Fall Bloom Research Articles

Phylogenetics and Biogeography of Alnus (Betulaceae) Inferred from Sequences of Nuclear Ribosomal DNA ITS Region

Sequences of nuclear ribosomal DNA ITS region were used to estimate phylogenetic relationships of Alnus. We recognize three major clades in Alnus, including subgenera Alnobetula, Clethropsis, and Alnus; subgenus Alnobetula is sister to subgenera Clethropsis and Alnus. The eastern Asian subgenus or section Cremastogyne is embedded in the subgenus Alnus clade. Alnus nepalensis is part of subgenus Alnus, not subgenus Clethropsis. Alnus maritima is part of subgenus Clethropsis (excl. A. nepalensis). Long and short branching pattern, sessile winter bud, and 2‐yr phenology are plesiomorphies in Alnus, while 1‐yr floral phenology and fall blooming are derived features. The simple axillary female inflorescence has evolved more than once in Alnus. Central and South American species of Alnus are derived from migrants from eastern Asia via the Bering land bridge and western North America. In subgenus Clethropsis, A. formosana of eastern Asia is more closely related to eastern North American species than to the other Asian species, A. nitida. The low sequence divergence within both the A. incana and A. viridis species complexes indicates their recent history of diversification in the circumpolar areas.

Are the spring and fall blooms on the Scotian Shelf related to short-term physical events?

Physical, chemical and biological data from the Scotian Shelf indicate that short-term physical events affect the dynamics of spring and fall blooms. This is based on results from a three-week mooring deployment measuring currents, temperature, salinity and fluorescence in October 2000, combined with biweekly sampling of temperature, salinity, nutrients and chlorophyll throughout the year at this mooring site. A wind-driven upwelling event in mid-October shows temperature, salinity and density iso-surfaces rising by approximately 20 m. During this event, a bloom with peak chlorophyll concentrations of about 2.5 mg m −3 began as nutrients are brought into the upper part of the water column. Gradient Richardson Numbers ( Ri), a proxy for vertical mixing, are estimated for the mooring period in 2 m vertical bins using SeaHorse CTD data and nearby ADCP current measurements. These data indicate that vertical mixing may have played a complementary role to the upwelling in bringing nutrients into the euphotic zone. A trend of decreasing Ri in the ocean mixed layer with increasing surface wind stress is suggested. It appears that this short-term physical event is a primary factor in initiating the fall bloom on the inner Scotian Shelf in 2000. In April of that year, the termination of the spring bloom coincided with a downwelling event suggesting that it played a role in determining the duration of the bloom. SeaWiFS ocean color satellite provided a spatial context for chlorophyll observations, however, the lack of temporal resolution due to poor atmospheric conditions means that these data provide limited information on short-term chlorophyll variability.

The effects of Apogee® on shoot growth, secondary flowering, fire blight, fruit quality, yield and return bloom in ‘Bartlett’ pear growing in California

SummaryApogee® sprays were applied to mature ‘Bartlett’ pear (Pyrus communis L.) trees as single or multiple sprays during the growing seasons of 1999 to 2003 at concentrations of 420 g ha–1 (125 mg –1) or 840 g ha–1 (250 mg–1): both reduced vegetative shoot growth. Two sprays of 840 g ha–1 applied 3–3.5 weeks apart were most effective and reduced shoot growth by approximately 40%. An application made 2 d after fall bloom was ineffective and led to more vegetative shoot growth. Single sprays of Apogee® made within 9–28 d after full bloom (DAFB) were equally effective in reducing vegetative shoot growth. Bourse shoot growth was reduced 43% by 3 April, 2001 (8 DAFB) treatment of 840 g ha–1 when bourse and vegetative shoots ranged from 2.5 to 7.5 cm in length. Subsequent single applications of 840 g ha–1 Apogee® (on April 12 or 23, 2001) did not reduce bourse shoot growth significantly. Vegetative shoot growth was also reduced by 12% (9 d after treatment) and by 38% (approximately one month after treatment) by 840 g ha–1 Apogee® applied on 3 April, 2001, (8 DAFB). In 2002, bourse shoot growth was controlled most effectively by split applications (840 + 420 g ha–1 or 840 2 g ha–1, 9 April and 24 May) and by 840 g ha–1 Apogee®, applied at 2.5 to 7.5 cm shoot growth (9 April). These split applications, as well as girdling, decreased shoot strikes in 2002, the year after treatment. Split applications of 840 g ha–1 Apogee® made in April to early May were most effective in controlling both vegetative and bourse shoot growth in most years, although single applications of Apogee® were effective in some years. Subsequent flushes of shoots tended to be controlled by split applications with the second application timed to the emergence of new shoots. Apogee® was not consistently effective in reducing the incidence of Type I or Type V secondary flowers in these trials. Single or multiple sprays of Apogee® had no measurable or consistent effect on return bloom, fruit size or shape, firmness, percentage soluble solids, or yield per tree over the period of these experiments. Apogee® appears to have promise as a shoot growth control agent in ‘Bartlett’ pear growing in California, USA, without deleterious effects.

THE SEASONAL CYCLE OF SURFACE CHLOROPHYLL ALONG THE PERUVIAN COAST: COMPARISON BETWEEN SEAWIFS SATELLITE OBSERVATIONS AND DYNAMICAL/BIOGEOCHEMICAL COUPLED MODEL SIMULATIONS

The seasonal cycle of surface chlorophyll along the Peruvian coasts is studied with SeaWiFS satellite observations and coupled dynamical/biogeochemical ORCA/PISCES model simulations. The observed mean spatial structure of surface chlorophyll is shown to be in good agreement with that of the model. However the seasonal cycles contrast: whereas the model produces a spring bloom consistent with maximum upwelling and deepest mixed layer in the winter season, the observed seasonal cycle shows two distinct blooms one in late spring-early summer and other in fall. Several hypotheses are suggested to explain the fall bloom and its non-occurrence in the model

Greedy algae reduce arsenate

Algae reduce and methylate arsenate, producing arsenite (As(III)) when the growth rates are high and dimethylarsinic acid (DMA) when the growth rates are low. In lakes, this leads to high As(III) concentrations in the early stages of spring and fall blooms and high DMA concentrations in the summer. We hypothesize that under phosphorus (P)‐limited conditions, which usually exist in the summer, algae take up phosphate (PO4) and, because of similar chemical characteristics, As(V) as well. Inside the cell, As(V) is reduced to As(III), methylated to monomethylarsonic acid (MMA) and DMA, and then excreted. However, under non—P‐limited conditions, which exist in the early stages of blooms, algae up‐regulate their PO4 transport system to take up excess P, a phenomenon known as luxury uptake. Since As(V) is taken up by the PO4 transport system, As(V) uptake also increases at this time. Within the cell, the reduction of As(V) to As(III) is fast, but methylation is slower, causing As(III) to build up in the cell and be excreted, which, in turn, causes an increase in extracellular As(III). This mechanism permits the synergistic (luxury uptake) and antagonistic (competition) effects of PO4 on As(V) uptake and can therefore explain the seemingly contradictory results found in the literature. A mathematical model is constructed on the basis of existing established algal—nutrient interaction models and is used to simulate As transformation in two laboratory batch experiments. In addition to algal and P responses, the model can reasonably well reproduce the observed As(III) peak during the log growth phase and the more gradual appearance of DMA during the stationary phase.

Satellite-measured phytoplankton variability in the Gulf of Maine

The first 4 years of SeaWiFS ocean color data (September 1997–August 2001) provide the first synoptic quantification of seasonal and interannual phytoplankton chlorophyll variability in the Gulf of Maine. Climatological monthly means show spatial patterns associated with the annual cycle. Concentrations are elevated throughout the year in coastal regions and over shallow banks (Georges Bank, Nantucket Shoals and Browns Bank) with a spring and fall bloom superimposed. Over deeper basins and the Scotia Shelf, a canonical North Atlantic seasonal cycle is present with low (< 1 mg m −3) winter (December–February) concentrations, an annual maximum in March–April (>2 mg m −3), reduced concentrations in summer and a fall bloom beginning as early as September in Jordan Basin but in October–November over other regions. Strong interannual variability over the 4-year time series shows the climatological seasonal features are often a biased picture of both timing and magnitude. The clearest interannual signal is of reduced chlorophyll concentrations throughout 1998, including weak spring and fall blooms. A connection between low concentrations in 1998 and local wind forcing is not evident. However, the low concentrations are coincident with negative anomalies in satellite surface temperature fields and follow the intrusion of relatively cold, low salinity slope water into the Northeast Channel which previous authors have argued is linked to changes in Labrador slope water transport induced by the North Atlantic Oscillation. Reduced concentrations in 1998 are consistent with both lower nitrate/nitrite concentrations in the intruding water as well as reduced subsurface stratification which would delay or reduce the onset of the spring bloom.

표층혼합층 생태계모델을 이용한 동해 식물플랑크톤의 계절변화

Seasonal variation of phytoplankton was investigated with surface mixed layer ecosystem model in the East Sea. The model consisted of four compartments (phytoplankton, zooplankton, nutrient, detritus) forced by mixed layer depths, photosynthetically available radiation and nutrient concentrations. From model results we estimated entrainment rate to reproduce the two annual blooms, and reproduced seasonal variation of phytoplankton at southern and northern regions by the difference of surface winter mixed layer depth (MLD) using the entrainment rate value . The spring blooms in the southern and northern regions closely related to deepening of a winter surface MLD. In the southern region where MLD was shallow and phytoplankton spring bloom occurs one month in advance to the northern region where MLD was deep. The amount of light increases within the MLD during the onset of stratification and water temperature increases faster in spring in the southern region than the northern region. Decrease of phytoplankton was mainly affected by zooplankton grazing in the southern region and by nutrient exhaustion in the northern region. The fall bloom in the two regions was caused by the nutrient availability and entrainment on the phytoplankton.

Seasonal and interannual variability of benthic foraminiferal faunas at 550 m depth in the Bay of Biscay

Live benthic foraminiferal faunas were sampled 10 times between October 1997 and April 2000 at a 550 m depth open-slope station in the Bay of Biscay. Duplicate cores for 5 samplings allow distinguishing between spatial and temporal variability of the foraminiferal faunas. Although spatial patchiness of the foraminiferal faunas is substantial, especially in the 63–150 μm fraction, the temporal variability appears to be larger. The foraminiferal patterns are compared with surface water primary production as assessed by the study of available SeaWIFS satellite images. In the study area, the primary production regime is marked by a pulselike and prolonged spring bloom and possibly a short fall bloom. Such periods of elevated chlorophyll- a concentration are followed, after a delay of about 4–6 weeks, by a strong frequency increase of the most opportunistic taxa of benthic foraminifera. Surprisingly, no change of bottom and interstitial water oxygenation and of redox conditions within the sediment is recorded. The small taxa Epistominella exigua, Reophax guttiferus, Bolivina spathulata, Cassidulina carinata and Nuttallides pusillus appear to respond first to a labile organic matter input, by a reproductive event marked by a strong patchy spatial distribution hypothetically resulting of the spatial heterogeneity of organic matter deposits. Uvigerina peregrina and Uvigerina mediterranea, the most opportunistic larger taxa, strongly dominate the >150 μm fraction during eutrophic periods (spring and fall blooms). Intermediate and deep infaunal taxa seem to depend less on fresh organic matter input, even if a small frequency increases are recorded in the >150 μm fraction during the most productive periods; Globobulimina affinis and Melonis barleeanus show reproductive events in rather shallow sediment layers in the more oligotrophic periods of the year. A conceptual model explains the increasing delay in the response to important phytoplankton bloom periods for the successive benthic ecosystem compartments.

Ocean color variability in the Tasman Sea

[1] The Tasman Sea contains the largest noncoastal surface chlorophyll-a concentrations within the South Pacific Ocean. Observations of ocean color from SeaWiFS demonstrate that the chlorophyll-a seasonal cycle is characterized by a large austral spring bloom and a much smaller fall bloom separated by periods of lower concentrations, typical of communities within the North Atlantic Ocean. However, the seasonal cycle of the mixed layer depth of the Tasman Sea is much more similar to the North Pacific Ocean, whose persistent winter stratification results in relatively constant chloropohyll-a concentrations. Examination of eddy kinetic energy from satellite altimetry (TOPEX/Poseidon and ERS-2 blended product) reveals that the western Tasman Sea contains a large number of eddies originating within the East Australian Current that coincide spatially with the blooms. Upwelling and downwelling associated with these eddies greatly increase vertical mixing within the upper ocean, offsetting the normally shallow winter mixed layer, which leads to a chlorophyll-a seasonal cycle much like that of the North Atlantic Ocean.

Role of cyst germination in the bloom initiation of Alexandrium tamarense (Dinophyceae) in Masan Bay, Korea

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 29:279-286 (2002) - doi:10.3354/ame029279 Role of cyst germination in the bloom initiation of Alexandrium tamarense (Dinophyceae) in Masan Bay, Korea Young-Ok Kim1, Myung-Hwan Park2, Myung-Soo Han1,2,* 1Department of Life Science, and 2Department of Environmental Science, Hanyang University, Seoul 133-791, South Korea *Corresponding author. E-mail: hanms@hanyang.ac.kr ABSTRACT: The role of cyst germination in the bloom initiation of the toxic dinoflagellate Alexandrium tamarense was examined in Masan Bay, Korea. Germination success was measured by the incubation of cysts isolated monthly from natural sediments and compared with vegetative cells and environmental factors (temperature, salinity and dissolved oxygen) in the water column. Germination maxima (80 to 90%) were observed during the period of decreasing water temperature in December 1996 and November 1997, while little or no germination occurred in summer. The seasonal germination exhibited an opposing pattern with temperature and similar seasonalities with salinity and dissolved oxygen, respectively. The bimodal nature of A. tamarense blooms, a large bloom in spring and a much smaller bloom in fall, was observed. Excysted cells in early spring can initiate the spring bloom and then proliferate to the bloom peak in increasing temperatures. Massive germination in fall contributes directly to the small bloom in fall. A temporal discrepancy between the peak of germination success and of vegetative population was found in A. tamarense dynamics from Korean coastal waters. KEY WORDS: Alexandrium tamarense · Cyst germination · Vegetative population Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 29, No. 3. Online publication date: October 23, 2002 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2002 Inter-Research.

Temporal and spatial variability of chlorophyll-a in the western subarctic Pacific determined from satellite and ship observations from 1997 to 1999

Abstract The objectives of this study are to describe and understand the processes controlling the temporal and spatial variability of chlorophyll-a (chl-a) in the subarctic northwestern Pacific Ocean from 1997 to 1999. Remotely sensed data from multi sensors, including ocean color (OCTS and SeaWiFS), sea-surface temperature (SST, AVHRR), and wind (SSM/I) datasets were utilized for the purpose of this study. Ocean-color imagery clearly showed seasonal and interannual variability in the spatial abundance and distribution of chl-a in the study area. Chl-a concentrations were generally low (0.53±0.24 mg m−3) for most part of the year, except for a few peaks (1.0–2.0 mg m−3) observed in the spring and fall bloom seasons (May, June, September, and October). Chl-a concentrations (>10 mg m−3) were consistently high along the Kuril Islands and in the coastal waters around the Kamchatka Peninsula, and in 1998 they were clearly higher than in 1999. The Western Subarctic Gyre (WSG) was characterized by positive sea-surface temperature anomalies (SSTA) during the summer to fall of 1998. These anomalies appear to be a high-latitude response to 1997/1998 ENSO event. High concentrations of chl-a appeared in WSG in September–November only in 1998. We suggest that the high chl-a around the WSG from summer to fall in 1998 was facilitated by (1) negative SSTA in winter, in spite of the negative wind anomaly, which provided larger amount of nutrients to the sea surface, (2) positive wind anomaly from April to June, which might cause light limitation of the phytoplankton growth, due to deepening of the surface-mixed layer in summer, and (3) positive SSTA, even with the slightly positive wind anomaly, which was accompanied with the water-column stabilization and hence recovered light limitation of the phytoplankton. Warmer SST also might have enhanced the phytoplankton growth. During summer to fall in 1999, the phytoplankton biomass between 42°N and 43°N along 165°E was greater than in other years. The enhanced chl-a concentration coincided with a distinct frontal temperature gradient located between 40°N and 45°N in September 1998 and 1999. The peak chl-a concentration in September 1999 (>2.0 mg m−3) within the temperature front was much larger than in 1998 (about 0.7 mg m−3). The position of this front in September 1999 (41°N) was south of its position in 1998 (43°N). Convergence of chl-a is linked to the temperature gradient and southward expansion of well-mixed subarctic water that is cold, low in salinity, and nutrient-rich. Our results showed significant interannual biological variability, and illustrate how remote sensing with multi sensors can aid in monitoring relationships between local ecosystems and global climate change.

Effect of inorganic sediment on whole-stream productivity

Sediment from agricultural, logging, and mining activities impairs more miles of rivers and streams in the United States than any other type of pollutant, including bacteria, nutrients, oxygen-depleting substances, and metals. However, specific impacts of sediment to streams have not been well studied or understood. To study the effect of inorganic sediment on plant and animal communities in stream ecosystems, we added clay to outdoor experimental streams 520 m long and 3.5 m wide at the Monticello Ecological Research Station (MERS). The streams take water from the Mississippi River and are designed to represent higher order streams in the upper midwestern United States. The sediment loading rates were 300, 200, 100, and 50 mg l−1. Our first dosing period (mid-August to November 1994) began at the start of a fall bloom in autotroph productivity, and the second (May to August 1995) began before the summer communities were established. During both treatment seasons, the addition of clay significantly increased turbidity and sedimentation, and decreased light penetration in treated streams corresponding roughly to 30–35, 25–30, 15–20, and 5–10 NTU, respectively. In general, the macrophyte and periphyton communities responded quickly after only a few weeks exposure to the sediment additions. Whole-stream respiration was significantly lower in treated streams, decreasing as the amount of sediment added increased. Periphyton biomass (chl a) on tiles and percent cover of macrophytes was significantly lower in treatment streams than in controls. In contrast to expectations and previous findings in two sets of field streams, total whole-stream productivity in the MERS streams was not significantly lower in streams receiving sediment loads than in control streams because the overall photosynthetic efficiency by the plant community compensated for the loss in irradiance.

AN ECOLOGICAL BASIS FOR EXTRACELLULAR CARBONIC ANHYDRASE IN MARINE UNICELLULAR ALGAE

Extracellular carbonic anhydrase (CAe) is expressed by many, but not all, autotrophic species of aquatic unicellular protists. We measured CAe activities in unicellular marine algae characteristic of either high nutrient spring, fall, and winter blooms or low nutrient summer populations to provide ecological/evolutionary information about the enzyme. Highest activities occurred in spring bloom and opportunistic diatoms exposed to long photoperiods (16 h) when pH was highest and CO2 was lowest. Lower activities were recorded for a fall‐bloom diatom exposed to the long photoperiod, and lowest values were found under all culture conditions for one diatom and a number of flagellated species typical of summer low nutrient environments. Other potential sources of variance in measurements of CAe activity were examined. Maximum activities of CAe were recorded for the diatom, Skeletonema costatum (Greville) Cleve, during late exponential phase of growth and within 8 h of the beginning of the photoperiod. We concluded that ecological factors are important in determining CAe activities in marine unicellular protists. Potential functions of CAe in the metabolism of marine unicellular algae are discussed.

Phytoplankton production patterns in Massachusetts Bay and the absence of the 1998 winter-spring bloom

The seasonal productivity cycle and factors controlling annual variation in the timing and magnitude of the winter–spring bloom were examined for several locations (range: 42°20.35′–42°26.63′N; 70°44.19′–70°56.52′W) in Boston Harbor and Massachusetts Bay, USA, from 1995 to 1999, and compared with earlier published data (1992–1994). Primary productivity (mg C m−2 day−1) in Massachusetts Bay from 1995 to 1999 was generally characterized by a well-developed winter–spring bloom of several weeks duration, high but variable production during the summer, and a prominent fall bloom. The bulk of production (mg C m−3 day−1) typically occurred in the upper 15 m of the water column. At a nearby Boston Harbor station a gradual pattern of increasing areal production from winter through summer was more typical, with the bulk of production restricted to the upper 5 m. Annual productivity in Massachusetts Bay and Boston Harbor ranged from a low of 160 g C m−2 year−1 to a high of 787 g C m−2 year−1 from 1992 to 1999. Mean annual productivity was higher (mean=525 g C m−2 year−1) and more variable near the harbor entrance than in western Massachusetts Bay. At the harbor station productivity varied more than 3.5-fold (CV=40%) over an 8 year sampling period. Average annual productivity (305–419 g C m−2 year−1) and variability around the means (CV=25–27%) were lower at both the outer nearfield and central nearfield regions of Massachusetts Bay. Annual productivity in 1998 was unusually low at all three sites ( 0.05) among years (1995–1999). The mean photic depth during the bloom period was significantly deeper (P < 0.05) in 1998, signifying greater light availability with depth. Nutrients were also in abundance during the winter–spring of 1998 with stratified conditions not observed until May. In general, the magnitude of the winter–spring bloom in Massachusetts Bay from 1995 to 1999 was significantly correlated with winter water temperature (r2=0.78) and zooplankton abundance (r2=0.74) over the bloom period (typically February–April). The absence of the 1998 bloom was associated with higher than average water temperature and elevated levels of zooplankton abundance just prior to, and during, the peak winter–spring bloom period.

Influences of diurnal and intraseasonal forcing on mixed‐layer and biological variability in the central Arabian Sea

A three‐dimensional, physical‐biological model of the Indian Ocean is used to study the influences of diurnal and intraseasonal forcing on mixed‐layer and biological variability in the central Arabian Sea, where a mooring was deployed and maintained from October 1994 to October 1995 by the Woods Hole Oceanographic Institution Upper Ocean Processes group. The physical model consists of four active layers overlying an inert deep ocean, namely, a surface mixed layer of thickness h1, diurnal thermocline layer, seasonal thermocline, and main thermocline. The biological model consists of a set of advective‐diffusive equations in each layer that determine nitrogen concentrations in four compartments: nutrients, phytoplankton, zooplankton, and detritus. Both monthly climatological and “daily” fields are used to force solutions, the latter being a blend of daily‐averaged fields measured at the mooring site and other products that include intraseasonal forcing. Diurnal forcing is included by allowing the incoming solar radiation to have a daily cycle. In solutions forced by climatological fields, h1 thickens steadily throughout both monsoons. When h1 detrains at their ends, short‐lived, intense blooms develop (the model's spring and fall blooms) owing to the increase in depth‐averaged light intensity sensed by the phytoplankton in layer 1. In solutions forced by daily fields, h1 thins in a series of events associated with monsoon break periods. As a result, the spring and fall blooms are split into a series of detrainment blooms, broadening them considerably. Diurnal forcing alters the mixed‐layer and biological responses, among other things, by lengthening the time that h1 is thick during the northeast monsoon, by strengthening the spring and fall blooms and delaying them by 3 weeks, and by intensifying phytoplankton levels during intermonsoon periods. Solutions are compared with the mixed‐layer thickness, phytoplankton biomass, and phytoplankton production fields estimated from mooring observations. The solution driven by daily fields with diurnal forcing reproduces the observed fields most faithfully.

Physical and biogeochemical variability from hours to years at the Bermuda Testbed Mooring site: June 1994–March 1998

Abstract The Bermuda Testbed Mooring (BTM), initiated in 1994, provides important information concerning periodic and episodic processes. The BTM enables collection of virtually continuous data during periods of inclement weather when traditional sampling is not possible, and provides otherwise inaccessible data in the important spectral range of minutes to a month. New methodologies and analyses are evolving for interdisciplinary mooring measurements. For example, BTM and shipboard temperature and spectral downwelling irradiance data sets have been compared and are in good agreement. Several meteorological parameters determined using operational analyses and climatological estimates also compare favorably with BTM calculations. Kinetic energy (by frequency domain), de-correlation time scales, and spectra were computed using the BTM data sets. The ratio of kinetic energy attributed to periods less than 2 days to that in periods greater than 2 days is generally greater at 45 m than at 71 m (the winter season being the exception). The upper layer has more kinetic energy due to inertial motions, while the lower layer is more influenced by mesoscale eddies. It is inferred that important interactions occur between these layers. It is hypothesized that the specific timing of the onset of spring stratification and fall breakdown of stratification, as well as accompanying phytoplankton blooms, are controlled by the specific synoptic wind forcing and mesoscale eddy conditions. An example of this scenario is described using unique BTM observations of a fall bloom event. Specifically, (1) a mode eddy with a shallow (roughly 80 m) nutricline passed the site, (2) deepening of the mixed layer (from about 50–175 m) caused entrainment of nutrients into the euphotic layer, and (3) a three-fold increase in depth-integrated chlorophyll was observed. Finally, de-correlation time scales were found to lie between 5 and 15 days for the key physical and biological variables. These de-correlation scales set upper limits on sampling intervals necessary to resolve the important physical and biogeochemical processes.

Larval fish diversity on the Scotian Shelf

We examined larval fish diversity on the Scotian Shelf using data, representing 91 genera, collected during the Scotian Shelf Ichthyoplankton Program from 1978 to 1982. Two diversity indices (genus richness (GR) and Shannon's entropy (H)) were relatively lower from December to February-March and relatively higher and stable from April to September-October. Taxon composition changed seasonally. Total median log abundance (log10(number of individuals + 1)·1000 m-3) was low from December to February, increased in March, was stable from April to June, and declined from July to October. Our results suggest that the abundance trends of most taxa were not coincident with either a spring or fall bloom of calanoid copepods. Log GR was significantly positively related to H (r = 0.62, p &lt; 0.001, n = 1853). A negative exponential best described the relationship between log GR and log abundance (R2 = 0.77; log GR = 1.37(1 – e-(1.13)(log abundance)), p &lt; 0.001, n = 2357). Shannon's H was not related to log abundance in winter or in summer-fall and was negatively correlated in spring-summer (r = -0.12, p = 0.003, n = 593). Thus, diversity increases with abundance but the composition is dominated by relatively fewer genera at higher levels of abundance. Western - Sable Island banks had higher levels of GR and abundance in all seasons. Additional banks were diverse and productive during warmer months.

Temporal and Spatial Variability of Phytoplankton Pigment Concentrations in the Japan Sea Derived from CZCS Images

Temporal and spatial variability of phytoplankton pigment concentrations in the Japan Sea are described, using monthly mean composite images of the Coastal Zone Color Scanner (CZCS). In order to describe the seasonal changes of pigment concentration from the results of the empirical orthogonal function (EOF) analysis, we selected four areas in the south Japan Sea. The pigment concentrations in these areas show remarkable seasonal variations. Two annual blooms appear in spring and fall. The spring bloom starts in the Japan Sea in February and March, when critical depth (CRD) becomes equal to mixed layer depth (MLD). The spring bloom in the southern areas (April) occurs one month in advance of that in the northern areas (May). This indicates that the pigment concentrations in the southern areas may increase rapidly in comparison with the northern areas since the water temperature increases faster in spring in the southern than in the northern areas. The fall bloom appears first in the southwest region, then in the southeast and northeast regions, finally appearing in the northwest region. Fall bloom appears in November and December when MLD becomes equal to CRD. The fall bloom can be explained by deepening of MLD in the Japan Sea. The pigment concentrations in winter are higher than those in summer. The low pigment concentrations dominate in summer.

Effect of light: dark cycles and cell apical length on the sexual reproduction of the pennate diatom Pseudo-nitzschia multiseries (Bacillariophyceae) in culture

Sexual reproduction in the domoic acid–producing pennate diatom Pseudo-nitzschia multiseries (Hasle) Hasle is dioecious and involves pairing of two morphologically isogamous parent cells (gametangia) and the production of two gametes per gametangium. Gamete fusion leads to the formation of zygotes, which elongate into auxospores. Within each auxospore, a long initial cell is formed, thereby restoring the longer cell sizes in the population. Mating experiments were performed by mixing active “male” and passive “female” cells from pairs of clones and growing them under different light : dark (L : D) cycle regimes. Two pairs of clones were studied: one pair was ontogenetically older and therefore shorter than the other. After mating, the relative abundance of gametes, zygotes, auxospores, and initial cells was determined for a minimum of four consecutive days. Cell size, which reflects population age, influences sexualization. The short-celled clones had a lower maximum proportion of gametes per vegetative cell (4%) than the long-celled clones (49%), suggesting that the former were nearing the minimal cell length capable of sexualization. The size range within which P. multiseries is able to reproduce sexually is 23–70% of the maximum cell length. A positive correlation was found between hours of light exposure per 24 h at approximately 100 μmol photons m−2 s−1 and sexual cell production of the ontogenetically younger clones. Greatest production of initial cells per female gamete (26%) occurred in 10 h of light. Results from this study indicate that the most biologically successful light regimen in culture corresponds in nature to the day length of the fall bloom from which these clones were isolated.

Biological and physical signatures in the tropical and subtropical Atlantic

The variability of sea surface chlorophyll concentration in the tropical and subtropical Atlantic during the first year of Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) imagery is examined. An Ocean General Circulation Model (OGCM) is used, along with TOPEX/Poseidon dynamic height observations and global gridded wind stress data sets, to explain the physical forcing of surface ocean color signals. Regions of high surface chlorophyll are strongly correlated with mesoscale and large‐scale physical processes such as the strong upwelling off the west coast of Africa, the relatively high oceanic production within the Guinea Dome region, and the generation and propagation of large anticyclonic eddies along the coast of South America, north of the equator. The major river outflows (Amazon, Orinoco, and Congo) have strong signatures with plumes of apparently high Chl a in excess of 10 mg m−3 near their deltas. The fall bloom in the eastern tropical Atlantic observed by the Coastal Zone Color Scanner (CZCS) was absent in 1997, whereas a bloom was observed in this region in July‐September 1998, which was not observed by the CZCS. We attribute these apparent anomalies to the projection of the 1997–1998 El Niño event into the tropical Atlantic basin; these signals are correlated with sea surface temperature anomalies known to be associated with ENSO. The SeaWiFS images show that there are seasonal blooms within the hydrographic provinces of the Guinea and Angola domes. These hydrographic provinces are characterized by the dynamic uplift of the thermocline at the North Equatorial Current southern boundary (Guinea Dome) and the Benguela Current eastern boundary (Angola Dome). Within these domes, the Ekman pumping and transport are significant due to the strong trade winds at the surface. The Ekman drift plays a major role in the spreading of surface blooms. The spreading of the oceanic bloom at 12°N, 30°W, the Congo River plume, and the areal extent of the upwelling blooms off the coast of Africa, parallels the strength and extent of the Ekman surface drift. Upwelling, when broadly defined to include large scale vertical excursions of the thermocline, explains virtually all of the surface chlorophyll observations in excess of 0.5 mg m−3, except in the river plumes.