Decline of Pseudodiaptomus hessei (Copepoda, Calanoida) in two water bodies located in the Senegal River hydrosystem (West Africa): Hypotheses and perspectives

Pseudodiaptomus hessei is a key species in many water bodies in the Senegal River hydrosystem but it became rare or completely disappeared from two ecosystems (Lake Guiers and Dakar Bango Reservoir; Senegal, West Africa) after major hydrological changes caused by human action, mainly impoundments on the river in 1985, and the opening of a new estuary mouth in 2003. Kâ et al. [Kâ, S., Pagano, M., Ba, N., Bouvy, M., Leboulanger, C., Arfi, R., Thiaw, O.T., Ndour, E.H.M., Corbin, D., Defaye, D., Cuoc, C., Kouassi, E., 2006. Zooplankton distribution related to environmental factors and phytoplankton in a shallow tropical lake (Lake Guiers, Senegal, West Africa). International Review of Hydrobiology 91(5), 389–405] put forward several hypotheses to explain the reasons for this decline: salinity and chemical changes in the water, predation by a cyclopid predator Mesocyclops ogunnus and/or the inhibiting effects of cyanobacteria and/or diatoms (allelopathy). This study assessed these hypotheses by studying the distribution of P. hessei in 13 stations (including the Dakar Bango reservoir and Lake Guiers) in relation to physical, chemical and biological (phyto- and zooplanktons) factors at each station. We produced a distribution pattern for this species in the Senegal River hydrosystem. Rank correlations and principal component analysis showed that P. hessei was not correlated with conductivity but was positively correlated with pH and alkalinity, suggesting chemical effects. The clear association with two filamentous cyanobacteria (Cylindrospermopsis raciborskii and Anabaena sp.) did not appear to support the hypothesis of cyanobacteria inhibition but blooming conditions were never encountered during the study. Negative correlation with diatoms (especially with Fragilaria sp.) suggested that aldehyde producing diatoms had a negative effect. Negative correlations with cyclopids such as Mesocyclops supported the hypothesis of cyclopid predation to explain the decline of P. hessei. This study proposes several lines of research for future studies to test these hypotheses.     

Effect of crab size and habitat type on the locomotory activity of juvenile shore crabs, Carcinus maenas

Post-settlement processes are a major focus in the study of the dynamics of marine populations and communities. Post-settlement movement of juveniles is an important, but often ignored, process which affects local predator–prey and competitive interactions. We used benthic suction sampling and pitfall traps to examine density and locomotory activity of Carcinus maenas juveniles in different intertidal habitat types in the Rio Mira Estuary, Portugal, to better understand intra-specific interactions in a system where density-dependent processes are known to regulate population dynamics. As expected, significantly higher densities of juvenile shore crabs were found from bare mud compared to densely vegetated habitats. At the time of sampling, small and intermediate stages together outnumbered by far the larger juveniles. Conversely, larger crabs were much more frequent than smaller ones in traps. A locomotory index (LI), i.e. the ratio between crab catch in pitfall traps and their density within their moving range, is proposed as a measure of movement. LI analyses indicated that: (1) movement is an order of magnitude higher in large than small juveniles and much higher in sparse than dense vegetation cover; (2) activity of small juveniles is mostly crepuscular, regardless of vegetation cover; and (3) movement of large juveniles is very limited in dense Zostera patches, but very high in sparsely vegetated areas, during the day and night. These results suggest that small juveniles are relatively protected under dense vegetation cover due to lower mobility of larger crabs, and provide evidence of temporal segregation of activity windows between juvenile crabs of different sizes, which may be a key mechanism to reduce cannibalism and therefore increase the carrying capacity of nursery habitats.     

Influence of the vertical distribution of cyanobacteria in the water column on the remote sensing signal

An increased intensity of cyanobacterial blooms and their potentially harmful effects have attracted the attention of environmental agencies, water authorities and the general public worldwide. Reliable operational monitoring methods of coastal waters, lakes and ponds are needed. Mapping of the surface extent of cyanobacterial blooms with remote sensing is straightforward, but recognizing waters dominated by cyanobacteria throughout the water column and quantitative mapping of cyanobacterial biomass with remote sensing is more complicated. Unlike most algae, cyanobacteria can regulate their buoyancy and move vertically in the water column. We used the Hydrolight 4.2 radiative transfer model and the specific optical properties of three species of cyanobacteria to study the impact of vertical distribution of cyanobacteria on the remote sensing signal. The results show that the vertical distribution of cyanobacteria in the water column has a significant impact on the remote sensing signal. This result indicates that developing remote sensing methods for quantitative mapping of cyanobacterial biomass is much more complex than quantitative mapping of an algal biomass that is uniformly distributed in the top mixed layer of water column.     

Regional and temporal changes in bivalve diversity off the south coast of Portugal

From 2000 to 2006, a total of 75 bivalve species were identified, varying from 29 (spring 2001) to 54 species (spring 2005) per year. Seasonal tendencies in diversity varied according the year, thus the interpretation of long-term and regional scales is essential before drawing any conclusions in other studies. Richness and diversity consistently decreased with depth and increased with sediment grain size (from low in very coarse sand to high in coarse silt). Diversity decreased progressively from 3 to 16 m depth, thus the harsher shallower environments (due to waves and tidal air exposure) showed greater diversity than the most stable areas. Communities in finer sediments were more diverse than those in coarser sand. Evenness showed patterns opposite to diversity, overall.Diversity and evenness maps (produced with multivariate universal kriging), showed that most geographic areas with greater diversity were farer from river outflows and wastewater treatment plants. Two types of geographic pattern were observed: areas with persistently greater bivalve diversity through time and areas that changed locally from year to year. This spatial analysis can be used to establish priority conservation areas for management purposes, and to analyse the persistency of regional diversity patterns. The area with most habitat heterogeneity (Sotavento) corresponded to greatest diversity.There was a positive relationship between Spisula solida and Chamelea gallina landings and bivalve diversity 2 years and 1 year later, respectively. Possibly, local fisheries, by selectively withdrawing the commercial numerically dominant species from the ecosystem, increased diversity 1 to 2 years later, as the ecological niches of the dominants are quickly filled by several other species thereby creating a more even community. On regional scales, no significant impact was found on long-term bivalve diversity in local fisheries,     

Silver in Tokyo Bay estuarine waters and Japanese rivers

Dissolved and particulate concentrations of silver in Tokyo Bay estuarine waters and Japanese rivers were determined in this study. The dissolved silver concentrations in the surface water of Tokyo Bay range from 5.9 to 15.1 pmol kg⁻¹, which is comparable to those in the surface water of the Japan Sea, but two or three times higher than those in the surface water of the open ocean. However, elevated concentrations of dissolved silver are not found in Tokyo Bay compared with those in other highly urbanized estuaries, such as San Francisco Bay (20∼243 pmol kg⁻¹). In the Tokyo Bay estuary, silver typically exhibits non-conservative mixing behavior, which is a common feature in the other estuaries reported previously. Dissolved silver concentrations decrease with salinity from the rivers to the mouth of Tokyo Bay. Silver is efficiently scavenged by suspended particulates, as evidenced by the high conditional distribution coefficients for silver throughout the estuary (log K_d > 5.0 ± 0.6). The silver fluxes into Tokyo Bay via inflowing rivers and atmospheric deposition were estimated as 83 kg y⁻¹ and 15 kg y⁻¹, respectively. A simple budget calculation shows that the silver supplied from rivers and atmosphere must be rapidly scavenged within the Tokyo Bay estuary.     

济南北部地热田地热地质特征浅析

济南北部地热田地热资源类型属于层状裂隙岩溶型,热源是北部齐河-广饶断裂的沟通导热,盖层是第四系、新近系、石炭-二叠系、侏罗系.可利用的、具有开发价值的热储层为奥陶系灰岩热储,该热储层顶板埋深在700～2500m左右,热储层厚度由南向北逐渐增大,单井涌水量2000m3/d左右,孔口水温一般在38～57℃,地热田东部地热水矿化度1.4～3.5g/L左右,西部5.1～7.2g/L左右,地热水中富含氟、锶、偏硅酸等微量元素,具腐蚀性,结垢性弱,具较好的开发利用价值.经计算奥陶系热储层单井可采资源量为7.3×105m3/a,合理井间距为5000m.     

聊城西部地热田地热流体特征及开发利用

聊城西部地热田位于山东省莘县凹陷的南部区内,属C1-Na型地下热水。其中锶达到了命名矿水浓度,碘化物、偏硅酸达到了矿水浓度,偏硼酸达到了有医疗价值浓度。地热水中还含有铁、锰、锂等多种对人体有益的微量元素。该区地热井出水量大,出水温度高,具有极大的开发利用前景。     

山东苍山王埝沟铁矿床地质特征及找矿方法探讨

王埝沟铁矿床为隐伏矿床,产于泰山岩群山草峪组地层中,发育2条主矿带,总体走向为280°-290°,平行展布,相向而倾,具不对称向斜构造特征。该铁矿床2条主矿带发育5个矿体,北翼矿带发育3个矿体,南翼矿带发育2个矿体,矿体呈层状、似层状产出,产状与地层产状一致。综合分析研究成矿地质条件及区域成矿理论,并充分利用地面高精度磁法剖面测量成果,二者有机结合的综合式找矿方法,是目前寻找深部沉积变质型“鞍山式”铁矿盲矿体行之有效的方法。     

Mechanism on bipolar distribution of Permian brachiopods

By reasearch on geographic distribution, nine genera in bipolar distribution are selected from Permian brachiopods. These taxa originated from middle-high latitude areas in the boreal realm, of which five genera were derived from Late Carboniferous, and other four genera originated from Permian. They were all in bipolar distribution during some different stages in Permian. Specific diversity for each genus was high in the boreal realm, whereas in the Gondwana realm was very low. Perdurability was long in the boreal realm, and short in the Gondwana realm. It was the time when these nine genera came to their maximum diversity that these genera appeared in the Gondwana and formed bipolar distribution; while they also migrated to the low latitude from high latitude. This shows very close relationship between several main cooling events in Permian and the migration of genera from the boreal realm to the Gondwana realm through the Tethys. Therefore, the cooling events might be the main drive which caused these cold-water-type brachiopods migrated to the Gondwana realm and being bipolar distribution. In this process, the planula tolerance to warm water would be another important factor.     

舟山本岛北部灌门水道及邻近海域潮波特性初步研究

依据2004年在舟山灌门水道及邻近海域获取的同步潮位和潮流资料,对该海域的潮波特性进行了统计和分析,并对分析过程中发现的主要半日分潮经过灌门水道时振幅有较大幅度减小的现象进行了初步研究,认为截面积急剧变化的水道,潮波势能向动能的转换是产生主要半日分潮振幅减小的一个重要因素。这一结论或许有助于解释M2分潮波通过舟山群岛海域振幅明显减小的现象。