Aims The cordgrass Spartina alterniflora is one of the highly successful invasive plants in coastlines worldwide. Although the S. alterniflora invasion is threatening mangroves and the increasing heavy metal pollution of oceans and coasts are of growing concerns, especially in China, the effects of S. alterniflora invasion on the enrichment of sedimental heavy metals in mangrove wetlands are not known. The objectives of this study are to determine the effects of S. alterniflora invasion on enrichment of sedimental heavy metals in the mangrove wetland and the underlying mechanisms.Methods We investigated differences in the contents of sedimental heavy metals, including As, Cd, Cr, Cu, Ni, Pb, Zn, and Mn, for two pairs of comparisons (unvegetated shoal vs S. alterniflora monoculture and Avicennia marina monoculture vs A. marina + S. alterniflora mixture), and their relationships with environmental factors in Zhanjiang Mangrove National Natural Reserve, Guangdong, China.Important findings Spartina alterniflora invasions in mangrove wetlands increased the contents of sedimental heavy metals, with the effects being significant on Cr, Ni, Cu, Zn, and Mn. The intermediate level of pollution was only detected in the sedimental Cd. The presence of S. alterniflora resulted in enrichment in the sedimental heavy metals in the mangrove wetland in Zhanjiang, but not to the degree of concerns for contaminations. The contents of sedimental organic matter, total C, total N, total S and total K were strongly related to the contents of sedimental heavy metals in the invaded mangrove wetland. Ultimately, the dense above-and below-ground architectures of the invasive S. alterniflora likely play a predominant role in causing enrichment of sedimental heavy metals.
Based on a year round survey conducted in the mangrove swamp of Luoyangjiang Estuary in Fujian from August 2013 to April 2014, macrobenthic diversity, seasonal changes, and the impact of mangrove rehabilitation on the macrobenthic community were analyzed. We recorded a total of 78 species from 7 phyla in the study area and the community was dominated by annelids and arthropods. The gastropod, Assiminea brevicula (Assimineidae), was the most dominant species and was more abundant in mangrove forests than in mudflats. ANOSIM analysis showed that faunal communities were significantly different between mangrove forests and mudflats, with the former characterized by much lower macrobenthic density and biomass. Moreover, some of dominant species, such as Parasesarma plicata and Phascolosoma arcuatum, were only found in mangrove forests. Higher value of macrobenthic density was found in winter and spring, while mean biomass was higher in spring and summer. Significant differences in macrobenthic communites were observed among seasons except between winter and spring. The present study demostrated that, species composition of the mangrove macrobenthos indicated characteristics of a young mangrove plantation and seasonal changes in macrobenthic communities might be due to different breeding seasons of the dominant species. Mangrove vegetation had a noticeable impact on macrobenthic communities, as evidenced by significant difference in macrobenthic communites between the two habitats. Density of macrobenthos in mangrove forests was much lower than that found in 2009, but the sesarminid crab Parasesarma plicata became much abundant. Since mangrove forests and mudflats support different species composition of macrobenthos, planning is needed in mangrove rehabilitation for the protection of habitat diversity and heterogeneity.
To examine our current understanding on biological invasions in mangrove forests, relevant information from literature was reviewed and several key points were summarized based on the database of ISI Web of Science and the information analysis software HistCite. First, most of the studies have focused on the invasion of plant species in mangrove forests, and little attention are paid to other organisms. Secondly, there is an obvious bias on the locations of study sites, with most being situated in the southern and southeastern coasts of China (especially in the Pearl River Estuary and west of the Leizhou Peninsula) and the southeastern coast and Hawaiian Islands of the United States. Thirdly, that whether Sonneratia apetala can result in invasion is still a hot but controversial topic. Introduction of this species should be cautious. Forth, Spartina alterniflora and Mikania micrantha are the most notorious invaders around the world; both possess fast growth rate, high reproductive and competitive capacity, and strong allelopathic effects. They have invaded mangrove forests and caused severe ecological consequences, and apparently deteriorated the microhabitat and changed the benthic organisms’ community. Fifth, Rhizophora mangle has invaded Hawaiian Islands as an exotic mangrove species, modified the sedimentary environment, and enriched the benthic organisms, but the impacts are yet to be considered at the global scale. In general, studies on biological invasions in mangrove forests are still at the infant stage and we know little about the underlying mechanisms of the invasions. Specific strategies are lacking for controlling the invasion. The state of invasion and corresponding impacts should be continually focused in future studies. Exploration of the mechanisms and controlling strategies of invasion in mangroves should be launched as soon as possible. The assessment of the effects of biological invasion on ecological services of mangroves should also be emphasized. Finally, a sound management system for the control of biological invasions in mangrove forests is urgently needed.
In order to assess the ecological impacts of Spartina alterniflora on mangrove ecosystems, we investigated macro-invertebrate communities in S. alterniflora wetlands and a mangrove wetland between October 2012 and September 2013, in the Xicungang estuary, Guangxi Zhuang Autonomous Region. The species composition, biomass and diversity of macro-invertebrates were compared at different times between the mangrove habitat and S. alterniflora community. Sixteen species from Arthropoda, Mollusca, Annelida, Cnidadia and Sipuncula were collected from the two habitats. Twelve species were found in mangrove wetlands whereas 10 species were found in S. alterniflora wetlands. Perhaps due to the invasion of S. alterniflora, Glauconome chinensis became the predominant species, leading to a greater macro-invertebrate biomass in S. alterniflora wetlands than in mangrove wetland. On the other hand, the Margalef, Shannon-Wiener index, Simpson and Pieous diversity indices of macro-invertebrates were lower in S. alterniflora habitat than in mangrove habitat. Two-way ANOVA was used to analyze the effect of sampling periods and habitats on the number of species, biomass and diversity indices of macro-invertebrates. Our results showed that Shannon- Wiener index and Simpson diversity indices differed between the two habitats, the Margalef and Pieous diversity indices differed among sampling periods, number of species and biomass were affected by both habitats and sampling periods. Based on multiple linear regression analyses, macro-invertebrate biomass was related to the density of S. alterniflora, and Shannon-Wiener, Simpson diversity and species richness of macro-invertebrates were all related with the height of S. alterniflora. According to our NMDS (non-metric multidimensional scaling) analysis, macro-invertebrate communities in S. alterniflora habitat mainly differed from those of mangrove habitats due to sampling periods. In conclusion, the invasion of S. alterniflora in mangrove wetlands in Xicungang estuary increased the biomass of macro-invertebrates, while decreased the diversity of them, and also changed the community structure of macro-invertebrate assemblages.
Research on the biodiversity of mangrove ecosystems should include not only the plants but other components, such as the macrobenthos. In order to understand the response of the macrobenthos to a man-grove habitat with high organics and nutrients, we compared the mangrove and non-mangrove macrobenthic communities, and analyzed their spatial-temporal distributions in these two habitats from April 2006 to Janu-ary 2007 in Tong’an Bay, Fujian. Six sampling stations were set in Tong’an Bay, four of them (FL1, FL2, XA-A and XA-B) were in the mangrove habitat, the other two (FL3 and XA-C) were in the non-mangrove habitat. An analysis of sediment properties showed that total organic matter (TOM) of the three sampling sta-tions at Fenglin exceeded the critical threshold, namely 3.4%, and TOM in mangrove stations was higher than in the non-mangrove ones. A total of 91 macrobenthic taxa were obtained from the six sampling stations in Tong’an Bay, including 77 and 67 taxa from the mangrove and non-mangrove habitats, respectively. Mean macrobenthic densities in the mangrove and non-mangrove habitats were 4,445.8 inds/m2 and 1,707.2 inds/m2, respectively. Mean biomasses in the mangrove and non-mangrove habitats were 51.1 g/m2 and 94.6 g/m2, respectively. The results of an independent-samples t-test showed that mean density and mean biomass were significantly different in the two habitats. The present study revealed that the mangrove habitat has a positive influence on the Oligochaeta, such as Limnodriloides sp., that thrives in the high TOM sediments. Because of the shorter inundation period in the mangrove habitat, however, free-living molluscs and crusta-ceans preferred the non-mangrove habitat. Other sediment properties such as interstitial salinity and median particle diameter also affected the macrobenthic community.
Using a static chamber technique, methane fluxes from sediments of five mangrove communities at four sites were studied. An average value of 0.81mg·m-2·d-1 was observed. Using polyethylene bags, methane fluxes through leaves of six mangrove species were also studied. It indicates that mangrove leaves generally absorbed atmospheric methane as an overall effect. Diurnal variations of methane fluxes from sediments of Bruguiera sexangula community at Changning site were related to tidal conditions in the forest while flat variations of methane fluxes from sediments of this community were related to soil water contents. There were two different seasonal patterns of methane flux from soils in the five mangrove communities.
This paper describes research on change of the decay leaf microorganisms and leaf-litter decomposition in process of natural decomposition by man-made initation in Kandelia mangroves of Jiulongjiang River Fsturay.The results showed that:
1.Total amounts of microorganisms of the decay leaves varies significantly during the decomposition process, all along the bacterial amounts was preponderance. The amounts of bacterial increase from 200 × 104 to 8800 × 104ind./ g.d.w, with decomposition time of leaves. That accounted for 96 to 99% of total amounts of microorganisms (including three grounp of bacteria, actinomyces and filamentous fungi etc. ) which showed the bacteria as major microorganisms in leaf-litter decomposition.
2.The ammonifying bacteria preponderate in number from 26× 104 to 180 × 104 (ind./g.d.w.in various physiologic group of microorganisms; whereas nitrite bacteria, denitrifying bacteria and celluase decomposing microorganisms were (ind./g.d.w) 0.03×104 to 0.24×104, 0.03×104 to 0.10 ×104 and 1.14× 10 to 7.33×10 respectively. This showed that the ammonifying bacteria was the major physiologic group of organic mineralization. Ammonification, nitrification and denitrifying were the accompying processes with increasing intensity as time elapsed which reflect the features of marsh. The amounts of cellulose decomposing microorganisms had changed exceptional, population increased at earlier stage of decomposition until the fourth week to the its peck value, and decreased thereafter. The microbial activation testing result showed the similar trends in the change of microbial physiologic group mentioned above.
3. The leaf-litter decomposition speed proceeded rapidly. One week after the drop of the leaves on the soil surface, one quarter of the organic matters was decomposed and half-decomposition time was about 6 weeks. The contents of soluble sugar and total phosphorus decreased, but total nitrogen increased in remainder leaves.
This paper is a part of studies of the mangrove forests in Dongzhai harbour of Hainan island, China. It deals mainly with the accumulation and biological cycle of K and Na elements of 55-year-old Bruguiera sexangula community.
The main results of the measurements are as follows:
1. The amounts of K and Na elements in standing crop of this community were 669.9kg/ha and 2591.3kg/ha in which the amounts of two elements in aerial part of biomass were 425.6 for K and 908.9 for Na (kg/ha), and that of below ground biomass were 244.3 for K and 2042.4 for Na(kg/ha) respectively.
2. In biological cycle of K and Na of this stand, the annual value of vegetation mineral uptake were 89.6 for K and 204.4 for Na(kg/ha), of its return were 49.0 for K and 99.8 for Na(kg/ha) and of its retention were 40.6 for K and 104.6 for Na(kg/ha), respectively.
3. The turnover period of K (14 yrs.) is faster than that of Na (30 yrs .)
The mangrove is a characteristic vegetation in tropical zone, but so far as China is concerned it may also extend to Fuding district (27˚20′ N), situated at the north-eastern part of Fujian, South China.The subtropical mangrove of Fujian consists of six species belonging to five families. They are Bruguiera gymnorrhiza and Kandelia candel of Rhizophoraceae, Excoecaria agallocha of Euphorbiaceae, Acanthus ilicifolius of Acanthaceae, Aegiceras corniculatum of Myrsinaceae and Avicennia marina of Verbenaceae. In the southern coastal regions from Zhaoan to Xiamen all six species are present. The communities are composed of kandelia candel+Bruguiera gymnorrhiza-Aegiceras corniculatum association, Kandelia candel-Aegiceras corniculatum association, Avicennia marina association and Kandelia candel association. The most widely distributed community is Kandelia candel-Aegiceras corniculatum association. Kandelia candel is the dominant and the hightest trees reaching a height of eight metres. In the middle coastal regions from Xiamen to Putian, there are four species (Kandelia candel, Aegiceras corniculatum, Acanthus ilicifolius and Avicennia marina). In the northern coastal regions from Putian to Fuding, there is only one association dominated by Kandelia candel. The salinity of sea water may greatly affect the morphological and physiological characters of mangrove plants. It usually shows that as the osmotic pressure raises, the leaves become thick and coriaceous, whilst their stomata sink into the epidermis. In addition, it is also related with the growth and development of mangrove plant and coexisted condition of aquatic animals. Our observation indicates that when the salinity of sea water is low, for instance at 7.5–21.2%, Kandelia candel can grow normally and bring forth blossoms and fruits; the five-year-old trees may reach 1.6-2 metres in height and Balanus adhere to it in much less in number or may be absent. When the salinity of sea water is high, at 25.6–37.4‰ Kandelia candel grows weakly and the five-year-old trees are only about one meter in height and their leaves become small and succulent; they do not bloom normally, some may even die (about 30% in the area surveyed) and there often are large number Balanus attaching to the trunk. The growth in height of Kandelia candel may be related with the edaphic nitrogen content(%) of the second layer (20–40cm.), since the content of the first layer soil (0–20cm.) is not stable, and is readily influenced by the waves, the contents from the second layer were determined. There exist semilogarithmic linear correlation between them, its formula is as follows:
log y = 0.9397 + 3.124x
where y is the tree height (m.), x is the edaphic nitrogen content(%). r=0.8875, df=7, determined range: tree height in 0.5–2.2m., edaphic nitrogen content in 0.3–0.43(%).
The correlation between the growth in the height of Kandelia candel and the soil salinity appears to be a parabolic curve.
In the mangrove ecosystem, the ecological function of animals is also significant, but former investigators paid little attention to this. The insect could eat more than 30% of the leaves of mangrove plants, for example, in the community of Kandelia candel of Sanjiangkou of Putian, 95% of the leaves were found eaten by a species of tortrix moths. There are two kinds of animals adhering to the trunk and leaves of tidal forest, i. e. Chithamalus sp., which adhere to blade and Balanus amphitrite albicostatus which affix on the trunk and branches. Since they are so large in number that even the whole surface of the trunk can be covered with them. The amount of animals on the trunk of a Kandelia candel tree (height 53 cm., diameter 2 cm.) was calculated, which totals to 506 Balanus. This explains why the growth of the plant is seriously affected.
There are benthic animals under the tidal forest, such as Sesarma sp., Pachygrapsus crassipes and Littorinopsis melanostoma and so on. They dig holes into the ground. For example, there are 122 holes, each of 0.5–1.2 cm. diameter in a 70× 70cm2 quadrat; this porous ground is greatly in favour of edaphic ventilation, favourable to the growth of plants. The mangrove is a natural shelterbelt, which has the effect of decreasing the tidal force, so it provides the tidal establishment and the building of the sludge beach. It is also of great economic value, such as the utilization of hypocotylar starch, corticose tannin and trunk wood etc. Therefore, care should be taken to protect such plant communities
Vivipary in plants refers to a phenomenon that sexually reproduced offsprings germinate while still attached to the maternal bodies. This is mostly manifested in mangrove plants, which occur in tropical and subtropical intertidal zones and encounter harsh environmental conditions such as high salinity, high temperatures, waterlogging, hypoxia and tidal waves. Vivipary has long been recognized as one of the most important adaptive features under such a complex environment. Here we discuss four aspects of vivipary: morphological anatomy, physiology and biochemistry, molecular biology and ecological adaptation. We also discuss shortcomings in current studies and prospect of future directions. Differing from regular seed development, viviparous seeds in mangroves are evolved with many special structures, indicating a genetically based process. Hormones play an important role in regulating the process, whilst the dynamics of salt ion concentration during embryo and propagule development seems to be an adaptive feature. The ecological significance of vivipary is fully exhibited in the propagules that can effectively establish themselves on muddy tidal zones. Such a success heavily relies on sound functional features developed on the mother plants. However, the molecular mechanism and the regulation of viviparous seed development in mangroves remain elusive. Systematic studies of vivipary in mangroves not only help to understand the nature and evolutionary process of this distinct adaptive phenomenon, but also provide the foundation for mangrove forest restoration and protection in many parts of the world.
Aims Sonneratia apetala, a native mangrove species in India, Bengal and Sri-Lanka, was introduced in 1985 to Dongzhaigang Mangrove Nature Reserve in Hainan Island, China from Sundarban, southwest of Bangladesh. Laguncularia racemosa, another mangrove species from Mexico was introduced to the same reserve in 1999. Our objective was to investigate the salinity tolerance mechanism of S. apetala and L. racemosa in order to elucidate adaptive strategies of the halophytes in stressful saline habitat.
Methods We investigated the effects of increasing soil NaCl (100–400 mmol·L–1) on gas exchange, O2–· production rate, activity of antioxidant enzymes, and the relevance to salt tolerance over four weeks in 1-year-old seedlings of S. apetala and L. racemosa.
Important findings Seedlings of the two mangrove species acclimated to different salinity levels through changing physiological and morphological traits. However, there were significant differences between S. apetala and L. racemosa in photosynthesis and anti-oxidant defense under salt stress. Increasing NaCl stress significantly elevated net photosynthetic rate (Pn), and stomatal conductance (Gs), intercellular CO2 concentration (Ci) and transpiration rate (Tr) decreased. As a result, water use efficiency (WUE) increased in leaves of S. apetala seedlings. But L. racemosa showed a rapid increase of Pn in the initiation of salt stress, and Pn remained lower than control levels at the end of the experiment. As a result, Ci and Gs increase with the decrease of Pn, Tr and WUE. The reduction occurred after exposure of L. racemosa seedlings to severe salinity, 400 mmol·L–1 NaCl (28 d). These results indicated that the inhibitory effects of severe salinity were more pronounced in L. racemosa under the same salinity. Moreover, the magnitude of variation of S. apetala maximum photochemical efficiency of PSII (Fv/Fm) was significantly less than that of L. racemosa leaves. We speculated that photosynthetic capacity of S. apetala was higher than L. racemosa. O2–· production rate markedly increased after the two seedlings were subjected to 100 mmol·L–1 NaCl and 200 mmol·L–1 NaCl for 7 days and 14 days, respectively. However, O2–· production rate in S. apetala leaves markedly increased upon increasing salinity and reached the highest level after seedlings were subjected to 400 mmol·L–1 NaCl for 28 days, which was 5.3 fold of that in controls. In contrast to S. apetala, O2–· production rate in L. racemosa leaves remained lower than control levels at the end of the experiment. Activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD) and glutathione reductase (GR) was elevated corresponding to the increased O2–· production in the salt-stressed two mangrove plants; however, the magnitude of increase of L. racemosa antioxidant enzyme activities was significantly greater than that of S. apetala, during the period of salt stress. We suggest that L. racemosa plants were able to sense salt stress and up-regulated the antioxidant enzymes to reduce salt-induced lipid peroxidation and membrane permeability, which contributed to maintenance of membrane integrity and salt tolerance in L. racemosa. Sonneratia apetala seedlings might adapt resistance to severe salinity through improving photosynthesis by higher WUE and maximum photochemical efficiency of PSII (Fv/Fm).
Aims Mangrove plants are usually categorized as true mangrove plants and semi-mangrove plants on the basis of their distribution in inter-tidal regions. However, the identification of some fringe mangrove species found mainly on the landward transitional zones is controversial. Specific leaf area (SLA, leaf area per unit dry mass) and mass- and area-based leaf nitrogen concentrations (Nmass and Narea) are important leaf traits for plants, but relevant comparative research on true and semi-mangrove plants is unavailable. Our objective was to determine differences between the two groups and to classify the controversial species according to their leaf traits. Ultimately, this will assist in the management, protection and utilization of mangrove forest.
Methods Three individuals in similar growth sites were chosen for each species from Hainan Island. Fully expanded mature leaves were sampled from the upper canopy of all plants. Succulence (water content per unit leaf area), SLA, Nmass and Narea of mature leaves were studied for 33 species, representing all but three of the mangrove species in China.
Important findings True mangrove plants accumulated more Cl and water per unit leaf area than semi-mangrove plants, except for Pemphis acidula, Hernandia sonora and Clerodendrum inerme. Cl and water content per unit leaf area of true mangrove plants were generally >2.5 mg·cm－2 and >2.4 g·dm－2, respectively. Cl concentrations were positively related to succulence for all mangrove species. True mangrove plants had low SLA (<100 cm2·g－1) and high Narea; however, semi-mangrove plants had high SLA (mean of 160.4 cm2·g-1). Pemphis acidula had much lower SLA than other semi-mangrove species. Our study suggested that there are significant differences between true mangrove plants and semi-mangrove plants in leaf Cl concentration, succulence, SLA, Nmass and Narea. Heritiera littoralis, Excoecaria agallocha, Acrostichum aureum and Acrostichum speciosum are better classified as semi-mangrove plants, while Acanthus ilicifolius and Acanthus ebrecteatus are classified as true mangrove plants, and Xylocarpus granatum needs further research.
Four species of diatoms from the mangroves in Fujian Province and Shenzhen City of China are described. They are Cymbella cucumis A. Schmidt, Navicula elegantoides Hustedt, N. platyventris Meister, and N. tenera Hustedt. They represent new records for China. Detailed description of the taxonomic characters of the four species and of their ecological behavior is given. Cymbella cucumis was defined as a freshwater and brackish water species for it occurred, though occasionally, where water salinity was more than 15.
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