The preservation potential of ash layers in the deep‐sea: the example of the 1991‐Pinatubo ash in the South China Sea

Following the eruption of Mount Pinatubo on 15 June 1991, volcanic ash was transported westward to the South China Sea in an atmospheric plume, falling out and settling to the sea floor within days and forming an up to 10 cm thick layer on an area >400 000 km². Immediately after deposition, surviving deep‐burrowing animals re‐opened their connection to the sea floor to obtain water for respiration and/or food take‐up. Later, small‐sized meiofauna and then macrofauna re‐colonized the sea floor, mixing newly deposited organic fluff with the underlying ash. Consequently, ash deposits thinner than 1 mm have not often been observed as a continuous layer when cored six years after the eruption, while ash about 2 mm thick is now patchily bioturbated. In areas covered by ash thicker than 5 mm, mixing by benthic animals is controlled mainly by the adaptation of the burrowing fauna to variations in grain‐size, the rate of background sedimentation, the availability of benthic food on and within the sediment and pore water oxygen levels. With respect to these factors, four provinces can be distinguished: (i) Along the Philippines margin run‐off from land fuels primary production that, in turn, leads to a high benthic food content. The benthic fauna is adapted to a variable grain‐size and rapid sedimentation. Therefore, mixing is intense and the preservation potential of the ash layer is low. (ii) In areas affected by deposition of hyperpycnites and turbidites, i.e. in canyons in front of river mouths and in the Manila Trench, the ash layer is preserved due to rapid burial. (iii) The area to the west to about 116° E receives low amounts of benthic food, benthic mixing is less intense and the preservation potential of the ash is high. (iv) The central South China Sea, where the ash is thinner than 3 cm, is affected by intense wind mixing and upwelling and the benthic food content is high; thus, the chance that the ash will be preserved as a sharp‐based layer is low. Consequently, the style of ash preservation has palaeo‐environmental significance. Older buried and burrowed event layers provide further information to elucidate the fate of the 1991 Pinatubo ash layer; in general their appearance fits with observations in the Recent.     

Benthos of a perennially-astatic, saline, soda lake in Mexico

The effects of multiple stressors on the benthic macroinvertebrate community were monitored in Tecuitlapa Norte, a shallow, perennially-astatic, warm, mesosaline, sodaalkaline lake in Mexico. Physico-chemical and biological variables were determined monthly for one year. Tecuitlapa Norte displayed a clear seasonal environmental pattern (dry and rainy seasons). The benthic macroinvertebrate community consisted of five species:Culicoides occidentalis sonorensis Jorgensen,Ephydra hians Say,Stratiomys sp.,Eristalis sp., andLimnophora sp. of which the first two were dominant and the rest scarce.C. occidentalis was the most important species numerically (76 percent of the total), whileE. hians dominated the biomass (73 percent of the total). Primarily salinity and secondarily pH appear to be the most important environmental factors controlling dominance of benthic organisms in Tecuitlapa Norte. Seasonal abundance dynamics of the dominant organisms was associated with phases in their reproductive cycles: environmentally-triggered (i.e., temperature rise, water-level descent) pupation and emergence periods. We concluded that whereas physical and chemical factors (i.e., salinity, pH) exerted the primary control on benthic macroinvertebrate community composition in Tecuitlapa Norte, another assembly of variables (e.g., water-level, temperature) influenced species distribution and abundance.     

太湖流域上游西苕溪源头溪流中毛竹、石栎和山胡椒落叶分解比较

比较了毛竹、石栎和山胡椒叶片的理化属性,采用粗网叶袋法研究了三种落叶在太湖流域上游西苕溪中的分解过程,探讨了毛竹叶成为溪流优势外来能源后对溪流生态过程和底栖动物群落结构的影响.三种落叶的氮、磷含量及叶片厚度都存在显著差异,毛竹叶的氮含量(30.23 g/kg)远高于石栎(20.98 g/kg)和山胡椒(9.69 g/kg),其中毛竹叶的分解速率最快(k=0.00592 d-1),山胡椒(0.00297 d-1)和石栎叶(0.00212 d-1)较慢.三种落叶叶袋间的大型底栖无脊椎动物包括各取食功能团的多度和生物量无显著差异,而4次采样间的差异很显著.大型底栖动物的取食功能团中,撕食者的数量比例最高(40.3%),生物量比例为41.6%,是落叶分解的重要功能类群.撕食者中,利用阔叶筑巢的鳞石蛾Lepi-dostoma数量最多,占全部底栖动物的14%,是该溪流中主要的撕食者类群.因此,由于毛竹叶具有氮、磷含量较高、叶形较窄,以及两年进行一次换叶的特点,当毛竹叶替代其他阔叶秋季落叶的树种成为源头溪流优势外来能源后,可能会改变源头溪流中的氮磷含量、溪流外来能源的量和滞留时间以及底栖动物群落结构.     

新疆乌伦古湖大型底栖无脊椎动物的群落结构

乌伦古湖是我国十大内陆淡水湖之一,同时也是新疆维吾尔自治区的第二大湖泊和主要渔业基地.近年来,随着气候变化和人为因素的影响,湖区水体营养状况、生物群落组成等均发生了较大变化.为揭示该湖大型底栖无脊椎动物的群落结构特征及其对生态系统变化的响应,2006年11月至2008年7月设28个采样点对大型无脊椎底栖动物的群落结构特...     

A Late Pleistocene marine clay succession at Kriegers Flak,westernmost Baltic,southern Scandinavia

In the Baltic Sea south of Skåne county in southern Sweden, an over- consolidated marine clay succession on the northeastern slope of Kriegers Flak was observed in shallow seismic data as a unit overlain by younger Weichselian sediments. Two cores were taken from the clay succession. The Foraminifera present were predominantly of two species, Elphidium excavatum and Elphidium albiumbilicatum, reflecting deposition under arctic– boreal conditions. Stable oxygen isotope analyses were performed on foraminiferal tests, and the results show extremely light δ¹⁸O values ranging between −11‰ and −12‰. The cause of these extreme values is uncertain but may result from the high influence of meltwater. Brackish conditions are also indicated by the tolerance for low salinity shown by the Foraminifera. Radiocarbon dating shows an infinite age >40000 yr BP. The pollen flora seems mainly to have been redeposited, which makes interpretation difficult. The sea may have entered the Baltic basin during periods with high eustatic levels, an isostatic downloading of the crust, or a combination of both. It is suggested that the deposition of the overconsolidated marine clay succession occurred in the Late Saalian, Early Eemian or Early Weichselian. © 1998 John Wiley & Sons, Ltd.     

黄海夏季典型站位的底边界层动物

2002年8月25~26日,在黄海夏季冷水团区域内的抛锚站位(35°22′N,121°59′E),使用柱状界面采样器进行了昼夜连续取样,对底边界层动物的种类组成与昼夜丰度变化进行了研究,以获得对黄海底边界层动物的初步认识。共记录底边界层动物21种,隶属18科、19属。超底栖动物和中型浮游动物是黄海夏季底边界层动物的2个重要类群,主要种类有尖额真猛水蚤(Euterpina acutifrons)、挪威小毛猛水蚤(Microsetella norvegica)、异厚盖钩虾(Synchelidium miraculum)、双刺纺缍水蚤(Acartia bifilosa)和小拟哲水蚤(Paracalanus parvus),其丰度皆有明显的昼夜波动现象。以桡足类无节幼体为代表的小型浮游动物也是底边界层动物中不容忽视的类群之一。采集到5个黄海区的新记录物种:美丽猛水蚤(Nitocrasp.)、跛足猛水蚤(Mesochrasp.)、咸水剑水蚤(Halicyclopssp.)、掌刺梭剑水蚤(Lubbockia squillimana)和异厚盖钩虾(Synchelidi-um miraculum),显示出底边界层动物种类组成的特殊性。     

无定河流域不同水土流失区底栖动物生物完整性指数构建与健康评价

无定河流域位于黄土高原与毛乌素沙地过渡带,水土流失严重,生态环境具有脆弱性和波动性。于2021年春季(4月)和秋季(10月)对无定河流域上、中、下游及其6条支流和流域内的3个淤地坝开展水生态系统调查,旨在厘清无定河流域底栖动物群落特征,构建底栖动物生物完整性指数并开展健康评价。无定河流域春季共采集到底栖动物105种,平均密度为181 ind./m²,平均生物量为0.760 g/m²,秋季共采集到底栖动物67种,平均密度为94 ind./m²,平均生物量为0.454 g/m²。通过对两季度研究区域内底栖动物27个生物参数开展分布范围检验、判别能力分析和相关性分析,构建无定河流域底栖动物生物完整性指数,对全流域40个样点(6个参照点和34个受损点)进行B-IBI健康评价。评价结果表明,总体上无定河流域底栖动物生物完整性较好,40个样点中春季有19个处于健康或亚健康状态,秋季有23个处于健康或亚健康状态,其中无定河上、中游干支流大都以健康和亚健康为主,无定河下游干支流以及3个淤地坝水体健康状况较差。在不同水土流失类型区域,底栖动物群落特征和生物完整性评价具有显著性差异。本研究结果可为无定河流域河流健康评估提供科学依据。     

基于形态学与核糖体DNA及其cDNA高通量测序的海洋沉积物中纤毛虫多样性比较

高通量测序技术广泛应用于环境真核微生物多样性的研究,可检获较之传统形态学方法更高的多样性。然而,检获的高分子多样性与基于形态的物种多样性在构成上的差异仍然不明。本研究首次对比分析了基于形态学的南黄海沉积物中的纤毛虫物种多样性与基于核糖体18S DNA和c DNA高通量测序的多样性异同。结果表明:形态鉴定获得8纲、20目、30科、36属共97种纤毛虫;DNA测序检获10纲、28目、55科、76属共174个OTUs;而通过c DNA测序获取的纤毛虫多样性最高,获10纲、31目、68科、99属共284个OTUs。研究发现,形态学方法检获的纤毛虫均为底栖生纤毛虫;两种分子手段检获的多样性更高,群落结构更为近似,覆盖了形态鉴定所获的绝大部分类群。但DNA测序还检获了序列比例高达90%的浮游类群,可能源于包囊或死亡沉降的物种;而c DNA测序检获了约7%的浮游纤毛虫序列。较之DNA测序,c DNA法检获的底栖纤毛虫在群落结构上与形态学结果更为接近。本研究表明,分子手段有助于更全面地揭示沉积物中的纤毛虫多样性,DNA测序可同时揭示休眠包囊、胞外DNA及过去群落的信息,而c DNA测序在研究活动纤毛虫多样性上更有优势。     

Symbiosis between the holothurian Scotoplanes sp. A and the lithodid crab Neolithodes diomedeae on a featureless bathyal sediment plain

Vulnerability to predation may be high for many megafaunal taxa in deep‐sea sedimentary habitats where physical heterogeneity is low. During ROV observations in a bathyal sediment plain off Central California, juveniles of the lithodid crab Neolithodes diomedeae were frequently observed on or under the holothurian (sea cucumber) Scotoplanes sp. A, and are hypothesized to benefit from this association as a nursery or refugium from predation. Ninety‐six percent (n = 574 of 599) of the juvenile N. diomedeae observed (density varied from 0.02–0.75/m² among sites and seasons) in the study area were associated with Scotoplanes sp. A. Of the 2596 Scotoplanes sp. A observed (density varied from 0.48 to 25.90/m²), 22% were attended by at least one juvenile crab, and rarely two crabs (n = 4). Solitary N. diomedeae were rarely observed. This decapod–holothurian symbiosis appears to be largely commensal, with juvenile crabs (carapace width = 0.03–0.31 ×  holothurian length) observed on or beneath Scotoplanes sp. A in a habitat with few refugia from epibenthic predators. Other hypotheses may explain or enhance the potential benefits of the association for N. diomedeae, such as elevated food availability due to the activities of Scotoplanes sp. A. The relationship may be mutualistic if there is a benefit for the holothurian, including the removal of epizoic parasites. Ultimately, the nursery or other effects on the population dynamics of N. diomedeae may be minimal in low‐relief, sediment‐dominated habitats, as very few sub‐adult crabs were observed in the study area and were likely consumed upon outgrowing their refugia. While sedimentary habitats may be a sink for N. diomedeae populations, growth of juvenile crabs during their association with Scotoplanes sp. A should increase energy flow to its predator populations. This association has not been reported previously but may be expected in sediment‐dominated habitats where these species overlap.     

山东荣成天鹅湖海草场大型底栖贝类时空分布研究

为了了解天鹅湖不同微生境条件下底栖贝类的群落结构及时空分布特征,于2013年12月至2014年11月,对天鹅湖矮大叶藻区、空白区、大叶藻区边缘及其内部的底栖贝类和环境特征进行了调查。共发现15种大型底栖贝类,隶属14科15属;贝类种类组成、分布密度、生物量以及物种多样性指数在4种生境中差异显著,但均无明显的季节变化。空白区域中贝类总密度和单位面积生物量最高,大叶藻区内部最低,但矮大叶藻区和大叶藻区内部多样性指数较高。大叶藻区内部的贝类以腹足类锈凹螺、日本月华螺、刺绣翼螺等刮食者为主,而双壳贝类则更倾向于选择无海草覆盖的空白区或者海草较为稀疏的草场边缘。综合分析表明,天鹅湖底栖贝类的分布和多样性受底质特征和海草覆盖影响最为显著,同时与水深密切相关。