Stable soil pH of thai mangroves in dry and rainy seasons and its relation to zonal distribution of mangroves

Soil characteristics of mangrove forests at Amphur Laemngob, Trat Province, east Thailand were investigated in both dry andrainy seasons. Sonneratia alba, Avicennia alba andRhizophora mucronata mainly grew as seaward mangroves.Rhizophora apiculata, Ceriops tagal, Excoecaria agallocha andBruguiera gymnorrhiza grew as meso mangroves in most cases.Lumnitzera racemosa was found as a landward mangrove. The salinity of the soil in which these 8 species grew was significantly higher in the dry season than in the rainy season. Soil pH did not change irrespective of the season. Each species seemed to grow at inherent soil pH. Bruguiera gymnorrhiza, Sonneratia alba andAvicennia marina were found both in Japan and Thailand. The soil pH of each mangrove species was similar in Japan and Thailand. The soil salinity of each mangrove species in Japan was similar to that in Thailand in the dry season. It was suggested that soil pH and salinity in the dry season are the important factors governing the zonal distribution of mangroves.     

Salinity tolerance in some mangrove species from Pakistan

Growth, ionic and water relations of three mangrove species viz. Avicennia marina, Ceriops tagal and Rhizophora mucronata werestudied in different seawater concentrations (0, 25, 50, 75 and 100%).All mangrove species showed optimal growth at 50% seawater. Relativelymore biomass was accumulated by R. mucronata while C. tagalhad the tallest individuals. Tissue water potential became more negativewith the increase in salinity and stomatal conductance was decreased in allplants. Higher stomatal conductance was noted in R. mucronata,followed by A. marina and C. tagal. Sodium and chloride ionsincreased with the increase in salinity and this accumulation was muchhigher in A. marina.     

An exploratory study on grapsid crab zonation in Kenyan mangroves

Despite earlier efforts to understand the role played by grapsid crabs inmangroves, their importance in the structuring and functioning of suchsystems is fully appreciated, particularly with regard to small-scalestudies. The present study provides some new data on the interaction between mangroves and crabs, namely the link between the distribution of particular mangrove tree species and the distribution of certain crab species at the assemblage level. Floristicand faunistic relevés were made in Gazi Bay (2 sites) and Mida Creek(3 sites), 140 km apart on the Kenyan coast, along five transects in aseries of quadrats covering the width of the mangrove belts. Zonation ofboth mangrove vegetation and brachyuran fauna was described and heightabove datum and distance to the mainland (limit of non-flooded area)measured. The relationship between the presence and the absence of crabs andtrees was analysed using detrended correspondence analysis.Summarized, the mangrove tree zonation pattern contains four assemblageswith a particular dominant species: first a landward Avicennia marinazone, followed by a mixed zone with Ceriops tagal, Rhizophoramucronata and Bruguiera gymnorrhiza, and finally a R.mucronata zone and a Sonneratia alba zone, both of which can mixwith seaward A. marina. Ordination results show that the distributionof Neosarmatium meinerti and Sesarma ortmanni is linked to thelandward A. marina zone, that of Neosarmatium smithii, Sesarma guttatum and Sesarma leptosoma corresponds to the R. mucronata zone and that of Metopograpsus thukuhar and Sesarma elongatum to the seaward A. marina and S. albazone. There appears to be one major underlying factor in the zonation of bothcrabs and trees, with most likely a complex multiple causality. In certaincases the association between crabs and trees are causal, whereas in othercases it can be the result of an independent restriction to the same zonesby a common cause.     

Effects of experimental sedimentation on the phenological dynamics and leaf traits of replanted mangroves at Gazi bay,Kenya

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Mangrove Tree Specificity and Conservation Implications of the Arboreal Crab <Emphasis Type="Italic">Parasesarma leptosoma</Emphasis> at Mngazana,a Mangrove Estuary in the Eastern Cape,South Africa

The arboreal crab Parasesarma leptosoma has been recently discovered at Mngazana, a southerly mangrove system in southern Africa, where crab tree preferences were studied using an indirect (browse leaf damage) and a direct (tree traps) method. The extent of crab induced leaf damage was compared for three mangrove species at two sites, one next to a tidal creek and one away from the creek. Using ANOVA, significant differences were found between tree species (P < 0.001) at different distances from the creek (P < 0.022). Crabs were found to occur on Rhizophora mucronata and Brugueira gymnorrhiza, but not on Avicennia marina. This reflected a gradient in browsing, from well-browsed R. mucronata (100% near the creek and 25.7% away from the creek), to medium browsing of B. gymnorrhiza (51.5% near and 0% away) and no browsing on A. marina (near or away). These differences could be explained in terms of palatability, as both R. mucronata and B. gymnorrhiza are salt excluders, while A. marina secretes salt from its leaves. Leaf consumption levels averaged between 1.73% and 2.6% of leaf area for R. mucronata and 0–1.76% for B. gymnorrhiza. For both R. mucronata and B. gymnorrhiza there was a significant correlation between the number of crabs caught directly and the amount of browse leaf damage (P < 0.01). Crab number was also significantly correlated with tree circumference for R. mucronata (r ² = 0.67) and B. gymnorrhiza (r ² = 0.76, P < 0.05), with crabs more prevalent on the former tree species and no crabs trapped on A. marina (91.7%, 38.3% and 0% catches, respectively), thus reflecting the results obtained by the indirect method. Total Nitrogen and Phosphate were measured for both sediment and leaves of the three mangrove species at the two sites. Leaf comparisons showed significant differences (P < 0.01) for both Total Nitrogen and Phosphate with R. mucronata having the highest values, followed by A. marina and lastly B. gymnorrhiza. Total Nitrogen was significantly higher for both B. gymnorrhiza and R. mucronata compared with A. marina, while leaf phosphate was significantly lower for B. gymnorrhiza when compared with both R. mucronata and A. marina. No significant differences were found for leaf nutrients between sites, with the exception of A. marina and R. mucronata Total Nitrogen, which was significantly higher at the near creek sites (P < 0.05). Sediment analysis showed no significant differences (P > 0.05) in either nutrients or median particle size. Thus, R. mucronata, especially near the creek, had higher nutrient value and was probably more palatable and could explain observed differences in crab distribution. Very little browse damage was encountered in saplings below 10 cm. Most poles chopped by the local communities are R. mucronata in the 15–20 cm category, which coincides with peak crab frequencies in the 15–25 cm size classes for R. mucronata and B. gymnorrhiza, so that this selective harvesting is affecting this crab population maximally. Predictions were made as to the effect of crab loss, tree replacement rate and alternatives to chopping, which would boost community socio-economic levels and reduce the anthropogenic pressure on this biodiverse southerly mangrove system.     

Coal Dust Pollution Effects on Wetland Tree Species in Richards Bay,South Africa

In this study, the effects of coal dust on four, sympatric, wetland tree species in Richards Bay Harbour were investigated. We tested the hypothesis that leaf micromorphology influenced dust accumulation and that coal dust occluded stomata and reduced photosynthetic performance of three mangroves, Avicennia marina, Bruguiera gymnorrhiza and Rhizophora mucronata, and a mangrove associate, Hibiscus tiliaceus. To investigate leaf micromorphology, leaf blade material of the four species was prepared following standard procedures and viewed under scanning electron microscopy. Gas exchange and chlorophyll fluorescence measurements were made at saturating light (>1000 μmol m⁻² s⁻¹) and high temperature (>25 °C) on leaves that were either covered or uncovered with coal dust. There was no evidence of occlusion of stomata by dust. Dust accumulation in A. marina and H. tiliaceus was exacerbated by the presence of a dense mat of trichomes on the undersurface of the leaves, as well as by the sticky brine secreted by salt glands in the former species.Coal dust significantly reduced CO₂ exchange, Photosystem II (PS II) quantum yield and electron transport rate (ETR) through PS II in A. marina and H. tiliaceus but not in the other two mangroves. Reduction in photosynthetic performance was attributed to reduction in light energy incident on the photosynthetic tissues.     

Pyridine salvage and nicotinic acid conjugate synthesis in leaves of mangrove species

The metabolic fate of [carbonyl-¹⁴C]nicotinamide was surveyed in leaf disks of seven mangrove species, Bruguiera gymnorrhiza, Rhizophora stylosa, Kandeliaobovata, Sonneratia alba, Pemphis acidula, Lumnitzera racemosa and Avicennia marina, with and without 250 mM NaCl. Uptake of [¹⁴C]nicotinamide by leaf disks was stimulated by 250 mM NaCl in K. candel, R. stylosa, A. marina and L. racemosa. [Carbonyl-¹⁴C]nicotinamide was converted to nicotinic acid and was utilised for the synthesis of nucleotides and nicotinic acid conjugates. Formation of nicotinic acid by the deaminase reaction was rapid; there was little accumulation of nicotinamide in the disks 3 h after administration. Radioactivity from [carbonyl-¹⁴C]nicotinamide was incorporated into pyridine nucleotides (mainly NAD and NADP) in all mangrove leaves, and the rates varied from 2% (in L. racemosa) to 15% (S. alba) of the total radioactivity taken up. NaCl generally reduced nicotinic acid salvage for NAD and NADP. In all mangrove leaf disks, the most heavily labelled compounds (up to 70% of total radioactivity) were trigonelline (N-methylnicotinic acid) and/or nicotinic acid N-glucoside. Trigonelline was formed in all mangrove plants, but N-glucoside synthesis was found only in leaves of A. marina and K. obovata. In A. marina, incorporation of radioactivity into N-glucoside (51%) was much greater than incorporation into trigonelline (2%). In general, NaCl stimulates the synthesis of these pyridine conjugates. The rate of decarboxylation of nicotinic acid in roots of A. marina seedlings was much greater than for the corresponding reaction observed in leaves.     

Comprehensive dataset of mangrove tree weights in Southeast Asia

We assembled a dataset tabulating the weights of Thai and Indonesian mangrove trees that we measured between 1982 and 2001. We selected four Thai study sites in Phang Nga, Ranong, Satun, and Trat Provinces and one site in eastern Indonesia on Halmahera Island in Maluku Province. The stands in Ranong Province and on Halmahera Island were in primary forests with data collected in the 1980s and the remaining stands were in secondary forests with data collected later. We collected 124 tree samples from ten species (Avicennia alba, Bruguiera cylindrica, B. gymnorrhiza, Ceriops tagal, Rhizophora apiculata, R. mucronata, Sonneratia alba, S. caseolaris, Xylocarpus granatum, and X. moluccensis) and measured the root weights of 32 individuals of nine species (A. alba, B. cylindrica, B. gymnorrhiza, C. tagal, R. apiculata, R. mucronata, S. alba, S. caseolaris, and X. granatum). All sampled trees were subjected to a standardized protocol to obtain aboveground weights. The trunks were divided into horizontal segments from which the leaves and branches were collected separately. Roots were collected by winching them out of the ground, by trench digging, or by complete excavation. Thus, we were able to compile the weights of the trunk, branches, leaves, and roots of each tree sampled. Aerial roots were included in root weight measurements, although they were collected above ground. We compiled separate lists of trunk diameters, trunk heights, heights of the lowest living branches, and the heights of aerial roots on the trunks of trees in different size categories. Our dataset includes a wide range of tree sizes (maximum trunk diameter 48.9 cm), geographical locations (1°10′N–12°24′N, 98°32′E–123°49′E) and organ weights (trunks, branches, leaves, and roots), and therefore should prove useful in future biomass studies of mangrove forests.     

Fungi associated with the aerial parts of Malaysian mangrove plants

The leaf surface fungi associated with nine species of mangrove plants includingAvicennia alba, A. officinalis, Bruguiera parviflora, Ceriops tagal, Rhizophora apiculata, R. mucronata, Sesuvium portulacastrum, Sonneratia alba, andXylocarpus mollucensis were studied using direct observation techniques and leaf washings. Over 40 fungal taxa were isolated from the leaf washings. Of these, species ofAspergillus, Choanephora, Cladosporium, Curvularia, Fusarium, Nigrospora, Penicillium, Pestalotiopsis, Trichoderma, andZygosporium were frequently encountered in the washings of all nine mangrove plants. Fewer species of fungi includingCladosporium oxysporum, Corynespora cassiicola, Fusarium, Penicillium, Pestalotiopsis, andZygosporium were capable of growth on the washed leaves. The major phylloplane fungus on plants with higher leaf tannin content (e.g.B. parviflora, C. tagal, Rhizophora spp., andX. mollucensis) wasPestalotiopsis. Leaves with relatively lower amounts of tannin supported the proliferation ofFusarium as the major fungus. Fungi were present on the plumule and cotyledonous sheath even before the leaves opened.Pestalotiopsis persisted throughout the development and growth of the leaves. Many of the fungi encountered on senescent leaves have been reported in earlier studies to be the primary colonisers of submerged decaying leaves.     

盐沼草—白骨壤混种减轻污损动物危害的生物防治效果研究

广西北仑河口区新造高程约220 cm 的潮间带裸滩,移植白骨壤与茳芏、沟叶结缕草、芦苇和南水葱四种盐沼草进行混种,研究盐沼草-红树混种减轻污损动物对人工红树林危害的生物防治效果。结果表明：沟叶结缕草和茳芏可快速生长和扩展,缓流、促淤能力高于长势较差的南水葱和芦苇。在盐沼和白骨壤上发现19种污损动物,其中潮间藤壶、白条地藤壶、黑口滨螺和粗糙滨螺为优势种。茳芏和沟叶结缕草受污损程度较南水葱和芦苇轻。四种盐沼草受污损程度均低于白骨壤。白骨壤＋茳芏、白骨壤＋沟叶结缕草混种均可有效减轻污损动物对白骨壤苗木危害,这两类树-草混种处理区苗木的高度、叶数、枝数、枝下高和存活率等指标均较其他处理区好。初步判断“盐沼草-红树林协同生态修复体系”对于营造人工红树林有较高应用价值。     

Isolation and characterization of chloroplast microsatellite markers in four mangrove species,Aegiceras corniculatum,Avicennia marina,Acanthus ilicifolius and Lumnitzera racemosa

One, three, seven, and six of polymorphic chloroplast microsatellite (cpSSR) markers were developed from four mangrove species, Acanthus ilicifolius, Aegiceras corniculatum, Avicennia marina, and Lumnitzera racemosa, respectively. Characterization of 229, 509, 369, and 216 individuals of A. ilicifolius, A. corniculatum, A. marina, and L. racemosa, collected from different natural mangrove populations (A. ilicifolius, 6; A. corniculatum, 14; A. marina, 10; L. racemosa, 6) in the southern coastline of China showed that these loci provide cpSSR markers with polymorphisms ranging from two to four alleles per locus and gene diversity between 0.005 and 0.675. Combining the polymorphic cpSSR loci of each species, 3, 5, 11, and 4 of cpSSR haplotypes were separately detected in populations of A. ilicifolius, A. corniculatum, A. marina, and L. racemosa in the southern coastline of China. These cpSSR markers will be useful for analyzing the maternal lineage distributions and population genetic structures of these four species.     

The distribution and abundance of barnacles in a mangrove forest

Abstract The grey mangrove tree, Avicennia marina, forms a hard substratum in an area otherwise dominated by soft-sediment. Various intertidal organisms attach to and move about on the trees. The abundant barnacles Elminius covenus, Hexaminius popeiana and Hexaminius foliorum live on a variety of substrata in mangrove forests. Their patterns of distribution and abundance were recorded and models proposed to explain these patterns. Densities of barnacles on bark, leaves and twigs of A. marina were estimated in a locality near Sydney. Elminius covenus were more abundant on bark than on leaves or twigs of A. marina. Hexaminius popeiana, although less abundant on bark than E. covenus, were not found on twigs or leaves. In contrast, H. foliorum were more abundant on twigs than leaves and were not found on the bark of A. marina. Densities of barnacles were greater in the seaward than in landward parts of the forest. Elminius covenus were the most abundant barnacles, H. foliorum were less abundant and H. popeiana were virtually absent in the landward zone. Barnacles in the seaward zone were most abundant at mid-tidal levels, less at high and low tidal levels of trunks and more abundant on lower than upper surfaces of trunks and leaves. The densities of barnacles differed according to the orientation of the bark or leaf. Models are proposed to explain the patterns of distribution and abundance of these barnacles. Each involves larval supply, settlement and post-settlement mortality. It is concluded that similar processes determining patterns of distribution and abundance for sessile organisms living on rock platforms may be applicable to sessile organisms living in the very different habitats of mangrove forests.     

Quantitative character variations of cambial derivatives in mangroves and their functional significance

Quantitative character variations of xylem cambial derivatives during secondary growth of the trunk are described for five representative mangrove species: Rhizophora stylosa (Rhizophoraceae), Bruguiera gymnorrhiza (Rhizophoraceae), Kandelia candel (Rhizophoraceae), Sonneratia alba (Sonneratiaceae) and Avicennia marina (Avicenniaceae). Two variation patterns in tracheary element length were revealed among these species. For R. stylosa, A. marina and S. alba, both vessel elements and fibers showed an increase in length during the early stages of secondary growth, then tended to be constant in later growth. In the other two species, little change occurred in the length of either vessel elements or fibers throughout the thickening growth period. Variation patterns in tracheary element length appeared to correspond with the different mangrove species' adaptations to their habitats. In addition, these five species exhibited diverse variation patterns in quantitative characters of the rays as well as in other quantitative characters of the vessels and fibers during secondary growth of their trunk.     

Development and characterization of microsatellite markers for a mangrove tree species Sonneratia caseolaris (L.) Engler (Lythraceae sensu lato)

Sonneratia caseolaris is a typical non-viviparous mangrove species and a key component of mangrove community in the Indo-West Pacific region. Here we isolated nine microsatellite simple sequence repeat (SSR) loci from the genome of S. caseolaris. Our isolated loci provided SSR markers with polymorphism of 2–6 alleles per locus. The expected and observed heterozygosities ranged from 0.242 to 0.745 and from 0.083 to 0.417, respectively. Cross-species amplification in S. alba and S. ovata showed that a subset of these markers holds promise for these congeneric species. These polymorphic SSR markers would be useful tools for population genetics studies on S. caseolaris as well as other congeneric species.     

Tidal exchange of macrolitter between a mangrove forest and adjacent seagrass beds (Gazi Bay,Kenya)

In the present study the tidal transport of macrolitter between the mangrove forest in Gazi bay (Kenya) and the adjacent seagrass meadows in the bay was investigated, by deploying large standing nets, which extended over the entire height of the water column, in the transition zone between both ecosystems. In addition, the presence of macrolitter on the floor ofRhizophora mucronata andCeriops tagal stands was studied. The macromaterial (>2 mm) that was collected with the nets consisted of mangrove material (26%, mostly leaf material), seagrass leaves (60%) and macroalgae (14%). Transport was bidirectional, indicating shuttle movements of the litter, driven by the opposite flow direction of flood and ebb tides. Litter from the mangrove species consisted mainly of leaves from species occurring at the outer zone of the forest,i.e., Rhizophora mucronata andSonneratia alba. This finding suggests that the complex spatial structure of the forest hampers outflow of macrolitter from the more inner parts. Consequently, this material remains trapped within the forest. The dominant presence of seagrass litter in the macromaterial transported with the tidal water, and the conspicuous and persistent presence of seagrass litter in the low lying, peripheralR. mucronata plots (but not in the more elevatedC. tagal plots) suggest that the mangrove forest of Gazi bay is the recipient of carbon and nutrients from the seagrass system. It is hypothesized that the element cycling of the inner parts of the mangrove forest proceeds as that of a rather closed system, whereas element cycling in the outer parts has conspicuous reciprocal connections with the adjacent seagrass meadows.     

广西北部湾典型海岛红树林的结构特征、空间格局及种间种内关联性

为研究广西北部湾茅尾海自然保护区海岛红树林群落的空间点格局和演替规律,在典型红树林海岛设置调查样地,以样地内的桐花树(Aegiceras corniculatum)、秋茄(Kandelia obovata)、白骨壤(Avicennia marina)等红树植物为研究对象,构建单变量函数的完全空间随机模型、异质泊松模型与双变量函数的环形转变模型,分析3种红树林种群的结构特征、空间格局及种内种间关联性。结果发现：(1)桐花树种群的小树和中树的个体数目较多,种群年龄结构呈金字塔型,种群处于增长状态;秋茄种群的中树个体数目较多,种群结构呈钟型,种群数量处于稳定状态;白骨壤个体数相对较少,且幼树较少老树较多,种群更新受阻,种群结构呈纺锤型,属于衰退型种群。(2)红树林群落整体上呈现出空间集聚的分布特征,从不同种群的集聚程度来看：桐花树>白骨壤>秋茄。(3)随着空间尺度的增大,红树林群落在空间分布上依次表现出聚集、随机和均匀3种特征。(4)桐花树与秋茄、白骨壤的种间关系随着尺度增加均表现为空间无关联性-空间负关联性-空间无关联性的演变特征,秋茄与白骨壤的种间关系则为全尺度的空间无关联性。(5)桐花树种内不同龄级之间存在空间正关联性、空间无关联性和空间负关联性,秋茄种内不同龄级之间均表现出空间无联性,白骨壤种群则在不同龄级之间均出现空间正关联性。(6)红树植物种群的空间格局受到自身繁殖特性、生境异质性、种内和种间竞争、病虫害等多种因素的影响。红树林人工种植和恢复需要结合沿海地区的自然生态条件,按照红树林种群的适应形态学特点、群落类型和自然演替规律,种植乡土红树植物,适当引进外来物种,研制出近似天然的人工红树林林分结构,提高群落的生物多样性和群落稳定性,发挥红树林湿地生态系统的生态环境效应。     

Radiative properties of hardwood leaves to ultraviolet irradiation

Spectral reflectance and transmittance of leaves to ultraviolet irradiation were determined under laboratory conditions for seven species of hardwood trees, namely red oak (Quercus rubra, L), black oak (Q. velutina, Lamarch), white oak (Q. alba, L.), sugar maple (Acer saccharum), Norway maple (A. plantanoides), hickory (Carya tomemtosa), sweetgum (Liquidambar styraciflua), and black oak litter. The experimental system consisted of a solar simulator, an integrating sphere, and a spectroradiometer. Experiments were repeated three to five times for both adaxial and abaxial surfaces of fresh leaves chosen at randomly. The spectral distributions and simple averages of the radiative properties in the wavelength ranges of ultraviolet-B (UV-B, 280–320 nm) and ultraviolet-A (UV-A, 320–400 nm) were determined. The spectral distributions of reflectance were similar between adaxial and abaxial surfaces, although the magnitude varied among tree species. Leaf reflectance was very low for the ultraviolet spectrum in general and varied among species and between adaxial and abaxial surfaces. It was generally higher over the UV-A waveband compared to UV-B, and higher on the abaxial than adaxial surface. The broadband reflectance in the UV-A range (over all species) was 5.0 and 3.9% for abaxial and adaxial surface, respectively, compared to 3.5 and 2.8% in UV-B. The transmittance through leaves was extremely small in the UV-B (<0.1%) and nearly zero in the UV-A spectral range. Consequently, the absorptance of ultraviolet radiation by leaves, as determined from the measured reflectance and transmittance, was quite high, being more than 90% for all the combinations of species and wavebands examined. The reported results are useful for studies requiring spectral radiative properties of the examined leaves with respect to ultraviolet irradiation.     

Disentangling the effects of global climate and regional land-use change on the current and future distribution of mangroves in South Africa

The mangrove distribution in South Africa is fragmented and restricted to small forest patches occupying only 16 % of the estuaries within the current range. In this study we used species distribution models to test (1) whether the absence of mangrove forest and its species (Avicennia marina, Bruguiera gymnorrhiza and Rhizophora mucronata) within their current range is driven by climate or by climate combined with human or geomorphic perturbation and (2) how climate change may potentially affect the latitudinal limit of the mangrove forests and its species in South Africa. We used three modelling techniques (generalized linear models, generalized additive models and gradient boosting machines) and a set of three climate-based predictive variables (minimum air temperature of the coldest month, waterbalance and growing-degree days) combined separately with an index of human or geomorphic perturbation. Climate variables for the future projections were derived from two general circulation models driven by two socio-economic scenarios (A2a and B2a). Within the range of the mangrove forest, the fragmented distribution of the mangroves in South Africa was not explained by our set of climate variables alone. The index of human perturbations slightly improved the predictions but the index of geomorphic perturbation did not. Climate change will create climatically suitable sites for the mangrove forest and the two species A. marina and B. gymnorrhiza beyond their current limits, but model outcomes did not agree on the future potential distribution of R. mucronata. We were able to successfully predict range limits and to detect future climatically suitable sites beyond the current limits. Factors controlling mangrove distribution within its range are still to be identified although absences were partly explained by human perturbations.     

An inverse relationship between allelopathic activity and salt tolerance in suspension cultures of three mangrove species,Sonneratia alba,S. caseolaris and S. ovata: development of a bioassay method for allelopathy,the protoplast co-culture method

A bioassay method for allelopathy, the ‘protoplast co-culture method’ was developed to study the relationship between salt tolerance and allelopathy of three mangrove species, Sonneratia alba, S. caseolaris, and S. ovata. Plants of S. alba grow in the seaward-side high salinity region and plants of the latter two species grow in upstream-side regions of a mangrove forest, respectively. Effects of five sea salts (NaCl, KCl, MgCl₂, MgSO₄ and CaCl₂) on the growth of the suspension cells of the latter two species were first investigated by a small-scale method using 24-well culture plates. S. ovata cells showed higher tolerance than S. caseolaris cells to NaCl and other salts, but were not as halophilic as S. alba cells. Protoplasts isolated from suspension cells were co-cultured with lettuce protoplasts in Murashige and Skoog’s (MS) basal medium containing 1 μM 2,4-dichlorophenoxyacetic acid, 0.1 μM benzyladenine, 3 % sucrose and 0.6–0.8 M osmoticum. S. caseolaris protoplasts had a higher inhibitory effect on lettuce protoplast cell divisions than S. alba protoplasts at any lettuce protoplast density, and the effect of S. ovata was intermediate between the two. These results were similar to those obtained from a different in vitro bioassay method for allelopathy, the ‘sandwich method’ with dried leaves. The inverse relationship between allelopathic activity and salt tolerance in suspension cells of Sonneratia mangroves is discussed.