Feeding preferences and food searching strategies mediated by air- and water-borne cues in the mud whelk Terebralia palustris (Potamididae: Gastropoda)

The gastropod T. palustris is one of the major species responsible for leaf consumption and degration within the Indo-Pacific mangrove forests, and it strongly competes with herbivorous sesarmid crabs in consuming fallen leaves. This snail feeds at high and low tides and it is able to locate food items by means of chemical cues. The aim of this study was to assess the food preferences of T. palustris and to define its feeding strategies at low and high tides, by conducting field trials on water-borne mediated food location at high tide, grazing rate and the chemical attraction exerted by different mangrove leaves. The results showed that T. palustris was able to perceive underwater grazed leaves. In addition, we demonstrated that T. palustris consumes all the mangrove species (preferentially the Rhizophoraceae leaves) but Xilocarpus granatum. Moreover, this snail is differentially attracted to different mangrove species: the major attractive power is wielded by the rhizophoracean species and Pemphis acidula, while X. granatum does not attract this snail at all. The efficacy and adaptive value of a chemically mediated food searching strategies is unquestionable since by using this ability T. palustris can locate and reach the leaves it preferentially consumes. Moreover, T. palustris is the only macrobenthic species of East Africa mangroves able to search, detect and consume mangrove leaves at both high and low tides. Such an expanded feeding window permits T. palustris to occupy temporal niches left empty by the sesarmid crabs.     

红树林植被对大型底栖动物群落的影响

大型底栖动物是红树林生态系统的重要组成部分,从红树林大型底栖动物种类、红树林与其周边生境大型底栖动物群落的比较,以及生境变化对动物群落的影响等方面阐述了红树林植被与大型底栖动物群落的关系.从物种数量上看,软体动物和甲壳类动物构成了红树林大型底栖动物的主要部分.影响大型底栖动物分布的环境因素包括海水盐度、潮位和土壤特性等,但在小范围区域,林内动物的分布更多地与红树林植被特性和潮位有关.因此,由于红树林植被破坏或者恢复引起的生境变化,将导致大型底栖动物群落和常见物种种群的变化,尤其对底上动物影响明显;随着人工恢复红树林的发育,林内底栖动物的多样性相应增加,优势种也发生变化.相比位于相同潮位的无植被滩涂,红树林可促进潮间带生物多样性.     

Subtropical Brazilian mangroves as a refuge of crab (Decapoda: Brachyura) diversity

This study characterized seven mangrove areas of different sizes, located on the southeastern Brazilian coast, with respect to their sediment and vegetation features. We also estimated the richness and composition of the brachyuran assemblages in these mangroves. Crab, vegetation and sediment data were collected during low tide. The larger mangroves showed richer and complex forests, and may be more ecologically stable than smaller mangroves. Twenty-eight species of crabs were recorded, members of nine families: Panopeidae, Pinnotheridae, Gecarcinidae, Grapsidae, Sesarmidae, Varunidae, Ocypodidae, Ucididae, and Portunidae. Ocypodoidea predominated over Grapsoidea in the smaller mangrove areas in pioneer stages of forest establishment, whereas the opposite was recorded for larger and more stable mangroves, where the forest can reach advanced stage of development. Comprido is a small mangrove, but its crab assemblage was similar to the larger ones, probably because of other factors not investigated here (e.g., megalopa settling rate). This study provided basic knowledge for developing conservation strategies for vulnerable mangrove ecosystems.     

Functionality of restored mangroves: A review

Widespread mangrove degradation coupled with the increasing awareness of the importance of these coastal forests have spurred many attempts to restore mangroves but without concomitant assessment of recovery (or otherwise) at the ecosystem level in many areas. This paper reviews literature on the recovery of restored mangrove ecosystems using relevant functional indicators. While stand structure in mangrove stands is dependent on age, site conditions and silvicultural management, published data indicates that stem densities are higher in restored mangroves than comparable natural stands; the converse is true for basal area. Biomass increment rates have been found to be higher in younger stands than older stands (e.g. 12 t ha⁻¹ year⁻¹ for a 12 years plantation compared to 5.1 t ha⁻¹ year⁻¹ for a 80-year-old plantation). Disparities in patterns of tree species recruitment into the restored stands have been observed with some stands having linear recruitment rates with time (hence enhancing stand complexity), while some older stands completely lacked the understorey. Biodiversity assessments suggest that some fauna species are more responsive to mangrove degradation (e.g. herbivorous crabs and mollusks in general), and thus mangrove restoration encourages the return of such species, in some cases to levels equivalent to those in comparable natural stands. The paper finally recommends various mangrove restoration pathways in a functional framework dependent on site conditions and emphasizes community involvement and ecosystem level monitoring as integral components of restoration projects.     

红树林湿地相手蟹科动物摄食生态研究进展

相手蟹科物种是红树林湿地的主要底栖动物类群,在生态系统中起着重要的作用。我国大陆地区目前已记录的相手蟹科物种数量为12种,低于其它红树林地区(国内常用的采样方法会造成螃蟹物种数量和密度的低估),其中褶痕相手蟹(Sesarma plicata)、无齿相手蟹(S.deaani)和双齿相手蟹(S.bidens)等是常见种。红树植物叶片是相手蟹科动物的主要食物来源,相手蟹科动物通过地表摄食和洞穴贮存的形为消耗了大量的红树植物凋落叶,使这些凋落叶的有机质和营养元素得以保留在生态系统内,在凋落叶的周转和物质归还方面起到重要的作用。它们同时也摄食红树植物的繁殖体并且对不同物种的繁殖体具有摄食偏好,这可能对一些红树物种的植被更新能力和红树植被群落结构产生影响。相手蟹科动物对不同物种和不同状态的红树叶片也存在摄食偏好,通常对腐烂的叶片摄食偏好较强;螃蟹的摄食偏好与叶片的营养成份、粗纤维和单宁含量以及C/N比等性质有关;但在恶劣的野外环境下,螃蟹则会表现出随机性摄食。目前关于相手蟹科动物生态学作用的认识仍不充分,例如它们的种群大小和对凋落物的转化作用等,有待于进一步研究。     

中国红树林生态系统主要害虫种类、 防控现状及成灾原因

红树林湿地是中国东南沿海的关键生态系统之一。近年来, 我国红树林陆续出现多种害虫种群暴发成灾的现象, 使红树林湿地的可持续利用面临严重挑战。本文归纳了近20年来中国红树林生态系统的主要害虫种类, 危害较严重的有海榄雌瘤斑螟Acrobasis sp., 毛颚小卷蛾Lasiognatha cellifera, 丽绿刺蛾Latoia lepida, 白囊袋蛾Chalioides kondonis, 蜡彩袋蛾Chalia larminati和小袋蛾Acanthopsyche subferalbata等; 对红树林虫害的防控现状进行总结, 目前开展的防控工作主要以生物农药、 昆虫生长调节剂、 昆虫天敌等生物防治方法为主, 结合灯光诱杀等物理防治手段的运用, 对暴发期的害虫种群可以取得较好的控制效果; 并从红树林生态系统健康水平和昆虫群落多样性等方面对害虫种群的成灾原因进行初步探讨; 最终提出以虫害可持续控制为目标的红树林生态系统生境调控策略, 以期为提高红树林湿地虫害管理水平以及促进红树林的可持续发展提供重要的理论参考和科学指导。     

底栖动物对红树林生态系统的影响及生态学意义

底栖动物是红树林生态系统的重要组成部分。本文总结了近年来国内外红树林底栖动物的生物多样性、分布模式及其影响因素的研究进展,并从以下5个方面阐述了底栖动物(尤其是相手蟹)对红树林生态系统的影响:1)维持系统初级生产;2)丰富系统有机物生产;3)影响红树植物生长;4)降低幼苗竞争压力;5)改变沉积物性质。除传统的群落结构、生物多样性和个体生物学研究外,目前红树林底栖动物生态学的研究正逐步向红树林沙蟹等其他海洋无脊椎动物的种间关系、底栖生物区系与栖息地间相互关系研究发展。有必要重新认识蟹类的生物扰动对红树林更新和红树林生态系统能量流动的积极意义。     

Observations on the Ecology of Weaver Ants (Oecophylla smaragdina Fabricius) in a Thai Mangrove Ecosystem and Their Effect on Herbivory of Rhizophora mucronata Lam.

Ants of the genus Oecophylla are predators of other insects and are able to protect a variety of terrestrial plants against pest insects; however, observations on the ecology of these ants in mangrove forests are lacking. General observations on the ecology of Oecophylla smaragdina were carried out in a Thai mangrove forest to determine if these ants can protect their host plants in less favorable mangrove habitats. Leaf herbivory and the density of O. smaragdina ants were measured on Rhizophora mucronata trees at two sites. The results showed a negative correlation between ant density and herbivory. At both sites, the mean percent damaged leaf area was more than four times higher on trees without ants compared to “ant‐trees.” A significant negative correlation was found between tree mean percent leaf damage and the density of ants on the tree. Furthermore, on trees with ants, there was less herbivory on leaves close to ant nests compared to other leaves on the tree. Most damage was caused by chrysomelid beetles (62%) and sesarmid crabs (25%) and both types of herbivory were significantly reduced on ant‐trees.     

Participatory appraisal for potential community-based mangrove management in East Africa

Mangroves are among the most threatened ecosystems in the world and the coastal forests of East Africa are no exception to this trend. Although conservation, rehabilitation and sustainable management plans have been developed in various tropical regions, only a few locally based approaches have been launched along the Indian Ocean coast of Africa. In order to identify possible conditions for sustainable management of mangroves based on socio-economic and ecological considerations, we present a participatory approach designed to evaluate the relationships between mangroves and human activities and the use of multi-criterion analysis to identify management solutions. To achieve this goal, all the subjects involved in mangrove management (local communities, institutions and researchers) took an active part in the process. The research was carried out in three communities relying on mangrove swamps: Kisakasaka village on the island of Zanzibar, Mida Creek in Kenya, both relying on mangrove forests known to be endangered by over-exploitation, and Inhaca Island in Mozambique, where mangroves are more pristine. Families were the hub of the research and the importance of each of their economic activities was assessed. We then examined the methods by which mangroves are exploited by the local community and by other stakeholders working in the study areas. Our results show that the mangroves in Inhaca are exploited only for household needs and the pressure on the forests is still ecologically sustainable. In contrast, there is a well-established demand for mangrove products in Kisakasaka and Mida Creek and the mangroves represent an essential source of income for the families, resulting in an ecologically unsustainable rate of exploitation. Therefore, possible alternatives to the current management practices were identified in the two areas by means of a participatory approach. Multi-criterion analysis was then used to compare and discuss the alternatives in terms of social, economic and ecological criteria.     

红树林水生动物栖息地功能及其渔业价值

红树林生长于热带、亚热带海陆交界的生态敏感带,其根系为生活于潮间带高度异质环境下的生物提供了适宜生境:藻类、双壳类、甲壳类等大量附生于红树根部;红树的呼吸根、支柱根、树干、倒落的枝条和残骸等,与沉积物形成的松软基质为大量底栖动物提供栖息地,根部结构间的空隙成为虾类、蟹类和鱼类等游泳动物的优良避难所和索饵场。红树林凋落物以碎屑形式进入食物网,连同浮游植物、附生藻类和底栖微藻等,是红树林生态系统的碳循环重要组成部分,为红树林区水生动物提供了丰富的食物来源。可见,食物来源丰富、隐蔽性强、捕食压力低等特点使得红树林成为水生动物的理想栖息地,许多水生动物选择在其中度过部分或完整生活史。另外,红树林也是重要经济动物(鱼、虾、蟹类)的育苗场,为近岸鱼类种群的补充和渔业活动提供支持。为合理开发红树林区渔业和有效保护红树林湿地生态系统,从生境价值、凋落物在红树林生态系统食物网中的贡献等方面总结了红树林栖息地功能及其渔业价值,提出今后的研究方向应将红树林的栖息地功能从其它河口、近岸栖息地中分离出来,甄别不同栖息地间的动态关系及其对渔业的影响。     

Mangrove sesarmid crab feeding experiments in Peninsular Malaysia

The feeding ecology of mangrove sesarmid crabs in Peninsular Malaysia was investigated by field and laboratory experiments using four mangrove leaf species (Avicennia officinalis, Bruguiera gymnorrhiza, B. parviflora and Rhizophora apiculata) and leaves of different condition (fresh and senescent). Leaves tethered on strings at high (Bruguiera zone) and low (Rhizophora zone) intertidal positions, both upstream (Sungai Pasir) and downstream (Lower Merbok) showed significant amounts of leaf litter removal in 24 h (mean 79±3% initial dry mass). Significantly more B. gymnorrhiza was consumed in Bruguiera zones and significantly less senescent A. officinalis in the upstream Rhizophora zone. In Bruguiera zones, significant numbers of leaves were taken down burrows but there were no preferences for leaf species or condition of leaf taken down burrows at all sites. In 24 h, under laboratory conditions, the sesarmid crabs Sesarma (Perisesarma) eumolpe and S. (Perisesarma) onychophorum were offered with a mangrove species choice of either fresh or senescent leaves. There was no difference in mangrove species taken when the leaves were senescent for both crab species, but when the leaves were fresh, significantly more A. officinalis leaves were consumed by both sesarmid crab species. S. onychophorum ate significantly more B. parviflora than did S. eumolpe. The crab distribution in the field was related to the preferred tree species dominance, indicating that tree species may be important for crab species distribution, or vice versa. The mean rate of leaf consumption was not significantly different between the crab species; S. eumolpe was 29.9±5.9 and S. onychophorum was 35.3±7.2 mg dry mass per wet mass gram of crab in 24 h. Rhizophora spp. were the least preferred species in all feeding experiments, a finding which may have implications for ecosystem functioning in monoculture rehabilitation projects.     

The influence of crabs on litter processing in high intertidal mangrove forests in tropical Australia

Summary Measurements of litter fall and litter removal by crabs, in conjunction with estimates of litter decay by microbes and tidal export of litter from three high-intertidal mangrove forests were made during a year-long study in tropical northeastern Australia. In forests dominated by Ceriops tagal and Bruguiera exaristata, litter standing stocks remained low on the forest floor (mean 6 g·m^-2), although litter fall was high; 822 and 1022 g·m^-2·y^-1, respectively. Sesarmid crabs removed 580 (Ceriops) and 803 (Bruguiera) g·m^-2·y^-1, or 71 and 79%, of the total annual litter fall from the forest floor. Relative to the rate of litter removal by crabs, microbial turnover of whole, unshredded litter was insignificant, accounting for <1% of annual litter fall. Export of litter by tides was estimated to remove 194 (Ceriops) and 252 (Bruguiera) g·m^-2·y^-1 or 24 and 25% of annual litter fall. In a forest dominated by Avicenniamarina, in which an ocypodid crab was more abundant than sesarmids, litter standing stocks were higher (mean 84 g·m^-2) and crabs removed less litter; 173 g·m^-2·y^-1 or 33% of the annual litter fall of 519 g·m^-2·y^-1. Microbial turnover of intact litter was more important in the Avicennia forest (168 g·m^-2·y^-1 or 32% of annual litter fall), and tides exported 107 g·m^-2·y^-1 or 21% of litter production. In areas where sesarmid crabs were absent or rare in Ceriops forests, there were significantly higher standing stocks of litter and slower rates of leaf removal. Taking into account the probable assimilation efficiencies of sesarmid crabs feeding on mangrove leaves, we estimate that in Ceriops and Bruguiera forests leaf processing by crabs turns litter over at >75 times the rate of microbial decay alone, thus facilitating the high sediment bacterial productivity in these forests. The importance of litter processing by crabs increases with height in the intertidal in tropical Australia, in contrast to New World mangrove forests, where the reverse is true.Contribution No. 445 from the Australian Institute of Marine Science     

Spatial and temporal variation in diets of the crabs <Emphasis Type="Italic">Metopograpsus frontalis</Emphasis> (Grapsidae) and <Emphasis Type="Italic">Perisesarma bidens</Emphasis> (Sesarmidae): implications for mangrove food webs

The diets of the mangrove crabs, Metopograpsus frontalis Miers and Perisesarma bidens de Haan, were investigated monthly for 13 months at two Hong Kong mangroves, to examine possible spatial and temporal influences on their feeding ecology. In both species, a higher degree of gut fullness was observed in summer (May–September) than in winter, suggesting a reduction in winter foraging activity. M. frontalis was omnivorous, with animal and plant materials and inorganic sediments being the major food items. P. bidens was detritivorous, with plant materials and inorganic sediment dominating the gut contents. M. frontalis is, therefore, an opportunistic feeder, whilst P. bidens, like many other members of the Sesarmidae, is a detritivore. Some degree of seasonal variation was shown in the diet of M. frontalis (with more algal material in winter) and P. bidens (with more sediments in summer), but diets were similar between sexes in both species. The dietary pattern of M. frontalis also varied between sites. The diets of the crabs, therefore, appear to be a result of the interplay between the seasonal, physical climate and biological factors, especially food availability and the crabs’ ecology. Results suggest that the predatory role of Metopograpsus, which has been poorly studied, is potentially important to estuarine food webs; whilst the trophic importance of sesarmid crabs, such as Perisesarma, especially in mangrove outwelling, should be critically re-evaluated.     

Processes of organic carbon in mangrove ecosystems

In addition to carbon accumulation in plants, processes of organic carbon in mangrove ecosystems include origins of sediment organic carbon, carbon fluxes between mangroves and their adjacent systems (coastal waters and atmosphere), and cycling processes. Sediment organic carbon originates from suspending solids in coastal waters, mangrove plants and benthic algae. In mangroves with low organic carbon content in sediments, tidal seawater is the main origin of sediment organic carbon, while in mangroves with high sediment organic carbon contents, sediment organic carbon mainly originates from mangrove plants. Due to tidal flush, there is large material exchange between mangrove ecosystems and their adjacent coastal waters. In China, exports of organic carbon in litter falls and dissolved organic carbon from mangroves to their adjacent coastal waters have not been documented. Processes of mangrove litter falls, including production, decomposition, export and animal consumption, determine linkages among organic carbon among mangrove plants, secondary production and coastal ocean. Consumers especially benthic animals may influence organic carbon in mangrove ecosystems, because (1) their consumption rates are high, and their selective feeding on some food sources will change the relative quantities of export, bury and mineralization of organic carbon from different origins; (2) their consumption is much more than assimilation, resulting in the changes in sizes, forms and qualities of non-assimilated organic matters, and then the changes in availability of export, consumption or mineralization of organic carbon. Respiration and sulfate reduction are important mineralization processes of organic carbon in mangrove sediments. Mineralization rates of organic carbon in mangrove sediments are influenced by quantities, activities and particle sizes of organic matters, and other factors such as forest ages, root activities and animal burrowing activities. Researches on processes of mangrove organic carbon should be based on open systems, and ecological processes of organic carbon should be coupled with vegetation restoration.     

Processes of organic carbon in mangrove ecosystems

In addition to carbon accumulation in plants, processes of organic carbon in mangrove ecosystems include origins of sediment organic carbon, carbon fluxes between mangroves and their adjacent systems (coastal waters and atmosphere), and cycling processes. Sediment organic carbon originates from suspending solids in coastal waters, mangrove plants and benthic algae. In mangroves with low organic carbon content in sediments, tidal seawater is the main origin of sediment organic carbon, while in mangroves with high sediment organic carbon contents, sediment organic carbon mainly originates from mangrove plants. Due to tidal flush, there is large material exchange between mangrove ecosystems and their adjacent coastal waters. In China, exports of organic carbon in litter falls and dissolved organic carbon from mangroves to their adjacent coastal waters have not been documented. Processes of mangrove litter falls, including production, decomposition, export and animal consumption, determine linkages among organic carbon among mangrove plants, secondary production and coastal ocean. Consumers especially benthic animals may influence organic carbon in mangrove ecosystems, because (1) their consumption rates are high, and their selective feeding on some food sources will change the relative quantities of export, bury and mineralization of organic carbon from different origins; (2) their consumption is much more than assimilation, resulting in the changes in sizes, forms and qualities of non-assimilated organic matters, and then the changes in availability of export, consumption or mineralization of organic carbon. Respiration and sulfate reduction are important mineralization processes of organic carbon in mangrove sediments. Mineralization rates of organic carbon in mangrove sediments are influenced by quantities, activities and particle sizes of organic matters, and other factors such as forest ages, root activities and animal burrowing activities. Researches on processes of mangrove organic carbon should be based on open systems, and ecological processes of organic carbon should be coupled with vegetation restoration.     

Ecosystem carbon stocks of mangrove forests along the Pacific and Caribbean coasts of Honduras

Among the many ecosystem services provided by mangrove ecosystems, their role in carbon (C) sequestration and storage is quite high compared to other tropical forests. Mangrove forests occupy less than 1 % of tropical forested areas but account for approximately 3 % of global carbon sequestration by tropical forests. Yet there remain many areas where little data on the size and variation of mangrove C stocks exist. To address this gap and examine the range of C stocks in mangroves at landscape scales, we quantified C stocks of Honduran mangroves along the Pacific and Caribbean coasts and the Bay Islands. We also examined differences in ecosystem C stocks due to size and structure of mangrove vegetation found in Honduras. Ecosystem C stocks ranged from 570 Mg C ha^?1 in the Pacific coast to ~1000 Mg C ha^?1 in Caribbean coast and the Bay Islands. Ecosystem C stocks on the basis of mangrove structure were 1200, 800 and 900 Mg C ha^?1, in low, medium and tall mangroves, respectively. We did not find significant differences in ecosystem C stocks on the basis of location (Pacific coast, Caribbean coast and Bay Islands) or mangrove type (low, medium and tall). Mangrove soils represented the single largest pool of total C in these ecosystems, with 87, 81 and 94 % at the Pacific coast, Caribbean coast and the Bay Islands, respectively. While there were no significant differences in total ecosystem stocks among mangrove types, there were differences in where carbon is stored. Mangrove soils among low, medium and tall mangroves contained 99, 93 and 80 % of the total ecosystem C stocks. In addition, we found a small yet significant negative correlation between vegetation C pools and pore water salinity and pH at the sampled sites. Conversion of mangroves into other land use types such as aquaculture or agriculture could result in loses of these soil C reserves due to mineralization and oxidation. Coupled with their other ecosystem services, an understanding of the size of mangrove ecosystem C stocks underscores their values in the formulation of conservation and climate change mitigation strategies in Central America.     

Threats to mangroves from climate change and adaptation options: A review

Mangrove ecosystems are threatened by climate change. We review the state of knowledge of mangrove vulnerability and responses to predicted climate change and consider adaptation options. Based on available evidence, of all the climate change outcomes, relative sea-level rise may be the greatest threat to mangroves. Most mangrove sediment surface elevations are not keeping pace with sea-level rise, although longer term studies from a larger number of regions are needed. Rising sea-level will have the greatest impact on mangroves experiencing net lowering in sediment elevation, where there is limited area for landward migration. The Pacific Islands mangroves have been demonstrated to be at high risk of substantial reductions. There is less certainty over other climate change outcomes and mangrove responses. More research is needed on assessment methods and standard indicators of change in response to effects from climate change, while regional monitoring networks are needed to observe these responses to enable educated adaptation. Adaptation measures can offset anticipated mangrove losses and improve resistance and resilience to climate change. Coastal planning can adapt to facilitate mangrove migration with sea-level rise. Management of activities within the catchment that affect long-term trends in the mangrove sediment elevation, better management of other stressors on mangroves, rehabilitation of degraded mangrove areas, and increases in systems of strategically designed protected area networks that include mangroves and functionally linked ecosystems through representation, replication and refugia, are additional adaptation options.     

Using expert knowledge and modeling to define mangrove composition,functioning, and threats and estimate time frame for recovery

Mangroves are threatened worldwide, and their loss or degradation could impact functioning of the ecosystem. Our aim was to investigate three aspects of mangroves at a global scale: (1) their constituents (2) their indispensable ecological functions, and (3) the maintenance of their constituents and functions in degraded mangroves. We focused on answering two questions: “What is a mangrove ecosystem” and “How vulnerable are mangrove ecosystems to different impacts”? We invited 106 mangrove experts globally to participate in a survey based on the Delphi technique and provide inputs on the three aspects. The outputs from the Delphi technique for the third aspect, i.e. maintenance of constituents and functions were incorporated in a modeling approach to simulate the time frame for recovery. Presented here for the first time are the consensus definition of the mangrove ecosystem and the list of mangrove plant species. In this study, experts considered even monospecific (tree) stands to be a mangrove ecosystem as long as there was adequate tidal exchange, propagule dispersal, and faunal interactions. We provide a ranking of the important ecological functions, faunal groups, and impacts on mangroves. Degradation due to development was identified as having the largest impact on mangroves globally in terms of spatial scale, intensity, and time needed for restoration. The results indicate that mangroves are ecologically unique even though they may be species poor (from the vegetation perspective). The consensus list of mangrove species and the ranking of the mangrove ecological functions could be a useful tool for restoration and management of mangroves. While there is ample literature on the destruction of mangroves due to aquaculture in the past decade, this study clearly shows that more attention must go to avoiding and mitigating mangrove loss due to coastal development (such as building of roads, ports, or harbors).     

Global biodiversity and biogeography of mangrove crabs: Temperature,the key driver of latitudinal gradients of species richness

Mangroves are ideal habitat for a variety of marine species especially brachyuran crabs as the dominant macrofauna. However, the global distribution, endemicity, and latitudinal gradients of species richness in mangrove crabs remains poorly understood. Here, we assessed whether species richness of mangrove crabs decreases towards the higher latitudes and tested the importance of environmental factors such as Sea Surface Temperature (SST) in creating the latitudinal gradients in species richness of mangrove crabs. A total of 8262 distribution records of 481 species belonging to six families of mangrove crabs including Camptandriidae, Dotillidae, Macrophthalmidae, Ocypodidae, Sesarmidae, and Oziidae were extracted from open-access databases or collected by the authors, quality controlled, cleaned, and analyzed. Species richness was plotted against 5° latitudinal bands in relation to environmental factors. The R software and ArcGIS 10.6.1 were used to analyze the species latitudinal range and richness as well as to map the distribution of mangrove forest, endemic species, species geographical distribution records, and biogeographic regions. The Indo-West Pacific showed the highest species richness of mangrove crabs where more than 65% of species were found in the Indian Ocean and along the western Pacific Ocean. Our results showed that there are 11 significantly different biogeographic regions of mangrove crabs. The highest endemicity rate was observed in the NW Pacific Ocean (29%). Latitudinal patterns of species richness in Macrophthalmidae, Ocypodidae, and Sesarmidae showed an increasing trend from the poles toward the intermediate latitudes including one dip near the equator. However, latitudinal gradients in Camptandriidae, Dotillidae, and Oziidae were unimodal increasing from the higher latitudes towards the equator. Species richness per 5° latitudinal bands significantly increased following mean SST mean (°C), calcite, euphotic depth (m), and mangrove area (km²) across all latitudes, and tide average within each hemisphere. Species richness significantly decreased with dissolved O₂ (ml l⁻¹) and nitrate (μmol l⁻¹) over all latitudes and in the southern hemisphere. The climax of global latitudinal species richness for some mangrove was observed along latitudes 20° N and 15°–25° S, not at the equator. This can suggest that temperature is probably the key driver of latitudinal gradients of mangrove crabs’ species richness. Species richness and mangrove area were also highly correlated.     

The habitat function of mangroves for terrestrial and marine fauna: A review

Mangroves are defined by the presence of trees that mainly occur in the intertidal zone, between land and sea, in the (sub) tropics. The intertidal zone is characterised by highly variable environmental factors, such as temperature, sedimentation and tidal currents. The aerial roots of mangroves partly stabilise this environment and provide a substratum on which many species of plants and animals live. Above the water, the mangrove trees and canopy provide important habitat for a wide range of species. These include birds, insects, mammals and reptiles. Below the water, the mangrove roots are overgrown by epibionts such as tunicates, sponges, algae, and bivalves. The soft substratum in the mangroves forms habitat for various infaunal and epifaunal species, while the space between roots provides shelter and food for motile fauna such as prawns, crabs and fishes. Mangrove litter is transformed into detritus, which partly supports the mangrove food web. Plankton, epiphytic algae and microphytobenthos also form an important basis for the mangrove food web. Due to the high abundance of food and shelter, and low predation pressure, mangroves form an ideal habitat for a variety of animal species, during part or all of their life cycles. As such, mangroves may function as nursery habitats for (commercially important) crab, prawn and fish species, and support offshore fish populations and fisheries. Evidence for linkages between mangroves and offshore habitats by animal migrations is still scarce, but highly needed for management and conservation purposes. Here, we firstly reviewed the habitat function of mangroves by common taxa of terrestrial and marine animals. Secondly, we reviewed the literature with regard to the degree of interlinkage between mangroves and adjacent habitats, a research area which has received increasing attention in the last decade. Finally, we reviewed current insights into the degree to which mangrove litter fuels the mangrove food web, since this has been the subject of long-standing debate.