三峡库区澎溪河鱼类时空分布特征的水声学研究

为了解三峡库区支流澎溪河鱼类时空分布变化,2009—2010年的秋季、冬季和春季,使用Simrad EY60鱼探仪对澎溪河的鱼类资源量及其时空分布特征进行3次声学调查。结果表明:3个季节鱼类水平分布不均匀,鱼类最大密度分别为67.07尾/1000 m3,19.66尾/1000m3,17.25尾/1000m3且不同季节上层、中层鱼类密度水平分布有显著性差异(P≤0.01,P=0.03);各季节鱼类密度垂直分布也有一定差异,冬季上层鱼类密度和下层鱼类密度差异较为显著(P=0.05);另外鱼类密度昼夜分布有显著性差异(P<0.05),造成该现象的原因主要是由于鱼类的昼夜垂直节律(Diel Vertical Migration,DVM)引起;3个季节的鱼类目标强度(TS值)的差异极其显著(P<0.01),其中秋季鱼类TS最高((-57.0±5.6)dB),春季TS值最低((-58.6±4.9)dB),造成该差异的原因是4—6月是长江上游鱼类繁殖季节,仔稚鱼居多。鱼类空间分布及其位点的水深关系分析显示,鱼类密度水平分布秋季、冬季与水深不相关(︱r︱<0.2),春季与水深中度负相关(r=-0.5,P≤0.05)。     

山东半岛南部产卵场温跃层对鳀鱼鱼卵垂直分布的作用

2000～2004年5～7月"北斗"号生物资源调查船对山东半岛南部产卵场进行多学科综合调查期间,于2003年6月17～18日和6月27～30日分别在35°01.9′N、120°32.9′E海区和35°03.3′N、120°26.4′E海区进行了25 h和64 h的水团追踪观测调查,鳀鱼鱼卵的数量、垂直分布与水温的分布为重点调查内容.调查结果表明:水温垂直分布的变化、海水混合的强弱、水体的辐聚/辐散等物理过程对水体中鳀鱼鱼卵数量和鳀鱼鱼卵在不同水层的分布有很大影响.温跃层分布深度的波动引起水体的垂直交换(混合)、水平对流(辐聚/辐散)和跨跃层的物质交换.温跃层深度变浅时,上混合层水体的厚度变薄,跨跃层的向上混合,将下混合层水体中和温跃层中的鳀鱼鱼卵输运到温跃层和上混合层中,同时表层水体发生辐散现象,使得下混合层、温跃层和上混合层水体中鳀鱼鱼卵数量减少、密度减小,导致整个水柱内鳀鱼鱼卵的数量减少;温跃层深度加深时,上混合层水体的厚度增加,跨跃层的向下混合,将上混合层水体中和温跃层中的鳀鱼鱼卵输运到温跃层和下混合层水体中,同时表层水体发生辐聚现象,使得上混合层、温跃层和下混合层水体中的鳀鱼鱼卵数量增多、密度增大,导致整个水柱内鳀鱼鱼卵的数量增多;温跃层水体中鱼卵数量和密度的变化较上混合层和下混合层水体更为显著.水体中温跃层的存在、温跃层分布深度的波动及其波动的程度对上混合层和温跃层中鳀鱼鱼卵的数量和密度的变化起着主导作用,导致鳀鱼鱼卵数量垂直分布的剧烈变化.     

大沙河水库拟柱孢藻昼夜垂直分布特征

为了解大沙河水库拟柱孢藻(Raphidiopsis raciborskii)昼夜垂直分布模式,于2018年9月20—21日(丰水期)和2018年12月31日(枯水期)对该水库拟柱孢藻进行昼夜定点分层采样,分析影响拟柱孢藻垂直分布的主要环境因子。用Morisita指数和平均滞留深度定量检验拟柱孢藻垂直分布格局;用方差分析检验拟柱孢藻是否存在昼夜垂直迁移现象,并采用多元回归方法分析拟柱孢藻垂直分布格局和环境因子的关系。结果表明:拟柱孢藻在丰水期呈现集群分布模式,主要分布于0.5～2 m水层,平均滞留深度为1.5 m;枯水期在6 m水深以上的水层呈现随机分布模式;丰水期和枯水期均无明显的昼夜垂直迁移现象;大沙河水库温跃层的出现是影响拟柱孢藻的昼夜垂直分布模式的主导因素。     

东湖放养鱼类时空分布的水声学研究

2000年,用鱼探仪逐月对东湖鱼类的空间分布进行探测的结果表明：东湖鱼类主要分布在1．5m以下的水层,1．5m以上与1．5m以下的水层的鱼类密度分布存在显差异,此外,东湖中不同区域的鱼类密度分布亦有显性差异,统计分析显示,这种水平分布差异与水深,离岸距离等因素没有明显的相关,可能主要由群聚行为引起,由不同月份群聚程度不一致,推测水温的变化可能会影响鱼类的群聚行为,污水排放对鱼类空间分布也可能有一定的影响。     

禁渔初期鄱阳湖鱼类时空分布特征

研究于2020—2021年使用Simrad EY60鱼探仪对鄱阳湖进行了秋季、春季和冬季共3次的水声学调查,并同步开展渔获物调查作为补充,分析鄱阳湖鱼类资源时空分布变化特征。结果表明:在季节分布上,鱼类目标强度和密度值都存在显著差异(P<0.05),在目标强度上表现为冬季[(–51.0±14.13) dB]>春季[(–52.10±4.59) dB]>秋季[(–52.71±9.95) dB],在鱼类密度上表现为冬季(54.61 ind./1000 m3)>秋季(46.10 ind./1000 m3)>春季(18.54 ind./1000 m3);在水平分布上,鱼类资源空间分布不均且不同湖区间有显著差异(P<0.05),秋季鱼类主要分布在中部湖区松门山,冬季鱼类主要分布在北部湖区通江水道;在垂直分布上,秋季和冬季均表现为底层>中层>表层,春季表现为表层>中层>底层。综合来看,鄱阳湖鱼类时空分布与鱼类的生活习性如产卵、育肥和越冬等因素密切相关。研究结果为从宏观空间尺度分析区域鱼类时空变动特征提供参考,也为鄱阳湖禁捕效果评估及生物完整...     

基于水声学方法的天目湖鱼类资源捕捞与放流的生态监测

本文在天目湖捕捞赶鱼前（2011年12月）、赶鱼后（2012年1月）、捕捞与放流后（2012年3月）3个渔业阶段,结合渔业捕捞统计,采用水声学方法对天目湖鱼类资源（赶鱼后为不包括集鱼网箱的湖区鱼类资源）的捕捞与放流进行了生态监测,并构建GIS模型,得到鱼类种群结构、大小组成、鱼类密度、鱼类集群、鱼类资源量及其分布,为天目湖保水渔业的实施和渔业生产提供科学依据。天目湖鱼类种群以鲤科鱼类为主,鲢鳙2011年捕捞统计重量占比为98.07%,单网簖采样尾数占比为68.72%,鱼类资源受放流种类和规格影响较大;赶鱼前后和捕捞与放流后3个渔业阶段的鱼类平均目标强度（TS）分别为（-47.84?4.79）dB、（-48.58?4.98）dB、（-47.24?5.10）dB,且差异性显著（P<0.05）,捕捞与放流后TS在-45—-40 dB的鱼类明显升高到24.40%;3个渔业阶段的鱼类密度（FPCM）分别为（0.0124?0.0292）ind/m3、（0.0062?0.0227）ind/m3、（0.0098?0.0185）ind/m3,捕捞赶鱼作业显著（P<0.05）降低了鱼类密度,而捕捞与放流后鱼类密度显著（P<0.05）低于赶鱼前则是由于水深上升所致;在冬季的中下层水体出现典型的鱼类聚群,且随温度降低团聚程度提高;通过构建GIS模型评估鱼类资源量,赶鱼前约61万尾、赶鱼后约38万尾、捕捞与放流后约67万尾,资源量在中下游分布较高。     

中国季节性昼夜增温的不对称性及其对植被活动的影响

基于1982—2015年气象数据,采用线性趋势分析和GIS空间分析方法对我国近34年季节性昼夜增温的时空格局进行分析;并结合GIMMS-NDVI 3g遥感数据和植被区划数据,采用偏相关分析方法探讨不同植被分区植被对季节性不对称性增温的响应。结果表明:(1)近34年来中国昼夜气温普遍存在极为显著的上升趋势;昼夜增温在各季节均表现出不对称特征,且该不对称特征存在明显的季节性差异,春季、夏季、秋冬和冬季白天增温速率分别为夜间增温速率的1.49倍、0.98倍、0.73倍和1.69倍;(2)不同分区植被对季节性昼夜不对称增温的响应各异:相对于夜间增温,白天增温对植被活动影响程度更大,影响区域更为广泛;春季和冬季昼夜增温对植被活动的影响范围更广,且春、秋季昼夜增温对植被NDVI的上升普遍起到促进作用;(3)季节非对称性昼夜增温对不同分区的植被活动有不同的影响,这种影响程度随季节的变化存在明显差异。通过分析中国昼夜增温的季节性变化趋势及其对不同类型植被的影响,有助于加深我们对全球气候变化背景下季节性昼夜不对称增温对中国陆地植被动态影响的认识。     

有蹄类昼夜活动时空动态——以岩羊(Pseudois nayaur)为例

调整时间分配和空间利用是有蹄类应对食物资源和环境胁迫周期性波动的常见生存策略。为探索高山有蹄类对这种波动的行为响应和策略,于2018年6月-2019年8月利用红外相机对四川王朗国家级自然保护区内的岩羊（Pseudois nayaur）种群进行了调查,并利用Wilcoxon秩和检验初步分析了它们的昼夜活动时空动态（所涉及分析的数据监测时间为2018年7月底至2019年8月初）。基于前人的研究结论和观点,预测岩羊的昼夜活动在不同季节和不同空间类型将呈现显著差异。结果表明,岩羊的行为基本符合预测：（1）岩羊夏季昼间和冬季夜间较多出现在林缘（夏季昼间：43.64±3.39;冬季夜间：10.00±0.26）和林内（夏季昼间：34.21±3.21,P=0.065;冬季夜间：8.40±0.64,P=0.026）,可能与躲避极端气温有关;（2）岩羊在食物较匮乏的冬季,夜间的活动强度均显著高于其他季节（冬季：23.00±0.73;春季：2.00±0.39;夏季：4.80±1.36;秋季：15.00±1.31）,且在昼间选择易于觅食的草甸生境内活动（林缘：31.79±3.54,草甸：22.79±3.16;P=0.081）。有趣的是,岩羊冬季夜间更多选择林缘（10.00±0.26）,而非预期的林内生境（8.40±0.64,P=0.026）。岩羊在夜宿地附近（林缘）活动强度最大可能是权衡食物和环境胁迫的结果。因为,夜间集中在距离夜宿地和觅食地都比较近的环境中活动,无疑是一种经济的选择。随着近年来气候变化的加剧,高山生态系统受到的威胁越来越明显。基于本研究的发现,建议更多关注高山物种的生存状况和高山生态系统的健康程度,为认识和评价气候变化对生物多样性的影响提供参考。     

白马雪山黑白仰鼻猴(Rhinopithecus bieti)垂直迁移(英文）

2000-2001年间,在白马雪山国家级自然保护区南任村附近,通过在四个山坡每隔海拔100米的样带（宽5.0米）内搜集黑白仰鼻猴的粪便来研究猴群不同季节的垂直迁移模式。同时,通过在每个地区山脊上和山沟内搜集2.5米宽垂直样带内的粪便,来研究猴群不同季节对山脊和山沟的选择性。结果表明：猴群在海拔3500-4300米的区域活动。虽然猴群全年集中利用3900-4200米的林带;但是具有季节性差异：夏季最高（4200米）,依次是秋季（4100米）和冬季（4000米）,夏季最低（3900米）。另外,冬季山沟中的粪便多于山脊说明猴群在沟中停留时间长,这与沟中少风且温度高有关。不同海拔带上的粪便密度和松萝量间正相关,这意味着食物资源的垂直分布是影响猴群垂直迁移的重要因素。春季,猴群会下到低海拔采食嫩芽/叶,而冬季则下到低海拔处躲避首次大雪,这很可能导致猴群集中利用第二个海拔带。     

白马雪山黑白仰鼻猴(Rhinopithecus bieti)垂直迁移

2000-2001年间,在白马雪山国家级自然保护区南任村附近,通过在四个山坡每隔海拔100米的样带(宽5.0米)内搜集黑白仰鼻猴的粪便来研究猴群不同季节的垂直迁移模式。同时,通过在每个地区山脊上和山沟内搜集2.5米宽垂直样带内的粪便,来研究猴群不同季节对山脊和山沟的选择性。结果表明:猴群在海拔3500-4300米的区域活动。虽然猴群全年集中利用3900-4200米的林带;但是具有季节性差异:夏季最高(4200米),依次是秋季(4100米)和冬季(4000米),夏季最低(3900米)。另外,冬季山沟中的粪便多于山脊说明猴群在沟中停留时间长,这与沟中少风且温度高有关。不同海拔带上的粪便密度和松萝量间正相关,这意味着食物资源的垂直分布是影响猴群垂直迁移的重要因素。春季,猴群会下到低海拔采食嫩芽/叶,而冬季则下到低海拔处躲避首次大雪,这很可能导致猴群集中利用第二个海拔带。     

Diurnal dynamics of the vertical distribution of zooplankton in an oligotrophic lake

The diurnal dynamics of the vertical distribution of zooplankton was studied in an oligotrophic lake with a high water transparency. Those sedentary species which occupy the upper water layers in waterbodies with low water transparency shift to a border between epy- and metalimnion and stay there during most of the day in Koskovskoye Lake, which has a high water transparency. Active diurnal vertical migrations are characteristic of large organisms. Increased water transparency weakly affects large zooplankters that occupy metalimnial layers in mesotrophic waterbodies. The relationship between the zooplankton’s vertical distribution and the distribution of phytoplankton and fish is analyzed.     

Studies on Plover Cove Reservoir, Hong Kong

The zooplankton fauna of the Plover Cove Reservoir has been investigated using two sampling series. The first series involving a 3-year investigation using 6-ft vertical hauls at three stations in the reservoir, revealed the presence of two copepod and four cladoceran species with little variation in terms of seasonal peak occurrence and abundance in any of the stations and so no evidence of the horizontal distribution patterns referred to by other authors. In all three stations Diaptomus gracilis was the dominant copepod species and Diaphanosoma leuchtenbergianum the dominant cladoceran species. The second series, involving a 13-month investigation of vertical sets of water samples collected both day and night at 4-h intervals for 24-h periods, revealed that in terms of seasonal vertical distribution, all six species occurred at all depths during the survey, but with a tendency to be concentrated in the surface waters. In terms of diurnal vertical distribution, differences in the migration pattern occurred from season to season in the case of Diaptomus gracilis. Thus, during spring, summer and autumn, concentrations occurred at the surface at 10.00 and 22.00 hours followed by migration to greater depth, whereas in winter, surface accumulations persisted even into the daylight hours. However, both Cyclops hyalinus and Diaphanosoma leuchtenbergianum showed surface accumulations at night and a movement away from the surface by day during all seasons. Investigations of the seasonal variation in environmental parameters conducted during both sampling series revealed that, as in the case of similar surveys, water temperature was the major controlling factor governing the seasonal variation in composition of the zooplankton fauna as well as its seasonal vertical distribution since in the case of Diaptomus gracilis and Ceriodaphnia reticulata low water temperatures corresponded with peak seasonal occurrence whereas in the case of the other species high water temperatures corresponded with peak seasonal occurrence, and since Diaptomus gracilis and Diaphanosoma leuchtenbergianum showed maximum concentration near the surface when surface water temperatures were high, whereas the remaining species showed their maximum concentration near the surface when lower water temperatures prevailed. It would also appear, however, that seasonal changes in zooplankton densities closely followed algal densities since Diaptomus gracilis, Diaphanosoma leuchtenbergianum and Bosmina longirostris had their maxima in late spring and Cyclops hyalinus in late summer while algal densities in this reservoir were highest in early spring and early summer. With regard to the diurnal vertical distribution of the zooplankton, light appeared to be the only factor alternating by an amount likely to be correlated with such diurnal vertical changes in zooplankton density.     

Diel vertical migrations of invertebrate predators (Leptodora kindtii ,Thermocyclops taihokuensis, andMesocyclops sp .) in a shallow, eutrophic lake

We studied vertical distribution patterns of three invertebrate predators – Leptodora kindtii, Mesocyclopssp., and Thermocyclops taihokuensis– in a shallow eutrophic lake, Lake Suwa , Japan. From June to October in 2000 and 2001, we collected samples in the lake center in order to examine the vertical distribution patterns and the densities of the predators in the water column during the day (0900) and at night (2330). We also examined phototactic behavior of Leptodora in the laboratory. The three invertebrate predators showed clear migration patterns. Leptodora and Thermocyclops displayed a typical migration, avoiding the surface and maintaining a high abundance in deeper water during the day, and being distributed uniformly during the night. Mesocyclops, on the other hand, showed no clear vertical distribution pattern in the water column. However, Mesocyclops showed higher densities in the water column during the night than during the day. It suggests that they stayed just above the bottom during the day and migrated upward during the night. Leptodora also showed such a density difference between day and night. In the laboratory, Leptodora showed strong negative phototactic behavior. The observed density changes between day and night in Leptodora and Mesocyclops suggests the possible underestimation of their population density by usual sampling methods, and thus the impact of predation on populations of prey zooplankton species may also be underestimated in shallow water bodies.     

Habitat selection and diel distribution of the crustacean zooplankton from a shallow Mediterranean lake during the turbid and clear water phases

1. The fish fauna of many shallow Mediterranean Lakes is dominated by small‐bodied exotic omnivores, with potential implications for fish–zooplankton interactions still largely unknown. Here we studied diel variation in the vertical and horizontal distribution of the crustacean plankton in Lake Vela, a shallow polymictic and eutrophic lake. Diel sampling was carried out on three consecutive days along a horizontal transect, including an open‐water station and a macrophyte (Nymphaea alba) bed. Since transparency is a key determinant of the predation risk posed by fish, the zooplankton sampling campaigns were conducted in both the turbid (autumn) and clear water (spring) phases. 2. In the turbid phase, most taxa were homogeneously distributed along the vertical and horizontal axes in the three consecutive days. The only exception was for copepod nauplii, which showed vertical heterogeneity, possibly as a response to invertebrate predators. 3. In the clear water phase, most zooplankton taxa displayed habitat selection. Vertically, the general response consisted of a daily vertical migration (DVM), despite the limited depth (1.6 m). Horizontally, zooplankters showed an overall preference for the pelagic zone, independent of the time of the day. Such evidence is contrary to the postulated role of macrophytes as an anti‐predator refuge for the zooplankton. 4. These vertical (DVM) and horizontal (macrophyte‐avoidance) patterns were particularly conspicuous for large Daphnia, suggesting that predation risk from size‐selective predators (fish) was the main factor behind the spatial heterogeneity of zooplankton in the spring. Thus, the difference in the zooplankton spatial distribution pattern and habitat selection among seasons (turbid and clear water phases) seems to be mediated the predation risk from fish, which is directly related to water transparency. 5. The zooplankton in Lake Vela have anti‐predator behaviour that minimises predation from fish. We hypothesise that, due to the distinct fish community of shallow Mediterranean lakes, aquatic macrophytes may not provide adequate refuge to zooplankters, as seen in northern temperate lakes.     

Diel vertical and horizontal distribution of crustacean zooplankton and young of the year fish in a sub-alpine lake: an approach based on high frequency sampling

Understanding the spatial dynamics of predators and their preyis one of the most important goals in aquatic ecology. We studiedspatial and temporal onshore–offshore distribution patternsin young of the year (YOY) Eurasian perch (Perca fluviatilis)and crustacean zooplankton (Daphnia hyalina, Cyclops prealpinus)along a transect in Lake Annecy (France). Our study representsa first attempt at coupling hydroacoustic fish survey and highfrequency zooplankton recording to assess simultaneously thelarge-scale distribution patterns of YOY fish and their zooplanktonprey over a diel cycle (day, dusk and night sampling). We hypothesizedthat the spatial distribution of zooplankton could be shapedby both anti-predator behaviour (horizontal and vertical migrations)and predation losses. Fish biomass, size structure and dietwere assessed from split-beam echosounding and net trawlingsamples, whereas crustacean abundances were estimated with asmall modified Longhurst–Hardy continuous plankton recorder.We evaluated the diel changes in the spatial distribution patternsof fish and zooplankton and determined the overlap between theirdistributions. Fish biomass was dominated by YOY perch in upperwarmer layers and salmonids (Coregonus lavaretus and Salvelinusalpinus) in the colder and oxygenated deep layers. YOY perchwere aggregated in dense schools in the epilimnion during theday and dispersed at night. Fish biomass was distributed alonga strong increasing onshore–offshore gradient at night,whereas crustacean prey showed a decreasing gradient. This onshore–offshorenegative gradient in crustacean distribution, expressed on ashorter scale during the day, shifted toward the surface watersat night. A distinct kinetic of diel vertical migration (DVM)patterns was exhibited by daphnid and cyclopoid populationsand resulted in distinct vulnerability to perch predation. Spatio-temporaldistribution of crustaceans in Lake Annecy during the diel cyclestudy was probably shaped both by predation loss to YOY perchand by anti-predator behaviour (DVM, DHM) by zooplankton. Theimplications for fine-scale studies of fish-zooplankton interactionsare discussed.     

Vertical distribution and feeding pattern of Euphausiacea (Crustacea) in the eastern Banda Sea (Indonesia) during the SE and NW monsoons

The vertical distribution of Euphausiacea (Crustacea) in theeastern Banda Sea (Indonesia) during the SE and NW monsoon seasonswas studied. In August 1984 and February/ March 1985, stratifiedday and night sampling was carried out between 0 and 500 m atfour stations. A total of 31 species was found, of which mostwere present in both monsoon seasons. Species with a high presencein samples and performing diurnal vertical migration in bothmonsoon seasons were Euphausia diomedeae, Euphausia pseudogibba,Thysanopoda monacantha, Thysanopoda iricus-pidaia and Nematoscelismicrops. Species with a high presence in samples showing nodiurnal vertical migration in both monsoon seasons were Euphausiasimilis, Nematobrachion boopis. Nematoscelis tenella, Stylocheironmaximum and Thysanopoda orientalis. The density of Euphausiaceaat the sampled stations was higher, but more heterogeneous,in the nutrient-enriched SE monsoon period than in the relativelynutrient-poor NW monsoon season, when densities were lower andmore similar. The vertical distributions and diurnal verticalmigration of species did not show a unanimous and strong responseto seasonal hydrographic differences. The day–night depthdistribution pattern of the Euphausiacea population in the upper500 m is largely the same in both seasons, with comparable migrationranges. Some species showed a somewhat upward shifted depthdistribution in the nutrient-enriched period. For mesopelagicand bathypelagic species especially, food resources were thenfavourable in the upper layers, as indicated by rare recordsof Thysanopoda crisiata. Analyses of stomach contents snowedmainly a nocturnal feeding pattern for the diurnal verticalmigrating species and a continuous feeding pattern for the non-migratingspecies.     

Evidence for a diurnal horizontal migration in Daphnia hyalina lacustris Sars

Diurnal sampling of a transect across a shallow, eutrophic gravel pit suggested that a diurnal horizontal migration was present in Daphnia hyalina lacustris, in which it remained in the littoral zone during the day and moved out into the open water at night. The avoidance of fish predation seemed the most likely ultimate cause of this migration.     

Modification of the diel vertical migration of Bythotrephes longimanus by the cold-water planktivore, Coregonus artedi

1. The weak diel vertical migration observed in the large cladoceran Bythotrephes longimanus seems contradictory to the predator‐avoidance hypothesis that predicts large zooplankton should have long migration amplitudes. However, cold‐water planktivores, especially Coregonus spp., are a main source of mortality for Bythotrephes and hence a deeper migration would result in a greater overlap with these hypolimnetic planktivores. We hypothesized that Coregonus artedi (cisco) modifies the normal vertical migration pattern of Bythotrephes, such that the latter stays higher in the water column during the day and thus migrates less extremely at night. 2. The vertical distribution of Bythotrephes during the day was determined from single visits to six lakes in Ontario, Canada, all of which contain warm‐water, epilimnetic planktivores but differing in whether they contain cisco. One lake of each fish type was sampled day and night every 2–3 weeks over the ice‐free season to examine daytime depths and migration amplitude. 3. The vertical migration of Bythotrephes differed in the presence and absence of cisco. In the lakes with cisco, there were significantly fewer Bythotrephes in the hypolimnion and they were higher in the water column during the day. Migration amplitude was smaller in the cisco than in the non‐cisco lake. These observations were not attributable to differences in physical factors, and, although not conclusively attributable to cisco, are consistent with an effect of cisco. 4. We suggest that diurnal depth selection by Bythotrephes in lakes containing cisco is a trade‐off between the risk of predation by warm‐ versus cold‐water predators, balanced by the benefits of increased temperature and feeding rates near the surface. Even in lakes without cisco, however, the vertical migration of Bythotrephes was less than expected, suggesting that diurnal depth selection is a balance between the risk from warm‐water planktivores and access to sufficient light to feed effectively.     

Taxonomy of cyanobacteria: a contribution to consensus approach

Temporal migrations by aquatic organisms have important implications for fundamental ecosystem processes and community interactions. Mysid crustaceans, key planktivores and fish prey in aquatic food webs, frequently undertake diurnal vertical migrations, but there are limited reports of horizontal movements. Using seasonal and diurnal field surveys in Lough Derg on the Shannon River (Ireland), we tested the hypotheses that (i) the euryhaline mysid Mysis salemaai expands seasonally its horizontal distribution and that (ii) the diurnal pattern of vertical migration within the shallows overlaps with the introduced mysid Hemimysis anomala. M. salemaai, previously considered an exclusively offshore species, changed its horizontal distribution significantly with seasons, being restricted to ≥8 m in summer and extending to all depths in winter. During winter, the distribution of M. salemaai overlapped with H. anomala in shallows and there was a highly significant overlap in their diurnal emergence in the open water, indicating a strong temporal synchrony of planktonic foraging. The seasonal range expansion of M. salemaai is likely to have important implications for horizontal redistribution of nutrients. Interactions with the sympatric H. anomala are likely, adding to existing physico-chemical pressures on the glacial relict M. salemaai and potentially contributing to its further extirpations.