Global Patterns of Pre-Dispersal Propagule Predation in Mangrove Forests1

Mangroves in disparate families produce viviparous seedlings (propagules) that are attacked by many crab and insect predators both before and after dispersal. While post-dispersal predation is viewed as an important factor in structuring many mangrove communities, pre-dispersal predation rates and agents have been characterized for few species. Ten species of mangrove and 3299 propagules were surveyed for pre-dispersal propagule predation at 42 sites around the world. Pre-dispersal predation rates were variable among sites and species, ranging from 0 to 93 percent within sands, with a global total predation rate of 23.3 percent (across all propagules examined) and a mean level of 28.3 percent across sites. Grapsid crabs, Coleoptera and Lepidoptera were the primary predators identified. Forests near human population centers and stands occurring at high intertidal sites exhibited higher levels of propagule predation than those in unpopulated or low-intertidal sites. Predation rates on a species were weakly, negatively correlated with conspecific seedling density at a site. To explore temporal variation in, and ramifications of pre-dispersal predation for propagule growth and abscission dynamics, Rhizophora mangle propagules were monitored over two years at three sites in Belize, Central America. Predation did not significantly reduce hypocotylar growth of germinated propagules on the parent tree, but nearly doubled the abscission rate of premature propagules. Pre-dispersal propagule predation is a ubiquitous feature of mangrove forests world-wide, and must be accounted for in estimates of reproductive output, stand health, and propagule availability for forestry and restoration efforts.     

Association between pore water sulfide concentrations and the distribution of mangroves

At Humingbird Cay, Exuma, Bahamas, distributions of bothRhizophora mangle (red mangrove) andAvicennia germinans (black mangrove) are closely correlated with amounts of hydrogen sulfide (H₂S) in the soil.R. mangle is primarily distributed within large areas of low to moderate H₂S concentrations (mean= 40 mg/l). H₂S levels underA. germinans are lower (mean = 22 mg/l), but the area immediately beyond their root zone often has extremely high sulfide concentrations (mean= 120 mg/l). These results suggest that past attempts to explain mangrove distribution in terms of monotonic soil gradients, the dispersal characteristics of propagules, and interspecific competition are incomplete, and that it will be necessary to examine the link between soil sulfur chemistry and mangrove distribution more fully.     

Gas exchange responses of a mangrove species, Avicennia marina, to waterlogged and drained conditions

This study was undertaken in summer on fully expanded leaves of Avicennia marina trees in the Beachwood Mangroves Nature Reserve, Durban,South Africa. Data sets were obtained over 5–7 days of relatively dry conditions and over two periods of 5 days during which the swamp was continuously inundated with dilute seawater (< 150 mol m⁻³NaCl). Gas exchange responses were strongly influenced by photosynthetic photon flux density (PPFD), leaf temperature and leaf to air vapour pressure deficit (Δw). Carbon dioxide exchange was saturated at a PPFD of about 800 μmol m⁻² s⁻¹. Maximal CO₂ exchange rates ranged from 8.5 to 9.9 μmol m⁻² s⁻¹ with no differences between drained and waterlogged conditions. Under drained conditions, leaf conductance,transpiration and internal CO₂ concentrations were generally lower, and water use efficiencies higher, than during waterlogging. Continuous waterlogging for 5 days had no adverse effect on CO₂ exchange. Xylem water potentials ranged from −1.32to −3.53 MPa during drained and from −1.02 to −2.65 Mpa during waterlogged conditions. These results are discussed in relation to anatomical and metabolic adaptations of A. marina to waterlogging stress. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ecology of Mangrove Growth and Recovery in the Lesser Antilles: State of Knowledge and Basis for Restoration Projects

Whereas the increasing knowledge on tropical coastal wetlands highlights the ecological and economical importance of such ecosystems, anthropogenic activities within the coastal zone have caused substantial, irreversible losses of mangrove areas in the Lesser Antilles during the last decades. Such a paradox gives strength to compensatory policy efforts toward mangrove restoration. We review the available knowledge on the ecology of mangrove growth and recovery in the Lesser Antilles as a contribution to possible restoration projects in such islands. Distribution of species follows a general pattern of seaward/landward zonation according to their respective tolerance to flooding and to pore‐water salinity. An experimental study of seedling growth following simulated oil spill has documented the tolerance of Rhizophora mangle and Avicennia germinans seedlings to oil concentration in soils and the effects of natural biotic and abiotic factors on seedlings growth and survival. Monitoring mangrove recovery following hurricane Hugo has given information on growth patterns, from seedling to sapling stages, according to species and site conditions. Forest recovery was mostly due to pre‐established seedlings. For the large Rhizophora propagules, buoyancy appears to be a quite inefficient way of dispersal far inland from the sea shore or riversides. Causes of recovery failure are discussed. From these results we attempt to answer the questions when, where, how to plant mangroves, and what species to use.     

红海榄红树林的氮、磷积累和生物循环

本文讨论广西山口英罗湾中红海榄群落的氮、磷含量及其生物循环。结果表明,红海榄群落现存量中,含氮、磷总量分别为221.15和13.27g/m~2。其中地上部分别为134.90和8.73g/m~2;地下部分别为86.25和4.54g/m~2。该群落的氮、磷元素生物循环中,年吸收量分别为12.91和1.27g/m~2,年存留量分别为7.04和0.65g/m~2;年归还量分别为5.86和0.61g/m~2。富集率分别为1.11和1.60。群落各组分的氮含量均大干磷含量;周转期氮需38a,比磷(22a)慢。     

海南三亚河红树凋落物产量与季节变化研究

在海南三亚河红树 (Rhizophora apiculata)纯林区设置 4个 1 m2 凋落物收集网于 1 999年全年逐旬收集 ,4个网的平均年凋落物总产量为 1 388.2 4 g/ (m2· a) ,其中叶 79.9% ,枝 8.8% ,花 6.4% ,果 4.9%。与国内外有关资料对比 ,三亚河红树纯林凋落物产量是很高的 ,主要与树较高、低纬度、河流型和林带窄有关。凋落物总产量有多峰值的季节变化 ,峰月依次为 1 0～ 1 1月份、4月份和 8月份 ,谷月依次为 1 2月份、5月份和 9月份。叶的产量的峰谷变化与总产量相一致。枝的产量 77%的网次为 0 ,仅 2、8、9、1 0、1 1月份形成 5个峰值 ,其中后两个最大的峰值对总产量峰值的贡献达占 31 .7%和 31 .2 %。花的产量在 3～ 5月份略显平坦的峰值 ,8～ 1 2月份维持较低的产量。果的产量在 6～ 7月份有一个较宽的峰 ,1 0和 1 1月份有两个窄峰 ,1 2月份至来年 4月份基本上没有产量。花和果的凋落物产量变化明显与植物物候期有关。取 1 999年逐旬平均气温、降水量和平均风速资料与相应的凋落物产量进行相关分析显示 ,平均气温宏观控制叶凋落物产量和凋落物总产量 ,枝凋落物产量主要受平均风速影响。估算整个三亚河 1 4 hm2 红树林区可年产凋落物1 9 4t,大部分输送到三亚湾并成为三亚湾海洋生物资源有机碎屑食物链的物质和     

Population dynamics of mangrove Avicennia bicolor on the Pacific coast of Costa Rica

Deterministic and stochastic class structured population models were used to simulate the life cycle of Avicennia bicolor of the Pacific coast of Costa Rica. The models were based on an extensive data set collected during a 6 year period in a 0.52 ha plot of monospecific A. bicolor. This data set included density, growth, mortality and transition rates of seedlings, saplings and trees of eight different diameter classes, as well as propagule production for the reproductive tree classes. Model simulations carried out over a 100 year period indicated a stable size class structure of the forest. Sensitivity analysis showed a significantly greater sensitivity of the model population to simulated changes in the mortality of seedlings, in comparison with the mortality of saplings and trees. An increase of 1% in the mortality of seedlings, for example, was sufficient to cause significant changes in the density of individual size classes. In contrast, neither a 10% increase in the mortality of saplings and trees nor a 20% decrease in the propagule production of fecund trees significantly affected the overall forest structure.     

红树植物秋茄和红海榄叶片元素含量及季节动态的比较研究

研究了福建九龙江口秋茄（Kandelia candel L.）和红海榄（Rhizophora stylosa G.）成熟叶片N、P、K、Na、Ca、Mg和CI等元素含量的季节变化和元素间的关系。结果表明秋茄和红海榄同为红树科树种,生境相同且同属拒盐植物,但在元素积累及季节变化模式上存在较大差别。秋茄和红海榄叶片高盐分和Ca含量及低K／Na比,这是我们对盐渍生境的一种适应。秋茄无机渗透调节剂（主要指K^ 、Na^ 、Ca^2 、Mg^2 和CI^-）含量夏季高于冬季,而红海榄与之完全相反。秋茄能够通过主动积累有机渗透调节剂来适应低温,而红海榄不能。对秋茄和红海缆抗寒机制进行了讨论。     

Genetic diversity enhanced by ancient introgression and secondary contact in East Pacific black mangroves

Regional distribution of genetic diversity in widespread species may be influenced by hybridization with locally restricted, closely related species. Previous studies have shown that Central American East Pacific populations of the wide-ranged Avicennia germinans , the black mangrove, harbour higher genetic diversity than the rest of its range. Genetic diversity in this region might be enhanced by introgression with the locally restricted Avicennia bicolor . We tested the hypotheses of ancient hybridization using phylogenetic analysis of the internal transcribed spacer region (ITS) of the nuclear ribosomal DNA and intergenic chloroplast DNA; we also tested for current hybridization by population level analysis of nuclear microsatellites. Our results unveiled ancient ITS introgression between a northern Pacific Central American A. germinans lineage and A. bicolor . However, microsatellite data revealed contemporary isolation between the two species. Polymorphic ITS sequences from Costa Rica and Panama are consistent with a zone of admixture between the introgressant ITS A. germinans lineage and a southern Central American lineage of A. germinans . Interspecific introgression influenced lineage diversity and divergence at the nuclear ribosomal DNA; intraspecific population differentiation and secondary contact are more likely to have enhanced regional genetic diversity in Pacific Central American populations of the widespread A. germinans .     

Growth rings, growth ring formation and age determination in the mangrove Rhizophora mucronata

BACKGROUND AND AIMS: The mangrove Rhizophora mucronata has previously been reported to lack annual growth rings, thus barring it from dendrochronological studies. In this study the reported absence of the growth rings was reconsidered and the periodic nature of light and dark brown layers visible on polished stem discs investigated. In addition, the formation of these layers in relation to prevailing environmental conditions, as well as their potential for age determination of the trees, was studied. METHODS: Trees of known age were collected and a 2.5-year cambial marking experiment was conducted to determine the periodic nature of the visible growth layers. KEY RESULTS: Annual indistinct growth rings were detected in R. mucronata and are defined by a low vessel density earlywood and a high vessel density latewood. The formation of these growth rings and their periodic nature was independent from site-specific environmental conditions in two forests along the Kenyan coast. However, the periodic nature of the rings was seriously affected by slow growth rates, allowing accurate age determination only in trees with radial growth rates above 0.5 mm year(-1). The onset of the formation of the low vessel density wood coincided with the onset of the long rainy season (April-May) and continues until the end of the short rainy season (November). The high vessel density wood is formed during the dry season (December-March). Age determination of the largest trees collected in the two studied forests revealed the relatively young age of these trees (+/-100 years). CONCLUSIONS: This study reports, for the first time, the presence of annual growth rings in the mangrove R. mucronata, which offers further potential for dendrochronological and silvicultural applications.     

Diversity and distribution of the mangrove forests in Taiwan

In a survey of 1992 to 1994, mangrove forests withfour species of true mangroves, Kandelia candel(L.) Druce, Avicennia marina(Forsk.) Vierh.,Rhizophora stylosaGriff., and Lumnitzera racemosaWilld., were found at 22locations in the west coast of Taiwan. The northernrange of their distribution was at Tanshui Estuary(Latitude 25^°11N) and the southern range atTapen Bay (22^°28N). The total area wasestimated to be 286.95 ha. There was an obvious changein species composition and a decrease in speciesnumber of true mangroves from south to north: the fourspecies dominated by A. marinain thesouth and K. candelas thesole species in the north. Air temperature associatedwith sea surface temperature and oceanic currents inwinter, but not soil property, was found to be theprimary environmental factor, affecting the diversityand distribution of true mangroves in Taiwan as wellas in the northeast region of Asia.     

The role of freezing in setting the latitudinal limits of mangrove forests

Mangrove trees dominate coastal vegetation in tropical regions, but are completely replaced by herbaceous salt marshes at latitudes above 32 degrees N and 40 degrees S. Because water deficit can increase damage caused by freezing, we hypothesized that mangroves, which experience large deficits as a result of saline substrates, would suffer freeze-induced xylem failure. Vulnerability to freeze-induced xylem embolism was examined in the most poleward mangrove species in North America, in an area where freezing is rare but severe, and in Australia, in an area where freezing is frequent but mild. Percentage loss in hydraulic conductivity was measured following manipulations of xylem tension; xylem sap ion concentration was determined using X-ray microanalysis. Species with wider vessels suffered 60-100% loss of hydraulic conductivity after freezing and thawing under tension, while species with narrower vessels lost as little as 13-40% of conductivity. These results indicate that freeze-induced embolism may play a role in setting the latitudinal limits of distribution in mangroves, either through massive embolism following freezing, or through constraints on water transport as a result of vessel size.     

Two new nitrogen-fixing bacteria from the rhizosphere of mangrove trees: Their isolation, identification and in vitro interaction with rhizosphere Staphylococcus sp.

Abstract Two new diazotrophic bacteria, Listonella anguillarum and Vibrio campbellii , and one non-nitrogen-fixing bacterium, Staphylococcus sp., were isolated from the rhizosphere of mangrove trees. Strains of these newly-defined diazotrophs are known as pathogenic bacteria in fish and shellfish. During the purification of diazotrophic species from the entire rhizosphere population, N₂-fixation of the bacterial mixtures decreased. When grown in vitro in mixed cultures, the non-fixing bacterium Staphylococcus sp. increased the nitrogen-fixing capacity of L. anguillarum by 17% over the pure culture; the nitrogen-fixing capacity per bacterial cell increased 22%. This interaction was not due to a change in O₂ concentration. Staphylococcus sp. decreased the nitrogen-fixing capacity of V. campbellii by 15%.
These findings indicate that (i) other species of rhizosphere bacteria, apart from the common diazotrophic species, should be evaluated for their contribution to the nitrogen-fixation process in mangrove communities; and (ii) the nitrogen-fixing activity detected in the rhizosphere of mangrove plants is probably not the result of individual nitrogen-fixing strains, but the sum of interactions between members of the rhizosphere community.     

The population dynamics of the mangrove Avicennia marina; demographic synthesis and predictive modelling

Population dynamics of the widespread mangrove Avicennia marina was studied over the complete life-history from zygotes through to adults in southeastern Australia. Zygote survival, propagule dispersal, seedling establishment, seedling recruitment and sapling recruitment were examined by demographic censuses over a range of spatial and temporal scales. Hypotheses about factors regulating survival were tested by manipulative field experiments. Life table statistics for survival and fecundity were used to calculate transition probabilities and their variance for seven stages of life history. These parameters were used as the basis of a stochastic model that predicts population structure after small and large scale perturbations.