rDNA analysis of the Red Sea seagrass, Halophila, reveals vicariant evolutionary diversification

Ghani NI, Bujang JS. Morphological and genetic identification of Halophila species and a new distribution record of Halophila nipponica at the Tanjung Adang Laut shoal, Johor, Malaysia

The Halophila species exhibit complex characteristics due to their high degree of variation across different bioregions. This study delves into the intricate characteristics of Halophila species in the Tanjung Adang Laut shoal, Johor, Malaysia, and offers valuable insights through morphological and genetic evidence. Employing internal transcribed sequences (ITS), we investigated the phylogeny of Halophila species, revealing distinct clades for H. ovalis, H. major, H. spinulosa, and the newly recorded H. nipponica. Notably, H. nipponica from the Tanjung Adang Laut shoal formed a conspecific relationship with its counterparts from Japan and Korea (98.3-98.5% similarity; 5-11 bp differences). Morphologically, distinguishing features, including the ratio of the half-lamina width (1:4.76-6.13 mm) and cross-vein count (4-7 pairs), supported the identification of H. nipponica. Genetic distance analyses revealed differences between H. nipponica, H. ovalis, and H. major, indicating haplotype diversity. Geographical variations were evident, as H. nipponica presented unique haplotypes (H24) in its clade. The 47 haplotypes network identified significant mutation sites, providing a comprehensive understanding of genetic and morphological distinctions. In conclusion, this study highlights the intricate characteristics and phylogeny of Halophila species in the Tanjung Adang Laut shoal, Johor, and provides valuable insights into their genetic and morphological diversity.

Current advances in seagrass research: A review from Viet Nam

Seagrass meadows provide valuable ecosystem services but are fragile and threatened ecosystems all over the world. This review highlights the current advances in seagrass research from Viet Nam. One goal is to support decision makers in developing science-based conservation strategies. In recent years, several techniques were applied to estimate the size of seagrass meadows. Independent from the method used, there is an alarming decline in the seagrass area in almost all parts of Viet Nam. Since 1990, a decline of 46.5% or 13,549 ha was found. Only in a few protected and difficult-to-reach areas was an increase observed. Conditions at those sites could be investigated in more detail to make suggestions for conservation and recovery of seagrass meadows. Due to their lifestyle and morphology, seagrasses take up compounds from their environment easily. Phytoremediation processes of Thalassia hemprichii and Enhalus acoroides are described exemplarily. High accumulation of heavy metals dependent on their concentration in the environment in different organs can be observed. On the one hand, seagrasses play a role in phytoremediation processes in polluted areas; on the other hand, they might suffer at high concentrations, and pollution will contribute to their overall decline. Compared with the neighboring countries, the total C _org stock from seagrass beds in Viet Nam was much lower than in the Philippines and Indonesia but higher than that of Malaysia and Myanmar. Due to an exceptionally long latitudinal coastline of 3,260 km covering cool to warm water environments, the seagrass species composition in Viet Nam shows a high diversity and a high plasticity within species boundaries. This leads to challenges in taxonomic issues, especially with the Halophila genus, which can be better deduced from genetic diversity/population structures of members of Hydrocharitaceae. Finally, the current seagrass conservation and management efforts in Viet Nam are presented and discussed. Only decisions based on the interdisciplinary cooperation of scientists from all disciplines mentioned will finally lead to conserve this valuable ecosystem for mankind and biodiversity.

Liao L, Papenbrock J. 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.

Marinomyxa Gen. Nov. Accommodates Gall-Forming Parasites of the Tropical to Subtropical Seagrass Genus Halophila and Constitutes a Novel Deep-Branching Lineage Within Phytomyxea (Rhizaria: Endomyxa)

Marine representatives of Phytomyxea (SAR: Rhizaria: Endomyxa), a peculiar class of obligate endobiotic parasites, are a greatly understudied ecological group of protists infecting many algal, diatom, and seagrass species. Very little is known about the actual diversity, ecology, and pathogenic potential of these organisms and their taxonomic treatment in many cases follows outdated morphotaxonomic concepts. Here we focused on resolving the phylogenetic relations of the phytomyxean parasites of the widespread seagrass genus Halophila. We report the first finding of Plasmodiophora halophilae, the parasite of ovate-leaf Halophila species, after more than 100 years since its original description in 1913. We provide additional information on its anatomy, morphology, distribution, and host range, together with a phylogenetic evidence that it is congeneric with the recently rediscovered species infecting the invasive seagrass Halophila stipulacea in the Mediterranean Sea. Despite the previously hypothesized affiliation of the latter to Tetramyxa, our phylogenetic analyses of the 18S rRNA gene place Tetramyxa parasitica (a parasite of brackish water phanerogams and the type species of the genus) in the freshwater/terrestrial phytomyxean order Plasmodiophorida and reveal that phytomyxids associated with Halophila spp. form a separate deep-branching clade within the class proposed here as Marinomyxa gen. nov. We further argue that M. marina infecting H. stipulacea is most likely a species-specific parasite and implies their comigration through the Suez Canal.

Taxonomy of the Genus Halophila Thouars (Hydocharitaceae): A Review

The seagrass genus Halophila Thouars has more than twenty described species and is predominately distributed over a wide geographic range along the tropical and the warm temperate coastlines in the Indo-West Pacific Oceans. A brief history of the Halophila taxonomic development is presented. Based on reproductive and vegetative morphology, the genus is divided into eight sections including three new sections: section Australes, section Stipulaceae and section Decipientes. A rewritten taxonomic description of the type species for the genus Halophila,H. madagascariensis Steudel ex Doty et B.C. Stone, is provided. The lectotype of H. engelmannii Asch. as well as neotypes of H. hawaiiana Doty et B.C. Stone and H. spinulosa (Br.) Asch. are designated. Furthermore, H. ovalis ssp. bullosa, ssp. ramamurthiana and ssp. linearis together with H. balforurii have been recognised as distinct species. Nomenclature, typification, morphological description and botanical illustrations are presented for each taxon. Recent molecular phylogenetic surveys on certain Halophila taxa are also discussed. Field surveys for the deep water Halophila in West Pacific regions are suggested. Morphological studies combined with molecular investigations for the Halophila on the east coast of Africa and the West Indian Ocean are urgently needed and highly recommended.