Relative importance of estuarine nurseries for species of the genus Diplodus (Sparidae) along the Portuguese coast

The relative importance of estuarine nursery areas for species of the genus Diplodus and their relations with several environmental variables was evaluated along the Portuguese coast. Nine estuarine systems were sampled with beam trawl surveys. Species of the genus Diplodus were only present in estuaries south of the Ria de Aveiro (40°38′). A latitudinal gradient of increasing species richness and abundance towards the south was found. Estuarine nurseries of Diplodus vulgaris, Diplodus sargus and Diplodus puntazzo were characterized by mud substrate, lower salinity and lower dissolved oxygen, with the exception of Ria Formosa. Diplodus bellottii was associated with estuaries with large areas and high volumes, the Tejo and the Sado. Diplodus bellottii nursery grounds were characterized by low depth. Diplodus annularis was associated with seagrass and saltmarsh habitats, certainly because it is the only species of the genus Diplodus which recruits exclusively to seagrass meadows. Diplodus annularis nursery grounds were also characterized by sand substrate, higher salinity and higher dissolved oxygen. Niche breath varied widely amongst species and location. Diplodus vulgaris generally presented the highest values of niche breath, except when D. bellottii was present. Niche overlap was not high, the highest value being that between D. vulgaris and D. sargus in the Mira estuary, with 76% spatial niche overlap. Considerations were made on these species progress towards the north in a climate warming context, taking into account the habitat associations described here.     

龙门山北段观雾山组地层时代分布、沉积充填及其古地理意义

自四川盆地西北部(川西北)泥盆系观雾山组油气勘探取得重要进展以来,观雾山组的沉积储层研究受到了广泛重视。然而,由于观雾山组地层划分方案的变动和地层的穿时性,导致目前对观雾山组的时代分布和充填过程认识不清,从而影响了沉积古地理格局的恢复。本文以四川广元西北乡、潜溪河剖面泥盆系观雾山组牙形石生物地层研究为基础,结合区域古生物地层资料,认为江油马角坝以北的观雾山组绝大多数沉积于晚泥盆世早—中弗拉期,且地层沉积时间自南西向北东逐渐变晚。龙门山北段观雾山组具有自西向东、自南向北地层厚度减薄和地层时代变新的特征,表明来自扬子地台西部的古特提斯洋海水向东侵入龙门山地区,因地形差异和渐进式海侵形成了自南西向北东的超覆沉积。由于岩相分异,超覆沉积形成的观雾山组与金宝石组在区域上既表现为上下叠置关系,也表现为同期异相的相变关系。该研究不仅对约束川西北地区观雾山组地层时代提供了可靠的古生物证据,而且对认识龙门山地区泥盆系的充填过程、沉积古地理格局均具有重要意义。     

台湾海峡及邻近海域主要无脊椎动物食性特征及其食物关系研究

对台湾海峡及邻近海域14种主要经济无脊椎动物的胃含物进行了鉴定分析。结果表明：这些无脊椎动物对饵料生物无明显的选择性，均为混合食性。其食性类型可分为：游泳生物食性类型、游泳动物和底栖动物混合食性类型、底栖生物和浮游动物食性类型、底栖生物食性类型、浮游动物和游泳动物食性类型。10种甲壳动物和4种头足类的营养级范围分别为1．64～2．60级和2．04～2．88级。除周氏新对虾(Metapenaeus joyneri)、角突仿对虾(Parapenaeopsis cornuta)和鹰爪虾(Trachypenaeus curdrostris)属第二营养层次的杂食性动物外，其它的均属第三营养层次的肉食性动物。拥剑梭子蟹(Portunus haanii)、秀斑好(Caarybdis feriatus )、哈氏仿对虾(Parapenaeopsis harduickii)和杜氏枪乌贼(Loligo duvaucelii)的食物生境宽度较大，它们对各种饵料生物的利用更趋均衡。4种头足类之间、3种蟹类之间食物重叠显著。长尾类、短尾类、鱼类和腹足类是台湾海峡主要无脊椎动物营养层次能量传递中的关键功能类群。     

人工鱼礁区三种习见肉食性软体动物营养生态位研究

以小黑山岛人工鱼礁区为研究区,利用稳定同位素技术分析该海域三种习见肉食性软体动物长蛸（Octopus minor）、短蛸（Octopus fangsiao）和脉红螺（Papana venosa）的营养生态位,进而判断物种种间关系。分析结果显示：食物来源范围由大到小依次为长蛸、脉红螺、短蛸,其中长蛸食物来源包含短蛸食物来源范围,但脉红螺与两种蛸类食物来源无交叉;营养级由高到低依次为长蛸、短蛸、脉红螺。长蛸与短蛸营养生态位重叠比例较高,存在明显的竞争关系,与短蛸相比,长蛸营养级更高,食物来源范围更广,在竞争中处于优势地位;脉红螺的营养生态位与两种蛸类无重叠,其营养级比两种蛸类更低且无捕食或竞争关系。     

基于稳定同位素方法的东海中南部海域主要饵料生物营养生态位季节变动的研究

饵料生物在海洋生态系统中处于承上启下的关键地位,为准确评估东海中南部海域饵料生物的营养关系,基于2018年11月和2019年4月两个航次调查中收集的饵料生物的碳氮稳定同位素数据,对其营养生态位的季节变动特征及种间竞争关系进行了研究。结果表明：该海域饵料生物的碳氮稳定同位素比值跨度较大,海域整体食源多样性水平较高,营养结构较稳定;饵料生物δ13C和δ15N值存在明显的季节差异,春季饵料生物的营养级显著低于秋季;浮游动物的营养生态位在两个季节间未发生明显的偏移,但其他饵料生物的生态位的位置和重叠度发生了一定变化,这或许与饵料生物摄食选择的季节差异有关;鱼类、虾类和头足类的营养生态位在不同采样时期分别表现出不同的重叠和分化特征,证明了不同饵料生物对食物选择的差异性。相关研究结果可为类似海域生物营养生态位的研究提供参考,也可为东海海域渔业资源的可持续开发利用和生态环境的保护提供科学资料。     

辽东湾西海岸潮间带大型底栖动物群落生态位特征

基于2014年9月和2015年4月辽东湾西海岸潮间带10个断面3个潮区的调查数据,对12个优势种的生活型、生态位宽度和生态位重叠度进行了分析,结果表明:12个优势种分别隶属于3门4纲12科;面上生活类群和面下生活类群的比值GS/GSB表现为春季秋季;秀丽织纹螺、日本大眼蟹和丽核螺的生态位宽度较宽(2.171、2.170和2.169),猫爪牡蛎和短角双眼钩虾的生态位宽度较窄(0.637和0.173);生态位重叠较为显著的种类有四组,均是生态位宽度较宽的物种。以上结果也从一个侧面反映了底栖生物对季节和生境的适应情况,由于季节变化和生境不同,使物种生态位宽度值发生了变化,从而影响物种之间的生态位重叠值。     

The existence of a chaotic region due to the overlap of secular resonances ν5 and ν6

A nonlinear theory of secular resonances is developed. Both terms corresponding to secular resonances ₅ and ₆ are taken into account in the Hamiltonian. The simple overlap criterion is applied and the condition for the overlap of these resonances is found. It is shown that in given approximation the value p = (1 - e²)^1/2(1 - cosI) is an integral of motion, where the mean eccentricity e and mean inclination I are obtained by eliminating short-period perturbations as well as the nonresonant terms from the planets. The overlap criterion yields a critical value of parameter p depending on the semi-major axis a of the asteroid. For p greater than the critical value, resonance overlap occurs and chaotic motion has to be expected. A mapping is presented for fast calculation of the trajectories. The results are illustrated by level curves in surfaces of section method.     

Partitioning of temperature resources amongst an estuarine fish assemblage

Temperature (i.e. habitat at any given temperature) is an ecological resource for which organisms compete to maximise growth and other fitness measures, but the temperature (thermal habitat)-resource concept has not been widely applied to the study of estuarine fish. Temperature–abundance relationships for 16 fish and four invertebrate species from the Thames estuary were analysed to test hypotheses regarding temperature resource partitioning. Significant temperature–abundance models were apparent, explaining >65% of the variability in 13 fish species and 50% of variability in three invertebrate species. Fish demonstrated differential responses to temperature across the range. Invertebrates generally preferred warmer conditions than fish. Calculated thermal niche breadths indicated species preferenda spread across the recorded temperature range and some separation along the thermal niche axis within the same functional guild or taxonomic group. Calculated overlap coefficients and resource separation ratios provided some evidence for resource separation and demonstrated that species closely aligned on other niche axes (e.g. physical habitat use, feeding type) were most likely to be separated in terms of their use of thermal habitat resources, suggesting where other niche axes variables are not separating species, division of the temperature resources may be preventing competition between fish species. Few fish species demonstrated significant overlap with potential invertebrate prey, suggesting facultative use of the estuary to exploit optimal thermal habitat rather than food supply. The temporal migration pattern of fish in estuaries is therefore interpreted as a response to resource separation along the temperature axis which limits potential competition between functionally or taxonomically similar species. Thermal resource partitioning in estuaries has temporal rather than spatial dimensions and provides an example of the niche compression/expansion hypothesis.