Seasonal variations in carbon and nitrogen content of Acartia clausi (Copepoda,Calanoida) in the Gulf of Trieste (Northern Adriatic Sea)

A yearly study was made on total and cephalothorax lengths, dry weight, carbon and nitrogen contents and C:N ratio of the species Acartia clausi (Copepoda, Calanoida) which is always abundant, particularly in spring, in the net zooplankton community of the Gulf of Trieste (Northern Adriatic Sea). The samples of net zooplankton were carried out every month at the permanent station located 200 m offshore and preserved for about one year in 4% buffered formalin to insure weight loss stabilization. A. clausi was separated from other zooplankton specimens; washed and dried. For each monthly sample the average total and cephalothorax lengths and the average dry weight of adult organisms of A. clausi were measured. The mean carbon and nitrogen contents, as a percentage of dry weight, were determined by using a CHN analyser. Linear regression models were computed on the log-transformed data in order to check the relationships between dry weight, total and cephalothorax lengths, carbon and nitrogen contents and C:N ratio of A. clausi. The best of the various established correlations, was between dry weight and carbon content. Our study pinpointed a high seasonal variability of the C:N ratio, mainly due to seasonal fluctuations in the nitrogen content.     

Mesoscale advection of Upogebia pusilla larvae through an upwelling filament in the Canaries Coastal Transition Zone (CTZ)

Larval transport has a strong influence on marine populations and ecosystem function. Traditional hypotheses establish that larvae of coastal species are swept offshore during strong upwelling periods producing low recruitment rates; however, recent studies have demonstrated that this hypothesis is not supported by larval distribution data. The present study examines the influence of upwelling filaments on larval advection and wastage. During August 1993, the transport of Upogebia pusilla was analysed in relation to an offshore filament off Northwest Africa. This mesoscale structure was generated by a trapped, quasi-permanent cyclonic eddy located between the Canary Islands and the African shelf and extended 150?km westward into the oligotrophic open ocean waters. The horizontal distribution depicted by U. pusilla larvae was strongly influenced by the oceanographic features of the Canaries Coastal Transition Zone (CTZ). Specifically, the larvae were closely associated with upwelling front and filament position, showing that these neritic larvae can be advected 10–100s of kilometres offshore through the filament. However, the low larval densities observed in the samples suggest that many larvae might remain close to the coast, thus avoiding seaward transport. This implies that filaments probably do not significantly affect the recruitment success of intertidal invertebrates such us U. pusilla in upwelling systems.     

福建中部近海浮游动物数量分布与水团变化的关系

根据2009—2010年在福建中部近海24°55'—25°13'N、119°11'—119°32'E水域冬、春、夏3个季节的调查资料,探讨了该水域浮游动物总丰度与生物量的平面分布、季节变化及其与台湾海峡水团变化的关系。结果表明,调查水域浮游动物的数量在冬、春之交变化较大,而在春、夏季变化较小。浮游动物冬、春两季的平均丰度分别为8.90 个/m³和245.65 个/m³,夏季为236.82 个/m³。冬、春两季,该水域浮游动物的分布特征相近。其数量在近岸较高,向外侧水域逐渐降低。冬季浮游动物的丰度最高为31.56 个/m³,春季最高达到831.67 个/m³。中华哲水蚤(Calanus sinicus)是冬、春季影响总丰度变化最主要的种类。与冬、春季不同,夏季浮游动物的数量在离岸水域较高,丰度最高达1053.13 个/m³,而在近岸较低,最低值仅19.17 个/m³。汉森莹虾(Lucifer hanseni)、双生水母(Diphyes chamissonis)是影响总丰度变化最主要的种类。浮游动物在各季的不同分布特征与台湾海峡的季节性水团变化有关。受季风转换影响,从冬季到夏季,海峡内沿岸流势力逐渐减弱,台湾暖流水势力逐渐增强,并影响到沿岸的水文环境。这导致调查水域内浮游动物的优势种类由暖温种向暖水种演替。由于冬、春季的重要优势种类中华哲水蚤与夏季的汉森莹虾、双生水母具有不同的温度适应性,受不同性质水团的影响,在近岸和离岸水域各自呈现出不同的数量高低。从而进一步影响到各季浮游动物总数量的分布。     

Near anoxia and sulfide as possible factors influencing the spatial distribution of Acartia tonsa and Acartia clausi: Comparative evaluation of egg tolerance

In many coastal and estuarine areas the planktonic copepods Acartia tonsa and Acartia clausi show a spatial separation with A. tonsa restricted to brackish waters and confined environments and A. clausi inhabiting areas more influenced by sea water. The hatching and viability of A. tonsa and A. clausi eggs exposed to anoxia and anoxia/sulfide (conditions that are frequent in bottom waters of the most confined areas) was evaluated to determine if these stress factors play a role in the distribution of these species. Subitaneous eggs, spawned by laboratory reared organisms, were incubated in near anoxia (< 7.59 × 10^− 3 mmol O₂ L^− 1) or anoxia/sulfide (∼ 1 mmol L^− 1) for different periods (1, 4, 8 and 15 days), then transferred to normoxic conditions. The exposure of the eggs to near anoxia and sulfide appears to induce the same response (quiescence) in both species. Exposure times ≤ 8 days to near anoxia or anoxia/sulfide did not affect egg viability, while 15 day exposure caused significant declines in hatching success of both species. A significant difference between the effects of near anoxia and anoxia/sulfide was observed when incubation lasted 15 days; hatching of eggs exposed to sulfide being higher than that of eggs exposed to near anoxia for both species. No significant differences were observed between the two species in hatching success of eggs exposed to both near anoxia and anoxia/sulfide (with the exception of eggs incubated in near anoxia for 4 days). The results indicate that the impact of anoxia and sulfide on the eggs of the two Acartia species cannot be a factor explaining the spatial distribution in coastal and brackish environments of these copepods.Feeding experiments on A. clausi were also performed. Suitability of different algal species to rear this copepod was evaluated and the results were compared with data previously obtained for A. tonsa. Differences in feeding needs between A. clausi and A. tonsa are discussed.     

Variation nycthémérale de la répartition verticale et de l'efficacité de collecte du zooplancton en lagune Ebrié (Côte d'Ivoire)

Vertical distribution and night and day collecting efficiencies of both nets and a Schindler trap, were studied in two shallow (4 m) unstratified bays of the Ebrié Lagoon. Some of the organisms migrate (Mysidacae, copepodite and adult stages of Acartia clausi and Pseudodiaptomus hessei) and others do not (all the nauplii, copepodite and adult stages of Oithona brevicornis, rotifers, mollusca larvae). The first are found more or less near the bottom at noon and are evenly distributed throughout the water at the beginning of the night. Mysidaceae and P. hessei strongly exhibit this pattern, none (Mysidacea) or very few specimens being collected in the water during the day. For A. clausi, depth concentration increases from C1 to adult. Net and trap estimated night densities are higher than the day ones for migrating organisms, except for C1 or A. clausi. The Night/Day ratios are equal to 28 (net) and 25 (trap) for P. hessei, 5 and 13 for the adults of A. clausi and lies between 2 and 5 for the different copepodite stages of this last species. The possible causes and consequences of the vertical distribution are discussed, the interference of turbulence on vertical distribution being outlined.     

Organic Matter,Carbon, Nitrogen and Phosphorus Contents of the Mesozooplankton,Mainly Acartia clausi,in a Tropical Brackish Lagoon (Ebrié Lagoon,Ivory Coast)

Mesozooplankton samples were collected over a period of one year in five stations of the Ebrié lagoon and analysed for organic, carbon, nitrogen and phosphorus contents. When zooplankton was dominated by A. clausi, body composition was relatively stable compared with the broad variability of environmental factors (mainly salinity, food abundance and composition), although a negative hypothetic influence of salinity may have occurred. Body composition was comparable when zooplankton was dominated by Pseudodiaptomus hessei and freshwater species, but contents were significantly lower for assemblages dominated by more exclusively marine species (Paracalanus spp., Oithona spp., marine cladocerans, chaetognates, etc.).     

Spatial structure of the zooplankton community in the Cabo Frio region (Brazil) influenced by coastal upwelling

Cabo Frio area (Central-southern Brazilian littoral) is characterized by a coastal upwelling due to prevailing E-NE winds, mainly during the spring-summer season. The geographic distribution of the zooplankton was described in order to separate ecological areas in terms of specific communities. Cluster analysis by weighted pair-group method (WPGA) and principal component (PC) analysis was performed on the most important hydrological parameters and zooplankton taxa. The first PC, explaining 38% of the total zooplankton variability, represented the influence of the nearshore-offshore gradient. Zooplankton communities and ecological areas were defined as follows:

1. nearshore neritic: the richest region with more than 5 000 org. m-3. In this very narrow nearshore region we observed 3 groups of taxa deliminated by upwelling effects and trophic conditions: a) Ctenocalanus vanus, Penilia avirostris, Calanoides carinatus and Copepod larva, all herbivorous species associated with the phytoplankton blooms in the upwelling zone; b) Creseis acicula and Temora stylifera; c) Siphonophora, Chaetognaths and a high diversity of Copepoda dominated by Coryceus amazonicus, C. giesbrechti, Eucalanus pileatus, Clausocalanus acuicornis, all carnivorous or omnivorous feeders representing a high degree of complexity of the ecosystem.
2. offshore neritic: characterized by appendicularians, this region constitutes an intermediate zone between coastal and oceanic waters.
3. oceanic: occupied by the Brazil Current where zooplankton is poor, but diversified, with typical copepods from tropical warm water: Clausocalanus furcatus, Mecynocera clausi, Corycella gracilis, Oithona setigera, Coryceus typicus, Oncea conifera, Undinula vulgaris, Calocalanus pavo, Haloptilus longicornis, Lucicutia flavicornis.

     

The results of zooplankton studies in the Bering Sea under the NPAFC Program (BASIS expedition). Part 1. Eastern areas

Data on zooplankton in the eastern Bering Sea are presented. Samples were collected and processed by the planktonologists of the Pacific Fisheries Research Center (TINRO Center) aboard American vessels in the summer and fall from 2003 through 2011. Based on the analysis of the averaged values of bottom temperature, surface temperature, ice cover index, and also on maps of temperature distribution on the surface and near the bottom, the years 2003–2006 are referred to as “warm” and 2007–2011 as “cold.” A comparison of these two periods showed that with the advent of the “cold” period, the overall stock of zooplankton in the eastern part of the sea grew, particularly in the shelf zone, where it increased more than three times exclusively at the expense of the large fraction. Chaetognaths and copepods constituted the major proportion of this increase; stocks of euphausiids, mysids, hyperiids, and pteropods also grew, while a loss was observed in decapods (larval crabs and shrimps) and coelenterates. In the southern part of the shelf zone, a vast area with a higher biomass of the large fraction occurred, which was mainly due to copepods and chaetognaths. At the same time, areas with denser concentrations were formed by euphausiids and amphipods. The horizontal distribution of small and medium-sized zooplankton almost did not change; meanwhile, the main species of the small fraction, viz., Pseudocalanus newmani and Oithona similis, exchanged their significance and the neritic species Centropages abdominalis, Eurytemora herdmani, and Acartia longiremis, as well as cladocerans and meroplankton (larval Cirripedia, Bivalvia, and Polychaeta) almost completely vanished from the plankton by 2011. In most of cases, the mean biomass of the profiling species of the large fraction (Calanus marshallae, Neocalanus flemingeri, N. cristatus, Eucalanus bungii, Thysanoessa raschii, Themisto libellula, Limacina helicina, and Sagitta elegans) grew during the cold period. In the large fraction, S. elegans constituted half of the biomass (52% in the warm period and 49% in the cold one); the following two species were the copepods E. bungii and C. marshallae (both amounted to 26% and 39%, respectively), while Th. raschii, which is usually predominant among euphausiids, was only the last in the top five species. According to the example of the eastern areas of the sea, it becomes evident that the hyperiid Themisto libellula is brought into the studied area with cold waters from the north and disappears when their inflow stops. This species responds later to cooling and earlier to warming as compared to other species or groups. It appears that the end of the “cold” period can be expected in 2012.     

哥斯达黎加外海夏季表层浮游动物种类组成及分布

根据2009年7—8月在东热带太平洋哥斯达黎加外海(4°30’—10°24’N、91°20’—100°00’W)进行茎柔鱼探捕调查期间采集的表层浮游动物资料,对其种类组成、生物量及其分布进行了分析。结果表明,调查海域,鉴定出腔肠动物8目10科17属23种;甲壳动物8目30科43属74种;毛颚动物1目1科1属4种;尾索动物3目3科5属5种;环节动物为1目3科5属6种;软体动物1目1科3属3种;其他浮游动物有头足类的幼体、鱼卵和仔稚鱼以及浮游幼虫。调查海域总生物量和丰度的平均值分别为(124.78±176.83)mg/m3和(848±1219)个/m3,生物量较大的类群主要是甲壳动物的桡足类和毛颚动物的箭虫类其中桡足类的丰度(727个/m3)为最高,其次为箭虫类(373个/m3);出现频率较高的为桡足类、箭虫类、长尾类、头足类和鱼类仔稚鱼。     

Impacts of very warm temperature on egg production rates of three Acartiidae (Crustacea,Copepoda) in a Northern African lagoon

The daily Egg Production Rate (EPR) of the three Acartiidae copepods namely Acartia clausi, Paracartia latisetosa and Paracartia grani in the North Lagoon of Tunis was compared to temperature and food availability every season from March, 2003 to February, 2004 corresponding to the major seasonal peaks of their abundance and over a 20-days period. The daily EPR was evaluated by assuming a direct correlation with chlorophyll a, particulate organic carbon (POC), and some easily extractable macromolecular compounds from the seston, such as proteins, carbohydrates and lipids. The results showed significant differences in EPR between seasons and species. Temperature and salinity negatively affected the fecundity of A. clausi and positively that of P. latisetosa and P. grani. The A. clausi EPR was supported by chlorophyll a and sestonic proteins while that of P. latisetosa and P. grani correlated with POC suggesting that these two taxa feed on microzooplankton and detritus more than on phytoplankton. Overall, EPR data showed potential population recruitment evidently the highest in P. latisetosa in summer, P. grani in autumn and A. clausi in winter. Our results indicate that temperature and food quality are the determining factors of both abundance and reproduction of the copepods under study.     

Rostock zooplankton studies off West Africa

Since the beginning of the seventies, upwelling research has become increasingly popular in the path of the Canary and Benguela Current, because of economic consideration, particularly in the relation to fisheries and marine geology. Many expeditions were carried out between 1970 and 1977, including 8 cruises of the German R. V. “A. v. Humboldt” operating from Rostock. Measurements covered scales ranging in time from minutes to several years and in space from hundreds of metres to several thousands of kilometres. Zooplankton studies focussed on quantitative, metabolic, taxonomic, and parasitological aspects. Plankton was collected with a WP-2-UNESCO standard net to a maximum depth of 200 m. The epipelagic mesozooplankton consists mainly of copepods, especially calanoids with developmental times of about 20 to 23 days. After an upwelling event, zooplankton is able to double its biomass. This typical biomass increase is independent of coastal distance and depth. The upwelling response lasts about 3 weeks in nearsurface waters, and 6 to 8 weeks in depths below 75m. A relationship was observed between the duration of seasonal upwelling (that means the numbers of single upwelling events) and the cumulative increase of biomass. This net growth rate of zooplankton biomass is most pronounced at the shelf break, the area with the highest fish biomass, and in the upper 25 m. Differences between the expected and the real rate values in conjunction with the known amount of nutritive demands of fishes allow the estimation of the fish biomass in a given area. The near coastal Ekman upwelling, which is an event in the time scale of about two weeks, also shows seasonality in some areas. Off Northwest Africa the largest expansion was recorded in the first half of the year, extending from 10° N to 24° N, more than 400 km offshore and at least down to 200 m. It contracts in the second half of the year to an area between 20°N and 22°N, 100 to 200 km off the coast and in an average depth of 25 m. These zooplankton biomass patterns are superimposed by mesoscale phenomena, originated by other than Ekman upwelling events. Those are, for example, long coastal parallel waves, producing cells of intensified upwelling and downwelling, and eddies, caused by instabilities in a frontal zone parallel to the coast. Different water masses can be distinguished by indicator species, species combinations or the significant absence of species. This was demonstrated for chaetognaths. The calanoidCalanus helgolandicus (Claus, 1863), a typical species of the North Atlantic, indicates North Atlantic Central Water, whereasCalanoides carinatus (Krøyer, 1849) is an indicator of South Atlantic Central Water. Finally, comparisons of near coastal current regimes, transport velocities, and developmental rates of calanoids allow one to conclude that a suitable mechanism is present to maintain plankton in the coastal environment.     

Structure of the zooplankton community in a subtropical shallow lake (Itapeva Lake – South of Brazil) and its relationship to hydrodynamic aspects

The structure of the zooplankton community in Itapeva Lake was formed by four groups and more than 127 zooplankton species, in which microplankton was the predominant size structure. The largest richness recorded was of the protists group and in autumn seasonal campaign. Protists were characteristic of the lake, regarding density, except during spring at the Center point (copepods) and autumn at the South point (rotifers). The seasonal distribution revealed that during summer, mean density increased in the zooplankton community, exactly the opposite of phytoplankton (that blooms during the cold season). However, the maximum density was recorded during autumn. High density was recorded for the ciliate Codonella sp. at all points and during all seasons. The abundance of the tecamoeba Difflugia tuberculata was strongly associated with the maximum effects of fetch in the lake. Rotifers were generally the second most representative groups in terms of density. Rotifers and Cladocera were more abundant in summer, whereas copepods were in spring and winter/98. The Shannon–Wiener index showed that the smallest zooplankton diversity average occurred during the winter/98 (H=1.44), while in autumn the largest zooplankton diversity average (H=2.36) was observed. Correlations (r-Pearson, p<0.05) with wind velocity were significant for zooplankton density (groups and/or abundant species), diversity, and richness. The analysis of variance (ANOVA) showed a seasonally significant spatial-temporal variation for the factors sampling point, day and shift (p<0.01). Temporal alterations in density, diversity and richness were closely dependent on the hydrodynamic action induced by the wind on the spatial distribution of the zooplankton community in the Itapeva Lake.     

Viability of dinoflagellate cysts after the passage through the copepod gut

Several dinoflagellate species form nonmotile, thick-walled resting cysts in their life cycle. Cysts can be ingested by planktonic and benthic organisms, but there is scarce information concerning their survival after the passage through the digestive apparatus of the grazers. We tested the germination capability of cysts produced by two neritic dinoflagellates, Scrippsiella trochoidea (F. Stein) A.R. Loeblich and Scrippsiella ramonii Montresor, after their ingestion by four copepod species. Experiments have been carried out with four species: Acartia clausi Giesbrecht, 1889; Centropages typicus Kröyer, 1849; Temora stylifera Dana, 1849; and Clausocalanus lividus Frost and Fleminger, 1968. Copepods were fed either with motile cells or cysts, and feeding and clearance rates were estimated for A. clausi, C. lividus and T. stylifera. Grazing rates on both dinoflagellates was much higher for vegetative cells than for cysts. Resting cysts were isolated from the faecal pellets and incubated to test their germination capability. S. trochoidea cysts eaten by C. typicus and T. stylifera showed a high germination rate, while cysts of the same species were not viable after the passage through the gut of A. clausi and C. lividus. In contrast, S. ramonii cysts were never able to germinate after being ingested by copepods. The observed variation in viability among the two cyst types and the different survival rates observed for S. trochoidea cysts might be related to differences in cyst morphology and to differences in the digestive process among the tested copepod species.     

A simulation of the distribution of Acartia clausi during Oregon Upwelling, August 1973

The distribution of the estuarine copepod Acartia clausi incoastal waters off Oregon during an upwelling period in August1973 is simulated. A time dependent, two dimensional (x, z,t) model relates maximum offshore extent of the copepod's fourlife stages (egg, nauplius, copepodite, and adult) to intensityof the wind stress driving the upwelling circulation, stagedevelopment time, and mortality. Realistic solutions are obtainedby using actual intermittent wind forcing recorded by an anemometerat Newport. Offshore transport is overestimated when the circulationmodel is driven by theoretical continuous winds, suggestingzooplankton may be washed out of coastal upwelling zones (e.g.off Northwest Africa) which undergo periods of prolonged upwelling. With an accurate model of offshore transport and stage developmenttime, the mismatch between predicted and observed distributionsmay be used to estimate field mortality of the various stages.     

Zooplankton community structure and copepod egg production in coastal waters of the central Great Barrier Reef lagoon

We describe zooplankton community structure and copepod eggproduction in the vicinity of the coastal boundary zone of theGreat Barrier Reef lagoon, Australia. The abundance and eggproduction rate of constituents of the zooplankton assemblagecharacteristic of the coastal zone rapidly increase subsequentto events such as flooding and upwelling. Our sampling spannedtwo summer monsoonal seasons, the first of which (1990-91) wasvery wet. The second monsoonal season (1991-92) was very dryand was characterized by intrusive upwelling events from theCoral Sea. Chlorophyll a concentrations did not rise in thewet year, probably because of light limitation, but did riseas a result of upwelling. Terrestrial run-off in the wet yearhad a greater apparent effect on zooplankton abundance patternsthan did upwelling in the dry year, except where coastal trappingallowed sufficient time for increases in zooplankton abundanceto occur. Egg production rates by the copepods Acrocalanus gibberand Acrocalanus gracilis showed haphazard spatial differences.Nitrogen-specific egg production ranged between 0.03 and 0.21day^–1 for A.gibber, and between 0.13 and 0.41 day^–1for A.gracilis. The egg production rate by A.gibber was foodlimited for most of the year and showed a poor correlation withtemperature. ³Present address: Department of Biological Sciences, FloridaTech, 150 W University Boulevard, Melbourne, FL 32901, USA     

Phytoplankton distribution in the upwelling areas of the Moroccan Atlantic coast localized between 32°30'N and 24°N

Marine phytoplankton was studied in January and July 2002 along of four transects: 32°30′N, 29°N, 24°30′N and 24°N. A total of 142 taxa were recorded in this area. The maximal specific richness, both in summer and in winter, was registered around Dakhla (24°N). The global spatiotemporal variability of species richness and specific diversity showed that the most structured and species-rich populations are situated in the coastal areas. The vertical variation of the two parameters showed homogeneity between depth levels. The maximal phytoplanktonic densities are recorded in the southern transects due to the permanent upwelling activity in the southern Atlantic coast. The bathymetric distribution of densities was more heterogeneous during summer, characterized by a high intensity of upwelling. The species Thalassionema nitzschioides, Asterionellopsis glacialis, Melosira, Chaetoceros and Leptocylindrus minimus are indicators of upwelling.     

Spatio-Temporal Variability of Copepod Abundance along the 20°S Monitoring Transect in the Northern Benguela Upwelling System from 2005 to 2011

Long-term data sets are essential to understand climate-induced variability in marine ecosystems. This study provides the first comprehensive analysis of longer-term temporal and spatial variations in zooplankton abundance and copepod community structure in the northern Benguela upwelling system from 2005 to 2011. Samples were collected from the upper 200 m along a transect at 20°S perpendicular to the coast of Namibia to 70 nm offshore. Based on seasonal and interannual trends in surface temperature and salinity, three distinct time periods were discernible with stronger upwelling in spring and extensive warm-water intrusions in late summer, thus, high temperature amplitudes, in the years 2005/06 and 2010/11, and less intensive upwelling followed by weaker warm-water intrusions from 2008/09 to 2009/10. Zooplankton abundance reflected these changes with higher numbers in 2005/06 and 2010/11. In contrast, zooplankton density was lower in 2008/09 and 2009/10, when temperature gradients from spring to late summer were less pronounced. Spatially, copepod abundance tended to be highest between 30 and 60 nautical miles off the coast, coinciding with the shelf break and continental slope. The dominant larger calanoid copepods were Calanoides carinatus, Metridia lucens and Nannocalanus minor. On all three scales studied, i.e. spatially from the coast to offshore waters as well as temporally, both seasonally and interannually, maximum zooplankton abundance was not coupled to the coldest temperature regime, and hence strongest upwelling intensity. Pronounced temperature amplitudes, and therefore strong gradients within a year, were apparently important and resulted in higher zooplankton abundance.     

北部湾北部生态系统结构与功能——浮游动物空间生态位及其分化

根据2006—2007年北部湾北部海域4个航次调查资料,采用K-优势度曲线法对浮游动物种(类)群进行排序分析,运用Levins公式和Pianka指数分析了主要优势种(类)群的生态位宽度值和生态位重叠程度,并通过除趋势典范对应分析(DCCA)研究生态位分化状况。结果表明,该海区浮游动物优势种(类)群按生态位宽度值可划分为广生态位、中生态位和窄生态位三大类型。其中,广生态位的种(类)群如肥胖软箭虫、亚强次真哲水蚤、长尾类幼体等具有较强的生态适应性,生活范围较广;窄生态位的种(类)群,对环境的适应性较差,对海流和水团等环境因素的变化具有指示意义。生态位宽度能够反映种(类)群丰度季节变化,但不能反映具体丰度大小。北部湾北部全年主要优势种(类)群的生态位宽度值介于0.08—0.77之间,并且各优势种(类)群的生态位宽度差异较大,种对间生态位重叠值介于0.02—0.89之间,平均生态位重叠指数为0.45,种(类)群之间利用资源环境的互补性较强,这与海域内生境多样化并且各优势种对环境适应能力的差异存在一定联系。DCCA分析表明,影响浮游动物分布的主要因子是水深、温度和盐度,其次是叶绿素a和溶解氧。     

Seasonal dynamics of zooplankton community in four Mediterranean reservoirs in humid area (Beni Mtir: north of Tunisia) and semi arid area (Lakhmes,Nabhana and Sidi Saâd: center of Tunisia)

The zooplankton community was studied in four Mediterranean reservoirs to assess the relative importance of environmental factors as determinants of zooplankton dynamic in the four seasons. The water temperature and hydrology variations affect the distribution of zooplankton. A positive correlation was established between the total zooplankton and the water temperature (r=0.9, n=9, p<0.05). Fourteen zooplankton species were identified. Seasonal changes in the density (ANOVA, F=3.7, d.f=36, p<0.01) and the biomass of total zooplankton (ANOVA, F=4.4, d.f=36, p<0.001) were observed. Our results suggest that planktivorous fish may not modify the zooplankton dynamics in Beni Mtir reservoir (oligotrophic). On the contrary, in Sidi Saâd reservoir (mesotrophic), fish predation has major effects on seasonal zooplankton dynamics.     

Role of macrophytes as microhabitats for zooplankton community in lentic freshwater ecosystems of South Korea

Zooplankton community distribution depends largely on the microhabitat characteristics of the water body. It has been reported that macrophytes provide microhabitats for zooplankton (e.g., space and food resources). To date, studies have focused on the overall influence of macrophytes on zooplankton (e.g., positive relationships with zooplankton diversity); however, the morphological characteristics of macrophytes have not been intensively studied. To fill this gap in knowledge, we investigated zooplankton abundance and diversity, macrophyte characteristics (types, dry weight, and species number), and physicochemical parameters (water temperature, dissolved oxygen, pH, conductivity, and chlorophyll a) by using the 1 × 1 m quadrat method. We surveyed 164 wetlands in South Korea during spring (May to June), prior to the summer monsoon. Patterning zooplankton distribution was accomplished using a Self-organizing map (SOM). We used 34 input variables (zooplankton genera) to train the model. The distribution of five plant habit parameters (no plant, emergent, free-floating, floating-leaved, and submerged) was investigated with a trained SOM plane, by environment data masking. Based on a U-matrix, three clusters were identified from the model. Zooplankton assemblages were positively related to macrophyte characteristics (i.e., dry weight, species number, and plant type). In particular, free-floating plants supported rotifers, such as Testudinella, and cladocerans, such as Alona, Chydorus, Diaphanosoma, and Ilyocryptus (mostly epiphytic). Submerged plants were associated with planktonic rotifers, such as Filinia, Ploesoma, Synchaeta, cladocerans, such as Daphnia, and copepods, such as Eucyclops and Macrocyclops. On the basis of these results, we suggest that the microhabitat structure, created by macrophytes, is an important factor in determining the diversity and abundance of zooplankton communities, because the different species compositions of macrophytes support diverse zooplankton genera in these habitats. The results indicate that macrophytes are the key components of lentic freshwater ecosystem heterogeneity, and the inclusion of diverse plant species in wetland construction or restoration schemes will result in ecologically healthy food webs.