Onset Of Bloom Research Articles

Seasonal variations in the contribution of zooplankton fecal pellets to the particulate organic carbon fluxes over the slopes of the Pacific Arctic region

As part of the Korea Arctic Mooring System (KAMS), sequential sediment traps were deployed at KAMS1 over the East Siberian Sea slope (∼115 and ∼335 m) and at KAMS2 over the Chukchi Sea slope (325 m) to collect sinking particles from August 2017 to August 2019. Fecal pellet carbon (FPC) fluxes and their contribution to the particulate organic carbon (POC) fluxes were measured to assess the role of zooplankton fecal pellets in the biological carbon pump at both sites. FPC fluxes increased at the onset of an under-ice bloom and peaked during the melt period at both sites in 2018. At KAMS1, a remarkable increase in FPC fluxes reflected the enhanced grazing of large copepods during the anomalously productive spring and summer of 2018, however their contributions to the POC fluxes mostly remained <10%. At KAMS2, relatively low FPC fluxes during the under-ice bloom suggested the export of a larger proportion of pellets produced by small copepods. Sustained FPC fluxes from January to May 2018 at KAMS2 contributed up to 24% of the POC fluxes, possibly resulting from pellet production by overwintering copepods grazing on particles laterally transported into the region in the presence of ice. These results indicate that despite their limited contribution to the POC fluxes, FPC fluxes varied with food availability, zooplankton community structure, and hydrographic conditions over the East Siberian and Chukchi Sea slopes.

Functional diversity of bacterial microbiota associated with the toxigenic benthic dinoflagellate Prorocentrum.

Interactions between bacterial microbiota and epibenthic species of the dinoflagellate Prorocentrum may define the onset and persistence of benthic harmful algal blooms (bHABs). Chemical ecological interactions within the dinoflagellate phycosphere potentially involve a complex variety of organic molecules, metabolites, and toxins, including undefined bioactive compounds. In this study, the bacterial diversity and core members of the dinoflagellate-associated microbiota were defined from 11 strains of three epibenthic Prorocentrum species, representing three geographically disjunct locations within Mexican coastal waters. Microbiota profiles in stable monoclonal Prorocentrum cultures were obtained by sequencing amplicons of the V3-V4 region of the 16S rRNA gene. Thirteen classes of bacteria were identified among dinoflagellate clones, where Alphaproteobacteria, Gammaproteobacteria, and Bacteroidia were consistently dominant. The bacterial community structure exhibited significantly different grouping by the location of origin of dinoflagellate clones. No significant diversity difference was found among free-living or unattached bacteria in the dinoflagellate culture medium (M) compared with those in closer association with the dinoflagellate host cells (H). Twelve taxa were defined as core members of the bacterial assemblage, representing the genera Algiphilus, Cohaesibacter, Labrenzia, Mameliella, Marinobacter, Marivita, Massilia, Muricauda, Roseitalea, and an unclassified member of the Rhodobacteraceae. The core members are inferred to significantly contribute to primary and secondary metabolic functions, but no direct correlation with dinoflagellate toxigenicity was apparent. Overall the bacterial profile and implied gene functionality indicated a suite of positive interactions, suggesting either mutualism or commensalism with the dinoflagellate. The further characterization and interpretation of specific gene functions and interactions between bacteria and dinoflagellates, such as epibenthic members of genus Prorocentrum, are key to understanding their role in toxigenesis and bHAB development.

Recurring seasonality exposes dominant species and niche partitioning strategies of open ocean picoeukaryotic algae

Ocean spring phytoplankton blooms are dynamic periods important to global primary production. We document vertical patterns of a diverse suite of eukaryotic algae, the prasinophytes, in the North Atlantic Subtropical Gyre with monthly sampling over four years at the Bermuda Atlantic Time-series Study site. Water column structure was used to delineate seasonal stability periods more ecologically relevant than seasons defined by calendar dates. During winter mixing, tiny prasinophytes dominated by Class II comprise 46 ± 24% of eukaryotic algal (plastid-derived) 16S rRNA V1-V2 amplicons, specifically Ostreococcus Clade OII, Micromonas commoda, and Bathycoccus calidus. In contrast, Class VII are rare and Classes I and VI peak during warm stratified periods when surface eukaryotic phytoplankton abundances are low. Seasonality underpins a reservoir of genetic diversity from multiple prasinophyte classes during warm periods that harbor ephemeral taxa. Persistent Class II sub-species dominating the winter/spring bloom period retreat to the deep chlorophyll maximum in summer, poised to seed the mixed layer upon winter convection, exposing a mechanism for initiating high abundances at bloom onset. Comparisons to tropical oceans reveal broad distributions of the dominant sub-species herein. This unparalleled window into temporal and spatial niche partitioning of picoeukaryotic primary producers demonstrates how key prasinophytes prevail in warm oceans.

Environmental controls and phenology of sea ice algal growth in a future Arctic

The future of Arctic sea ice algae is examined using a regional ocean and sea ice biogeochemical model, with a simulation from 1980 to 2085, considering a future scenario with strong warming. To analyze the impacts of climate change, we computed key dates in the development of sympagic blooms, corresponding to the occurrence of specific growth conditions, and designed diagnostics of ice algal phenology to estimate the onset and peak of blooms. These diagnostics help understand how the timing of light and nutrient availability governs the growth of ice algae and how environmental controls will be altered by climate change across regions. With thinner ice, photosynthetically active radiation in bottom ice will reach levels sufficient for growth earlier, resulting in a better synchrony of high levels of light and nutrients. Increases in snow cover can potentially offset the effect of thinner ice, leading to shorter periods of favorable growth conditions in certain regions. The loss of sea ice cover before the late 21st century only impacts sympagic blooms at lower latitudes, as the timing of sea ice break-up shows little change relative to other key dates at higher latitudes. In response to climate change, the model simulates a modified spatial distribution of blooms, with the emergence of highly productive areas and the loss of blooms in other regions. However, the changes in the timing of growth conditions do not substantially alter the timing of blooms, and both onset and peak ice algae see little change. The simulated lack of sensitivity of bloom onset is attributed to the delay in sea ice freeze-up projected by the model, causing a reduction of overwintering ice algae. The resulting lower initial biomass at the beginning of spring then causes a delay in the development of blooms, offsetting earlier light from thinner ice.

Analysis of the Spatiotemporal Distribution of Algal Blooms and Its Driving Factors in Chaohu Lake Based on Multi-source Datasets

Eutrophication and harmful algae blooms are one of the common ecological and environmental problems faced by freshwater lakes all over the world. As a typical inland freshwater lake, Chaohu Lake exhibits a high level of eutrophication and algae blooms year-round and shows a spatiotemporal difference in different regions of the lake. In order to understand the basic regularity of the development and outbreak of algal blooms in Chaohu Lake, the data from the comprehensive water observation platform and remote sensing were integrated to obtain the spatiotemporal distribution of algal blooms from 2015 to 2020. Then, an evaluation model based on Boosted Regression Trees (BRT) was constructed to quantitatively assess the importance and interactions of various environmental factors on algal blooms at different stages. The results indicated that:① The occurrence of algal blooms in Chaohu Lake exhibited significant seasonal variations, with the cyanobacteria beginning to recover in spring and bring about a light degree of algal blooms in the western and coastal areas of Chaohu Lake. The density of cyanobacteria reached its maximum in summer and autumn, accompanied by moderate and severe degrees of algal bloom outbreaks. ② During the non-outbreak period, the variation in the cyanobacteria density was greatly affected by physical and chemical factors, which explained 80.3% of the variance in the change in cyanobacteria density. The high concentrations of dissolved oxygen content in the water column and the weak alkalinity (7.2-7.6) and appropriate water temperature (about 3℃) provided a favorable environmental condition for the breeding and growth of cyanobacteria. In addition, the onset of algal blooms was closely related to the air temperature steadily passing through the threshold. According to the statistics, the date of first outbreak of algal blooms in Chaohu Lake was 11 days or so after the air temperature steadily remained above 7℃. ③ During the outbreak period, the occurrence of algal blooms was influenced by the combination of cyanobacterial biomass and meteorological conditions such as temperature, wind speed, and sunshine duration. The cumulative contribution ratio of the four factors was as high as 95%, and each factor had an optimal interval conductive to the outbreak of algal blooms. Furthermore, the results of multi-factor interaction analysis indicated a larger probability of the outbreak of algal blooms in Chaohu Lake under the combined effect of high cyanobacteria density, suitable temperature, and the breeze. This study analyzed and revealed the spatiotemporal characteristics and the dominant influencing factors of algal blooms in Chaohu Lake at different stages, which could provide the scientific basis for the prediction, early warning, and disposal of algal blooms under the context of climate change.

Mapping Potential Timing of Ice Algal Blooms From Satellite

AbstractAs Arctic sea ice and its overlying snow cover thin, more light penetrates into the ice and upper ocean, shifting the phenology of algal growth within the bottom of sea ice, with cascading impacts on higher trophic levels of the Arctic marine ecosystem. While field data or autonomous observatories provide direct measurements of the coupled sea ice‐algal system, they are limited in space and time. Satellite observations of key sea ice variables that control the amount of light penetrating through sea ice offer the possibility to map the under‐ice light field across the entire Arctic basin. This study provides the first satellite‐based estimates of potential sea ice‐associated algal bloom onset dates since the launch of CryoSat‐2 and explores how a changing snowpack may have shifted bloom onset timings over the last four decades.

Effects of typhoon events on coastal hydrology, nutrients, and algal bloom dynamics: Insights from continuous observation and machine learning in semi-enclosed Zhanjiang Bay, China

Typhoons can induce variations in hydrodynamic conditions and biogeochemical processes, potentially escalating the risk of algal bloom occurrences impacting coastal ecosystems. However, the impacts of typhoons on instantaneous changes and the mechanisms behind typhoon-induced algal blooms remain poorly understood. This study utilized high-frequency in situ observation and machine learning model to track the dynamic variations in meteorological, hydrological, physicochemical, and Chlorophyll-a (Chl-a) levels through the complete Typhoon Talim landing in Zhanjiang Bay (ZJB) in July 2023. The results showed that a delayed onset of algal bloom occurring 10 days after typhoon's arrival. Subsequently, as temperatures reached a suitable range, with an ample supply of nutrients and water stability, Chl-a peaked at 121.49 μg L−1 in algal bloom period. Additionally, water temperature and air temperature decreased by 1.61 °C and 2.8 °C during the typhoon, respectively. In addition, wind speed and flow speed increased by 1.34 and 0.015 m s−1 h−1 to peak values, respectively. Moreover, the slow decline of 8.2 % in salinity suggested a substantial freshwater input, leading to an increase in nutrients. For instance, the mean DIN and DIP were 2.2 and 8.5 times higher than those of the pre-typhoon period, resulting in a decrease in DIN/DIP (closer to16) and the alleviation of P limitation. Furthermore, pH and dissolved oxygen (DO) were both low during the typhoon period and then peaked at 8.93 and 19.05 mg L−1 during the algal bloom period, respectively, but subsequently decreased, remaining lower than those of the pre-typhoon period. A preliminary learning machine model was established to predict Chl-a and exhibited good accuracy, with R2 of 0.73. This study revealed the mechanisms of eutrophication status formation and algal blooms occurrence in the coastal waters, providing insights into the effects of typhoon events on tropical coastal biogeochemistry and ecology.

Biotic transformation of methylmercury at the onset of the Arctic spring bloom

Despite the lack of local anthropogenic mercury sources, methylated mercury (MeHg) concentrations in Arctic biota are higher than in biota from lower latitudes. The main entry route occurs during the bioconcentration of seawater monomethylmercury (MMHg) into phytoplankton. Despite the known seasonal changes in biological activity in the region, little is known about the seasonal cycling of total mercury (THg) and MeHg in the Arctic Ocean. Here, we report the concentrations of THg and MeHg in seawater sampled from the northwestern Barents Sea water column during late winter and spring. In the upper 500 m, the THg concentrations are significantly higher in spring (0.64 ± 0.09 pmol L-1) compared to late winter (0.53 ± 0.07 pmol L-1), driven by seasonal inputs to surface waters from atmospheric deposition and the dynamics of changing sea ice conditions. Contrastingly, the MeHg concentrations in spring were significantly lower (41 ± 39 fmol L-1) compared to late winter (85 ± 42 fmol L-1). We suggest that most MeHg is biotically demethylated by both phytoplankton and bacteria, with additional losses from photodemethylation and evasion. Our observations highlight the importance of demethylation during potential uptake of methylmercury coinciding with the Arctic spring bloom. Lastly, we use our new data together with previously published seasonal data in the region to construct a simplified seasonal mercury cycle in an Arctic marginal ice zone.

Optimal phenology of life history events in Calanus finmarchicus: exit from diapause in relation to interannual variation in spring bloom timing and predation.

Respiration of lipids by copepods during diapause (overwintering dormancy) contributes to ocean carbon sequestration via the seasonal lipid pump (SLP). Parameterizing this flux in predictive models requires a mechanistic understanding of how life history adaptation in copepods shapes their timing of exit from diapause. We investigate the optimal phenology of Calanus finmarchicus in the Norwegian Sea using an individual-based model in which diapause exit is represented as a trait characterized by phenotypic mean and variance. Without interannual variability, optimal exit correlated with the onset of the spring phytoplankton bloom and phenotypic variance was of no benefit. In contrast, copepods endured reduced fitness and adopted bet-hedging strategies when exposed to interannual variability in bloom timing and predation: later exit from diapause and phenotypic variance maintained adult numbers in anomalous late-bloom years. Exit nevertheless remained well before the peak of the bloom which is a favorable strategy when low predation early in the year enhances survival of eggs and early developmental stages. Our work highlights the complex interactions between C. finmarchicus and its environment and the need for improved understanding of bet-hedging strategies and the cues of diapause exit to progress the representation of the SLP in global biogeochemical models.

Nutrient fluxes from recent deposits of fine-grained, organic-rich sediments in a Florida estuary

Nutrient fluxes from fine-grained, organic-rich sediments in estuaries can hasten the onset and progression of eutrophication and harmful algal blooms. Targeted efforts to manage degraded sediments and improve estuarine water quality require a better understanding of physicochemical controls and the relative importance of benthic fluxes. Toward that end, we determined fluxes from organic-rich, high porosity sediments deposited during the past 5-6 decades along 60 km of the Indian River Lagoon, a barrier island lagoon in Florida, USA. Highly bioavailable ammonium and phosphate were the predominant chemical forms of interstitial nitrogen and phosphorus in these highly-reducing sediments. Median fluxes of ammonium and phosphate were 320 µmol m-2 h-1 and 11 µmol m-2 h-1, respectively. Fluxes were 3-10 times greater when sediment temperatures were &amp;gt;28°C and interstitial sulfide concentrations were &amp;gt;1 mM. Temperature-compensated fluxes of ammonium and phosphate were significantly correlated with sediment organic matter content; total organic carbon averaged 5.3 ± 2.4% and the maximum was 12.4% for the sediments studied. Fine-scale physical probing, plus lidar data, showed that these organic-rich sediments covered &amp;lt;10% of our study area; however, fluxes from these sediments were estimated to supply 20-40% of internal + external annual loads of nitrogen and phosphorus. Furthermore, 60% of nitrogen and phosphorus fluxes from sediments in the northern Indian River Lagoon came from just 22% of the total surface area. Lagoon segments with high benthic fluxes overlapped in part with areas prone to harmful algal blooms. Effective strategies to manage degraded sediments in the Indian River Lagoon depend on knowing the relative magnitude of internal loading of nutrients as well as appropriate techniques to mitigate sediment fluxes.

A paleoecological investigation of recent cyanobacterial blooms and their drivers in two contrasting lakes

Cyanobacterial blooms are one of the most significant threats to global water security and freshwater biodiversity. Interactions among multiple stressors, including habitat degradation, species invasions, increased nutrient runoff, and climate change, are key drivers. However, assessing the role of anthropogenic activity on the onset of cyanobacterial blooms and exploring response variation amongst lakes of varying size and depth is usually limited by lack of historical records. In the present study we applied molecular, paleolimnological (trace metal, Itrax-µ-XRF and hyperspectral scanning, chronology), paleobotanical (pollen) and historical data to reconstruct cyanobacterial abundance and community composition and anthropogenic impacts in two dune lakes over a period of up to 1200 years. Metabarcoding and droplet digital PCR results showed very low levels of picocyanobacteria present in the lakes prior to about CE 1854 (1839–1870 CE) in the smaller shallow Lake Alice and CE 1970 (1963–1875 CE) in the larger deeper Lake Wiritoa. Hereafter bloom-forming cyanobacteria were detected and increased notably in abundance post CE 1984 (1982–1985 CE) in Lake Alice and CE 1997 (1990–2007 CE) in Lake Wiritoa. Currently, the magnitude of blooms is more pronounced in Lake Wiritoa, potentially attributable to hypoxia-induced release of phosphorus from sediment, introducing an additional source of nutrients. Generalized linear modelling was used to investigate the contribution of nutrients (proxy = bacterial functions), temperature, redox conditions (Mn:Fe), and erosion (Ti:Inc) in driving the abundance of cyanobacteria (ddPCR). In Lake Alice nutrients and erosion had a statistically significant effect, while in Lake Wiritoa nutrients and redox conditions were significant.

Monitoring the Efficiency of a Catchment Restoration to Further Reduce Nutrients and Sediment Input into a Eutrophic Lake

The restoration of eutrophic river and lake ecosystems is an important task that has been conducted in numerous ways and at many locations around the world. However, such improvements of water quality are often temporary, as such ecosystems are dynamic, and restoration measures must be reassessed and modified. The restored catchment of a shallow eutrophic lake, Lake Seeburg, in central Germany, was monitored over a 13-month period. The restoration of the inflowing river a decade earlier included riverbed prolongation, gradient reduction, and the construction of wetlands upstream, which reduced the sediment input and silting up of the lake. As nutrient fluxes in the tributaries were still high, these restoration measures seemed to be insufficiently effective. This study aimed to locate nutrient hotspots and quantify the nutrient balances of the catchment. Nitrogen and phosphorous concentrations, river discharge, hydrochemical parameters (pH, temperature, oxygen concentrations) and turbidity, as a proxy for suspended particulate matter (SPM), were monitored monthly. Our data show that the lake functions as a nitrogen sink, whereas the phosphorous fluxes follow a seasonal trend with the negative balance in winter turning into a positive balance in summer with the onset of cyanobacterial blooms. The release of phosphorous from the wetland throughout the year indicates supersaturation and thus a permanent input of phosphorous into the lake. Consequently, phosphorus loading in the lake is quite high, fostering eutrophication. Furthermore, the very low precipitation rates during the study highlighted that the lake was not only controlled by external nutrient loads but rather was sustained by high internal phosphorous loading. Consequently, the remediation action of creating the wetland to restore the sedimentation trap and nutrient accumulation capacity was not sufficient.

Feeding Behavior Responses of the Small Copepod, Paracalanus parvus, to Toxic Algae at Different Concentrations.

The feeding relationship between copepods and phytoplankton has immense ecological significance. This study investigated the feeding behavior of copepods by studying the feeding selectivity of Paracalanus parvus, a key small copepod species, using a high-speed camera. The feeding behavior of P. parvus separately fed on three algae, Prorocentrum minimum, Alexandrium minutum, and Thalassiosira weissflogii, was studied at five different concentrations. The factors characterizing feeding behavior, including the beating frequency (BF), beating time (BT), and rejection behavior, were analyzed. The average BT and BF of P. parvus fed on toxic algae were significantly lower than those of copepods fed on nontoxic algae, indicating that the toxic algae negatively affected their feeding behavior. There were no significant differences in feed rejection among the three algae during the short period of experimentation, indicating that the rejection behavior was insignificant in the early period (within 20 min) of feeding on toxic algae. The feeding behavior was inhibited when the concentration reached 250 cells/mL. The BT was initially affected at increasing concentrations followed by the BF, and P. minimum and A. minutum reduced the BF at concentrations of 250 and 1000 cells/mL, respectively. Analysis of the average BFs revealed that P. parvus was more significantly affected by P. minimum containing diarrheal shellfish poison than by A. minutum containing paralytic shellfish poison. The BF of copepods fed on P. minimum was significantly lower than that of copepods fed on A. minutum at 250-500 cells/mL but was not significantly different from that at 1000 cells/mL. This indicated that the inhibitory effect of P. minimum on the feeding behavior was more significant at concentrations observed at the onset of red tide blooms (0.25-0.5 × 102 cells/mL), but insignificant at concentrations reaching those in advanced red tides (>103 cells/mL). This study demonstrates that toxic dinoflagellates alter the feeding behavior of copepods and describes the variations in their feeding response to different algal species and concentrations. The findings provide crucial insights for further studies on the feeding relationship between copepods and phytoplankton and on functional assessment of plankton ecosystems.

In situ cell division and mortality rates of SAR11, SAR86, Bacteroidetes, and Aurantivirga during phytoplankton blooms reveal differences in population controls.

Net growth of microbial populations, that is, changes in abundances over time, can be studied using 16S rRNA fluorescence in situ hybridization (FISH). However, this approach does not differentiate between mortality and cell division rates. We used FISH-based image cytometry in combination with dilution culture experiments to study net growth, cell division, and mortality rates of four bacterial taxa over two distinct phytoplankton blooms: the oligotrophs SAR11 and SAR86, and the copiotrophic phylum Bacteroidetes, and its genus Aurantivirga. Cell volumes, ribosome content, and frequency of dividing cells (FDC) co-varied over time. Among the three, FDC was the most suitable predictor to calculate cell division rates for the selected taxa. The FDC-derived cell division rates for SAR86 of up to 0.8/day and Aurantivirga of up to 1.9/day differed, as expected for oligotrophs and copiotrophs. Surprisingly, SAR11 also reached high cell division rates of up to 1.9/day, even before the onset of phytoplankton blooms. For all four taxonomic groups, the abundance-derived net growth (-0.6 to 0.5/day) was about an order of magnitude lower than the cell division rates. Consequently, mortality rates were comparably high to cell division rates, indicating that about 90% of bacterial production is recycled without apparent time lag within 1 day. Our study shows that determining taxon-specific cell division rates complements omics-based tools and provides unprecedented clues on individual bacterial growth strategies including bottom-up and top-down controls. IMPORTANCE The growth of a microbial population is often calculated from their numerical abundance over time. However, this does not take cell division and mortality rates into account, which are important for deriving ecological processes like bottom-up and top-down control. In this study, we determined growth by numerical abundance and calibrated microscopy-based methods to determine the frequency of dividing cells and subsequently calculate taxon-specific cell division rates in situ. The cell division and mortality rates of two oligotrophic (SAR11 and SAR86) and two copiotrophic (Bacteroidetes and Aurantivirga) taxa during two spring phytoplankton blooms showed a tight coupling for all four taxa throughout the blooms without any temporal offset. Unexpectedly, SAR11 showed high cell division rates days before the bloom while cell abundances remained constant, which is indicative of strong top-down control. Microscopy remains the method of choice to understand ecological processes like top-down and bottom-up control on a cellular level.

The summer bacterial and archaeal community composition of the northern Barents Sea

Climate change related alterations in the Arctic have influences on the marine ecosystems, in particular on phytoplankton bloom dynamics. Since phytoplankton blooms are the main provider of carbon sources to the microbial loop, the bacterial and archaeal community are affected by the changes as well. Warmer water and less sea ice can lead to an earlier onset of phytoplankton blooms and consequently also to changes in the bacterial and archaeal community dynamics throughout Arctic summers. Here, we compared the bacterial and archaeal community composition during three summers (2018, 2019, and 2021) along a transect from the Barents Sea to the Arctic Ocean north of Svalbard. We used 16S rRNA gene sequencing to investigate changes in the communities in time and space. The main results showed that, Gammaproteobacteria (Nitrincolaceae), Bacteroidia (Polaribacter), and Alphaproteobacteria (SAR11 clade 1a members) dominated the bacterial and archaeal community in the surface waters but varied in abundance patterns between the years. The variations are potentially a result of different phytoplankton bloom stages and consequently differences in the availability of carbon sources. The distinctly different deep water communities were dominated by Candidatus Nitrosopumilus, Marinimicrobia, and members of the SAR324 clade in all years. The results indicate that changes in phytoplankton bloom dynamics can influence bacterial and archaeal community and thereby marine carbon cycling in surface waters, although direct links to the effects of global warming remain uncertain.

Biogeochemical‐Argo floats show that chlorophyll increases before carbon in the high‐latitude Southern Ocean spring bloom

AbstractIn the Southern Ocean, phytoplankton blooms are an annually recurring prominent feature that play a significant role in ocean CO2 uptake. Understanding the timing of the phytoplankton bloom is necessary to provide insights into the underlying physiological drivers, for the study of ecosystem dynamics and consequent patterns in downward carbon export. Previous studies have used chlorophyll (chl) and particulate organic carbon, from either satellites or biogeochemical‐Argo (BGC‐Argo) floats, to investigate bloom phenology, but provide inconsistent findings regarding bloom timing. Here, we compare bloom dynamics based on three diagnostics from 7114 BGC‐Argo float profiles, south of 60°S. Bloom onset consistently occurs earlier when calculated using chl than when based on phytoplankton carbon or nitrate uptake, and the decoupling increases with latitude. This suggests that phytoplankton synthesize increased chl to acclimate to low‐light conditions, before increasing their biomass. These results highlight the importance of considering phytoplankton physiology when choosing proxies for phytoplankton growth.

Long-term shift and recent early onset of chlorophyll-a bloom and coastal upwelling along the southern coast of Java

Long-term change in the timing of coastal upwelling due to climate variations alters the heat budget and biogeochemical balance in the regional ocean and is an important issue in local fisheries. In this study, we investigated decadal changes in the onset of coastal upwelling along the southern coast of Java over the past two decades (2003–2020) based on the timing of chlorophyll-a (Chl-a) bloom. We estimated the bloom from satellite Chl-a concentration data. On average, the onset of coastal upwelling observed (the first Chl-a bloom of the year) was around mid-June. In the most recent decade (2011–2020), earlier-onset upwelling (before early June) was observed frequently, and the linear trend for the onset date during 2003–2020 was about 2 weeks earlier/decade. To explore the causes of the change in the timing of the upwelling, we focused on the season (April–June) during which these earlier upwelling onsets occurred, and investigated decadal changes in atmosphere and ocean conditions associated with climate change. While sea surface temperature (SST) trends reflected a basin-wide warming pattern in the Indian Ocean, warming was not significant in the southeastern Indian Ocean. During the onset period of coastal upwelling, significant SST warming trends were also observed west of Sumatra. In association with the SST warming pattern, enhanced convective activity and convergent zonal winds around Sumatra were observed. Atmospheric forcing revealed trends favoring Ekman downwelling in the equatorial eastern Indian Ocean and upwelling in the southeastern Indian Ocean, which was consistent with the trends in thermocline depth. This study provides the first results regarding the recent decadal shift in the onset timing of coastal upwelling. Ongoing monitoring is needed to better understand the long-term change of the upwelling system in the eastern tropical Indian Ocean.

Toxicity-mediated regime shifts in a contaminated nutrient-plankton system.

In this article, we contemplate the dynamics of a three-tier system of nutrient, phytoplankton, and zooplankton with a gestation delay of discrete type and a distributed delay in nutrient recycling. Phytoplankton secretion-mediated alteration in the grazing pattern of zooplankton is encapsulated by a Monod-Haldane functional response. We carry out global sensitivity analysis for identifying the crucial model parameters having a significant impact on zooplankton density. The system potentially exhibits bistable configurations under identical ecological conditions by allowing different bifurcation scenarios, including multiple saddle-node and transcritical bifurcations with varying input rates of nutrients and inhibitory effects of phytoplankton against zooplankton. We observe that the gestation delay in zooplankton is responsible for the emergence of noxious bloom events. Interestingly, when the delay parameter crosses a threshold, the system experiences chaotic disorder, which prognosticates the onset of irregular bloom. Furthermore, by adding Gaussian white noise, we have extended the deterministic model to its stochastic counterpart. We found that white noise appears to regulate the survival and extinction of interacting populations. Comprehensive numerical simulations are consistent with mathematical results prognosticated by linear analysis.

Precision Monitoring of Honey Bee (Hymenoptera: Apidae) Activity and Pollen Diversity during Pollination to Evaluate Colony Health.

Certain crops depend upon pollination services for fruit set, and, of these, almonds are of high value for Australia. Stressors, such as diseases, parasites, pesticides, and nutrition, can contribute to honey bee Apis mellifera L. colony decline, thereby reducing bee activity and pollination efficiency. In Australia, field studies are required to monitor honey bee health and to ascertain whether factors associated with colony decline are impacting hives. We monitored honey bee colonies during and after pollination services of almond. Video surveillance technology was used to quantify bee activity, and bee-collected pollen was periodically tested for pesticide residues. Plant species diversity was also assessed using DNA metabarcoding of the pollen. Results showed that bee activity increased in almond but not in bushland. Residues detected included four fungicides, although the quantities were of low risk of oral toxicity to bees. Floral diversity was lower in the pollen collected by bees from almonds compared to bushland. However, diversity was higher at the onset and conclusion of the almond bloom, suggesting that bees foraged more widely when availability was low. Our findings suggest that commercial almond orchards may sustain healthier bee colonies compared to bushland in early spring, although the magnitude of the benefit is likely landscape-dependent.

Algal population growth and dynamics of Asan Wetland

A one year study of the phytoplankton community composition was carried out in the Asan wetland, a reservoir fed by River Yamuna in Uttarakhand India. In terms of bio-volume, phytoplankton community was generally dominated by Bacillariophyceae. Mean phytoplankton standing crops were highest in the wetland. The frequency and severity of algal blooms was increased significantly. To control their expansion, it was essential to identify the factors responsible for blooming of waters. Nutrient enrichment (mainly due to anthropogenic activities) and environmental factors (including the climate change) were considered the major catalyst for onset, proliferation and development of blooms. The phytoplankton of the Asan wetland was studied for one year with physical and chemical variables in relation to a pollution gradient. Analysis of the physical and chemical variables and phytoplankton density indicated that the wetland is experiencing heavy pressure of pollution due to anthropogenic activities. The dominant phytoplankton community mainly comprises of family, Chlorophyceae, Bacillariophyceae and Myxophyceae. Physical factors, though vital, had an indirect effect in facilitating the interaction among various available nutrients. In terms of phytoplankton density and diversity common genera observed include Chlorella, Chlaymydomonas, Spirogyra, Ulothrix, Hydrodictyon, Cladophora, Cosmarium, Chlorococcum, Oedogonium, Microspora, Desmidium, Chara, Zygenema, Syndesmus, Volvox, Ceratoneis, Amphora, Caloneis, Fragilaria, Navicula, Synedra, Diatoms, Gomphonema, Pinnularia, Melosira, Tabellaria, Denticula, Cymbella, Cyclotella, Nostoc, Anabaena, Oscillatoria, Rivularia, Coccochloris and Phormidium. Several genera were found most prominent during the study period having no seasonal impact on their abundance and variation. The spatial and temporal patterns observed in some of these dominant species were attributable to patterns in key environmental variables including temperature, flow, pH, dissolved oxygen and nutrient concentrations.