervals in patches of bare sand, patches of H. stipulacea and patches of the native Caribbean seagrasses Thalassia testudinum and Syringodium filiforme. Traps were then deployed in Brewers Bay for 12 h intervals in stands of H. stipulacea and S. filiforme. Relative and total abundances of juvenile fish, identified at least to family, were compared across treatment habitats for each trap deployment period. The catch from H. stipulacea, compared to native seagrasses, comprised a greater abundance of nocturnal carnivores Lutjanus synagris (family Lutjanidae) and Haemulon flavolineatum (family Haemulidae). Additionally, the herbivore species Sparisoma aurofrenatum (family Labridae) and Acanthurus bahianus (family Acanthuridae) and the diurnal carnivore species Pseudopeneus maculatus (family Mullidae) were relatively scarce in H. stipulacea. The catch from sand was much smaller, compared to vegetated habitats, and comprised only L. synagris, H. flavolineatum, and H. aurolineatum. These results provide evidence of reduced family diversity and altered juvenile fish assemblages in H. stipulacea, driven by an abundance of some nocturnal carnivores and scarcity of herbivores and diurnal carnivores. The findings from the present work underpin the need for further investigation and mitigation of this invasion, particularly where H. stipulacea is driving seascape-alterations of key juvenile fish habitats. [ABSTRACT FROM AUTHOR]

The non-native seagrass species Halophila stipulacea has spread throughout the Eastern Caribbean since 2002, and could potentially impact the functioning of local seagrass ecosystems. Important characteristics for invasiveness, such as dispersal, recruitment and expansion of H. stipulacea at a local scale, are unknown. We assessed H. stipulacea expansion rates within Lac Bay, Bonaire, Dutch Caribbean (7 km²), since its establishment in 2010 and tested the settlement potential of uprooted vegetative fragments of H. stipulacea. Using 49 fixed locations, we observed that between 2011 and 2015 the occurrence of H. stipulacea in the bay increased significantly from 6% to 20% while native Thalassia testudinum occurrence decreased significantly from 53% to 33%. Free-floating H. stipulacea fragments that were collected and tethered above the sediment rooted within 10 days with a settlement success rate of 100%. The growth of settled fragments was on average 0.91 shoots d-1. The ongoing shift from native T. testudinum to introduced H. stipulacea dominated meadows may have important consequences for multiple Caribbean seagrass ecosystem functions. Given the large difference in size between the two seagrass species, functions such as coastal protection, habitat structure, food availability, and the stability and resilience of these systems can be altered. The next steps towards modelling future expansion of H. stipulacea throughout the Caribbean and beyond should include the assessment of fragment viability and dispersal distance, and the impacts of natural and anthropogenic disturbance on vegetative fragment density, dispersion and settlement by this species. [ABSTRACT FROM AUTHOR]

The growth dynamics of two co-occurring seagrass species, Zostera marina and Halophila nipponica, were examined on the southern coast of the Korean peninsula. Zostera marina is a native dominant seagrass species in Korean coastal waters, whereas H. nipponica is a non-native tropical and subtropical species that has extended its distributional range to the temperate coastal areas of Korea. To examine the differences in the growth dynamics of H. nipponica and Z. marina, their morphology, density, productivity and biomass, as well as local environmental conditions, were monitored monthly from January 2008 to July 2009. Underwater irradiance at the study site was the highest in April 2009 and the lowest in January 2008. Water temperature ranged from 10.4°C in January 2009 to 24.8°C in September 2008. Significant differences in growth dynamics were observed between the species, due to the effect of water temperature at the study site. Density and areal productivity were the highest in April 2008 and June 2008, respectively, for Z. marina but the highest in July 2008 for H. nipponica. Leaf size, shoot height and shoot weight were the highest in July 2008 for Z. marina but the highest in August 2008 or September 2008 for H. nipponica. The productivity of both species was strongly correlated with water temperature at the study site. However, the productivity of these species was not strongly correlated with underwater irradiance or the nutrient availability of either the water column or sediment pore water. Zostera marina exhibited the ecological characteristics of a temperate seagrass, whereas H. nipponica retained the features of a subtropical/tropical seagrass, even after adapting to the temperate coastal waters of Korea. [ABSTRACT FROM AUTHOR]

Halophila beccarii is a threatened tropical seagrass which has a narrow, restricted distribution in the shallow coastal areas of the Indo-Pacific. The monoecious H. beccarii reproduces both sexually or asexually and such mixed reproduction mode is important to stay resilient in a dynamic coastal environment. This study examined genetic diversity and structure of H. beccarii to determine its survival strategy within a tropical coastal lagoon of Southeast Asia (Central Viet Nam). Seven microsatellite loci gave an overall low level of allelic richness ( A r = 1.9), gene diversity ( H E = 0.233) and clonal diversity (R = 0.27). A small neighborhood size and short dispersal distance together with a significant fine-scale genetic structure within each site indicated that its survival strategy is through local seed recruitment over very short distances and a limited local clonal extension (< 5 m). These estimations together with a low selfing rate, no inbreeding and significant recent bottlenecks, all indicated that the main resilience strategy of H. beccarii meadows is through sexual reproduction and within site dispersal. Implications for conservation are that environmental conditions of the lagoon should allow to maintain a local recruitment, establishment and development of H. beccarii beds at site level. [ABSTRACT FROM AUTHOR]

To evaluate the impact of invading seagrass on biogeochemical processes associated with sulfur cycles, we investigated the geochemical properties and sulfate reduction rates (SRRs) in sediments inhabited by invasive warm affinity Halophila nipponica and indigenous cold affinity Zostera marina. A more positive relationship between SRR and below-ground biomass (BGB) was observed at the H. nipponica bed (SRR = 0.6809 × BGB − 4.3162, r = 0.9878, p = 0.0006) than at the Z. marina bed (SRR = 0.3470 × BGB − 4.0341, r = 0.7082, p = 0.0357). These results suggested that SR was more stimulated by the dissolved organic carbon (DOC) exuded from the roots of H. nipponica than by the DOC released from the roots of Z. marina. Despite the enhanced SR in spring-summer, the relatively lower proportion (average, 20%) of acid-volatile sulfur (AVS) in total reduced sulfur and the strong correlation between total oxalate-extractable Fe (Fe) and chromium-reducible sulfur (CRS = 0.2321 × total Fe + 1.8180, r = 0.3344, p = 0.0076) in the sediments suggested the rapid re-oxidation of sulfide and precipitation of sulfide with Fe. The turnover rate of the AVS at the H. nipponica bed (0.13 day) was 2.5 times lower than that at the Z. marina bed (0.33 day). Together with lower AVS turnover, the stronger correlation of SRR to BGB in the H. nipponica bed suggests that the extension of H. nipponica resulting from the warming of seawater might provoke more sulfide accumulation in coastal sediments. [ABSTRACT FROM AUTHOR]

As a result of anthropogenic influences and global climate change, emerging infectious marine diseases are thought to be increasingly more common and more severe than in the past. The aim of our investigation was to confirm the presence of Labyrinthula, the aetiological agent of the seagrass wasting disease, in Southeastern Australia and provide the first isolation and characterisation of this protist, in Australia. Colonies and individual cells were positively identified as Labyrinthula using published descriptions, diagrams, and photographs. Their identity was then confirmed using DNA barcoding of a region of the 18S rRNA gene. Species level identification of isolates was not possible as the taxonomy of the Labyrinthula is still poorly resolved. Still, a diversity of Labyrinthula was isolated from small sections of the southeast coast of Australia. The isolates were grouped into three haplotypes that are biogeographically restricted. These haplotypes are closely related to previously identified saprotrophic clades. The study highlights the need for further investigation into the global distribution of Labyrinthula, including phylogenetic pathogenicity and analysis of host-parasite interactions in response to stressors. Given the results of our analyses, it is prudent to continue research into disease and epidemic agents to better prepare researchers for potential future outbreaks. [ABSTRACT FROM AUTHOR]

Although seagrass species in the genus Halophila are generally distributed in tropical or subtropical regions, H. nipponica has been reported to occur in temperate coastal waters of the northwestern Pacific. Because H. nipponica occurs only in the warm temperate areas influenced by the Kuroshio Current and shows a tropical seasonal growth pattern, such as severely restricted growth in low water temperatures, it was hypothesized that this temperate Halophila species diverged from tropical species in the relatively recent evolutionary past. We used a phylogenetic analysis of internal transcribed spacer (ITS) regions to examine the genetic variability and evolutionary trend of H. nipponica. ITS sequences of H. nipponica from various locations in Korea and Japan were identical or showed very low sequence divergence (less than 3-base pair, bp, difference), confirming that H. nipponica from Japan and Korea are the same species. Halophila species in the section Halophila, which have simple phyllotaxy (a pair of petiolate leaves at the rhizome node), were separated into five well-supported clades by maximum parsimony analysis. H. nipponica grouped with H. okinawensis and H. gaudichaudii from the subtropical regions in the same clade, the latter two species having quite low ITS sequence divergence from H. nipponica (7–15-bp). H. nipponica in Clade I diverged 2.95 ± 1.08 million years ago from species in Clade II, which includes H. ovalis. According to geographical distribution and genetic similarity, H. nipponica appears to have diverged from a tropical species like H. ovalis and adapted to warm temperate environments. The results of divergence time estimates suggest that the temperate H. nipponica is an older species than the subtropical H. okinawensis and H. gaudichaudii and they may have different evolutionary histories. [ABSTRACT FROM AUTHOR]

Two new eudesmane-type sesquiterpene lactones were isolated by column chromatography from the CHCl extract of the endemic plant Artemisia halophila. Their structures were elucidated based on PMR and C NMR spectral data and an X-ray crystal structure analysis. The eudesmanolide artesin and 7-methoxycoumarin were identified for the first time from this Artemisia species. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The nomenclature for the seagrass clover grass continues confused. • H. baillonii or H baillonis ? • The correct name is Halophila baillonii Ascherson. Abstract Seagrasses in the Tropical Atlantic region include ten species, five of which are from the Halophila genus. One of these species, the clover grass Halophila baillonii , is currently considered as vulnerable by the IUCN (Red List), with a fragmented distribution in the Caribbean, Atlantic Ocean in Brazil and in the Eastern Tropical Pacific. There is confusion as to the correct nomenclature for this species with both H. baillonii and H baillonis treated as synonyms. Here, we clarify that given that the first description of the species was provided by Ascherson in 1875, following the International Code of Nomenclature for algae, fungi, and plants based on the first valid publication with a diagnosis of the taxon, the correct name to be used for this species is Halophila baillonii Ascherson and should be referred to as such in the future. [ABSTRACT FROM AUTHOR]

Seagrass beds are the largest organism-built marine habitat in Dominica, yet have only been surveyed since 2007. Standardized examinations along a depth gradient between 0 and 24m, focusing on magnoliophyte species composition and benthic cover of shoots at 17 seagrass bed sites, were carried out between September 10 and December 7, 2008. The Cymodoceaceae Syringodium filiforme (Kuetzing 1860) and Halodule wrightii (Ascherson 1868), as well as the Hydrocharitaceae Halophila decipiens (Ostenfeld 1902), H. stipulacea (Fosskal & Ascherson 1867) and Thalassia testudinum (Banks ex König 1805) displayed distinct regional and horizontal distribution patterns. Syringodium filiforme is the island’s dominant seagrass along the western and northern coasts, occurring at depths between 2 and 18m and with a mean benthic cover ranging from 0.9-10% along the West coast. Along the North coast it grew between 0.2 and 1m depth with a mean maximum benthic cover of 48.9%. Halodule wrightii grew along the North and West coasts, in depths between 1 and 14m in areas of recent and chronic disturbances. Its delicate morphology and sparse benthic cover (Pastos marinos son los ambientes más grandes constituidos por organismos en Dominica. Sin embargo, sólo se han examinado desde 2007. Entre el 10 de septiembre y 9 de diciembre 2008, se examinaron la composicion de especies y la densidad de magnoliofitas en profundidades de 0 a 24m. Los Cymodoceaceae: Syringodium filiforme y Halodule wrightii, tal como los Hydrocharitaceae: Halophila decipiens, H. stipulacea y Thalassia testudinum, mostraron una distribución regional y horizontal muy distinta. Syringodium filiforme fue la especie dominante en las costas del oeste y del norte de la isla. Se encontró en profundidades de 2 a 18m y con un promedio de cobertura béntica de 0.9-10% en la costa del oeste. En las costas del norte creció entre 0.2 y 1m de profundidad con un pormedio de cobertura béntica de 48.9%. Halodule wrightii creció en las costad del norte y oeste, en profundidades de 1 a 14m en áreas de perturbaciones recientes o crónicas. Su morfología delicada y su baja cobertura béntica (

Halophila stipulacea is a small tropical seagrass species. It is the dominant seagrass species in the Gulf of Aqaba (GoA; northern Red Sea), where it grows in both shallow and deep environments (1-50 m depth). Native to the Red Sea, Persian Gulf, and Indian Ocean, this species has invaded the Mediterranean and has recently established itself in the Caribbean Sea. Due to its invasive nature, there is growing interest to understand this species' capacity to adapt to new conditions, which might be attributed to its ability to thrive in a broad range of ecological niches. In this study, a multidisciplinary approach was used to depict variations in morphology, biochemistry (pigment and phenol content) and epiphytic bacterial communities along a depth gradient (4-28 m) in the GoA. Along this gradient, H. stipulacea increased leaf area and pigment contents (Chlorophyll a and b, total Carotenoids), while total phenol contents were mostly uniform. H. stipulacea displayed a well conserved core bacteriome, as assessed by 454-pyrosequencing of 16S rRNA gene reads amplified from metagenomic DNA. The core bacteriome aboveground (leaves) and belowground (roots and rhizomes), was composed of more than 100 Operational Taxonomic Units (OTUs) representing 63 and 52% of the total community in each plant compartment, respectively, with a high incidence of the classes Alphaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria across all depths. Above and belowground communities were different and showed higher within-depth variability at the intermediate depths (9 and 18 m) than at the edges. Plant parts showed a clear influence in shaping the communities while depth showed a greater influence on the belowground communities. Overall, results highlighted a different ecological status of H. stipulacea at the edges of the gradient (4-28 m), where plants showed not only marked differences in morphology and biochemistry, but also the most distinct associated bacterial consortium. We demonstrated the pivotal role of morphology, biochemistry (pigment and phenol content), and epiphytic bacterial communities in helping plants to cope with environmental and ecological variations. The plant/holobiont capability to persist and adapt to environmental changes probably has an important role in its ecological resilience and invasiveness. [ABSTRACT FROM AUTHOR]

Seagrasses comprise 78 species and are rarely invasive. But the seagrass Halophila stipulacea , firstly recorded in the Caribbean in the year 2002, has spread quickly throughout the region. Previous works have described this species as invasive in the Caribbean, forming dense mats that exclude native seagrass species. During a reconnaissance field survey of Caribbean seagrass meadows at the islands of Bonaire and Sint Maarten in 2013, we observed that this species was only extremely dense at 5 out of 10 studied meadows. Compared to areas with sparse growth of H. stipulacea , these dense meadows showed consistently higher nutrient concentrations, as indicated by higher leaf tissue N contents of the seagrass Thalassia testudinum (dense when C:N < 22.5) and sediments (dense when %N > 11.3). Thus, the potential invasiveness of this non-native seagrass most likely depends on the environmental conditions, especially the nutrient concentrations. [ABSTRACT FROM AUTHOR]

Pb tolerant mechanisms, plant physiological response and Pb sub-cellular localization in the root cells of Iris halophila were studied in sand culture and the Pb mine tailings. Results showed that the activities of superoxide dismutase (SOD) and peroxidase (POD) in the underground parts and the activity of catalase (CAT) in the aboveground and underground parts increased as Pb level was enhanced. Glutathione (GSH) and ascorbic acid (AsA) contents increased by Pb treatments. Pb deposits were found in the middle cell walls or along the inner side of epibiotic protoplasm of some cells which accumulated a large quantity of Pb and died. The dry weights (DWs) of aboveground parts under all Pb tailings treatments decreased insignificantly, while the DW of the underground parts growing in the pure Pb tailings decreased significantly. Pb, Cu, Cd, and Zn contents increased significantly as the levels of Pb tailings were enhanced and Pb contents in the aboveground and underground parts reached 64.75 and 751.75 μg/g DW, respectively, at pure Pb tailings treatment. The results indicated that I. halophila is a promising plant in the phytoremediation of Pb contaminated environment. Some antioxidant enzymes, antioxidants and compartmentalization of Pb were played major roles in Pb tolerance of I. halophila. [ABSTRACT FROM AUTHOR]

Seagrasses are a critical component of the healthy functioning of many coastal marine ecosystems. Capturing the dynamics of seagrass communities requires both a detailed representation of processes such as seagrass nutrient uptake and photosynthesis, as well as models of light penetration, water column and sediment biogeochemical processes and other ecosystem characteristics that determine the environmental state. Here we develop a new two-state, 13-parameter seagrass model with the aim of providing sufficient detail to represent light and nutrient limitation, but simple enough to be coupled into a 60 state variable biogeochemical model. The novel formulation is built around a nitrogen-specific leaf area parameter, Ω , that is well-constrained and is used in calculating both the rate of photosynthesis and the fraction of the seafloor covered by seagrass, A eff , where A eff = 1 − exp(− ΩSG A ) and SG A is the aboveground areal seagrass biomass. The model also contains terms for the uptake of nutrients from multiple layers of varying-porosity sediments, translocation of organic matter between leaves and roots, respiration and simple mortality terms. The model is applied to Gladstone Harbour, a macro-tidal sub-tropical estuary in northeast Australia, and is able to simulate realistic spatial seagrass distributions. A simplified form of the model is derived, which can be used to predict seagrass light-limited growth based on five measurable species-specific parameters (maximum growth rate, mortality rate, compensation irradiance, leaf blade angle and nitrogen-specific leaf area). The steady-state percent coverage of seagrass achieved at varying light levels and mortality intensity is calculated as a means of understanding the dynamics of the new seagrass model. [ABSTRACT FROM AUTHOR]