The recovery of benthos following the impact of low oxygen content in the German Bight

The oxygen deficiency in the German Bight and in Danish waters 1981–1983 with ensuing benthos mortality was the reason for studying the development and re-establishment of the macrofauna in the following years. These years, from 1984–1987, exhibited more favourable oxygen conditions.The macrofauna of this region with its predominantly sandy substrate belongs to the Tellina fabula community. It is dominated by regular seasonal and ephemeral species such as Spio filicornis, Phoronis spec., Spiophanes bombyx and Lanice conchilega.In 1983, a year with exceptionally low oxygen content in bottom waters (< 1 mg O₂ dm⁻³), the macrofauna showed, in some parts of the investigated area, as reduction of approx. 30–50% in species numbers. Concurrently, the individual numbers of the remaining species were reduced. Beginning in 1984, a rapid recovery of benthic communities was observed. By 1986, biomass as well as species- and individual numbers rose to values similar to those determined by other authors in earlier surveys of the German Bight. In particular, juvenile Echinocardium cordatum and crustaceans have been observed since 1984 in larger numbers.     

Distribution of flatfish eggs in the 1989 egg surveys in the southeastern North Sea,and mortality of plaice and sole eggs

From January to July 1989 eight egg surveys were carried out in the southeastern North Sea. The first three surveys were designed to estimate the egg production of plaice (Pleuronectes platessa) and cod (Gadus morhua). The other five surveys were aimed at the eggs of sole (Solea solea) and horse mackerel (Trachurus trachurus) Of a selection of the samples collected in 1989 all fish eggs were identified to species. This paper presents data on the distribution, timing and intensity of spawning of the flatfish species plaice, flounder (Platichthys flesus), dab (Limanda limanda), long rough dab (Hippoglossoides platessoides), sole, solenette (Buglossidium luteum), turbot (Scophthalmus maximus) and scaldfish (Arnoglossus laterna).Egg mortality was studied in plaice and sole and compared to previous estimates. Plaice egg mortality in 1988 and 1989 was higher than in 1987, coinciding with higher ambient temperatures. Egg production in sole was recorded earlier in the year in 1988 to 1990 than in 1984, and at lower ambient temperatures. Sole egg mortality rates were shown to be lower in 1988 to 1990 than in 1984.     

Factors controlling the summer development of copepod populations in the southern bight of the North Sea

In two consecutive years an intensive sampling programmed was implemented at a fixed station in Dutch coastal waters to obtain a detailed record of the summer development of copepod populations in relation to phytoplankton and macroplankton abundance. The central question was whether densities of copepods are controlled by predation, in particular by invertebrate pelagic carnivores, or by food limitation. Methods applied to estimate daily predation by observed stocks of carnivores included analysis of gut contents and digestion rate, extrapolation of experimental feeding rates and of literature data on daily rations and maintenance needs. Chlorophyll-a and cell concentrations served as a rough measure for algal food supply.Since a decline in copepod densities manifested itself most clearly in decreasing naupliar numbers in both years, populations were assumed to be regulated mainly by recruitment or survival of these early life stages. Naupliar declines coincided with maximum densities of the hydromedusa Phialidium hemisphaericum, which dominated the macroplankton both in abundance and in biomass and reached a maximum density of 467 specimens·m⁻³ or 7 mg C·m⁻³. Copepod eggs appeared by far the most frequent prey item in their guts. However, these eggs are digested very slowly, if at all, and may often be ejected without any visible damage. The effect of egg predation on naupliar recruitment seems therefore relatively unimportant. Predation on swimming copepod stages was generally low. There was no evidence of selective feeding on nauplii. The maximum values of calculated predation pressure exerted by Phialidium populations matched daily copepod production only by way of exception. Impact of other invertebrate carnivores was negligible. As predation did not play a significant role, food availability seems the key factor underlying copepod population dynamics. The consequences of food limitation (reduced egg production, production of diapause eggs and enhanced cannibalism) are discussed. The observed coincidence of maximum predator abundance and minimum chlorophyll-a and diatom concentrations does not support the hypothesis that carnivores are able to indirectly benefit phytoplankton growth by reducing grazing pressure of herbivores.     

梨茶翅蝽研究初报

茶翅蝽是北京地区梨生产上为害最重的一种害虫,害果率可达80%以上.本文对对梨茶翅蝽的卵、若虫、成虫形态学进行了描述;报道了年生活史及习性,不同季节不同虫态为害梨果的特征;并讨论了化学防治及其他各种防治的有效措施.     

Significance of tintinnid grazing during blooms of Phaeocystis pouchetii (haptophyceae) in Dutch coastal waters

Extremely dense populations of tintinnids (24 000 to 118 000·dm⁻³) were found during the spring bloom of the alga Phaeocystis pouchetii in the Dutch Wadden Sea and coastal North Sea. Microscopic observations showed that these Protozoa grazed on the single-cell stage of the colony-forming Phaeocystis. At the end of the bloom, the biovolume of the tintinnid population equalled or even exceeded that of the Phaeocystis population, indicating that microfaunal grazing prevented further growth of the Phaeocystis spring bloom.     

Seasonal and annual variation in phaeocystis pouchetii (haptophyceae) in the westernmost inlet of the Wadden Sea during the 1973 to 1985 period

Data on seasonal and annual variation in densities of Phaeocystis pouchetii s.I. in the Marsdiep tidal inlet of the western Wadden Sea are reported for 1973 to 1985 inclusive. Each year a spring peak was observed followed by one or more smaller peaks in summer; no peaks were observed after September or before March. In 1985 Phaeocystis colonies were for the first time observed in winter (January/February). Over the 12-year observation period, an increase was found in cell numbers during the spring peak and summer, as well as in the duration of the spring peak and the length of the period that Phaeocystis pouchetii occurred in the plankton. No relation appears to exist between temperature and the timing of rapid increase or occurrence of peaksof Phaeocystis. Such inconsistency might be explained, among others, by the occurrence of different strains of Phaeocystis pouchetii s.I. More taxonomic work is also needed to indicate whether antarctic and tropical records of Phaeocystis pouchetii pertain to the same species.     

On the trophic fate of Phaeocystis pouchetii (hariot): VI. Significance of Phaeocystis-derived mucus for vertical flux

The development and decline of a phytoplankton spring bloom dominated by the prymnesiophyte Phaeocystis pouchetii were studied in Balsfjord, northern Norway between 30 March and 27 May 1992. At a fixed station, the concentration and composition of suspended particulate matter was monitored and compared to the particulate matter collected in sediment traps at six different depths. Direct sedimentation of phytoplankton contributed a minor fraction to particle flux and was confined to a few diatom genera. No evidence was found for pronounced aggregation of Phaeocystis colonies during bloom decline or direct sedimentation of either Phaeocystis colonies or single cells. Particle flux was dominated by faecal-pellet sedimentation during most of the study period, suggesting zooplankton grazing to be a main loss factor. Despite an abrupt decrease in faecal-pellet sedimentation after the decline of the bloom, particulate-carbon sedimentation rates remained high. High post-bloom sedimentation rates were characterized by elevated C/N and C/Chl a ratios of largely amorphous sedimented material. Post-bloom sedimentation coincided with a decrease in transparent exopolymeric particles (TEP) in the surface layer, suggesting that this change resulted from aggregation and sedimentation of carbon-rich exopolymeric material accumulated in the surface layer in the course of the bloom. While organic-carbon accumulation indicates the significance of disintegration of Phaeocystis colonies, post-bloom mucilage sedimentation could be secondary pathway for the vertical flux of Phaeocystis-derived organic matter.     

Nutritional status and pigment composition of phytoplankton during spring and summer Phaeocystis blooms in Dutch coastal waters (Marsdiep area)

The general nutritional status and pigment composition of the phytoplankton population during the 1991 spring and summer Phaeocystis blooms in Dutch coastal waters was analysed using the 480/665 nm absorption ratio of 90% acetone extracts as well as reverse-phase HPLC-pigment analysis. A 100% increase in this ratio was indicative of moderate nutrient deficiency at the end of the Phaeocystis spring bloom in the Marsdiep area. During the summer, nitrate was more likely to be the limiting nutrient than phosphate. Both physiological adaptation and species composition were found to influence the absorption ratio. Variations in the absorption ratio did not completely reflect the variations in fucoxanthin and chlorophyll a. Therefore it was concluded that besides nutrient limitation dynamics, the variable abundances of in particular chlorophyll-c3 containing species (such as Prymnesiophyceae) may effect the absorption ratio.     

?两种色型黄粉虫的选育与繁殖特性研究

为给黄粉虫优良品种培育提供基础的遗传材料和理论依据。以60日龄黄粉虫幼虫体壁颜色为基准,对两种典型色型黄粉虫进行了连续多代的定向选育,并对选育出的两种色型黄粉虫的繁殖特性进行了比较。历经4年多、连续12代的定向选育,成功获得遗传稳定的黄、黑两种色型黄粉虫。这两种色型黄粉虫同日龄幼虫和成虫的体色差异明显：黄色型的幼虫和成虫分别为金黄色和黄褐色;黑色型的幼虫和成虫分别为黑褐色和黑色。进一步对其成虫的繁殖特性进行研究表明：黄、黑两种色型黄粉虫成虫的性比、寿命及雌成虫产卵历期无显著差异,它们的雌雄性比约为1.0:1.0、雌、雄成虫平均寿命均在100天以上、雌成虫的平均产卵历期约为3~4个月。但不同试验条件下,两种色型黄粉虫雌成虫的产卵前期、产卵高峰及产卵量差异显著：它们的孤雌成虫产卵前期为10天、无明显产卵高峰、产卵量极低（黄色型：40粒/雌,黑色型：28粒/雌）;配对后的雌成虫产卵前期缩短为4天、且有2个明显的产卵高峰、产卵量也较孤雌成虫明显提高（单配组1♀+1♂：黄色型为438粒/雌,黑色型为406粒/雌;群配组50♀+50♂：黄色型为653粒/雌,黑色型为530粒/雌）。由此可见,雌雄配对可以大大提高黄粉虫雌成虫的产卵量,并且群配雌成虫的产卵量远远高于单配雌成虫,因此黄粉虫的养殖宜采用群养群配方式。此外,群配条件下黄色型雌成虫的平均产卵量显著高于黑色型雌成虫,这提示,黄、黑两种色型黄粉虫成虫的繁殖能力可能存在一定差异。上述研究结果既为黄粉虫新品种培育积累了宝贵的遗传材料和基础数据,也为黄粉虫成虫的科学养殖提供了有益参考。     

卵高温胁迫对木薯单爪螨发育与繁殖的影响?研究

为探讨木薯单爪螨的生态适应性机理,揭示其种群扩散蔓延机制,本研究开展了卵高温胁迫对木薯单爪螨生长发育与繁殖的影响研究。将木薯单爪螨卵在梯度高温(30、33、36、39、42℃)人工气候箱中处理不同时间(0.5、1、2、4、8、16、24 h)后置于室温(25℃)下饲养,观察其卵孵化率、发育历期、后代性比（雌性百分率）及后代成螨寿命。结果表明：卵高温处理显著影响木薯单爪螨的发育与繁殖。随着温度的升高和处理时间的延长,木薯单爪螨的发育历期显著延长,卵孵化率、后代雌性百分率与后代雌成螨寿命显著下降。温度越高,对木薯单爪螨发育与繁殖的影响越显著,尤其对卵和幼螨的发育;卵经42℃高温处理2 h以上（包括2 h）后在25℃下均不能孵化和完成任何发育历期;42℃高温1 h为木薯单爪螨卵热最敏感时间。因此,卵高温胁迫显著影响木薯单爪螨的生长发育与繁殖,从而可能影响木薯单爪螨种群的变化。本研究结果可为木薯单爪螨扩散蔓延范围及生态适应性提供理论依据,为科学制定中国针对木薯单爪螨的检疫政策和防控措施,以防其进一步扩散蔓延提供理论依据和前期工作基础。     

The availability and quality of the mussel prey (Mytilus edulis) of oystercatchers (Haematopus ostralegus)

Spatial variations in the availability and quality of the mussel Mytilus edulis food supply of Oystercatchers Haematopus ostralegus on the Exe estuary, England, are described. Oystercatchers open mussels by stabbing into gaping mussels (or prising open closed ones) or by hammering a hole in either the dorsal or ventral shells. Spatial variations in the food supply are considered at four scales. In decreasing order of size, these are (i) whole mussel beds, (ii) zones within a mussel bed, (iii) different places within one zone, and (iv) different places within one clump of mussels. The first two scales are clearly related to exposure time. Both between and within the 12 main mussel beds of the estuary, most upshore mussels are up to 10% less likely than downshore mussels to be hidden under mud. However, upshore mussels of a given length contain less flesh, have thicker ventral shells and, except on high-level beds subject to wave erosion, have thicker dorsal shells than downshore mussels. Mussels at the top of the shore also contain the highest infestations of the helminth parasite of Oystercatchers, Psilostomum brevicolle. At a particular shore level, mussels of a given length have less flesh and thicker shells, though only on the dorsal side, in areas of high mussel density. Within one clump, mussels of a given length with thick dorsal shells have more flesh than those with thin shells. In contrast, flesh content is slightly higher in mussels that are thin on the ventral side. Flesh content and shell thickness on both sides are unaffected by whether a mussel is visible at the edge of a clump or hidden inside. Simulations with a model of foraging Oystercatchers suggested that variations in mussel availability (visibility and shell thickness) and flesh content at all four scales could sometimes have an important influence on intake rate. Most published values of intake rates of Oystercatchers eating surface-dwelling mussels may be biassed (and often considerably over-estimated) by the erroneous assumption that prey of average flesh content are taken.     

The spring bloom of phaeocystis pouchetii (haptophyceae) in Dutch coastal waters

A Phaeocystis pouchetii (Harlot) Langerh. bloom, which contained up to 22×10⁶ cells ·dm⁻³, occurred in the spring of 1984 along the Dutch coast of the North Sea. The largest cell numbers of P. pouchetii were observed near the coast, with cell numbers decreasing towards the open sea. In contrast to a shark peak in the cell numbers along the coast in May, P. pouchetii cell numbers in the open sea slowly increased towards June.During a preceding bloom of diatom, P. pouchetii was already present from an early stage onwards while at the end of the P. pouchetii bloom a high percentage of the cells was observed as microflagellates.The distribution of dissolved nutrients (Si, N, P) showed a typical pattern with highest values near the coast, apparently due to the Rhine outflow, and a gradual decrease towards the open water. This distribution pattern coincided with particular stages of the P. pouchetii bloom. Whereas growth of the P. pouchetii population may be due to increasing temperature and irradiance, its decline is probably caused by phosphate limitation.Total primary production measured at one station and based on short term ¹⁴C incubation experiments was 121 gC·m⁻² for the period 17 March to 20 May with a daily rate of production of up to 4.8 gC·m⁻². The mean proportion of extracellular carbon release based on 4 h incubation periods was 7.5%.     

Abundance,growth and food demand of the scyphomedusa Aurelia aurita in the western Wadden Sea

Medusae of Aurelia aurita are found in the western Wadden Sea from the beginning of May till August with maximum numbers of 250 to 500 individuals per 10³ m³ during May-June. The existence of a continuous ebb surplus suggests an origin from polyps living in the inner parts of the estuary and a transport or migration of the released medusae towards the North Sea. Growth is fast; a bell size of 20 cm diameter is reached within 3 to 4 months. The species is important as a predator from May to July, reaching maximum carbon biomass values of 12 to 18 g C·10³ m⁻³. Predation by A. aurita may affect the recruitment of one of its food sources, viz. fish larvae.     

Distribution and abundance of the zooplankton of the Ems estuary (North Sea)

From 1974 to 1977 a study was made of the abundance and the distribution of the zooplankton species of the Ems estuary (The Netherlands and the Federal Republic of Germany), an area of about 500 km² with extensive tidal flats.The most important component of the zooplankton consisted of holoplanktonic calanoid copepods with, during the summer, a significant contribution of meroplankton, mainly consisting of polychaete and cirripede larvae. Zooplankton abundance showed a marked seasonality, with a pronounced spring peak and a smaller late summer/autumn peak. In the low salinity area the spring bloom was dominated by Eurytemora affinis, which persisted in the salinities below S=5 upriver during the whole year. In the polyhaline area Acartia bifilosa was the main component of the spring bloom. The late summer maximum from August to October was dominated by Acartia tonsa in the meso- and polyhaline area and by A. discaudata and Centropages hamatus in the euhaline part of the estuary bordering on the Wadden Sea proper. The number of abundant (> 1000 ind·m⁻³) species increased from the inner, fresher part of the estuary towards the Wadden Sea but, except for April, average zooplankton density in salinities <18 was similar (2768 ind·m⁻³) to the density in salinities >18 (2817 ind·m⁻³).The distribution patterns show that there are only a few autochthonous species and that the majority of species is allochthonous and penetrates more or less deeply into the estuary from the Wadden Sea and North Sea, varying with species and season.     

Nitrogen Balance of Legume-Wheat Cropping Sequences

In a lysimeter trial the legumes faba bean ( Vicia faba ), red clover ( Trifolium repens ), and alfalfa ( Medicago sativa ) were grown for two years, followed by winter wheat on all plots in the third year. Plots fertilized with mineral nitrogen and a rye/maize – wheat cropping sequence were included for comparisons. These four cropping sequences were replicated twice in 1982–1984 and 1985–1987, respectively. Two soils, a loamy sand and a sandy loam were used.
On average of both soils:
– N fixation during two years was 461 kg N/ha, 803 kg N/ha, and 790 kg N/ha for faba bean, red clover, and alfalfa, respectively.
– Leaching of nitrogen occurred mainly during the periods of winter fallow or, in case of the perennial legumes, after incorporation of residues into the soil and planting of wheat. Average leaching for all 6 years was 49, 28, and 29 kg ha⁻¹ year⁻¹ for faba bean, red clover, and alfalfa, respectively.
– In the period of wheat growth and before planting the new crop (1.5 years) in 1984/85 51–64 kg N/ha and 1986/87 68–94 kg N/ha were leached after growing legumes. Leaching was less for rye/maize fertilized with mineral N, 41 kg N/ha in 1984/85, and 51 kg N/ha in 1986/87, respectively.
– Winter wheat grown after legumes took up 18 kg N/ha < 47 kg N/ha < 65 kg N/ha on average of both soils and 2 years (1984, 1987) after faba bean, red clover, and alfalfa, respectively. This indicates a nitrogen recovery of 24–44% of the legume N potentially available, and consequently a loss by leaching from 56 to 76 %.
On the sandy loam amount of drainage water and N leaching were lower, and faba bean and wheat yields higher than on the loamy sandy soil.     

Comparison of the pigmentation of two strains of the prymnesiophyte Phaeocystis sp.

Two strains of Phaeocystis sp., one isolated from the Weddell Sea region (Antarctica) and one from the North Sea, were compared for their growth characteristics and pigmentation during growth in batch cultures. Experiments were performed starting with identical nutrient and light conditions at 2°C, 7°C and 10°C. Division rates ranged from 0.17 to 0.94 d⁻¹ depending on strain and temperature: the Antarctic strain grew fastest at 2°C (μ=0.71 d⁻¹), the strain from the North Sea at 10°C (μ=0.94 d⁻¹). Growth phase, phase in the diurnal cycle and temperature influenced the 19'hexanoyloxyfucoxanthin to chlorophyll a ratio in both strains. Large differences in this ratio were found between flagellates and colony cells from the same strain. Despite variability within each strain, mean levels of 19'hexanoyloxyfucoxanthin were always higher in the Antarctic strain. Another fucoxanthin-related pigment, 19'butanoyloxyfucoxanthin, showed the same trends during growth as 19'hexanoyloxyfucoxanthin in the antarctic strain but was undetectable in the strain isolated from the North Sea. A comparison was made with field data collected during the Phaeocystis blooming period in the coastal zone of the North Sea. During this period relative amounts of 19'hexanoyloxyfucoanthin as well as the absence of 19'butanoyloxyfucoxanthin matched with the results from the North Sea strain in culture. Environmental factors influence pigment content and ratio, yet the two investigated Phaeocystis strains can be distinguished on the basis of their pigment characteristics.     

Macrofauna standing stock of the Dogger Bank. A comparison: II. 1951–1952 versus 1985–1987 are changes in the community of the northeastern part of the Dogger Bank due to environmental changes?

During April/May 1985–1987 some of Ursin's (Ursin, 1960) stations on the Dogger Bank from April/May 1951–1952 were revisited. This paper concentrates on results from the ‘Tail End’, the northeastern part of the Dogger Bank. The polychaete species Ophelia borealis and Goniada maculata, which were dominant species in 1951–1952, showed similar distributions in 1985–1987 on the whole of the Dogger Bank. Changes in the macrofauna distribution are obvious in the increase of opportunistic small polychaete species like Spiophanes bombyx, Scoloplos armiger and Magelona spp. In 1985–1987 these species occurred in high individual numbers per m² all over the Dogger Bank in contrast to 1951–1952, when they were found only in few individuals. Extensive patches of the bivalve species Spisula subtruncata discovered at the northeastern border of the Dogger Bank in the fifties were not found. Only small, fast-growing species like Abra prismatica, Tellina fabula and Montacuta bidentata occurred in high individual numbers per m². In 1987 the total biomass shows a reduction of about 30% in the area compared with 1950–1954Some hypotheses are given to explain the changes in macrofauna distribution on the Dogger Bank between 1950–1954 and 1985–1987, taking into account the increasing eutrophication and pollution.     

Food intake and growth of Sarsia tubulosa (SARS, 1835), with quantitative estimates of predation on copepod populations

In laboratory tests food intake by the hydromedusa Sarsia tubulosa, which feeds on copepods, was quantified. Estimates of maximum predation are presented for 10 size classes of Sarsia. Growth rates, too, were determined in the laboratory, at 12°C under ad libitum food conditions. Mean gross food conversion for all size classes averaged 12%.From the results of a frequent sampling programme, carried out in the Texelstroom (a tidal inlet of the Dutch Wadden Sea) in 1983, growth rates of Sarsia in the field equalled maximum growth under experimental conditions, which suggests that Sarsia in situ can feed at an optimum level. Two estimates of predation pressure in the field matched very closely and lead to the conclusion that the impact of Sarsia predation on copepod standing stocks in the Dutch coastal area, including the Wadden Sea, is generally negligible.     

Temperature beat on a tidal flat: Potential cue for harpacticoid bloom

Temperature was recorded in the sediment on a tidal flat in the Fraser estuary (Canada) from February 15 to July 1985, and from February 19 to July 9 in 1986, with continuous recording thermographs. Within these periods, the abundance of an assemblage of harpacticoid copepods (Tisbe spp., Zaus aurelii, Harpacticus uniremis) was monitored bi-weekly by sampling the water column with a sled-sampler. Temperature time-series of both years showed the expected fortnightly beats in the daily temperature cycle. A reversal in the direction of the change of temperature in the sediment during exposure was observed on March 12 in 1985, and on March 1 in 1986. This reversal initiated the seasonal warming beat in the sediment when exposed at lower low waters, and is caused by the precessing of the timing of the lower low waters relative to the solar day. Blooming period of harpacticoids was centred on March 21 in 1985, and on March 12 in 1986. Closeness and apparent co-phasing of warming beat initiation and bloom onset suggest that the reversal in the direction of temperature change at lower low waters exposure could be a cue for harpacticoid blooming. The predictability of the timing of this clear signal in the thermal regime could provide the basis for an unequivocal definition of the link between harpacticoid abundance and temperature on tidal flats.     

Availability of phosphorus sources for blooms of phaeocystis pouchetii (haptophyceae) in the north sea: Impact of the river rhine

The distribution and uptake of various phosphorus fractions such as soluble reactive phosphorus (SRP), enzymatically hydrolysable phosphorus (EHP) and soluble unhydrolysable phosphorus (SUP) were studied in coastal waters of the North Sea with special emphasis on those areas inhabited by dense blooms of Phaeocystis pouchetii (Hariot) Lagerheim. A comparison was made between the uptake rates of SRP and the capacity of the phytoplankton to utilize the EHP fraction as a phosphorus source. In areas not directly influenced by the discharge of the river Rhine the phytoplankton depleted the SRP down to the detection level of 0.02 μmol·dm⁻³, while the concentration of EHP was always higher. Inorganic phosphate (SRP) was rapidly assimilated by the microplankton (algae and bacteria) as measured by the uptake of ³²P-orthophosphate. Concurrently, the alkaline phosphatase activity (APA) was high and appeared to be associated with the phytoplankton mainly. The various measurements indicated that the plankton was P-limited. The calculated rate of enzymatic hydrolysis of EHP was highly variable, but could provide the cells with orthophosphate at a rate comparable with that eeasured for the direct uptake of inorganic phosphate.The diversity and availability of phosphate sources in the area near the river Rhine varied strongly. The abundant supply of phosphorus by the river to the coastal waters can cause further growth of the phytoplankton, unrestricted by nutrient limitation. Here it seemed that EHP and APA played only an insignificant role. The dominance of Phaeocystis in these coastal waters is discussed in view of its capacities to exploit transient phosphate supply.