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1.
Blooms of drifting green algae often develop in shallow coastal zones that receive significant nutrient inputs. Each spring and summer, some fifty bays and coves in Brittany (France) are affected in this way. Until now, in this region, only the algae present in the surf zone or stranded ashore, constituting an intertidal stock, have been taken into account. Another stock of algae, which was subtidal and of the same species (Ulva spp.), was found in the Bay of Douarnenez, one of the ten areas most affected by these algal blooms. This subtidal Ulva stock was located beyond the surf zone, at depths reaching 15 m. It was about the same size as the intertidal stock, viz., a few thousand tons on average. Subtidal Ulva stocks were generally found lying on the sandy bottom in a distribution showing no particular pattern. Biomass ranged from almost zero to 1.547 kg m−2 of fresh and spun-dried algae. However, at depths from 3 to 7 m they were often arranged in strips a few dm wide, due to the swell's effect. The bottom conditions of temperature, salinity, irradiance and dissolved inorganic nitrogen measured during spring and summer are suitable for the growth of Ulva in the subtidal zone. Both intertidal and subtidal drifting Ulva stocks are mobile and capable of exchanging material. In spring, the intertidal stock's inoculum is likely to come from the subtidal. Later in the season, the subtidal stock could be supplied, at least partially, by the intertidal.  相似文献   

2.
The Mondego estuary is a well-described system located on the North Atlantic Ocean, where cultural eutrophication progressed over the last decades of the 20th century. Consequently, and due to a large productivity of Ulva spp., Zostera noltii meadows were severely reduced with a concomitant decrease in environmental quality. In 1998, experimental mitigation measures were implemented, via changes in hydrology to increase circulation and diversion of nutrient-rich freshwater inflow, to reverse the process in the most affected area of the estuary – its South arm.The objective of this study was to assess the differences in response of primary producer assemblages to the implemented measures to reduce eutrophication.Results show that the mean concentrations of DIN suffered a notorious decrease due to a significant reduction in the ammonium concentration in the water column, while DIP increased significantly. Primary producer assemblages showed different responses to these changes: phytoplankton, measured as concentration of chlorophyll a, did not show any significant changes; green macroalgae, mostly Ulva spp., suffered a large reduction in biomass, whereas Gracilaria gracilis and the macrophyte Zostera noltii biomasses increased greatly. Results show that phytoplankton biomass has remained constant and suggest that the reduction in ammonium could have been responsible for the changes in the green macroalgal biomass. Light was the most likely factor in the response of seagrass whereas red macroalgal reaction seemed to be dependent on both light and ammonium.  相似文献   

3.
The effects of temperature and different forms of nutrients on Chattonella marina growth have been investigated in strains isolated from the Daya Bay,the South China Sea.The strain of C.marina preferred high temperatures, with an optimal temperature of 25°C,and 18 °C was the minimum for its survival.Higher cell number and growth rate were obtained in high nitrogen and phosphorus concentrations (500 μ g/L, 74 μ g/L) than under nutrient limitation.Nitrogen influenced the growth most, as the specific growth rate and maximum cell density were lower in nitrogen-limited cultures than noted under phosphorus limitation or under limitation from both.C.marina was capable of using many kinds of organic nitrogen sources including L-serine (L-Ser),glycine (Gly),alanine (Ala),L-threonine (L-Thr), glutamic acid (Glu) and urea, but could not utilize uric acid.Various forms of organic phosphorus compound such as glucose-6-phosphate (G6P),sodium glycerophosphate (GYP),adenosine triphosphate (ATP),adenosine monophosphate (AMP),cytidine monophosphate (CMP),guanosine monophosphate (GMP),uridine monophosphate (UMP),4-nitrophenylphosphate (NPP) and triethyl phosphate (TEP) supported the growth as well. Algal cells had the ability to sustain growth under nitrogen-and/or phosphorus-free conditions particularly under phosphorus depleted condition.These results led to the hypothesis that high loading of nitrogen has played an important role in frequent C.marina blooms in the past decade,and its capability for utilization of diverse forms of organic nutrients and growth in low nutrient conditions make this species a likely recurrent dominant in the Daya Bay phytoplankton assemblages,visible as  相似文献   

4.
秦皇岛海域属于我国渤海区域典型的大型海藻分布区,该海区资源丰富,在我国大型海藻区系中占有较为重要的位置。于2021年秋季在该海域采集石花菜(Gelidium amansii)样品进行活体培养,对其藻体附生的其他季节大型海藻的状况加以观察研究。通过实验生物学方法对石花菜附生藻生殖特征和生态习性进行了观察,结合附生藻形态特征进行物种分类鉴定。经过培养与鉴定,确定该水域石花菜的附生大型海藻共有7种,其中红藻4种,即丛出旋体藻(Audouinelladaviesii)、旋体藻(Auduinella sp.)、茎丝藻小枝变型(Stylonema alsidii f. ramosum)和日本新管藻(Neosiphonia japonica);绿藻2种,即苍白刚毛藻(Cladophora albida)和浒苔[Enteromorpha (Ulva) prolifera];蓝藻1种,即丝状鞘丝藻(Lyngbya confervoides);丛出旋体藻、茎丝藻小枝变型和苍白刚毛藻为河北海域的新记录物种。研究结果表明,室内人工培养可作为个体微小的附生大型海藻分类鉴定的有效补充方法,也能为分子鉴定提供纯净的...  相似文献   

5.
Distribution and biomass of green algal mats were studied in marine shallow (0–1 m) soft-bottom areas on the Swedish west coast from 1994 to 1996, by combining aerial photography surveys with ground truth sampling. Filamentous green algae, dominated by species of the genera Cladophora and Enteromorpha, were generally present throughout the study area during July and August, and largely absent in late April and early May. These algae occurred at 60 to 90% of the locations investigated during the summer, and were estimated to cover between 30 and 50% of the total area of shallow soft bottoms of the Swedish Skagerrak archipelago. The distributional patterns were similar during the three years of the investigation and appeared unrelated to annual local nutrient inputs from point sources and river discharge. We postulate that the apparent lack of such a relationship is due to an altered state of nutrient dynamics throughout the archipelago. Mechanisms are likely to involve long-term, diffuse elevations in nutrient levels in coastal waters of the Skagerrak and the Kattegat over several decades leading to current eutrophic conditions, exceeding nutrient requirements for abundant filamentous algal growth. Patterns of algal abundance in our study were largely related to physical factors such as exposure to wind, waves and water exchange under conditions where nutrient loads among embayments seemed to be unlimited. Further, our results show that sediments covered by algal mats had higher carbon and nitrogen contents than unvegetated sediments. We hypothesise that sustained high nutrient loads, manifested in extensive biomass of filamentous algae during summer months, are re-mineralised via decay and sedimentation in the benthic realm. Hence, accumulated carbon and nutrients in the sediment could, in turn, constitute the basic pool for future algal mat production overlying soft bottoms in areas where tidal exchange is limited.  相似文献   

6.
Salt marsh formation can be initiated by the colonization of bare tidal flats by pioneer halophytes such asSpartina anglica. In the present study, growth ofS. anglicain the edge and centre zones of pioneer patches colonizing a tidal flat in a marine bay in the south-west Netherlands was investigated. Average biomass and shoot length was significantly lower in centre zones than in edge zones of the patches. Multiple linear regression showed that 84% of the variance in aboveground biomass in the centre zones could be explained by sediment phosphorus and nitrogen concentrations. No such relationship existed in the edge zone. This suggests that biomass production in the centre zones of the patches is nutrient limited, but that factors other than sediment nitrogen and phosphorus content determine growth ofSpartinain the edge zones.The sediment nitrogen and phosphorus concentrations in the centre zones of the patches were significantly related with sediment carbon concentrations, indicating that the pool of particle-bound nutrients in the sediment to an important extent is associated with organic particles. Determination of stable carbon isotope signatures of the sedimentary organic matter showed that an increasing carbon content of the sediment in the centre zone of the patches (and a rise in plant biomass) coincides with a higher contribution of non-Spartinaderived carbon to the sedimentary organic matter pool. Sustained biomass production in the centre zones of the patches, thus, probably depends on deposition of allochthonous organic particles and the nutrient inputs inherent in this process. Due to the construction of large-scale hydro-engineering works, however, conditions for deposition of waterborne particles are currently unfavourable. The consequences of reduced carbon and nutrient inputs into the patches will be particularly in the (older) centre zones, where the nutrient pools in non-refractory organic matter have been drained in the years of previous growth. Accordingly, it is hypothesized that the canopy-enhanced sedimentation for whichSpartinais well- known, via positive feed-back effects on plant growth can be crucial for plant vitality, and, hence, for successful colonization of unvegetated areas.  相似文献   

7.
研究了福建九龙江口秋茄(Kandelia candel)红树林潮间带的红藻鹧鸪菜(Caloglossa leprieurii)的氮、磷、钾、钠、钙与镁6种营养元素含量的季节变化。氮、磷、钾与钠均以春季含量最高；钙与镁分别以秋季和冬季最高。氮与磷含量冬季最低，钾含量秋季最低；钠、钙、镁均以夏季含量最低，6种元素含量的季节变化模式不一致。营养元素含量的季节变化表明鹧鸪菜春季富集的营养物质较多，与春季有较高的生物量一致。营养元素含量的季节变化反映了鹧鸪菜的生长与环境因子的季节变化。鸥鸪菜的氮、磷含量高于土壤含量。并明显高于水体氮、磷含量，说明鹧鸪菜能强烈富集环境中的氮、磷，因此鸥鸪菜类的大型藻类的存在可能是红树林区赤潮极少发生的原因之一。  相似文献   

8.
为探讨海马齿(Sesuvium portulacastrum)对水域环境修复作用,本文研究了水培海马齿对不同盐度水质的碳汇作用以及不同形态氮的利用情况。实验设计0、10、20、30、35盐度梯度,海马齿水培时间82 d,然后测定植株干重、营养元素含量以及积累速率,最后在抑菌与不抑菌条件下研究海马齿根际与铵态氮(NH4+-N)、硝态氮(NO3--N)、无机磷(PO43-)以及色氨酸(Trp)吸收转化关系。研究结果表明,盐度10条件下海马齿植株干重、有机元素含量以及积累速率最高,有机碳、有机氮与有机磷积累速率分别为(5.572±1.611)、(0.313±0.058)、(0.057±0.013)mg/(d·ind.),而高盐环境35盐度条件下对海马齿生长造成一定胁迫。盐度0～35范围,海马齿均未出现死亡现象。不同盐度抑菌培养条件下,色氨酸与无机氮共存时均能被能被海马齿利用,色氨酸利用量远高于硝态氮、铵态氮;不抑菌条件下铵态氮则表现出增加的结果。海马齿作用在盐度...  相似文献   

9.
The influence of salinity on growth and Cu uptake in the green macroalga Ulva reticulata collected from the intertidal area in the Western Indian Ocean was studied under controlled laboratory conditions. Exposure concentrations ranged from 5 to 500 μg Cu l−1 at five salinities (ranging 20–40). The accumulation of Cu increased with decreasing salinity, so that the uptake at 500 μg Cu l−1 was approximately 2.7, 2.4 and 2.0 times higher at salinities of 20, 25, and 30 respectively, than uptake at salinity of 35, and with uptake being lowest at salinity of 40. Ulva maintained a positive growth rate over the whole salinity range (20–40), with highest rates at salinity of 35. When exposing to Cu at low salinities (20 and 25), the growth rate of Ulva was strongly inhibited suggesting an increase in toxicity of Cu with decreasing salinity. EC50 and NOEC increased with increase in salinity, implying a reduced Cu toxicity at high salinities. It was concluded that salinity needs to be considered when using macroalgae, such as U. reticulata, as a bioindicator of heavy metals in areas with heavy rainfall, underground fresh water intrusion or in estuaries, as they might accumulate more metals and be more negatively affected.  相似文献   

10.
Enrichments with five types of organic carbon, differing in nitrogen content and type of organic carbon, were made to a marine sediment in order to study effects on nitrogen fluxes. The enrichments used were Ulva lactuca, Ascophyllum nodosum, Zostera marina, Ceratium spp., lignin, and mixtures of U. lactuca and A. nodosum. Fluxes of ammonium, nitrate, and phosphate were measured in short-term (48 h) microcosm experiments, using a carbon enrichment loading similar to that at the sampling site. Changes in microbial community growth and structure due to three types enrichments were also detected using molecular methods in a microcosm experiment run for 4 days to allow for detection at DNA-level.Ammonium fluxes changed from an efflux in the control to an influx for all enrichments apart from U. lactuca. The change was significantly related to the added material's C:N ratio when Ceratium spp. was excluded. All enrichments induced an influx of nitrate suggesting the formation of anoxic micro zones, but there was no relationship with C:N ratio. Instead, the magnitude of the nitrate influx is suggested to be related to the structure of the organic carbon, where enrichments containing a large pool of cellulose and lignin (Z. marina and lignin) gave rise to a lower influx, compared to algal material with more easily degraded organic matter like lipids and starch, which induced the highest influx of nitrate (Ceratium spp., U. lactuca, and A. nodosum). The occurrence of an ammonium influx together with increased nitrate influx and a lower efflux of phosphate in the enrichments suggests a growth of heterotrophic bacteria. This was also confirmed using molecular methods (PCR-DGGE) where the relative abundance of bacterial species in the enrichments increased.The sum of ammonium and nitrate fluxes showed that total nitrogen removal was enhanced in all enrichments compared to the nonenriched control sediment, but in different ways. Ceratium spp. induced the highest removal followed by A. nodosum, U. lactuca, Z. marina, and lastly, by lignin. The same pattern was observed also in a second experiment. These results indicate that easily degradable organic carbon, together with a lower C:N ratio of the added material, will remove nitrogen from the water phase, making the recycling of nitrogen to the overlying water mass smaller.  相似文献   

11.
Tropical coastal marine ecosystems including mangroves, seagrass beds and coral reef communities are undergoing intense degradation in response to natural and human disturbances, therefore, understanding the causes and mechanisms present challenges for scientist and managers. In order to protect our marine resources, determining the effects of nutrient loads on these coastal systems has become a key management goal. Data from monitoring programs were used to detect trends of macroalgae abundances and develop correlations with nutrient availability, as well as forecast potential responses of the communities monitored. Using eight years of data (1996–2003) from complementary but independent monitoring programs in seagrass beds and water quality of the Florida Keys National Marine Sanctuary (FKNMS), we: (1) described the distribution and abundance of macroalgae groups; (2) analyzed the status and spatiotemporal trends of macroalgae groups; and (3) explored the connection between water quality and the macroalgae distribution in the FKNMS. In the seagrass beds of the FKNMS calcareous green algae were the dominant macroalgae group followed by the red group; brown and calcareous red algae were present but in lower abundance. Spatiotemporal patterns of the macroalgae groups were analyzed with a non-linear regression model of the abundance data. For the period of record, all macroalgae groups increased in abundance (Abi) at most sites, with calcareous green algae increasing the most. Calcareous green algae and red algae exhibited seasonal pattern with peak abundances (Φi) mainly in summer for calcareous green and mainly in winter for red. Macroalgae Abi and long-term trend (mi) were correlated in a distinctive way with water quality parameters. Both the Abi and mi of calcareous green algae had positive correlations with NO3−, NO2−, total nitrogen (TN) and total organic carbon (TOC). Red algae Abi had a positive correlation with NO2−, TN, total phosphorus and TOC, and the mi in red algae was positively correlated with N:P. In contrast brown and calcareous red algae Abi had negative correlations with N:P. These results suggest that calcareous green algae and red algae are responding mainly to increases in N availability, a process that is happening in inshore sites. A combination of spatially variable factors such as local current patterns, nutrient sources, and habitat characteristics result in a complex array of the macroalgae community in the seagrass beds of the FKNMS.  相似文献   

12.
Copper and iron concentrations in three brown algae, Ascophyllum nodosum, Fucus vesiculosus and Laminaria digitata (and additionally Mn in L. digitata) from the Irish west coast were determined using flame atomic absorption spectrophotometry. Metal concentrations in the three species were indicative of prevailing bioavailable metal concentrations in situ but varied greatly between functional tissue parts, between sites and over time. Cu concentrations in actively growing tips of A. nodosum decreased over a 4-month period during autumn/winter, while Fe concentrations increased. Both Fe and Cu concentrations in different thallus sections of A. nodosum and F. vesiculosus increased with increasing age of thallus part in a clean site, but there was no consistent trend for F. vesiculosus from an industrialized site. Within sites, concentrations of all Cu and Fe were similar in both fucoids, but concentrations at the industrialized site were about twice as high as at the pristine site. In L. digitata, all three metals were highest in holdfasts, but had distinctly different distribution patterns in stipes and blade sections, which were most likely related to growth pattern and tissue function. Fe was lowest in meristematic and young blade regions, suggesting small-scale Fe limitation in actively growing tissue. Mn concentrations were higher in distal blade sections than in stipes, and Cu concentrations were highest in meristematic and young thallus parts.  相似文献   

13.
Rocky shores in the North Atlantic are known for their zonation patterns of both algae and animals, which can be expected to greatly affect food availability to consumers at different height levels on the shore. We tested the hypothesis that consumers would feed on the most abundant suitable food source in their surroundings. In total 36 species/taxa of common primary producers and consumers were sampled for stable isotope analyses from a sheltered fucoid shore at Hvassahraun in south-western Iceland. A selection of these species was also collected seasonally and from different height levels. Feeding experiments, field observations and gut analyses were also conducted. Our results were in good overall agreement with pre-existing knowledge of trophic relationships in the rocky intertidal. Consumers often appeared to be assimilating carbon and nitrogen from the most common diet in their immediate surroundings. The predator Nucella lapillus was thus feeding on different prey at different height levels in accordance with different densities of prey species. When tested in the laboratory, individuals taken from low on the shore would ignore the gastropod Littorina obtusata, uncommon at that height level, even when starved, while individuals from mid-shore readily ate the gastropod. This indicated that some kind of learned behaviour was involved. There were, however, important exceptions, most noteworthy the relatively small contribution to herbivores, both slow moving (the gastropod L. obtusata) and fast moving (the isopod Idotea granulosa and the amphipod Gammarus obtusatus) of the dominant alga at this site, Ascophyllum nodosum. The recent colonizer Fucus serratus seemed to be favoured. Selective feeding was indicated both by isotope signatures as well as by results of feeding experiments. Seasonal migrations of both slow and fast moving species could partly explain patterns observed.  相似文献   

14.
利用2009-2018年在南黄海苏北浅滩海域的现场调查数据，分析和研究了该海域漂浮绿藻和马尾藻的长期变化和季节性波动特征。研究显示，漂浮绿藻于每年4月中旬至下旬在浅滩中部筏架周围开始出现。5月－6月，漂浮绿藻生物量迅速增加，并漂移扩散至深水区。漂浮绿藻密度年际变化较大，但这十年间总体呈上升趋势。相比较而言，漂浮马尾藻仅在2013、2017和2018年在浅滩聚集形成春季藻华；且这三年，漂浮马尾藻密度超过同期漂浮绿藻。浅滩漂浮马尾藻的发生与发展过程与漂浮浒苔明显不同。3月，漂浮马尾藻开始出现于浅滩离岸海域，4-5月，漂浮马尾藻大量侵入浅滩，因此浅滩漂浮马尾藻现并非起源于本地。受高强度人类活动以及浅滩以外海域物理化学和生物过程的影响，浅滩环境因素与漂浮绿藻生物量的关系不甚明确。对于漂浮马尾藻的起源以及与漂浮绿藻的相互关系也需要进一步研究。  相似文献   

15.
The littoral zone of Chesapeake Bay contains a mosaic of shallow vegetated and nonvegetated habitats with biotic components that are sensitive to changes in biological and physical driving factors. Static and dynamic modelling frameworks provide an integrative way to study complex hydrodynamic and biogeochemical processes in linked estuarine habitats. In this study we describe a spatial simulation model developed and calibrated relative to a specific littoral zone, estuarine ecosystem. The model consisted of four distinct habitats that contained phytoplankton, sediment microalgae, Zostera marina (eelgrass), and Spartina alterniflora. There was tidal exchange of phytoplankton, particulate and dissolved organic carbon and dissolved inorganic nitrogen between the littoral zone ecosystem and the offshore channel. Physical exchange and biogeochemical transformations within the habitats determined water column concentrations in each habitat. Predicted subtidal water column concentrations and Z. marina and S. alterniflora biomass were within the variability of validation data and the predicted annual rates of net primary production were similar to measured rates. Phytoplankton accounted for 17%, sediment microalgae 46%, the Z. marina community 24% and S. alterniflora 13% of the annual littoral zone primary production. The linked habitat model provided insights into producer, habitat and ecosystem carbon and nitrogen properties that might not have been evident with stand-alone models. Although it was an intra-ecosystem sink for particulate carbon, the seagrass habitat was a DOC source and responsible for over 30% of the littoral zone carbon and nitrogen primary production. The model predicted that the Goodwin Islands littoral zone was a sink of channel derived POC, but a source of DOC to the surrounding estuary. The framework created in this study of estuarine ecosystem dynamics is applicable to many different aquatic systems over a range of spatial and temporal scales.  相似文献   

16.
近年来，海水富营养化导致近海海域大型海藻过量繁殖，成为世界性的环境问题。自2007年以来，浒苔绿潮在黄海海域连续暴发，造成巨大经济损失。为探究浒苔大规模暴发与氮磷比值(N/P)的关系，及其与其他大型绿藻在不同N/P下的竞争机制，研究了浒苔(Ulva prolifera)与石莼(Ulva lactuca)在不同N/P下单独培养和共培养时的生长情况，探究了浒苔及石莼生长的变化；结合苏北浅滩海域现场N/P的调查结果，分析了浒苔绿潮暴发的可能机制。研究结果表明:(1)浒苔单独培养时，在一定范围内高N/P能促进浒苔的生长，氮对于浒苔的影响大于磷。(2)石莼单独培养时，低N/P下石莼长势最好，但改变N/P对石莼的影响并不显著。(3)浒苔和石莼共培养时，浒苔生长受到了一定限制，低N/P下浒苔生长受限更显著。(4)苏北浅滩海域高N/P更适合浒苔的生长，可能是浒苔绿潮能够大规模暴发的原因之一。  相似文献   

17.
Nereis diversicolor is generally considered to be a predator and deposit feeder, but have also been found to graze on benthic algae in shallow coastal areas. In this study we investigated the grazing effects on the development and growth of green algae, Ulva spp. Algal growth was studied in an experiment including two levels of sediment thickness; 100 mm sediment including macrofauna and 5 mm sediment without macrofauna, and three treatments of varying algal biomass; sediment with propagules, sediment with low algal biomass (120 g dry weight (dwt) m− 2) and sediment with high algal biomass (240 g dwt m− 2). In the 100 mm sediment, with a natural population of macrofauna, N. diversicolor was the dominating (60% of total biomass) species. After three weeks of experimentation the result showed that N. diversicolor was able to prevent initial algal growth, affect growth capacity and also partly reduce full-grown algal mats. The weight of N. diversicolor was significantly higher for polychaetes in treatments with algae added compared to non-algal treatments. There were also indications that a rich nutrient supply per algae biomass counteracted the grazing capacity of N. diversicolor.  相似文献   

18.
采用室内培养实验方法,研究了褐藻海黍子(Sargassum muticum)和红藻脆江蓠(Gracilaria chouae)在不同质量浓度的锌和镉溶液里15 d,藻体的生长和体内金属离子含量的变化。结果表明:两种藻的生长速率与暴露溶液金属质量浓度呈负相关,藻体内积累金属离子的量和溶液的金属质量浓度呈正相关,藻体内金属离子的含量均在培养3 d后显著增加,且随着培养时间的延长而持续增加。海黍子和脆江蓠对重金属Zn~(2+)的富集能力明显高于对Cd~(2+)的富集能力,在相同条件下,海黍子对重金属Zn~(2+),Cd~(2+)的积累量明显高于脆江蓠。以上研究结果对利用藻类修复重金属污染的海洋水体能起到一定的指导和参考作用。  相似文献   

19.
Concentrations of biogenic silica(BSi) in the southern Yellow Sea were determined during four cruises(spring:April–May 2014; autumn: November 2014; summer: August–September 2015; winter: January 2016). Samples of BSi were measured using the double extraction method. Seasonal and spatial variations of BSi and the potential correlation between chlorophyll a(Chl a) content and BSi in four seasons were measured in this study. Significant spatial variability was observed in seawater BSi concentrations. The average concentration of BSi was highest in winter and lowest in spring. Furthermore, the relationships between concentrations of BSi and hydrological parameters were also discussed. There was a significant positive correlation between Chl a and BSi. The concentrations of BSi showed significant relationships with temperature and the concentrations of silicates, total inorganic nitrogen and total inorganic phosphorus, indicating that distribution of BSi was affected by temperature and nutrient level.  相似文献   

20.
The spatial and temporal dynamics of dissolved inorganic nitrogen, dissolved phosphate, dissolved silica and chlorophyll a were measured seasonally at eight stations in the Ria de Aveiro. Between December 2000 and September 2001, the seasonal succession of phytoplankton assemblages, inferred after the spatial and seasonal variation of silica and of chlorophyll a concentrations, showed that diatoms (μmol Si L−1) dominated from late autumn until early spring, while chlorophytes (μg Chl a L−1) bloomed during late spring and summer. The Si:N:P ratios and Si concentrations indicated no seasonal depletion in dissolved silica, as in other temperate systems, possibly because of abnormal precipitation and flood events prolonging the supply of dissolved Si to the system. The Si:N:P ratios suggested P limitation at the system level. Despite the relative proportions of available nutrients, the mean phosphorus concentration (5.3 μmol L−1) was above the reported half-saturation constants for P uptake by phytoplankton. Thus, in Ria de Aveiro, the seasonal succession of phytoplankton assemblages may also be dependent on the grazing capacity of the pelagic community through top-down regulation.  相似文献   

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