EGG PRODUCTION AND HATCHING SUCCESS IN NORTH ADRIATIC SEA POPULATIONS OF THE COPEPOD Acartia clausi

Egg production, fecal pellet production and hatching success are reported for Acartia clausi females sampled during three cruises in February 1997, 1998 and June 1997 at 20-24 stations along 4 transects in the North Adriatic Sea. Dramatically low hatching rates were recorded during both diatom bloom events in February as opposed to much higher rates during post-bloom conditions in June, even though A. clausi productivity during the bloom was apparently high. These results are discussed in the light of recent findings on the negative impact of diatoms on copepod reproductive potential.     

Opposing selective pressures on hatching asynchrony: egg viability, brood reduction, and nestling growth

At least 19 hypotheses have been proposed to explain the evolutionary significance of avian hatching asynchrony, and hatching patterns have been suggested to be the result of several simultaneous selective pressures. Hatching asynchrony was experimentally modified in the black kite Milvus migrans by manipulating the onset of incubation during the laying period. Delayed onset of incubation reduced egg viability of first-laid eggs, especially when ambient temperature during the laying period was high. Brood reduction (nestling mortality by starvation or siblicide) was more commonly observed in asynchronous nests. The growth rate was slower in synchronous broods, probably due to stronger sibling rivalry in broods with high size symmetry. Last-hatched chicks in synchronous broods fledged at a small size/mass, while in control broods, hatching order affected growth rates, but not final size. Brood reduction, variable growth rates, and the ability to face long periods of food scarcity are probably mechanisms to adjust productivity to stochastic food availability in a highly opportunistic predator. The natural pattern of hatching asynchrony may be the consequence of opposing selective forces. Extreme hatching synchrony is associated with slow growth rates, small final size of last-hatched chicks, and low viability of first-laid eggs, while extreme hatching asynchrony is associated with high mortality rates. Females seem to facultatively manipulate the degree of hatching asynchrony according to those pressures, because hatching asynchrony of control clutches was positively correlated with temperature during laying, and negatively correlated with the rate of rabbit consumption. Received: 25 October 1999 / Revised: 30 May 2000 / Accepted: 25 June 2000     

The effect of egg versus seston quality on hatching success,naupliar metabolism and survival of <Emphasis Type="Italic">Calanus finmarchicus</Emphasis> in mesocosms dominated by <Emphasis Type="Italic">Phaeocystis</Emphasis> and diatoms

We studied the effect of a developing Skeletonema marinoi/Phaeocystis spp. bloom on Calanus finmarchicus hatching success, early naupliar survival and metabolism. Our focus was (1) on the development of reproductive rates during a bloom initiation, peak and decline in relation to the production of potentially toxic algal metabolites and (2) on the proportional importance of female nutrition versus naupliar food environment for the production of viable nauplii. Despite polyunsaturated aldehyde (PUA) production by both S. marinoi and Phaeocystis sp., we did not observe any harmful effects on hatching success or naupliar survival and condition in any stages of the short-term (<1 week) algal bloom. Hatching success appeared to be controlled by egg lipid composition, while the beneficial effect of a high food concentration was reflected in naupliar RNA:DNA ratio, protein content and total production of viable nauplii. The egg lipids reflected seston lipids, indicating that the egg fatty acid composition was not modified by the females. Our results suggest that unselective feeding and/or retention of specific lipids can induce qualitative food limitation, although recruitment during the S. marinoi/Phaeocystis sp. bloom was high.     

Carbon partitioning among the first trophic levels in the North Western Adriatic Basin

In the frame of PRISMA II Project samples for plankton analyses were carried out during four cruises (June, 1996; February and June, 1997; February, 1998) in order to assess the relative importance in term of biomasses of the three main size fractions (pico- <2 r µm, nano- 2-20 r µm and micro-plankton >20 r µm). Spatial and temporal distribution of the three plankton fractions were described as abundance and contribution to the total carbon content in an area between Po River mouth and Rimini. The relative contribution of picoplankton resulted higher in the offshore zone, while that of nanoplankton in the inshore waters. In February 1998 microphytoplankton, mainly constituted by diatoms, was very abundant in the inshore waters. Micro-zooplankton was always very scarce. Cluster analyses performed on these data grouped the stations on the basis of their community structure, and agreed with the hydrological features. Small size classes contributed more significantly to the total plankton carbon content in most of the situations. Microplankton fraction contribution was relevant only during spring diatom bloom of February 1998 and with a less extent in the confined coastal summer blooms.     

High reproduction of <Emphasis Type="Italic">Calanus finmarchicus</Emphasis> during a diatom-dominated spring bloom

Feeding, egg production, hatching success and early naupliar development of Calanus finmarchicus were measured in three north Norwegian fjords during a spring bloom dominated by diatoms and the haptophyte Phaeocystis pouchetii. Majority of the copepod diet consisted of diatoms, mainly Thalassiosira spp. and Chaetoceros spp., with clearance rates up to 10 ml ind⁻¹ h⁻¹ for individual algae species/groups. Egg production rates were high, ranging from ca 40 up to 90 eggs f⁻¹ d⁻¹, with a hatching success of 70–85%, and fast naupliar development through the first non-feeding stages. There was no correlation between the egg or nauplii production and diatom abundance, but the hatching success was slightly negatively correlated with diatom biomass. However, the overall high reproductive rates suggested that the main food items were not harmful for C. finmarchicus reproduction in the area, although direct chemical measurements were not conducted. The high population egg production (>1,20,000 eggs m⁻² d⁻¹) indicated that a large part of the annual reproduction took place during the investigation, which stresses the importance of diatom-dominated spring phytoplankton bloom for population recruitment of C. finmarchicus in these northern ecosystems.     

Microbial respiratory and ectoenzymatic activities in the Northern Adriatic Sea (Mediterranean Sea)

The carbon transfer through the microbial community in two areas of the Northern Adriatic Sea was estimated by proteolytic and respiratory activities during four oceanographic surveys carried out in June, 1996, 1997 and February, 1997, 1998. In front of the Po Delta (area A), the mean rates of proteolytic activity range from 4.9 to 9.9 r µg r C r h r l; near Ancona (area B), they range from 3.1 to 7.6 r µg r C r h r l. Respiratory rates vary between 0.19 and 2.29 and between 0.24 and 1.40 r µg r C r h r l in areas A and B, respectively. In general, high rates occur in the surface layers, within the first 10 r m of depth. In area A, proteolytic and respiratory rates undergo seasonal course, with high activity in warm periods. In area B, respiration and bacterioplankton abundance increase from the first to the second year, whilst proteolytic activity decreases. The sequence of metabolic steps in the carbon transfer within the bacteria, from the biotic vs . the abiotic compartment, was drawn in order to define the actual role of bacterial biomass in the biogeochemical fluxes in an ecosystem which often suffers distrophic crises. Respiratory turnover rates, in the upper 10 r m depth, reach low values in cold periods and high values in June, 1997. The carbon transfer versus mineralization flows better in the summer period, in particular in June, 1997. However, the bacterial growth efficiency ranges from 17 to 38% in area A and from 13 to 44% in area B with highest values in February, 1997, when bacteria contribute in a relevant way to the overall respiration.     

Effects of territory quality, food availability and sibling competition on the fledging success of oystercatchers (Haematopus ostralegus)

We investigated the fledging probability of oystercatcher, Haematopus ostralegus, chicks as a function of hatching order, brood size, territory quality and food availability. Sibling dominance was related to the hatching order in both low- (’leapfrogs’) and high-quality (’residents’) territories. Differences in hatchling mass might have aided the establishment of a dominance hierarchy, since breeders produced small late eggs and hatchlings. These mass differences were most pronounced in leapfrogs, and in large broods in years with lower food availability (’poor’ years). Late hatchlings fledged less often and with lower body masses compared to early hatchlings in all situations. Leapfrogs produced smaller broods and hatched their broods more asynchronously in poor years than leapfrogs breeding in years with more available food (’good’ years) and residents breeding in both poor and good years. Large brood sizes resulted in lower survival of hatchlings in poor years. These results favour the ’brood reduction’ hypothesis. However, contrary to the expectations of this hypothesis, hatching order also affected fledging success in residents. Moreover, large brood size resulted in higher survival of hatchlings in good years, particularly in residents. Thus, although large broods experienced losses due to sibling competition in some years, they nevertheless consistently produced more fledglings per brood in all years, both as leapfrogs and residents. We believe this effect is due to parental quality correlating with initial brood size. Most leapfrogs, at best, fledged one chick successfully each year, losing chicks due to starvation. Nevertheless, leapfrog broods were reduced in size after hatching significantly less quickly than resident broods. These results suggest that breeders lay and hatch insurance eggs to compensate for unpredictable losses due to the high predation rates on both nests (ca 50%) and chicks (ca 90%), in accordance with the ’nest failure’ hypothesis. Received: 14 February 2000 / Revised: 27 September 2000 / Accepted: 10 June 2000     

Annual population development and production by Calanus finmarchicus, C. glacialis and C. hyperboreus in Disko Bay, western Greenland

The populations of the copepod species Calanus finmarchicus, C. glacialis and C. hyperboreus were investigated in Disko Bay during a 14-month period in 1996-1997. The three species were predominant in the copepod community. The biomass reached a maximum at the beginning of June (127 mg C m^-3). From the end of July until the end of April the following year, the biomass was <1-6 mg C m^-3. All three species showed seasonal ontogenetic migration. The spring ascent for all three species was just prior to or in association with the break-up of sea ice and the development of the spring bloom, whereas descent occurred over a larger time span during summer. The main overwintering stages were CV for C. finmarchicus, CIV and CV for C. glacialis and C. hyperboreus. Peak abundance of juvenile copepodites, representing the new generation, was in August for C. finmarchicus, in July for C. glacialis and in May/June for C. hyperboreus. From the timing of reproduction and the population development, the life cycles were deduced to be 1 year for C. finmarchicus and at least 2 years for C. glacialis and C. hyperboreus. Secondary production and potential grazing impact of the Calanus community were estimated by two methods based on specific egg-production rates and temperature-dependent production. The Calanus community was not able to control the primary producers during the spring bloom but probably did during post-bloom. The estimates also indicated that grazing on ciliates and heterotrophic dinoflagellates contributes as an essential food source in the post-bloom period.     

Filter feeding by Oikopleura vanhoeffeni: grazing impact on suspended particles in cold ocean waters

Because of the abundance and size of Oikopleura vanhoeffeni its quantitative role as a suspension feeder in cold ocean waters needs to be defined. To minimize the effect of manipulation and containment, and to assess the effect of naturally occurring factors on clearance rate, I used an in situ latex microbead technique in Logy Bay, Newfoundland, from February 1985 to June 1986. Individual clearance rates ranged from 8–944 ml h^-1, increasing exponentially with increasing trunk length. Partial correlation and principal components analysis indicated that trunk length and the concentration of ingestible chlorophyll a accounted for a majority of the variation in clearance rate. At densities of 4–110 m^-3, O. vanhoeffeni populations removed from >1 to 13% of the standing stock of ingestible food particles each day. Grazing by near-surface populations was lowest during the spring diatom bloom (>1.4% of daily particle production removed per day), and was highest in June during the post-bloom crash (4 to 10% of daily production removed). Some populations in mid-depth waters had much higher population clearance rates (ca. 50% of daily production removed) because of a greater proportion of large animals. The median percentage daily ration (g Cxg C^-1xd^-1x100%) of 64% accounted for observed house production rates (1 to 2 d^-1, with each house=23% of body carbon).     

Nutrient balance in the ecosystem of the North Western Adriatic Sea

The effects of biological processes on dissolved inorganic nutrients, dissolved organic nitrogen (DON) and phosphorus (DOP) are considered in the north western Adriatic Sea. The budgets of these nutrients, which represent the sum of production and consumption processes in comparison to advection, are discussed with regard to dissolved inorganic nitrogen ( 15 N labelled) uptake, which basically indicates the biological demand of this fraction of nitrogen by phytoplankton community. The presented data show that, although important, the continental input of dissolved inorganic nitrogen (DIN), mainly nitrate, is utilised and recycled within the coastal marine environment (budget of m 15 r µmol-N·dm m 3 ). In fact, during four cruises (June, 1996; February, 1997; June, 1997; February, 1998), phytoplankton production was mainly driven by regenerated nutrients ( f h 0.4). Regarding dissolved inorganic phosphorus (DIP), the negative budgets observed in most cases (down to m 0.4 r µmol-P·dm m 3 ) confirm, above all, its scarce availability in this basin. Recycling processes rather than continental inputs regulate the availability of this nutrient. In addition, the comparison between DIN and DIP budgets indicates that, in this ecosystem, dissolved inorganic phosphorus is recycled faster than nitrogen through the living particulate and dissolved organic pools. As a consequence of biological activities, a strong production of dissolved organic nitrogen (DON) can occur in summer (up to +22 r µmol-N·dm m 3 ) while DOP shows a more independent behaviour both with respect to its accumulation in the environment and to the observed nitrogen variations.     

Plankton of the fladen ground during FLEX 76 II. Population dynamics and production of Thysanoessa inermis (Crustacea: Euphausiacea)

Samples taken in the northern North Sea with the Continuous Plankton Recorder (CPR), the Undulating Oceanographic Recorder (UOR) and the Longhurst-Hardy Plankton Recorder (LHPR) during the Fladen Ground Experiment in 1976 (FLEX 76) are used to describe the vertical distribution and population dynamics of Thysanoessa inermis (Krøyer) and to provide estimates of the production and carbon budget of the population from 19th March to 3 June 1976. Spawning occurred in late April and early May, in near synchronisation with the start of the spring bloom of phytoplankton. Eggs, nauplii and calyptopes reached maximum abundance in succession, and furciliae were numerous when sampling ceased in early June. Adults increased in length from a mean of 12.1 mm in mid-March to 17.5 mm in early June and the estimated production was 2.40 mg m^-3 over the 74 d period. Total carbon ingested by the population of T. inermis was estimated to be 10 mg C m^-2 d^-1 in the upper 100m which was only 1.5% of the daily primary production of 0.68 gC m^-2 measured over the FLEX period 26 March to 4 June 1976. The grazing by T. inermis on the phytoplankton population was assumed to have little effect on the control and depletion of the spring phytoplankton bloom during FLEX 77.JOSDAP Contribution No. 50     

Reproductive cycles of three dominant Calanus species in Disko Bay, West Greenland

This study describes the annual reproductive cycles of the three dominant Calanus species, C. finmarchicus, C. glacialis and C. hyperboreus, in Disko Bay (West Greenland) in relation to seasonal phytoplankton development. Relative abundance of females, copepodite stage V (CV) and males, and the developmental stage of the female gonad were examined from plankton samples collected at weekly to monthly intervals from May 1996 to June 1997 with a WP2 net or a pump. During spring and summer, egg production rates were determined. Females of all three species were present year round. Maximum relative abundance was reached by C. hyperboreus females at the beginning of February, by C. glacialis in mid-February, and by C. finmarchicus in April. All three species reproduced successfully in Disko Bay. Their reproductive cycles were considerably different with respect to the timing of final gonad maturation and spawning, and hence in their relation to seasonal phytoplankton development. In all three species, early gonad development took place during winter, before living food became plentiful, suggesting that these processes were largely food independent. Final gonad maturation and spawning in C. finmarchicus was related to the phytoplankton concentration, reflecting that final gonad maturation processes are food dependent in this species. C. glacialis females matured and spawned prior to the spring bloom. Our results indicate that first internal lipid stores and later ice alga grazing supplied final gonad maturation and egg production. Maximum egg production rates of C. glacialis were found in spring and summer, when the chlorophyll a concentration was high. Mature female C. hyperboreus were found from February until mid-April, when the chlorophyll a concentration was still low. In this species, reproductive activity was decoupled from phytoplankton development, and final maturation processes and spawning were solely fuelled by internal energy stores.     

Benthic Response to Mucilaginous Aggregates in the Northern Adriatic Sea: Biochemical Indicators of Eutrophication

In summer 1997, gelatinous aggregates appeared in the Adriatic Sea, covering large areas of the northern basin. This study deals with the comparison between the biochemical composition of the sedimentary organic matter in summer, 1996 (when no aggregates appeared), and in summer, 1997 (during the appearance of aggregates). the biochemical composition of organic matter in surface sediments (determined in terms of proteins, carbohydrates, lipids, phytopigments and nucleic acids) has been investigated in two areas along the coast of the NW-Adriatic Sea in order to characterize benthic processes during aggregate deposition on the sea floor. During mucilage accumulation, a significant increase of biochemical compounds was observed, and chlorophyll-a and carbohydrate concentrations doubled their concentrations. in contrast, protein concentrations decreased, so that overall biopolymeric carbon content (expressed as the sum of lipid, protein and carbohydrate carbon equivalents) did not display significant differences between sampling periods (1579.3 in June, 1996 1678.8 μgCg^-1 and June, 1997). the protein to carbohydrate ratio decreased from 4.9 in June, 1996 to 1.8 in June, 1997. Mucilage production in June, 1997, modified significantly the biochemical composition of the sedimentary OM, thus affecting the potential availability of OM to benthic consumers. We hypothesise that the production of highly refractory composition of the sedimentary OM during mucilage accumulation might have an important biogeochemical implications.     

Microstructural growth in otoliths of conger eel (Conger myriaster) leptocephali during the metamorphic stage

Otolith growth during metamorphosis and some aspects of the early life history of conger eel (Conger myriaster) were determined as indicated from microstructure in otoliths of the leptocephali collected from Cheonsu Bay, Korea during May and June 1988. The leptocephali occurred from early May to late June in the study area. Larvae collected in early May were in the late leptocephalus stage, and the proportion of the metamorphosing leptocephali increased over time. Otoliths in the late leptocephalus stage showed a translucent zone only. Although the fish did not feed and the body length diminished during metamorphosis, the otolith continued to grow and, consequently, the opaque zone was formed outside the translucent zone. The inner translucent zone can be considered a leptocephalus zone, and the outer opaque zone a metamorphic zone. Assuming that the growth increments were deposited daily from hatching, the conger eel can be considered to have hatched between September and February. The number of increments in the inner hyaline zone ranged from 124 to 239, and was assumed to represent the number of days from hatching to the onset of metamorphosis. The duration of metamorphosis was estimated as 51 to 75 d based on the number of increments in the opaque zone at the end of the metamorphic stage.     

Benthic Response to Mucilaginous Aggregates in the Northern Adriatic Sea: Biochemical Indicators of Eutrophication

Abstract

In summer 1997, gelatinous aggregates appeared in the Adriatic Sea, covering large areas of the northern basin. This study deals with the comparison between the biochemical composition of the sedimentary organic matter in summer, 1996 (when no aggregates appeared), and in summer, 1997 (during the appearance of aggregates). the biochemical composition of organic matter in surface sediments (determined in terms of proteins, carbohydrates, lipids, phytopigments and nucleic acids) has been investigated in two areas along the coast of the NW-Adriatic Sea in order to characterize benthic processes during aggregate deposition on the sea floor. During mucilage accumulation, a significant increase of biochemical compounds was observed, and chlorophyll-a and carbohydrate concentrations doubled their concentrations. in contrast, protein concentrations decreased, so that overall biopolymeric carbon content (expressed as the sum of lipid, protein and carbohydrate carbon equivalents) did not display significant differences between sampling periods (1579.3 in June, 1996 1678.8 μgCg^?1 and June, 1997). the protein to carbohydrate ratio decreased from 4.9 in June, 1996 to 1.8 in June, 1997. Mucilage production in June, 1997, modified significantly the biochemical composition of the sedimentary OM, thus affecting the potential availability of OM to benthic consumers. We hypothesise that the production of highly refractory composition of the sedimentary OM during mucilage accumulation might have an important biogeochemical implications.     

Long-lasting consequences of elevated yolk testosterone levels on female reproduction

Maternal yolk androgens in bird eggs represent an important pathway along which offspring phenotype is shaped. Most of the hormone-mediated maternal effects are highly important in the context of sibling competition. However, there is also increasing evidence for long-lasting effects far beyond the nestling period, and these effects may have important consequences on the reproductive success of the offspring. Here, we investigated the effects of experimentally elevated yolk testosterone concentrations on growth and reproduction in female canaries. Elevated yolk testosterone concentrations enhanced the post-natal growth rate, but not the asymptotic mass, and reduced the survival probability. The latter may be a consequence of the higher growth rate, which may have rendered females hatching from testosterone-treated eggs (T-females) more vulnerable to harsh environmental conditions. Adult T-females made a larger investment in their clutch by laying more but not heavier eggs than females hatching from control-treated eggs. Our results suggest that the observed long-lasting effect on clutch size relates to changes in the growth trajectory rather than being a direct consequence of testosterone, since studies manipulating early growth conditions obtained similar results. Clearly, further studies are now required in order to investigate the intriguing relationship between yolk testosterone, elevated growth rates, and clutch size.     

An individual-based model to study the reproduction of egg bearing copepods: Application to Eurytemora affinis (Copepoda Calanoida) from the Seine estuary,France

Limited empirical studies have elucidated the daily egg production and associated reproductive processes of egg bearing copepod. Herein, we present an individual-based model which constitutes a realistic representation of the reproduction in egg bearing copepods. The model has been parameterized using an extensive set of experimental data obtained from the literature and from the laboratory and field experiments on the estuarine copepod Eurytemora affinis. The proposed model takes into account the adult female longevity, the clutch size and interclutch duration, which is a function of egg maturation time and latency time required by the female after egg hatching to produce a new clutch. The embryonic development time and hatching success are also taken into account. The effect of temperature on the means and variances of above-mentioned reproductive parameters has been also incorporated. A multi agent system based generic platform “Mobidyc” has been used to generate and calibrate the model. The model demonstrates the reproductive parameters of females of E. affinis which is validated through individual based experiments. Temperature specific simulations provide a dynamical explanation of temperature effect on the cumulative egg production. The daily survival principally affects the number of clutches produced per female during its life span. The results obtained in the present study by combining temperature and survival effects reveal the relatively greater importance of the first factor on the daily egg production of egg-carrying copepods. The present model is generic and hence easily applicable to other animals with comparable reproductive strategy.     

Spring bloom sedimentation in a subarctic ecosystem

A 5-yr study (1985 to 1989) of spring bloom sedimentation in Auke Bay, Alaska, indicates that the sinking response of diatoms to ambient nutrients influences both species succession during the spring bloom and the subsequent sedimentation of new production. Diatoms from the genera Thalassiosira, Chaetoceros and Skeletonema formed the bulk of the spring bloom each year. Growth of Thalassiosira spp. consistently initiated the primary bloom, while Skeletonema costatum tended to grow later in, or after, the primary bloom. We postulate that this successional pattern is driven by interspecific nutrient competition. Overall, sedimentation flux of the dominant species of bloom diatoms was correlated with surface concentrations of cells integrated over the bloom period. In fact, different linear relationships existed when Thalassiosira and Chaetoceros spp. were considered separately, but not for Skeletonema sp., indicating that marked differences exist between the sedimentation tendencies of these genera. The observed inter-generic differences are explicable by the different overall sinking rates, as well as different nutrient-sensitivities of the sinking rates of each genus. Thalassiosira spp., the fastestsinking and most nutrient-sensitive species, contributed up to 10 x more carbon to the benthos in all years of the study, reaching a maximum of 11.1 gCm^-2 over a single spring bloom event in 1988. This study indicates that the tendency to sink to the benthos during and/or after a bloom is highly dependent on species-specific cell physiology, and supports the idea that it is the fast-sinking, nutrient-sensitive diatoms, such as Thalassiosira species, that constitute the major source of vertical carbon flux in this embayment and other such coastal ecosystems during the spring bloom.     

Growth and grazing loss rates in single-celledPhaeocystis sp. (Prymnesiophyceae)

Growth and grazing loss rates of naturalPhaeocystis sp. single cells were measured using a seawater dilution technique. Measurements were performed during an intensePhaeocystis sp. bloom in the North Sea between 19 April and 5 May 1988. Experimental results yielded rapid carbon turnover rates. Population growth rates varied from 0.033 to 0.098 h^–1, grazing loss rates from 0.037 to 0.174 h^–1. From measured growth rates, average doubling rages of 1.3 doublings d^–1 were calculated. The growth rates would have resulted in maximum carbon production rates of 146 mg C m^–3 d^–1. Grazing rates increased in the course of the bloom and exceeded growth rates at the end. Grazing loss was caused primarily by microzooplankton feeding. Ciliates and heterotrophic dinoflagellates were identified as the major potential consumers of single cells ofPhaeocystis sp. at the beginning of the bloom. The grazing impact of larger microzooplankton species appeared to increase during the progressing bloom.     

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%).