Welcome mats? The role of seagrass meadow structure in controlling post-settlement survival in a keystone sea-urchin species

Processes acting on the early-life histories of marine organisms can have important consequences for the structuring of benthic communities. In particular, the degree of coupling between larval supply and adult abundances can wield considerable influence on the strength of trophic interactions in the ecosystem. These processes have been relatively well described in rocky systems and soft-sediment communities, and it is clear that they are governed by very different bottlenecks. Seagrass meadows make interesting study systems because they bear structural affinities to both soft sediments as well as rocky substrates. We examined the early-life history of Paracentrotus lividus, one of the dominant herbivores in Mediterranean seagrass meadows, to identify the drivers of population dynamics in this species. We measured spatial and temporal variability in sea urchin post-settlement in 10 Posidonia oceanica meadows in the North-Western Mediterranean over a period of two years, and compared the numbers with the one-year old cohort a year later (i.e. the new population recruitment) as well as between successive size–age groups. Urchin post-settlers differed substantially between meadows but were present in both years in all meadows surveyed, suggesting that larval supply was not limiting for any of the studied sites. However, in six of the studied meadows, the one-year cohort of urchins was absent in both years, indicating that post-settlement processes strongly affected urchins in these meadows. In contrast, in four of the studied meadows, there was a strong coupling between post-settlers and one-year cohort individuals. These meadows were structurally different from the others in that they were characterised by an exposed matrix of rhizomes forming a dense seagrass mat. This mat apparently strongly mediates post-settlement mortality, and its presence or absence dictates the successful establishment of urchin populations in seagrass meadows. As the population aged, the relationship between size–age groups decreased evidencing the action of other processes. Yet, these results indicate that differences in physical structure are a vital bottleneck for sea urchin populations in seagrass meadows. Exploring the interaction between ecosystem structure and early-life history may provide a broader and more unified framework to understand the dynamics of a range of benthic habitats, including rocky substrates, soft sediments and seagrass meadows.     

Distribution of soft-bottom polychaetes in two coastal areas of the Tyrrhenian Sea (Italy): Structural analysis

Multidimensional statistical analysis was used to study the polychaete distribution in soft-bottoms of two coastal areas of the Tyrrhenian Sea (Italy), which are influenced by the discharges of the rivers Tiber and Ombrone. In both areas the distributional patterns of these organisms are determined mainly by sediment types and related factors such as hydrodynamics, river input, and sedimentation. The grain-size gradient from the coast to the open sea affects not only species composition, but also species richness, diversity and abundance.In both areas three main communities have been identified: a sandy biocoenosis, a mixed-sediment biocoenosis and a muddy biocoenosis. The sandy coastal community is characterized by only a few species, while the intermediate zone of sandy-mud sediments presents the highest species richness and diversity. At the mouth of the River Tiber the influence of the river is more evident than at the mouth of the River Ombrone. This is due to the Tiber's greater river flow, which determines an environmental uniformity and a ‘cenotic continuum’ from sandy to muddy communities. This does not occur at the mouth of the Ombrone, where the river flow is less important and the polychaete communities are better defined.     

浙江主要气象灾害概述

气象灾害每年都有,只是轻重程度不同。就全国和全省范围来说,很少有真正风调雨顺的年份。本文根据1951～1988年38年的气象历史资料及有关政府部门的材料、简报、报道,统计出台风、洪涝、海上大风和强对流等几种主要气象灾害对浙江经济造成损失和伤亡人数。文中对主要气象灾害的特点、一般规律和灾情作了概述,并列出一些典型实例,提出了预防气象灾害的意见。     

北太平洋风海流季节变化的数值模拟

用绝热表层风海流模式,以1949～1979年COADS资料,研究北太平洋表层风海流及相应水位场随季节变化的特点、某些特定年表层风海流的异常。模式采用二次动量守恒的有限差分方法,保证了计算稳定性。在数值积分中考虑了陆界、水界条件和近岸地形对风海流及水位场的影响。计算表明:模式反映了北太平洋主要流系的季节变化规律,能较敏感地反映上层海洋对大气动力作用的响应。给出了北太平洋主要流系的强弱与黑潮大弯曲的对应关系。     

南海輓近海平面变化与构造升降初步研究

揭示南海輓近海平面变动和古岸线诸多遗迹,探讨晚更新世以来海平面变化一般规律,初步分析南海周缘中全新世和现代地壳构造升降速率,得出本区海平面上升率适中参考值为0.10—2.0mm/a,初步估算未来50年内海平面变化趋势在1.26—4.0mm/a之间;而构造升降受块断差异运动控制,一般规律是南海北部沿岸自东向西递减,由福建南部1.15mm/a至海南岛南部0.54mm/a。近代地壳形变资料亦证实这种变化规律。     

Mussel Periostracum from Deep-Sea Redox Communities as a Microbial Habitat: 3. Secondary Inhabitants

Abstract. Vacated microborings in periostracum of live mussels of the Florida Escarpment redox community (depth of 3266 m) become a habitat for a prolific secondary microbiota consisting of a variety of prokaryotic and a few eukaryotic organisms. Periostracum surface is also colonized by diverse microorganisms, dominated by presumed chemolithotrophic bacteria with stacks of intracellular lamellae. Unlike sheltered microflora within borings, the surface community is heavily grazed upon by numerous archaeogastropods and ciliates.     

Interaction between trench retreat and Anatolian escape as recorded by neogene basins in the northern Aegean Sea

The evolution of the North Aegean Sea is studied through the development of three deep basins: the North Aegean Trough, the North Skyros Basin and the Ikaria Basin. Bathymetric data, a 2D seismic dataset and the well-investigated stratigraphic records of the onshore deep basins of northern Greece and Western Turkey were used to make structural and seismic stratigraphic interpretations. The study area shows two sharp unconformities that correspond to the Eocene-Oligocene transition and the Miocene-Pliocene shift. These discontinuities were used as marker horizons for a more detailed structural and seismic stratigraphic interpretation resulting in the identification of several seismic units. A general seismic signature chart was established using onshore basin stratigraphy and well data, which was then used to constrain the ages of the different seismic units. The main features observed in the basins are interpreted as: 1) trans-tensional growth patterns in Pliocene and Quaternary sediments that combine NE–SW trending and steeply dipping fault zones that likely correspond to strike-slip corridors and E-W/WNW-ESE trending normal faults, 2) regional erosional truncations of Miocene sediments, likely related to the Messinian Salinity Crisis (MSC), 3) thick delta-turbidite deposits of Neogene age. Only the North Aegean Trough shows evidence of earlier development and polyphase deformation through inversion structures, and additional seismic units. Extension processes in the Aegean region have been driven by the Hellenic slab rollback since the middle Eocene. The widespread development of Neogene basins at the whole Aegean scale attests to a major tectonic change due to an acceleration of the trench retreat in the middle Miocene. The present study shows that the Neogene basins of the North Aegean Sea developed in dextral transtension with the northward migration of the associated NE-SW trending strike-slip faults. At regional scale, this tectonic pattern indicates that the westward escape of Anatolia started to interact with the trench retreat in the middle Miocene, around 10 Myr before the arrival of the North Anatolian Fault in the North Aegean Sea.     

渤黄海沿海2月份海平面异常偏高成因分析

使用1980—2010年的水位、气温、海温、气压和风场资料,对中国渤黄海沿海2月份的海平面变化特征以及异常偏高成因进行了探讨,分析结果表明:近30年,渤黄海沿海2月份海平面呈现明显的上升趋势,2009年和2010年2月份的海平面达到近30年的高值,冬季高海平面导致全年平均海平面偏高。近两年2月份海平面处于多个长周期振动的高位重合期,各振幅叠加的结果近100 mm,对海平面起了明显的抬升作用。高海平面使得辽宁、河北以及山东等沿岸地区的海水入侵距离和土壤盐渍化程度均有所增加,海岸侵蚀加重;上海在2009—2010年连续2年2月份发生了近年较严重的咸潮入侵。2009年和2010年2月份,气压较常年同期显著偏低,冬季季风显著偏弱,是海平面上升的主要原因之一。     

海洋二号微波散射计极地海冰识别算法研究

An Antarctic sea ice identification algorithm on the HY-2A scatterometer(HSCAT) employs backscattering coefficient(σ0) and active polarization ratio(APR) for a preliminary sea ice identification.Then standard deviation(STD) filtering and space filtering are carried out.Finally,it is used to identify sea ice.A process uses a σ0,STD threshold and an APR as sea ice indicators.The sea ice identification results are verified using the sea ice distribution data of the ASMR2 released by the National Snow and Ice Data Center as a reference.The results show very good consistence of sea ice development trends,seasonal changes,area distribution,and sea ice edge distribution of the sea ice identification results obtained by this algorithm relative to the ASMR2 sea ice results.The accuracy of a sea ice coverage is 90.8% versus the ASMR2 sea ice results.This indicates that this algorithm is reliable.     

福建省平潭岛东北部软质海崖蚀退特征研究

为了揭示软质海崖的侵蚀机制,现场利用量测方法研究了福建省平潭岛东北部软质海崖的蚀退特征、蚀退模式和影响因素,并利用自制崩解仪测试了砂土和粉质黏土的崩解速率。结果表明,软质海崖滑塌物体积、堆积距离均随海崖高度增加而增大,每次滑塌海崖蚀退距离位于0.08~1.23 m;滑塌物覆盖住崖脚后具有临时保护崖脚的作用,但由于其受到扰动较易发生再次蚀退;崖脚海蚀槽的形成对滑塌起到重要控制作用;降雨、海洋水动力、强风和人为活动是造成蚀退的四大因素;在土体抗侵蚀方面,砂土的抗侵蚀能力最弱,粉质黏土的居中,黏土的最强;现场干燥粉质黏土的崩解速率为2.4 cm/min。