Comparative ecology of the copepods Calanoides carinatus and Calanus agulhensis — the influence of temperature and food

Hypotheses regarding temperature, food abundance and food size were tested to explore niche separation between Calanoides carinatus, an abundant copepod in the cool and food-rich southern Benguela upwelling system, and Calanus agulhensis, the dominant copepod on the warmer, relatively food-poor Agulhas Bank off the south coast of South Africa. Under non-limiting food conditions, egg production by both species increased linearly with temperatures between 9°C and 18°C. Egg production by C. carinatus was relatively faster at 21°C, but was offset by greater mortality. Both species showed similar functional responses to food concentration in the field, reaching satiation at ～15mg Chl a m^?3, or ～3–4ppm. Food abundance was the most important predictor of egg production, whether measured as Chl a or as particle volume. Both species preferred larger particles that dominated the biomass peak, but particle size appeared more important for C. carinatus, with increasingly faster rates of egg production as the proportion of large cells (>10μm) exceeded 50%, and slower ingestion of small (<10μm) cells. Omnivory may be more important to C. agulhensis. Niche separation between the two species appears unrelated to temperature, food abundance or diel vertical migratory behaviour, and is more likely a function of variability in food availability, although food size may also play a role.     

Life strategies,energetics and growth characteristics of Calanoides carinatus (Copepoda) in the Angola-Benguela frontal region

Rates of daily egg production, moulting and egg hatching success, as well as total lipid content and composition of Calanoides carinatus, were measured in the region of the southern Angola Curre nt SAC), the Angola-Benguela Front (ABF) and the coastal upwelling area of the northern Benguela Current (NBC) system during February–March 2002. There were distinct differences in the vertical distribution, growth characteristics, lipid content and composition of populations in the SAC/ABF and NBC regions, indicative of different physiological states. Whereas in the NBC, C. carinatus was actively growing in response to elevated chlorophyll a levels associated with coastal upwelling, it comprised deep-living C5 copepodids with very large wax ester reseves (c. 40–50% dry mass) and extremely low metabolism in the SAC/ABF, suggesting diapause. This study provides the first data on lipid composition (lipid classes, fatty acids and alcohols) of this copepod in the region; in particular, the diapausing C5 contained high-levels of long-chain, mono-unsaturated fatty acids (23% of all fatty acids) and alcohols (69% of all fatty alcohols) in addition to trophic markers of diatoms, viz. 16:1(n-7) and 20:5(n-3). Based on total lipidcontent, the maximum survival time of the diapausal component of C. carinatus was estimated to be 149–192 days, whereas active surface-dwelling C5s and females could not survive for more than 10 days without feeding.     

Zooplankton dynamics in the northern Benguela ecosystem,with special reference to the copepod Calanoides carinatus

Main features of the zooplankton distribution and the ecological characteristics of the dominant species in the northern Benguela during different phases of upwelling are discussed. The composition of the zooplankton between 17 and 27°S was similar each year. Among the 20°30 most abundant species, 3°4 copepods dominated, influencing the distribution of total zooplankton biomass. During quiescent upwelling, zooplankton abundance was low and there were no significant differences in the inshore-offshore distribution of zooplankton biomass, the maximum occurring over the slope. During active upwelling, zooplankton biomass increased significantly, the maximum over the shelf being constituted almost entirely of developmental stages of herbivorous copepods. Over the inner shelf, all stages of the copepod Calanoides carinatus were feeding actively, removing up to 5 per cent per day of the standing stock of phytoplankton. Comparison of daily ration, respiration rate and biochemical composition of C. carinatus revealed active storage of energy inshore. Offshore populations of C. carinatus, found deeper than 200 m, comprised mainly copepodite stage V, which were not feeding and were characterized by decreased mobility and respiration and a high lipid content. It is estimated that the energy stored during active upwelling enables copepods to survive up to six months without any additional source of energy.     

Fine-scale vertical distribution of coastal and offshore copepods in the Golfo de Arauco, central Chile, during the upwelling season

In order to understand the mechanism by which zooplankters from different origins co-occur during the upwelling season within Golfo de Arauco, one of the most productive areas in central Chile, we assessed short term variations in the vertical distribution of the most abundant copepod species. Fine-scale, day and night vertical zooplankton sampling was done with a pump over 12 days in summer. The water column in the gulf consisted of three layers: Equatorial Subsurface Water of low dissolved oxygen content in the deeper part of the water column, strong temperature and oxygen gradients at mid-depth (15-25 m), and a layer of warmer, more oxygenated, less saline water at the surface. Copepods within the gulf originated from offshore, from the continental shelf, and from the coastal area. Most taxa showed distinctive vertical distributions. Three copepod groups were identified by their mean weighted depths of residence. One group included shallow residents found above the thermocline/oxycline (Acartia tonsa, Centropages brachiatus, Corycaeus sp., Paracalanus parvus, Oncaea sp.). A second group was comprised by species distributed at or below the thermocline/oxycline (Oithona sp., Oncaea conifera, Lucicutia sp., Metridia sp., Heterorhabdus papilliger). The third group was composed of vertical migrators that crossed the thermocline/oxycline (Calanus chilensis, Calanoides patagoniensis, Aetideus armatus, Pleuromamma piseki). In spite of their different vertical distribution ranges, the most abundant and frequent copepod species (P. parvus, C. chilensis, C. patagoniensis, C. brachiatus) share a common capacity to withstand wide ranges of oxygen concentration and temperature. This characteristic, along with the capacity to vary their life strategies under different environmental conditions, seems to facilitate the maintenance of large numbers of copepods in coastal waters along the Humboldt Current.     

Metabolic adaptations and reduced respiration of the copepod Calanoides carinatus during diapause at depth in the Angola-Benguela Front and northern Benguela upwelling regions

Stage C5 copepodids and adult females of the herbivorous copepod Calanoides carinatus were sampled in the Angola-Benguela frontal region and northern Benguela upwelling area off Namibia in February–March 2002, using a multiple opening/closing net system. Respiration rates of C5s collected between 400m and 700m were measured onboard at the simulated in situ temperature of 8°C and at sea surface temperature (SST ≥20°C). These data were compared to the oxygen demand of epipelagic individuals of C. carinatus caught in the upper 30m and incubated at ambient SST. Deep-living C5s consumed 0.21 ± 0.08ml O₂ h^?1 (g dry mass)^?1 at 8°C and 0.96ml O₂ h^?1 (g dry mass)^?1 (range 0.84–1.09) at 25.9°C. These results were substantially lower than respiration rates of 5.23 ± 0.55ml O₂ h^?1 (g dry mass)^?1 in epipelagic individuals incubated at SST. The results reveal a reduction by 96% of metabolic rate in deep-living, diapausing C5s relative to surface-dwelling, active individuals. Only 14.4% of this metabolic reduction is explained by the lower ambient temperature at depth and a Q₁₀ value of 2.34. Therefore, the major fraction (81.6%) of the metabolic reduction is attributable to active physiological changes or processes during diapause at depth. The study emphasises the importance for herbivorous copepods, in areas with a highly variable food supply, to adopt a dormant phase in their life cycle in order to survive long periods of starvation.     

浙江南部沿岸产卵场春、夏季鱼卵、仔稚鱼种类组成与分布

根据2011年4月、5月与6月对浙江南部沿岸产卵场进行的共3个航次的调查资料,对该海域的鱼卵、仔稚鱼的种类组成和数量分布进行了分析,结果表明,共发现鱼卵、仔稚鱼72个种类,分别隶属11目38科48属。其中鱼卵29种,分别隶属6目18科24属;仔稚鱼55种,分别隶属10目29科40属。4—6月仔稚鱼数量呈逐月递减的趋势,而鱼卵数量6月最多,5月最少。鱼卵优势种4月以斑鰶、棱鱚、小黄鱼与蓝点马鲛为主,5月以斑鰶、鳀、龙头鱼、银鲳、蓝点马鲛与石首鱼科为主,6月以鳀、龙头鱼、多鳞鱚与鲱科鱼类为主;仔稚鱼优势种4月以虾虎鱼类、褐菖鲉与平鲉科为主,5月以鳀、虾虎鱼类、棱鱚、斑鰶与长鳍篮子鱼为主,6月以鳀与虾虎鱼类为主。斑鰶、鲳鱼、小黄鱼、棱鱚、蓝点马鲛与褐菖鲉的产卵盛期为4月,而鳀与龙头鱼的产卵盛期为6月。     

Temporal changes in pelagic copepod assemblages off Ubatuba,Brazil

The inner shelf waters off Southeastern Brazil are periodically enriched by bottom intrusions of the cold and nutrient‐rich South Atlantic Central Water (SACW), which is transported offshore by the Brazil Current. This study examined the temporal contrasts in abundance and structure of pelagic copepod assemblages in a neritic station off Ubatuba, in relation to hydrography and phytoplankton biomass, to investigate the effects of SACW bottom intrusions on copepod population dynamics during three consecutive years. The water‐column characteristics shifted from a well‐mixed, more turbid and phytoplankton‐poor scenario during subsidence conditions to a stratified, less turbid and high Chl‐a concentration scenario during SACW bottom intrusions, leading to increased copepod diversity, abundance, and biomass. The rise in copepod diversity during SACW intrusions was related to the contribution of oceanic species in addition to coastal water species. The copepod community was numerically dominated by small‐sized species, such as Oncaea waldemari, Oithona plumifera, and clausocalanid and paracalanid copepodids, regardless of seasonality and SACW intrusions. Some large calanoid species contributed considerably to the total copepod biomass during intrusions. In addition to confirming that SACW seasonal intrusions play a key role in pelagic processes off Southeast Brazil, this study showed that the multiannual variability of SACW seasonal intrusions is important in regulating the structure and dynamics of copepod communities in this subtropical area.     

Vertical zonation and distributions of calanoid copepods through the lower oxycline of the Arabian Sea oxygen minimum zone

This paper provides the first comprehensive analysis of calanoid copepod vertical zonation and community structure at midwater depths (300–1000 m) through the lower oxygen gradient (oxycline) (0.02 to 0.3 ml/L) of an oxygen minimum zone (OMZ). Feeding ecology was also analyzed. Zooplankton were collected with a double 1 m² MOCNESS plankton net in day and night vertically-stratified oblique tows from 1000 m to the surface at six stations during four seasons as part of the 1995 US Joint Global Ocean Flux Study (JGOFS) Arabian Sea project. The geographic comparison between a eutrophic more oxygenated onshore station and an offshore station with a strong OMZ served as a natural experiment to elucidate the influence of depth, oxygen concentration, season, food resources, and predators on the copepod distributions.Copepod species and species assemblages of the Arabian Sea OMZ differed in their spatial and vertical distributions relative to environmental and ecological characteristics of the water column and region. The extent and intensity of the oxycline at the lower boundary of the OMZ, and its spatial and temporal variability over the year of sampling, was an important factor affecting distributional patterns. Calanoid copepod species showed vertical zonation through the lower OMZ oxycline. Clustering analyses defined sample groups with similar copepod assemblages and species groups with similar distributions. No apparent diel vertical migration for either calanoid or non-calanoid copepods at these midwater depths was observed, but some species had age-related differences in vertical distributions. Subzones of the OMZ, termed the OMZ Core, the Lower Oxycline, and the Sub-Oxycline, had different copepod communities and ecological interactions. Major distributional and ecological changes were associated with surprisingly small oxygen gradients at low oxygen concentrations. The calanoid copepod community was most diverse in the most oxygenated environments (oxygen >0.14 ml/L), but the rank order of abundance of species was similar in the Lower Oxycline and Sub-Oxycline. Some species were absent or much scarcer in the OMZ Core. Two copepod species common in the Lower Oxycline were primarily detritivorous but showed dietary differences suggesting feeding specialization. The copepod Spinocalanus antarcticus fed primarily on components of the vertical particulate flux and suspended material, a less versatile diet than the co-occurring copepod Lucicutia grandis. Vertical zonation of copepod species through the lower OMZ oxycline is probably a complex interplay between physiological limitation by low oxygen, potential predator control, and potential food resources. Pelagic OMZ and oxycline communities, and their ecological interactions in the water column and with the benthos, may become even more widespread and significant in the future ocean, if global warming increases the extent and intensity of OMZs as predicted.     

几种单胞藻对双刺纺锤水蚤雌体繁殖的影响

研究6种饵料微藻：微绿球藻（Nannochloropsis oculata）、小球藻（Chlorella．sp）、球等鞭金藻（Isochrysis galbana）、三角褐指藻（Phaeodactylum tricornutum）、亚心形扁藻（Platymonas subordi-formis）、中肋骨条藻（Skeletonema costatum）对双刺纺锤水蚤（Acartia bifilosa）雌体繁殖的影响，以探索适合培养双刺纺锤水蚤的藻类。应用解剖镜下计数方法对雌体存活率、产卵率、孵化率、排粪率几个指标进行检测。结果表明微绿球藻、小球藻和球等鞭金藻明显不适于用作雌体饵料；中肋骨条藻组产卵率最高，亚心形扁藻和三角褐指藻组的产卵率没有显著差异；亚心形扁藻组的排粪率明显低于中肋骨条藻和三角褐指藻组；摄食三角褐指藻的雌体所产的卵其平均孵化率要显著低于亚心形扁藻和中肋骨条藻；亚心形扁藻组雌体的产卵率尽管较中肋骨条藻组低，但却保持最高的雌体存活率，而且排粪率也要比中肋骨条藻低得多。综合比较得出结论：6种饵料微藻中，亚心形扁藻和中肋骨条藻是两种最适宜培养双刺纺锤水蚤雌体的优良饵料，二者混合使用效果会更好。     

Living on the edge: feeding of subtropical open ocean copepods

The objective of this study was to provide quantitative information on environmental feeding rates of warm water oceanic epipelagic copepods. We determined clearance rates at 23 °C for various particle size ranges in shipboard studies in the western oligotrophic subtropical Atlantic Ocean for females of the calanoid species Clausocalanus furcatus and Mecynocera clausii. These in situ clearance rates were then applied to the various particle size ranges of environmental particle spectra of auto‐ and heterotrophs at different depths from three stations in the western Atlantic. After calculating the metabolic demands of each of these two copepod species and applying an assimilation efficiency of 90%, we determined that C. furcatus meets its metabolic demands in all six cases, and M. clausii in two of six cases. Clausocalanus furcatus would also meet its energy demands at 25 °C, where it is often found, while M. clausii at 20 °C, where it is regularly found, would cover its metabolic needs in four of six cases. It is hypothesized that these species, and most likely most of the other co‐occurring copepod species, are limited in their abundance by food availability, or, better said, are ‘living on the edge’ in relation to food abundance.     

基于时空矩阵方法对福建省海湾水质变化特征分析

基于2005—2011年8月和2012—2015年5月、8月的水质监测数据，应用水质指标的主成分分析结果，对福建省海湾划分环境单元，通过时空矩阵方法对福建省海湾水质指标变化特征进行了分析。结果显示:（1）通过主成分分析，4个水质指标聚成两类成分，磷酸盐和叶绿素a聚为一类主成分，硝酸盐和溶解氧聚为另一类主成分；（2）以主成分权重值为坐标，划分福建省海湾表层水体为6个环境单元，以此建立水质指标相对含量的时间序列组合矩阵，对福建省海湾水质指标变化分析；（3）水质指标时空矩阵表现出一定的周期性变化趋势，环境单元的指标变化模式具有同步性，指标含量变化的绝对值从叶绿素a到营养盐再到溶解氧呈轻微增长；（4）两类主成分具有一定相关性，营养水平高低影响营养-浮游植物动态关系，当磷酸盐含量高于0.03 mg/L、硝酸盐含量高于0.25 mg/L，且营养盐时间周期变化显著时，叶绿素a时间周期变化与营养盐发生同步联动效应；（5）夏季福建省海湾水体生产力较低，大量陆源有机物输入、降解耗氧，表层溶解氧含量降低明显；（6）福建省海湾主要受两种性质差异很大的水体影响，富含高营养盐径流水团影响了河口及邻近海域的环境单元，而福建省南部海湾主要受台湾暖流及上升流影响，台湾暖流是东海海域磷酸盐的重要来源。     

The fauna and chemical composition of some athalassic saline waters in New Zealand

The fauna and chemical composition of two athalassic saline waters located near central Otago are discussed, and available rainfall and evaporation data for the region summarised. One water (dominated by Na and C1) had a salinity of 15‰ and contained the rotifer Brachionus plicatilis, the copepod Microcyclops monacanthus, the ostracod Diacypris, and larvae of the dipteran Ephydrella The second water (dominated by Na and HCO₃) had a salinity of 6‰ and contained larvae of Ephydrella (adults of E. novaezealandiae occurred on the shore), and the hemipterans Sigara arguta, Anisops wakefieldi and Anisops assimilis The relationship between Microcyclops monacanthus and M. arnaudi (an Australian species), and the basis of their current taxonomic separation is discussed in some detail.

At a minimum, the faunas of Australian and New Zealand athalassic saline waters have in common the following distinctive (non‐cosmopolitan) forms: Ephydrella, Diacypris, and two closely related halobiont species of Microcyclops     

雷州半岛沿岸海域浮游桡足类的分布特征及其影响因素

根据2017年10月和2018年1、5、7月对雷州半岛沿岸海域浮游动物四个季度的调查数据,分析了浮游桡足类群落组成的季节变化及其影响因素.结果共鉴定出浮游桡足类80种,其中哲水蚤目55种,占总种类数的68.7％;剑水蚤目21种,占总种类数的26.2％;猛水蚤目3种,占总种类数的3.8％;鱼虱目1种,占总种类数的1.3％...     

Direct examination of the dietary preference of the copepod<Emphasis Type="Italic">calanus helgolandicus</Emphasis> using the colorimetric approach

The food selectivity of tethered females of the copepodCalanus helgolandicus was examined by using the colorimetric approach. First, feeding behavior of the copepod did not show any differences between the red-color stained with neutral red and non-stained diets using the diatomCoscinodiscus curvatulus. Then, the copepods were fed a mixtures of two diets, the diatomC. curvatulus, stained with neutral red, and the dinoflagellateGymnodinium sanguineum for 14~60 minutes of feeding duration. The foregut colors of females were examined using a stereo-microscope and a video monitor. The foreguts of animals fed with a high density of diatoms in mixed diets showed a dark red color, whereas those fed with a high density of dinoflagellate in mixed diets were a dark yellow. The results suggest that this species of copepod may not selectively feed either one of the diets used for this study. Their feeding activity may be more likely related to the density of available prey in their environment. Therefore, this quick and easy colorimetric approach could provide very useful information, like the pre-screening procedure before designing and conducting the time-consuming and complex feeding experiments to understand the feeding ecology of copepods.     

Spatial and long-term temporal variation of meiobenthic-hyperbenthic copepods in Lake Pontchartrain,Louisiana

The distribution and abundance of the meiobenthic-hyperbenthic copepods of Lake Pontchartrain (a large, 1630 km², shallow, mean depth of 3·7m, brackish, 0·3–5‰, lake in Southeastern Louisiana) were characterized monthly from August 1978 to August 1979. Ten stations, all with water depth > 2m, were established and sampled quantitatively by removing four benthic subsamples (containing as much as 25 cm overlying water) from replicated box cores. Averaged across stations over time, total copepod densities ranged from 31–89 × 10 cm^?2. A total of only 15 copepod species were identified from benthic samples; 8 harpacticoids, 4 cyclopoids and 3 calanoids. The copepod assemblage in Pontchartrain differs from all other known benthic assemblages in that the species composition is dominated by species which are often associated with the water column; true infaunal species are rare or found in reduced abundance. Four species comprised 90% of all individuals collected. All four are epibenthic or commonly collected as zooplankton and include Scottolana canadensis which comprised 47% of all individuals collected, Halicyclops fosteri which dominated fall collections, Acartia tonsa and Pseudobradya sp. Burrowing species were largely restricted to the more saline eastern stations. The rarity of burrowing species might be related to low salinity, however the highly unstable bottom in Pontchartrain with silty-clayey sediments commonly resuspended into the water column, may also influence burrowers. Cluster analysis reveals diffuse seasonal grouping of stations for all seasons except fall, with spatial groupings from the central and western sides. Physical processes appear to dictate the community structure of benthic-hyperbenthic copepods in Lake Pontchartrain.     

火腿伪镖水蚤对抑食金球藻中国株的摄食行为及摄食后的表现

全球河口海域屡屡爆发褐潮，但我们对致因种抑食金球藻和浮游桡足类之间的营养关系还不甚清楚。我们就浮游桡足类火腿伪镖水蚤摄食抑食金球藻中国株的单种或混合饵料时的摄食行为和生长、发育等表现进行了研究。研究发现：火腿伪镖水蚤的无节幼体、桡足幼体和成体摄食单种抑食金球藻饵料时，摄食率和食物浓度之间的关系符合米氏方程。较之桡足类幼体和成体，无节幼体摄食抑食金球藻时的I_max（最大摄食率）值最大，同时大于其摄食中肋骨条藻的I_max值。通常情况下，火腿伪镖水蚤在摄食抑食金球藻和中肋骨条藻的混合饵料时避食抑食金球藻，但于无节幼体，这种情况并不明显。无节幼体摄食单种抑食金球藻饵料在无节幼体期末期死亡，无法进入桡足类幼体期，与饥饿状态下的个体相似。但是，饵料中抑食金球藻的存在对桡足幼体的生长无明显效应，但却极大地减少了成体的生殖率。我们的研究表明火腿伪镖水蚤无节幼体，在褐潮的控制中有潜在作用，然而，这种潜在控制作用由于桡足类种群的衰落难以持续。     

Predatory Promesostoma species (Plathelminthes, Rhabdocoela) in the Wadden Sea

Laboratory experiments were performed on the food ecology of four congeneric species of free-living plathelminths, Promesostoma caligulatum, P. marmoratum, P. rostratum, and P. meixneri, all inhabiting an intertidal sandflat near the island of Sylt (North Sea). Their prey spectrum is within the microcrustaceans: P. caligulatum preferred ostracods, while the other three species favoured copepods, with species-specific differences for copepod species and size classes. Daily consumption of prey species varied with the size of both the predator and the prey. On average, P. marmoratum consumed 0.76 Harpacticus flexus per day while this rate decreased to 0.06 in P. meixneri, the smallest predator. When these Promesostoma species were fed with Tachidius discipes, a smaller prey species, their predation rates were about 25% higher. While the larger predators preferred the larger harpacticoids as prey, the small P. meixneri preferred small cyclopoids over larger harpacticoids. In terms of biomass, P. marmoratum's mean consumption of T. discipes per day was about half the predator's own weight. This average varied with prey density and temperature. A comparison of these consumption rates with the field densities of the predators and their prey shows that the plathelminth predators may consume as much as 10% per day of their copepod prey populations, thus strongly influencing these prey populations on these sandflats. The predation pressure of P. caligulatum on ostracods was about 1% per day of the prey population. Since ostracods usually have fewer generations per year, the total effect on the population dynamics may be similar to that on copepods. Therefore, nocturnal swimming of copepods in the water column may be interpreted as an attempt to escape plathelminth predators.     

长江口滴水湖大型底栖动物群落结构及其与环境因子的关系

2009年6月—2010年5月,在滴水湖设置8个采样点调查研究了大型底栖动物群落结构特征的时空变化及其与环境因子的关系。在滴水湖共采集到25种大型底栖动物,隶属3门6纲,其中甲壳纲8种(32%)、昆虫纲6种(24%)、寡毛纲和多毛纲各4种(16%)、双壳纲2种(8%)、蛭纲1种(4%)。日本旋卷蜾蠃蜚、微小摇蚊、背蚓虫、黄色羽摇蚊为优势种。底栖动物年均密度和生物量分别为(910.5±107.64)ind./m2和(8.62±2.01)g/m2。底栖动物群落结构包括物种组成、现存量和多样性均无显著季节和空间变化。RDA分析结果表明,活性磷酸盐、叶绿素a、CODMn、pH、溶解氧是影响大型底栖动物物种分布的关键环境因子,日本旋卷蜾蠃蜚、日本大螯蜚、红裸须摇蚊和背蚓虫与溶解氧正相关,与营养盐水平和水温负相关,微小摇蚊和黄色羽摇蚊正好相反。Shannon-Wiener多样性指数和BPI生物指数水质生物学评价表明,滴水湖处于中度污染状态。     

Surface cyclopoid copepod assemblages in relation to environmental conditions near undisturbed coral reefs of Minicoy,southeastern Arabian Sea,a part of the Indian Ocean

The cruise conducted in the spring inter-monsoon (pre-monsoon) of April 2015 in the frame of a funded project epitomized an open ocean survey that allowed procuring a quasi-synoptic picture of cyclopoid copepod community structure in 18 open ocean stations of the Minicoy Island, Lakshadweep archipelago, off the southwestern Indian coast, based on the analysis of standing stock and composition in the integrated 0–10 m water column. The main objective was to explore the community structure of cyclopoid copepods prevailing here and which environmental variable influences the same. It is witnessed that sea surface temperature (SST) (30.42 ± 0.19°C), sea surface salinity (SSS) (33.56 ± 1.15 psu), and dissolved oxygen (DO) (4.32 ± 0.06 ml/L) with SSS and DO are the best matching variables diversifying cyclopoid copepod species (av. abundance 700 ± 386 no. of individuals/100 m³). Average zooplankton biomass (0.03 ml/m³) and abundance (8,989 ± 3,866 no. of individuals/100 m³) were also observed. Fifty-one cyclopoid copepod species belonging to four families and seven genera were identified, with the dominance of high saline species such as Sapphirina, Copilia, Farranula, and Oncaea. An abundance biomass curve (ABC) plot analysis indicated an undisturbed community with normal environmental conditions. TAXDTEST (taxonomic distinctness) depicted a diverse condition where all points clustered together within a 95% confidence level. Our results indicate that the cyclopoid copepod assemblage near Minicoy Island is a diverse, undisturbed community and hypothesize that the stable environmental conditions during pre-monsoon (spring inter-monsoon) preferred the diversification of cyclopoid copepods with the prevalence of high saline species. The data evolved could be used as a standard reference/benchmark to detect any deviation from an undisturbed/diverse community status of Minicoy Island in the looming scenario of climate change in and around the Indian Ocean.     

Seasonal and regional patterns in egg production of Calanus glacialis/marshallae in the Chukchi and Beaufort Seas during spring and summer, 2002

Understanding the physical and biogeochemical processes that control the exchange of biogenic carbon within and between the arctic shelves, slopes, and deep basins is a key objective of the Western Arctic Shelf-Basin Interaction program (SBI). Here, egg production (EP) of the dominant copepod Calanus glacialis/marshallae was used as an indicator of food limitation for the mesozooplankton community in the Chukchi and Beaufort Seas in spring and summer, 2002. Both C. glacialis and C. marshallae may occur in this region but the two cannot easily be differentiated visually. Four oceanographic regions were objectively identified that roughly corresponded to the different pathways in circulation of nutrient-rich Pacific water. A ‘transition’ region characterized by ‘older’ Pacific water was located at the shelfbreak and separated the nutrient-rich shelf water and the low-nutrient waters of the deep basin. The observed spatial pattern in EP in C. glacialis/marshallae in spring and summer resulted both from the different water mass environments and from the reproductive cycle of the species. EP was greater on the shelf than in the basin, corresponding to differences in body size and nitrogen condition factor (NCF) in females, while the egg viability was generally high throughout the study area. EP showed no relationship with low-chlorophyll a biomass under heavy ice-cover in spring, while a significant relationship was observed in the more open water in summer. Adult female carbon condition factor (CCF) was much higher in summer, reflecting the accumulation of lipids during the growth season. Small animals with a markedly greater NCF dominated on the shelf. The shelfbreak region contained a mixture of females from the shelf and the basin with intermediate sizes, conditions, and EP rates. The occurrence of water typical of the ‘transition’ shelfbreak region and elevated EP in C. glacialis/marshallae offshore on the Barrow Canyon and East Barrow sections indicated offshore transport of productive shelf water and the associated plankton community. The input of nutrient-rich Pacific water and accompanying elevated production to the northern Chukchi Sea and the Chukchi-Beaufort shelfbreak region may contribute to the reproductive success of C. glacialis/marshallae in this region.