Top-down control of spring surface phytoplankton blooms by microzooplankton in the Central Yellow Sea,China

Phytoplankton growth and microzooplankton grazing were studied during the 2007 spring bloom in Central Yellow Sea. The surveyed stations were divided to pre-bloom phase (Chl a concentration less than 2 μg L⁻¹), and bloom phase (Chl a concentration greater than 2 μg L⁻¹). Shipboard dilution incubation experiments were carried out at 19 stations to determine the phytoplankton specific growth rates and the specific grazing rates of microzooplankton on phytoplankton. Diatoms dominated in the phytoplankton community in surface waters at most stations. For microzooplankton, Myrionecta rubra and tintinnids were dominant, and heterotrophic dinoflagellate was also important in the community. Phytoplankton-specific growth rates, with an average of 0.60±0.19 d⁻¹, were higher at pre-bloom stations (average 0.62±0.17 d⁻¹), and lower at the bloom stations (average 0.59±0.21 d⁻¹), but the difference of growth rates between bloom and pre-bloom stations was not statistically significant (t test, p=0.77). The phytoplankton mortality rate by microzooplankton grazing averaged 0.41±0.23 d⁻¹ at pre-bloom stations, and 0.58±0.31 d⁻¹ during the blooms. In contrast to the growth rates, the statistic difference of grazing rates between bloom and pre-bloom stations was significant (after removal of outliers, t test, p=0.04), indicating the importance of the top-down control in the phytoplankton bloom processes. Average potential grazing efficiency on primary productivity was 66% at pre-bloom stations and 98% at bloom stations, respectively. Based on our results, the biomass maximum phase (bloom phase) was not the maximum growth rate phase. Both phytoplankton specific growth rate and net growth rate were higher in the pre-bloom phase than during the bloom phase. Microzooplankton grazing mortality rate was positively correlated with phytoplankton growth rate during both phases, but growth and grazing were highly coupled during the booming phase. There was no correlation between phytoplankton growth rate and cell size during the blooms, but they were positive correlated during the pre-bloom phase. Our results indicate that microzooplankton grazing is an important process controlling the growth of phytoplankton in spring bloom period in the Central Yellow Sea, particularly in the “blooming” phase.     

2017年春季季风间期南海中北部浮游植物生长与微型浮游动物摄食

Phytoplankton growth rates and mortality rates were experimentally examined at 21 stations during the 2017 spring intermonsoon(April to early May) in the northern and central South China Sea(SCS) using the dilution technique, with emphasis on a comparison between the northern and central SCS areas which had different environmental factors. There had been higher temperature but lower nutrients and chlorophyll a concentrations in the central SCS than those in the northern SCS. The mean rates of phytoplankton growth(μ_0) and microzooplankton grazing(m) were(0.88±0.33) d~(–1) and(0.55±0.22) d~(–1) in the central SCS, and both higher than those in the northern SCS with the values of μ_0((0.81±0.16) d~(–1)) and m((0.30±0.09) d~(–1)), respectively.Phytoplankton growth and microzooplankton grazing rates were significantly coupled in both areas. The microzooplankton grazing impact(m/μ_0) on phytoplankton was also higher in the central SCS(0.63±0.12) than that in the northern SCS(0.37±0.06). The microzooplankton abundance was significantly correlated with temperature in the surface. Temperature might more effectively promote the microzooplankton grazing rate than phytoplankton growth rate, which might contribute to higher m and m/μ_0 in the central SCS. Compared with temperature, nutrients mainly affected the growth rate of phytoplankton. In the nutrient enrichment treatment,the phytoplankton growth rate(μn) was higher than μ_0 in the central SCS, suggesting phytoplankton growth in the central SCS was nutrient limited. The ratio of μ_0/μn was significantly correlated with nutrients concentrations in the both areas, indicating the limitation of nutrients was related to the concentrations of background nutrients in the study stations.     

Effects of suction-dredging for cockles on non-target fauna in the Wadden Sea

Suction dredging for cockles removes large cockles from tidal flats and may also cause mortality of non-target fauna and make the habitat less suitable for some species. This study examines whether suction dredging for cockles on tidal flats of the Dutch Wadden Sea had affected densities of non-target fauna, directly after fishing and one year later. Densities of non-target fauna in two randomly chosen undredged locations were compared to densities at the surrounding heavily commercially dredged area. A significant negative effect of cockle dredging on densities of 0-group Macoma balthica was observed and this effect persisted one year after dredging. The dredged area appeared to be less suitable for settlement of mussels Mytilus edulis. No significant effects of dredging on the mudsnail Hydrobia ulvae and on 0 and 1-group C. edule were found. For the mobile young Macoma balthica it seems unlikely that the effect found after one year was still due to the mortality caused by dredging and this suggests that the habitat was less suitable as a consequence of dredging. Thus, even in the highly dynamic ecosystem of the Wadden Sea, effects of bottom disturbance by cockle dredging may persist after one year.     

The balance between microzooplankton grazing and phytoplankton growth in a highly productive estuarine fjord

During 24, three-day cruises to Dabob Bay, Washington State, USA, from February 4 to April 26, 2002, and February 4 to May 1 2003, we examined the relative growth and grazing rates of phytoplankton and microzooplankton using dilution experiments. Experiments were conducted over two time intervals: 8–10 h during the nighttime only, or 24 h from noon to noon. We used water from two depths during each cruise: from the surface mixed layer, and from a deep layer below the seasonal thermocline. During 2002, there was one mid-sized bloom consisting mainly of Thalassiosira spp. in early February, and a larger bloom in April comprised of two Chaetoceros spp. and Phaeocystis sp. During 2003, there were also two blooms, one in early February, which was again dominated by Thalassiosira spp., and a second larger bloom in mid-April, comprised mainly of Thalassiosira spp. and Chaetoceros spp. During all four of these blooms, and for both water source depths, specific grazing rates of microzooplankton were most often as high or higher than the calculated phytoplankton specific growth rates. The major microzooplankton categories that could have accounted for this were (1) a large Gyrodinium spp., (2) a group of fusiform-shaped mid-sized Protoperidinium species, and (3) three loosely defined taxonomic groups consisting of naked ciliates, tintinnids, and unidentified heterotrophic dinoflagellates. Based on our measurements, it appears that the microzooplankton community grazing pressure can often exert significant control on phytoplankton biomass, even during the extremely productive spring bloom periods and under several different diatom-dominated bloom types. These results suggest that even in highly productive estuarine ecosystems, which are often nurseries to economically important fisheries species, microzooplankton play a critical role and may significantly alter the availability and efficiency of transfer of energy to higher trophic levels.     

Effects of current exposure on habitat preference of mobile 0-group epibenthos for intertidal seagrass beds (Zostera noltii) in the northern Wadden Sea

In the northern Wadden Sea, the extent of intertidal seagrass beds, their plant biomass and shoot density highly depends on local current regimes. This study deals with the role of intertidal Zostera noltii beds as nursery for mobile epibenthic macrofauna and the impact of seagrass bed characteristics on their abundance and distribution patterns. According to their exposure to the main tidal gullies, sampling sites were separated into exposed, semi-exposed and sheltered. Dominant species of crustaceans and demersal fish were studied in respect of their abundances within seagrass beds and adjacent unvegetated areas. Quantitative sampling was performed at day and night high tide using a portable drop trap. In general, species composition varied little between seagrass beds and bare sand. However, the presence of vegetation had a quantitative effect increasing individual numbers of common epifaunal species. Abundances of 0-group shore crabs (Carcinus maenas), common gobies (Pomatoschistus microps) and brown shrimps (Crangon crangon) were highest within sheltered seagrass beds. With decreasing plant density habitat preference of epibenthos changed on species level. By regulating the habitat complexity the currents regime is profoundly influencing the nursery function of intertidal seagrass beds in the Wadden Sea.     

Depth-stratified phytoplankton dynamics in Cyclone Opal, a subtropical mesoscale eddy

As part of E-Flux III cruise studies in March 2005, we investigated phytoplankton community dynamics in a cyclonic cold-core eddy (Cyclone Opal) in the lee of the Hawaiian Islands. Experimental incubations were conducted under in situ temperature and light conditions on a drift array using a two-treatment dilution technique. Taxon-specific estimates of growth, grazing and production rates were obtained from analyses of incubation results based on phytoplankton pigments, flow cytometry and microscopy. Cyclone Opal was sampled at a biologically and physically mature state, with an 80–100 m doming of isopycnal surfaces in its central region and a deep biomass maximum of large diatoms. Depth-profile experimentation defined three main zones. The upper (mixed) zone (0–40 m), showed little compositional or biomass response to eddy nutrient enrichment, but growth, grazing and production rates were significantly enhanced in this layer relative to the ambient community outside of the eddy. Prochlorococcus spp. dominated the upper mixed layer, accounting for 50–60% of its estimated primary production both inside and outside of Opal. In contrast, the deep zone of 70–90 m showed little evidence of growth rate enhancement and was principally defined by a 100-fold increase of large (>20-μm) diatoms and a shift from Prochlorococcus to diatom dominance (80%) of production. The intermediate layer of 50–60 m marked the transition between the upper and lower extremes but also contained an elevated biomass of physiologically unhealthy diatoms with significantly depressed growth rates and proportionately greater grazing losses relative to diatoms above or below. Microzooplankton grazers consumed 58%, 65% and 55%, respectively, of the production of diatoms, Prochlorococcus and the total phytoplankton community in Cyclone Opal. The substantial grazing impact on diatoms suggests that efficient recycling was the major primary fate of diatom organic production, consistent with the low export fluxes and selective export of biogenic silica, as empty diatom frustules, in Cyclone Opal.     

Environmental controls on phytoplankton community composition in the Thames plume, U.K.

The aim of this study was to investigate controls on the phytoplankton community composition and biogeochemistry of the estuarine plume zone of the River Thames, U.K. using an instrumented moored buoy for in situ measurements and preserved sample collection, and laboratory-based measurements from samples collected at the same site. Instrumentation on the moored buoy enabled high frequency measurements of a suite of environmental variables including in situ chlorophyll, water-column integrated irradiance, macronutrients throughout an annual cycle for 2001 e.g. nitrate and silicate, and phytoplankton biomass and species composition. The Thames plume region acts as a conduit for fluvial nutrients into the wider southern North Sea with typical winter concentrations of 45 μM nitrate, 17 μM silicate and 2 μM phosphate measured. The spring bloom resulted from water-column integrated irradiance increasing above 60 W h m^− 2 d^− 1 and was initially dominated by a diatom bloom mainly composed of Nitzschia sp. and Odontella sinesis. The spring bloom then switched after  30 days to become dominated by the flagellate Phaeocystis reaching a maximum chlorophyll concentration of 37.8 μg L^− 1. During the spring bloom there were high numbers of the heterotrophic dinoflagellates Gyrodinium spirale and Katodinium glaucum that potentially grazed the phytoplankton bloom. This diatom–flagellate switch was predicted to be due to a combination of further increasing water-column integrated irradiance > 100 W h m^− 2 d^− 1 and/or silicate reaching potentially limiting concentrations (< 1 μM). Post spring bloom, diatom dominance of the lower continuous summer phytoplankton biomass occurred despite the low silicate concentrations (Av. 0.7 μM from June–August). Summer diatom dominance, generally due to Guinardia delicatula, was expected to be as a result of microzooplankton grazing, dominated by the heterotrophic dinoflagellate Noctiluca scintillans, controlling 0.7–5.0 μm ‘flagellate’ fraction of the phytoplankton community with grazing rates up to 178% of ‘flagellate’ growth rate. The Thames plume region was therefore shown to be an active region of nutrient and phytoplankton processing and transport to the southern North Sea. The use of a combination of moorings and ship-based sampling was essential in understanding the factors influencing nutrient transport, phytoplankton biomass and species composition in this shelf sea plume region.     

Differential reproductive strategies of two bivalves in the Dutch Wadden Sea

Cerastoderma edule and Mya arenaria are two common bivalve species in European waters. Longevity and maximum size are much greater in the latter species. Because comparison of species life-history strategies states that a long life span (i.e. high annual survival) generally goes with lower fecundity, we hypothesise that reproductive output would be lower in M. arenaria than in C. edule. In the present paper, we studied the reproductive strategies of these two species in an intertidal and a subtidal area of the western Dutch Wadden Sea, by following seasonal changes in absolute and relative weights of somatic and gonadal tissues in these bivalves. Starting of spawning was similar in the two species, around May, except for intertidal M. arenaria, which initiated spawning in August. Individual energy investment in reproduction was similar for the two species but, unlike M. arenaria, C. edule spawned completely, releasing all energy of gonadal mass in the form of gametes. Mya arenaria used the gonad not only for reproduction but also for storage. In the intertidal area, we found a trade-off between longevity and reproduction, i.e. maximum reproductive output (expressed as a proportion of body mass) was higher in C. edule than in M. arenaria. However, since body size is larger and life span longer in M. arenaria than in C. edule, mean lifetime reproductive output per individual must be higher in the first than in the latter. Based on the differences in reproductive strategies of these two species, we hypothesise that the negative effects of warming climate on bivalve population dynamics in the Wadden Sea will be stronger in C. edule than in M. arenaria.     

2011年春夏季黄海和东海微型浮游动物类群组成及其摄食的研究

为了解春夏季黄海和东海微型浮游动物类群及其摄食生态,于2011年春季和夏季在黄海、东海,通过稀释法测定浮游植物生长率及微型浮游动物对浮游植物的摄食率,同时应用显微分析技术研究了微型浮游动物丰度及其类群组成．结果表明：（1）春季,黄海、东海微型浮游动物丰度为1800～21833个／dm3,夏季的为67～6175个／dm3;春季,其微型浮游动物生物量为8．71-60．58ug/dm3,夏季的则为0．44～30．25ug／dm3（其生物量以c含量计）．（2）春季、夏季黄海和东海浮游植物的生长率及其标准偏差分别为0．78±0．35、1．62±0．83d-1,而春季的显著低于夏季（P〈0．05）．春季、夏季其微型浮游动物的摄食率及其标准偏差分别为0．98±0．32、0．92±0．57d-1,无显著性差异（p〉0．05）．春季,微型浮游动物摄食浮游植物现有生物量的61％±13％,占初级生产量的131％±58％;夏季,微型浮游动物摄食浮游植物现有生物量的54％±22％,占初级生产量的70％±44％．春、夏季,黄海和东海微型浮游动物对浮游植物初级生产量的摄食比例较高．     

Contribution of different generations of the brown shrimp Crangon crangon (L.) in the Dutch Wadden Sea to commercial fisheries: A dynamic energy budget approach

In this paper a contribution is made to the ongoing debate on which brown shrimp generation mostly sustains the autumn peak in coastal North Sea commercial fisheries: the generation born in summer, or the winter one. Since the two perspectives are based on different considerations on the growth timeframe from settlement till commercial size, the Dynamic Energy Budget (DEB) theory was applied to predict maximum possible growth under natural conditions. First, the parameters of the standard DEB model for Crangon crangon L. were estimated using available data sets. These were insufficient to allow a direct estimation, requiring a special protocol to achieve consistency between parameters. Next, the DEB model was validated by comparing simulations with published experimental data on shrimp growth in relation to water temperatures. Finally, the DEB model was applied to simulate growth under optimal food conditions using the prevailing water temperature conditions in the Wadden Sea. Results show clear differences between males and females whereby the fastest growth rates were observed in females. DEB model simulations of maximum growth in the Wadden Sea suggest that it is not the summer brood from the current year as Boddeke claimed, nor the previous winter generation as Kuipers and Dapper suggested, but more likely the summer generation from the previous year which contributes to the bulk of the fisheries recruits in autumn.     

Biological components of Ross Sea short-term particle fluxes in the austral summer of 1995–1996

The Ross Sea, a region of high seasonal production in the Southern Ocean, is characterized by blooms of the haptophyte Phaeocystis antarctica and of diatoms. The different morphology, structural composition and consumption of these two phytoplankton by grazing zooplankton may result in different carbon cycling dynamics and carbon flux from the euphotic zone. We sampled short-term (2 days) particle flux at 5 sites from 177.6°W to 165°E along a transect at 76.5°S with traps placed below the euphotic zone at 200 m during December 1995–January 1996. We estimated carbon flux of as many eucaryotic organisms and fecal pellets as possible using microscopy for counts and measurements and applying volume:carbon conversions from the literature. Eucaryotic organisms contributed about 20–40% of the total organic carbon flux in both the central Ross Sea polynya and in the western polynya, and groups of organisms differed in contribution to the carbon flux at the different sites. Algal carbon flux ranged from 4.5 to 21.1 mg C m⁻² day⁻¹ and consisted primarily of P. antarctica (cell plus mucus) and diatom carbon at all sites. Different diatom species dominated the diatom flux at different sites. Carbon fluxes of small pennate diatoms may have been enhanced by scavenging, by sinking senescent P. antarctica colonies. Heterotrophic carbon flux ranged from 9.2 to 37.6 mg C m⁻² day⁻¹ and was dominated by athecate heterotrophic dinoflagellate carbon in general and by carbon flux of a particular large athecate dinoflagellate at two sites. Fecal pellet carbon flux ranged from 4.6 to 54.5 mg C m⁻² day⁻¹ and was dominated by carbon from ovoid/angular pellets at most sites. Analysis of fecal pellet contents suggested that large protozoans identified by light microscopy contributed to ovoid/angular fecal pellet fluxes. Carbon flux as a percentage of daily primary production was lowest at sites where P. antarctica predominated in the water column and was highest at sites where fecal pellet flux was highest. This indicates the importance of grazers in carbon export.     

冬季南海北部海域微型浮游动物及其对浮游植物摄食压力研究

2009年1月在南海北部海域的5个站位,采用稀释法和显微分析技术研究了浮游植物生长率及微型浮游动物对浮游植物的摄食压力,同时测定了微型浮游动物的丰度及类群组成.结果表明:南海北部微型浮游动物类群主要以无壳纤毛虫为主,南海北部微型浮游动物类群细胞丰度为33～529个/dm3.南海北部浮游植物生长率为0.45～1.83 d-1,微型浮游动物摄食率为0.44～1.76 d-1,摄食压力占浮游植物现存量的42.6%～82.8%,占初级生产力的97.3%～225.1%.近岸区摄食压力比陆架区高,表明冬季南海近岸区微型浮游动物摄食能够有效的控制浮游植物的生长,而陆架区浮游植物生长率大于摄食率,浮游植物存在着现存量的积累,微型浮游动物并不能完全控制浮游植物的生长.     

2014年夏季南海北部超微型浮游植物分布及环境因子影响

利用流式细胞仪BD Accuri C6对2014年夏季南海北部超微型浮游植物进行了现场的观测研究,发现了3类超微型光合自养浮游植物,聚球藻(Synechococcus,Syn)、原绿球藻(Prochlorococcus,Pro)和超微型真核藻类(pico-eukaryotes,Euk),并对其丰度与分布以及环境因子影响进行了研究。结果表明,Syn、Pro和Euk丰度总平均值分别为5.13×103个/mL,3.27×104个/mL和1.85×103个/mL,碳生物量均值分别为1.19μg/L,1.86μg/L和4.51μg/L。Syn、Pro和Euk的丰度表现出不同的分布特征。Syn、Pro和Euk丰度分布趋势呈现近海低而外海高,Syn和Euk丰度高值区分别出现在沿岸带与陆架和上升流影响海域,Pro丰度高值区出现在沿岸带与陆架,低值区出现在上升流影响海域。Syn、Euk丰度高值区主要分布在次表层,Pro丰度高值区主要分布在真光层底部,Euk丰度垂直变化差异相对Syn和Pro较小。超微型浮游植物与环境因子的相关性分析结果表明,Syn、Pro和Euk的碳生物量均与硝酸盐、硅酸盐浓度和深度呈现负相关关系,Pro的碳生物量与磷酸盐浓度呈现正相关关系。     

Erodibility of a mixed mudflat dominated by microphytobenthos and Cerastoderma edule, East Frisian Wadden Sea,Germany

Sediment erodibility and a range of physical and biological parameters were measured at an intertidal site in the German Wadden Sea area in June, September and November 2002 and February and April 2003 in order to examine the influence of macrozoobenthos and microphytobenthos on sediment erodibility and the temporal variation. The study site was a mixed mudflat situated in the mesotidal Baltrum–Langeoog tidal basin at the East Frisian barrier coast. The mud content at the site was about 35% and the filter-feeding cockle Cerastoderma edule was the dominating macrozoobenthic species (by biomass). The erodibility of the sediment showed strong temporal variation with high erosion thresholds in spring and late summer and significantly lower thresholds during the rest of the study period. The erosion thresholds were strongly dependent on the contents of chlorophyll a (chl a) and colloidal carbohydrates, both indicators of the content of microphytobenthos, in this environment primarily benthic diatoms. The content of microphytobenthos was high in September 2002 and April 2003, and regression analysis indicated that this was the only likely reason for the low erodibility found at these times. A biostabilisation index of about 4.5 was found for a situation with both abundant biofilms and cockles.     

南海北部秋季微型浮游动物摄食和种类组成的初步研究

2004年9月到10月间在南海北部海区对微型浮游动物的种类组成进行了调查,同期运用现场稀释法,以叶绿素a为监测对象,估计了该海区内微型浮游动物摄食率和摄食压力的水平。结果表明,南海北部海区纤毛虫群体中以多膜纲寡毛目为主,有16种,其中寡毛亚目纤毛虫4种,砂壳亚目纤毛虫11种。各站纤毛虫丰度比较低,在9~102ind/m3之间。浮游植物瞬时增长率(k)在0.03/d~2.13/d之间;微型浮游动物的摄食率(g)在0.01/d~1.06/d之间。微型浮游动物对浮游植物现存量的摄食压力(Pi)在0.089%~65.23%之间,对初级生产力的摄食压力(Pp)在33.63%~86.04%之间。微型浮游动物的摄食水平主要受其丰度的影响,同时微型浮游动物对浮游植物现存量和初级生产力的摄食压力显示,在南海北部海区微型浮游动物在初级生产力传递方面具有重要的科学意义和研究价值。     

黄、东海春季和秋季微型浮游动物对浮游植物的摄食压力

2000年秋季(10月21日-11月7日)和2001年春季(4月30日-5月15日)用稀释培养法在黄海和东海测定了微型浮游动物对浮游植物的摄食,结果表明:(1)秋季表层浮游植物叶绿素α(Chl α)的内禀生长率为0.40～0.59 d<'-1>,微型浮游动物对Chl α的摄食率为0.21～0.63 d<'-1>,对Ch...     

Variability of the water temperature in the western Wadden Sea on tidal to centennial time scales

Daily observations of the sea surface temperature in the Marsdiep tidal inlet, which connects the shallow Dutch western Wadden Sea with the deeper North Sea, already started in the summer of 1860, over 140 years ago. Since the year 2000 the sampling frequency has strongly increased because of the use of electronic sensors and data logging by computer. Analysis of these temperature data has revealed variations with time scales from tidal, daily, seasonal, inter-annual, to centennial. The tidal temperature variations are generated by advection of the seasonally varying temperature gradient between Wadden Sea and North Sea, while the daily variations are mainly caused by the daily variation of solar radiation. The seasonal variation in sea surface temperature only lags a few days behind the coastal surface air temperature, contrary to the sea surface temperature in the deeper nearby North Sea, which is delayed with about 1 month. The North Atlantic Oscillation index has been used as large-scale proxy for the atmospheric forcing of the Wadden Sea temperature. Only for the winter and spring a significant correlation is found between temperature and the winter index. However, this correlation is so strong that also the annual mean temperature is correlated significantly with the North Atlantic Oscillation. At longer time scales, from decadal to centennial, also large temperature variations are observed, of the order of 1.5 °C. However, these are not related to long-term changes of the North Atlantic oscillation. These long-term temperature changes involve a cooling of about 1.5 °C in the first 30 years of the record and a similar warming in the last 25 years. In between, these long-term changes were smaller and more irregular. Similar conclusions can also be applied to individual seasons as well as to the date of the onset of spring.     

Variability of the salinity in the western Wadden Sea on tidal to centennial time scales

Daily observations of the salinity of the Marsdiep tidal inlet, which connects the Dutch western Wadden Sea with the North Sea, already started over 140 years ago, in 1860. Since the year 2000 the sampling frequency has increased because of the use of electronic sensors. Analysis of these salinity data have revealed variations on time scales from tidal (~ 12 hour), seasonal, inter-annual, and multi-decadal, to centennial. The contributions of the salinity variations in the Marsdiep for these different spectral bands or time scales are all of the order of a standard deviation of 0.5 to 1. The centennial variation, which can be expressed as a 140 year long salinity trend, is related to engineering works on the rivers Rhine and IJssel, which already started in the early 18-th century, and more than doubled the magnitude of the freshwater content of the western Wadden Sea since then. In contrast with this anthropogenic salinity trend, the climatic variability of the precipitation over western Europe, and the connected changes in the Rhine discharge, are mainly responsible for the inter-annual variations in the salinity and/or freshwater content of the western Wadden Sea. Since variations in salinity and freshwater content also reflect variations in the terrigeneous and river influence on the Wadden ecosystem, e.g. via the nutrient content, it can be expected that the ecology of the Wadden Sea also experienced changes on centennial time scales.