Analyzing the habitat suitability for migratory birds at the Chongming Dongtan Nature Reserve in Shanghai,China

The Dongtan Nature Reserve, one of the largest nature reserves in East Asia, is located in the mouth of the Yangtze Estuary and is an important habitat for migratory birds. The Dongtan wetlands were listed in the Chinese Protected Wetlands in 1992, and were designated as internationally important under the Ramsar Wetlands Convention in 2001 and as a national nature reserve in 2005. By their very nature and location, the estuarine and coastal habitats are dynamic and their biodiversity conservation and management relies on up-to-date spatial information. By establishing qualitative and quantitative relationships between bird populations and key habitat factors such as elevation, land cover type, tidal creek density and macrophytobenthos biomass, we developed an object-oriented image approach, in conjunction with Geographical Information Systems and the data from current field surveys, to analyze and assess the habitat suitability for the main types of birds, namely Anatidae, Charadriidae, Ardeidae and Laridae, at the reserve. The results from this study showed that about 40% of the total area of the Dongtan Reserve contained suitable habitats for these four bird families. The Scirpus mariqueter zone, mudflat zone, and tidal creeks were the most important habitats for these birds. This study indicated the potential of this approach for objective and effective evaluation of the species habitat suitability in a dynamic estuarine and coastal area. The implications of the results as a tool for biodiversity conservation, wetland conservation, and ecosystem management are discussed.     

Contrasting effects of ecosystem engineering by the cordgrass Spartina maritima and the sandprawn Callianassa kraussi in a marine-dominated lagoon

Ecosystem engineering by plants and animals significantly influences community structure and the physico-chemical characteristics of marine habitats. In this paper we document the contrasting effects of ecosystem engineering by the cordgrass Spartina maritima and the burrowing sandprawn Callianassa kraussi on physico-chemical characteristics, microflora, macrofaunal community structure and morphological attributes in the high shore intertidal sandflats of Langebaan Lagoon, a marine-dominated system on the west coast of South Africa. Comparisons were made at six sites in the lagoon within Spartina and Callianassa beds, and in a “bare zone” of sandflat between these two habitats that lacks both sandprawns and cordgrass. Sediments in Spartina habitats were consolidated by the root-shoot systems of the cordgrass, leading to low sediment penetrability, while sediments in beds of C. kraussi were more penetrable, primarily due to the destabilising effects of sandprawn bioturbation. Sediments in the “bare zone” had intermediate to low values of penetrability. Sediment organic content was lowest in bare zones and greatest in Spartina beds, while sediment chl-a levels were greatest on bare sand, but were progressively reduced in the Spartina and Callianassa beds. These differences among habitats induced by ecosystem engineering in turn affected the macrofauna. Community structure was different between all three habitats sampled, with species richness being surprisingly greater in Callianassa beds than either the bare zone or Spartina beds. In general, the binding of surface sediments by the root systems of Spartina favoured rigid-bodied, surface-dwelling and tube-building species, while the destabilising effect of bioturbation by C. kraussi favoured burrowing species. The contrasting effects of these ecosystem engineers suggest that they play important roles in increasing habitat heterogeneity. Importantly, the role of bioturbation by C. kraussi in enhancing macrofaunal richness was unexpected. By loosening sediments, reducing anoxia and enhancing organic content, C. kraussi may engineer these high shore habitats to ameliorate environmental stresses or increase food availability.     

Invasive Spartina alterniflora-induced factors affecting epibenthos distribution in coastal salt marsh, China

Artificially introduced cordgrass, Spartina alterniflora, rapidly colonized the intertidal flats of the Jiangsu coast, eastern China. The epibenthos on an intertidal flat invaded by S. alterniflora were studied, to identify how local epibenthos species react to an altered environment. Epibenthic samples and surficial sediment samples were collected along a shore-normal profile in 50 quadrats at ten stations across the Spartina salt marsh; and five control quadrats for a station located on the barren sandy-mud flat. The grain size parameters of the surficial sediments show that S. alterniflora altered the grain size gradient along the profile of the intertidal zone by trapping fine-grained sediments. Spartina alterniflora could inhabit lower elevations than indigenous salt marsh vegetation, thus creating larger areas of finer surficial sediments, which was suitable for not only native epibenthic species but also species which do not exist on the barren sandy-mud flat. Correlation analyses show that the epibenthos were sensitive to sediment grain size and type, on the invaded S. alterniflora salt marsh. Further, there was an interspecific relationship affecting the distribution of epibenthos. The results show that epibenthos preferred ecological niches, within the Spartina salt marsh, even in the same sampling station.     

基于水动力ROMS与BOX耦合模型的长江口及邻近水域水通量及水体交换特性

本研究将水动力模型ROMS(regional oceanic modeling system,区域海洋模式系统)与箱式(box)模型结合,详细阐述了长江口及邻近水域四个季节的水通量特征及水体交换特性。研究发现:总的水通量整体受季风控制,季风的作用在于使水体在南北方向上交替输送,而台湾暖流对春夏季底层水南向输运具有重要作用;直接进入123.5°E以东外海区域的水通量很小,而是先从南边界流出研究区域,然后通过海洋环流系统进入外海。在强烈季风下,水体更新依赖于季风方向的水平通量,主要是同层水体而不是表底层水体之间的交换。虽然水体更新时间较长的区域与缺氧区基本一致,但本研究认为该区域底层水体缺氧的本质原因是跃层阻隔了表底层水体之间的交换。     

Invading cord grass vegetation changes analyzed from Landsat-TM imageries: a case study from the Wanggang area, Jiangsu coast, eastern China

Cord grass colonization on the Jiangsu coast, eastern China, modifies the native salt marshes in terms of ecosystem structure. The Landsat TM images from 1992 to 2003 were analyzed to identify salt-marsh vegetation distribution patterns and their changes over this coastal region, in order to evaluate the effects of the spreading of the artificially introduced halophyte Spartina. Supervised classification was performed using Bands 3, 4 and 5 in conjunction with in situ training samples, to derive the distribution pattern of the vegetation in the study area. Further, in order to identify the intertidal areas with different tidal elevations, a data treatment procedure was designed to combine regional water level data using harmonic analysis with the waterlines on the TM images extracted by density slice. The results show that: (1) the Spartina alterniflora area has been expanding towards the sea rapidly since it was introduced, especially at initial stages; (2) in the upper part of the inter-tidal zone, the local marsh plant Suaeda salsa and the exotic species Spartina anglica were present only near the sea dyke, occupying only a small part of the entire salt marsh, and the area of these two species has been reduced by land reclamation; (3) there has been a trend for Spartina alterniflora to become the dominant species in the salt marshes in the study area; and (4) the elevation of Spartina alterniflora’s seaward fringe was close to mean high water on neaps, and its landward boundary was slightly higher than mean high water. The salt marsh environment of the study area has been modified rapidly by the Spartina vegetation for the last 12 years.     

Effect of native and invasive cordgrass on Macoma petalum density, growth, and isotopic signatures

Ecosystem engineers can influence community and ecosystem dynamics by controlling resources, modifying the flow of energy or biomass, or changing physical characteristics of the habitat. Invasive hybrid cordgrass (Spartina alterniflora × Spartina foliosa) is an ecosystem engineer in salt marshes in San Francisco Bay, California, U.S.A. that raises intertidal elevations and may be either increasing C₄ plant carbon input into food webs or tying up carbon in a form that is not usable by consumers. A manipulative experiment compared abundance, growth, and stable isotope (δ¹³C and δ¹⁵N) composition of the clam Macoma petalum (=M. balthica) among native marsh, hybrid Spartina, and mudflats in central San Francisco Bay. We found higher densities (individuals m⁻²) of M. petalum on mudflats compared to either native or hybrid Spartina (p < 0.001). Macoma petalum shell growth was significantly greater in mudflats than in either vegetation type in 2002 (p = 0.005) but not 2003. Differences in shell growth between native and hybrid Spartina were not significant. Stable isotope results showed differences between habitats in δ¹³C but not δ¹⁵N. Carbon signatures of M. petalum placed in Spartina were much more depleted than the isotopic signature of Spartina. Neither native nor hybrid Spartina appears to be a significant carbon source for M. petalum in San Francisco Bay, and we found no evidence that hybrid Spartina contributes carbon to M. petalum beyond what is provided by S. foliosa, despite the hybrid's much greater biomass. Our results show that loss of mudflat habitat, rather than increased input of C₄ carbon, is the greatest effect of the invasion of hybrid Spartina on M. petalum.     

Exotic species and estuaries: managing Spartina anglica in Tasmania,Australia

The spread of exotic Spartina anglica (rice grass) occurs in temperate estuaries of the USA, UK, Netherlands, France, China, New Zealand and Australia. In Australia S. anglica infestations are found in the southern States of Tasmania and Victoria. The ecological, social and economic costs associated with its continued spread in Tasmania have resulted in the development of a management program supporting eradication and control. The paper begins by outlining the suite of problems associated with the management of exotic S. anglica infestations. The legislative framework for S. anglica is then critically evaluated. Recent developments that facilitate integrated coastal zone management are presented and assessed with respect to S. anglica. The paper makes recommendations on resolving legislative and institutional responsibility, promoting sustainable development practices in the coastal zone and raising the profile of environmental and aquatic weeds such as S. anglica.     

长江口潮沼植物对动力沉积过程的影响

为探讨潮沼植物对动力沉积过程的影响,在长江口南汇东滩沼泽和邻近的光滩上进行了近底层流速、波浪、悬沙浓度、沉积物粒径和滩面淤积速率等对比实验,并在九段沙潮沼中做了两种先锋植物黏附悬沙的实验.结果表明,沼泽和同高程的邻近光滩近底层平均流速的比值为0.16～0.84;两种环境平均波周期、平均波高和平均悬沙浓度的比值分别为1.4,0.43,和0.71.波浪传入沼泽后,一方面波高大大降低,另一方面变得规则有序.海三棱草和草两种先锋植物群落黏附的悬沙分别达到298和40g/m2.由于水动力降低和植物的捕沙功能,细颗粒泥沙易于在沼泽中沉积下来,导致沼泽环境沉积物明显较相邻光滩细;沼泽中沉积速率加快,侵蚀受到抑制.     

Seasonal dynamics of the populations of intertidal harpacticoids (Harpacticoida: Copepoda) in the White Sea

In May to October 2001, seasonal variations in the population structure of four species of intertidal harpacticoids—Paraleptastacus kliei, Huntemannia jadensis, Heterolaophonte minuta, and Stenhelia palustris—were studied at three sites in the middle intertidal zone of Chernorechenskaya Bay (White Sea) with different sediment compositions. At different sites, the changes in the harpacticoid abundance, and the times and amplitudes of the peaks were different. The features of the local dynamics of the population are determined both by the intensity of its reproduction at the reproductive habitats and by the intensity of subsequent migrations. A comparison of the data available on the seasonal dynamics of the intertidal harpacticoids at various latitudes allows one to suggest that they are mainly determined by the temperature regime.     

Molluscan assemblages of seagrass-covered and bare intertidal flats on the Banc d'Arguin,Mauritania, in relation to characteristics of sediment and organic matter

The Banc d'Arguin, a non-estuarine area of shallows and intertidal flats off the tropical Saharan coast of Mauritania, is characterised by extensive intertidal and subtidal seagrass beds. We examined the characteristics of intertidal seagrass (Zostera noltii) meadows and bare areas in terms of the presence and abundance of molluscs (gastropods and bivalves). To explain observed differences between molluscan assemblages in seagrass and bare patches, some aspects of the feeding habitat (top-5 mm of the sediment) and of food (organic materials) of molluscs were examined. The novelty of this study is that phytopigments were measured and identified to assess source and level of decay (freshness) of organic material in the sediment and to study their importance as an explanatory variable for the distribution of molluscs. Over an area of 36 km² of intertidal flats, at 12 sites, paired comparisons were made between seagrass-covered and nearby bare patches. Within seagrass meadows, dry mass of living seagrass was large and amounted to 180 ±10 g AFDM m^− 2 (range 75–240). Containing twice the amount of silt per unit dry sediment mass, seagrass sediments were muddier than bare areas; the relative amount of organic material was also larger. The total number of species of bivalves and gastropods amounted to 27, 14 of which were found only in seagrass areas, 4 only in bare and 9 in both types of habitat. Among the three numerically most abundant species, the bivalves Anadara senilis, Dosinia hepatica and Loripes lacteus, the first was numerically most abundant in bare and the other two in seagrass-covered areas. Bare intertidal areas had greater mean total biomass of molluscs (80.5 g AFDM m^− 2) than seagrass meadows (30.0 g AFDM m^− 2). In both habitats, the bulk of the biomass was made up by A. senilis. Excluding this species, bare mudflats contained on average only 3.1 g AFDM m^− 2 and seagrass meadows 6.9 g AFDM m^− 2. As compared to previous surveys in 1980–1986, the biomass of A. senilis had increased almost 10-fold and D. hepatica, previously found in very small numbers, had become the most numerous species. However, the total biomass excluding that of A. senilis was similar. Concentrations of phytopigments were similar to those observed at temperate mudflats, indicating that the Banc d'Arguin might not be as oligotrophic as previously thought. Per unit of dry sediment mass, smaller amounts of phytopigments were found in bare than in seagrass areas. Per unit of dry organic material, bare sediments contained most (fresh) phytopigments. This suggests that in seagrass-covered meadows the organic material is more degraded than in bare sediments. Overall, the composition of phytopigments, quite surprisingly, indicated a benthic-diatom-dominated trophic system. Multivariate statistics revealed that patterns of zoobenthic assemblages were correlated with patterns of a combination of four environmental parameters: grain size of the sediment, amount of fresh phytopigments and amounts of leaves and roots of seagrass.     

Comparative study on the fauna composition of intertidal invertebrates between natural and artificial substrata in the northeastern coast of Jeju Island

This study was carried out to learn about differences in the sessile macrobenthic fauna communities between the artificial and natural habitats. There were some differences in terms of species composition and dominant species and community structure between two habitat types. The dominant species include Pollicipes mitella and Granuilittorina exigua in natural rocky intertidal zones; Monodonta labio confusa, Ligia exotica, Tetraclita japonica in the artificial rocky intertidal zones. Among all the species, L. exotica and T. japonica occurred only in the artificial rocky intertidal zone. The results of cluster analysis and nMDS analysis showed a distinct difference in community structure between artificial and natural rocky intertidal zones. The fauna in the natural rocky intertidal zones were similar to each other and the fauna in the artificial rocky intertidal zones were divided depending on the slope of the substratum. In the case of a sloping tetrapod, M. labio confusa and P. mitella were dominant, but at the vertical artificial seawall, Cellana nigrolineata, L. exotica T. japonica were dominant. The analysis of the species presented in natural and artificial rocky intertidal areas showed the exclusive presence of 10 species on natural rocks and 12 species on artificial rocks. The species in the natural rocky intertidal area included mobile gastropods and cnidarians (i.e. rock anemones), and the species in the artificial rocky intertidal area mostly included non-mobile attached animals. The artificial novel structure seems to contribute to increasing the heterogeneity of habitats for marine invertebrate species and an increase the species diversity in rocky coastal areas.     

Pathways of organic matter through food webs of diverse habitats in the regulated Nakdong River estuary (Korea)

The benthic macroinvertebrates of the Nakdong River estuary were sampled at three different habitats: two salt marsh (Scirpus triqueter and Phragmites australis) beds and a bare intertidal flat. Fishes were sampled in the main channel. The trophic importance of marsh vascular plants, microphytobenthos, and riverine and channel particulate organic matter to macroinvertebrate and fish production was studied using stable carbon and nitrogen isotope tracers. There was a dramatic change in coverage of macrophytes (salt marshes and seagrass) after the construction of an estuarine barrage in 1987 in the Nakdong River estuary, with the S. triqueter bed increasing, the P. australis bed decreasing, and Zostera marina habitats being nearly lost. Although the invertebrate δ¹³C were within a narrower range than those of the primary producers, the values varied considerably among consumers in these habitats. However, the isotope signatures of consumers showed similarities among different habitats. Cluster analysis based on their isotopic similarity suggested that the isotope variability among species was related more to functional feeding groups than to habitats or taxonomic groups. While δ¹³C values of suspension feeders were close to that of the channel POM (mainly phytoplankton), other benthic feeders and predators had δ¹³C similar to that of microphytobenthos. Isotopic mixing model estimates suggest that algal sources, including microphytobenthos and phytoplankton, play an important role in supporting the benthic food web. Despite the huge productivity of emergent salt marshes, the contribution of the marsh-derived organic matter to the estuarine food webs appears to be limited to some nutrition for some invertebrates just within marsh habitats, with little on the bare intertidal flats or in the channel fish communities. Isotope signatures of the channel fishes also confirm that algal sources are important in supporting fish nutrition. Our findings suggest that benthic and pelagic microalgae made a large contribution to consumer diets, while marsh plants may not have a large role in supporting food webs in this estuarine system.     

Growth dynamics of eelgrass, Zostera marina, in the intertidal zone of Seomjin Estuary, Korea

To examine the growth dynamics of eelgrass, Zostera marina, in the intertidal zone of Seomjin Estuary, Korea, we surveyed environmental factors such as water temperature, underwater irradiance, tidal exposure, and nutrient concentrations in the water column and sediment pore water in relation to the shoot density, biomass, morphological characteristics, and growth of Z. marina inhabiting the upper and lower intertidal zones. The survey was conducted monthly from January 2003 to December 2004. The water temperature of the two areas displayed seasonal fluctuations. Underwater irradiance was significantly higher in the upper intertidal zone than in the lower intertidal zone. Tidal exposure was also markedly longer in the upper intertidal zone than in the lower intertidal zone, whereas tidal exposure was highest in the spring and lowest in the summer in both areas. Water column NH₄ ⁺ and sediment pore water NO₃ ^?+NO₂ ^? concentrations were significantly higher in the upper intertidal zone than the lower intertidal zone. The eelgrass shoot density, biomass, morphology, and leaf productivity were significantly higher in the lower intertidal zone than in the upper intertidal zone. Both areas displayed a clear seasonal variation depending on changes in water temperature. However, leaf turnover time was significantly shorter in the upper intertidal zone than in the lower intertidal zone, with a higher turnover rate in the upper intertidal zone. Compared to the seagrasses in the lower intertidal zone, those in the upper intertidal zone showed more effective adaptations to the stress of long tidal exposure through downsizing and increased turnover time. These results suggest that tidal exposure, coupled with desiccation stress, can be a limiting factor for seagrass growth in the intertidal zone, along with underwater irradiance, water temperature, and nutrient availability.     

海岸圈围对雁鸭类种群及生境的影响研究——以长江口横沙东滩为例

滨海湿地是雁鸭类的重要栖息地,然而高强度的海岸圈围工程对滨海湿地生态系统和鸟类栖息地造成了显著影响,因此分析和研究海岸圈围对雁鸭类种群及栖息地的影响,对水鸟保护和滨海湿地资源可持续利用具有重要的理论和实践意义。位于长江口的横沙东滩,于2003年启动了海岸圈围促淤工程,工程的实施导致湿地生境和水鸟种群都发生着快速变化。本研究分别对2013、2015、2016和2017年,横沙东滩雁鸭类种群和生境因子的时空变化进行了调查与分析,通过拟合回归分析了两者的相关关系,探讨海岸圈围后生境的快速变化对雁鸭类种群产生的影响,从而提出海岸带圈围后水鸟栖息地的保护与管理对策。结果表明:1)海岸圈围工程的实施显著改变了滨海湿地的水鸟生境及种群特征。随着工程的推进,自然潮滩的盐沼湿地呈动态变化趋势;促淤区则随着泥沙的补给,新生了大面积的沼泽湿地;成陆区逐渐向淡水生态系统演替。伴随着生境的变化,雁鸭类种群逐渐从成陆区和自然潮滩向促淤区转移。2)不同生境类型影响雁鸭类种群数量特征的生境因子不同。未实施圈围的自然潮滩影响雁鸭类数量的主要因素是海三棱藨草/藨草群落面积;正在实施圈围的促淤区的主要影响因素是挺水植物面积、植被归一化指数(NDVI)和无植被覆盖水域面积;已圈围的成陆区主要影响因素为沉水植物面积。综上,雁鸭类偏向选择具有开阔水域、充足食物供给和相对较低植被盖度的生境类型。对于海岸圈围区域,若能合理利用圈围土地,保留部分区域为湿地,并根据水鸟的生境需求,适当营造水鸟适宜的栖息地,可在一定程度上减缓圈围工程对水鸟的影响,实现滨海湿地水鸟栖息地保护和湿地资源可持续利用的动态平衡。     

The application of cutting plus waterlogging to control Spartina alterniflora on saltmarshes in the Yangtze Estuary,China

Control and eradication of the exotic and invasive plant Spartina alterniflora within the Chongming Dongtan nature reserve, Shanghai, China, is vital for the management and conservation of the saltmarshes. A demonstration project was established using waterlogging and cutting to control this invasive species. Results from 2007 to 2008 showed that, although the managed waterlogging significantly reduced biomass and seed production of S. alterniflora at an early stage, the species subsequently showed rapid adaptation to the long-term waterlogging stress. Thus, managed waterlogging alone was insufficient for the effective eradication of S. alterniflora. However, managed waterlogging for around 3 months, combined with cutting the above-ground part of S. alterniflora at a key stage (flowering period in July), controlled and eradicated the plant successfully. Both the above-ground and below-ground parts of S. alterniflora were killed and the plants began to decompose after 3 months. Furthermore, there was no re-growth of the emergent part of S. alterniflora in the following years. However, once the impounded water was released restoring the natural hydrodynamic regime of the saltmarshes, the seeds and seedlings of S. alterniflora reinvaded the controlled site from the neighboring areas and the S. alterniflora community was re-established. Thus, after eradication of S. alterniflora, control measures should be maintained to prevent the re-establishment of S. alterniflora. The results of this demonstration project indicate a potentially useful and effective approach for the control and management of large-scale invasion by S. alterniflora on saltmarshes in the Yangtze Estuary, China.     

Environmental patchiness,litter decomposition and associated faunal patterns in a Spartina alterniflora marsh

Spartina alterniflora leaf litter bundles were placed in a North Carolina salt marsh to study the effects of environmental heterogeneity on decomposition and animal colonization. Sediment type (mud vs. sand), tidal inundation zone (near bay, mid-marsh and upper marsh) and Spartina growth form (tall vs. short) were studied. Tidal zone had the greatest effect on decomposition rate. The main effects of sediment type and growth form were not significant. All treatments affected animal distribution patterns in the leaf bundles. Nearly all common taxa were more common on mud than sand. Most taxa showed a strong association with one tidal zone. Half of the taxa were associated with one of the Spartina growth forms. Many interactions among the treatments were also significant.This study demonstrates the significance of environmental heterogeneity in a Spartina marsh both for litter decomposition and animal distributions.     

Spatial organisation of macrozoobenthic communities in response to environmental factors in a coastal lagoon of the NW African coast (Merja Zerga,Morocco)

Merja Zerga lagoon, located on the Moroccan Atlantic coast, is a site of international value (Ramsar Site) in terms of its ornithological diversity. However, the lagoon is heavily exploited for its clams and fishes. In an effort to further understanding of lagoon ecosystems, and thus to facilitate the management and conservation of their resources, an ecological survey of its benthic component was carried out. Benthos is a valuable food source for birds, fishes and humans. This work involved identifying the macrozoobenthic communities in the lagoon and assessing their spatial distribution. The study was based on monthly sampling of the intertidal zone and seasonal sampling in subtidal zone, over a one-year period. In the intertidal zone, salinity and median diameter and silt content of the sediment exhibited a gradient extending from the entrance to the inner lagoon, according to tidal flow. Sediment grain size characteristics reflected a gradual decrease of tidal currents from the lagoon entrance towards the inner parts of the lagoon, i.e. silt content increased with distance from the entrance. In the subtidal zone, the tidal currents were fairly strong throughout the lagoon, leading to the presence of coarser sediments than in the intertidal zone. Based on these physical, chemical and substratum characteristics, three communities were identified: (i) Cerastoderma edule and (ii) Scrobicularia plana communities were located in both the intertidal and subtidal zones; and (iii) a Tapes decussata community that was only found in the subtidal zone. The assemblages in the subtidal zone were more diverse and the mean abundances of the constituent species were higher than in the intertidal zone, which is an interesting feature for a lagoon environment. Communities were distributed along an ecological gradient, without showing a discontinuity or ecotone. The lagoon functioned like an estuary in which the community structure was controlled by edaphic factors in the intertidal zone, and by the hydrological factors in the subtidal zone.     

Carbon and nitrogen dynamics of the intertidal seagrass, <Emphasis Type="Italic">Zostera japonica</Emphasis>, on the southern coast of the Korean peninsula

Seagrasses require a large amount of nutrient assimilation to support high levels of production, and thus nutrient limitation for growth often occurs in seagrass habitats. Seagrasses can take up nutrients from both the water column and sediments. However, since seagrasses inhabiting in the intertidal zones are exposed to the air during low tide, the intertidal species may exhibit significantly different carbon (C) and nitrogen (N) dynamics compared to the subtidal species. To examine C and N dynamics of the intertidal seagrass, Zostera japonica, C and N content and stable isotope ratios of above- and below-ground tissues were measured monthly at the three intertidal zones in Koje Bay on the southern coast of Korea. The C and N content and stable isotope (δ¹³C and δ¹⁵N) ratios of seagrass tissues exhibited significant seasonal variations. Both leaf and rhizome C content were not significantly correlated with productivity. Leaf δ¹³C values usually exhibited negative correlations with leaf productivity. These results of tissue C content and δ¹³C values suggest that photosynthesis of Z. japonica in the study site was not limited by inorganic C supply, and sufficient inorganic C was provided from the atmosphere. The tissue N content usually exhibited negative correlations with leaf productivity except at the upper intertidal zone, suggesting that Z. japonica growth was probably limited by N availability during high growing season. In the upper intertidal zone, no correlations between leaf productivity and tissue elemental content and stable isotope ratios were observed due to the severely suppressed growth caused by strong desiccation stress.     

Invasive plants on disturbed Korean sand dunes

The sand dunes in coastal regions of South Korea are important ecosystems because of their small size, the rare species found in this habitat, and the beautiful landscapes they create. This study investigated the current vegetative status of sand dunes on three representative coasts of the Korean peninsula, and on the coasts of Cheju Island, and assessed the conditions caused by invasive plants. The relationships between the degree of invasion and 14 environmental variables were studied. Plots of sand dunes along line transects perpendicular to the coastal lines were established to estimate vegetative species coverage. TWINSPAN (Two-Way Indicator Species Analysis), CCA (Canonical Correspondence Analysis), and DCCA (Detrended Canonical Correspondence Analysis) were performed to classify communities on sand dunes and assess species composition variation. Carex kobomugi, Elymus mollis, and Vitex rotundifolia were found to be the dominant species plotted on the east, the west, and the peripheral coasts of Cheju Island, respectively. Vegetation on the south coast was totally extinct. The 19 communities, including representative C. kobomugi, C. kobomugi–Ixeris repens, C. kobomugi–Oenothera biennis, E. mollis, Lolium multiflorum–Calystegia soldanella, and V. rotundifolia–C. kobomugi, were all classified according to TWINSPAN. Oenothera biennis and L. multiflorum were exotics observed within these native communities. CCA showed that invasive native and exotic species distribution was segregated significantly, according to disturbance level, exotic species number, gravel, sand and silt contents, as well as vegetation size. It further revealed that human disturbance can strongly favor the settlement of invasive and exotic species. Restoration options to reduce exotic plants in the South Korean sand dune areas were found to be the introduction of native plant species from one sand dune into other sand dune areas, prohibition of building and the introduction of exotic soils, and conservation of surrounding sand dune areas.     

Differential response of benthic macrofauna to the formation of novel oyster reefs (Crassostrea gigas,Thunberg) on soft and rocky substrate in the intertidal of the Bay of Brest,France

When the Pacific oyster (Crassostrea gigas, Thunberg) was introduced into France for aquaculture in the mid-sixties, it was initially confined to the sites where it was farmed. Subsequent global warming most likely facilitated the establishment of wild populations throughout the French coastline. This phenomenon of spread has become so great that oyster reefs have recently appeared in sheltered estuaries, on both soft and hard substrate. The present study examined two such sites in the Bay of Brest, Brittany. It is the first to investigate the impacts of this new substrate on the biocoenosis of uncolonised intertidal habitats in France. Increased species richness and abundance of intertidal macrofauna were observed in the presence of oyster reefs on both, mud (4 and 20 fold respectively) and rock (5 fold for both). The dominance of suspension feeders in mud changed to carnivores in reefs and their underlying sediment. Calculation of biotic coefficients (BC) of the soft-bottom fauna revealed only a slight organic enrichment, and the organic and silt composition in the sediment beneath oyster reefs were not significantly different from that on bare sites. On rock, the dominance of grazers remained unchanged between bare rock and oyster reef, while reef on rock was also characterised by deposit and detritic feeders. C. gigas is suspected to cause a homogenisation of coastal habitats with an impoverishment of overall quality but we detected only 11 common species between reefs on mud (60 species) and those on rock (55 species).