Carbonate production of an emergent reef platform, Warraber Island, Torres Strait, Australia

Complex relationships exist between tropical reef ecology, carbonate (CaCO₃) production and carbonate sinks. This paper investigated census-based techniques for determining the distribution and carbonate production of reef organisms on an emergent platform in central Torres Strait, Australia, and compared the contemporary budget with geological findings to infer shifts in reef productivity over the late Holocene. Results indicate that contemporary carbonate production varies by several orders of magnitude between and within the different reef-flat sub-environments depending on cover type and extent. Average estimated reef-flat production was 1.66 ± 1.78 kg m⁻² year⁻¹ (mean ± SD) although only 23% of the area was covered by carbonate producers. Collectively, these organisms produce 17,399 ± 18,618 t CaCO₃ year⁻¹, with production dominated by coral (73%) and subordinate contributions by encrusting coralline algae (18%) articulated coralline algae, molluscs, foraminifera and Halimeda (<4%). Comparisons between the production of these organisms across the different reef-flat zones, surface sediment composition and accumulation rates calculated from cores indicate that it is necessary to understand the spatial distribution, density and production of each major organism when considering the types and amounts of carbonate available for storage in the various reef carbonate sinks. These findings raise questions as to the reliability of using modal production rates in global models independent of ecosystem investigation, in particular, indicating that current models may overestimate reef productivity in emergent settings. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

PrP106-126 amide causes the semi-penetrated poration in the supported lipid bilayers

A major hallmark of prion diseases is the cerebral amyloid accumulation of the pathogenic PrP^Sc, an abnormally misfolded, protease-resistant, and β-sheet rich protein. PrP106-126 is the key domain responsible for the conformational conversion and aggregation of PrP. It shares important physicochemical characteristics with PrP^Sc and presents similar neurotoxicity as PrP^Sc. By combination of fluorescence polarization, dye release assay and in situ time-lapse atomic force microscopy (AFM), we investigated the PrP106-126 amide interacting with the large unilamellar vesicles (LUVs) and the supported lipid bilayers (SLBs). The results suggest that the interactions involve a poration-mediated process: firstly, the peptide binding results in the formation of pores in the membranes, which penetrate only half of the membranes; subsequently, PrP106-126 amide undergoes the poration-mediated diffusion in the SLBs, represented by the formation and expansion of the flat high-rise domains (FHDs). The possible mechanisms of the interactions between PrP106-126 amide and lipid membranes are proposed based on our observations.     

长江口潮间带大型底栖动物群落演替

2006年1月在崇明岛西端的潮间带湿地进行了一项生态工程,经过土方工程的区域被选为大型底栖动物群落演替区,因为其中的大型底栖动物群落受到了较大破坏,在其周边未受干扰区设立对照样点。试图通过群落重建群的研究分析3个问题：（1）在群落恢复过程中不同的生态学指标如何变化？（2）群落演替过程中什么先增长,生物量还是复杂性？（3）是否可以选择生态学指标以利于演替过程中3类不同增长模式（生物量、网络结构和信息量）的识别？多变量分析用于检验被干扰区群落是否已经得到恢复。Shannon-Wiener指数、Margalef指数、Pielou均匀度指数、能质（exergy）和结构能质（Specificexergy）用于分析演替过程中群落状态的变化。结果显示物种随时间的更替与群落结构变化密切相关。物种丰富度增长迅速,而且对照区和演替区的物种组成非常相似。演替进行1个月左右之后,演替区的生物多样性已经超过了对照区。能质和结构能质提供了群落结构发展的有用信息,但仍然缺乏鉴别系统所处信息状态的能力。多样性分析结果可以从中度干扰假说（Intermediate Disturbance Hypothesis）得到很好地解释。总体而言,干扰的空间尺度决定了群落的恢复特征,如果干扰区域明显小于周边未受干扰的区域,那么群落的复杂性（信息量和网络结构）将先于生物量得到恢复。     

Nitrogen addition does not reduce belowground competition in a salt marsh clonal plant community in Mississippi (USA)

Previous studies have suggested that belowground competition for nutrients influences plant zonation in salt marshes. In this study, I tested the hypothesis that competition for nitrogen structured a clonal plant community in a nitrogen-limited salt marsh in coastal Mississippi, USA. In contrast to most previous field studies that have investigated mechanisms of competition, I examined clonal growth responses of established genets of a nitrogen-demanding low-intertidal species (Spartina alterniflora) to nitrogen addition and the removal of a nitrogen-conserving high-intertidal species (Juncus roemerianus). Nitrogen addition stimulated clonal invasion of the Juncus zone by Spartina but did not reduce the significant competitive effects of Juncus on Spartina. Simulated Juncus shade did not reduce invasion of the Juncus zone by Spartina, indicating that belowground competition reduced clonal invasion. In the last year of the study, the border shifted unexpectedly towards the Spartina zone, resulting in competitive displacement of Spartina by Juncus. Nitrogen addition did not prevent or slow this displacement, further contradicting the nitrogen competition hypothesis. Although growth rates were much more strongly limited by nitrogen in Spartina than in Juncus, nitrogen addition did not cause the displacement of Juncus by Spartina after three growing seasons. I conclude that zonation of Spartina and Juncus is maintained by preemption of space and greater tolerance of low nitrogen supplies by Juncus in the high marsh. These results contrast sharply with findings of reduced belowground competition with nutrient addition in previous studies and highlight the important role of nutrient-mediated competition for space between clonal plants.     

Foraging by the mud snail, Ilyanassa obsoleta (Say), modulates spatial variation in benthic community structure

We investigated the foraging behavior of the mud snail, Ilyanassa obsoleta, and its consequences for macrobenthic community structure on mud flats on Long Island, NY, USA. Field sampling demonstrated strong spatial heterogeneity in the population densities of I. obsoleta. We experimentally tested three hypotheses: (i) I. obsoleta are strongly attracted to areas with high levels of detritus; (ii) local abundances of deposit-feeding annelids are limited by detritus; and (iii) the foraging activities of I. obsoleta negatively affects annelid assemblages. We manipulated the density of mud snails using inclusion fences and the levels of detritus using dried Ulva. Results showed that high densities of I. obsoleta were attracted to areas enriched with Ulva detritus. In addition, high densities of snails negatively affected abundances of annelids, with the opportunistic species, Capitella spp. and Paranais litoralis, being most affected. The addition of Ulva detritus had more specific effects on annelid assemblages. Only Capitella spp. showed a significant positive response, although previous evidence has demonstrated that higher experimental detrital inputs stimulated growth of other species of annelids and microphytobenthos. In an experimental treatment with enhanced detritus and low densities of snails, we found population abundances of opportunistic annelids (up to 200,000 m⁻²) substantially larger than has ever been recorded in 5 years of sampling. Because mud snails in natural areas actively search, locate and exploit areas with enhanced detritus and their foraging negatively affects abundances of opportunistic worms, I. obsoleta probably controls the upper limits of annelid abundance in the field. Foraging behavior of I. obsoleta therefore modulates spatial variation in benthic community structure in an environment where limiting resources are patchily distributed.     

Role of fiddler crabs of a subtropical intertidal flat on the fate of sedimentary fatty acids

Fatty acid compositions of three ocypodid crabs, Uca vocans, U. lactea and Scopimera globosa, collected on a subtropical intertidal flat (Okinawa, Japan), were analysed as well as the surrounding surface sediment of their burrows, their food pellets and their faeces. U. vocans and U. lactea exhibited a higher concentration of fatty acids than S. globosa. Food pellets revealed a higher relative contribution of saturated fatty acids and lower amounts of polyunsaturated and branched fatty acids than in the surface sediment samples. These differences of fatty acid compositions suggest an initial selection of food before the particle sorting in the buccal region. This result, and also because of the relatively high fatty acid content of faeces, indicate that fiddler crabs play a significant role in the fate of these lipids in the subtropical intertidal flats. Comparative analysis of the fatty acid compositions of the different samples indicates that these fiddler crabs actively sorted bacteria in order to ingest them. Diatoms seem to be used in larger amount by U. vocans may be because of its higher mobility while looking for food. Other primary producers present in the environment, mangrove leaves and algae, have been sorted but contributed weakly to the organic matter pool of the surface sediment and therefore to the diet of the crabs.     

Effects of a macroalgal mat (Ulva lactuca) on estuarine sand flat copepods: an experimental study

The effects of a macroalgal mat (Ulva lactuca) on intertidal sand flat copepods were studied in Jamaica Bay, NY. In 1999, Ulva was removed from paired quadrats in the algal mat. Density and species richness were estimated from sediment cores over seven biweekly periods and compared with Ulva-removal quadrats and with an unvegetated reference site. In a separate analysis at the same site, species composition and density of all copepods within the algal mat were determined from replicated quadrat samples over seven dates. Emergence traps were deployed in all treatments in 1999 to quantify copepod movements from sediments into the water column during flooding tide. Dissolved oxygen (DO) was continuously monitored over several 96-h periods in and above the algal mat. In 2000, three biomass levels of Ulva (0, 100, 200 g DW per m²) were added to paired quadrats in the unvegetated zone. Density and species richness were estimated over eight time periods. Ulva removal resulted in significant increases in density and species richness, but levels remained lower than at the unvegetated site. Likewise, addition of Ulva biomass produced significant declines in copepod density. However, the differences between low- and high-Ulva-addition treatments were insignificant. Increases in phytal copepods after Ulva addition did not compensate for losses of epibenthic and infaunal species. The overall effect of the Ulva mat was a net loss of copepod density, including the loss of nearly all infaunal species. Anoxia in sediments and within the algal mat are correlated with declines in infaunal species and with escape by some infaunal species from the sediment into the water column.     

Historic mussel beds (Mytilus edulis) in the sedimentary record of a back-barrier tidal flat near Spiekeroog Island, southern North Sea

Mussel beds show irregular cycles of appearance, disappearance and reappearance at preferred distinct locations on intertidal flats. These cycles are documented in the depth profile by the presence of shell-rich sediments intercalated with sandy layers. Such mussel bed layers were regularly found over the past 12 years on the Swinnplate, a back-barrier tidal flat south of Spiekeroog Island, southern North Sea. They are characterised by the occurrence of sub-articulated pairs of Mytilus shells. Based on life span considerations, a period of at least 35–40 years over which mussel beds may have repeatedly established themselves is suggested. A survey in spring 2000 revealed a reduced occurrence of old, embedded beds on the Swinnplate. The present results, based on core profiles from 1992 to 2000 and amino acid age determination, show that alternations of shell layers indicative of former Mytilus beds and sediment layers provide insight into the historic development of tidal flat environments. The frequent occurrence of sub-articulated valve pairs in the shell layers documents that the embedding of the mussel beds took place soon after the death of the organisms without prior physical disturbance. Successions of historic Mytilus beds provide evidence that mussel beds are a regular, but not necessarily permanent, faunal feature of back-barrier tidal flats of the North Sea. Electronic Publication     

Model erroneously predicts failure for restoration of Lake Apopka,a hypereutrophic,subtropical lake

There are six main species of shellfish of commercial importance within the UK (mussels, flat oysters, cockles, king scallops, Manila clams and lobsters) which can be thought of as ranched to varying degrees. A seventh (Pacific oysters) can be included, since a very small proportion of the production may undergo a period of growth on natural habitats in some areas. An eighth species (Palourdes or native clams) appeared in the statistics for the first time in a number of years in 1998. Seafish, as part of its role in promoting the sustainable management of resources, has examined the current state of the shellfish aquaculture industry in the UK.     

崇明东滩南部盐沼植被空间分布及影响因素分析

崇明东滩南部滩面高程、土壤盐度在空间上呈明显的梯度变化规律。高程整体西高东低、北高南低, 盐度东北高、西南低, 两者共同限制着盐沼植物在空间上的分布。该文围绕崇明东滩南部主要植被类群及其空间分布, 探讨了土壤盐度、潮滩高程两大环境因子与植物种群分布的对应关系。基于2013年夏、秋季植被空间网格采样和空间插值, 分析了东滩南部植物的空间分布现状, 发现不同植物类群在高程和土壤盐度上存在极显著的差异(p < 0.01)。高程差异: 莎草科类群主要分布于高程区间2.93-4.07 m的低潮滩, 禾本科主要集中分布在高程3.13-4.31 m的中、高潮滩; 盐度差异: 海三棱藨草(Scirpus mariqueter)和互花米草(Spartina alterniflora)优势种群植被覆盖区表层30 cm的平均土壤盐度为(3.2 ± 0.6) g·kg^-1, 显著高于其他类群植物分布区的平均土壤盐度(2.0 ± 0.3) g·kg^-1 (p < 0.01)。崇明东滩湿地生态系统的关键种兼先锋种——海三棱藨草, 分布高程介于2.53-3.97 m, 而互花米草能适应海三棱藨草80%的高程区间, 两者在高程上存在竞争关系。统计数据显示, 研究区域中近90%的海三棱藨草分布在研究区东北部, 土壤盐度范围为1.6-4.5 g·kg^-1, 海三棱藨草、互花米草能较好地适应该空间内的盐度胁迫, 两种植物在此交替出现。但是在高程和土壤盐度的综合作用下, 互花米草的生长状况更好, 因此该区的海三棱藨草很可能会被互花米草逐步取代。对各类群植被分布和优势面积的研究发现, 海三棱藨草总分布面积为294 hm², 优势群落面积120 hm², 海三棱藨草仅占莎草科植物总优势面积的15.7%, 占研究区总面积的6.9%, 在6种主要植物(芦苇(Phragmites australis)、白茅(Imperata cylindrica)、互花米草、糙叶薹草(Carex scabrifolia)、藨草(Scirpus triqueter)、海三棱藨草)中比重最小, 这给保护区内海三棱藨草种群的恢复和保护带来极大的挑战。