An ecological study on the Mollusca in mangrove areas in the estuary of the Jiulong River

Based on the surveying data obtained in February, May, August and November, 1987, the ecology of Mollusca in mangrove areas in the estuary of the Jiulong River in Fujian Province was studied. The results are as follows: There are 52 species of Mollusca in the areas, and species and abundance distribution increase with salinity. Biomass and density average 7.99 g m² and 25 ind. m² respectively, with higher values in autumn and winter, and lower in spring and summer. Vertical distribution of biomass is highest in high tide zones and lowest in low tide zones, and density is highest in mid-tide zones and lowest in tide zones. The relationship between the distribution of Mollusca and the environmental factors are discussed.     

福建漳江口红树林和盐沼湿地的多毛类动物群落

为了比较漳江口4种植物生境之间多毛类动物群落的差异性,2010年对漳江口潮间带秋茄、桐花树、白骨壤和互花米草4种植物生境的多毛类动物进行4个季度的定量取样.共获得15种多毛类动物,4个季度在4种植物生境中均出现三角洲双须虫、溪沙蚕、拟突齿沙蚕、凿贝才女虫、小头虫和加州中蚓虫.多毛类动物栖息密度、生物量、丰度指数、均匀度指数和多样性指数的季节变化不明显;但4种植物生境之间多毛类动物栖息密度、生物量、丰度指数、均匀度指数和多样性指数有显著差异,且互花米草生境与3种红树林生境之间多毛类动物优势种不同.Pearson相关分析表明,漳江口红树林和盐沼湿地除了多毛类物种数与泥温显著相关外,多毛类动物栖息密度、生物量、丰度指数、均匀度指数和多样性指数均与泥温、盐度、总有机碳、总氮无显著相关关系,其原因是漳江口4种植物生境多毛类动物常见种小头虫、加州中蚓虫和溪沙蚕均是广温、广盐及耐高有机质含量的种类.     

The turbidity maximum in the Tamar estuary

Many estuaries of medium to high tidal range exhibit an accumulation of fine cohesive material in their upper reaches in the region of the limit of saline intrusion. Much, or all, of this material is suspended each tidal cycle and the entire region undergoes a seasonal variation which appears to depend on fluvial input. Two factors which are throught to influence the formation and maintenance of turbidity maxima are the differing magnitudes of the bed shear stress (τ₀) on flood and ebb tides and the large vertical density gradient which developes on the ebb tide. Crucial to the importance of the first factor is that τ₀ exceeds a critical value, at which erosion occurs, for a greater period on the flood than on the ebb. The effect of the density gradient is that upward propagation of bed generated eddies is inhibited and the sediment is not transported into the upper part of the flow where it will be most effectively transported. It is not clear which, if either, of these mechanisms is dominant. Data consisting of vertical profiles of velocity, salinity and suspended solids were collected at four stations in the Tamar estuary during a high range tidal cycle. One station, at which the depth mean salinity (S _d ) varied from 0.0 to ∼ 12.0‰, was occupied permanently. The other stations were occupied such that data were collected asS _d varied in the range 0.0 to ∼ 4.0‰. In this way each station was occupied for a period of time on the ebb and flood tide. Observations show that during the early ebb, when the flow is relatively deep and slow, stratification persist untilS _d ∼ 0.0‰ and that no significant transport occurs while the flow is saline but that there is a rapid increase in suspended solids concentrations after this time. During the later ebb the shallower faster flow allowed the density gradient to be erode and significant transport was observed atS _d ∼ 5.0‰. On the flood tide the flow in the low salinity region is well-mixed troughout. Computation of the fluxes and total transport per unit breath of estuary show that on the ebb tide the quantity of solid material being transported by the low salinity (0–3‰) region remains nearly constant as this region of the flow is advebted seaward. On the flood tide, however, as the same region is advected landward the quantity of material being transported increases. It is concluded that in the Tamar estuary the early ebb tide stratification contributed to the formation and maintenance of a turbidity maximum which is strongly associated with the low salinity region of the flow. It is also speculated that the differences in the ebb and flood tide transport are caused by differences in the availability of mobile material on the bed at different stages of the tidal cycle.     

漳江口红树林沉积物可培养真菌多样性

红树林真菌由于其独特的生态特征、多样性特点和丰富的新型生物活性代谢产物而引起了广泛的关注。本文以漳江口红树林保护区4个采样点的沉积物为研究对象,采用8种筛选培养基（RBM、PDA、CDA、Martin、YM、SDA、ISP2和R2A）分离可培养真菌,根据ITS序列分析对其进行物种鉴定,并利用多样性指数分析评价不同采样点真菌群落的差异。结果共分离到274株真菌,隶属于2门12纲23目39科52属,其中优势属为枝顶孢属（Acremonium）（20.8%）和青霉属（Penicillium）（11.3%）,其次是枝孢属（Cladosporium）（7.3%）和帚枝霉属（Sarocladium）（7.3%）。8种筛选培养基中,分离出真菌种属类型最丰富的培养基是RBM,其次是PDA。根据Shannon-Wiener多样性指数（H′）、Simpson优势度指数（D）、Magalef丰富度指数（R）和Pielou均匀度指数（J）的分析结果,在属的水平上,距海洋的位置越近,真菌的群落多样性越高,真菌分布越均匀。     

The role of salinity in structuring the fish assemblages in a tropical estuary

The present study describes the seasonal changes of the fish species composition in three areas of the main channel of the Caeté River estuary, Brazil. The fish faunas of each habitat differed in density, biomass and species composition. Mean fish density and biomass for the Caeté River estuary channel was 0·25 individuals m⁻² and 0·9 g m⁻² respectively. Analysis of catch data showed that the number of species, total density and total biomass differed significantly between areas and seasons. For the most important species, the mean density of Cathorops spixii, Aspredinichthys filamentosus, Aspredo sp. 2, Pimelodus blochii, Pseudauchnipterus nodosus and Macrodon ancylodon , differed significantly between seasons while the mean density of Stellifer rastrifer , Stellifer microps, Aspredo aspredo , Aspredo sp. 1 and Cynoscion acoupa did not. The mean biomass of these species, with exception of S. microps and Aspredo sp. 1, also differed significantly between seasons. In the Caeté estuary seasonal salinity fluctuations appeared to be the main factor that structured the fish assemblage in the entire estuarine system. At least 85% of the species captured by the artisanal and subsistence fisheries in the Bragantine region required estuarine conditions to complete their life cycle.     

Forest structure and biomass of mangroves in the Mgeni estuary,South Africa

Forest structure and biomass were determined in a mangrove stand dominated by Bruguiera gymnorrhiza (L.) Lam. Trees in 5 m² sample plots were harvested at ground level and then further cut into 1 m strata for separation into living wood, dead wood, leaves, reproductive material and pneumatophores. Mean above-ground living biomass was calculated at 94.49±7.83 t dry matter ha^–1, while dead wood contributed a mean mass of 7.63±0.89 t dry matter ha^–1. Excavations of roots yielded a below-ground biomass of 9.67 t dry matter ha^–1 which represented only 9.8% of the above-ground value. There was a mean density of 4700 living stems ha^–1 with plant heights ranging from 0.57 m to 5.80 m. Mean LAI was 4.95±0.80. As a basis for estimating standing biomass, regression lines were fitted to biomass values from individual trees of B. gymnorrhiza and Avicennia marina (Forssk.) Vierh. of various sizes. A comparison of these relationships with methods used by previous workers for estimating biomass suggests that most other methods cannot be applied without modification for local stands of mangroves.     

Influence of freshwater flows on the distribution of eggs and larvae of black bream Acanthopagrus butcheri within a drought-affected estuary

This study tested the hypothesis that variable freshwater flow in the Gippsland Lakes, Australia, influences the location and extent of environmental conditions suitable for spawning and larval development of black bream, Acanthopagrus butcheri. Freshwater flow had a large influence on the salinity and level of stratification (difference between bottom and surface salinity) in the Gippsland Lakes. Freshwater flows throughout this study varied from no or low flows through to major flooding in 2007. Eggs of A. butcheri were found in similar concentrations throughout the lakes and rivers. More than 99% of larvae, however, were collected from within rivers, with very few larvae being collected from the lakes. A comparison of two spawning seasons revealed that the year with higher freshwater flows also had greater spawning activity and higher concentrations of larvae. Interestingly, there was a significant relationship between the distribution of eggs and larvae with the level of stratification. The highest concentrations of larvae occurred at sites with a difference in bottom and surface salinities of 15-20. This study demonstrates that despite A. butcheri spawning in the lakes and rivers, it is only locations with a halocline that function as larval nursery habitat.     

Influence of moon phase on fish assemblages in estuarine mangrove tidal creeks

Significant differences in the composition of fish assemblages during different moon phases were detected in mangrove tidal creeks of the Goiana Estuary. The numbers of Zabaleta anchovy Anchovia clupeoides, Tarpon snook Centropomus pectinatus and Guavina Guavina guavina as well as at least 15 other species showed significant changes according to moon phase and were higher in terms of individuals (32%) and mass (34%) during the new moon.     

Threat and stress in the Clarence River estuary of Northern New South Wales

The estuarine system of the Clarence River in northern New South Wales, Australia is examined. Although many such systems in Australia have been placed at risk as a result of human-induced environmental pressure, it is contended that this is not the case with the Clarence River system. Rather it is suggested that perceived environmental threats in this case are the result of particular local environmental cognitions and that actual stress exerted on the system is largely independent of human use.     

Physical processes in the Rufiji delta and their possible implications on the mangrove ecosystem

The physical processes such as coastal currents, estuarine circulation and monsoon winds prevailing in the Rufiji delta are discussed. The relationship between these processes and the occurrence of long-term trapping of the river discharge and the outflow of waters from the mangrove swamps into the nearshore zone has been observed. The trapped waters in the nearshore zone significantly reduce the mixing between the estuarine and offshore waters, leading to the two waters having distinctive properties. The existence of the trapped waters in the nearshore zone is supported by evidence from a satellite image and aerial photograph and measurements of salinity and suspended sediment concentration. The trapping phenomenon is discussed in the light of its possible implications on the ecology of mangrove ecosystems. Trapping may explain the enhanced growth of the mangrove in the delta compared to other areas. This trapping effect may be providing more time for nutrient retention in the mangrove zone, incorporation of the decomposed leaf litter and fine sediments in the substrate, and settling of fruits and seedlings in the swamps, thereby enhancing the regeneration of the mangrove.     

福建漳江口红树林湿地自然保护区的生物多样性及其保护

福建漳江口红树林湿地自然保护区位于东经117024/07//～117030/00// ,北纬23053/45//～23056/00//的云霄县内,总面积2 360 hm2;是福建省唯一的一个红树林国家级保护区。本文介绍了保护区的生物多样性现状,保护区内现有生物物种688种,其中国家一级保护动物2种,国家二级保护动物19种,“三有”动物162种,中日协定保护候鸟77种,中澳协定保护候鸟41种,有全国最大面积的白骨壤林。并提出了符合保护区管理的生物多样性保护策略:落实生物多样性保护工程实施政策、尽快在保护区建立生态旅游区、加强保护区的科学研究和扩大国内外联系,搞好管护。     

Integrative ecosystem analyses of phytoplankton dynamics in the York River estuary (USA)

The relative importance of biotic (top-down) vs. abiotic (bottom-up) controls on phytoplankton dynamics was investigated in the York River estuary, Virginia (USA) by a combination of extensive analyses of long-term data sets collected by the U.S. Environmental Protection Agency (EPA) monitoring program over 17 years (1984–2001), field studies (1996–1997) and ecosystem modeling analyses. Results from the analysis of long-term data records collected at three stations along the salinity gradient suggested that phytoplankton are more likely controlled by abiotic mechanisms such as resource limitation than biotic mechanisms such as grazing since annual cycles of primary production and phytoplankton biomass were similar and no grazing effects were evident based on the observed relationship between phytoplankton and zooplankton biomass (R ² < 0.2, p > 0.1). This scenario was supported by short-term field observations made over an annual cycle at three stations in the mid-channel of the estuary where both chlorophyll a and primary production demonstrated similar patterns of seasonal variation. Ratios of fluorescence before and after acidification at all study sites were relatively high suggesting low grazing pressure in the estuary. A tidally-averaged, size-structured plankton ecosystem model was previously developed and verified for the lower York River estuary. The validated ecosystem model was also used to examine this issue and simulation results supported the importance of bottom-up control in the York River estuary.     

Ontogenetic changes in the longitudinal distribution of two species of larval fish in a turbid well-mixed estuary

The relationship between vertical migration, estuarine retention and species-specific patterns of longitudinal distribution of the pelagic larvae of rainbow smelt, Osmerus mordax , and tomcod, Microgadus tomcod , was investigated in the upper section of the St Lawrence Middle Estuary. We hypothesized that the species-specific use of the vertical pattern of current exhibited by the two species results in the partitioning of the estuarine habitat in the longitudinal plane while assuring retention. Important differences in the longitudinal distribution of tomcod and smelt larvae were related to the ontogeny of their vertical distribution in the water column. In June, small tomcod and smelt larvae are generally associated with waters of salinities less than 5%o. As the larvae grow, their vertical distribution patterns change, leading to a horizontal separation of the two species. Tomcod juveniles migrate downstream into colder, more saline waters, whereas larger smelt larvae migrate upstream into warmer, tidal fresh waters. Ontogenetic changes in vertical distribution serve to concentrate larvae in specific conditions that may optimize physiological conditions and also permit population persistence.     

Growth and respiration in two mangrove species at a range of salinities

Growth and dark respiration rates were measured in leaves and roots of seedlings of Avicennia marina (Forsk.) Vierh, (grey mangrove), and Aegiceras corniculatum (L.) Blanco (river mangrove). Plants were grown in a soil mixture at ambient temperatures and watered with 0.25 and 100% sea-water. Oxygen uptake was measured in excised root and leaf samples. In both species growth was maximal in 25% sea-water, and root respiration was lowest in 100% sea-water. Differences were found between the two species in the responses of leaf respiration to salinity. In A. corniculatum leaf respiration was raised in both 25 and 100% sea-water, while in A. marina only leaves in 100% sea-water showed higher rates of respiration. These results are consistent with the view that A. marina is the more salt-tolerant of the two species. In A. corniculatum the respiration rates of the hypocotyl were also measured, and were much higher in 100% sea-water than in the other two treatments. The results suggest that at high salinities there is a high metabolic cost in the shoots of both species, and that at such salinities rates of root respiration may be limited by the supply of substrate from the shoots.     

Heterogeneity in intertidal fish fauna assemblages along the world's longest mangrove area in northern Brazil

The first comparison of the intertidal fish fauna from three estuaries within the longest contiguous mangrove area of the world, in north Brazil, revealed a significant heterogeneity in the species composition and functional and ecological guilds with an increase of Tetraodontidae and Engraulidae and a decrease of Sciaenidae and Mugilidae towards the Amazon mouth. A classification of the mangrove estuaries to identify types of estuaries and coastal sectors is urgently required to provide a tool for regional management systems in order to improve research, monitoring and conservation of this unique mangrove ecosystem.     

海岸红树林地沙丘移动对林内大型底栖动物的影响

沙丘在广西北海大冠沙白骨壤红树林内的移动,破碎了原有的平滩,形成了埋没滩、过渡滩、侵蚀滩３种沙化滩涂生境。比较研究了不同滩涂生境间大型底栖动物群落的差异。结果表明：除藤壶外,研究地点共有大型底栖动物３１种。平滩跟其它滩涂生境间的动物群落相似度都小于０．５,表明沙丘移动使原有底栖动物群落异质化。沙化不仅使原有底栖动物群落的种类、密度和生物量分别下降了３５．１％,７４．６８％和８９．７６％,而且还降低     

Ecology of mangrove fungi and their role in nutrient cycling: what gaps occur in our knowledge?

Recent investigations have increased our knowledge of the ecology of mangrove fungi. In this paper this information is reviewed with emphasis on biogeography, biodiversity, differences in the tropical and subtropical mycoflora, fungal distribution on mangroves trees, host specificity, vertical zonation and distribution with salinity. Gaps in our knowledge are discussed. There is little knowledge of the role of mangrove fungi in nutrient cycling which is also reviewed. Areas in which knowledge is deficient include quantification techniques for fungal abundance, the nature and activities of fungal extracellular enzymes and fungal modification of mangrove detritus matter, especially the dissolved form.     

The influence of density gradients on the transport of solutes in a deep estuary

This paper reports on an investigation into the lower Forth estuary where a combination of hydrody namic, dye and salinity measurement techniques have been employed to quantify the effects of temporally varying vertical and transverse density gradients on the diffusion and dispersion processes. It is concluded that the interaction of velocity shear and weak longitudinal salinity induced density gradient produces a complex and profound effect on estuarine solute mixing processes.     

The value of a mangrove area in Sarawak

Many arguments have been presented to justify the conservation of tropical forests. In the case of mangrove forests, their preservation can be argued using economic and employment grounds alone. A case study of the Sarawak Mangroves Forest Reserve, Malaysia is presented. Here, the mangroves support marine fisheries worth US$21.1 million p.a. and up to 3000 jobs, timber products worth US$123,217 p.a., and a tourist industry worth US$3.7 million p.a. If the mangroves were to be damaged, all of the fisheries and timber and many of the tourism benefits would be lost. In addition, highly expensive civil engineering works would be incurred to prevent coastal erosion, flooding and other damage. The area is also one of the only remaining refuges for mangrove flora and fauna in Sarawak. If the area were to be converted to aquaculture ponds or oil palm plantations, levels of revenue would be greatly reduced, and the multiple other benefits of mangroves would be lost. Coastal land pressure is not a limiting factor in the State. Considering their economic, employment, coastal protection and species conservation values, mangroves should be conserved and their importance taken into account at all levels in development planning.     

Spatial patterns of benthic diatoms,carbohydrates and mud on a tidal flat in the Ems-Dollard estuary

The chlorophyll a content and two operational fractions of carbohydrate (water extractable and EDTA extractable) were measured every three months during one year along transects on a tidal flat in the Ems-Dollard estuary (The Netherlands). Chlorophyll a was used as an indicator of microphytobenthos biomass, which was composed predominantly of epipelic diatoms. Both carbohydrate fractions correlated significantly with chlorophyll a. EDTA extractable carbohydrates were more resistant towards degradation than the water extractable fraction. During most of the year, concentrations of chlorophyll a and carbohydrates were low, but in June, high concentrations of up to 90 g chlorophyll a/g sediment were found in a narrow zone running parallel to the channel. Maximum concentrations of water extractable carbohydrates and EDTA extractable carbohydrates ranged between 800–1200 and 600–800 g/g sediment, respectively. The mud content was high (± 90%) at the margin of the tidal flat. This was not limited to the growth season of the diatoms, but was observed throughout the year. This indicated that the high mud content at the mudflat margin was mainly caused by hydrodynamic factors, and not by biostabilization. In June, exceptionally high diatom densities were found in sediment with a high mud content. There was only minor evidence that biostabilization by epipelic diatoms lead to a further increase in the mud content of the sediment.