Variations in leaf soluble amino acids and ammonium content in subtropical seagrasses related to salinity stress

A survey of leaf soluble amino acids was conducted for four subtropical seagrasses grown at several salinities. Proline functioned as an organic osmoticum in Halodule wrightii Aschers., Thallasia testudinum Banks ex Koenig, and Ruppia maritima L., while alanine functioned in an osmoregulatory capacity in Halophila engelmanni Aschers. When light-and salinity-induced variations in leaf NH₄ and amide-N levels were compared in Halodule, Thalassia, and Halophila, ability to regulate leaf NH₄ levels was correlated with osmoregulatory capacity and maintenance of selected amino acid contents.     

Seagrasses in the Zeit Bay area and at Ras Ghârib (Egyptian Red Sea coast)

The distribution and ecology of seagrasses along parts of the Egyptian Red Sea coasts have been investigated. Five of the 10 species ever reported from the Red Sea have been found in this area, i.e. Halodule uninervis (Forssk.) Aschers., Thalassodendron ciliatum (Forssk.) den Hartog, Halophila stipulacea (Forssk.) Aschers., Halophila ovalis (R. Br.) Hook. f. and Halophila ovata Gaud. H. ovata is recorded here for the first time for the west coast of the Red Sea. The finding of Halophila decipiens Ostenfeld represents a new record to the Red Sea; this species has been found at a depth of 30 m, near Ras Ghârib in the Gulf of Suez.     

Photosynthetic response of seagrasses to ultraviolet-a radiation and the influence of visible light intensity

Inhibition of photosynthesis by ultraviolet-A radiation (UV-A, 315-380 nanometers) was examined in three marine angiosperms: Halophila engelmannii Aschers, Halodule wrightii Aschers, and Syringodium filiforme Kütz. Sensitivity to UV-A and photosensitization to UV-A by photosynthetically active radiation (PAR, 380-700 nanometers) were characterized.     

Inhibition of seagrass photosynthesis by ultraviolet-B radiation

Effects of ultraviolet-B radiation on the photosynthesis of seagrasses (Halophila engelmanni Aschers, Halodule wrightii Aschers, and Syringodium filiforme Kütz) were examined. The intrinsic tolerance of each seagrass to ultraviolet-B, the presence and effectiveness of photorepair mechanisms to ultraviolet-B-induced photosynthetic inhibition, and the role of epiphytic growth as a shield from ultraviolet-B were investigated.     

Comparison of cell wall compositions of the rhizomes of three seagrasses

Cell walls from rhizomes of Halophila ovalis (R. Br.) Hook.f., Halophila stipulacea (Forsk.) Aschers. and Halodule univervis (Forsk.) Aschers. were analysed. The non-cellulosic polysaccharides contained glucose as the most abundant sugar and arabinose as the next most abundant sugar in all cases. Only small amounts of pectin were found. Halodule uninervis differed from the two Halophila species in its large amount of cell wall material per gram fresh weight and in its high proportion of non-cellulosic polysaccharides. The lignin from all three plants contained non-conjugated phenols, with relatively few conjugated phenols.     

Productivity and respiration of three seagrass species from the gulf of Aqaba (Jordan) and some related factors

Net productivity and rates of respiration of the seagrasses Halodule uninervis (Forsk.) Aschers., Halophila ovalis (R. Brown) Hooker fil. and Halophila stipulacea (Forsk.) Aschers., from Aqaba (Jordan) are presented in this paper. The effect of some physical and chemical parameters on the productivity of H. stipulacea is discussed in some detail. Of the three species, H. stipulacea is considered a shade plant since it is photoinhibited at light intensities near 100 Wm^?2 and has a productivity/respiration ratio of 1.8 at 30 m depth.     

Occurrence of Halophila baillonii meadows in Belize,Central America

Halophila baillonii Ascherson was found in Belize, Central America in 2003 and 2005. The observation extends the known range of this seagrass species to the western Caribbean. H. baillonii was previously recorded only in the eastern Caribbean and at one Pacific site in Panama. Both fruits and flowers of H. baillonii were observed at two locations in Belize in 2005. H. baillonii in Belize is an important food for manatee, forms a productive seagrass-based ecosystem, and is adversely affected by shoreline development and watershed run-off.     

Northern range extension of the seagrass Halodule emarginata Hartog

The seagrass Halodule emarginata is an endemic tropical species of Brazil, previously found from São Paulo to Bahia. The present study gives more ecological information of this species and report the extension of its northern range where it occurs in an estuarine area of Aquiraz‐Ceará, semiarid coast of Brazil. In November 2014, the meadow was discovered, georeferenced and mapped. Five cores were collected for morphometrical analyses of H. emarginata and associated florofaunistic species. Two beds of H. emarginata with areas of 177.8 m² and 5012.3 m² were identified in the estuary of the Pacoti River, indicating an extension of its known range by 1500 km to the north. Despite the emarginate apex, morphological patterns revealed that specimens were slightly less developed than previously described in the literature, probably due to estuarine stress. However, algal biodiversity (seven species) in the studied meadows was within the range observed for other estuarine meadows in Brazil, with presence of Rhodophyta and Chlorophyta. The main groups of invertebrate megafauna were present, including 13 taxa mainly of Mollusca, Crustacea and Polychaeta. This meadow will be monitored in order to understand its dynamics and relationships with other florofaunistic species and its responses to environmental variations.     

Starch grain morphology of the seagrasses Halodule wrightii, Ruppia maritima, Syringodium filiforme, and Thalassia testudinum

Starch grains are a ubiquitous component of plants that have been used in tandem with phytoliths, pollen, and macrofossils to reconstruct past floral diversity. This tool has yet to be fully explored for aquatic plants, specifically seagrasses, which lack phytoliths and are rarely preserved as macrofossils or pollen. If starch grains in seagrasses are morphologically distinct, this method has the potential to improve seagrass identification in the fossil record in such cases where its starch is preserved (e.g. scratches and occlusal surfaces of tooth enamel from seagrass consumers). The goals of this study were twofold: (1) to determine if starch is present in seagrass material and (2) to assess how starch grain morphology differs between different seagrasses.This study focused on four abundant and ecologically distinct seagrasses from the Caribbean: Halodule wrightii, Ruppia maritima, Syringodium filiforme, and Thalassia testudinum. Starch grains were observed in all species except S. filiforme. Grains from H. wrightii are typically observed in side-on orientation, are sub-round to angular, and are fairly small (3-19 μm, end-on). Grains of R. maritima are small spherical grains (4-8 μm) that have a centric hilum and a straight extinction cross with a median angle between the arms of 90°. Grains from T. testudinum are large (9-31 μm, end-on), conical in side-on and round/sub-round in end-on orientation, have a slightly eccentric hilum with an obvious particle, and prominent lamellae.Visual assessment and comparative statistics demonstrate that the morphology of starch grains from T. testudinum, R. maritima, and H. wrightii are significantly different. With more extensive research, there is potential for the positive identification of starch grains from an unknown seagrass. The ability to identify seagrass from starch grains could facilitate the identification of seagrasses in the fossil record and supply information on seagrass evolution and distribution, climate effects on seagrass distribution, and the diets of seagrass consumers.     

Growth patterns in some indo-west-pacific seagrasses

The plastochrone interval of the rhizomes (PIR) was determined in the monopodially branching seagrasses Cymodocea rotundata Ehrenb. et Hempr. ex Aschers. (1981), Cymodocea serrulata (R.Br.) Aschers. et Magnus (1981), Syringodium isoetifolium (Aschers.) Dandy (1982), Halodule uninervis (Forssk.) Aschers. (1982) and Halophila ovalis (R.Br.) Hook.f. (1982). The growth rate during 1981 was in all species, including Thalassia hemprichii (Ehrenb.) Aschers., constant during the year and the PIR amounted to 6.7 days (Cymodocea serrulata) and 3.9 days (Cymodocea rotundata). However, the PIR observed in 1982 showed in all species a unimodal pattern and a decrease during June, July and August. The PIR was 6.3 days in Halodule uninervis while an interval of 5.2 days was calculated in Syringodium isoetifolium.The growth rates of the horizontal and vertical axes (rhizomes and shoots) were correlated. A regression between the number of leaves on the shoot and the number of nodes on the rhizome resulted for most species in a linear correlation. The slopes of the calculated correlation were rather similar in the tree species with a comparable morphology: 0.44 in Cymodocea serrulata, 0.43 in Cymodocea rotundata and 0.49 in Halodule uninervis. In Syringodium isoetifolium, the longevity of the leaves increased during ageing of the shoot.The proliferation ratio (the ratio shoots/rhizome apices) was measured in all species. A maximum of 0.41 was observed in Thalassia hemprichii. This species and Cymodocea rotundata showed a unimodal pattern. In the last species, the ratio ranged from 0.03 to 0.13. The ratio was constant during the year in Cymodocea serrulata and Syringodium isoetifolium. Proliferation by means of monopodially branching of the rhizome was of little importance in Halodule uninervis. The pattern of proliferative and reiterative branching in the Cymodoceoideae is illustrated by an image of 123 days of growth in the fastest growing specimen.Most species showed growth in fronts. The expansion of monospecific seagrass fringes was monitored by repetitive mapping. The pattern of succession in subtidal meadows was determined.     

Morphological diversity under controlled conditions for the Halophila ovalis-H. minor complex and the Halodule uninervis complex from Shark Bay,Western Australia

The wide range of leaf types that occurs within the populations of Halophila and Halodule in Shark Bay, Western Australia, was studied for plants under laboratory conditions. In the Halophila ovalis-H. minor complex, two types of plants appeared in the cultures, a large-leaved variant that is similar to typical H. ovalis (R.Br.) Hook. f. and a small-leaved variant that is more similar to H. minor (Zoll.) den Hartog. In Shark Bay, the two variants were not clearly separated because both produced leaves that varied in size, degree of waviness of leaf margins and intensity of anthocyanin pigmentation. In the Halodule uninervis (Forsk.) Aschers. complex, two types of plants, wide- and narrow-leaved variants, appeared in the cultures. In Shark Bay, the narrow-leaved plants differed in leaf width in muddy and silty microsites, but were always narrower than the wide-leaved variants. Only the narrow-leaved Halodule plants produced anthocyanin pigmentation both under field and laboratory conditions. The studies under controlled conditions indicate that the highly diverse leaves in Shark Bay result primarily from environmental influences on two types of Halophila and two types of Halodule.     

Quantitative and dynamic aspects of a mixed seagrass meadow in Papua New Guinea

Aspects of production and biomass were studied from November 1981 to November 1982 in six seagrass species which together from the mixed seagrass meadows in Papua New Guinea. These species, viz. Thalassia hemprichi (Ehrenb.) Aschers., Cymodocea serrulata (R.Br.) Aschers. et Magnus, Cymodocea rotundata Ehrenb. et Hempr. ex Aschers., Syringodium isoetifolium (Aschers.) Dandy, Halodule uninervis (Forssk.) Aschers. and Halophila ovalis (R.Br.) Hook. f. have been previously studied in monospecific seagrass beds. Thalassia hemprichii was the dominant species, followed by Syringodium isoetifolium. These two species were present in all samples and evenly distributed. Cymodocea serrulata and C. rotundata were recorded in 91 and 86%, respectively, of the quadrats sampled. The density, however, varied considerably. Shoots of the remaining two species were found in < 50% of the samples. The percentage presence increased when below-ground plant parts were taken into account.Significant differences in the shoot density were only found in Syringodium isoetifolium. The distribution of the five other species remained unchanged during the year. Annual mean shoot density amounted to 860 for Thalassia hemprichii, 2100 for Syringodium isoetifolium, 200 for Cymodocea serrulata, 250 for C. rotundata and 54 for both Halodule uninervis and Halophila ovalis. All species reached their maximum density from September to November. The mean aboveground production was 3.9 g ash-free dry weight (ADW) m⁻² day⁻¹, of which 64% was contributed by Thalassia hemprichii. Syringodium isoetifolium, which had the highest shoot density, contributed only 17%.The plastochrone interval of the leaves (PIL) was constant in all species and the mean ranged from 10.1 to 11.1 days. The PIL was virtually the same in this mixed meadows as in monospecific seagrass beds. Furthermore, the above-ground relative growth rate was constant during the year. Thalassia hemprichii was the most productive seagrass (mean 0.043 day⁻¹), whereas the lowest mean relative production was observed for Syringodium isoetifolium (0.030 day⁻¹). Total mean production was 6.4 g ADW m⁻² day⁻¹, of which 39% was contributed by the vertical axes, the rhizomes and the roots. The caloric production efficiency of the meadows was 0.58% of the total insolation at the water surface.Thalassia hemprichii was, because of its morphology, the stable element in the meadow. All other species were present at all times and exhibited a continuative process of recolonization.     

Heterozostera tasmanica (Martens ex aschers.) den Hartog in Chile

A 1.2 km² meadow of Heterozostera tasmanica (Martens ex Aschers.) den Hartog was found at Pto. Aldea, Bahia Tongoy, 60 km south of Coquimbo, 30°S on the coast of Chile. This provides documented evidence of seagrass occurrence on the west coast of South America. Since H. tasmanica is widespread throughout southern Australia, the Chilean stock represents a highly disjunct population. It appears from several growth parameters (density, leaf biomass, leaf area index, specific leaf area, δ ¹³C) that the H. tasmanica meadow at Pto. Aldea is very similar to those found in other parts of the world.     

A method for the culture of tropical seagrasses

Three tropical seagrass species were planted into 1.5 m² culture tanks and grown under the same conditions for 2 years. New shoot production and vegetation growth of both Syringodium filiforme Kütz. and Halodule wrightii Aschers. resulted in complete cover in monoculture tanks within the first year. The vegetative spread of Thalassia testudinum Banks ex König was slower than that of the other species. The culture of seagrasses in open mesocosm systems was most successful when continuous current circulation was maintained, water column nutrients were kept low, and extreme high temperatures (> 36°C) were avoided. Seagrass colonized and grew equally well in Indian River mud substratum and in quartz sand.     

Shoot demography and morphology of Zostera japonica and Ruppia maritima from British Columbia,Canada

Shoot dynamics and morphology were studied in co-occuring intertidal populations of Zostera japonica Aschers. and Graebn. and Ruppia maritima L. s.l. in southwestern British Columbia. Repeated mapping and examination of cohorts of shoots (ramets) in permanent plots on a gradient in elevation showed that the appearance and loss of shoots, age structure, survivorship and leaf and rhizome dimensions were all affected by position on the gradient. For both species, the area having the greatest exposure t o air had fewer shoots and a greater percentage of shoots flowering early in the season. The duration of vegetative growth in R. maritima was the same regardless of elevation, while plants of Z. japonica at high elevation initiated and ended flowering and entered a quiescent overwintering state earlier than plants at lower elevation.     

Distributional range extension of the seagrass Halophila nipponica into coastal waters off the Korean peninsula

Eight temperate seagrass species (five in the genus Zostera, two in the genus Phyllospadix, and Ruppia maritima) have been previously reported in coastal waters off the Korean peninsula, which lies between 33°N and 43°N. Recently, a species of Halophila, a genus which occurs predominantly in tropical and subtropical areas, has been observed on the southern coast of Korea for the first time. The species was identified as Halophila nipponica. H. nipponica is distributed in warm temperate regions of Japan influenced by the warm Tsushima Current and was previously unknown outside the Japanese archipelago. Thus, we are able to report a range extension into Korea. The Korean Halophila meadow that we observed covered an area of about 2.1 ha, with average shoot density of about 1300 m⁻². We measured morphological features of vegetative and reproductive organs between June and September 2007. Morphological and reproductive features of the Halophila species in Korea were similar to those of the species in Japan. Increased water temperature in the coastal waters of Korea may at least partially account for the persistence of this new population.     

Seed germination in Halodule wrightii and Syringodium filiforme from Texas and the U.S. Virgin Islands

Seed germination under laboratory conditions was nearly continuous in both Halodule wrightii Aschers. and Syringodium filiforme Kütz. Halodule seeds that were sieved from sediments in Texas and St. Croix in 1978 continued to germinate for over 3 years in artificial seawater. Syringodium seeds that were collected on reproductive shoots in 1979 continued to germinate for 3 years. The potential longevity of seeds of Halodule and Syringodium may exceed that of seeds of any other seagrass.     

Growth of Halodule wrightii in culture and the effects of cropping,light, salinity and atrazine

The interaction of three environmental variables, light, salinity and cropping, with the effects of the herbicide atrazine on Halodule wrightii Ascherson was investigated in the laboratory. Atrazine at 30 ppm caused a significant reduction in survival of ramets, production of new ramets, above-ground biomass and growth, when compared to Halodule wrightii not exposed to atrazine. The three levels of each environmental condition did not alter the toxicity of atrazine to Halodule wrightii.     

Phytal Marine Nematode Assemblages and their Relation with the Macrophytes Structural Complexity in a Brazilian Tropical Rocky Beach

The nematofauna from the seaweeds Sargassum polyceratium Montagne, Hypnea musciformis Küetzing, Padina gymnospora Küetzing and the seagrass Halodule wrightii Ascherson was studied in March 2001, at Pedra do Xaréu, Pernambuco, Brazil, in order to investigate the associations of organisms, as well as the relation between the plant architecture and the associated fauna. Soft sediments adjacent to phytal environments were also investigated. Thirty-eight genera were found, including two new records (Odontanticoma sp. and Wieseria sp.) for the Brazilian coast. Multivariate analyses were carried out in order to verify the relation between nematode assemblages on plants and in sediments. The results showed that these assemblages were different in structure and composition between macrophytes and sediments. They were different in structure but not in composition among macrophytes, so the nematode biodiversity was related to the structural features of macrophytes’ habitats.