Release and growth of Cyanea capillata (L.) ephyrae in the Gullmar Fjord,western Sweden

In an investigation carried out in the Gullmar Fjord, western Sweden, the autecology of the scyphozoans Aurelia aurita (L.) and Cyanea capillata (L.), has been studied. This paper focuses on results concerning C. capillata, but comparisons with Aurelia aurita are made and discussed. The main period of strobilation was in winter and early spring. The extent of ephyrae release was only one tenth of that of A. aurita. The period of rapid growth of ephyrae and medusae during the spring was delayed one month compared to the pattern for Aurelia. The Cyanea scyphistomae are exposed to predation by the nudibranch Coryphella verrucosa and only very limited settling of Cyanea planulae occurred in the area. Immigration from the North Sea is probably a major factor regulating the appearance of Cyanea capillata along the western coast of Sweden.     

Relationship between planktonic dinoflagellate abundance, cysts recovered in sediment traps and environmental factors in the Gullmar Fjord, Sweden

In order to study the relationship between planktonic dinoflagellates,cyst production and environmental factors, a sediment trap studywas conducted in the Gullmar Fjord, Swedish west coast, during21 days in May–June 1998. Five locations for sedimenttraps were randomly selected every third day. The traps weremoored at the five locations and moved to new locations after3 days. At every location, a CTD depth profile was obtainedand water samples were collected for plankton, chlorophyll aand nutrient analysis. Meteorological and hydrographic datafor the period were obtained from continuous monitoring. Threedinoflagellate species, which have not previously been recordedfrom the Kattegat or the Skagerrak (Scrippsiella crystallina,Scrippsiella lachrymosa and Scrippsiella trifida), were encounteredduring the analysis of cysts from the sediment traps. The abundanceof the different species in the motile form encountered in thewater column and cyst form encountered in the sediment trapsvaried greatly. The discrepancy between the number and speciesencountered in traps and water samples is discussed. No density-dependentrelationship between the abundance of planktonic cyst-formingdinoflagellates and the number of cysts recovered could be observed.A multiple regression showed that the variation in cyst yieldfrom the traps for the most abundant species was correlatedwith water surface temperature, ambient light radiation andthe depth of the halocline. The nutrient concentrations (NH₄⁺,NO₂^–, NO₃^– and PO₄^3–), which are known toplay a crucial role in induction of sexuality and cyst formationunder laboratory conditions, correlated poorly with the numberof dinoflagellate cysts encountered in the traps.     

Niche differentiation between two littoral prawns in Gullmar Fjord, Sweden: Palaemon adspersus and P. squilla

Palaemon squilla (L.) at the Swedish west coast occurred on bottoms covered with Zostera marina L., on bare sand bottoms, in moving water and in rock pools, while P. adspersus Rathke was found on Zostera covered bottoms only. During summer 1978 the increase in length of P. adspersus was 2.2 times greater than that of P. squilla , the former species also attaining a larger maximal size. Laboratory studies showed a wide tolerance in both species to combinations of temperature and salinity. P. squilla tolerated higher temperatures than P. adspersus. The locomotory activity of P. squilla was more than twice that of P. adspersus and concentrated to the dark period. Stomach analyses revealed no interspecific differences in food selection. P. squilla appears to be an opportunistic species able to survive in many different habitats, with a higher dispersal ability, smaller size and larger tolerance to extreme values of abiotic parameters, while P. adspersus is a K-strategist with a high competitive ability, a larger proportion of availably energy devoted to growth, and with larger body size and lower mobility. Although these differences enable the two species to coexist in certain habitats, their habitat segregation still appears to be of primary importance to reduce competition between them.     

Comparative studies of carotenoids in the fauna of the Gullmar Fjord (Bohuslan,Sweden) III. Echinodermata

The author investigated the presence of various carotenoids in the Echinodermata from Gullmar Fjord (Bohuslan, Sweden) by means of columnar and thin-layer chromatography. The investigations revealed the presence of the following:

- inHenricia sanguinolenta:β-carotene, echinenone, canthaxanthin, guraxanthin, lutein-5, 6-epoxide and astaxanthin.

- inAmphiura filiformis: canthaxanthin, cryptoxanthin, lutein, lutein-5, 6-epoxide, isozeaxanthin, zeaxanthin, astaxanthin and 4-hydroxy-4-keto-β-carotene.

- inAmphipholis squamata:β-carotene, cryptoxanthin, lutein, lutein-5, 6-epoxide, astaxanthin, astaxanthin ester, asterin-acid and rubixanthin derivative.

- inOphiopholis aculeata: canthaxanthin, cryptoxanthin, isozeaxanthin, astaxanthin, astaxanthin ester, asterinacid, 4-hydroxy-4-keto-β-carotene, hydroxy rubixanthin and gazaniaxanthin-like substances.

- inOphiothrix fragilis: canthaxanthin, lutein-5, 6-epoxide, isozeaxanthin, astaxanthin, astaxanthin ester, 4-hydroxy-4-keto-β-carotene, and hydroxy rubixanthin.

- inAntedon petatus:canthaxanthin, guaraxanthin, isozeaxan-thin, zeaxanthin, astaxanthin, astaxanthin ester and 4-keto-4-ethoxy-β-carotene.

- inEchinocardium cordatum:β-carotene,γ-carotene, canthaxanthin, lutein, isozeaxanthin, zeaxanthin, astaxanthin and astaxanthin ester.

- inSpatangus purpureus: isozeaxanthin, astaxanthin, astaxanthin ester and 4-hydroxy-4-keto-β-carotene.

     

Short-term variations in the zooplankton community related to water exchange processes in the Gullmar fjord, Sweden

Short-term variations in the zooplankton community in relationto hydrographical exchange processes were studied from Februaryto April 1985 in the sill area of the Gullmar fjord, situatedon the west coast of Sweden. It was concluded that the hydrodynamicprocesses were of great importance for the short-term variationsin the zooplankton abundance and species composition. Furthermore,it was found that due to the complex nature of the exchangeprocesses and zooplankton patchiness, the predictability ofthe development of the zooplankton community in the fjord ispoor. Fractionated sampling in stratified waters is discussed,as well as the effect of different water retention times aboveand below the halocline.     

A review of important concepts in the trophic organization of pelagic ecosystems

The physical environment has an important influence on the size composition of primary producers in plankton communities. This effect is transmitted through the trophic structure by size selective feeding processes at each level. A pictorial representation of trophic organization in pelagic ecosystems is presented which illustrates the complex involvement of individual species in the food web and the dynamic nature of ecosystem development along alternate pathways.This research was supported in full by the National Science Foundation, Grant No. NSF OCE76-02035.     

Spatial dynamics of rotifers in a large lowland river,the Elbe,Germany: How important are retentive shoreline habitats for the plankton community?

A stable nitrogen isotope analysis was used to clarify the relative importance of denitrification and nitrate uptake by plants in the nitrate reduction in a reed belt of L. Kamisagata (N 37°49′, E 138°53′, alt. 4.5 m, depth 30–80 cm, area 0.025 km²), one of about 20 sand dune lakes in Japan. A very high concentration of NO ₃ ⁻ -N with 19.0 ± 5.9 mg N l⁻¹ in spring sources decreased during passage through the reed belt along two set transect lines about 120 m long in any season, whereas progressive enrichment in ¹⁵N-NO ₃ ⁻ in flowing water was detected. Loss rate of nitrate ranged from 38.4 to 73.1% with an average of 56.7 ± 11.6%. Enrichment factors calculated using a Rayleigh curve method ranged from −1.03 to −5.12‰. The contribution of denitrification to nitrate loss ranged from 6 to 28%, with a mean of 19.5% (±7.0), whereas that of plant uptake was from 72 to 94%, with a mean of 80.5% (±7.0), indicating the importance of vegetation in a sand dune riparian zone. A technique using the variation of natural abundance of ¹⁵N may provide useful information on the nitrate dynamics in artificial or natural wetlands under a non-destructive condition.     

Stability patterns and trophic structure in a Delaware Bay plankton community.

Using qualitative loop analysis we have extended our examination of a Delaware Bay plankton community to include an investigation of the roles played by the various entities (population, guild or nutrient) in the community. In an entity removal exercise, we used stability relationships as a probe into community structure. Six types of stability change are possible as a result of entity removal from the system: stable to stable (s-->s); stable to unstable (s-->u); stable to disconnected (s-->d); unstable to stable (u-->s); unstable to unstable (u-->u); unstable to disconnected (u-->d). Using these changes as an investigative tool, we found that in order to account for the stability-instability patterns, it was necessary to construct a refined trophic structure model. The observed connections between the entities in the larger model could be grouped into two different types of stability substructures: a simple pattern and a more complex branching pattern. These patterns map easily onto the refined trophic structure model. Using stability analysis it is also possible to model community structure in ways other than the traditional trophic approach. Patterns of system necessity and relative contribution to stability are observed. These patterns match the refined trophic structure model derived previously. The roles that the various entities play in the overall community were followed over an annual cycle. Entities were seen to change their roles as a function of time and status within a subgroup. These results show that stability determinations have the potential to be used as a valuable tool in community analysis.     

Relationship between trophic state and plankton community structure in 21 Sicilian dam reservoirs

The relationship between the trophic state of 21 Sicilian dam reservoirs and their taxonomic community structure of phytoplankton (87 taxa) as well as zooplankton (45 taxa) have been examined by means of cluster analysis performed using annual average biomass values. The phytoplankton community structure was closely connected with the trophic state of the reservoirs, whereas the zooplankton community structure was related to hydrological regimes peculiar to the individual water bodies and not to the trophic state.     

Microalgal plankton composition in shallow coastal inlets in contrasting trophic and alternative community states

As the trophic state of the environment changes, communities develop into divergent states. These community states are conventionally reflected through primary producers, because they are directly affected by nutrient availability. Studies of submerged macrophytes often focus on community composition to decipher the vegetative (community) state of the environment, while planktic microalgae are usually viewed more cursorily. Although microalgal plankton composition has been related to the trophic state of shallow temperate lakes, corresponding qualitative knowledge is lacking for shallow inlets in the sea. We assessed the composition of microalgal plankton in relation to that of submerged macrophytes in shallow inlets in the northern Baltic Sea during one ice-free season. Microalgal plankton composition varied distinctively among inlets in different trophic and vegetative states especially during early and mid-season, before becoming comparably uniform. These patterns were consisted both inside and outside of macrophyte beds and during day and night. Local and diurnal variation was comparably high in eutrophic and charophyte-dominated inlets, but only during early season. Microalgal plankton composition not only reflects the state of littoral communities in varying trophic conditions, but it may also be important for the whole trophic structure of those communities.     

Distribution and ecology of tintinnids in the plankton of Lebanese coastal waters (eastern Mediterranean)

The tintinnids of Jounieh Bay in Lebanon were identified andtheir numerical abundance determined in horizontal and verticalnet samples from February 1979 to December 1980. Large fluctuationsin abundance and composition of the tintinnid fauna occurredduring the period of investigation. Two distinct peaks werenoted, a major one in May–June and a minor one in November–December.The first followed the main phytoplankton peak, suggesting apositive nutritional relationship between the two populations.The most abundant species were Tintinopsis beroidea and Eutintinnuslusus-undae. A few other species showed great abundance duringshorter periods. In all, 121 species were recorded during thisperiod, and of these 12 belong to the genus Tintinnopsis and11 to Eutintinnus.     

香溪河库湾轮虫现状及水质评价初探

香溪河是长江三峡水库湖北省最大的支流。通过对香溪河库湾(下游河段)一周年的调查,发现轮虫80种,其中占优势的有13种。轮虫密度在不同样点差异显著,样点Ⅸ最低(仅为68.96 ind./L),样点Ⅵ最高(为1505.83ind./L);对9个样点进行聚类分析,可分为4组,第1组为样点Ⅰ至Ⅴ,第2组为样点Ⅵ,第3组为样点Ⅶ、Ⅷ,第4组为样点Ⅸ;除样点Ⅸ外,沿着水流方向,轮虫密度逐渐降低;在时间上差异也显著(P<0.01),9月份最高(2664.17ind./L),12月份最低(85.00ind./L)。水质评价表明香溪河库湾属于中污染。     

广东省大中型供水水库营养现状及浮游生物的响应

于2000年调查了广东省18座大中型供水水库的水质现状并探讨了浮游生物对营养水平的响应。总氮、总磷、透明度和叶绿素a分别为0．15～7.15mg／L、0．003～0．387mg／L、0．4～6．3m和0．6～32．3ug／L。总氮、总磷、透明度均与叶绿素a呈较高的相关性。根据这4个因子的综合加权营养状态指数为23．7～55．1,季节差异不大,大多数水库处于中营养状态。金藻在中-富及富营养型水库中没有分布,而蓝藻、绿藻、硅藻和甲藻在调查水库中均有比较广的营养生态位,但它们的密度及相对优势度在各营养型水库中有一定的差异。高营养水平水库有较高的细胞密度和叶绿素a含量。营养水平较低的水库浮游植物以硅藻-甲藻、硅藻-绿藻或金藻-硅藻为主;营养水平较高的水库以蓝藻-硅藻或蓝藻-绿藻为主,并有较高的裸藻密度。浮游动物基本上以桡足类为优势种群,但在中-富营养和富营养型水库中,哲水蚤种类比低营养型水库中少。枝角类优势种类在各营养型水库差别不大。轮虫对水体营养水平的响应相对比较显著。低营养水平水库的轮虫以广营养型、中营养型或寡中营养型种类为主,种类数目比较少;富营养和中-富营养型水库的轮虫以喜在中营养到富营养条件下生长的种类为主,且轮虫种类数目比较多。     

黄河上游玛曲段春季浮游生物群落结构特征

为了了解黄河上游玛曲段的水质状况,于2006年4—5月对黄河玛曲段干流浮游生物的群落组成进行了调查。结果表明：全段的浮游植物共有5门23种（属）,浮游植物密度为3.2×10⁴～54×10⁴ cells·L^-1,平均密度为19.7×10⁴ cells·L^-1,生物量为0.069～0.464 mg·L^-1,平均生物量为0.228 mg·L^-1,其中密度最高的为齐哈玛,生物量最高的为玛曲大桥;浮游动物共有2门10种（属）,密度为670～1273 cells·L^-1,平均为881.56 cells·L^-1,生物量为0.044～0.089 mg·L^-1,平均为0.064 mg·L^-1;该河段浮游生物组成多以冷水性为主;浮游植物多样性指数介于2～3,表明黄河上游玛曲段水质呈轻度污染;浮游生物丰富度与均匀度值均较低,群落结构组成不稳定,易受外界环境的干扰。     

Predators, resources, and trophic chains in the regulation of plankton population and biomass in oligothrophic lakes

The relative strength of "top-down" versus "bottom-up" control of plankton community structure and biomass in two small oligotrophic lakes (with and without fish), located near the Polar circle (Russia), has been investigated for two years, 1996 and 1997. The comparative analyses of zooplankton biomass and species abundance showed strong negative effect of fish, stickeback (Pungitius pungitius L.), on the zooplankton community species, size structure and biomass of particular prey species but no effect on the biomass of the whole trophic level. An intensive predation in Verkhneye lake has lead to: 1) sixfold decline in biomass of large cladoceran Holopedium gibberum comparing to the lake lacking predator, 2) shift in the size mode in zooplankton community and the replacement of the typical large grazers by small species--Bosmina longirostris and rotifers. Their abundance and biomass even increased, demonstrating the stimulating effect of fish on the "inefficient" and unprofitable prey organisms. The analysis of contributions of different factors into the cladoceran's birth rate changes was applied to demonstrate the relative impact of predators and resources on zooplankton abundance. An occasional introduction of the stickleback to Vodoprovodnoye lake (the reference lake in 1996) in summer 1997 lead to drastic canges in this ecosystem: devastating decrease of zooplankton biomass and complete elimination of five previously dominant grazer species. The abundance of edible phytoplankton was slightly higher in the lake with fish in 1996 and considerably higher in the lake where fish has appeared in 1997 showing the prevailing "top-down" control of phytoplankton in oligotrophic ecosystem. The reasons of trophic cascade appearance in oligotrophic lakes are also discussed.     

Trophic role of rotifers in the plankton of lake Kozjak (Plitvice Lakes)

The trophic role of rotifers in the zooplankton community of dimictic, oligotrophic lake Kozjak, the largest lake of the Plitvice Lakes, NW Dinarid Mountains, is analyzed. Their spatial and temporal biomass distribution in relation to that of protozoans, cladocerans and copepods shows that they form a significant part of the non-predatory zooplankton of this karstic standing water.     

Biomass changes and trophic amplification of plankton in a warmer ocean

Ocean warming can modify the ecophysiology and distribution of marine organisms, and relationships between species, with nonlinear interactions between ecosystem components potentially resulting in trophic amplification. Trophic amplification (or attenuation) describe the propagation of a hydroclimatic signal up the food web, causing magnification (or depression) of biomass values along one or more trophic pathways. We have employed 3‐D coupled physical‐biogeochemical models to explore ecosystem responses to climate change with a focus on trophic amplification. The response of phytoplankton and zooplankton to global climate‐change projections, carried out with the IPSL Earth System Model by the end of the century, is analysed at global and regional basis, including European seas (NE Atlantic, Barents Sea, Baltic Sea, Black Sea, Bay of Biscay, Adriatic Sea, Aegean Sea) and the Eastern Boundary Upwelling System (Benguela). Results indicate that globally and in Atlantic Margin and North Sea, increased ocean stratification causes primary production and zooplankton biomass to decrease in response to a warming climate, whilst in the Barents, Baltic and Black Seas, primary production and zooplankton biomass increase. Projected warming characterized by an increase in sea surface temperature of 2.29 ± 0.05 °C leads to a reduction in zooplankton and phytoplankton biomasses of 11% and 6%, respectively. This suggests negative amplification of climate driven modifications of trophic level biomass through bottom‐up control, leading to a reduced capacity of oceans to regulate climate through the biological carbon pump. Simulations suggest negative amplification is the dominant response across 47% of the ocean surface and prevails in the tropical oceans; whilst positive trophic amplification prevails in the Arctic and Antarctic oceans. Trophic attenuation is projected in temperate seas. Uncertainties in ocean plankton projections, associated to the use of single global and regional models, imply the need for caution when extending these considerations into higher trophic levels.     

Diatoms in the plankton and sediments of two lakes of different trophic type

Species composition, quantity and distribution of diatoms in both the plankton and the surface sediments (0–30 cm) of mesotrophic Lake Krasnoye and eutrophic Lake Vishnevskoye (Karelian Isthmus) were studied. In the mesotrophic lake the composition of dominant diatoms (mainly Melosira) corresponded to those in the plankton. The Araphidineae/Centrales (A/C) ratio was 0.2–0.3%, increasing in the upper layers to 7%. Alkaliphilous and alkalibiontic forms constituted 60% of the total. In the eutrophic lake diatoms with thin valves (mainly Synedra) predominated in the plankton but their quantity in the sediments was insignificant in comparison with other plankton. Nevertheless, the A/C ratio was much higher, 17–35%. Alkaliphilous and alkalibiontic forms accounted for 78–90% of the total number of valves. In both lakes the highest number of diatom valves was registered in the upper layer of the sediments. From the ratio of the total number of diatoms in the upper 5 cm layer to their annual flux to the sediment from the plankton the approximate sediment accumulation rate was calculated to be 1.9 mm a^?1 for the mesotrophic lake and 2.5 mm a^?1 for the eutrophic one.