Winter Spring Phytoplankton Bloom Research Articles

Remote Sensing and Argo Float Observations Reveal Physical Processes Initiating a Winter-Spring Phytoplankton Bloom South of the Kuroshio Current Near Shikoku

BIO-Argo float (chlorophyll a (Chl-a), temperature, and salinity profiles) and remote sensing data (Chl-a, photosynthetic available radiation (PAR), and wind) located south of the Kuroshio current near Shikoku from September 2018 to May 2019 were used to study phytoplankton bloom and their mechanisms of development in open oceans. Results show that higher (lower) Chl-a concentrations are correlated with a deeper (shallower) mixed layer (RPearson = 0.77, Rcrit = 0.12 (alpha = 0.05, n = 263)) compared to the average of Chl-a and mixed layer depth (0.13 mg/m3 and 105 m). The average net accumulation rates (r) of phytoplankton were close to 0.08 d−1. An increasing r corresponds to a gradually increasing surface Chl-a (S (Chl-a): 0–20 m average Chl-a) and integrated Chl-a inventory (I (Chl-a): integrated Chl-a from surface to euphotic depth). These phenomena indicate that the mechanism of winter-spring phytoplankton blooms is consistent with the dilution-recoupling hypotheses (DRH). During the bloom formation, winter deep mixing and eddy-wind Ekman pumping are enhanced by a strong winter monsoon. The enhancement may disturb predator–prey interactions and dilute zooplankton in deep mixed layers. Moreover, winter deep mixing and eddy-wind Ekman pumping can cause the nutrients to be transported into the euphotic layer, which can promote the growth of phytoplankton and increase grazing. During the bloom extinction, the stratification strengthens and the intensity of light increases; this increases grazing and nutrient consumption, and decreases the phytoplankton bloom significantly (S (Chl-a) and I (Chl-a) increase by 0.3 mg/m3 and 27 mg/m2, respectively). The output from a biogeochemistry model shows that nutrients are consistent with the temporal distribution of S (Chl-a) and I (Chl-a). Our results suggest that physical processes (deep winter mixing and eddy-wind Ekman pumping) under the DHR framework are critical factors for winter-spring blooms in open oceans with an anticyclone eddy.

Feeding Access of Eastern Oysters to the Winter–Spring Phytoplankton Bloom: Evidence from Jamaica Bay, New York

The filtering capacity of dense bivalve populations can exert strong controls on phytoplankton biomass, leading to increased water clarity and reduced hypoxia. Bivalves, particularly oysters, therefore are the focus of many restoration efforts and ecosystem-based management plans. The hypothesis is tested that oysters have feeding access to the classic major phytoplankton bloom of the year in winter–spring. Jamaica Bay is a highly eutrophic urban estuary where oyster restoration is being considered as a means to improve water quality. Strong winter–spring and summer phytoplankton blooms occur in Jamaica Bay, and oyster feeding rates and oxygen consumption were examined to see if oysters would be able to feed during both seasonal pulses of phytoplankton. Temperature-related feeding rates were found to vary to the degree that feeding did not occur at the cold temperatures that exist during the winter–spring blooms. Indeed, feeding rate and proportion feeding were found to be zero at 10°C, which corresponds to March–April. But feeding would be vigorous in late spring and summer. Oysters, therefore, do not have the ability to regulate a major fraction of phytoplankton during the year in Jamaica Bay and likely in the rest of the mid-Atlantic states region and New England. Feeding rates are much higher during the time of the summer blooms, and oysters in shallow well-mixed waters would, therefore, have access to feeding and possibly control of phytoplankton biomass at this time.

Spatio-temporal dynamics of mesozooplankton in the subantarctic Beagle Channel: The case of Ushuaia Bay (Argentina)

The Beagle Channel is the southernmost South American fjord. Although it has been the focus of many biological studies, more in-depth knowledge of plankton and their linkage with environmental variables is lacking. The main objective of this study was to analyse the spatio-temporal variations in mesozooplankton assemblages of Ushuaia Bay, an ecologically and economically relevant area in the middle Beagle Channel, on the basis of samples collected during summer (March), autumn (June), winter (September) and spring (December) 2012 from environmentally different sites. Mesozooplankton composition and abundance exhibited strong seasonal variations, closely associated with the late winter–springphytoplankton bloom. The appendicularian Fritillaria borealis and the cyclopoid copepod Oithona similis were the dominant species during summer and autumn, whereas meroplanktonic larvae and the cladocerans Evadne nordmanni and Podon leuckarti dominated during late winter and spring, respectively. Mesozooplankton abundance was lower at coastal sites receiving freshwater and sewage discharges. Contrary to data reported a decade earlier, small-sized omnivorous species were dominant in Ushuaia Bay in 2012. The increased abundance of these species and decrease in the abundance of calanoids (e.g. Drepanopus forcipatus and Eurytemora americana) may reflect the natural year-to-year variability in phytoplankton structure and water physico-chemical properties. However, since this bay suffers from chronic pollution, other explanations, such as the influence of eutrophication on plankton structure, should also be considered. This study provides a baseline for future research on the effects of natural and anthropogenic environmental change on the Beagle Channel, thereby expanding our knowledge of plankton in subantarctic fjords.

Phenology and drivers of the winter–spring phytoplankton bloom in the open Black Sea: The application of Sverdrup’s hypothesis and its refinements

The phenology of the winter–spring phytoplankton bloom in the Black Sea was investigated on the basis of the satellite-derived chlorophyll concentration (Chl) for the recent 18-year period. Data for the 8-day Chl were analysed, together with changes in the nutrient concentration, sea surface temperature (SST), photosynthetically available radiation, wind velocity and duration. Based on Sverdrup’s Critical Depth hypothesis and its recent refinements, the Pulsing-Bloom hypothesis was proposed for the highly stratified waters of the Black Sea. This hypothesis relates the biological response to physical forcing and chemical fluxes to the photic zone and predicts the pulsing growth of phytoplankton and different patterns of phytoplankton changes in the upper layer in winter–spring during cold and regular years. The hypothesis was supported by Chl dynamics and several Chl peaks were observed during winter-spring. Normally, the highest Chl occurred in winter and a spring peak was absent, whereas in cold years, a relatively low Chl in winter was followed by a spring bloom. These events were observed only in 15% of cases and the magnitude of the bloom was associated with the intensity of winter convection that was revealed by the negative inter-annual correlation between the March Chl and the February SST. In contrast, the February Chl was positively correlated with the SST. The proposed hypothesis provides an explanation of this phenomenon on the basis of an alternation between the low-turbulence and deep-mixing regimes. This mechanism was confirmed by the positive relationships between Chl and the duration of light wind during the current period and strong wind in the previous period. Inorganic nitrogen was depleted disproportionately during the winter–spring, whereas the phosphate concentration remained relatively high. Following a cold winter, the highest phosphate concentration and extremely low nitrogen-to-phosphorus molar ratios (2) were observed in the upper 25-m layer in late spring. The regular absence of spring blooms might represent one of the consequences of the regional climate change.

On the spatial–temporal variations in the chlorophyll-a concentration on the Peter the Great Bay shelf during the winter–spring phytoplankton bloom according to satellite and subsatellite data

Chlorophyll-a concentration (Cchl) variations in the cross section within and outside the Peter the Great Bay shelf during different stages of the winter–spring phytoplankton bloom in 2003–2005 has been considered based on a ship (obtained during the R/V Akademik M.A. Lavrent’ev voyage of February 26 to March 9, 2003) and MODIS-Aqua spectroradiometer and the SeaWiFS color-scanner satellite data. A comparison of the Cchl variability obtained from the ship and satellite data indicates that these data are inconsistent. According to satellite data obtained at the MUMM atmospheric correction, the Cchl variability is distorted less than the NIR-correction data. Studying the variations in the coefficients of light absorption by the detritus and yellow substance (adg) and light backscattering by suspended particles (bbp), Cchl, chlorophyll-a fluorescence (Fchl) according to the satellite data allow us to state that the variations in the discrepancy between the satellite and ship Cchl values are mainly caused by the variations in the content of the detritus and yellow substance in water. Based on the satellite data, it has been revealed that the adg values increase with increasing wind mixing after the phytoplankton bloom (about 2–5 km areas where the adg, Cchl, Fchl, and bbp values abruptly increased in 2005, apparently due to eddy formation). It has been indicated that the Fchl characteristic, which is close to Cchl, increases when the favorable conditions for the phytoplankton bloom deteriorate. Therefore, this characteristic cannot be used to identify Cchl under the indicated conditions.

Winter–spring diatom production in Lake Erie is an important driver of summer hypoxia

Abstract Re-eutrophication and harmful algal blooms in Lake Erie have resulted in a renewed call for remedial measures such as reductions of phosphorus loads to the lake's western basin. The action of further nutrient reductions may also reduce the intensity of seasonal central basin hypolimnetic anoxia by reducing algal biomass. However, winter–spring blooms of diatoms have not been fully recognized as a source of algal biomass that might contribute significantly to summer hypoxia. We compared spring and summer phytoplankton abundance in central and western Lake Erie based on monitoring data to show that spring phytoplankton biovolume was 1.5- to 6-fold greater than summer biovolume and that most spring biovolume was composed of filamentous diatoms, primarily Aulacoseira islandica , that is likely supported by an increasing silica load from Lake Huron. The rise of silica export was attributed to the dreissenid mussel invasion and establishment that reduced diatom abundance in Lake Huron and thereby increased silica availability in the receiving water body of Lake Erie. The relationship between phosphorus and winter–spring diatom blooms was unclear, but diatoms probably contributed the majority of the algal biomass that accumulated annually in the hypolimnion of the central basin of Lake Erie. Remedial measures aimed at reducing hypoxia must consider the winter–spring phytoplankton bloom in Lake Erie as an important and reoccurring feature of the lake that delivers a considerable quantity of algal biomass to the profundal zone of the lake.

Mapping the spatial distribution of the biomass and filter‐feeding effect of invasive dreissenid mussels on the winter‐spring phytoplankton bloom in Lake Michigan

Summary The effects of the invasive bivalves Dreissena polymorpha (zebra mussel) and Dreissena rostriformis bugensis (quagga mussel) on aquatic ecosystems, including Lake Michigan, are a topic of current interest to scientists and resource managers. We hypothesised that the winter–spring phytoplankton bloom in Lake Michigan is reduced at locations where the fraction of the water column cleared per day by Dreissena filter feeding approached the net growth rate of phytoplankton, when the water column was not stratified. To test this hypothesis, we compared the spatial distribution of Dreissena filter‐feeding intensity (determined from geostatistical modelling) to the spatial distribution of chlorophyll (determined from satellite remote sensing). To map the spatial distribution of Dreissena biomass and filter‐feeding intensity, we developed a geostatistical model based on point observations of mussel biomass measured in Lake Michigan in 1994/1995, 2000, 2005 and 2010. The model provided fine‐scale estimates of the spatial distribution of biomass for the survey years and provided estimates, with their uncertainty, of total biomass lakewide and within subregions. The approach outlined could be applied more generally to map the distribution of benthic biota in lakes from point observations. Total biomass of Dreissena in Lake Michigan, estimated from the geostatistical model, increased significantly over each five‐year period. The total biomass in units of 106 kg ash‐free dry mass (AFDM) (with 90% confidence interval) was 6 (4–8) in 1994/1995, 18 (14–23) in 2000, 408 (338–485) in 2005 and 610 (547–680) in 2010. From 1994/1995 to 2005, increases were observed in all regions of the lake (northern, central and southern) and in all depth zones (<30, 30–50, 50–90 and >90). However, from 2005 to 2010, for depths of <50 m, biomass declined in the northern region, remained constant in the central region and increased in the southern region; biomass continued to increase in all three lake regions for depths >50 m. The filter‐feeding intensity of Dreissena exceeded the benchmark spring phytoplankton growth rate of 0.06 day−1 in 2005 for depths <50 m (lakewide). In 2010, the filter‐feeding impact exceeded 0.06 day−1 within depths <90 m (lakewide), which greatly increased the spatial area affected relative to 2005. A regression analysis indicated a significant relationship between the reduction in satellite‐derived chlorophyll concentration (pre‐D. r. bugensis period to post‐D. r. bugensis period) and spatially co‐located filter‐feeding intensity (fraction of water column cleared per day) during periods when the water column was not stratified (December to April).

Drivers of the winter–spring phytoplankton bloom in a pristine NW Mediterranean site, the Bay of Calvi (Corsica): A long-term study (1979–2011)

This work is based on a long time series of data collected in the well-preserved Bay of Calvi (Corsica island, Ligurian Sea, NW Mediterranean) between 1979 and 2011, which include physical characteristics (31years), chlorophyll a (chl a, 15years), and inorganic nutrients (13years). Because samples were collected at relatively high frequencies, which ranged from daily to biweekly during the winter–spring period, it was possible to (1) evidence the key role of two interacting physical variables, i.e. water temperature and wind intensity, on nutrient replenishment and phytoplankton dynamics during the winter–spring period, (2) determine critical values of physical factors that explained interannual variability in the replenishment of surface nutrients and the winter–spring phytoplankton bloom, and (3) identify previously unrecognised characteristics of the planktonic ecosystem. Over the >30year observation period, the main driver of nutrient replenishment and phytoplankton (chl a) development was the number of wind events (mean daily wind speed >5ms−1) during the cold-water period (subsurface water ⩽13.5°C). According to winter intensity, there were strong differences in both the duration and intensity of nutrient fertilisation and phytoplankton blooms (chl a). The trophic character of the Bay of Calvi changed according to years, and ranged from very oligotrophic (i.e. subtropical regime, characterised by low seasonal variability) to mesotrophic (i.e. temperate regime, with a well-marked increase in nutrient concentrations and chl a during the winter–spring period) during mild and moderate winters, respectively. A third regime occurred during severe winters characterised by specific wind conditions (i.e. high frequency of northeasterly winds), when Mediterranean “high nutrient – low chlorophyll” conditions occurred as a result of enhanced crossshore exchanges and associated offshore export of the nutrient-rich water. There was no long-term trend (e.g. climatic) in either nutrient replenishment or the winter–spring phytoplankton bloom between 1979 and 2011, but both nutrients and chl a reflected interannual and decadal changes in winter intensity.

The interactive roles of temperature, nutrients, and zooplankton grazing in controlling the winter-spring phytoplankton bloom in a temperate, coastal ecosystem, Long Island Sound

We examined biological, chemical, and physical processes controlling the onset and demise of the winter–spring bloom in the third largest US estuary, Long Island Sound (LIS), during 2010 and 2011. The spring bloom in LIS initiated in the absence of thermal stratification and peaked in early February when water temperatures were at an annual minimum (≤1.0°C). Bloom initiation occurred when phytoplankton cellular growth exceeded zooplankton grazing and bloom demise occurred as temperatures rose and grazing exceeded algal growth. During the bloom collapse, nutrients were drawn down by >90% and the phytoplankton community was nutrient limited. A highly significant (r2 = 0.81, p = 0.001), multivariate linear regression model using the percentage of primary production consumed daily by zooplankton and dissolved silicate concentrations hind-casted the timing and magnitude of the bloom within 10% of observed values each year. Mesocosm experiments performed during the winter–spring bloom demonstrated that higher seawater temperatures (+3.0°C) increased zooplankton densities and grazing rates and decreased phytoplankton biomass. The winter–spring bloom in LIS was controlled by the interaction of phytoplankton growth and zooplankton grazing but not thermal stratification. Phytoplankton growth and zooplankton grazing were, in turn, influenced by nutrient availability and temperature. Continued climatic warming may lessen the intensity of the winter–spring bloom in this and other ecosystems in the future.

Heterotrophic bacterial responses to the winter–spring phytoplankton bloom in open waters of the NW Mediterranean

The response of planktonic heterotrophic prokaryotes to the NW Mediterranean winter–spring offshore phytoplankton bloom was assessed in 3 cruises conducted in March, April–May and September 2009. Bulk measurements of phytoplankton and bacterioplankton biomass and production were complemented with an insight into bacterial physiological structure by single-cell analysis of nucleic acid content [low (LNA) vs. high (HNA)] and membrane integrity (“Live” vs. “Dead” cells). Bacterial production empirical conversion factors (0.82±0.25SEkgCmolleucine−1) were almost always well below the theoretical value. Major differences in most microbial variables were found among the 3 periods, which varied from extremely high phytoplankton biomass and production during the bloom in March (>1gCm−2d−1 primary production) to typically oligotrophic conditions during September stratification (<200mgCm−2d−1). In both these periods bacterial production was ~30mgCm−2d−1 while very large bacterial production (mean 228, with some stations exceeding 500mgCm−2d−1) but low biomass was observed during the April–May post-bloom phase. The contribution of HNA (30–67%) and “Live” cells (47–97%) were temporally opposite in the study periods, with maxima in March and September, respectively. Different relationships were found between physiological structure and bottom-up variables, with HNA bacteria apparently more responsive to phytoplankton only during the bloom, coinciding with larger average cell sizes of LNA bacteria. Moderate phytoplankton–bacterioplankton coupling of biomass and activity was only observed in the bloom and post-bloom phases, while relationships between both compartments were not significant under stratification. With all data pooled, bacteria were only weakly bottom-up controlled. Our analyses show that the biomass and production of planktonic algae and bacteria followed opposite paths in the transition from bloom to oligotrophic conditions.

Modeling the influence of low-salinity water inflow on winter-spring phytoplankton dynamics in the Nova Scotian Shelf–Gulf of Maine region

Previous analyses of SeaWiFS ocean color and hydrographic data [fi, R., Davis, C. S., Chen, C. et al. (2007) Influence of ocean freshening on shelf phytoplankton dynamics. Geophys. Res. Lett., 34, L24607. doi: 10.1029/2007GL032010] have suggested that changes in the intensity of low-salinity Scotian Shelf Water (SSW) inflow can significantly influence the winter-spring phytoplankton dynamics in the Scotian Shelf and Gulf of Maine region. In the present study, a 3-D coupled biological-physical model was applied to examine underlying mechanisms through a quantitative comparison of circulation pattern, water column stability, nutrient/ phytoplankton concentrations and net primary productivity between low and high freshening scenarios. The model results revealed that observed levels of surface freshening can significantly change water column stability and therefore control the winter-spring phytoplankton bloom dynamics in different regions. Freshening caused earlier blooms both on the Scotian Shelf and in the eastern Gulf of Maine, agreeing with inferences drawn from prior empirical analyses. Earlier phytoplankton blooms in the low surface salinity case were followed by earlier depletion of nutrients at the surface along with earlier decline of blooms compared with the high surface salinity case. The model results also suggested that surface water freshening can impede vertical nutrient exchange between surface and deep waters, thus reducing the overall spring primary productivity throughout the region. The coupled model described in this study provides a unique tool to quantify the response of lower trophic level production to climate-scale environmental disturbances in a complex but ecologically important shelf ecosystem that has a history of such alternations in surface salinity.

Annual Primary Production in Narragansett Bay with no Bay-Wide Winter–Spring Phytoplankton Bloom

Primary production was estimated over the annual cycle from 14C incubations conducted in 5m deep enclosures and modeled for 16 stations in Narragansett Bay with data from biweekly surveys in which light, chlorophyll, attenuation coefficients and other parameters were measured. Annual values ranged from 160gCm−2 y−1 in the lower West Passage to 619gCm−2 y−1 at the mouth of the Providence River. The annual bay-wide, area mean fell near the middle of this range at 323gCm−2 y−1 and was not apparently different from previous surveys. In the 1998 warm, El Niño winter, no bay-wide winter–spring phytoplankton flowered. Bloom limitation was correlated with warm temperatures which may have stimulated grazing rates. The lack of a bloom did not change annual levels of primary production but this alteration in carbon flow may impact macrofauna in the benthic infauna community.

Changes in the development of the winter-spring phytoplankton bloom in the Bay of Calvi (NW Mediterranean) over the last two decades: a response to changing climate?

The development of the winter-spring phytoplankton bloom was investigated in the Bay of Calvi (Corsica, Ligurian Sea, northwestern Mediterranean) in 1979, 1986, 1988, 1997 and 1998. A drastic reduction of phytoplankton biomass was evidenced over the last 2 decades, in relation to long- term changes in climatic and environmental conditions. Between 1979 and 1998, the monthly aver- aged chlorophyll a concentrations at 1 m decreased by about 80% during February, March and April. Simultaneously, major changes to hydrodynamic conditions include warmer water, overall decrease of salinity at 10 m depth, longer periods of bright sunshine and lower wind stress. The changes in environmental conditions were large enough to affect the vertical stability of the water column dur- ing the winter-spring period and to reduce nutrient replenishment of the surface layer prior to the usual period of phytoplankton growth. Until 1986, the main factor driving nutrient replenishment was the winter upward mixing of nutrient-rich deep waters, while the progressive reduction of mixing from 1988 induced nutrient limitation of surface waters in the last decade. The following hypotheses on changes in the development of the winter-spring phytoplankton bloom are made: (1) Until 1986, phytoplankton peaks took place in relatively high-nutrient waters and were diatom-dominated. (2) Between 1986 and 1988, decreasing Si availability led to Si limitation which caused a reduction in diatom abundance. This resulted in the disappearance of the diatom-dominated pulses and in lower phytoplankton biomass and was accompanied by a shift toward non-siliceous phytoplankton. (3) In 1988, 1997 and 1998, decreasing nitrate availability led to nitrate limitation, thus explaining the pro- gressive reduction in non-siliceous phytoplankton biomass. Other, associated changes in benthos assemblages and ichthyofauna are documented. The conclusions from the Bay of Calvi are extended to the whole western Corsican coast. This confirms that the Mediterranean reacts rapidly to external perturbations, which are driven by climate change in that particular area.

Winter–spring transition of phytoplankton chlorophyll and inorganic nutrients on Georges Bank

Phytoplankton chlorophyll and inorganic nutrients were measured monthly during the winter–spring transition in 1997 on Georges Bank as part of the US Globec Program. We measured only chlorophyll and hydrography in January and June; nutrients were included in the February, March, April and May cruises. The winter–spring phytoplankton bloom on the Bank began early in 1997. Phytoplankton chlorophyll a concentrations were lowest in January (<1.0 μg l −1), but by February concentrations ranged between 2 and 3 μg l −1 on the western half of the top of the Bank (e.g., inside the 60 m isobath). Near-surface nitrate+nitrite concentrations in February were less than 6 μM over most of the Bank and below 4 μM on the western half. Near-surface silicate concentrations were generally less than 6 μM over most of the Bank in February, and were reduced to 2–3 μM inside the 60 m isobath; concentrations were depleted most on the western half of the top of the Bank, where they were less than 1 μM. Scotian Shelf Water intruded onto the Bank in February and remained distinct through April; near-surface nutrient concentrations in this Scotian Shelf Water in March were also low, and chlorophyll concentrations were high (4–5 μg l −1). The spring bloom was still underway in March, with increased chlorophyll concentrations spreading over most of the Bank. Silicate appeared to be the limiting nutrient beginning as early as February, with concentrations becoming depleted in March before nitrate+nitrite did. During April and May both silicate and nitrate concentrations were reduced to less than 1 μM in the near-surface waters over much of the top of the Bank; however, there were indications that silicate was being recycled on some parts of the Bank in May, which, in addition to recycled nitrogen, may have contributed to locally high chlorophyll concentrations observed in May and June. Higher near-surface nutrient concentrations also ringed the deeper edges of the Bank in late spring, where chlorophyll concentrations were generally high (greater than 5 μg l −1) but also very patchily distributed.