Seagrass Genera Research Articles

Analysis of rDNA reveals a high genetic diversity of Halophila major in the Wallacea region.

The genus Halophila shows the highest species diversity within the seagrass genera. Southeast Asian countries where several boundary lines exist were considered as the origin of seagrasses. We hypothesize that the boundary lines, such as Wallace's and Lydekker's Lines, may act as marine geographic barriers to the population structure of Halophila major. Seagrass samples were collected at three islands in Vietnamese waters and analyzed by the molecular maker ITS. These sequences were compared with published ITS sequences from seagrasses collected in the whole region of interest. In this study, we reveal the haplotype and nucleotide diversity, linking population genetics, phylogeography, phylogenetics and estimation of relative divergence times of H. major and other members of the Halophila genus. The morphological characters show variation. The results of the ITS marker analysis reveal smaller groups of H. major from Myanmar, Shoalwater Bay (Australia) and Okinawa (Japan) with high supporting values. The remaining groups including Sri Lanka, Viet Nam, the Philippines, Thailand, Malaysia, Indonesia, Two Peoples Bay (Australia) and Tokushima (Japan) showed low supporting values. The Wallacea region shows the highest haplotype and also nucleotide diversity. Non-significant differences were found among regions, but significant differences were presented among populations. The relative divergence times between some members of section Halophila were estimated 2.15-6.64 Mya.

A review of the known distribution of Halophila spinulosa in Indonesia with herbarium from Laikang in South Sulawesi

Seagrasses are true plants living in the marine realm. The Coral Triangle is also the centre of seagrass diversity with 14 species recorded in Indonesian waters. There is a growing awareness of the ecological and socio-economic importance of seagrass meadows as well as the growing threats to these valuable coastal ecosystems. However, there is a lack of accessible data on seagrass distribution at ecosystem and species scales. The most speciose seagrass genus is Halophila, with at least 7 species (Halophila beccarii, H. decipiens, H. major, H. minor, H. ovalis, H. sulawesii and H. spinulosa) known to occur in Indonesia. Reported from Malaysia to eastern Australia, Halophila spinulosa is a data deficient tropical seagrass. We review the known distribution of H. spinulosa based on a search of Indonesian and international literature. We also present an annotated herbarium of H. spinulosa samples collected from Laikang in South Sulawesi, Indonesia. Samples were collected in September 2020 at low tide at depths of around 0.75 to 1.25 m on a silty sand substrate along with samples of other seagrass species present. Herbarium specimens were cleaned of epiphytes and sand. The samples were laid out carefully on A4 paper, arranged so that all parts were clearly visible, covered with gauze, and placed on folded newspaper. The prepared samples were then sandwiched between piles of newspaper and placed in a wooden press. The herbarium specimens will be preserved in the Marine Biology Laboratory collection, Marine Science Department, Universitas Hasanuddin. We consider the distribution data for H spinulosa are far from complete; this review and herbarium should inform and spur further research on this species and it’s distribution at macro (site) and micro (within site) scales.

Effects of Epiphytes and Depth on Seagrass Spectral Profiles: Case Study of Gulf St. Vincent, South Australia.

Seagrasses are a crucial indicator species of coastal marine ecosystems that provide substratum, shelter, and food for epiphytic algae, invertebrates, and fishes. More accurate mapping of seagrasses is essential for their survival as a long-lasting natural resource. Before reflectance spectra could properly be used as remote sensing endmembers, factors that may obscure the detection of reflectance signals must be assessed. The objectives in this study are to determine the influence of (1) epiphytes, (2) water depth, and (3) seagrass genus on the detection of reflectance spectral signals. The results show that epiphytes significantly dampen bottom-type reflectance throughout most of the visible light spectrum, excluding 670–679 nm; the depth does influence reflectance, with the detection of deeper seagrasses being easier, and as the depth increases, only Heterozostera increase in the exact “red edge” wavelength at which there is a rapid change in the near-infrared (NIR) spectrum. These findings helped improve the detection of seagrass endmembers during remote sensing, thereby helping protect the natural resource of seagrasses.

Secondary dispersal of seagrass seeds in complex microtopographies

Motivated by observational and experimental evidence, a theoretical model is proposed to relate the secondary dispersal of seagrass seeds with the complexity of microtopography in natural environments. Complexity is encoded in terms of the Hurst exponent of a fractal description of the microtopographical geometry. The percentage of a seafloor transect where secondary dispersal of seagrass seeds occurs, is quantified in terms of the mainstream velocity, bottom complexity and properties of the seeds. Theoretical expressions are validated considering the cases of Zostera marina and Posidonia oceanica seeds and using computational fluid dynamics (CFD). A total of 200 CFD simulations with different bottom complexities and flow conditions, were done for each seagrass genus to validate the theoretical model. Numerical results agree with theoretical predictions. This finding provides a management tool to assess the degree of seed retention in seed-based restoration areas.

First report of hybridization in the seagrass genus Posidonia (Posidoniaceae)

Hybridization is common among plants and has been crucial in the evolution of many aquatic plant groups. However, hybrid individuals are often difficult to identify, particularly in the marine environment. We aim to confirm a hybrid origin between two seagrass species for a morphologically-intermediate plant observed in shallow subtidal environments near Perth, Western Australia. Both morphological measures and DNA markers demonstrated a clear case for hybridization among two sympatric Posidonia species from different species complexes: Posidonia australis and P. coriacea. All five samples with the intermediate morphology had the same multilocus genotype (MLG), providing evidence that it resulted from a single hybridization event, followed by local clonal (rhizome) expansion. This result highlights weak reproductive barriers within the genus Posidonia, a trait common among other seagrass genera with sympatric ranges, apparently overlapping morphologies and low phylogenetic divergence.

Morphology and Genetic Studies of Cymodocea Seagrass Genus in Tunisian Coasts

The presence along the Tunisian coasts of different morphological and anatomical Cymodocea specimens suggest the presence of different species while the Mediterranean is threatened by the introduction of a great number of aliens. So, in order to survey any introduction of Cymodocea alien species, we aimed in this work to verify (i) the identity of the new forms and (ii) to evaluate the genetic diversity of the Tunisian Cymodocea populations and (iii) the validity of the existing identification keys. Samples were collected from four stations situated in two regions of the Tunisian coasts located in the eastern Mediterranean basin. We measured on mature leaves the biometric parameters (number of cross veins, width of the apex, absence of teeth on the apex margins and shape of apices). Three chloroplast DNA barcoding was used to discriminate taxonomically between Cymodocea populations. Biometrics parameters leaded to distinguish three Cymodocea nodosa morphotype wish are described here for the first time. However, the DNA markers rbcL, matK and trnHpsbA has not allowed to discriminate taxonomically between the morphological new types. The observed morphological variations might be phenotypical variations induced by different ecological conditions or genetic specific characters that can't be detected by the used markers.

Timing anthropogenic stressors to mitigate their impact on marine ecosystem resilience

Better mitigation of anthropogenic stressors on marine ecosystems is urgently needed to address increasing biodiversity losses worldwide. We explore opportunities for stressor mitigation using whole-of-systems modelling of ecological resilience, accounting for complex interactions between stressors, their timing and duration, background environmental conditions and biological processes. We then search for ecological windows, times when stressors minimally impact ecological resilience, defined here as risk, recovery and resistance. We show for 28 globally distributed seagrass meadows that stressor scheduling that exploits ecological windows for dredging campaigns can achieve up to a fourfold reduction in recovery time and 35% reduction in extinction risk. Although the timing and length of windows vary among sites to some degree, global trends indicate favourable windows in autumn and winter. Our results demonstrate that resilience is dynamic with respect to space, time and stressors, varying most strongly with: (i) the life history of the seagrass genus and (ii) the duration and timing of the impacting stress.

Seagrass Ecosystem Services and Their Variability across Genera and Geographical Regions.

Threats to and loss of seagrass ecosystems globally, impact not only natural resources but also the lives of people who directly or indirectly depend on these systems. Seagrass ecosystems play a multi-functional role in human well-being, e.g. food through fisheries, control of erosion and protection against floods. Quantifying these services reveals their contributions to human well-being and helps justify seagrass conservation. There has been no comprehensive assessment as to whether seagrass ecosystem services are perceived to vary over the globe or amongst genera. Our study compiles the most complete list of ecosystem services provided by seagrasses so far, including bioregional- and genus-specific information from expert opinion and published studies. Several seagrass ecosystem services vary considerably in their (known) provision across genera and over the globe. Seagrasses genera are clearly not all equal with regard to the ecosystem services they provide. As seagrass genera are not evenly distributed over all bioregions, the presence of an ecosystem service sometimes depends on the genera present. Larger sized seagrass genera (e.g. Posidonia, Enhalus) are perceived to provide more substantial and a wider variety of ecosystem services than smaller species (e.g. Halophila, Lepilaena). Nevertheless, smaller species provide important services. Our findings point out data gaps, provide new insight for more efficient management and recommend caution in economic valuation of seagrass services worldwide.

Phenolic fingerprint of the seagrassPosidonia oceanicafrom four locations in the Mediterranean Sea: first evidence for the large predominance of chicoric acid

AbstractThe phenolic fingerprint of the leaves ofPosidonia oceanicacollected from four different Mediterranean Sea regions was determined using a panel of analytical techniques. It was found to be dominated by caffeic tartrates, along with low amounts of coumaric and ferulic tartrates. Chicoric acid (CA) was unambiguously identified as the major phenolic compound, regardless of the sample or collection site. Caftaric acid (CAF) was the second most abundant phenolic, but in much lower average concentrations. These results contrast with most of the previous works, in which CA was not even mentioned. The dramatic influence of extract handling, as well as the importance of choosing the adequate criteria of identity to standards, was demonstrated. These results show the importance of analyzing the crude extract to avoid some of the major pitfalls in determining the phenolic fingerprints. This is the first report to identify and quantify CAF in the Posidoniaceae and to identify CA as the dominant phenolic inPosidonialeaves. The large accumulation of CA in both living (10.12–12.78 mg g-1dw) and detrital leaves (2.49–12.11 mg g-1dw) across large geographical scales is noteworthy. The lack of significant concentrations of flavonoids contrasts with other seagrass genera. Importantly, the phenolic signature ofP. oceanicashows significant similarities to those ofCymodocea nodosaandSyringodium filiforme, both belonging to the Cymodoceaceae. These results are discussed in terms of metabolic pathways and phylogenetic relationships.

Linking Seed Photosynthesis and Evolution of the Australian and Mediterranean Seagrass Genus Posidonia.

Recent findings have shown that photosynthesis in the skin of the seed of Posidonia oceanica enhances seedling growth. The seagrass genus Posidonia is found only in two distant parts of the world, the Mediterranean Sea and southern Australia. This fact led us to question whether the acquisition of this novel mechanism in the evolution of this seagrass was a pre-adaptation prior to geological isolation of the Mediterranean from Tethys Sea in the Eocene. Photosynthetic activity in seeds of Australian species of Posidonia is still unknown. This study shows oxygen production and respiration rates, and maximum PSII photochemical efficiency (Fv : Fm) in seeds of two Australian Posidonia species (P. australis and P. sinuosa), and compares these with previous results for P. oceanica. Results showed relatively high oxygen production and respiratory rates in all three species but with significant differences among them, suggesting the existence of an adaptive mechanism to compensate for the relatively high oxygen demands of the seeds. In all cases maximal photochemical efficiency of photosystem II rates reached similar values. The existence of photosynthetic activity in the seeds of all three species implicates that it was an ability probably acquired from a common ancestor during the Late Eocene, when this adaptive strategy could have helped Posidonia species to survive in nutrient-poor temperate seas. This study sheds new light on some aspects of the evolution of marine plants and represents an important contribution to global knowledge of the paleogeographic patterns of seagrass distribution.

English

The tropical seagrass genus, Halodule, is distributed in warm to tropical areas throughout the world. We performed separate molecular phylogenetic analyses of Halodule based on both plastid and nuclear DNA sequences, followed by haplotype analysis, focusing on plants in the western Pacific area. One western tropical Atlantic species, H. wrightii s.l., and two western Pacific species, H. pinifolia and H. uninervis, were recognised and characterised by leaf morphology. Because samples from the western tropical Atlantic and the western Pacific were nested with each other, allopatric differentiation into both areas may have occurred during the early stages of the evolution of the genus. A hybrid of Halodule was detected at two nearby localities in Okinawa, Japan, together with its co-occurring maternal and paternal species, H. uninervis and H. pinifolia, respectively. Haplotype analysis provided evidence that the hybrid resulted from a single hybridisation event, followed by clonal dispersal to its present localities.

The importance of reproductive strategies in population genetic approaches to conservation: an example from the marine angiosperm genus Zostera

Knowledge of the levels of genetic diversity maintained in natural populations can play a central role in conservation programmes, particularly in threatened habitats or species. Fluctuations in population size can lead to loss of variation and, consequently, increase the risk of extinction. We have examined whether such a genetic bottleneck has occurred in populations of two species in the seagrass genus Zostera, which are believed to have been affected by an outbreak of wasting disease at the start of the last century. A test for heterozygote excess at five nuclear microsatellite loci did not suggest the occurrence of a genetic bottleneck, but analysis of seven chloroplast microsatellite loci and sequence data from two regions did suggest a bottleneck in the chloroplast genome. Extremely low levels of between-population diversity suggest that all subpopulations can be treated as a single management unit for each species. Comparable levels of nuclear genetic diversity were found in the three populations of the primarily sexual Zostera marina var. angustifolia studied but a wider range of within-population diversity was found in Zostera noltii, which displays both sexual and vegetative reproductive strategies. This may be due to an increase in sexual recruitment due to localised fresh water inflow into the study site near to the most diverse population. Such populations should be prioritised as source material for any replanting or remediation due to natural or anthropogenic loss of Zostera beds in the area.