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821.
822.
The structure and composition of subtidal rocky seaweed assemblages were studied at 69 sites on the Canary Islands (northeastern Atlantic). This group of islands are situated at the southern boundary of the warm temperate region and adjacent to the cold waters from the northwest African coastal upwelling, which creates a difference of almost 2 °C in surface seawater temperature from the eastern to the western islands. This thermal variation allows an examination of the transition between the warm temperate and the tropical regions along this longitudinal gradient together with the hypothesised Fucales-dominated assemblages towards the eastern islands in contrast to the Dictyotales-dominated assemblages towards the western ones. Environmental and biological parameters were considered in order to investigate which were the main factors explaining spatial variation along the gradient in a multi-scaled approach. Although seventy-nine macroalgae were identified, 87.63% of the total mean cover was due to six taxa (Lobophora variegata, nongeniculate corallines, Canistrocarpus cervicornis, Jania adhaerens, Cystoseira abies-marina and Pseudolithoderma adriaticum). At a large scale, sea urchin density explained the highest variation in seaweed assemblages (26.94%), and its pattern of distribution across the islands. The expected pattern of distribution according to the upwelling distance only occurred in restricted areas of the Canarian Archipelago in absence of herbivore pressure and habitat degradation. Spatial variations within islands (medium scale) were mainly related to wave exposure, while at a small scale these were mostly due to the degree of sedimentation. 相似文献
823.
热带西太平洋海域上层海洋热含量的CSEOF分析 总被引:4,自引:0,他引:4
基于月平均Argo温、盐度剖面、纬向风和Ni o3.4指数等资料,利用循环平稳经验正交函数(CSEOF)分解法、最大熵谱分析和相关分析等方法,研究了热带西太平洋海域上层(0—700m)海洋热含量的时空变化特征,并探讨了其年际变化的可能原因。结果表明,热带西太平洋海域上层海洋热含量距平场具有显著的东-西向反位相振荡,且这种振荡除了具有较明显的季节变化外,还存在着较强的准2a振荡。此外,热含量距平场还存在着负-正-负的三极式经向模态,该模态除了具有明显的季节变化外,还存在着显著的准4a振荡。进一步分析表明,热含量的准2a振荡与ENSO事件的发生有着非常密切的联系,并对赤道西太平洋纬向风异常有1—2月的滞后响应。 相似文献
824.
基于高空间分辨率的红树林卫星遥感监测技术进展 总被引:1,自引:0,他引:1
卫星遥感技术是红树林生态系统监测的重要手段。文章系统地总结了红树林的光谱特征,给出了目前应用于红树林生态监测的高空间分辨率卫星包括IRS-P6、SPOT-5、IKONOS、OrbView-3、QuickBird的主要技术参数以及它们在红树林遥感监测中的应用程度,叙述了目视解译法、波段组合法、图像分类法、专家分类法、模糊分类法和面向对象分类法等遥感监测技术方法在红树林的生态参数包括类外区分和类内区分、生物量和健康状况等的遥感提取的应用和精度对比情况。另外,对应用高分辨率卫星遥感资料监测红树林的技术发展趋势进行了讨论。 相似文献
825.
826.
通过分析2005年-2010年北塘口及其邻近海域水环境现场调查资料,同时结合历史数据进行对比,结果表明:(1)北塘口河口水体中COD和BOD5超标严重,整体污染态势以2008年为界呈现先降低后升高的趋势;邻近海域水体中无机氮为最主要污染物,其中硝酸盐是无机氮中最主要组成部分,但丰水期时亚硝酸盐氮和枯水期时铵盐氮所占比例逐年升高,说明区域水体氧化还原环境的潜在变化;N/P比值远高于正常的Redfield 16比值表明,区域水体已处于潜在严重P限制状态,同时,区域严重富营养化状态也极易诱导区域赤潮爆发;(2)丰水期陆源无机氮大量输入,使区域水体大部分时间超该区域功能区划要求的Ⅳ类海水水质标准,但底质沉积物环境相对比较稳定,各监测项目全部符合一类海洋沉积物质量标准要求;(3)丰水期和枯水期时,活性磷酸盐含量1983年-1998年分别增加了16.6倍和17.2倍,1998年-2010年由于监控措施的加强,极大地降低了P排放,丰水期和枯水期时活性磷酸盐含量最大增幅分别降到了5.84倍和2.33倍,无机氮含量增幅也呈现明显减小趋势,1983年-1998年丰水期和枯水期分别增加了8.37倍和13.7倍,而1998年-2010年丰水期和枯水期最大增幅也仅为3.52倍和3.28倍;整体看来水质和底质环境有缓和趋势,但潜在威胁仍然严重. 相似文献
827.
828.
Miriam J. Doyle Kathryn L. Mier Morgan S. Busby Richard D. Brodeur 《Progress in Oceanography》2002,53(2-4)
The coastal regions of the northeast Pacific support large, economically valuable fishery resources and provide nursery areas for many fish species. Over the last few decades, there have been dramatic shifts in species abundance and composition in this area. In this paper, we examine the springtime spatial patterns in the ichthyoplankton of three oceanographically different regions, the Southeast Bering Sea, the Gulf of Alaska and the U.S. West Coast. The data examined are a subset of a larger database (comprising data from cruises conducted from 1972 to 1997) that is being used to investigate spatial, seasonal and interannual patterns in ichthyoplankton of the northeast Pacific in relation to environmental conditions. Ichthyoplankton were collected during seven cruises using 60-cm bongo nets. Spatial patterns of ichthyoplankton were examined using both classification and ordination techniques. Relative Bray-Curtis dissimilarity coefficients calculated from the log10 (n+1) of abundance data were used as input to the numerical classification of species and stations. Nonmetric multidimensional scaling was also applied to the abundance data to examine geometric patterns in the data. The numerical analyses of the species abundance data sets for each cruise revealed spatial patterns in the ichthyoplankton that suggest the occurrence of geographically distinct assemblages of fish larvae in each region. For all three sampling regions, the assemblage structure is primarily related to bathymetry, and Shelf, Slope, and Deep-Water assemblages are described. This shallow to deep-water gradient in species occurrence and abundance reflects the habitat preference and spawning location of the adult fish. Another degree of complexity is superimposed on this primary assemblage structure in each region and seems to be related to local topography and the prevailing current patterns. The patterns in ichthyoplankton assemblages of the three regions in the northeast Pacific Ocean described here form the basis for future investigations of spatial and temporal patterns in the ichthyoplankton of the subarctic Pacific.Regional Index Terms: Northeast Pacific Ocean, Southeast Bering Sea, Gulf of Alaska, U.S. West Coast. 相似文献
829.
830.