The role of diatom resting stages in the onset of the spring bloom in the East China Sea

The abundance and species composition of diatoms were investigated along the PN line from the Okinawa Islands to the inner continental shelf in the East China Sea in the early spring of 1996. Viable diatom resting stages in sediments on the shelf were also enumerated by the extinction dilution method (most probable number method). Clear differentiation in the water masses was observed, with less saline, cold water (shelf water) on the shelf region, and warm, saline water (Kuroshio water) prevalent off the shelf and on the shelf edge. In the Kuroshio water, the abundance of diatoms was generally low but species diversity of diatoms was relatively high. In contrast, the spring bloom of diatoms was clearly observed in the shelf water where the water column was weakly stratified. The bloom was dominated by Chaetoceros debilis, contributing occasionally >80% of the diatom community. Resting stages of this species were also the most abundant taxon in the sediments on the shelf. Resuspension of the sediment during winter mixing of the water column should have enabled the resting stages to germinate at the surface. Subsequent vegetative growth after germination led to the formation of an early spring bloom of C. debilis when the water column was stratified and light availability had increased. Intermittent resuspension of sediment on the shelf, driven by strong winds and tidal currents, probably provides opportunities for diatoms with a resting stage to exploit favorable conditions for their germination and subsequent vegetative growth. It is further suggested that complex hydrographic conditions in the East China Sea result in a dynamic bloom with contributions by both autochthonous and allochthonous species.Communicated by T. Ikeda, Hakodate     

Continuous Plankton Records: Seasonal cycles of phytoplankton and copepods in the North Atlantic ocean and the North Sea

Data from the Continuous Plankton Recorder survey of the North Atlantic Ocean and the North Sea are used to study geographical variations in the amplitude, duration and timing of the seasonal cycles of total phytoplankton and total copepods. It is shown that the distribution of overwintering stocks influences the distributions throughout the year. There is a relationship between the timing of the spring increase of phytoplankton and the amplitude of the seasonal variation in sea surface temperature. In the open ocean, the timing of the spring increase of phytoplankton corresponds with the spring warming of the surface waters. In the North Sea the spring increase occurs earlier, associated, perhaps, with transient periods of vertical stability, resulting in a relatively slower rate of increase. It is suggested that in the open ocean the higher rate of increase is under-exploited by copepods due to low overwintering stocks and longer generation times. Exceptionally early spring increases of phytoplankton off the west coast of Greenland and over the Norwegian shelf are probably associated with permanent haloclines. A high and late autumn peak of phytoplankton off the coast of Portugal may be associated with coastal upwelling.     

Ecological Study of Spring-Early Summer Phytoplankton Blooms in A Semi-Enclosed Estuary

A sampling station in the Eastern Harbour of Alexandria was operated for 51 days between 2 March and 12 June, 1991. the harbour had different wide physical and chemical variations. Six distinct phytoplankton blooms occurred during this period. It is concluded that the physicochemical conditions affected the phytoplankton community structure and species composition. A dense diatom bloom could be maintained in a very weak and/or stabilized water column. A diatom bloom does not necessarily accompany an enhanced nutrient period. the depletion of nutrients and establishment of thermal stratification probably created favourable conditions for dinoflagellate and flagellate species to achieve blooms. the species composition could be shifted over the short term and a dense phytoplankton bloom could possibly dissipate in a few days.     

Growth and development of Calanus spp. (Copepoda) during spring phytoplankton succession in the North Sea

Experiments were carried out to determine growth and development rates of the herbivorous copepod Calanus finmarchicus (Gunnerus) under natural conditions during the phytoplankton spring bloom in the northern North Sea. From 28 April to 25 May 1983 copepodite stages I, IV and V were incubated for a 3-d period on board a ship in vessels with naturally occurring phytoplankton or cultured algae as food. Highest rates of growth and development were achieved while the diatom Chaetoceros sp. was the dominant phytoplankton organism. These rates decreased considerably when this chain-forming diatom was succeeded after one week by the small-celled diatom Thalassiosira conferta. Again one week later, during the bloom of the succeeding colonial microflagellate Corymbellus aureus, copepodite stage IV still managed to maintain moderate rates of growth and development, but these rates dropped to almost zero in CV, suggesting the start of a resting stage. Nevertheless, brood collected from this generation and from Calanus helgolandicus (Claus) was raised in the laboratory to the adult stage at high speed. Since temperature and the total phytoplankton concentration in the sea remained almost constant it seems that the retardation and arrestment of growth and development were an immediate response to a qualitative change of the food composition related to the successive blooms of different algal species.     

Neural network modelling for the analysis of forcings/temperatures relationships at different scales in the climate system

A fully non-linear analysis of forcing influences on temperatures is performed in the climate system by means of neural network modelling. Two case studies are investigated, in order to establish the main factors that drove the temperature behaviour at both global and regional scales in the last 140 years. In particular, our neural network model shows the ability to catch non-linear relationships among these variables and to reconstruct temperature records with a high degree of accuracy. In this framework, we clearly show the need of including anthropogenic inputs for explaining the temperature behaviour at global scale and recognise the role of El Niño southern oscillation for catching the inter-annual variability of temperature data. Furthermore, we analyse the relative influence of global forcing and a regional circulation pattern in determining the winter temperatures in Central England, showing that the North Atlantic oscillation represents the driven element in this case study. Our modelling activity and results can be very useful for simple assessments of relationships in the complex climate system and for identifying the fundamental elements leading to a successful downscaling of atmosphere–ocean general circulation models.     

Recurrent and changing seasonal patterns in phytoplankton of the westernmost inlet of the Dutch Wadden Sea from 1969 to 1985

Data for phytoplankton composition and abundance in the Marsdiep are presented for the period from 1969 to 1985 inclusive. Only a few species dominated the phytoplankton. A recurrent pattern was observed in the seasonal succession: in winter, total cell numbers were invariably low, but freshwater algae, sluiced into the Wadden Sea from IJssel Lake, showed highest densities in winter. A diatom spring peak was observed around mid-April, followed by a Phaeocystis pouchetii peak about three weeks later. Later in summer usually two more diatom peaks followed by non-diatom peaks were present. The exact timing of the spring peak varied from year to year, with the extremes being late March and early May. A relatively late spring peak usually coincided with a relatively high turbidity in the preceding winter. An increase in total cell numbers was found over the 17-year observation period. Diatoms decreased from 1969 to 1974 but have increased since then, reaching values above those of 1969 during recent years. Flagellates showed a consistent increase over the entire observation period.     

Annual cycles of phytoplankton community-structure and bloom dynamics in the Neuse River Estuary, North Carolina

The spatiotemporal distributions of major phytoplankton taxa were quantified to estimate the relative contribution of different microalgal groups to biomass and bloom dynamics in the eutrophic Neuse River Estuary, North Carolina, USA. Biweekly water samples and ambient physical and chemical data were examined at sites along a salinity gradient from January 1994 through December 1996. Chemosystematic photopigments (chlorophylls and carotenoids) were identified and quantified using high-performance liquid chromatography (HPLC). A recently-developed factor-analysis procedure (CHEMTAX) was used to partition the algal group-specific chlorophyll a (chl a) concentrations based on photopigment concentrations. Results were spatially and temporally integrated to determine the ecosystem-level dynamics of phytoplankton community-constituents. Seasonal patterns of phytoplankton community-composition changes were observed over the 3 yr. Dinoflagellates reached maximum abundance in the late winter to early spring (January to March), followed by a spring diatom bloom (May to July). Cyanobacteria were more prevalent during summer months and made a large contribution to phytoplankton biomass, possibly in response to nutrient-enriched freshwater discharge. Cryptomonad blooms were not associated with a particular season, and varied from year to year. Chlorophyte abundance was low, but occasional blooms occurred during spring and summer. Over the 3 yr period, the total contribution of each algal group, in terms of chl a, was evenly balanced, with each contributing nearly 20% of the total chl a. Cryptomonad, chlorophyte, and cyanobacterial dynamics did not exhibit regular seasonal bloom patterns. High dissolved inorganic-nitrogen loading during the summer months promoted major blooms of cryptomonads, chlorophytes, and cyanobacteria. Received: 12 September 1997 / Accepted: 12 December 1997     

Long-term changes in phytoplankton phenology and community structure in the Bahía Blanca Estuary, Argentina

The phytoplankton of the Bahía Blanca Estuary, Argentina, has been surveyed since 1978. Chlorophyll a, phytoplankton abundance, species composition and physico-chemical variables have been fortnightly recorded. From 1978 to 2002, a single winter–early spring diatom bloom has dominated the main pattern of phytoplankton interannual variability. Such pattern showed noticeable changes since 2006: the absence of the typical winter bloom and changes in phenology, together with the replacement of the dominant blooming species, i.e. Thalassiosira curviseriata, and the appearance of different blooming species, i.e. Cyclotella sp. and Thalassiosira minima. The new pattern showed relatively short-lived diatom blooms that spread throughout the year. In addition, shifts in the phytoplankton size structure toward small-sized diatoms, including the replacement of relatively large Thalassiosira spp. by small Cyclotella species and Chaetoceros species have been noticed. The changes in the phenology and composition of the phytoplankton are mainly attributed to warmer winters and the extremely dry weather conditions evidenced in recent years in the Bahía Blanca area. Changing climate has modified the hydrological features in the inner part of the estuary (i.e. higher temperatures and salinities) and potentially triggered the reorganization of the phytoplankton community. This long-term study provides evidence on species-specific and structural changes at the bottom of the pelagic food web likely related to the recent hydroclimatic conditions in a temperature estuary of the southwestern Atlantic.     

Phaeocystis pouchetii blooms in the East Frisian coastal waters (German Bight,North Sea)

In 1982 and 1983, blooms of the planktonic alga Phaeocystis pouchetii were studied in the East Frisian coastal waters off Norderney, FRG. Morphological variability of the colonies, population development, effects on inorganic nutrient and oxygen budget, and the role in the seasonal plankton bloom sequence were investigated. in both years two separate Ph. pouchetii blooms occurred in late spring and early summer that were formed by the globosa-type exclusively. The pouchetii-type was only present during the interval between the first and second blooms in 1982. Growth conditions for Ph. pouchetii seem to be most favourable after a breakdown of a diatom bloom when the silicate reserves have been exhausted, phosphate concentrations are relatively low, but a rich supply of dissolved inorganic nitrogen is available. Contrary to diatom blooms, Ph. pouchetii blooms result in a high production of particulate organic carbon (POC). Another characteristic is the release of great amounts of dissolved organic substances, which cause extensive sea foam formation during the peaks and the subsequent breakdown of the blooms. Due to increased assimilation during mass development and intense disintegration after the breakdown, variations of the oxygen content of the water are significant. Presumably the intensity of blooms has increased in the past decade as indicated by sea foam formation which has actually been excessive in some years.     

Changes in the timing of otolith zone formation in North Sea cod from otolith records: an early indicator of climate-induced temperature stress?

We examine the seasonal variation in otolith increment formation in southern North Sea cod as a means of monitoring how changes in sea temperature over the past 20 years have affected cod in the wild. Seasonal opaque zone formation was related to winter and early spring. Timing of opaque zone formation was not influenced by either temperature or fish length, but increasing age led to slightly earlier but slower opaque zone formation. In contrast, there was a clear shift in the timing of translucent zone formation with temperature. In warm years, translucent growth occurs up to 22 days earlier than in colder periods. Increasing age and smaller size-at-age resulted in an earlier transition from opaque to translucent edge formation. Translucent zone formation appears indicative of increasing metabolic stress, and the earlier onset provides direct evidence of the impact of increasing sea temperatures on wild North Sea cod stocks.     

Modeling regional impacts of climate teleconnections using functional data analysis

Teleconnections are quasi-periodic changes in atmospheric circulation that oscillate over long periods of time and impact climate over large regions. These patterns are often linked to long-term variations in climate and extreme weather events and may explain regional differences in climate vulnerability. We apply methods of functional data analysis to examine regional impacts of teleconnections on climate in British Columbia, Canada, between 1951 and 2000. We focus on monthly mean temperature as an overall determinant of crop growth and apply functional principal components analysis (FPCA) to study variations in the impacts of four major teleconnection indices affecting the Northern Hemisphere (the Southern Oscillation Index, the Pacific North American (PNA), Pacific Decadal Oscillation, and the North American Oscillation indices). Two challenges we consider are that the impacts of teleconnections cannot be observed directly and that fine scale data required to study regional variations may come from different sources with highly varied records. We first fit thin-plate regression splines to the raw data to construct complete series of pseudo-data at fixed grid points. Regression models incorporating Bayesian P-splines were then fit to the pseudo-data to estimate the impacts of the four teleconnections over time. Finally, FPCA was then applied to study regional variations in these effects. Our analysis identified strong variations in mean temperature associated with the PNA. The resulting spatial patterns also reveal areas of increased/decreased temperature variability that may have higher climate risk or be suitable for expansion of agricultural activity.     

Vertical distribution,and seasonal and diurnal migration of Calanus helgolandicus in the Celtic Sea

The vertical distribution and migration (seasonal, diel and ontogenetic) of Calanus helgolandicus are described from the shallow (100 m) shelf-seas to the south-west of the British Isles. In 1978 and 1979, the overwintering population of C. helgolandicus consisted primarily of Stage V copepodites and adults. By late winter/early spring the copepodites had moulted to adult females (>90%), which matured and bred the first cohorts of the year, prior to onset of the spring phytoplankton bloom in April/May. C. helgolandicus reached a peak of numerical abundance in August of 20x10³ copepodites m^-2 (over the depth range sampled -0 to 70 m), which was 200 times the population in winter. The seasonal peak of abundance occurred 4 mo after the peak of the bloom of phytoplankton in spring. The yearly development of the copepod was not always out of phase with the diatom bloom, as seen when the data from 1978 was placed in the context of a longer time-series collected at 10 m over 22 yr (1960–1981, inclusive). Large vertical migrations were observed in the younger copepodites (CI and II) in May from below to above the thermocline. In the remainder of the year, the CI and CII stages behaved differently and were located above the thermocline within the euphotic zone. The largest vertical displacements of biomass were seen in the summer months due to the migrations of the CV stages and adults, which had developed from the spring cohorts. It was contended that the seasonal and vertical migrations of C. helgolandicus are part of a more complex pattern of inherent behavior than has been reported previously and that, however difficult this is to discern in the natural populations, it always expresses itself.     

Inter-year differences in survival of Atlantic puffins Fratercula arctica are not associated with winter distribution

Miniature geolocator loggers (Global Location Sensing, GLS) that provide daily locations of birds have revolutionised the study of winter ecology and migration patterns of seabirds. A long-term study of ringing recoveries and analyses of heavy metals and pollutants in tissues of Atlantic puffins Fratercula arctica from the Isle of May, south-east Scotland, suggested that this population wintered mainly within the North Sea. However, deployment of GLS devices over the 2007/2008 winter showed that many breeding birds made major excursions into the east Atlantic. This winter was the second of two when survival was extremely low (survival in 2006/2007 and 2007/2008 was 0.696 and 0.695, respectively, compared to the average of 0.922 over the period 1984/1985–2005/2006). These low rates of survival suggested that the unexpected use of the Atlantic might have been associated with unusually poor conditions in the North Sea as indicated by very low breeding success in 2007. Survival rate returned to previous levels in 2008/2009 providing the opportunity to test whether higher survival was associated with birds remaining in the North Sea, or whether movements into the Atlantic are a feature of this population unrelated to survival. Accordingly, geolocators were deployed over the 2009/2010 winter when adult survival was subsequently established to be high (0.913). We found greater support for the hypothesis that winter distribution is not associated with survival. Thus, 8 (40 %) of 20 individuals followed in 2009/2010 went into the Atlantic, a rate not significantly different from 11 (58 %) of the 19 followed in the 2007/2008 winter. Indeed, birds actually spent longer in the Atlantic and used a wider variety of areas in 2009/2010, although the time spent away from the colony was significantly shorter than in 2007/2008. Since our data were from individuals that survived, remaining in or moving out of the North Sea can both be successful strategies during winters when the population as a whole shows either high or low survival rates. Unfortunately, we do not know where birds that died had gone, and hence, the relative survival of birds that did or did not move into the Atlantic. Determining the link between survival and wintering area for any seabird remains a formidable challenge and will have to await the development of technologies that can determine both where and when birds die.     

Spring phenological responses of marine and freshwater plankton to changing temperature and light conditions

Shifts in the timing and magnitude of the spring plankton bloom in response to climate change have been observed across a wide range of aquatic systems. We used meta-analysis to investigate phenological responses of marine and freshwater plankton communities in mesocosms subjected to experimental manipulations of temperature and light intensity. Systems differed with respect to the dominant mesozooplankton (copepods in seawater and daphnids in freshwater). Higher water temperatures advanced the bloom timing of most functional plankton groups in both marine and freshwater systems. In contrast to timing, responses of bloom magnitudes were more variable among taxa and systems and were influenced by light intensity and trophic interactions. Increased light levels increased the magnitude of the spring peaks of most phytoplankton taxa and of total phytoplankton biomass. Intensified size-selective grazing of copepods in warming scenarios affected phytoplankton size structure and lowered intermediate (20–200?μm)-sized phytoplankton in marine systems. In contrast, plankton peak magnitudes in freshwater systems were unaffected by temperature, but decreased at lower light intensities, suggesting that filter feeding daphnids are sensitive to changes in algal carrying capacity as mediated by light supply. Our analysis confirms the general shift toward earlier blooms at increased temperature in both marine and freshwater systems and supports predictions that effects of climate change on plankton production will vary among sites, depending on resource limitation and species composition.     

Climate effects on fire regimes and tree recruitment in Black Hills ponderosa pine forests

Climate influences forest structure through effects on both species demography (recruitment and mortality) and disturbance regimes. Here, I compare multi-century chronologies of regional fire years and tree recruitment from ponderosa pine forests in the Black Hills of southwestern South Dakota and northeastern Wyoming to reconstructions of precipitation and global circulation indices. Regional fire years were affected by droughts and variations in both Pacific and Atlantic sea surface temperatures. Fires were synchronous with La Ni?as, cool phases of the Pacific Decadal Oscillation (PDO), and warm phases of the Atlantic Multidecadal Oscillation (AMO). These quasi-periodic circulation features are associated with drought conditions over much of the western United States. The opposite pattern (El Ni?o, warm PDO, cool AMO) was associated with fewer fires than expected. Regional tree recruitment largely occurred during wet periods in precipitation reconstructions, with the most abundant recruitment coeval with an extended pluvial from the late 1700s to early 1800s. Widespread even-aged cohorts likely were not the result of large crown fires causing overstory mortality, but rather were caused by optimal climate conditions that contributed to synchronous regional recruitment and longer intervals between surface fires. Synchronous recruitment driven by climate is an example of the Moran effect. The presence of abundant fire-scarred trees in multi-aged stands supports a prevailing historical model for ponderosa pine forests in which recurrent surface fires affected heterogenous forest structure, although the Black Hills apparently had a greater range of fire behavior and resulting forest structure over multi-decadal time scales than ponderosa pine forests of the Southwest that burned more often.     

Importance of decadal scale variability in shoreline response: examples from soft rock cliffs,East Anglian coast,UK

Rapidly eroding soft rock cliffs typically retreat at rates in excess of several metres per year, thus allowing the resolution of linkages between cliff dynamics and a range of climatic and marine forcing factors. New evidence from UK coastline of East Anglian coastline, southern North Sea shows that unprotected soft rock cliffs at three widely-spaced locations all show similar variability in retreat behaviour on decadal timescales, which we attribute to changing patterns of storminess in these decades. The 1990s were characterized by frequent months in which the North Atlantic Oscillation (NAO; a well-established measure of inter-annual climatic variability in North-West Europe) was extremely positive (more positive than +3) or extremely negative (more negative than ?3), while the 2000s showed few occurrences of such extreme values. Depression tracks in positive NAO phases make the East Anglian coast prone to storm surges in which raised water levels result from deeply developed low pressure systems, generally associated with westerly air streams. In negative NAO phases the region is prone to easterly airflow which results in periods of strong onshore wind. Both phases are associated with high energetics in the forcing factors. Decadal-scale variability in cliffline retreat rates has implications for the practice of coastal management and policy making and suggests that cliff system responses to global environmental change are not simply driven by secular sea level rise.     

The reproductive cycle of the sea urchin Arbacia lixula in northwest Mediterranean: potential influence of temperature and photoperiod

We studied the reproductive cycle of the sea urchin Arbacia lixula in a subtidal population from northeast Spain over four years using a gonadosomatic index (GSI) and gonad histology. Our results show that the GSI of A. lixula follows a seasonal cycle which peaks in May–July and attains its lowest values in October–November every year. The time course of the GSI matched closely the photoperiod cycle. We also found a remarkable inter-annual variability in the maximum value of GSI, which correlated with mean water temperature during the gonad growth period (winter and spring). Gonad histology was also in agreement with a single gametogenic cycle per year in this species. We explored the application of circular statistics to present and analyse gonadal development data, which allowed us to adequately handle the high intra-individual variability detected, with several developmental stages commonly found within the same gonad. The picture that emerged is one of a gametogenic timing driven by photoperiod, while the amount of reproductive output is determined by temperature. This is coherent with the tropical origin of the species and lends support to recent warnings about an increase in the abundance of this species in the Mediterranean as a result of global warming, with associated increased impact potential in sublittoral communities.     

The Baltic Sea spring phytoplankton bloom in a changing climate: an experimental approach

The response of the Baltic Sea spring bloom was studied in mesocosm experiments, where temperatures were elevated up to 6°C above the present-day sea surface temperature of the spring bloom season. Four of the seven experiments were carried out at different light levels (32–202?Wh?m^?2 at the start of the experiments) in the different experimental years. In one further experiment, the factors light and temperature were crossed, and in one experiment, the factors density of overwintering zooplankton and temperature were crossed. Overall, there was a slight temporal acceleration of the phytoplankton spring bloom, a decline of peak biomass and a decline of mean cell size with warming. The temperature influence on phytoplankton bloom timing, biomass and size structure was qualitatively highly robust across experiments. The dependence of timing, biomass, and size structure on initial conditions was tested by multiple regression analysis of the y-temperature regressions with the candidate independent variables initial light, initial phytoplankton biomass, initial microzooplankton biomass, and initial mesozooplankton (=copepod) biomass. The bloom timing predicted for mean temperatures (5.28°C) depended on light. The peak biomass showed a strong positive dependence on light and a weaker negative dependence on initial copepod density. Mean phytoplankton cell size predicted for the mean temperature responded positively to light and negatively to copepod density. The anticipated mismatch between phytoplankton supply and food demand by newly hatched copepod nauplii occurred only under the combination of low light and warm temperatures. The analysis presented here confirms earlier conclusions about temperature responses that are based on subsets of our experimental series. However, only the comprehensive analysis across all experiments highlights the importance of the factor light.     

Vertical distribution of Calanus finmarchicus and C. helgolandicus in relation to the development of the seasonal thermocline in the Celtic Sea

The geographical distribution and annual mean abundance of Calanus finmarchicus (Gunnerus) and C. helgolandicus (Claus) in the northern North Atlantic Ocean were shown in relation to the seasonal and annual fluctuations of abundance of the species in the Celtic Sea from 1960 to 1981. These congeneric copepods, although showing allopatric distributions over most of their geographical range, have sympatric distributions in the Celtic Sea where they dominate the dry weight biomass of the plankton throughout the year. The two species respond differently to the development of the seasonal thermocline and halocline by taking up different vertical distributions in the water column. C. finmarchicus occurred in the colder, more saline water below the thermocline, while C. helgolandicus occurred in the warmer, less saline water above the thermocline. This behaviour is postulated as a mechanism by which these morphologically similar copepods more fully exploit the resources of their temporally and spatially heterogeneous environment and also minimise interspecific competition. The species have the same foraging techniques and are able to exploit the same size spectrum of particulates. The vertical depth strata in which the populations are found for most of the year in the Celtic Sea means that both species exploit the diatom bloom in early spring but, thereafter, C. helgolandicus grazes on the daily production of the autotrophs in the euphotic zone while C. finmarchicus, below the thermocline, has to rely for its food on sedimenting particulates (whole cells, detritus and faecal material). The isolating mechanisms whereby these two populations partition the habitat in the Celtic Sea are discussed.     

Interannual variability in the spring phytoplankton bloom in Auke Bay,Alaska

Data on phytoplankton primary production, biomass, and species composition were collected during a 5 yr (1985–1989) study of Auke Bay, Alaska. The data were used to examine the interannual differences in the timing, duration, and magnitude of the spring phytoplankton blooms during each year and to relate these differences to interannual variations in weather patterns. Within any given year, a pre-bloom phase was characterized by low available light, low rates of primary production, low biomass, and predominantly small (<10µm) diatoms. During the primary bloom, integrated production rates rose to 4 to 4.5 g C m^–2 d^–1, and integrated biomass levels reached 415 to 972 mg chlorophyll m^–2. Primary blooms were usually dominated by large diatoms (Thalassiosira spp.), and in a single year (1989) byChaetoceros spp. The primary blooms terminated upon nutrient depletion in the euphotic zone. Secondary blooms, triggered by nutrient resupply from below, occurred sporadically after the primary bloom and accounted for 4 to 31% of total spring production. The date of initiation and the duration of the primary bloom varied little from year to year (standard deviation 3 and 5 d, respectively). Seasonal production rates and biomass levels varied interannually by a factor of 2 to 3. In contrast, intra-annual variations of more than an order of magnitude, especially in biomass, occurred over periods as short as 10 d. These large variations over short time periods indicate the importance of synchronous timing between spring blooms and the production of larval fish and shellfish, which depend on an appropriate and adequate food supply for growth and survival. Parameters describing primary production (e.g. peak daily production, mean daily production, and total production during the primary bloom and the entire season) exhibited little interannual variation (coefficient of variation, CV = 10 to 19%), but a large degree of intra-annual variation (CV = 77 to 116%). Similarly, interannual variations in biomass (peak chlorophyll, mean chlorophyll) were also lower (CV = 20 to 33%) than intra-annual variations (CV = 85 to 120%).