An ordination study to view vegetation structure dynamics in disturbed and undisturbed mangrove forests in Kenya and Sri Lanka

The mangrove vegetation of a disturbed and undisturbed site in bothKenya and Sri Lanka was investigated in the field for three vegetation layers:adult trees, young trees, and juvenile trees. A minimum of 25 sample points, inwhich the vegetation was described and environmental factors (salinity, lightintensity, land/water ratio, abundance of herbivorous crabs and snailabundance)were measured or estimated, were taken on each site. Detrended correspondenceanalysis (DCA) and canonical correspondence analysis (CCA) were used tosummarize the data bulk, to investigate the vegetation dynamics(e.g., comparability of species distribution in the threevegetation layers), and/or to link the vegetation data to the environmentalfactors. Results showed that species clusters were relatively easy todelineate,whether mangrove zonation was present or not. Among the environmental factors,the abundance of propagule predators (mostly sesarmid crabs) contributedsignificantly to the variation in vegetation and could be an explanatoryparameter for the observed vegetation data in a majority of sites. In the sitewhere it was not, the most important factor in the ordination was theland/waterratio, which is important at the ecological level as well (link between waterlevel and vegetation dynamics). However, none of the environmental factorscouldsuccessfully explain the total variability in the vegetation data suggestingthat other, more determining factors exist. Our results further provideinformation on the dynamic or non-dynamic nature of a forest and on its abilityto rejuvenate, and may contribute to appropriate forestry management guidelinesin the future.     

Valuing mangrove ecosystem services: linking nutrient retention function of mangrove forests to enhanced agroecosystem production

Mangroves are highly productive wetland ecosystems strategically located at the interface between land and sea. They play an important role in the biogeochemical cycles of the coastal environment, acting as sources of nutrients to adjacent marine and terrestrial ecosystems through active and passive transport. We examined the nutrient contents in mangrove and nonmangrove soils in and around the Bhitarkanika National Park, India and assessed whether the local agricultural producers were aware of and placed a value on this contribution of mangrove forests in enhancing agroecosystem productivity. Soil samples from both mangrove and nonmangrove areas were analysed and quantity of organic carbon, total nitrogen, available phosphorus and potassium were derived. The replacement cost method was used to derive the value of nutrients in mangrove soils. We estimated that each hectare of mangrove contains additional nutrients worth US$232.49 in comparison to nonmangrove areas. The difference in nutrient content in mangrove versus nonmangrove areas gave the value of US$3.37 million for the nutrients in 145 km² of mangrove forests. The agricultural producers were aware that mangrove forests act as a source of nutrients and were willing to pay a higher price for the land adjoining mangrove forests. Around 92% of the producers ranked nutrient retention as a secondary function of mangrove forests. Despite crop depredation from wild ungulates and conflict with salt water crocodiles the agriculturist finds the benefit to cost ratio of mangrove forests high and more than 76% were in favour of mangrove restoration. This study provides an opportunity to highlight the importance of mangrove ecosystems to the livelihoods of the local people and the urgent need to sustain these through proper policy and market interventions.     

Seed predation by insects in tropical mangrove forests: extent and effects on seed viability and the growth of seedlings

Summary Although insects are known to be important seed predators in most terrestrial forests, their role in marine tidal (mangrove) forests has not been examined. Surveys at 12 sites in tropical Australia showed that between 3.1 and 92.7 percent of the seeds or propagules of 12 mangrove tree species had been attacked by insects. Seeds/propagules of six species (Avicennia marina, Bruguiera gymnorrhiza, B. parviflora, Heritiera littoralis, Xylocarpus australasicus and X. granatum) showed consistently high (>40%) levels of insect damage. Greater than 99% of H. littoralis seeds were attacked by insect predators. The survival and subsequent growth in height and biomass of insect-damaged and non-damaged control seeds/propagules of eight mangrove species were compared in shadehouse experiments. Mangrove species fell into 4 groups with regard to the effect of insect predators on their seeds and seedlings. Xylocarpus australasicus and X. granatum had significantly decreased survival (X 48 and 70%) and growth in height (X 61 and 96%) and biomass (X 66 and 85%). Bruguiera parviflora showed decreased survival (X 59%), but there was no effect of insects on the growth of surviving propagules. In contrast, there was no effect of insect damage on the survival of seedlings of Avicennia marina and Bruguiera exaristata, but decreased growth in height (X 22 and 25%) and biomass (X 22 and 26%). Survival and growth of seedlings of Rhizophora stylosa and Bruguiera gymnorrhiza were not affected. The influence of insect seed predators on the survival and growth of seeds of mangrove species in forests will depend on the relative abundance of seed-eating crabs and intertidal position in mangrove forests.This is Contribution No 499 from the Australian Institute of Marine Science     

Ethnobiology, socio-economics and management of mangrove forests: A review

There is growing research interest in the ethnobiology, socio-economics and management of mangrove forests. Coastal residents who use mangroves and their resources may have considerable botanical and ecological knowledgeable about these forests. A wide variety of forest products are harvested in mangroves, especially wood for fuel and construction, tannins and medicines. Although there are exceptions, mangrove forest products are typically harvested in a small-scale and selective manner, with harvesting efforts and impacts concentrated in stands that are closer to settlements and easiest to access (by land or by sea). Mangroves support diverse, local fisheries, and also provide critical nursery habitat and marine productivity which support wider commercial fisheries. These forests also provide valuable ecosystem services that benefit coastal communities, including coastal land stabilization and storm protection. The overlapping of marine and terrestrial resources in mangroves creates tenure ambiguities that complicate management and may induce conflict between competing interests. Mangroves have been cut and cleared extensively to make way for brackish water aquaculture and infrastructure development. More attention is now given to managing remaining forests sustainably and to restoring those degraded from past use. Recent advances in remotely sensed, geo-spatial monitoring provide opportunities for researchers and planners to better understand and improve the management of these unique forested wetlands.     

Seedling recruitment patterns in a Belizean mangrove forest: effects of establishment ability and physico-chemical factors

A field study was conducted to evaluate the relative importance of factors affecting seedling establishment and survival on a mangrove-dominated island in Belize. An examination of spatial patterns of seedling relative densities in relation to reproductive adults and physico-chemical conditions provided correlative information on factors affecting mangrove regeneration patterns. Distance from reproductive adults explained 89–94% of the variation in relative density of Rhizophora mangle seedlings, whereas availability of resources (light and NH₄) explained 73–80% of variation in Avicennia germinans seedling relative density. Just after dispersal (December), 89% of the variation in Laguncularia racemosa seedling relative density was attributable to distance from reproductive adults, but 7 months later (July) 74% of the variation was explained by intensity of flooding- and salinity-related stresses. Survivorship (after 2.5 years) of propagules and seedlings of R. mangle and A. germinans transplanted to zones of contrasting physico-chemical conditions demonstrated that: (1) mortality was highest during the establishment phase and major causes were failure to strand before viability was lost, consumption by predators and desiccation; and (2) after establishment, differences in sensitivity to physicochemical stress factors such as flooding (A. germinans) and initial orientation of the seedling axis (R. mangle) exerted a further influence on seedling survival. The results indicate that seedling recruitment in these neotropical forests is strongly influenced by dispersal patterns, differential establishment abilities and effects of physico-chemical factors that vary with elevation and distance from the shoreline.     

Organic carbon dynamics in mangrove ecosystems: A review

Our current knowledge on production, composition, transport, pathways and transformations of organic carbon in tropical mangrove environments is reviewed and discussed. Organic carbon entering mangrove foodwebs is either produced autochthonously or imported by tides and/or rivers. Mangrove litter and benthic microalgae are usually the most important autochthonous carbon sources. Depending on local conditions, phytoplankton and seagrass detritus imported with tides may represent a significant supplementary carbon input. Litter handling by the fauna not only affects microbial carbon transformations, but also the amount of organic carbon available for export. Most mangrove detritus that enters the sediment is degraded by microorganisms. Aerobic respiration and anaerobic sulfate reduction are usually considered the most important microbial respiration processes, but recent evidence suggests that iron respiration may be important in mangrove sediments as well. Organic carbon that escapes microbial degradation is stored in sediments and in some mangrove ecosystems, organic-rich sediments may extend to several meters depth. Many mangrove forests also lose a significant fraction of their net primary production to coastal waters. Large differences occur between mangrove forests with respect to litter production and export. Mangrove-derived DOC is also released into the water column and can add to the total organic carbon export. Numerous compounds have been characterized from mangrove tissues, including carbohydrates, amino acids, lignin-derived phenols, tannins, fatty acids, triterpenoids and n-alkanes. Many of these may, together with stable isotopes, exhibit a strong source signature and are potentially useful tracers of mangrove-derived organic matter. Our knowledge on mangrove carbon dynamics has improved considerably in recent years, but there are still significant gaps and shortcomings. These are emphasized and relevant research directions are suggested.     

人工红树林幼林藤壶危害及防治研究进展

随着近年来红树林恢复性造林面积的扩大,海洋污损生物藤壶对红树林幼林的危害问题日益突出.文中综述了藤壶附着的生物化学、藤壶在红树林附着的生态学、藤壶对人工红树林幼林的危害和国内所采用的化学药物防治措施等方面的研究进展,以及今后的研究方向.藤壶在红树林的附着和分布模式受海水盐度、浸淹深度、林分郁闭度、水文条件等环境因素和生物因素的影响.而藤壶胶粘蛋白的氨基酸组成、一维结构,胶粘蛋白在水下的交联、组装和胶粘的过程与机制,以及藤壶危害红树幼苗的机制和危害权重尚需要深入探讨.研究红树植物对藤壶附着的响应和长期适应机制将为藤壶的防治提供更多的启示.     

Investigating the role of impoundment and forest structure on the resistance and resilience of mangrove forests to hurricanes

The present study evaluates how a prolonged artificial flooding regime in impounded mangrove forests influences the regeneration after medium-sized forest destruction created by two hurricanes in 2004 in the Indian River Lagoon, Florida, USA. Disturbance patterns, forest structure, and regeneration were investigated. We found disturbed areas, characterized by uprooted and snapped trees, and intact forests in close proximity. The canopy turnover was greater in forests in higher succession stages with median tree diameter at breast height of 7.6 ± 5.7 cm compared to the intact forest with 3.7 ± 1.2 cm. Larger trees with lower densities were more susceptible to hurricane damage. We observed that regeneration of the open patches was dominated by the flood-tolerant species Rhizophora mangle (89.9%) instead of the faster-growing pioneer species Laguncularia racemosa (7.0%). Some of the disturbed areas created by the hurricanes were not recolonized. The regeneration rate of the disturbed areas expressed by vegetation closure >50% differed between almost zero to 100% in three different impoundments. We concluded that the artificial flooding regime imposed by impoundment is the predominant selective force in the successive process according to the species composition. However, we were not able to detect the driving factors that prevented mangrove establishment in disturbed areas.     

Tropical mangrove ecology: Physical and biotic factors influencing ecosystem structure and function

Our understanding of the ecology of tropical mangals has strong practical implications for the management and conservation of these threatened ecosystems. Earlier models of tropical mangals proposed overwhelming influences by physical forces and processes such as the tidal regime or geomorphology on ecosystem structure and function. Recent findings from especially the Indo-Pacific mangals suggest also considerable influence from biotic agents and processes such as sesarmine crab feeding and bioturbation activities in shaping the ecology of tropical mangals. I argue that more research attention should be paid to the study of the interplay between physical and biotic influences in the ecology of tropical mangals. Examples in litter dynamics and community determination are given to illustrate how biotic influences may respond to changes in the physical setting of mangals. This necessitates an approach integrating the two sources of influences. Despite decades of increased research effort, answers to many fundamental questions concerning practical management issues of tropical mangals are still largely unavailable. The often-acclaimed functions and values of tropical mangals also have to be critically assessed in the light of existing and future data. It is proposed that research effort should also be targeted towards the assessment and mitigation of the predicted impacts of urgent problems faced by tropical mangals (e.g. conversion to aquaculture ponds, pollution) in order to secure their long-term conservation and wise management.     

Chemical and biogeophysical impact of four-dimensional (4D) seismic exploration in sub-Saharan Africa, and restoration of dysfunctionalized mangrove forests in the prospect areas

Four-dimensional (4D) seismic exploration, an improved geophysical technique for hydrocarbon-data acquisition, was applied for the first time in the Nembe Creek prospect area of Nigeria. The affected soils were slightly alkaline in situ when wet (pH 7.2), but extremely acidic when dry (pH 3.0). The organic carbon content (4.6-26.8%) and other physicochemical properties of soils and water (N, P, and heavy-metal contents, etc.) were higher than the baseline values obtained in 2001 before seismic profiling. Most values also exceeded the baseline compliance standards of the Department of Petroleum Resources (DPR), the World Health Organization (WHO), and the Federal Environmental Protection Agency (FEPA). Rehabilitation of the affected areas was achieved by stabilizing the mangrove floor by liming and appropriate application of nutrients, followed by replanting the cut seismic lines over a distance of 1,372 km with different mangrove species, including juvenile Rhizophora racemosa, R. mangle, and Avicennia species, which were transferred from nursery points. Quicker post-operational intervention is recommended for future 4D surveys, because the time lag between the end of seismic activity and post-impact investigation is critical in determining the relationship between activity and impact: the longer the intervening period, the more mooted the interaction.     

Allometry, biomass, and productivity of mangrove forests: A review

We review 72 published articles to elucidate characteristics of biomass allocation and productivity of mangrove forests and also introduce recent progress on the study of mangrove allometry to solve the site- and species-specific problems. This includes the testing of a common allometric equation, which may be applicable to mangroves worldwide. The biomass of mangrove forests varies with age, dominant species, and locality. In primary mangrove forests, the above-ground biomass tends to be relatively low near the sea and increases inland. On a global scale, mangrove forests in the tropics have much higher above-ground biomass than those in temperate areas. Mangroves often accumulate large amounts of biomass in their roots, and the above-ground biomass to below-ground biomass ratio of mangrove forests is significantly low compared to that of upland forests (ANCOVA, P < 0.01). Several studies have reported on the growth increment of biomass and litter production in mangrove forests. We introduce some recent studies using the so-called “summation method” and investigate the trends in net primary production (NPP). For crown heights below 10 m, the above-ground NPP of mangrove forests is significantly higher (ANOVA, P < 0.01) than in those of tropical upland forests. The above-ground litter production is generally high in mangrove forests. Moreover, in many mangrove forests, the rate of soil respiration is low, possibly because of anaerobic soil conditions. These trends in biomass allocation, NPP, and soil respiration will result in high net ecosystem production, making mangrove forests highly efficient carbon sinks in the tropics.     

Dynamics of animal movement in an ecological context: dragonfly wing damage reduces flight performance and predation success

Much of our understanding of the control and dynamics of animal movement derives from controlled laboratory experiments. While many aspects of animal movement can be probed only in these settings, a more complete understanding of animal locomotion may be gained by linking experiments on relatively simple motions in the laboratory to studies of more complex behaviours in natural settings. To demonstrate the utility of this approach, we examined the effects of wing damage on dragonfly flight performance in both a laboratory drop–escape response and the more natural context of aerial predation. The laboratory experiment shows that hindwing area loss reduces vertical acceleration and average flight velocity, and the predation experiment demonstrates that this type of wing damage results in a significant decline in capture success. Taken together, these results suggest that wing damage may take a serious toll on wild dragonflies, potentially reducing both reproductive success and survival.     

红树林生态系统遥感监测研究进展

随着现代遥感技术的迅速发展,遥感监测已经成为红树林生态系统变化监测的重要手段和方法。从遥感技术在生态系统变化监测应用领域入手,综述了国内外红树林遥感监测的发展历程,系统总结了遥感技术在红树林湿地动态、种间分类、群落结构(叶面积指数、冠幅、树高等)、生物量、灾害灾情(病虫害、风暴潮等)、景观格局动态、驱动力、红树林湿地保护与管理等领域应用现状,归纳了不同应用领域遥感监测的理论、方法及研究现状。指出我国在红树林遥感监测中存在的不足。提出红树林遥感监测应在分类标准体系规范化、分类精度提升、红树林生态学特征参数(物种多样性、优势度等)、生态系统环境空间演变过程及遥感监测的尺度效应方面加大研究力度。充分发挥区域综合监测模型在红树林生态系统变化遥感监测中的作用。     

植物功能性状与森林生态系统服务的关系研究综述

植物功能性状途径是揭示生物多样性与生态系统服务关系的重要视角,尽管植物功能性状与生态系统服务的关系在单一地点的研究取得突出进展,但对于植物功能性状与生态系统服务的关系仍缺乏整体认识。以森林生态系统为对象,通过系统文献检索及筛选,收集了216篇文献,应用整合分析和二分网络分析等方法,探讨了植物功能性状对森林生态系统服务及其权衡与协同关系的影响。结果表明：植物叶片功能性状关注最多,占研究性状数量的48%,生态系统服务中关注最多是生物量、土壤肥力、病虫害控制和固碳服务;81.1%的植物功能性状与生态系统服务关系组表现为稳定的正向或负向关系,而关联植物功能性状多的生态系统服务（生物量、固碳服务、土壤水分、土壤肥力和病虫害控制）往往与植物功能性状表现为不稳定关系;森林生态系统中存在6组"植物功能性状-生态系统服务簇（简称"性状-服务簇"）：水循环相关的性状-服务簇、土壤保持相关的性状-服务簇、物质生产相关的性状-服务簇、灾害控制相关的性状-服务簇、养分循环相关的性状-服务簇和授粉相关的性状-服务簇,揭示了各性状-服务簇内生态系统服务的权衡或协同关系以及与各性状-服务簇关系密切的植物功能性状。该研究从总体上阐明了植物功能性状与森林生态系统服务关系的研究重点和进展、揭示了植物功能性状对森林生态系统服务影响效应的方向和强度,可为深化森林生态系统服务形成机制认识以及协调生态系统服务权衡关系提供科学依据。     

Long-term retrospection on mangrove development using transdisciplinary approaches: A review

Large ecosystem processes often take place beyond the observation time of a researcher. Yet, through retrospective research scientists can approach and understand ecosystem changes. This contributes to the fundamental understanding of both human-induced and natural dynamics in ecosystems world-wide. This also holds for fast changing coastal areas with mangrove ecosystems, which are important for biodiversity, for coastal protection, and for the daily livelihood of millions of people in tropical coastal developing countries. In addition, retrospective research generates a basis for predictions that can be used early on to protect an ecosystem. In attempting to protect ecosystems from adverse human-induced change and destruction, and to manage them for sustainability, scientists are only beginning to investigate and understand natural ecosystem dynamics. It is important and advisable to gather, combine and analyse all possible data that allow a researcher to look back in time. This paper reviews the available retrospective methods, and highlights the transdisciplinary way (i.e. combination between basic and applied sciences on one hand, and social and human sciences on the other) in which retrospective research on a scale between months and centuries can be carried out, but it also includes methods on larger scales that may be marginally relevant. The paper particularly emphasizes the lack of transdisciplinary (not interdisciplinary) integration between sciences in retrospective research on mangrove forests in the past.     

Regeneration of<Emphasis Type="Italic"> Rhizophora mangle</Emphasis> in a Caribbean mangrove forest: interacting effects of canopy disturbance and a stem-boring beetle

Current theory predicts that in low-density, seed-limited plant populations, seed predation will be more important than competition in determining the number of individuals that reach maturity. However, when plant density is high, competition for microsites suitable for establishment and growth is expected to have a relatively greater effect. This dichotomous perspective does not account for situations in which the risk of seed predation differs inside versus outside recruitment microsites. We report the results of a field experiment and sampling studies that demonstrate such an interaction between microsite quality and the risk of propagule predation in mangrove forests on the Caribbean coast of Panama, where it appears to play a key role in shaping the demography and dynamics of the mangrove, Rhizophora mangle. Rhizophora's water-borne propagules establish wherever they strand, but long-term sampling revealed that only those that do so in or near lightning-created canopy gaps survive and grow to maturity. These microsites afford better growth conditions than the surrounding understory and, as importantly, provide a refuge from predation by the scolytid beetle, Coccotrypes rhizophorae. This refuge effect was confirmed with a field experiment in which Rhizophora seedlings were planted at different positions relative to gap edges, from 5 m inside to 20 m outside the gap. Mortality due to beetle attack increased linearly from an average of 10% inside a gap to 72% at 20 m into the forest. The interaction between canopy disturbance and propagule predation may be having a large impact on the composition of our study forests. Being shade-tolerant, Rhizophora seedlings that escape or survive beetle attack can persist in the understory for years. However, the high rate of beetle-induced mortality effectively eliminates the contribution of advance regeneration by Rhizophora saplings to gap succession. This may explain why the shade-intolerant mangrove, Laguncularia racemosa, is able to co-dominate the canopy in low intertidal forests at our study sites.     

Climate change-induced ecosystem disturbance: a review on sclerophyllous and semi-deciduous forests in Tunisia

According to the sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC), global climate change is now unequivocal. Tunisia, like many other countries, has been affected by climate changes, including rising temperatures, intense heatwaves, and altered precipitation regimes. Tunisia's mean annual temperatures has risen about +1.4 °C in the twentieth century, with the most rapid warming taking place since the 1970s. Drought represents a primary contributing factor to tree decline and dieback. Long-term drought can result in reduced growth and health of trees, thereby increasing their susceptibility to insect pests and pathogens. Reported increases in tree mortality point toward accelerating global forest vulnerability under hotter temperatures and longer, more intense droughts. In order to assess the effect of these climate changes on the current state of forest ecosystems in Tunisia and their evolution, an investigative study was required. Here, we review the current state of knowledge on the effects of climate change on sclerophyllous and semi-deciduous forest ecosystems in Tunisia. Natural disturbance during recent years, as well as the adaptability and resilience of some forest species to climate change, were surveyed. The Standardized Precipitation Evapotranspiration Index (SPEI) is a multi-scalar drought index based on climate data that has been used to analyse drought variability. The SPEI time scale analysis showed a negative trend over the 1955–2021 period in Tunisian forest regions. In 2021, Tunisia lost 280 km² of tree cover to fires, which is equivalent to 26% of the total lost area between 2008 and 2021. Changing climate conditions have also affected phenological parameters, with an advance in the start of the green season (SOS) of 9.4 days, a delay at the end of the green season (EOS) of 5 days, with a consequent extended duration of the green season (LOS) by an average of 14.2 days. All of these alarming findings invite us to seek adaptation strategies for forest ecosystems. Adapting forests to climate change is therefore a challenge for scientists as well as policymakers and managers.     

Factors involved in the degradation of mangrove forests in Iran: A mixed study for the management of this ecosystem

In Iran, mangroves are located in the south of the country, where they fulfill essential ecosystem functions, but some parts of them have been destroyed for various reasons in recent years so that it seems necessary to have a management plan consistent with the conservation of this ecosystem. But, it needs knowledge of the trend of and reasons for the degradation of these forests. So, the primary idea of this research was to discover the factors involved in the degradation of these forests and how to manage them. So, the research first used the remote sensing technique to determine the rate of their degradation over the last 20 years. Then, using the Delphi technique, 45 factors were identified for the degradation of these forests and they were classified into five categories including climatic and environmental, anthropogenic, socioeconomic, psychological, and policymaking and legal. Finally, the analytic hierarchy process (AHP) was used to rank these factors within two management paradigms of remediability and preventability so that the ecosystem can be soundly managed by classifying these factors. Overall, the results can provide policymakers with new insights into forest management and the policies presented here can contribute to the sustainability of this ecosystem.     

Molecular ecology and biogeography of mangrove trees towards conceptual insights on gene flow and barriers: A review

In this review the most recent contributions to the field of molecular ecology and biogeography of mangrove trees are considered. Emphasis is on the obtained information of the different molecular marker methods used in mangrove genetics and on the potential to infer biogeographical patterns. Isozymes on average showed low or even no polymorphism in mangrove trees similar as known in seagrasses. The outcrossing Avicennia seems to be the most variable mangrove tree for isozymes. Both low amounts of interpretable allozymes and difficulties in maintaining the enzyme activity have reduced the number of successful studies during the isozyme era. Dominant marker methods (RAPD, AFLP and ISSR) were successful to demonstrate differences in amplified DNA products at large-scale geographical distances within Avicennia species and to estimate species relationships. Hybrid testing seldom revealed hybridization among tree species. The most promising markers (microsatellites or SSR) were only recently developed and will continue to provide evidence in future studies. SSR loci in Avicennia seem to show relatively low levels of polymorphism, though clearly demonstrating that populations located at the edge of the species range can be even more depauperated. Populations located more central in their native range and situated along the same coastline such as reported in Rhizophora, are expected to be only weakly differentiated due to increased levels of gene flow. Haplotypic chloroplast variants (PCR-RFLP) or sequences revealed strong genetic structuring between populations of Avicennia, Kandelia and Ceriops from different biogeographical oceanic regions. Recent views on long-distance dispersal and on gene flow across oceans as well as along the same coastline are discussed. A comparative analysis on genetic variables across species and regions indicated general trends in the partitioning of genetic variation. A conceptual map with a worldwide overview of those regions where high levels of gene flow were reported and of other regions that were considered as effective barriers, is presented. As an aim to increase the number of reliable comparisons of genetic variables across species or regions and to increase the relevance of mangrove genetics for local conservation issues, recommendations on the molecular markers and on the sampling design of individuals and populations are given within a conceptual context of evolutionary significant units.