Macrofauna impact on Ulva rigida C. Ag. production and relationship with environmental variables in the lagoon of Venice

The grazing pressure of the macrofaunal invertebrates associated with the biomass of Ulva rigida in the Venice lagoon, their species composition and relationship with environmental variables have been studied. Fifteen sampling campaigns were carried out during different seasons both in the central basin of the lagoon, dominated by macroalgae (especially U. rigida C. Ag.) and in the southern basin, prevalently populated by seagrasses (especially Zostera marina L.). Replicate experiments were conducted in the field by exposing Ulva fronds in net cages of 10 and 1 mm (control) mesh-sizes to allow or prevent grazer entrance. The grazing pressure was determined as Ulva growth rate difference in the cages. In the absence of invertebrate herbivores, Ulva exhibited per cent relative growth rates (%RGRs) ranging from 1.5 to 9.5% day(-1), whereas in their presence the %RGRs were significantly lower (from -2.5 to 3.4% day(-1)) and frequently negative, especially in the station dominated by macroalgae. In this area, peak grazing rates and macrofauna biomasses of up to 8.6% day(-1) and 1,480 g m(-2) fwt (84.4 ash-free dry weight), respectively, were found. On the whole, during in field experiments in the Ulva-dominated station, herbivores removed an amount of biomass whose percentage ranged from 59 to 165% (mean: 103%) of the biomass yield (grazers excluded) found in the cages. These results suggest the possibility that grazers could act as an important factor affecting Ulva production in the Venice lagoon. Macrofauna populations were analysed by means of multivaliate techniques applied to biological variables only and biological and environmental variables together. Data of individual abundance, after a log(x + 1) transformation and the calculation of the Bray-Curtis matrix, were classified using the Cluster Analysis and ordinated by means of the Non-Metric Multidimensional Scaling (MDS) technique, in accordance with the strategies used in the study of multispecies distributions. Finally, biological and environmental variables were analysed together by means of correlation matrices and the Principal Component Analysis.     

Measurement of DNA single-strand breaks in gill and hemolymph cells of mussels, Mytilus sp., collected on the French Atlantic Coast

DNA single-strand breaks were measured by the comet assay in both gill and hemolymph cells of mussels collected in 3 sampling areas of the French coast (Pointe du Castelli, Pen Bron and Saint-Nazaire Harbour). Whole mussel tissue samples were also collected for the chemical determination of PAH, PCB and heavy metal concentrations. In mussel, a higher level of DNA strand breaks was measured in gill than in hemolymph cells (p < 0.01). Despite a factor of contamination from 2 to 3 between sites, no difference in the extent of mussel DNA strand breaks was shown between sampling locations (p > 0.05), questioning the sensitivity of the assays used in biomonitoring studies.     

海洋微生物学的主要任务

海——微生物栖息的特殊环境。特殊的盐类成分,低温,高压,低浓度的有机物质,植物及动物区系的稀少等组成了微生物生命活动的广阔海洋区域一些主要生态特征。 海洋中最初的微生物学研究,早在上一世纪就已进行了,但足它们局限于较狭小的任务——     

A NEW MODEL FOR PEBBLE BEACH TRACER DISPERSAL

A series of eight tracer experiments were carried out over one year (1983) on a low energy, macro-tidal beach in South Wales, UK. Tracer movement was monitored and 30 pebbles adjacent to coloured tracer pebbles were measured. Measurements were of the A, B, and C axes, roundness, Maximum Projection Sphericity and Oblate-Prolate indices. Analysis shows that through time, the percentage rejection of these properties increased. It is theorised that the surface tracers are 'misfits' or 'rejects' which have not found their equilibrium position in the pebble facies.     

南海将成为我国天然气重要开采地

南海天然气勘探,从80年代对外合作开始,到现在已经走过了15个年头。这15年来,天然气勘探已经多次获得重大发现,有3个较大的天然气田得到证实。从现在获得的勘探成果来看,南海有一个前景非常美好的天然气大气区,几年后将成为我国重要的新的天然气生产基地。 目前,南海崖13-1天然气田开采工程正在     

激光器在水下的应用

激光(Laser)这个词最初是受激辐射光放大(Light Amplification by Stimu-lated Emission of Radiation)这个词组主要词的首字母缩合而成,现在已经使用了二十多年。虽然激光器长时间被认为是一种没有什么用途的器具,但是后来在大量的应用中它已经成为必不可少的东西了。当然,到目前为止,由于种种原因,基本的激光器系统在水下的应用还一直局限于实验性阶段,但是随着激光技术的快速发展和水下作业需求的日     

西南太平洋彭林海盆表层和埋藏锰结核成分和生长史

本文所研究的样品由《Hakurei—maru》号科学考察船进行的GH80—1和GH83—3两个航次所采集．这两次航行的目的是作为日本“中太平洋锰结核调查”五年计划(1979—1983)任务的一部分，在威克-塔希提横断层上进行地质调查(GSJ)。     

第23章 DNS模式:一种为大洋波浪预报而改进的谱模式

23.1 介绍 模拟与频率和方向相关的大洋波谱F（f,θ）的工作是极其困难的。唯一有点统一的理论（Hasselmann,1967）也还没有简化成一种实用形式。这篇研究中所探讨的是结合零散的,现有的理论,以达到这样一种目的:即发展一种与我们目前对风浪成长谱的了解相一致 ·95.的波谱模式。本章中我们将讨论一种离散的谱模式,这种模式采用了一种改进的能量传播的特征方法。数值方法最早是由Barnett等（1969）提出的。