Decline Of Phytoplankton Bloom Research Articles

Light supports cell-integrity and growth rates of taxonomically diverse coastal photoheterotrophs.

Despite the widespread distribution of proteorhodopsin (PR)-containing bacteria in the oceans, the use of light-derived energy to promote bacterial growth has only been shown in a few bacterial isolates, and there is a paucity of data describing the metabolic effects of light on environmental photoheterotrophic taxa. Here, we assessed the effects of light on the taxonomic composition, cell integrity and growth responses of microbial communities in monthly incubations between spring and autumn under different environmental conditions. The photoheterotrophs expressing PR in situ were dominated by Pelagibacterales and SAR116 in July and November, while members of Euryarchaeota, Gammaproteobacteria and Bacteroidetes dominated the PR expression in spring. Cell-membrane integrity decreased under dark conditions throughout most of the assessment, with maximal effects in summer, under low-nutrient conditions. A positive effect of light on growth was observed in one incubation (out of nine), coinciding with a declining phytoplankton bloom. Light-enhanced growth was found in Gammaproteobacteria (Alteromonadales) and Bacteroidetes (Polaribacter and Tenacibaculum). Unexpectedly, some Pelagibacterales also exhibited higher growth rates under light conditions. We propose that the energy harvested by PRs helps to maintain cell viability in dominant coastal photoheterotrophic oligotrophs while promoting the growth of some widespread taxa benefiting from the decline of phytoplankton blooms.

Algicidal potential of cultivable bacteria from pelagic waters against the toxic dinoflagellate Pyrodinium bahamense (Dinophyceae)

Associated and algicidal bacteria play roles in the succession and decline of phytoplankton blooms, including those of harmful algal bloom (HAB)-forming species. Limited studies on HAB-associated bacterial ecology have resulted in our incomplete understanding of HABs dynamics. Diverse phytoplankton-bacterial interactions have also led to studies on their potential as biocontrol tools for HABs mitigation. Here, we tested 48 cultivable pelagic bacteria from three HAB-affected areas in the Philippines (Bolinao, Sorsogon, and Matarinao) against non-axenic cultures of the toxic, thecate dinoflagellate Pyrodinium bahamense. Co-incubation with live cultures of these isolates exhibited varying levels of algicidal activities suggesting that it may not be a phylogenetically conserved property. Furthermore, majority of the isolates elicited activity against the thecate test species P. bahamense, which was not present in the area where the bacteria were isolated, implying non-specificity of action. Exposure to bacterial cells resulted in Pyrodinium pellicle cyst formation. Despite this, however, cell lysis and decline in total cell abundance were still observed, indicating strong algicidal potency of the isolates. In depth understanding of the interplay between environmental factors and algicidal bacteria-microalgal interactions may provide significant insights on the management of HABs.

Onset, intensification, and decline of phytoplankton blooms in the Southern Ocean

AbstractThe seasonal cycle of phytoplankton biomass in the Southern Ocean (SO) is characterized by a period of rapid accumulation, known as bloom, that is typical of high-latitude regions. Recent studies have illustrated how spatial and temporal dynamics of blooms in the SO are more complex than in other oceans. This complexity is likely related to differences in vertical mixing and the iron availability. In this work, we examine the sensitivity of bloom dynamics to changes in vertical mixing and iron availability using a biogeochemical model. Under idealized physical forcing, we produce seasonal cycles of phytoplankton for an ensemble of SO scenarios and we describe the bloom dynamics in terms of the net biomass accumulation rate. Based on this metric, we define three crucial bloom phases: the onset, the climax, and the apex. For the ensemble of modelled blooms, onsets always occur in winter and can be either bottom-up (increase in productivity) or top-down (decrease in grazing) controlled. Climaxes are mostly found in spring and their magnitudes are bottom-up controlled. Apexes are always found in late spring and strongly top-down controlled. Our results show that while a “strict” onset definition is consistent with a winter onset, the surface spring bloom is associated with the climax of the integrated bloom. Furthermore, we demonstrate that onset phase can be distinguished from climax phase using appropriate bloom detection methods based on surface satellite-based products. The ensemble of these results suggests that Sverdrup's blooming conditions are not indicative of the bloom onset but of the climax. We conclude that the recent bloom onset debate may partly be due to a confusion between what is defined here as the bloom onset and the climax, and that the SO observed complexity is due to the factors that control the climax.

The development and decline of phytoplankton blooms in the southern Benguela upwelling system. 1. Drogue movements, hydrography and bloom development

A drogue was placed in a patch of newly upwelled water on five different occasions between 1979 and 1981 in order to follow the temporal sequence of events after upwelling. The drogue moved over distances of 67 – 200 km within 4–7 days at mean speeds of 18–39 cm·s−1. Drogue movement was variable and generally in the direction of the prevailing wind. However, significant "up wind" movement occurred when the drogue was entrained in counter-currents. Variations in hydrographic parameters at the start of each sequence, and in the bottom mixed layer along the drogue tracks, indicate that upwelling source waters are not always uniform. However, nutrient concentrations in source water were high (mean concentrations for nitrate, silicate and phosphate were 20,8, 16,6 and 1,88 mmoln·m−3 respectively), whereas oxygen (4,0 dm3·m−3) and chlorophylls a (0,6 mg·m−3) concentrations were low. Once conditions stabilized, phytoplankton blooms developed rapidly in the upper layers, the cycle of bloom development and decline being completed in about 6–8 days. Nutrients decreased rapidly (and oxygen and chlorophyll a increased) with nitrates sometimes reaching concentrations of < 1 mmol·m−3, and oxygen and chlorophyll a peaking at concentrations of up to 9,8 dm3·m−3 and 21,2 mg·−3 respectively. Only once did light-limitation (due to deep mixing) influence bloom development. In this case, only moderately high chlorophyll a concentrations (∼ 10 mg·m−3) were attained. Bloom decline was usually associated with low nutrient concentrations and can be attributed mainly to sinking and dispersion of the phytoplankton, because zooplankton grazing appeared to have had an insignificant impact on the phytoplankton blooms.

The development and decline of phytoplankton blooms in the southern Benguela upwelling system. 2. Nutrient relationships

Five drogue studies on phytoplankton bloom dynamics in nutrient-rich newly upwelled water in the southern Benguela provided an opportunity to investigate the applicability of Redfield ratios to coastal upwelling regions. Mean atomic ratios of nutrient utilization and oxygen production (ΔP:ΔN:ΔSi:ΔO), as estimated from regression analyses (1:15,9:11,6:−283) and elemental changes along the drogue tracks (1:15,7:13,8:−206), were roughly similar to the equivalent Redfield ratios (1:16:15:−276). This implies that phytoplankton in upwelling areas also take up (or produce) these elements in proportions similar to those in which they occur in the cells themselves. As the upwelled water ages, changes in the ratios of N, Si and P imply that nitrate was used up fastest and is thus most likely to limit phytoplankton productivity in the southern Benguela region. However, regression analyses, calculations of times of nutrient depletion and published information on relative rates of nutrient regeneration suggest that silicate may also sometimes limit photosynthesis in this region.

The effect of sedimentation and microbial nitrogen regeneration in a plankton community: a simulation investigation

A computer simulation model was developed to investigate nitrogen fluxes associated with microbial interactions in plankton communities. A short time scale was used, appropriate to the build-up and decline of phytoplankton blooms in temperate shelf waters after a mixing or upwelling event. The model depicts a continuum of events, many of which have been observed in coastal, upwelling and oceanic systems, including two phytoplankton peaks corresponding to ‘new production’ and ‘regenerated production’. It predicts that nitrogen loss through sedimentation of phytoplankton and faeces may result in a smaller bloom with a delayed onset and prolonged duration. Microbial regeneration of nitrogen was found to be important in sustaining the middle stages of a phytoplankton bloom, whereas micro- and meso-zooplankton regeneration occurred towards the end of the bloom.

Switching between herbivory and carnivory by the planktonic marine copepod Calanus pacificus

Adult females of the omnivorous copepod Calanus pacificus, collected from the plankton off La Jolla, California, USA (June, 1978), fed disproportionately on the prey in greatest relative abundance when given mixtures of diatoms (Thalassiosira fluviatilis) and copepod (C. pacificus) nauplii as food. This switch from herbivorous to carnivorous behavior may be significant in nature during the decline of phytoplankton blooms. More generally, the widespread omnivorous habit among pelagic animals suggests a responsive and flexible trophic organization which contributes to the resiliency of planktonic communities in a dynamic physical environment.