Megagametogenesis in Halophila johnsonii, a threatened seagrass with no known seeds, and the seed-producing Halophila decipiens (Hydrocharitaceae) (original) (raw)
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Aquatic Botany, 2020
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Morphological plasticity in a Fijian Seagrass: Halophila ovalis subsp. bullosa
Regional Studies in Marine Science, 2019
Seagrasses are marine flowering plants found along both tropical and temperate coastlines; they possess great ecological importance as nurseries, nutrient sinks, and providers of critical marine habitat. Understanding the distribution and diversity of seagrass habitats is important for their conservation and management, however this is impeded by varying species' diversity, the extensive distribution of seagrasses and taxonomic uncertainty. In the Fiji Islands, the tropical seagrass Halophila ovalis and its subspecies H. ovalis bullosa are the subject of taxonomic controversy, as a singular morphological characteristic distinguishes the two. This characteristic is the bullated, or blister-like leaves of the latter, compared to the smooth leaves of the former, which in some instances have been observed on the same plant (S.S., pers. obs.). This study examined material from both taxa, along with three other seagrass species (Halodule pinifolia, H. uninervis and Syringodium isoetifolium; total n = 95) and used independent morphological and molecular barcoding approaches to assess the conspecificity of the two Halophila taxa. Examination of vegetative and reproductive characters was not able to distinguish between H. ovalis and H. ovalis subsp. bullosa, while phylogenetic reconstructions using ITS2, matK and trnH-psbA barcodes supported their monophyly. We recommend revision and merger of these taxa, while the approach used here is highly useful for taxonomic resolution in other seagrass taxa, for their conservation, restoration and management.
EVOLUTIONARY TRENDS IN THE SEAGRASS GENUS HALOPHILA (THOUARS): INSIGHTS FROM MOLECULAR PHYLOGENY
Relationships among members of the seagrass genus Halophila (Hydrocharitaceae) were investigated using phylogenetic analysis of the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA. The final aligned ITS sequence data set of 705 base pairs from 36 samples in 11 currently recognised species included 18.7% parsimony informative characters. Phylogenetic analysis yielded two most parsimonious trees with strong support for six groups within the genus. Evolutionary trends in Halophila appear to be toward a more reduced simple phyllotaxy. In addition, this study indicates that long distance 'jump' dispersal between major ocean systems may have occurred at least in the globally distributed H. decipiens. Results of ITS analyses also indicate that the widespread pacific species H. ovalis is paraphyletic and may contain cryptic species. Likewise, the geographically restricted species H. hawaiiana and H. johnsonii could not be distinguished from H. ovalis with these data and warrant further investigation.
Primary production of deep-water Halophila ovalis meadows
Aquatic Botany, 1999
Monospecific meadows of Halophila ovalis (R. Brown) Hooker f. were studied in deep waters (14-16 m) around Langkai island in South Sulawesi, Indonesia, during May-September 1990. The average shoot density of Halophila in biomass samples (n=10) taken from these meadows was 1099 ± 195 leaf pairs m −2 . Comparison with average leaf pair densities (427 ± 211 leaf pairs m −2 ) estimated by in situ counts under water (using SCUBA) revealed that more than 50% of the leaf tissue was covered under the sediment. The leaf area index (LAI) was 0.68 ± 0.32 m 2 m −2 (including sediment-covered leaves). Total seagrass biomass in the meadows averaged 10.93 ± 2.65 g ADW m −2 , of which 42% was contributed by above-ground plant parts. Metabolic measurements using the bell jar technique and plastochron interval measurements gave comparable results, revealing total plant production to range between 0.83 and 1.38 g C m −2 day −1 with a turn-over of total plant biomass of 3.9-6.6 days. Rhizome tagging experiments showed that 34% of this production may be contributed by the below-ground biomass. The light compensation point for Halophila ovalis at 15 m depth was 33 mol photons m −2 s −1 . The high primary production of these sparsely grown meadows at such considerable depths (14-16 m) and under high stress from sedimentation (at the bottom of a reef slope) is attributed to the strongly opportunistic character of this seagrass species, whose meadows can be found to depths of over 30 m in the study area. (P.L.A. Erftemeijer) 0304-3770/99/$ -see front matter ©1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -3 7 7 0 ( 9 9 ) 0 0 0 3 2 -7
Primary production of deep-water< i> Halophila ovalis meadows
Aquatic botany, 1999
Monospecific meadows of Halophila ovalis (R. Brown) Hooker f. were studied in deep waters (14-16 m) around Langkai island in South Sulawesi, Indonesia, during May-September 1990. The average shoot density of Halophila in biomass samples (n=10) taken from these meadows was 1099 ± 195 leaf pairs m −2 . Comparison with average leaf pair densities (427 ± 211 leaf pairs m −2 ) estimated by in situ counts under water (using SCUBA) revealed that more than 50% of the leaf tissue was covered under the sediment. The leaf area index (LAI) was 0.68 ± 0.32 m 2 m −2 (including sediment-covered leaves). Total seagrass biomass in the meadows averaged 10.93 ± 2.65 g ADW m −2 , of which 42% was contributed by above-ground plant parts. Metabolic measurements using the bell jar technique and plastochron interval measurements gave comparable results, revealing total plant production to range between 0.83 and 1.38 g C m −2 day −1 with a turn-over of total plant biomass of 3.9-6.6 days. Rhizome tagging experiments showed that 34% of this production may be contributed by the below-ground biomass. The light compensation point for Halophila ovalis at 15 m depth was 33 mol photons m −2 s −1 . The high primary production of these sparsely grown meadows at such considerable depths (14-16 m) and under high stress from sedimentation (at the bottom of a reef slope) is attributed to the strongly opportunistic character of this seagrass species, whose meadows can be found to depths of over 30 m in the study area. (P.L.A. Erftemeijer) 0304-3770/99/$ -see front matter ©1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -3 7 7 0 ( 9 9 ) 0 0 0 3 2 -7
Marine Ecology Progress Series, 2006
The role of vegetative seagrass fragments as a dispersal and recruitment mechanism has received little attention. Research on the potential of vegetative fragments as a dispersal mechanism can help us better understand the ability of seagrass beds to recover from disturbance events, to recruit into new areas, and to survive over long periods. The objectives of this study were to (1) determine the viability of vegetative fragments of Halodule wrightii and Halophila johnsonii as a function of time after removal from sediment, (2) determine whether season of collection affects the fragments' recruitment potential, (3) determine if the source of fragments of H. johnsonii affects viability, (4) determine how long fragments float, and (5) determine the frequency of fragment settlement and rooting vs. time. Mesocosm experiments with plants collected from Indian River Lagoon, Florida demonstrated that fragments of H. wrightii remain viable during spring for up to 4 wk with a marked decline in survival after 2 wk of drifting. Fall plants had a shorter period of viability with only 5% of fragments remaining viable by Week 2. Although the source location of the fragments did not influence viability for H. johnsonii, day and season were highly significant for viability, with spring plants remaining viable for up to 4 d and fall plants remaining viable for twice as long. The short viability of H. johnsonii illustrates the importance of rapid settlement when uprooted from a source bed, limiting dispersal to short distances. H. wrightii appears to maintain its viability for a longer period of time, indicating that this species may be able to utilize fragments as a dispersal mechanism over longer distances. The vegetative fragments of both H. wrightii and H. johnsonii had the ability to settle and root in mesocosms, demonstrating that fragmentation is a viable mechanism for dispersal and recruitment for these species.