Remote assessment of the fate of phytoplankton in the Southern Ocean sea-ice zone.

In the Southern Ocean, large-scale phytoplankton blooms occur in open water and the sea-ice zone (SIZ). These blooms have a range of fates including physical advection, downward carbon export, or grazing. Here, we determine the magnitude, timing and spatial trends of the biogeochemical (export) and ecological (foodwebs) fates of phytoplankton, based on seven BGC-Argo floats spanning three years across the SIZ. We calculate loss terms using the production of chlorophyll-based on nitrate depletion-compared with measured chlorophyll. Export losses are estimated using conspicuous chlorophyll pulses at depth. By subtracting export losses, we calculate grazing-mediated losses. Herbivory accounts for ~90% of the annually-averaged losses (169 mg C m-2 d-1), and phytodetritus POC export comprises ~10%. Furthermore, export and grazing losses each exhibit distinctive seasonality captured by all floats spanning 60°S to 69°S. These similar trends reveal widespread patterns in phytoplankton fate throughout the Southern Ocean SIZ.

Assessment of the Allelochemical Activity and Biochemical Profile of Different Phenotypes of Picocyanobacteria from the Genus Synechococcus.

Organisms belonging to Synechococcus sp. genera are observed in all freshwater, brackish, and marine waters of the world. They play a relevant role in these ecosystems, since they are one of the main primary producers, especially in open ocean. Eventually, they form mass blooms in coastal areas, which are potentially dangerous for the functioning of marine ecosystems. Allelopathy could be an important factor promoting the proliferation of these organisms. According to the authors' best knowledge, there is no information on the allelopathic activity and allelopathic compounds exhibited by different Synechococcus sp. phenotypes. Therefore, the research conducted here aimed to study the bioactivity of compounds produced by three phenotypes of Synechococcus sp. by studying their influence on the growth, chlorophyll fluorescence, and photosynthetic pigments of eighteen cyanobacteria and microalgae species. We demonstrated that three different Synechococcus sp. phenotypes, including a phycocyanin (PC)-rich strain (Type 1; green strain) and phycoerythrin (PE)-rich strains containing phycoerythrobilin (PEB) and phycocyanobilin (PCB) (Type 2; red strain and Type 3a; brown strain), had a significant allelopathic effect on the selected species of cyanobacteria, diatoms, and green algae. For all green algae, a decrease in cell abundance under the influence of phenotypes of donor cyanobacteria was shown, whereas, among some target cyanobacteria and diatom species, the cell-free filtrate was observed to have a stimulatory effect. Our estimates of the stress on photosystem II (Fv/Fm) showed a similar pattern, although for some diatoms, there was an effect of stress on photosynthesis, while a stimulatory effect on growth was also displayed. The pigment content was affected by allelopathy in most cases, particularly for chlorophyll a, whilst it was a bit less significant for carotenoids. Our results showed that Synechococcus sp. Type 3a had the strongest effect on target species, while Synechococcus sp. Type 1 had the weakest allelopathic effect. Furthermore, GC-MS analysis produced different biochemical profiles for the Synechococcus strains. For every phenotype, the most abundant compound was different, with oxime-, methoxy-phenyl- being the most abundant substance for Synechococcus Type 1, eicosane for Synechococcus Type 2, and silanediol for Synechococcus Type 3a.

The competitive exclusion principle in stochastic environments.

In its simplest form, the competitive exclusion principle states that a number of species competing for a smaller number of resources cannot coexist. However, it has been observed empirically that in some settings it is possible to have coexistence. One example is Hutchinson's 'paradox of the plankton'. This is an instance where a large number of phytoplankton species coexist while competing for a very limited number of resources. Both experimental and theoretical studies have shown that temporal fluctuations of the environment can facilitate coexistence for competing species. Hutchinson conjectured that one can get coexistence because nonequilibrium conditions would make it possible for different species to be favored by the environment at different times. In this paper we show in various settings how a variable (stochastic) environment enables a set of competing species limited by a smaller number of resources or other density dependent factors to coexist. If the environmental fluctuations are modeled by white noise, and the per-capita growth rates of the competitors depend linearly on the resources, we prove that there is competitive exclusion. However, if either the dependence between the growth rates and the resources is not linear or the white noise term is nonlinear we show that coexistence on fewer resources than species is possible. Even more surprisingly, if the temporal environmental variation comes from switching the environment at random times between a finite number of possible states, it is possible for all species to coexist even if the growth rates depend linearly on the resources. We show in an example (a variant of which first appeared in Benaim and Lobry '16) that, contrary to Hutchinson's explanation, one can switch between two environments in which the same species is favored and still get coexistence.

Water quality assessment of a neotropical pampean lowland stream using a phytoplankton functional trait approach.

The aim of this study was to test whether the water quality phytoplankton assemblage index adapted for rivers (Qr index) is useful to characterize the water quality of a neotropical stream. We were interested also in inferring the main pollutants through a phytoplankton functional trait characterization and assessing the phytoplankton groups which may influence the Qr index final estimations. Monthly sampling of environmental variables and phytoplankton were done in three sites (S1, S2, and S3). Phytoplankton was classified according to Reynolds Functional Groups (RFG) and water quality estimation was performed using the Qr index. Principal coordinates (PCO) and PERMANOVA were applied to identify the main pollutants through the RFG. RFG linkage to Qr values was assessed by general linear models (GLM). "Moderate" water quality was found in S1 the whole year, in all sampling stations during the winter, and in summer-autumn in S2. "Regular" water quality was found in S3 during the summer-autumn, and S2-S3 during the spring. S1 and S2 showed eutrophic, standing, or mix waters whereas S3 had high organic matter content and eutrophic conditions. Despite some RFG (X1 and MP) being linked to high Qr values and some other (M, S1 and Z) to low, their dominance did not influence water quality estimation performed by the Qr. We conclude that the Qr index was useful for assessing the water quality. Though RFG were valuable for inferring eutrophication, organic pollution, and mixing, but their dominance does not necessarily have a direct effect on the final Qr estimation.

Global pattern of phytoplankton diversity driven by temperature and environmental variability.

Despite their importance to ocean productivity, global patterns of marine phytoplankton diversity remain poorly characterized. Although temperature is considered a key driver of general marine biodiversity, its specific role in phytoplankton diversity has remained unclear. We determined monthly phytoplankton species richness by using niche modeling and >540,000 global phytoplankton observations to predict biogeographic patterns of 536 phytoplankton species. Consistent with metabolic theory, phytoplankton richness in the tropics is about three times that in higher latitudes, with temperature being the most important driver. However, below 19°C, richness is lower than expected, with ~8°- 14°C waters (~35° to 60° latitude) showing the greatest divergence from theoretical predictions. Regions of reduced richness are characterized by maximal species turnover and environmental variability, suggesting that the latter reduces species richness directly, or through enhancing competitive exclusion. The nonmonotonic relationship between phytoplankton richness and temperature suggests unanticipated complexity in responses of marine biodiversity to ocean warming.

Index of biotic integrity based on phytoplankton and water quality index: Do they have a similar pattern on water quality assessment? A study of rivers in Lake Taihu Basin, China.

Our study illustrated the ecological conditions in the rivers of Lake Taihu Basin (LTB) using an index of biotic integrity based on phytoplankton (P-IBI), and its performance was compared with the previously developed water quality index (WQI). Samples were collected seasonally at 96 sites covering the major rivers from September 2014 to January 2016. Three critical ecological indices, i.e., phytoplankton density, chlorophyll a (chl a), and Menhinick, were selected from a pool of 22 candidate indices mainly according to the correlations among indices and environmental parameters. The results indicated that the ecological status of LTB based on P-IBI was significantly different at spatial (especially between Tiaoxi and the other 5 river systems) and seasonal scales. Furthermore, the proposed P-IBI effectively identified the major environmental parameters (total nitrogen, ammonium, total phosphorus, and permanganate index) associated with each level (bad, low, and moderate). Moreover, the P-IBI was closely and positively correlated with the WQI at the spatial scale regardless of season. However, the ecological conditions were significantly worse according to the P-IBI at both the spatial (P < 0.001) and seasonal scales (P values of 0.018 in winter and < 0.001 in other seasons, respectively), and the seasonal distribution pattern differed between the two methods. Our study suggests that the P-IBI provides an essential supplement for the assessment of ecological conditions of rivers and that the selected critical indices (phytoplankton density, chl a, and Menhinick) are suitable for river ecosystems. Additionally, compared with WQI, the water quality condition was generally worse when using P-IBI, and this phenomenon requires further attention during water quality assessments, as well as different seasonal distribution patterns.

Phytoplankton community-level bio-optical assessment in a naturally mercury contaminated Antarctic ecosystem (Deception Island).

Mercury naturally contaminated environments, like Deception Island (Antarctica), are field labs to study the physiological consequences of chronic Hg-exposure at the community level. Deception Island volcanic vents lead to a continuous chronic exposure of the phytoplanktonic communities to potentially toxic Hg concentrations. Comparing Hg-contaminated areas (Fumarolas Bay - FB, Gabriel de Castilla station - GdC station), no significant differences in chlorophyll a concentrations were detected, indicating that biomass production was not impaired by Hg-exposure despite the high Hg levels found in the cells. Moreover, the electron transport energy, responsible for energy production, also presented rather similar values in phytoplankton from both locations. Regarding FB communities, although the cells absorbed and trapped lower amounts of energy, the effect of Hg was not relevant in the photochemical work produced by the electronic transport chain. This might be due to the activation of alternative internal electron donors, as counteractive measure to the energy accumulated inside the cells. In fact, this alternative electron pathway, may have allowed FB communities to have similar electron transport energy fluxes without using respiration as photoprotective measure towards excessive energy. Hg-exposed cells also showed a shift from the energy flux towards the PS I (photosystem I), alleviating the excessive energy accumulation at the PS II (photosystem II) and preventing an oxidative burst. Our findings suggest a higher energy use efficiency in the communities exposed to volcanic Hg, which is not observable in cultured phytoplankton species grown under Hg exposure. This may constitute a metabolic adaptation, driven from chronic exposure allowing the maintenance of high levels of primary productivity under the assumingly unfavourable conditions of Deception Island.

Preface.

In the new century, with rapid population growth, large-scale urbanization, global warming and many other factors, we are facing unprecedented ecological, health, social, and other challenges and issues. These include biological invasion, environmental degradation, sharp increase in cancer morbidity, high frequency of emerging and re-emerging infectious diseases, which pose a grave threat to biological diversity, public health, economic development and so on. Based on the solid research in population dynamics and disease dynamics, mathematical modeling, analysis and simulation have been widely used over the past decades to study various problems in life sciences and medicine, from the expression of gene sequence to the pathogenesis of cancer, from the control of molecular organisms to the resistance of bacteria and viruses, from immune response to diseases to the design and evaluation of treatments, and so on. To provide a platform for researchers in mathematical biology and related fields to present latest findings and research trends, to exchange ideas and approaches, and to enhance communication and cooperation, we organized a workshop entitled "Current Topics in Mathematical Biology (CTMB)" at Shanghai Normal University, December 18-20, 2015. We acknowledge the support from the Mathematics and Science College at Shanghai Normal University and Shanghai Gaofeng Project for University Academic Development Program.

Effects of prey of different nutrient quality on elemental nutrient budgets in Noctiluca scintillans.

Noctiluca scintillans (Noctiluca) is a cosmopolitan red tide forming heterotrophic dinoflagellate. In this study, we investigated its ingestion, elemental growth yield and excretion when supplied with different quality food (nutrient-balanced, N-limited and P-limited). Total cellular elemental ratios of Noctiluca were nearly homeostatic, but the ratio of its intracellular NH4+ and PO43- was weakly regulated. Noctiluca thus seems able to differentially allocate N and P to organic and inorganic pools to maintain overall homeostasis, and it regulated its internal N more strongly and efficiently than P. The latter was substantiated by its comparatively stable C:N ratio and compensatory feeding on N-limited prey. Using both starvation experiments and mass balance models, it was found that excretion of C, N, and P by Noctiluca is highly affected by prey nutritional quality. However, based on modeling results, nutrients seem efficiently retained in actively feeding Noctiluca for reproduction rather than directly released as was shown experimentally in starved cells. Moreover, actively feeding Noctiluca tend to retain P and preferentially release N, highlighting its susceptible to P-limitation. Recycling of N and P by Noctiluca may supply substantial nutrients for phytoplankton growth, especially following bloom senescence.

Development of an economical, autonomous pHstat system for culturing phytoplankton under steady state or dynamic conditions.

Laboratory investigations of physiological processes in phytoplankton require precise control of experimental conditions. Chemostats customized to control and maintain stable pH levels (pHstats) are ideally suited for investigations of the effects of pH on phytoplankton physiology, for example in context of ocean acidification. Here we designed and constructed a simple, flexible pHstat system and demonstrated its operational capabilities under laboratory culture conditions. In particular, the system is useful for simulating natural cyclic pH variability within aquatic ecosystems, such as diel fluctuations that result from metabolic activity or tidal mixing in estuaries. The pHstat system operates in two modes: (1) static/set point pH, which maintains pH at a constant level, or (2) dynamic pH, which generates regular, sinusoidal pH fluctuations by systematically varying pH according to user-defined parameters. The pHstat is self-regulating through the use of interchangeable electronically controlled reagent or gas-mediated pH-modification manifolds, both of which feature flow regulation by solenoid valves. Although effective pH control was achieved using both liquid reagent additions and gas-mediated methods, the liquid manifold exhibited tighter control (±0.03pH units) of the desired pH than the gas manifold (±0.10pH units). The precise control provided by this pHstat system, as well as its operational flexibility will facilitate studies that examine responses by marine microbiota to fluctuations in pH in aquatic ecosystems.

Energy cost and putative benefits of cellular mechanisms modulating buoyancy in aflagellate marine phytoplankton.

Little information is available on the energetics of buoyancy modulation in aflagellate phytoplankton, which comprises the majority of autotrophic cells found in the ocean. Here, we computed for three aflagellate species of marine phytoplankton (Emiliania huxleyi, Thalassiosira pseudonana, and Ethmodiscus rex) the theoretical minimum energy cost as photons absorbed and nitrogen resource required of the key physiological mechanisms (i.e., replacement of quaternary ammonium by dimethyl-sulfoniopropionate, storage of polysaccharides, and cell wall biosynthesis) affecting the cell's vertical movement as a function of nitrogen (N) availability. These energy costs were also normalized to the capacity of each buoyancy mechanism to modulate sinking or rising rates based on Stokes' law. The three physiological mechanisms could act as ballast in the three species tested in conditions of low N availability at a low fraction (<12%) of the total photon energy cost for growth. Cell wall formation in E. huxleyi was the least costly ballast strategy, whereas in T. pseudonana, the photon energy cost of the three ballast strategies was similar. In E. rex, carbohydrate storage and mobilization appear to be energetically cheaper than modulations in organic solute synthesis to achieve vertical migration. This supports the carbohydrate-ballast strategy for vertical migration for this species, but argues against the theory of replacement of low- or high-density organic solutes. This study brings new insights into the energy cost and potential selective advantages of several strategies modulating the buoyancy of aflagellate marine phytoplankton.

Phytoplankton dynamics with a special emphasis on harmful algal blooms in the Mar Piccolo of Taranto (Ionian Sea, Italy).

The response of phytoplankton assemblages to the closure of urban sewage outfalls (USOs) was examined for the Mar Piccolo of Taranto (Mediterranean Sea), a productive semi-enclosed coastal marine ecosystem devoted to shellfish farming. Phytoplankton dynamics were investigated in relation to environmental variables, with a particular emphasis on harmful algal blooms (HABs). Recent analyses evidenced a general reduction of the inorganic nutrient loads, except for nitrates and silicates. Also phytoplankton biomass (chlorophyll a) and abundances were characterized by a decrease of the values, except for the inner area of the basin (second inlet). The phytoplankton composition changed, with nano-sized species, indicators of oligotrophic conditions, becoming dominant over micro-sized species. If the closure of the USOs affected phytoplankton dynamics, however, it did not preserve the Mar Piccolo from HABs and anoxia crises. About 25 harmful species have been detected throughout the years, such as the potentially domoic acid producers Pseudo-nitzschia cf. galaxiae and P seudo-nitzschia cf. multistriata, identified for the first time in these waters. The presence of HABs represents a threat for human health and aquaculture. Urgent initiatives are needed to improve the communication with authorities responsible for environmental protection, economic development, and public health for a sustainable mussel culture in the Mar Piccolo.

Towards the determination of Mytilus edulis food preferences using the dynamic energy budget (DEB) theory.

The blue mussel, Mytilus edulis, is a commercially important species, with production based on both fisheries and aquaculture. Dynamic Energy Budget (DEB) models have been extensively applied to study its energetics but such applications require a deep understanding of its nutrition, from filtration to assimilation. Being filter feeders, mussels show multiple responses to temporal fluctuations in their food and environment, raising questions that can be investigated by modeling. To provide a better insight into mussel-environment interactions, an experiment was conducted in one of the main French growing zones (Utah Beach, Normandy). Mussel growth was monitored monthly for 18 months, with a large number of environmental descriptors measured in parallel. Food proxies such as chlorophyll a, particulate organic carbon and phytoplankton were also sampled, in addition to non-nutritious particles. High-frequency physical data recording (e.g., water temperature, immersion duration) completed the habitat description. Measures revealed an increase in dry flesh mass during the first year, followed by a high mass loss, which could not be completely explained by the DEB model using raw external signals. We propose two methods that reconstruct food from shell length and dry flesh mass variations. The former depends on the inversion of the growth equation while the latter is based on iterative simulations. Assemblages of food proxies are then related to reconstructed food input, with a special focus on plankton species. A characteristic contribution is attributed to these sources to estimate nutritional values for mussels. M. edulis shows no preference between most plankton life history traits. Selection is based on the size of the ingested particles, which is modified by the volume and social behavior of plankton species. This finding reveals the importance of diet diversity and both passive and active selections, and confirms the need to adjust DEB models to different populations and sites.

New methodology for analysing and increasing the cost-efficiency of environmental monitoring networks.

This study focuses on the coastal monitoring network established in the scope of WFD implementation. The objective of this network was to provide an ecological assessment of Valencian coastal waters. After three years, sufficient data had been collected to enable us to analyse and explore ways to increase the network's efficiency. A methodology was developed to select the best subset of sampling stations to be surveyed. This method was approached from the perspective of an inter-observer variability problem. In order to compare the concordance between the k-observers and the reference observer, two measures were considered: euclidean distance, and interclass correlation coefficient. The obtained results confirm that the current network can be reduced by over 50% and still guarantee accurate results. This methodology (not limited by indicators, geographically, or by type of water body) could be applied to different environmental monitoring networks and could significantly decrease the efforts and costs required by the WFD.

Marine phytoplankton motility sensor integrated into a microfluidic chip for high-throughput pollutant toxicity assessment.

A microfluidic chip was designed to assess the toxicity of pollutants in a high-throughput way by using marine phytoplankton motility as a sensor signal. In this chip, multiple gradient generators (CGGs) with diffusible chambers enable large scale of dose-response bioassays to be performed in a simple way. Two mobile marine phytoplankton cells were confined on-chip and stimulated by 8 concentrations (generated by CGG) of Hg, Pb, Cu and phenol singly, as well as Cu and phenol jointly. CASA system was used to characterize motility by motile percentage (%MOT), curvilinear velocity (VCL), average path velocity (VAP) and straight line velocity (VSL). In all cases, dose-dependent inhibitions of motility were observed. In the present system, only 2h was needed to predict EC50. Thus, the developed microfluidic chip device was proved to be useful as a rapid/simple and high-throughput test method in marine pollution toxicity assessment.

A unimodal species response model relating traits to environment with application to phytoplankton communities.

In this paper we attempt to explain observed niche differences among species (i.e. differences in their distribution along environmental gradients) by differences in trait values (e.g. volume) in phytoplankton communities. For this, we propose the trait-modulated Gaussian logistic model in which the niche parameters (optimum, tolerance and maximum) are made linearly dependent on species traits. The model is fitted to data in the Bayesian framework using OpenBUGS (Bayesian inference Using Gibbs Sampling) to identify according to which environmental variables there is niche differentiation among species and traits. We illustrate the method with phytoplankton community data of 203 lakes located within four climate zones and associated measurements on 11 environmental variables and six morphological species traits of 60 species. Temperature and chlorophyll-a (with opposite signs) described well the niche structure of all species. Results showed that about 25% of the variance in the niche centres with respect to chlorophyll-a were accounted for by traits, whereas niche width and maximum could not be predicted by traits. Volume, mucilage, flagella and siliceous exoskeleton are found to be the most important traits to explain the niche centres. Species were clustered in two groups with different niches structures, group 1 high temperature-low chlorophyll-a species and group 2 low temperature-high chlorophyll-a species. Compared to group 2, species in group 1 had larger volume but lower surface area, had more often flagella but neither mucilage nor siliceous exoskeleton. These results might help in understanding the effect of environmental changes on phytoplankton community. The proposed method, therefore, can also apply to other aquatic or terrestrial communities for which individual traits and environmental conditioning factors are available.

Food web de-synchronization in England's largest lake: an assessment based on multiple phenological metrics.

Phenological changes have been observed globally for marine, freshwater and terrestrial species, and are an important element of the global biological 'fingerprint' of climate change. Differences in rates of change could desynchronize seasonal species interactions within a food web, threatening ecosystem functioning. Quantification of this risk is hampered by the rarity of long-term data for multiple interacting species from the same ecosystem and by the diversity of possible phenological metrics, which vary in their ecological relevance to food web interactions. We compare phenological change for phytoplankton (chlorophyll a), zooplankton (Daphnia) and fish (perch, Perca fluviatilis) in two basins of Windermere over 40 years and determine whether change has differed among trophic levels, while explicitly accounting for among-metric differences in rates of change. Though rates of change differed markedly among the nine metrics used, seasonal events shifted earlier for all metrics and trophic levels: zooplankton advanced most, and fish least, rapidly. Evidence of altered synchrony was found in both lake basins, when combining information from all phenological metrics. However, comparisons based on single metrics did not consistently detect this signal. A multimetric approach showed that across trophic levels, earlier phenological events have been associated with increasing water temperature. However, for phytoplankton and zooplankton, phenological change was also associated with changes in resource availability. Lower silicate, and higher phosphorus, concentrations were associated with earlier phytoplankton growth, and earlier phytoplankton growth was associated with earlier zooplankton growth. The developing trophic mismatch detected between the dominant fish species in Windermere and important zooplankton food resources may ultimately affect fish survival and portend significant impacts upon ecosystem functioning. We advocate that future studies on phenological synchrony combine data from multiple phenological metrics, to increase confidence in assessments of change and likely ecological consequences.

[Study on influencing factors and universality of chlorophyll-a retrieval model in inland water body].

The semi-analytical three-and four-band model and bio-optical analytical model of chlorophyll-a were checked by the 'mh, constituents and optical properties with high spatio-temporal variation. The influencing factors and universality of the retrieval model were studied by the modeling checking results. The study results indicate that the unjversality of bio-optical analytical model is much higher than the three-and four-band model, and the accuracy of the retrieval model is acceptable, but the accuracy of the retrieval model was highly affected by the specific absorption coefficient of chlorophyll-a. The accuracy of the three-and four-band model higher than the bio-optical analytical model. However, the universality of the three-and four-band model is not very high, because of the optimal wavelength position of the retrieval factors and the greater variability of the retrieval model parameters. The spectral shape of particle backscattering coefficient and chlorophyll-a specific absorption coefficient are the dominant influencing factors of the three and four-band retrieval model.

Photo-physiological variability in phytoplankton chlorophyll fluorescence and assessment of chlorophyll concentration.

Photo-physiological variability of in vivo chlorophyll fluorescence (CF) per unit of chlorophyll concentration (CC) is analyzed using a biophysical model to improve the accuracy of CC assessments. Field measurements of CF and photosystem II (PSII) photochemical yield (PY) with the Advanced Laser Fluorometer (ALF) in the Delaware and Chesapeake Bays are analyzed vs. high-performance liquid chromatography (HPLC) CC retrievals. It is shown that isolation from ambient light, PSII saturating excitation, optimized phytoplankton exposure to excitation, and phytoplankton dark adaptation may provide accurate in vivo CC fluorescence measurements (R2 = 0.90-0.95 vs. HPLC retrievals). For in situ or flow-through measurements that do not allow for dark adaptation, concurrent PY measurements can be used to adjust for CF non-photochemical quenching (NPQ) and improve the accuracy of CC fluorescence assessments. Field evaluation has shown the NPQ-invariance of CF/PY and CF(PY-1-1) parameters and their high correlation with HPLC CC retrievals (R2 = 0.74-0.96), while the NPQ-affected CF measurements correlated poorly with CC (R2 = -0.22).

The effects of prolonged darkness on temperate and tropical marine phytoplankton, and their implications for ballast water risk management.

Phytoplankton assemblages from tropical (Goa) and temperate (UK) locations were exposed to a 28 day dark period, followed by a period of re-exposure to light. During this time phytoplankton survival and changes in nutrient concentrations were mapped. The tropical plankton water samples showed high nutrient levels after the dark period which were utilised by cells during the re-exposure period. UK experiments looked at the effect of three different water types on population recovery after the 28 day dark period, and differences due to seasonal effects. The population growth observed during the re-exposure period in the tropical population was comparable to that of the temperate population. Water type affected recovery and of the three tested media fresh seawater promoted the highest levels of growth. Seasonality had a significant influence on species survival. Understanding the effects of all these factors can aid the development of effective risk assessments in ballast water management.