Direct evidence of imbalanced seagrass (Posidonia oceanica) shoot population dynamics in the Spanish Mediterranean     

Núria Marbà  Carlos M. Duarte  Elena Díaz-Almela  Jorge Terrados  Elvira Álvarez  Regino Martínez  Rocío Santiago  Esperança Gacia  Antoni M. Grau 《Estuaries and Coasts》2005,28(1):53-62

Direct census of shoots tagged in permanent plots was used to assess the present (2000–2002)Posidonia oceanica population dynamics in 25 meadows along the Spanish Mediterranean Coast. Shoot density ranged from 154±8 to 1,551±454 shoots m⁻², absolute shoot mortality from 5±0 to 249±53 shoots m⁻² yr⁻¹, and absolute shoot recruitment from <5 ±1 to 62±42 shoots m⁻²yr⁻¹. Specific shoot mortality and recruitment rates, which are mathematically and statistically (p>0.05) independent of shoot density, varied from 0.015±0.006 to 0.282±0.138 yr⁻¹ and 0.018±0.005 to 0.302±0.093 yr⁻¹, respectively. Absolute shoot mortality rate was scaled to shoot density (Pearson correlation, r=0.78, p<0.0001), and variability in specific shoot recruitment rate was partially due to differences in the percentage of growing apexes, which produce most of the recruits within the population (Pearson correlation, r=0.50, p<0.001), demonstrating the existence of structural constraints on shoot demography. Shoot half-life was estimated to range from 2.5 to 60.4 yr and meadow turnover times between 6.7 yr and more than a century, provided current estimates of shoot mortality, recruitment rates, and density remain uniform. There were differences in shoot mortality and recruitment at the regional scale, with the meadows developing along the coast of the Spanish mainland experiencing the highest shoot mortality (Tukey test, p<0.05) and tending to exhibit the highest shoot recruitment. The low shoot recruitment did not balance shoot mortality in most (60%) of the meadows, showing a prevalence of declining populations among the 25 meadows studied (Wilcoxon ranked sign test, p<0.0005). This study demonstrates the power of direct census of seagrass shoots in permanent plots to evaluate the present status of seagrass meadows, to detect on-going population decline, and to provide some insight onto the possible factors involved. The incorporation of direct census of seagrass meadows to monitoring programs will help provide the early-warning signals necessary to support management decisions to conserve seagrass meadows.  相似文献   

Deep colour–magnitude diagrams of LMC field stars imaged with HST     

R. Castro  B.X. Santiago  G.F. Gilmore  S. Beaulieu  R.A. Johnson 《Monthly notices of the Royal Astronomical Society》2001,326(1):333-341

We present deep photometry ( V ≲26) in V and I bands obtained with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope for 7 fields ∼5° away from the Large Magellanic Cloud centre. The fields contain, typically, 2000 stars each. Isochrones were fitted to the colour–magnitude diagrams in order to identify different star populations in these fields. An old population ( τ >10 Gyr) has been found in all fields. Some events of enhanced star formation, with ages between 2 and 4 Gyr, were identified in the fields localized in the north to north-west regions. Luminosity functions of low-mass stars were also obtained for all fields. Kolmogorov Smirnov test results suggest differences smaller than 30 per cent in the mixture of stellar populations contributing to the fields. Finally, density profiles were derived for old and intermediate-age stars. The former shows a slightly steeper decline than the latter.  相似文献   

安第斯山脉中段的地质过程和冷生作用(英文)     

Santiago A. Grosso 《冰川冻土》1992,(4)

本文描述了安第斯山脉中段南纬35°,西经70°附近面积为370km~2的一个地区的地质情况和冻土情况。附有地质图、冻土图及露头-碎屑分布图。文中探讨了不同地质条件下的冻融作用及多年冻结效应。岛状多年冻土分布下界处在海拔3000m,这与安第斯山脉纬度较低地区的纬度-高度梯度相符。在5个地点发现了大型的古山坡堆积物,这些堆积物可能是由融冻泥流作用、碎石流和滑坡所形成的。在实验室内将不同种类的岩块在饱水条件下进行了250次冻融循环试验。根据以下4个方面来考虑这些岩类的野外地质冻融敏感性指标(FGFSC):1)露头指数(％);2)地貌情况;3)冻融过程的次数以及4)实验室冷生破碎情况。用这一指标解释各类岩石山地的高度规律。  相似文献   

Age and growth of redfish (Sebastes marinus, S. mentella, and S. fasciatus) on the Flemish Cap (Northwest Atlantic)     

Saborido-Rey  Fran; Garabana  Dolores; Cervino  Santiago 《ICES Journal of Marine Science》2004,61(2):231-242

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Post-processing of sequential indicator simulation realizations for modeling geologic bodies     

Jorge Kazuo Yamamoto  Paulo Milton Barbosa Landim  Antonio Tadashi Kikuda  Claudio Benedito Baptista Leite  Santiago Diaz Lopez 《Computational Geosciences》2015,19(1):257-266

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Monte Carlo simulations of the disc white dwarf population     

Enrique García-Berro  Santiago Torres  Jordi Isern  Andreas Burkert 《Monthly notices of the Royal Astronomical Society》1999,302(1):173-188

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Late Glacial to Early Holocene environmental adjustment in the Mediterranean semi-arid zone of the Salines playa-lake (Alacant, Spain)     

S. Giralt  F. Burjachs  J.R. Roca  R. Julia 《Journal of Paleolimnology》1999,21(4):449-460

The transition from the Late Glacial to the Early Holocene in the endorheic Salines sequence, which is characterized cyclical sedimentation, occurs between 5.50 and 2.85 m depth. From 5.50-3.50 m depth the cycles are composed of a centimetre alternation of layers of dolomitic marls and gypsarenites and from 3.50-2.85 m depth by the alternation of calcitic marls and calcarenites.Pollen, biotic assemblages and geochemistry provide evidence of a gap with respect to the new hydrological conditions that characterized the beginning of the Holocene. Mesic pollen taxa increased their percentages at the beginning of the Holocene, indicating climate improvement, which coincides with the 14C radiocarbon age of 10,000 years BP. The first biotic remains (gastropods, ostracods and foraminifers) found in this sequence appeared later, at 3.80 m depth, which corresponds to 9,500 years BP, whereas the mineralogical change occurred at 3.50 m depth, which corresponds to 9,000 years BP. The advanced adaptation of the vegetation and biotic aquatic assemblages with respect to the mineralogical response corresponds to a process of a gradual increase in water availability into the lacustrine system. During the Boreal, the calcitic cycles reached their maximum thickness, suggesting a more continuous water input. This assumption has also been corroborated by the expansion of the mesic pollen taxa and the occurrence of biota taxa which depend on a permanent water body for their development.The multiproxy approach in paleoclimate scenarios is an essential tool for understanding the ecosystem adjustment during climate changes. Our results demonstrate an interval of 1000 years between the vegetal and the mineralogical reaction.  相似文献   

Benthic input rates predict seagrass (Posidonia oceanica) fish farm-induced decline     

Díaz-Almela E  Marbà N  Alvarez E  Santiago R  Holmer M  Grau A  Mirto S  Danovaro R  Petrou A  Argyrou M  Karakassis I  Duarte CM 《Marine pollution bulletin》2008,56(7):1332-1342

Fish farms represent a growing source of anthropogenic disturbance to benthic communities, and efficient predictors of such impacts are urgently needed. We explored the effects of fish farm benthic organic and nutrient inputs on the population dynamics of a key seagrass species (Posidonia oceanica) in four Mediterranean deep meadows adjacent to sea bream and sea bass farms. We performed two annual plant censuses on permanent plots at increasing distance from farms and measured benthic sedimentation rates around plots. High shoot mortality rates were recorded near the cages, up to 20 times greater than at control sites. Recruitment rates increased in variability but could not compensate mortality, leading to rapid seagrass decline within the first 100 m from cages. Seagrass mortality increased with total sedimentation rates (K=0.55, p<0.0002), and with organic matter (K=0.50, p=0.001), total nitrogen (K=0.46, p=0.002) and total phosphorus (K=0.56, p<3.10(-5)) inputs. P. oceanica decline accelerated above a phosphorus loading threshold of 50mg m(-2)day(-1). Phosphorus benthic sedimentation rate seems a powerful predictor of seagrass mortality from fish farming. Coupling direct measurements of benthic sedimentation rates with dynamics of key benthic species is proposed as an efficient strategy to predict fish farm impacts to benthic communities.  相似文献   

Content analysis of dam break studies for tailings dams with high damage potential in the Quadrilátero Ferrífero,Minas Gerais: technical weaknesses and proposals for improvements     

de Paiva  Camilla Adriane  da Fonseca Santiago  Aníbal  do Prado Filho  José Francisco 《Natural Hazards》2020,104(2):1141-1156

Natural Hazards - Tailings dams are civil structures that have an intrinsic potential risk of failure that, if poorly managed or neglected, can lead to severe societal, environmental, and economic...  相似文献   

Virtual globes for UAV-based data integration: Sputnik GIS and Google Earth™ applications     

Marcos Arza-García  Mariluz Gil-Docampo  Juan Ortiz-Sanz  Santiago Martínez-Rodríguez 《International Journal of Digital Earth》2019,12(5):583-593

The integration of local measurements and monitoring via global-scale Earth observations has become a new challenge in digital Earth science. The increasing accessibility and ease of use of virtual globes (VGs) represent primary advantages of this integration, and the digital Earth scientific community has adopted this technology as one of the main methods for disseminating the results of scientific studies. In this study, the best VG software for the dissemination and analysis of high-resolution UAV (Unmanned Aerial Vehicle) data is identified for global and continuous geographic scope support. The VGs Google Earth and Sputnik Geographic Information System (GIS) are selected and compared for this purpose. Google Earth is a free platform and one of the most widely used VGs, and one of its best features its ability to provide users with quality visual results. The proprietary software Sputnik GIS more closely approximates the analytical capacity of a traditional GIS and provides outstanding advantages, such as DEM overlapping and visualization for its dissemination.  相似文献