Main characteristics of the boundary layer macrofauna in the English Channel

Four hundred and thirty two suprabenthic hauls with a modified Macer-GIROQ sledge were taken over the period 1988–1996. Fifteen sites within the English Channel were sampled from the Roscoff and Plymouth waters to the Dover Strait, including the Bay of Morlaix, Bay of Saint Brieuc, the Bay of Seine and the Seine Estuary. The main characteristics of the Benthic Boundary Layer (BBL) macrofauna in the English Channel were elucidated from these data. BBL macrofauna was found over the whole water column sampled (10–150 m). Firstly, the number of species collected was very high (up to 116 species for five hauls) except in the Seine estuary. Numerically, mysids were the dominant group of organisms collected with the sledge, followed by amphipods, cumaceans, isopods and decapods. Abundance and biomass of the fauna were very high in the Seine estuary, especially in the mesohaline and oligohaline zones (maximum >216000 ind. 100 m^-3; >200 g AFDW 100 m^-3) where the specialised mysids Neomysis integer and Mesopodopsis slabberi occurred in very high abundance. At other sites, the abundance and biomass were moderate (100–10000 ind. 100 m^-3; 15–2000 mg AFDW 100 m^-3). Abundance reached its maximum when mysids or swarms of amphipods of the genus Apherusa were collected, and during the reproduction of the amphipods of the genus Ampelisca, as in June in the Bay of Morlaix. The number of species, abundance and biomass showed seasonal changes in all sites with, in general, lowest values in winter or spring, and highest values in autumn. For the open sea sites, two main geographical gradients were identified: i) in spring, a higher number of species in the western part of the Channel compared with the eastern part of the Channel and, in autumn, a higher number of species in the eastern part of the Channel compared with the western part, and ii) an increasing density gradient from west to east at spring and a decreasing gradient from west to east during the autumn. The suprabenthic fauna of the Channel can be considered as a unique community including three kinds of species: (i) good swimmer species which were common at all the time and all sites: e.g. Anchialina agilis, Gastrosaccus spp., Haplostylus spp. and Apherusa spp., (ii) species present at all sites only at night: e.g. Atylus vedlomensis, Megaluropus agilis, Melphipidella macra, Orchomenella nana, Pseudocuma longicornis, Schistomysis ornata and Synchelidium maculatum, and iii) species collected at one or a limited number of sites only at night: e.g. Ampelisca spp. at Pierre Noire and Diastylis spp. at site F. The Seine estuary supports a typical suprabenthic estuarine community. Elements of the suprabenthic fauna also showed significant daily rhythms which took several forms depending on the species under consideration.     

2011—2020年长江口大型底栖动物群落结构变化趋势

对2011—2020年夏季长江口48个站位的大型底栖动物定量监测数据进行统计分析,研究长江口海域底栖生物群落时空结构演变特征。结果表明,近10年长江口海域共鉴定大型底栖动物284种,其中多毛类128种,占总种数的45.1%,甲壳类64种占22.2%,软体动物56种占19.7%,棘皮动物16种占5.6%,其他类合计20种。平均生物密度为(79.5±45.9)个/m²(年份变幅14.7—195个/m²)。平均生物量为(5.20±3.25)g/m²(年份变幅1.01—10.11g/m²),多毛类、软体动物、甲壳类是生物密度和生物量组成的主要类群。十年期间种类数、生物密度和生物量均呈现明显上升趋势,口外区贡献最突出。四个监测区域(南支、北支、杭州湾、口外)的优势种差异大。丝异须虫Heteromastus filiformis在各年份的优势种中出现的频度显著最大。总体来看,长江口监测区域大型底栖动物群落自然演变趋势向好。三项多样性指数统计结果表明,口外区大型底栖动物种类组成多样性水平显著高于口内三个区。生物群...     

Abundance,population dynamics and production of Chironomidae (Diptera) in an ul traoligotrophic lake in South Greenland

Macrozoobenthos of the ultraoligotrophic Lake 95 (61°N, 46°W, 8 ha, z_max=18 m, ) is composed of about 14 taxa dominated by 12 Chironomidae species. Abundance, life cycle, biomass and production were estimated for the six dominant taxa. Abundance declined fromca. 4150 at 2.5 m depth toca. 1400 ind m^–2 at 16 m depth and averagedca. 3200 ind m^–2 on a lakewide basis. By numbers,Heterotrissocladius changi andH. oliveri dominated the average fauna.H. changi was common at the 2.5 m and 5 m depth stations, whereasH. oliveri dominated from 5 m depth downwards. Chironomids showed mainly a 1-yr life cycle, but apparently bothHeterotrissocladius species had two contemporary cohorts with emergence in midsummer and late autumn/early spring, respectively. Average annual ratio was 4.2 and 4.6 forH. oliveri andH. changi, respectively. Annual production varied from 0.3 g ash-free dry weight (AFDW) m^–2 y^–1 at 16 m depth to 1.6 g AFDW m^–2 y^–1 at 2.5 m depthH. changi contributed 45%, fiveMicropsectra spp. 17% andH. oliveri 15% to total average production, which on a lakewide basis wasca. 1.1 g AFDW or 25 kJ m^–2 y^–1. Lake 95 thus belongs at the very low end of measured lake zoobenthic productions, which range from 10 kJ m^–2 y^–1 in Arctic lakes toca. 1600 kJ m^–2 y^–1 in highly eutrophic shallow lakes.     

不同植物配置下人工湿地大型底栖动物群落特征及其与环境因子的关系

大型底栖动物在人工湿地生态系统的物质循环和能量流动过程中发挥着重要作用,是保持湿地结构稳定、高效运行的重要因素。为了解大型底栖动物在人工湿地内的群落特征,于2013年8月—2014年5月对盐龙湖芦苇(Phragmites communis)、茭草(Zizania latifolia)、狭叶香蒲(Typha angustifolia)表流人工湿地的大型底栖动物群落进行调查。结合相对重要性指数(IRI)、多样性指数(Shannon-Wiener多样性指数,Pielou均匀度指数,Margalef丰富度指数)与相关性分析等手段,研究了不同植物配置下人工湿地大型底栖动物群落特征及其与环境因子的关系。调查共采集到大型底栖动物14种,主要优势物种为纹沼螺(Parafossarulus striatulus)、霍普水丝蚓(Limnodrilus hoffmeisteri)、长角涵螺(Alocinma longicornis)、摇蚊幼虫(Tendipes sp.),但不同植物配置下优势物种有所差别。芦苇、茭草及狭叶香蒲湿地的年均大型底栖动物密度分别为285、330、266个/m2,年均生物量分别为25.6、104.0、32.3 g/m2。茭草湿地的大型底栖动物群落在物种数量、均匀程度上要高于芦苇及狭叶香蒲湿地,而后两者多样性水平相当。茭草湿地底栖动物群落生物量与软体动物密度呈极显著(P0.01)正相关,总密度与水深呈显著(P0.05)负相关,环节动物的密度与全氮(STN)、有机质(SOM)之间分别呈极显著(P0.01)、显著(P0.05)正相关。研究为今后人工湿地生态系统的设计、管护以及长效运行提供新的思路。     

长江口潮下带春季大型底栖动物的群落结构

2005年4月对长江口全区域潮下带共10个采样站位的大型底栖动物进行了调查。调查采获大型底栖动物38种,分属5个生态类型,种类数较少,河口外缘站位种类数多于口内站位。各站位大型底栖动物的平均丰度为32.9个/m2、平均生物量为5.035g/m2(湿重);与20世纪七八十年代相比,平均生物量显著降低;口外缘站位的总丰度和总生物量均高于口内站位。环境因子相关分析表明,盐度是决定长江口大型底栖动物种类分布最重要的环境因子。群落聚类、标序分析显示,春季长江口潮下带大型底栖动物群落结构空间分异明显,完全符合目前长江口支、港、槽“三级分汊”的空间格局。其中,北支的大型底栖动物以混合高盐水种类为主,而南支则以淡水和半咸水种类为主。南支的南北槽分界处内外站位的群落差异也由盐度决定,因为靠近口内的群落均受长江冲淡水影响较大;而口外站位群落则受咸淡水影响。南支的南北港分界点内外的群落差异则主要受长江来水的影响,原因在于处在港分界点以内的群落所在区域,直接受长江来水的冲刷,底质环境极不稳定;而港、槽分界点之间的群落所在区域由于河口上段的诸多明暗沙体的阻挡,水势较为稳定,所以底质环境较稳定,从而使得港、槽分界点之间的群落出现了更多的沙蚕等底质环境类型种类。     

北部湾近岸海域浮游动物群落结构特征及季节变化

2017年3月(枯水期)、7月(丰水期)和10月(平水期)分别对北部湾近岸海域44个站位的浮游动物进行了调查。结果共检出浮游动物251种和浮游幼体24类,其中枯水期138种(类),丰水期134种(类),平水期191种(类),分属河口低盐、近岸暖温、近岸暖水和外海暖水4个生态类群。优势种9种,其中枯水期以原生动物占绝对优势,丰水期以枝角类、桡足类和浮游幼体类占优势,平水期以十足类和浮游幼体类占优势。浮游动物丰度年均值为789.95个/m~3,呈现出枯水期(1540.19个/m~3)明显高于平水期(457.58个/m~3)和丰水期(372.08个/m~3)的季节变化特征;浮游动物生物量年均值为252.40 mg/m~3,生物量的季节变化与丰度变化不一致,平水期生物量(385.01 mg/m~3)明显高于枯水期(221.41 mg/m~3)和丰水期(150.78 mg/m~3)。多样性指数平水期最高(3.16),丰水期(2.35)次之,枯水期(2.22)最低。枯水期和丰水期北部湾近岸海域浮游动物生物量和丰度水平分布特征基本呈现自河口近岸海域向外海递增的趋势,平水期浮游动物生物量与丰度的空间分布较为均匀。浮游动物的种类组成结构以及优势种的演替对浮游动物的生物量和丰度季节变化有着重要的决定作用。径流导致的悬浮物、营养盐等的变化可能是决定北部湾近岸海域浮游动物生物量和丰度空间分布的主要因素。研究还表明与其他海湾相比,北部湾近岸海域浮游动物群落结构趋于小型化,需加大关注。     

Periphyton biomass dynamics in gravel bed rivers: the relative effects of flows and nutrients

SUMMARY. 1. Periphyton chlorophyll a and ash free dry weight (AFDW) were monitored in nine rivers to examine the relative importance of flows and nutrients for regulating periphyton biomass in gravel bed rivers. 2. Mean annual flows in the rivers ranged from 0.94 to 169 m³ s^?1, mean dissolved reactive phophorus (DRP) from 1.3 to 68 μ g 1^?1, periphytic chlorophyll a from 4.6 to 73 mg m ^?2. and AFDW from 2.8 to 16 g m^?2. 3. For eight of the nine rivers NH₄-N. DRP, total Kjeldahl nitrogen, total phosphorus and total suspended solids were correlated (P<0.01) with flow, and for seven rivers conductivity was inversely correlated (P<0.05) with flow. 4. There was a hyperbolic relationship between flows and biomass, with chlorophyll a >100 mg m ^?2 and AFDW >20 g m^?2 occurring most frequently in flows of <20 m³ s^?1. 5. Floods prevented the development of medium term (i.e. up to 2 months) maxima in biomass in five of the rivers, but maxima occurred over summer-autumn and winter-spring in the three rivers where floods were absent. 6. Chlorophyll a biomass was more resistant to flooding than AFDW. Only 5993 of the forty-six recorded floods caused chlorophyll a scouring, whereas 74% of the floods caused AFDW scouring. The efficiency of scour was more influenced by the pre-flood biomass than the magnitude of the event. 7. Biomass maxima were significantly correlated (P<0.01) with mean DRP concentration during the accrual period. Overall, up to 53% of the mean annual biomass difference between rivers was explained by the mean annual DRP concentrations. However, the high correlations between nutrient concentrations and flow indicated that the nutrient data were also carrying hydrological information and that simple causal relationships between nutrients and biomass are difficult to establish in rivers. 8. It is concluded that hydrological factors contribute at least equally with nutrients to the differences in periphyton biomass between the gravel-bed study rivers. They combined to explain up to 63.3% of the variance in biomass, compared with 57.6% for nutrients. It is recommended that periphyton data from gravel-bed rivers should always be viewed within the context of the flow history of the site, and not just as a function of nutrient concentrations.     

Soil microarthropods and macrofauna in monsoon tropical forests of Cat Tien and Bi Dup-Nui Ba National Parks,southern Vietnam

The abundance, biomass, vertical distribution, and taxonomic composition of soil invertebrates (springtails, macrofauna, and termites) were studied in forest formations differing in edaphic and climatic conditions: lowland forests dominated by Lagerstroemia spp. or Dipterocarpus spp. in the Cat Tien National Park and in a mountain pine (Pinus kesiya) forest on the Da Lat Plateau, southern Vietnam. In the lowland forests, springtails had a relatively low density (10000–12000 ind./m²), but their diversity was high (41–43 species in each forest). The density of large soil invertebrates (without ants and termites) reached 500–700 ind./m² at a biomass of approximately 30 g/m² (with earthworms accounting for up to 230 ind./m² and 19–28 g/m²). Among termites, species of the genera Macrotermes and Odontotermes were dominant. Their total biomass in some areas exceeded 15–20 g/m². In the mountain pine forest, the total biomass of soil macrofauna was approximately 11 g/m², the abundance and diversity of springtails were low (7500 ind./m², 28 species), and wood-destroying species of the genera Schedorhinotermes sp. and Coptotermes sp. dominated among termites.     

Abundance, biomass and small-scale distribution of cryopelagic amphipods in the Franz Josef Land area (Arctic)

Arctic sea ice is inhabited by several amphipod species. Abundance, biomass and small-scale distribution of these cryopelagic (=ice associated) amphipods were investigated near Franz Josef Land in summer 1994. The mean abundance of all species was 420 ind./m²; the mean biomass was 10.61 g ww/m². Gammarus wilkitzkii was the dominant species, whereas Apherusa glacialis, Onisimus nanseni and O. glacialis were only scarcely found. Amphipods were concentrated at the edges of ice floes and were less frequent in areas further away under the ice. The relationship between the distribution and ecological/physiological requirements of cryopelagic amphipods, as well as the small-scale morphology of Arctic sea ice, are discussed. Received: 14 January 1998 / Accepted 14 April 1998     

Population demographics of Palaemon peringueyi (Macpherson 1990) (Decapoda: Palaemonidae) in a small intermittently open Eastern Cape estuary

The population demographics of the caridean shrimp Palaemon peringueyi was investigated monthly at four sites over a period of one year in the small, intermittently-open Grants River Estuary situated on the south-east coastline of southern Africa. Mean total abundance and biomass of P. peringueyi ranged between 0 and 23.2 ind m^?2 and 0 and 2.3mg wwt m^?2, respectively. A peak in its abundance coincided with a breaching event that occurred in December 2004, and could be attributed to the mass recruitment of juveniles (carapace length <9mm) into the estuary. Minor peaks in abundance were also associated with marine waters overtopping the sandbar that separates the estuary from the marine environment. The highest biomass values were recorded when the estuary was separated from the sea. Maximum abundance and biomass values of P. peringueyi were generally recorded in the middle reaches of the estuary where extensive beds of submerged vegetation, mainly Potamogeton pectinatus, predominated. Pearson correlation analysis indicated that the total abundance of P. peringueyi was significantly correlated (r = 0.49; p < 0.05) to percentage cover of submerged vegetation. The spatial pattern in abundance and biomass values of the shrimp is thought to reflect the availability of refuge areas against predation. A distinct spatial pattern in the community structure of the shrimp was evident, with juveniles numerically dominating the samples in the lower reaches of the estuary, while mature females predominated in the upper reaches of the system. In the middle reaches, the community comprised both juveniles and adults.     

洋山港潮间带大型底栖动物群落结构及多样性

2009-2010年在洋山港海域大洋山岛和圣姑礁进行四个季度潮间带大型底栖动物生态学研究。共采集到大型底栖动物61种,以广布种为主,部分为河口低盐种,其中软体动物22种,环节动物16种,节肢动物12种,苔藓动物5种,腔肠动物4种,星虫动物和棘皮动物各1种。优势种为短滨螺(Littorina brevicula)、多齿围沙蚕(Perinereis nuntia)、日本笠藤壶(Tetraclita japonica)、齿纹蜒螺(Nerita yoldii)和特异大权蟹(Macromedaeus distinguendus)。丰度和生物量在不同季节明显不同(P<0.05):丰度的最高值出现在春季,为(3204.9±837.84)个/m²,最低值出现在秋季,仅为(2213.2±731.27)个/m²;生物量的最高值则出现在夏季(2233.2±1493.42)g/m²,冬季最少,仅为(819.95±484.80) g/m²。大洋山岛和圣姑礁的丰度和生物量具有较大差异(P<0.05):年均丰度以大洋山断面较高,为(3090±742.74)个/m²,圣姑礁断面较低,为(2133±372.51)个/m²;而年均生物量则以圣姑礁断面较高,为(1711.1±1180.76) g/m²,大洋山断面较低,仅为(1028.5±627.61) g/m²。运用ABC曲线、等级聚类和MDS对大型底栖动物群落结构分析发现:大洋山潮带间大型底栖动物群落尚未受到干扰或干扰较轻,群落结构相对稳定;而圣姑礁断面的潮间带大型底栖动物群落受到了中度的干扰,群落结构稳定性下降。与15年前的研究相比,圣姑礁大型底栖动物的密度和生物量均有大幅度的降低,这与洋山港海域盐度的升高、生态环境变化和人为干扰强度增加等有关。     

Tree regeneration on rotten wood and on soil in old-growth stand

Forest regeneration on soil and on decaying wood was studied in natural mixed stand of Facus sylvatica L., Abies alba Mill. and Picea abies Karst. in Babia Góra National Park, Western Carpathians.Downed wood, divided into five decay classes covered around 6% of the forest floor. Among seedlings, Fagus and Abies codominated, while Picea was less numerous. The average seedling density on the soil with herb layer (240 ind./100 m²) was higher than on the logs, even on the strongly decayed ones (177 ind./100 m²). However, the density of Abies and Picea seedlings was higher on the rotten wood than on soil. Seedling survival of all species was better on the logs, especially in conifers. Because of the total dominance of Fagus among saplings, the presence of Abies and Picea in the next generation of canopy trees can strongly depend upon their regeneration on decaying wood.     

Production,nutrient dynamics and initial decomposition of floating leaves of Nymphaea alba L. and Nuphar lutea (L.) Sm. (Nymphaeaceae) in alkaline and acid waters

Production, turnover and nutrient dynamics of floating leaves of Nymphaea alba L. and Nuphar lutea (L.) Sm. were studied in four aquatic systems in The Netherlands, differing strongly in water quality. Production was 108–447 g AFDW.m⁻² for N. lutea and 319–348 g AFDW.m⁻² for N. alba. Turnover ranged from 3.6 to 4.4 without much difference between the sites and the species. During senescence 60–70% of the N and P from the leaves was resorbed by both of the plant species. The nutrient flow from the floating leaves into the detritus food chain differed considerably between the species and sites studied, mainly because of the differences in production. The data suggest that production is strongly influenced by the environment, whereas turnover and nutrient resorption during senescence seem to be plant characteristics. There was little difference in dynamics of the chlorophyll-α concentration in the leaves of the two species, irrespective of the growing site. Floating leaves of both species lost about 70% of their area due to fragmentation in the alkaline waters, whereas in the acid water very little fragmentation was observed.     

Mesozooplankton beneath the summer sea ice in McMurdo Sound,Antarctica: abundance,species composition,and DMSP content

The summer Phaeocystis antarctica bloom increases under-ice phytoplankton biomass in McMurdo Sound, Antarctica. The magnitude of mesozooplankton grazing on this bloom is unknown, and determines whether this production is available to the pelagic food web. We measured mesozooplankton abundance and body content of dimethylsulfoniopropionate (DMSP) during the McMurdo Sound austral summer (2006 and 2006–2007). Abundance varied from 20 to 4,500 ind. m⁻³ (biomass 0.02–274.0 mg C m⁻³), with peaks in mid-December and late-January/February. Abundance was higher but total zooplankton biomass lower in our study compared to previous reports. Copepods and the pteropod Limacina helicina dominated the zooplankton in both abundance and biomass. DMSP was detected in all zooplankton groups, with highest concentrations in copepod nauplii and L. helicina (95 and 54 nmol mg⁻¹ body C, respectively). Experiments suggested that L. helicina obtains DMSP by directly grazing on P. antarctica, which often accumulates to high biomass under the summer sea ice in McMurdo Sound.     

鲢鳙鱼养殖小型水库底栖动物群落季节动态

底栖动物是鱼类重要的天然饵料,评估水体中底栖动物的现存量可以指导渔业生产中鱼类的放养数量。为了探究淡水生态养殖水库中底栖动物群落的季节动态,于2013年4月、7月、10月和2014年1月对三河水库的底栖动物群落进行了调查分析。研究共采集到7个属的底栖动物,隶属于颤蚓科、摇蚊科和蠓科,未采集到软体动物。相对重要性指数(IRI)计算结果表明,菱跗摇蚊属Clinotanypus(IRI=7136)、颤蚓属Tubifex(IRI=6734)和尾鳃蚓属Branchiura(IRI=1384)是优势类群,分别占总捕获数量的34.26%、50.38%和10.96%。不同季节之间底栖动物的总密度和生物量差异显著(P0.05),均为冬季春季夏季秋季。冬季总密度(4100个/m~2)和总生物量(10.14 g/m~2)最高,春季(1446个/m~2;1.07 g/m~2)次之,夏季(579个/m~2;0.66 g/m~2)较低,秋季(492个/m~2;0.64 g/m~2)最低。非度量多维尺度分析(MDS)和群落相似性分析表明底栖动物群落结构季节差异显著(P=0.001),2013年三河水库的底栖动物群落可明显划分为3个:春季群落、夏秋季群落和冬季群落。皮尔森相关分析表明,底栖动物总密度与溶氧和营养盐呈正相关关系,与其他水理化因子呈显著负相关关系(P0.05)。冗余分析表明,氨氮、盐度、pH和浊度是三河水库底栖动物群落季节差异的显著影响因子(P0.05),总氮对底栖动物群落的季节差异具有边缘显著影响(P=0.08)。     

Brittle star fauna (Echinodermata: Ophiuroidea) of the arctic northwestern Barents sea: composition,abundance, biomass and spatial distribution

 Epibenthic brittle star assemblages were investigated on the northwestern Barents Sea shelf between 81° and 77°N in July 1991. At 9 drift stations in water depths between 80 and 360 m, series of 35–71 photographs, each depicting about 1 m² of the seabed, were taken along transects of about 150- to 300-m length to assess abundances and spatial distribution patterns of adult brittle stars (disc diameter ≥1 mm). Biomass values were derived by combining abundances with size-weight relationships and size frequencies established using specimens from trawl catches. Six brittle star species were identified on the seabed images. Ophiocten sericeum was the most abundant species on shallow shelf banks (≤100 m). Up to 2,800 individuals were counted on a single photograph; median abundances per station ranged from 32 to 524 ind.m^-2 and biomass from 0.3 to 5.0 g ash-free dry weight (AFDW) m^-2. The spatial distribution along the transects (i.e. on the 100-m scale) was, however, extremely patchy. Disc diameters of O. sericeum ranged between 1.6 mm and 15.4 mm. In deeper shelf habitats (>150 m), O. sericeum was rare or absent, and Ophiacantha bidentata dominated the brittle star fauna with median densities and biomasses of 2–49 ind.m^-2 and 0.07–1.9 g AFDW m^-2, respectively. Its disc diameters ranged from 2.9 to 14.4 mm. The other species (Ophiura sarsi, Ophiopholis aculeata, Ophioscolex glacialis, Ophiopleura borealis) occurred in distinctly lower numbers. Our findings provide further evidence that brittle stars dominate epibenthic communities on Arctic shelves and locally reach very high abundances. Dense beds of Ophiocten sericeum seem to be a general phenomenon on high-Arctic shallow shelf banks. Received: 30 March 1995/Accepted: 30 June 1995     

Temporal and spatial variability in the abundance,biomass and distribution of Palaemon peringueyi (Decapoda: Crustacea) are influenced by biological but not physico-chemical factors in the permanently open Kariega Estuary,South Africa

Biological and physico-chemical factors affecting abundance and biomass of shrimp Palaemon peringueyi were investigated in 2010–2011 in the lower, middle and upper reaches of the freshwater-deprived permanently open Kariega Estuary. Shrimp abundance and biomass ranged from 0 to 88 ind. m^?2 and 0 to 4.4 g wwt m^?2, respectively. Shrimps were most abundant in the lower reach, and highest abundances and biomasses were recorded in the lower reach in June when salinities were low. The shrimps were almost always absent in the upper reach. Juveniles were found mostly in the lower and middle reaches, whereas adults were distributed in all three reaches. Regression analyses showed no statistically significant relationship for either abundance or biomass of the shrimps with temperature, salinity and dissolved oxygen (p > 0.05). The relationship between shrimp abundance and biomass and vegetation cover was positive and statistically significant (R² = 0.109 and 0.185, respectively; p < 0.05). Vegetation cover plays an important role in determining the presence, distribution and abundance or biomass of P. peringueyi in this estuary.     

Abundance and biomass estimates of the benthic fauna in Admiralty Bay,King George Island,South Shetland Islands

Summary Quantitative benthic samples were collected along three transects in Admiralty Bay, King George Island, South Shetlands. At each of a total of 18 stations, between 15 and 250 m depth, we took 3 replicate samples with a van Veen grab. Animals collected were classed into major groups. Abundance and biomass per m² was calculated for each sampling site. Considerable population densities and high biomass values were found. Most abundant groups were Bivalvia, Polychaeta and Amphipoda, whereas the largest part of the biomass was due to Ascidiacea, Ophiuroidea, Echinoidea, Polychaeta and Bivalvia. The maximum abundance recorded was 36,000 ind m^-2 while the average was approximately 6500 ind m^-2. Maximum biomass was over 2400 g m^-2 with an average of ca. 700 g m^-2. The contribution to the total biomass by groups such as the Oligochaeta, Cumacea and Tanaidacea was higher in the inner shallow part of Admiralty Bay (Ezcurra Inlet) than in the deeper areas of the bay. Our results confirm the reports on an unusually high density and biomass of the Antarctic sublittoral benthic fauna. Sessile suspension feeders belonging to the Bivalvia, Ascidiacea, sedentary Polychaeta, and vagile scavengers of the Ophiuroidea, Amphipoda and errant Polychaeta are the most significant groups in the Antarctic Ecosystem. The total benthic biomass in Admiralty Bay, based on the present preliminary quantitative data, was estimated to be over 600,000 t. This value is probably still an underestimate.     

Seasonal growth of the submerged macrophyte Ceratophyllum demersum L. in mesotrophic Lake Vechten in relation to insolation,temperature and reserve carbohydrates

Seasonal growth of a Ceratophyllum demersum stand in Lake Vechten, The Netherlands, varied considerably during 1978, '79 and '81. The biomass was highest in 1981 (max. 115 g ash-free dry weight m^–2). The 1978 growth trend was similar to that of 1981 with slightly lower net annual production (max. 92 g AFDW m^–2). The vegetation almost disappeared in 1979 (max. 24 g AFDW m^–2). These large differences in biomass could not be explained by differences in insolation but were mainly attributed to the severe winter of 1978–'79 which slowed plant development and full maturity was attained only after the diurnal insolation had decreased.Reserve carbohydrates were primarily starch and water-soluble sugars. Starch concentrations varied between 71.5 and 24.7 mg g^–1 AFDW in the winter and summer, and total sugar concentrations between 24.9 and 20.2 mg g^–1 AFDW, respectively. The non-reducing sugars tended to predominate in summer and the reducing sugars in winter. The value of these reserves for maintenance, growth and survival was assessed by calculating plant carbon budgets for several seasons.It was concluded that C. demersum relies heavily on its developmental timing and energy-conserving physiological mechanisms to survive extended periods of stress and in these respects is analogous to a typical terrestrial shade plant.     

Spatial heterogeneity recognition in estuarine intertidal benthic macrofaunal communities: influence of sieve mesh-size and sampling depth

Estuarine intertidal soft-bottom macrobenthic infauna of the Tagus estuary was characterised using different mesh size sieves and sediment sampling depth. The study sampled 105 sites using a hand held 0.01 m² corer. The top layer (0–5 cm) was sieved through nested 1.0 and 0.5 mm meshes whereas the bottom layer (5–20 cm) was through a 1 mm mesh. The total survey took 26 taxa of more than 5800 individuals and a total wet weight biomass of over 650 g. The top layer, using both sieves, gathered 23 taxa (92% of the total), more than 5600 specimens (96%) but less than 8 g of biomass (1%) whereas the 1.0 mm sieve retained 21 taxa (91%), more than 1700 specimens (31%) and almost 7 g of biomass (1%). Abundance was dominated by small annelids, of which Streblospio shrubsolii was 68%, whereas biomass was dominated by molluscs, with the bivalve Scrobicularia plana representing 98%. Multivariate analyses showed an abundance pattern where the top layer data was very similar to that obtained with both layers. The bottom layer data were needed to accurately represent the total biomass pattern. The macrofaunal spatial pattern identified with the 0.5 mm sieve data differed from that identified by the 1.0 mm and was essential to discriminate a faunal assemblage located along the upper part of the shore. It was concluded that in order to characterize the macrofauna community structure, based on the presence/absence of taxa, the top layer and a 1.0 mm sieve would be sufficient. An abundance-based characterization requires the top layer and a 0.5 mm sieve whereas a biomass-based characterization requires data for both layers but it is sufficient to use the 1.0 mm sieve. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.