Reassessing the invasion of South African waters by the European shore-crab Carcinus maenas     

CA Mabin  JRU Wilson  JJ Le Roux 《African Journal of Marine Science》2017,39(3):259-267

The European shore-crab Carcinus maenas has been present in South Africa since 1983. Despite this species’ international reputation as a biological invader, its distribution in this region has only been considered by three outdated ‘snapshot surveys.’ The present study is the most comprehensive to date, providing an update on the species’ range and the first temporal assessment of its abundance and demographics. Along South Africa's Cape Peninsula and surrounding areas, C. maenas was absent from 12 intertidal sites surveyed, except for Sea Point, and no crabs were found during subtidal surveys along the open coastline. Subtidal harbour populations were recorded in the Cape Town harbours of Table Bay and Hout Bay (previously estimated as comprising approximately 164 200 and 6 500 individuals, respectively). Table Bay was surveyed monthly for one year, using baited traps, crab condos and postlarvae settlement collectors, to assess size distributions and reproductive seasonality of the crab. Reproductive females were recorded throughout most of the year. These results suggest that the harbour populations could be targeted by control programmes, but provide no strong evidence to support the initiation of management action during a particular season. The lack of detection of postlarval settlement, even among well-established populations, suggests this will not be a useful monitoring tool for detecting incursions.  相似文献   

阿尔泰生态功能区植被的周期性变化及影响因素分析     

李春娥 《测绘与空间地理信息》2022,45(1):95-99,107

针对植被与气候因子的分析多从研究区总体出发、缺少地域差异化研究的问题,本文提出了在不同地貌、坡度和植被类型区域进行植被覆盖度的时空分布特征及其影响因子分析研究的方法.该方法实现了植被在不同地理环境、不同植被类型中对气候因子响应机制的差异化研究.结果表明:1)植被覆盖度在平原和丘陵、坡度小于2°和大于15°区域递增趋势较...  相似文献   

Three-dimensional circulation in northern South China Sea during early summer of 2015     

Huiqun Wang  Yaochu Yuan  Weibing Guan  Chenghao Yang  Dongfeng Xu 《海洋学报(英文版)》2021,40(7):1-2

Using the hydrographic data obtained during two nearly simultaneous surveys in June 2015, we carried out semidiagnostic calculations with the help of a finite element model and a modified inverse method, to study the circulation in the northern South China Sea(NSCS) during the early summer of 2015. A number of new circulation features were found.(1) In most of the observation region, a large, basin-scale anticyclonic gyre appeared south of the 50-m isobath, which contained anticyclonic eddies. One anticyclonic eddy existed from the sea surface to 50-m depth, whose center showed no tilt, while the center of another eddy tilted eastward from the sea surface to 500-m depth. In the eastern part of the observation region, which is west of the Dongsha Islands, there was a sub-basinscale cyclonic gyre containing a cyclonic eddy whose center tilted southward from the sea surface to 200-m depth.(2) There was a cross-continental slope current(CCSC) in the area southwest of the Dongsha Islands. Its volume transport was about 2.0×10~6 m~3/s.(3) From the estimated order of magnitude of the stream function equation, the joint effect term of the baroclinity and relief(JEBAR) and β-effect term are two important dynamic mechanisms affecting the variation of the circulation in the NSCS.(4) The JEBAR, as a transport-generating term, resulted in the dynamic mechanism determining the pattern of the depth-averaged flow across the contours of potential vorticity fH~(–1). Furthermore, we show that the negative values of the JEBAR were the most dominant dynamic mechanism, causing the CCSC southwest of the Dongsha Islands to deflect from the isobaths and veer toward the deep water. The CCSC around the Dongsha Islands was located further southwest during the early summer of2015 than during the fall of 2005(revealed by a published study), which suggests that the location of the CCSC around the Dongsha Islands may vary with season.  相似文献   

Seasonality of Competition in Early Development of Subtidal Encrusting Communities   总被引：2，自引：0，他引：2  

Ben C. Maughan  & David K. A. Barnes 《Marine Ecology》2000,21(3-4):205-220

Abstract. Settlement panels immersed at Lough Hyne, County Cork, Ireland, at six stations with widely different flow regimes were retrieved at monthly intervals. Between 40 and 62 taxa were identified at each station during the study period. Percentage cover, number of interactions and number of recruits were recorded. Space occupied was found to vary more than 2.5 orders of magnitude between stations and seasons (0.3 – 82 %). Competition for space was most intense during summer, when recruitment was highest. More than 3600 interactions between pairs of species were recorded and competitive matrices are presented for the two stations with the most interactions. Both number of interactions and % cover were significantly higher at sites with greater water flow. The nature and the degree of competition varied between sites, with the most intense competition occurring in the very high flow sites with a large proportion of intra­specific encounters. Colonial species were more evident at the sites with high flow. Certain solitary species (notably Anomia ephippium and Pomatoceros spp.) were successful competitors in encounters with cheilostomatid bryozoans. Solitary species may prevent space monopolisation by the faster-growing bryozoans. 'Typical' early successional species, notably bryozoans such as Celleporella hyalina and Microporella ciliata, were more abundant at the more disturbed sites, implying either a larger adult population and/or preferential settlement of these species at such sites.  相似文献   

How much variation in land surface phenology can climate oscillation modes explain at the scale of mountain pastures in Kyrgyzstan?     

《International Journal of Applied Earth Observation and Geoinformation》2020

Climate oscillation modes can shape weather across the globe due to atmospheric teleconnections. We built on the findings of a recent study to assess whether the impacts of teleconnections are detectable and significant in the early season dynamics of highland pastures across five rayons in Kyrgyzstan. Specifically, since land surface phenology (LSP) has already shown to be influenced by snow cover seasonality and terrain, we investigated here how much more explanatory and predictive power information about climatic oscillation modes might add to explain variation in LSP. We focused on seasonal values of five climate oscillation indices that influence vegetation dynamics in Central Asia. We characterized the phenology in highland pastures with metrics derived from LSP modeling using Landsat NDVI time series together with MODIS land surface temperature (LST) data: Peak Height (PH), the maximum modeled NDVI and Thermal Time to Peak (TTP), the quantity of accumulated growing degree-days based on LST required to reach PH. Next, we calculated two metrics of snow cover seasonality from MODIS snow cover composites: last date of snow (LDoS), and the number of snow covered dates (SCD). For terrain features, we derived elevation, slope, and TRASP index as linearization of aspect. First, we used Spearman’s rank correlation to assess the geographical differentiation of land surface phenology metrics responses to environmental variables. PH showed weak correlations with TTP (positive in western but negative in eastern rayons), and moderate relationships with LDoS and SCD only in one northeastern rayon. Slope was weakly related to PH, while TRASP showed a consistent moderate negative correlation with PH. A significant but weak negative correlation was found between PH and SCAND JJA, and a significant weak positive correlation with MEI MAM. TTP showed consistently strong negative relationships with LDoS, SCD, and elevation. Very weak positive correlations with TTP were found for EAWR DJF, AMO DJF, and MEI DJF in western rayons only. Second, we used Partial Least Squares regression to investigate the role of oscillation modes altogether. PLS modelling of TTP showed that thermal time accumulation could be explained mostly by elevation and snow cover metrics, leading to reduced models explaining 55 to 70% of observed variation in TTP. Variable selection indicated that NAO JJA, AMO JJA and SCAND MAM had significant relationships with TTP, but their input of predictive power was neglible. PLS models were able to explain up to 29% of variability in PH. SCAND JJA and MEI MAM were shown to be significant predictors, but adding them into models did not influence modeling performance. We concluded the impacts of climate oscillation anomalies were not detectable or significant in mountain pastures using LSP metrics at fine spatial resolution. Rather, at a 30 m resolution, the indirect effects of seasonal climatic oscillations are overridden by terrain influences (mostly elevation) and snow cover timing. Whether climate oscillation mode indices can provide some new and useful information about growing season conditions remains a provocative question, particularly in light of the multiple environmental challenges facing the agropastoralism livelihood in montane Central Asia.  相似文献   

Short‐term dynamics in fish assemblage structure on a sheltered sandy beach in Guanabara Bay,Southeastern Brazil     

Ruan Managna Vasconcellos  Francisco Gerson Araújo  Joaquim Neto De Sousa Santos  Márcio De Araújo Silva 《Marine Ecology》2010,31(3):506-519

Short‐term dynamics in juvenile fish assemblage structure were studied to test whether the most abundant species show temporal segregation, in order to assess whether selected environmental variables could predict species groupings, and to examine the stability of sunset–day–sunrise–night differences. Samplings were collected at 3‐h intervals over 48 h on a seasonal basis between spring 2005 and winter 2006. Fish species richness and abundance were higher in spring, and the lowest values occurred in winter. Harengula clupeola occurred mainly in spring, whereas Atherinella brasiliensis peaked in summer and autumn. On the other hand, Trachinotus carolinus, Umbrina coroides and Mugil liza were abundant in winter. Although temperature, salinity and dissolved oxygen were not found to have a strong effect on the abundance patterns of most species, they did appear to have a significant influence on assemblage groupings, according to canonical correspondence analysis and Spearman rank correlation. There is no consistency of diel usage patterns by a given species across seasons. The relative abundance differed between the time of day, which differed among the seasons; this further complicates an understanding of the dynamics of an assemblage. Studies of diel changes that pooled the sampling period as day or night can miss important changes that occur in a short time scale, such as a 3‐h period.  相似文献   

An ontology-based framework for extracting spatio-temporal influenza data using Twitter     

Udaya K. Jayawardhana 《International Journal of Digital Earth》2019,12(1):2-24

Early detection of influenza outbreaks is one of the key priorities on a national level for preparedness and planning. This study presents the design and implementation of Fluwitter, which is a spatio-temporal web-based prototype framework for pseudo real-time detection of influenza outbreaks from Twitter. Specifically, the framework integrates PostgreSQL database server with PostGIS spatial extension, Twitter streaming client, pre-processor, tagger and similarity calculator for semantic information extraction (IE). The IE of tagged terms is supported by Natural Language Processing (NLP) techniques, DBpediaSpotlight and WordNet Similarity for Java (WS4J), while data analytics, visualization, and mapping are supported by GeoServer and other GIS Free Open Source Software (FOSS). The prototype was calibrated to maximize detection of influenza using rules developed from ontology-based semantic similarity scores. The Twitter-generated influenza cases were validated by weekly hospitalization records issued by Ohio Department of Health (ODH). The optimized rule produced a final F-measure value of 0.72 and accuracy (ACC) value of 94.4%. The validation suggested the existence of moderate correlations for the beginning of the time period Southeast region (r?=?0.52), the Northwestern region (r?=?0.38), and the Central region (r?=?0.33) and weak correlations for the entire time period. The potential strengths and benefits of the prototype are shown through spatio-temporal assessment and visualization of influenza potential in Ohio.  相似文献   

长江水下三角洲现代沉积速率厘定的新途径:季节性Bio-Si记录     

范德江  齐红艳  孙晓霞  郭志刚  杨作升 《中国海洋大学学报(自然科学版)》2009,39(5)

长江水下三角洲沉积层中高分辨生物硅(Bio-Si)曲线具有明显的波动规律,记录了该区硅藻生物量的季节性差异,据此对近14年来的沉积速率进行了估算。在1992～2005年里,该处沉积速率变化于1.2～3.4 cm/a之间,平均沉积速率2.1 cm/a,沉积速率与长江入海沙量具有较好的对应关系。研究结果表明长江水下三角洲Bio-Si沉积记录类似于季节性湖泊中的"年纹",可作为沉积速率估算的新指标。  相似文献   

Increasing discharge from the Mackenzie River system to the Arctic Ocean          下载免费PDF全文

Stewart B. Rood  Sobadini Kaluthota  Laurens J. Philipsen  Neil J. Rood  Karen P. Zanewich 《水文研究》2017,31(1):150-160

The Mackenzie River, Canada's longest and largest river system, provides the greatest Western Hemisphere discharge to the Arctic Ocean. Recent reports of declining flows have prompted concern because (1) this influences Arctic Ocean salinity, stratification and polar ice; (2) a major tributary, the Peace River, has large hydroelectric projects, and further dams are proposed; and (3) the system includes the extensive and biodiverse Peace–Athabasca, Slave and Mackenzie deltas. To assess hydrological trends over the past century that could reflect climate change, we analysed historic patterns of river discharges. We expanded the data series by infilling for short gaps, calculating annual discharges from early summer‐only records (typical r² > 0.9), coordinating data from sequential hydrometric gauges (requiring r² > 0.8) and advancing the data to 2013. For trend detection, Pearson correlation provided similar outcomes to non‐parametric Kendall's τ and Spearman's ρ tests. There was no overall pattern for annual flows of the most southerly Athabasca River (1913–2013), while the adjacent, regulated Peace River displayed increasing flows (1916–2013, p < 0.05). These rivers combine to form the Slave River, which did not display an overall trend (1917–2013). The more northerly, free‐flowing Liard River is the largest tributary and displayed increasing annual flows (1944–2013, p < 0.01, ~3.5% per decade) because of increasing winter, spring, and summer flows, and annual maximum and minimum flows also increased. Following from the tributary contributions, the Mackenzie River flows gradually increased (Fort Simpson 1939–2013, p < 0.05, ~1.5% per decade), but the interannual patterns for the Liard and other rivers were correlated with the Pacific Decadal Oscillation, complicating the pattern. This conclusion of increasing river flows to the Arctic Ocean contrasts with some prior reports, based on shorter time series. The observed flow increase is consistent with increasing discharges of the large Eurasian Arctic drainages, suggesting a common northern response to climate change. Analyses of historic trends are strengthened with lengthening records, and with the Pacific Decadal Oscillation influence, we recommend century‐long records for northern rivers. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Geostatistical study of annual and seasonal mean rainfall patterns in southwest Saudi Arabia / Distribution géostatistique de la pluie moyenne annuelle et saisonnière dans le Sud-Ouest de l’Arabie Saoudite     

《水文科学杂志》2013,58(5)

  相似文献