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Influence of environmental parameters on marine plankton diversity in the southern coastal waters of Korea: Emphasis on thermal stratification
... The presence and abundance of phytoplankton is closely related to the condition of the physical -chemical parameters of the waters (El Gammal et al., 2017;Lim et al., 2025;Zhang et al., 2025;O'Boyle & Silke, 2010;Herawati et al., 2021). These conditions can affect the distribution of phytoplankton, especially the intensity of light and nutrients (nitrate and phosphate), differences in these conditions directly cause the distribution of phytoplankton differently. ...
Background: The presence and abundance of phytoplankton are closely related to the physical and chemical parameters of water. Phytoplankton play a crucial role in aquatic ecosystems as primary producers and nutrient absorbers. This study aims to analyze the relationship between nitrate and phosphate nutrient content and the abundance of phytoplankton in the Arungkeke Waters, Jeneponto Regency. Methods: This research utilized a combination of field measurements and laboratory analysis. Direct measurements in the Arungkeke waters were conducted to assess surface water parameters, including temperature, salinity, current velocity, transparency, and pH. Water samples were collected for laboratory analysis of phytoplankton composition and abundance, as well as nitrate and phosphate concentrations. Regression analysis was performed to determine the relationship between nutrient concentrations and phytoplankton abundance. Findings: The study identified two classes of phytoplankton present in the Arungkeke waters: Bacillariophyceae and Dinophyceae. Oceanographic parameters were measured, with temperature ranging from 28.3°C to 29.7°C, current velocity from 0.039 m/s to 0.073 m/s, salinity from 29.3 ppt to 32 ppt, transparency from 1.9 m to 2.3 m, and pH from 7.3 to 7.4. Nitrate concentrations ranged from 0.042 mg/L to 0.076 mg/L, while phosphate concentrations ranged from 0.046 mg/L to 0.056 mg/L. The regression analysis revealed a moderate relationship between phytoplankton abundance and nutrient concentrations, with an R² value of 0.44. Conclusions: The study concludes that phytoplankton abundance in the Arungkeke Waters is influenced by nitrate and phosphate concentrations, with a moderate correlation observed. The presence of Bacillariophyceae and Dinophyceae classes indicates the ecological significance of these waters as a primary production area. Novelty/Originality of this article: This study provides valuable insights into the interaction between nutrient dynamics and phytoplankton abundance in the Arungkeke Waters, which is a relatively understudied area. By identifying the classes of phytoplankton present and quantifying their relationship with key nutrients, this research contributes to a better understanding of the ecological processes in coastal waters.
Estuary reopening is a means of restoring estuarine habitats, which has recently been implemented in a few developed countries. The regeneration of a brackish zone in the Nakdong River Estuary (NRE), South Korea, were tested through a series of barrage reopening. During the same period, we conducted extensive fish surveys in the upper part of the NRE barrage on a monthly basis from 2017 to 2021, and subsequently determined whether fish populations and communities were affected by the reopening. The results showed that the reopening of the NRE hardly affected the fish community structure, as non-native species such as Erythroculter erythropterus and Lepomis macrochirus maintained their dominance. Still, we discovered that certain euryhaline species are positively affected by estuary reopening, as total 46 Japanese eels (Anguilla japonica) were captured after the reopening, which had not been detected before the reopening. By comparing the size structure of various fish species, we discovered that size distribution of native and migratory species presented more positively skewed pattern after the reopening, while size structure in non-native species remained relatively unchanged normally distributed pattern. Piecewise structural equation modelling revealed that the NRE had become more complex ecosystem, as migratory fish species abundance and biomass started to show a positive correlation with hydraulic factors such as discharge and negative correlation with seasonality after the reopening. We concluded that estuary reopening created some changes in migratory and native freshwater species but such changes were not notably detected in non-native species. Therefore, appropriate sluice operation methodologies, such as considering the migration seasons of migratory species, should be developed. Additionally, human-involved management policies are required to regulate non-native species populations.
The primary production (PP) by phytoplankton in marine ecosystems is essential for carbon cycling and fueling food webs. Hence, estimating the PP in the territorial sea of each country is a necessary step to achieving carbon neutrality. To estimate the PP in the territorial sea of the Republic of Korea from 2005 to 2021, we analyzed various physiochemical parameters, such as sea surface temperature (SST), Secchi depth, and concentrations of chlorophyll-a and nutrients in the seas of five regions, including the East Sea, West Sea, western South Sea, eastern South Sea, and the waters off Jeju Island. During the 17-year study period, the SST tended to increase, while the nutrient concentrations declined, except in the Jeju area. Overall, the PP did not show a specific temporal trend, but daily PP in the western South Sea was the highest among the five regions. Moreover, the maximum PP in the Korean territorial waters (76,450 km2 ) was estimated at 11,227 Gg C y-1, which accounts for 0.03% of the global PP. The results may give insights into a better understanding of the PP, further resource utilization, and environmental sustainability in the studied region.
Using geographic sea surface current data, long-term changes in spatial and temporal variations in the Kuroshio Current 1993–2021 were analyzed, and the relationship between the Kuroshio Current and oceanic conditions, such as water column structure and intensity of East Korea Warm Current (EKWC) in the western part of the East Sea (WES), was investigated. Long-term changes in the Kuroshio Current intensity were positively correlated with the Pacific Decadal Oscillation and East Asian Winter Monsoon indices. When the Kuroshio Current was strong, its main axis passing around the Ryukyu Islands moved eastward, and the intensity of EKWC separated from the Kuroshio Current and flowed into the WES, indicating weakened conditions. When the intensity of the EKWC was weakened, its main axis moved away from the inshore area of the WES. As a result, the vertical distribution range of the cold and low saline water mass located in the bottom layer extended to shallower depths in the inshore area of the WES with increasing chlorophyll-a.
The phytoplankton absorption cross-section is a fundamental quantity in biogeochemical ocean models that alters the underwater spectral light field and the photosynthetic response of phytoplankton. Phytoplankton taxa are characterized by absorption spectra with defined absorption bands in the visible region of the light spectrum that govern the capability of different taxa of phytoplankton to exploit light as a resource for growth. The interplay between the spatial and temporal gradients of underwater spectral light and the light absorption characteristics of different phytoplankton types contribute to the interactions and selection among groups and hence can be a determinant in shaping phytoplankton diversity and biogeography. In this work, we used a biogeochemical model of the Mediterranean Sea to simulate nine optically different phytoplankton functional types (PFTs) and coupled it to a radiative transfer model to simulate the spectral underwater light field where the PFTs interact. We investigated the competitive advantage provided by the different absorption spectra and the possibilities of coexistence emerging from the availability of different light habitats. By considering non-spectrally resolved optical differences among PFTs, our model results led to the dominance of Synechococcus sp. within picophytoplankton, coccolithophores within nanophytoplankton and dinoflagellates within microphytoplankton. By including the spectral dependency of photosynthesis, we observed how the availability of different spectral light habitats led to the coexistence of picophytoplankton groups in clear waters, whereas for nano- and microphytoplankton PFTs, the extent of coexistence permitted by light fluctuations was minimal. By combining optical and functional differences in the PFT description, we obtained PFT distributions that were in relative agreement with observed phytoplankton distributions in the Mediterranean Sea estimated from satellite and in situ high-performance liquid chromatography sampling. This result suggests that combining spectrally resolved optical traits with functional traits in the description of the autotrophic community can be a valuable tool to improve simulations of the diversity and biogeography of primary producers in the ocean.
The future response of marine ecosystem diversity to continued anthropogenic forcing is poorly constrained. Phytoplankton are a diverse set of organisms that form the base of the marine ecosystem. Currently, ocean biogeochemistry and ecosystem models used for climate change projections typically include only 2−3 phytoplankton types and are, therefore, too simple to adequately assess the potential for changes in plankton community structure. Here, we analyse a complex ecosystem model with 35 phytoplankton types to evaluate the changes in phytoplankton community composition, turnover and size structure over the 21st century. We find that the rate of turnover in the phytoplankton community becomes faster during this century, that is, the community structure becomes increasingly unstable in response to climate change. Combined with alterations to phytoplankton diversity, our results imply a loss of ecological resilience with likely knock-on effects on the productivity and functioning of the marine environment.
The abundance of phytoplankton in water depends on the availability of nutrients. Nitrogen and phosphorus are two parameters that affect water. Phytoplankton require the elements of nitrate and phosphate in the production of fats and proteins. Nitrate and phosphate in water can be influenced by household waste discharges originating from residential areas around mangroves. The Wonorejo mangrove waters area is the estuary of an industrial waste journey. This study was conducted to determine the relationship of the N/P ratio to the abundance of phytoplankton in the Mangrove Waters of Wonorejo, Rungkut, Surabaya, East Java. Sampling was done at three stations with two replications. Identification or observation using a microscope. The results found that the most dominant class is the Bacillariophyceae consisted of two genus. Whereas the other classes found consisted of two genus Dynophyceae, one Clorophyceae, Coscinodiscophyceae, Fragilariophyceae and Cynophyceae. The results of the regression-correlation analysis showed a correlation coefficient of 0.885, meaning that the relationship obtained with an N / P ratio with an abundance of phytoplankton was very strong. The abundance of phytoplankton is influenced by the concentration of nitrogen and phosphate at 78.3% while the other 21.7% is influenced by physical and chemical factors of other waters.
The mixotrophic dinoflagellate Tripos furca causes red tides in the waters of many countries. To understand its popu-lation dynamics, mortality due to predation as well as growth rate should be assessed. Prior to the present study, the heterotrophic dinoflagellates Noctiluca scintillans, Polykrikos kofoidii, Protoperidinium steinii, and mixotrophic dino-flagellate Fragilidium subglobosum were known to ingest T. furca. However, if other common heterotrophic protists are able to feed on T. furca has not been tested. We explored interactions between T. furca and nine heterotrophic dinoflagel-lates and one naked ciliate. Furthermore, we investigated the abundance of T. furca and common heterotrophic protists in coastal-offshore waters off Yeosu, southern Korea, on Jul 31, 2020, during its red tide. Among the tested heterotrophic protists, the heterotrophic dinoflagellates Aduncodinium glandula, Luciella masanensis, and Pfiesteria piscicida were able to feed on T. furca. However, the heterotrophic dinoflagellates Gyrodiniellum shiwhaense, Gyrodinium dominans, Gyrodinium jinhaense, Gyrodinium moestrupii, Oblea rotunda, Oxyrrhis marina, and the naked ciliate Rimostrombidi-um sp. were unable to feed on it. However, T. furca did not support the growth of A. glandula, L. masanensis, or P. piscicida. Red tides dominated by T. furca prevailed in the South Sea of Korea from Jun 30 to Sep 5, 2020. The maximum abundance of heterotrophic dinoflagellates in the waters off Yeosu on Jul 31, 2020, was as low as 5.0 cells mL⁻¹, and A. glandula, L. masanensis, and P. piscicida were not detected. Furthermore, the abundances of the known predators F. subglobosum, N. scintillans, P. kofoidii, and Protoperidinium spp. were very low or negligible. Therefore, no or low abundance of effective predators might be partially responsible for the long duration of the T. furca red tides in the South Sea of Korea in 2020.
Species composition plays a key role in ecosystem functioning. Theoretical, experimental and field studies show positive effects of biodiversity on ecosystem processes. However, this link can differ between taxonomic and functional diversity components and also across trophic levels. These relationships have been hardly studied in planktonic communities of coastal upwelling systems. Using a 28-year time series of phytoplankton and zooplankton assemblages, we examined the effects of phytoplankton diversity on resource use efficiency (RUE, ratio of biomass to limiting resource) at the two trophic levels in the Galician upwelling system (NW Iberian peninsula). By fitting generalized least square models, we show that phytoplankton diversity was the best predictor for RUE across planktonic trophic levels. This link varied depending on the biodiversity component considered: while the effect of phytoplankton richness on RUE was positive for phytoplankton RUE and negative for zooplankton RUE, phytoplankton evenness effect was negative for phytoplankton RUE and positive for zooplankton RUE. Overall, taxonomic diversity had higher explanatory power than functional diversity, and variability in phytoplankton and zooplankton RUE decreased with increasing phytoplankton taxonomic diversity. Phytoplankton used resources more efficiently in warmer waters and at greater upwelling intensity, although these effects were not as strong as those for biodiversity. These results suggest that phytoplankton species numbers in highly dynamic upwelling systems are important for maintaining the planktonic biomass production leading us to hypothesize the relevance of complementarity effects. However, we further postulate that a selection effect may operate also because assemblages with low evenness were dominated by diatoms with specific functional traits increasing their ability to exploit resources more efficiently.
Eight benthic diatom taxa (Actinocyclus octonarius, Melosira moniliformis, Halamphora sp. 1, Halamphora sp. 2, Navicula perminuta, Navicula phyllepta, Nitzschia dubiiformis, Nitzschia pusilla) were isolated from sediments sampled in the southern coastal brackish Baltic Sea and established as unialgal cultures. The coastal shallow water sampling area lies close to a fen peat site (Hütelmoor) and both are connected through an underground peat layer, which might facilitate organic matter and nutrient fluxes along the terrestrial-marine gradient. The photosynthetic performance of these diatoms was measured at different photon fluence rates (0–1200 μmol photons m–2 s–1, always recorded at 20°C) and different temperatures (5–40°C, always measured at saturating ∼270 μmol photons m–2 s–1), resulting in light saturation points between 32 and 151 μmol photons m–2 s–1 and maximum net primary production rates of 23–144 μmol O2 mg–1 Chl a h–1. None of the species showed severe photoinhibition, and hence all displayed a high photo-physiological plasticity. Photosynthetic oxygen evolution and respirational oxygen consumption between 5 and 40°C revealed eurythermal traits for half of the studied taxa as photosynthetic efficiency was at least 20% of the maximum values at the extreme temperatures. The remaining taxa also indicated eurythermal characteristics, however, photosynthetic efficiency of at least 20% was at a narrower temperature range [5 (10) °C to 30 (35) °C]. Species-specific optimum temperatures for photosynthesis (15–30°C) were always lower compared to respiration (25–40°C). Actinocyclus octonarius and Nitzschia dubiiformis were grown in different defined media, some enriched with Hütelmoor water to test for possible effects of organic components. Hütelmoor water media stimulated growth of both diatom species when kept in a light dark cycle. Actinocyclus octonarius particularly grew in darkness in Hütelmoor water media, pointing to heterotrophic capabilities. The benthic diatoms studied are characterized by high photo-physiological plasticity and a broad temperature tolerance to maintain high primary production rates under wide environmental fluctuations. Organic carbon fluxes from the Hütelmoor into the Baltic Sea may support mixo- and/or heterotrophic growth of microphytobenthic communities. These are essential traits for living in a highly dynamic and variable shallow water environment at the coastal zone of the Baltic Sea.
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.
The present investigation studied the seasonal variation between physico-chemical parameters and phytoplankton diversity, community structure and abundance; quantitative samples were collected on a monthly basis from April 2015 to March 2016 at Parangipettai coast, the Bay of Bengal (BOB). Statistical analyses were performed on physico-chemical parameters such as salinity, dissolved oxygen (DO), pH, temperature, nitrate, nitrite, silicate, and inorganic phosphate (IP). The significant (P<0.0005) variation among seasons as well as a high influence of these parameters was observed on phytoplankton productivity. Totally, 117 species were identified, belonging to five different classes, Coscinodiscophyceae (62%), Bacillariophyceae (17%), Fragilariophyceae (8%), Dinophyceae (8%) and Cyanophyceae (5%). Throughout the study period, the occurrence of most dominant species was observed from class Coscinodiscophyceae and Bacillariophyceae. The phytoplankton species also showed significant changes according to seasonal variations as well as the nutrient availability. Phytoplankton attained their maximum population density during premonsoon; whereas minimum population was observed during monsoon. During performed statistical analysis on phytoplankton species, the Shannon & Wiener diversity index was found to be higher during postmonsoon and lower during monsoon season. The Canonical Correspondence Analysis (CCA) was used, to find out the seasonal relationship between phytoplankton and physicochemical parameters. Hence, the executed CCA results revealed that temperature, salinity, silicate, DO and IP have a higher influence on phytoplankton abundance.
The diversity and distribution of the diatom genus Chaetoceros (Bacillariophyceae) was studied at monthly, bi-weekly and weekly intervals over two periods (2009–2010, 2013–2014) in the Golden Horn Estuary. Chaetoceros was the most diverse genus in the diatom assemblage of the study area. A total of 23 Chaetoceros species were identified based on light and scanning electron microscopy. Three taxa, Chaetoceros aequatorialis, C. contortus and C. lorenzianus f. forceps were recorded for the first time in Turkish seas. The most common species were C. affinis, C. curvisetus, C. decipiens and C. holsaticus. The contribution of Chaetoceros species to the number of total phytoplankton species was between 15% and 17%. The highest abundance of Chaetoceros species was 507 × 103 cells L−1, dominated by C. affinis, C. constrictus, C. holsaticus, C. lauderi in the middle estuary in spring. Chaetoceros species were more abundant in the middle and lower estuary in April and May. In the upper estuary (UE), Chaetoceros species were rarely observed due to low water transparency caused by suspended particulate materials. Light limitation may be considered one of the most important factors affecting the diversity and spatial distribution of these species in the UE. The present work is the first detailed study on the diversity and distribution of Chaetoceros species for Turkish seas.
Occurrence of Cochlodinium polykrikoides red tides have resulted in considerable economic losses in the aquaculture industry in many countries, and thus predicting the process of C. polykrikoides red tides is a critical step toward minimizing those losses. Models predicting red tide dynamics define mortality due to predation as one of the most important parameters. To investigate the roles of heterotrophic protists in red tide dynamics in the South Sea of Korea, the abundances of heterotrophic dinoflagellates (HTDs), tintinnid ciliates (TCs), and naked ciliates (NCs) were measured over one- or two-week intervals from May to Nov 2014. In addition, the grazing impacts of dominant heterotrophic protists on each red tide species were estimated by combining field data on red tide species abundances and dominant heterotrophic protist grazers with data obtained from the literature concerning ingestion rates of the grazers on red tide species. The abundances of HTDs, TCs, and NCs over the course of this study were high during or after red tides, with maximum abundances of 82, 49, and 35 cells mL-1, respectively. In general, the dominant heterotrophic protists differed when different species caused red tides. The HTDs Polykrikos spp. and NCs were abundant during and following C. polykrikoides red tides. The mean and maximum calculated grazing coefficients of Polykrikos spp. and NCs on populations of co-occurring C. polykrikoides were 1.63 d-1 and 12.92 d-1, respectively. Moreover, during or after red tides dominated by the phototrophic dinoflagellates Prorocentrum donghaiense, Ceratium furca, and Alexandrium fraterculus, which formed serial red tides prior to the occurrence of C. polykrikoides red tides, the HTDs Gyrodinium spp., Polykrikos spp., and Gyrodinium spp., respectively were abundant. The maximum calculated grazing coefficients attributable to dominant heterotrophic protists on co-occurring P. donghaiense, C. furca, and A. fraterculus were 13.12, 4.13, and 2.00 d-1, respectively. Thus, heterotrophic protists may often have considerable potential grazing impacts on populations of these four red tide species in the study area.
The ichthyotoxic Cochlodinium polykrikoides red tides have caused great economic losses in the aquaculture industry in the waters of Korea and other countries. Predicting outbreak of C. polykrikoides red tides 1-2 weeks in advance is a critical step in minimizing losses. In the South Sea of Korea, large C. polykrikoides red tide patches have often been recorded offshore and transported to nearshore waters. To explore the processes of offshore C. polykrikoides red tides, temporal variations in three-dimensional distributions of red tide organisms and environmental parameters were investigated by analyzing 4,432 water samples collected from 2-5 depths of 60 stations in the South Sea, Korea 16 times from May to Nov, 2014. In the study area, the vegetative cells of C. polykrikoides were found as early as May 7, but C. polykrikoides red tide patches were observed from Aug 21 until Oct 9. Cochlodinium red tides occurred in both inner and outer stations. Prior to the occurrence of large C. polykrikoides red tides, the phototrophic dinoflagellates Prorocentrum donghaiense (Jun 12 to Jul 11), Ceratium furca (Jul 11 to Aug 21), and Alexandrium fraterculus (Aug 21) formed red tides in sequence, and diatom red tides formed 2-3 times without a certain distinct pattern. The temperature for the optimal growth of these four red tide dinoflagellates is known to be similar. Thus, the sequence of the maximum growth rates of P. donghaiense > C. furca > A. fraterculus > C. polykrikoides may be partially responsible for this sequence of red tides in the inner stations following high nutrients input in the surface waters because of heavy rains. Furthermore, Cochlodinium red tides formed and persisted at the outer stations when NO3 concentrations of the surface waters were <2 μM and thermocline depths were >20 m with the retreat of deep cold waters, and the abundance of the competing red-tide species was relatively low. The sequence of the maximum swimming speeds and thus potential reachable depths of C. polykrikoides > A. fraterculus > C. furca > P. donghaiense may be responsible for the large C. polykrikoides red tides after the small blooms of the other dinoflagellates. Thus, C. polykrikoides is likely to outgrow over the competitors at the outer stations by descending to depths >20 m and taking nutrients up from deep cold waters. Thus, to predict the process of Cochlodinium red tides in the study area, temporal variations in 3-D distributions of red tide organisms and environmental parameters showing major nutrient sources, formation and depth of thermoclines, intrusion and retreat of deep cold waters, and the abundance of competing red tide species should be well understood
We used natural phytoplankton communities from four coastal regions to test diversity-functioning relationships, relations of N2-fixing cyanobacteria to nutrient imbalance, and the importance of metacommunity dynamics. Resource availability was measured as total nitrogen and phosphorus. Resource imbalance was determined as (1) the ratio of dissolved inorganic nitrogen to total phosphorus and (2) an experimentally verified indicator quantified by modelling responses in 14C-based primary production to nutrient additions. Resource availability explained variance in biomass, productivity, and species richness, as expected by the Species Energy Theory, but not evenness. Linear mixed-effects models confirmed the overall relation between productivity and resource availability, whereas other resource availability relations showed also notable clustering by region. The Resource Ratio Theory predicting that diversity increases with the number of limiting resources was not supported. Nutrient imbalance had a weak effect on the biomass of N2-fixing cyanobacteria, but not their share of total phytoplankton biomass. Contrary to many previous studies on biodiversity-ecosystem functioning relationships, we found a highly significant inverse relationship between evenness and biomass. This indicates that species-rich natural phytoplankton communities form the basis for opportunistic species to temporarily monopolize resources and create blooms. The result was consistent across regions, although their community composition differed. Metacommunity dynamics were important, since distance between the regions explained higher percentage of the variability than local resources together. As the species able to monopolize resources vary widely in their role for aquatic food webs and environmental consequences (e.g., food quality, toxicity), species-level trait data is essential to understand better diversity-productivity relationships.
Functional ecology is a subdiscipline that aims to enable a mechanistic understanding of patterns and processes from the organismic to the ecosystem level. This paper addresses some main aspects of the process-oriented current knowledge on phagotrophic, i.e. heterotrophic and mixotrophic, protists in aquatic food webs. This is not an exhaustive review; rather, we focus on conceptual issues, in particular on the numerical and functional response of these organisms. We discuss the evolution of concepts and define parameters to evaluate predator-prey dynamics ranging from Lotka-Volterra to the Independent Response Model. Since protists have extremely versatile feeding modes, we explore if there are systematic differences related to their taxonomic affiliation and life strategies. We differentiate between intrinsic factors (nutritional history, acclimatisation) and extrinsic factors (temperature, food, turbulence) affecting feeding, growth, and survival of protist populations. We briefly consider intraspecific variability of some key parameters and constraints inherent in laboratory microcosm experiments. We then upscale the significance of phagotrophic protists in food webs to the ocean level. Finally, we discuss limitations of the mechanistic understanding of protist functional ecology resulting from principal unpredictability of nonlinear dynamics. We conclude by defining open questions and identifying perspectives for future research on functional ecology of aquatic phagotrophic protists.
Red tides – discolorations of the sea surface due to dense plankton blooms – occur regularly in coastal and offshore waters along much of the world's coastline. Red tides often cause large-scale mortalities of fish and shellfish and significant losses to the aquaculture and tourist industries of many countries. Therefore, understanding and predicting the mechanisms controlling the outbreak, persistence, spread, and decline of red tides are important concerns to scientists, officials, industry, and the public. With increasing knowledge of red-tide species and red-tide events, new mechanisms have been discovered. Based on the nutrition and behaviors of red-tide organisms and biological interactions among them, red-tide outbreaks can be categorized into a hierarchy of four generation mechanisms (GM1–GM4). In the simplest, GM1, all phototrophic red-tide species were treated as exclusively autotrophic organisms without the ability to swim. However, this GM cannot explain red-tide outbreaks in oligotrophic surface waters offshore. Vertical migration (considered in GM2) and mixotrophy (GM3) enable red-tide flagellates to acquire growth factors from nutrient-rich deep waters or co-occurring prey, respectively. In natural environments, all red tides occur by those species outgrowing co-occurring organisms; red-tide species dominate communities by eliminating other species or reducing their abundances. Thus, GM4 contains the direct biological interactions (i.e., inhibition by physical contact or chemical effects) and indirect biological interactions (i.e., acquiring resources faster than others) that can affect the dominance of red-tide species under given conditions. Correctly choosing one of these four GMs for red tides dominated by one causative species is important because the accuracy of predictions may be outweighed by the costs and time required to acquire the relevant information. In this study, mechanisms describing the outbreak, persistence, and decline of red tides were reviewed, the advantages and limitations of each mechanism were evaluated, and insights about the evolution of the mechanisms were developed.
Light-dependent growth of phytoplankton is a fundamental process in marine ecosystems, but we lack a comprehensive view of how light utilization traits vary across genotypes and species, and how this variation is structured by cell size, taxonomy, and environmental gradients. Here, we compile 308 growth-irradiance experiments performed on 119 species of marine phytoplankton from all major functional groups, and characterize growth-irradiance relationships in terms of the initial slope of the growth-irradiance curve (α), the optimal irradiance above which growth declines (Iopt), and the maximum growth rate (μmax). We find that α declines with increasing cell size, although cell size appears to be a weak constraint on this trait. There are significant differences across taxa in α and μmax, with dinoflagellates, raphidophytes, and diazotrophs having the lowest values for both traits, and Phaeocystis spp. and diatoms having relatively high values. Iopt does not vary among taxonomic groups, and all traits exhibit large variation within most groups. Open-ocean isolates tend to have higher α, lower Iopt, and lower μmax than coastal isolates, implying adaptation to low light and low productivity. The three traits are correlated across species such that α and Iopt are negatively related while μmax is positively correlated with both of these traits. There is some evidence that high α carries a cost of high N demand even when nitrogen (not light) is limiting. The results elucidate contrasting light-related ecological strategies across phytoplankton and should help improve the parameterization of major functional groups in biogeochemical models.
The shape of the productivity-diversity relationship (PDR) for marine phytoplankton has been suggested to be unimodal, that is, diversity peaking at intermediate levels of productivity. However, there are few observations and there has been little attempt to understand the mechanisms that would lead to such a shape for planktonic organisms. Here we use a marine ecosystem model together with the community assembly theory to explain the shape of the unimodal PDR we obtain at the global scale. The positive slope from low to intermediate productivity is due to grazer control with selective feeding, which leads to the predator-mediated coexistence of prey. The negative slope at high productivity is due to seasonal blooms of opportunist species that occur before they are regulated by grazers. The negative side is only unveiled when the temporal scale of the observation captures the transient dynamics, which are especially relevant at highly seasonal latitudes. Thus selective predation explains the positive side while transient competitive exclusion explains the negative side of the unimodal PDR curve. The phytoplankton community composition of the positive and negative sides is mostly dominated by slow-growing nutrient specialists and fast-growing nutrient opportunist species, respectively.
Marine phytoplankton are responsible for ∼50% of the CO 2 that is fixed annually worldwide, and contribute massively to other biogeochemical cycles in the oceans. Their contribution depends significantly on the interplay between dynamic environmental conditions and the metabolic responses that underpin resource allocation and hence biogeochemical cycling in the oceans. However, these complex environment-biome interactions have not been studied on a larger scale. Here we use a set of integrative approaches that combine metatranscriptomes, biochemical data, cellular physiology and emergent phytoplankton growth strategies in a global ecosystems model, to show that temperature significantly affects eukaryotic phytoplankton metabolism with consequences for biogeochemical cycling under global warming. In particular, the rate of protein synthesis strongly increases under high temperatures even though the numbers of ribosomes and their associated rRNAs decreases. Thus, at higher temperatures, eukaryotic phytoplankton seem to require a lower density of ribosomes to produce the required amounts of cellular protein. The reduction of phosphate-rich ribosomes in warmer oceans will tend to produce higher organismal nitrogen (N) to phosphate (P) ratios, in turn increasing demand for N with consequences for the marine carbon cycle due to shifts towards N-limitation. Our integrative approach suggests that temperature plays a previously unrecognized, critical role in resource allocation and marine phytoplankton stoichiometry, with implications for the biogeochemical cycles that they drive.
Diatoms and dinoflagellates are two important groups of phytoplankton that co-exist in the compe- tition for light and nutrients. Following the diatom-dominated spring bloom, the shelf sea subsurface chlorophyll maximum (SCM) is often dominated by motile species of phytoplankton, in particular dinoflagellates and sometimes coccolithophores. Turbulence in shelf seas, driven by surface winds and by tidal currents, is likely to easily counteract the typically weak swimming capabilities of phy- toplankton. The thermocline marks a low turbulence region, separating the nutrient-depleted surface (wind-mixed) layer, and the nutrient-replete bottom (tidally-mixed) layer, and so would seem to be an ideal environment for employing a strategy of vertical migration. However, the positioning within the thermocline is crucial, as turbulence in the adjoining boundary layers will act to remove cells that stray too close to the edges of the thermocline and mix them into resource-limited layers of the water column. We combine a Lagrangian random walk model, a k-" turbulence scheme and a simple photosyn- thesis model to track individual phytoplankton cells in a tidally-mixed, stratified water column (e.g. a summer, temperate shelf sea). By allowing motile and non-motile species to compete we find that an ability to use motility to balance resource requirements can offset modest physiological disadvan- tages compared to the non-motile phytoplankton, leading to either co-existence or even dominance of the motile species. However, more severe physiological disadvantages (e.g. combinations of growth rate, nutrient uptake capabilities, and/or respiration) cannot be compensated for by motility alone and further adaptations (such as mixotrophy) would be required. We also show that the SCM can be a place for significant new production (values of 1gC m−2 d−1 and f-ratios of over 0.5 are possible) which stresses its potential importance as a source of food to the pelagic throughout summer.
The profile of a fixed site at station M () in the Korea Strait was studied from March 2006 to February 2007. The aim was to understand the relationship between the annual thermal stratification pattern and seasonal variation in phytoplankton community structure. Physicochemical factors including temperature, salinity and nutrient concentrations, which strongly influence the proliferation and diversity of phytoplankton, were measured. The study period was divided into three due to the characteristic of thermohaline structures; mixed I (March-May 2006), stratified (June-November 2006) and mixed II(December 2006-Feburuary 2007). Diatoms dominated during the mixed I (89%) and II (48%) periods, while nanoplankton group occupied over 83% of total population during the stratified period. The dominant species during the mixed I and II was Chaetoceros socialis (47% and 29%, respectively), while during the stratified period Gyrodinium sp.(4%) was the most dominant. Averaged total chl a concentrations during the mixed I and II periods were 0.61 mg and 0.72 mg , respectively, which were at least two-fold higher than that during the stratified period (0.30 mg ). The vertical mixing and convection process of the water column induced nutrient supply from the bottom layer to the euphotic zone. It also led to the dominance of diatoms during the mixed periods, whereas small phytoplankton prevailed over large phytoplankton as stratification blocked the upward movement of nutrients to subsurface during the stratified period. During the mixed I and II periods, microplanktonic chl a dominated concentrations (50% and 48%, respectively), while picoplanktonic chl a occupied over 37% of total chl a during the stratified period.
The relationship between species diversity and ecosystem functioning has been debated for decades, especially in relation to the “macroscopic” realm (higher plants and metazoans). Although there is emerging consensus that diversity enhances productivity and stability in communities of higher organisms; however, we still do not know whether these relationships apply also for communities of unicellular organisms, such as phytoplankton, which contribute ≈50% to the global primary production. We show here that phytoplankton resource use, and thus carbon fixation, is directly linked to the diversity of phytoplankton communities. Datasets from freshwater and brackish habitats show that diversity is the best predictor for resource use efficiency of phytoplankton communities across considerable environmental gradients. Furthermore, we show that the diversity requirement for stable ecosystem functioning scales with the nutrient level (total phosphorus), as evidenced by the opposing effects of diversity (negative) and resource level (positive) on the variability of both resource use and community composition. Our analyses of large-scale observational data are consistent with experimental and model studies demonstrating causal effects of microbial diversity on functional properties at the system level. Our findings point at potential linkages between eutrophication and pollution-mediated loss of phytoplankton diversity. Factors reducing phytoplankton diversity may have direct detrimental effects on the amount and predictability of aquatic primary production.
• biodiversity
• carbon cycle
• ecosystem functioning
Recent decades have seen a remarkable increase in the number of studies examining biodiversity in nature. Beta diversity—the turnover of community composition in space and time—has received particular attention. Here, I discuss recent findings in spatial and temporal turnover along abiotic and biotic gradients at two different extents. Turnover in space and time seem to exhibit similar scale dependency along latitudinal gradients; turnover is faster in the tropics at narrow study extents, but the pattern is reversed at broad extents as turnover accelerates nearer to the poles. Moreover, organisms at high trophic positions have higher turnover rates in space at broad study extents than do organisms at low trophic positions, but trophic position does not affect temporal turnover rates. Future studies that simultaneously examine variation in community composition in space, time, and along environmental gradients would shed more light on the mechanistic basis of community organization.
The diurnal vertical migrations of 4 marine dinoflagellates (Cachonina niei, Ceratium furca, Gymnodinium splendens, and Prorocentrum micans) were studied in a thermally-stratified Plexiglas column (1.70 m deep, 0.61 m diameter). All species migrated through temperature gradients exceeding 7 C. Some species exhibited altered migration patterns at different salinities either between experiments or compared to observations by other investigators. P. micans exhibited complex changes in swimming speed that depended both on temperature and on the light cycle. These changes provide insight into the possible time course of a field organism's diurnal exposure to physical variability in the water column. P. micans exhibited compositional changes in response to the light cycle, but not to the cross-thermocline temperature differential. A multi-parameter response matrix is required to model coupling between organisms and biologically-active physical mechanisms realistically.
Inter-oceanic scale studies allow us to understand the global spread of micro-organisms in marine ecosystems. In this study, micro-eukaryotic communities in marine surface sediment were collected from tropical to Arctic sites. We found that micro-eukaryotic generalists had much higher intraspecific variation than specialists which allow them to distribute more widely through higher spatiotemporal asynchrony and complementary niche preferences among conspecific taxa. Moreover, comparing to the host-associated protozoa and small metazoa, the algae and free-living protozoa with higher intraspecific variation allow them to have wider distribution ranges. Species abundance also played an important role in driving the distribution ranges of generalists and specialists. The generalists had important effects on regional α-diversity even at an inter-oceanic scale which led to the micro-eukaryotic species richness in polar sites to be mainly influenced by the regional generalists but not the local specialists. In particular, more than 97% of algal species in polar sites were shared with the tropical and subtropical sites (including toxic dinoflagellate). Overall, our study suggests that the effects of global change and human activities on the vulnerable high latitude habitats may lead to biotic homogenization for the whole microbial community (not only the dispersal of some harmful algae) through the potential long-distance spread of generalists.
Based on survey data from the Bohai Sea of China in autumn (October) and winter (December) 2019, the structural characteristics of phytoplankton communities and their relationship with environmental factors were analysed. A total of 114 species of phytoplankton belonging to 84 genera and 3 phyla were identified. Warm-water species occurred frequently but cold-water species decreased in the Bohai Sea. This was associated with global warming and rising water temperatures. By comparing with historical data, Paralia sulcata gradually flourished and became the dominant species in autumn and winter, whereas the dominance of Skeletonema costatum decreased. The marine environment of the Bohai Sea has improved significantly in recent years, and phytoplankton biodiversity has increased. In autumn, both total phytoplankton and dinoflagellates were negatively correlated with salinity, and Pseudo-nitzschia delicatissima was positively correlated with nitrite and ammonia nitrogen. In winter, Nitzschia spp. showed a positive correlation with nitrate and a negative correlation with salinity.
Seychelles-Chagos thermocline ridge is one of the major upwelling area in the tropical Indian Ocean, where planktons are known to have large impacts on ocean ecosystem and biogeochemical cycles. Time series assessments of surface zooplankton abundance, biovolume, and community composition were carried out in the Indian Ocean during June 2014. In this paper, we explore the impact of phytoplankton size class biomass on trophic interaction in the thermocline ridge of the southwestern tropical Indian Ocean. Relatively, nitrate was a dominant contributor than the nitrite in the dissolved inorganic nitrogen pool. Size fractionated chlorophyll-a concentration clearly showed that the study area was a typical oligotrophic open ocean, in which picophytoplankton biomass was dominated, accounted for approximately 72% of total Chl a. We assumed that picophytoplankton biomass was most likely influenced by dissolved inorganic nutrients (chiefly nitrite), that showed a strong linear relationship with picophytoplankton biomass (r 2 = 0.41). These results support the key role of nitrite is not only supplying and promoting the growth of smaller phytoplankton biomass, but also controls the structure of zooplankton communities. As a result surface waters were dominated by picophytoplankton biomass, in this condition result in zooplankton being dominated by Poecilostomatoida, constituting approximately 68% of the total zooplankton count. These organisms were widely distributed and occurred in large numbers and displayed a strong linear relationship with picophytoplankton biomass (r 2 = 0.87). These empirical results suggest that abundance of poecilostomatoids presumably supports tertiary trophic levels, suggesting they might play a key role as carbon drivers in the vicinity of the thermocline ridge of the Indian Ocean.
High-throughput sequencing of microbial assemblages has been proposed as an alternative methodology to the traditional ones used in marine monitoring and environmental assessment. Here, we evaluated pico- and nanoplankton diversity as ecological indicators in NW Mediterranean coastal waters by comparing their diversity in samples subjected to varying degrees of continental pressures. Using metabarcoding of the 16S and 18S rRNA genes, we explored whether alphadiversity indices, abundance of Operational Taxonomic Units and taxonomic groups (and their ratios) provide information on the ecological quality of coastal waters. Our results revealed that only eukaryotic diversity metrics and a limited number of prokaryotic and eukaryotic taxa displayed potential in assessing continental influences in our surveyed area, resulting thus in a restrained potential of microbial plankton diversity as an ecological indicator. Therefore, incorporating microbial plankton diversity in environmental assessment could not always result in a significant improvement of current marine monitoring strategies.
Temperature is a major driver of phytoplankton growth and physiology, but despite decades of study on temperature effects, the influence of temperature fluctuations on the growth acclimation of marine phytoplankton is largely unknown. To address this knowledge gap, we subjected a coastal phytoplankton species, Heterosigma akashiwo, to ecologically relevant temperature shifts of 2–3°C, cumulatively totaling 3–16°C across a range from 6°C to 31°C over a 3‐week period. Using a symmetric design, we show time dependent differences between growth rates and that these changes were related to the magnitude of the temperature shift, but not the direction. Cell size scaled inversely with temperature at a rate of −1.9 to −3.3%°C−1 at all except the highest temperature treatments > 25°C. Intraspecific variability in growth rates increased exponentially with cumulative thermal shifts, suggesting thermal variability may be a driver of intraspecific variation. The observed acclimation effects on phytoplankton growth rates suggest that ignoring acclimation effects could systematically under or overestimate temperature‐dependent primary production. Empirical results, contextualized with in situ coastal ocean temperature record, demonstrated that daily primary production could differ from current model assumptions utilizing acclimated rates by −33% to +36%. If broadly applicable to diverse phytoplankton species, these results have ramifications for predicting the ecology and production of phytoplankton in present day dynamic ecosystems and in future climate scenarios where thermal variability is expected to increase.
Sriwijayanti LA, Djumanto, Setiawan RY, Firdaus MR, Fitriya N, Sugeha HY. 2019. Community structure of phytoplankton in the surface and thermocline layers of Sangihe and Talaud waters, Indonesia. Bonorowo Wetlands 9: 51-58. The aim of this study was to determine the species dominance and distribution, and community structure of phytoplankton in the surface and thermocline layers of Sangihe and Talaud waters Indonesia. Phytoplankton samples were collected at the Sangihe-Talaud waters in October 2018 at 14 research stations. Water samples were collected at 5 m (surface) and thermoclines layers using rosette sampler equipped with Conductivity, Temperature, and Depth (CTD) recorder. Samples were concentrated to 40 ml using hand plankton net (mesh size 20 µm), then preserved with 4% formaldehyde. Phytoplankton species were identified using a guidebook based on morphological character traits. The cell count of each species of plankton was calculated using a Sedgwick rafter counting cell chamber. The result showed that there were 4 classes of phytoplankton (Bacillariophyceae, Dinophyceae, Cyanophyceae, and Raphydophyceae) which consisted of 59 species in the surface and 56 species in the thermocline, respectively. The abundance of phytoplankton at surface ranged from 77,333-4,024,000 cell m-3, meanwhile in the thermocline layer 8,000-542,222 cell m-3. The average of phytoplankton diversity of the surface was 0.82 and the thermocline was 1.71. The surface layer was dominated by Leptocylindrus danicus (8.92 x 106 cell m-3), Trichodesmium erythareum (5.83 x 106 cell m-3), and Detonula converfacea (0.62 x 106 cell m-3). The thermocline layer was dominated by Chaetoceros affinis (2.74 x 105 cell m-3), Thalassionema nitzchioides (2.21 x 105 cell m-3), and Chaertoceros dichaeta (1.38 x 105 cell m-3). The low phytoplankton abundance was found at the stations 12 and 13 caused by higher salinity concentration. The highest phytoplankton abundance was found in the stations with warmer temperatures, both in the surface and in the thermocline. The shallow depth thermocline layer (75-100 m) has a higher abundance than the deeper thermocline layer (110-150 m). Temperature was the environmental parameter that has the greatest influence on the abundance and species of phytoplankton, the phytoplankton in the surface layer reached 10 times more abundant than the thermocline layer.
The aim of this study was to determine the species dominance and distribution, and community structure of phytoplankton in the surface and thermocline layers of Sangihe and Talaud waters Indonesia. Phytoplankton samples were collected at the Sangihe-Talaud waters in October 2018 at 14 research stations. Water samples were collected at 5 m (surface) and thermocline layers using a rosette sampler equipped with Conductivity, Temperature, and Depth (CTD) recorder. Samples were concentrated to 40 ml using hand plankton net (mesh size 20 µm), then preserved with 4% formaldehyde. Phytoplankton species were identified using a guidebook based on morphological character traits. The cell count of each species of plankton was calculated using a Sedgwick rafter counting cell chamber. The result showed that there were 4 classes of phytoplankton (Bacillariophyceae, Dinophyceae, Cyanophyceae, and Raphydophyceae) which consisted of 59 species in the surface and 56 species in the thermocline, respectively. The abundance of phytoplankton at surface ranged from 77,333-4,024,000 cell m-3 , meanwhile in the thermocline layer 8,000-542,222 cell m-3. The average of phytoplankton diversity of the surface was 0.82 and the thermocline was 1.71. The surface layer was dominated by Leptocylindrus danicus (8.92 x 106 cell m-3), Trichodesmium erythareum (5.83 x 106 cell m-3), and Detonula converfacea (0.62 x 106 cell m-3). The thermocline layer was dominated by Chaetoceros affinis (2.74 x 105 cell m-3), Thalassionema nitzchioides (2.21 x 105 cell m-3), and Chaertoceros dichaeta (1.38 x 105 cell m-3). The low phytoplankton abundance was found at the stations 12 and 13 caused by higher salinity concentration. The highest phytoplankton abundance was found in the stations with warmer temperatures, both in the surface and in the thermocline. The shallow depth thermocline layer (75-100 m) has a higher abundance than the deeper thermocline layer (110-150 m). Temperature was the environmental parameter that has the greatest influence on the abundance and species of phytoplankton, the phytoplankton in the surface layer reached 10 times more abundant than the thermocline layer.
The ocean is home to myriad small planktonic organisms that underpin the functioning of marine ecosystems. However, their spatial patterns of diversity and the underlying drivers remain poorly known, precluding projections of their responses to global changes. Here we investigate the latitudinal gradients and global predictors of plankton diversity across archaea, bacteria, eukaryotes, and major virus clades using both molecular and imaging data from Tara Oceans. We show a decline of diversity for most planktonic groups toward the poles, mainly driven by decreasing ocean temperatures. Projections into the future suggest that severe warming of the surface ocean by the end of the 21st century could lead to tropicalization of the diversity of most planktonic groups in temperate and polar regions. These changes may have multiple consequences for marine ecosystem functioning and services and are expected to be particularly significant in key areas for carbon sequestration, fisheries, and marine conservation. VIDEO ABSTRACT.
Intensive fish aquaculture has raised serious environmental concerns, including eutrophication, harmful algal blooms, fish kills, etc. Integrated multi-trophic aquaculture (IMTA) may be the most suitable aquaculture technology to achieve environmental and economic sustainability. The objectives of present study are to review the status of aquaculture and IMTA in Korea; and to determine the challenges to apply the principles of IMTA to intensive monoculture in Korean coastal waters. Korea has been one of the leading countries in aquaculture. Like other advanced countries in aquaculture, such as China and Japan, most aquaculture practices in Korea are intensive monoculture and farms are highly concentrated in bays or estuaries with restricted circulation. In intensive open water aquaculture in these waters, nutrient producers (finfish) are cultured mostly in southeastern Korea whereas extractive organisms (seaweeds) are farmed in the southwestern Korea. There are relatively small areas of overlap between these monocultures, causing environmental issues and reduction in the quality of aquacultured products. Recent attempts of IMTA in Korean coastal waters suggest that IMTA can be a good management tool for improving Korean aquaculture although there are still challenges to overcome. These challenges include development of temperature tolerant species/strains of extractive organisms such as seaweeds and sea cucumbers. Most aquacultured seaweed and sea cucumber species in Korea do not grow well during the summer months, when the release of finfish effluent is at its peak. It is essential to the future success of aquaculture in Korea that a coastal zone management (CZM) be developed that reflects coordinating fed and extractive organisms in coastal bays and estuaries rather them keeping them isolated from one another. The importance of a new regulatory framework advocating IMTA solutions will be essential for environmental protection and continued success of aquaculture in Korea. Although this review is a case study in Korea for IMTA, it will also provide critical information for coastal managers, aquaculturists and regulators in other countries where there are intensive monocultures of fed and extractive organisms.
1. Phytoplankton assemblages in the open ocean are usually assumed to be mixed on local scales unless large semi-permanent density discontinuities separating water masses are present. Recent modelling studies have, however, suggested that ephemeral submesoscale oceanographic features leading to only subtle density discontinuities may be important for controlling phytoplankton alpha- and betadiversity patterns. Until now, no empirical evidence has been presented to support this hypothesis.
2. Using hydrographic and taxonomic composition data collected near Iceland during the period of the 2008 spring bloom, we show that the distribution of phytoplankton alpha- and beta-diversity was related to submesoscale heterogeneity in oceanographic conditions. Distinct phytoplankton communities as well as differences in richness were identified on either side of a front delimiting surface
waters of slightly different (~0.03) salinities.
3. Alpha-diversity was significantly higher on the high salinity side of the front compared to the low salinity side. This difference was primarily driven by the presence of several large diatom species in the high salinity region, especially of the genus Chaetoceros which dominated the biomass here. By investigating beta-diversity in relation to environmental and spatiotemporal variables, we show that the regional distribution of phytoplankton taxa was influenced by both different environmental conditions on either side of the front and dispersal limitation across the front. Changes in beta-diversity were primarily driven by turnover rather than nestedness and were apparently controlled by different processes in each region.
4. Synthesis. This study shows that small-scale and ephemeral density discontinuities created by submesoscale frontal dynamics can play a major role in structuring patterns of phytoplankton diversity. Evidence is presented that they can generate changes in environmental conditions (leading to environmental filtering) and act as physical (dispersal) barriers for phytoplankton transport. The study suggests that dispersal barriers are potentially of much greater importance for phytoplankton diversity at local scales than currently recognized and indicates that drivers of marine phytoplankton diversity are similar to those structuring diversity of land plants.
A new algorithm was developed, not only to detect the existence of a thermocline, but also to extract the thermocline parameters (such as thermocline thickness, mixed layer thickness, maximum temperature gradient, and temperature difference of thermocline), using the vertical profile of water temperature. According to Kappa analysis, in order to find adequate threshold values of vertical water temperature gradients {\Delta}T (^{\circ}C/m), agreement and reliability were 87% and 0.74 respectively, in the conditions of maximum {\Delta}T{\geq}0.5 and surface and bottom layers . Also, three different kinds of methods, viz. 1. Gradient method, 2. Hyperbolic tangent method, and 3. Differential hyperbolic tangent method, were tested to extract the key parameters of a thermocline. Comparing the results of three different methods, the differential hyperbolic tangent method was the most appropriate to extract the start and end point of a thermocline curve.
A recently discovered paradoxical maximum of planktonic protistan species in the salinity gradient of the Baltic Sea revealed an inverse trend of species number/salinity relation in comparison to the previously accepted species-minimum model for macrozoobenthos. Here, we review long-term data on organisms of different size classes and ecological groups to show that eukaryotic and prokaryotic microbes in plankton demonstrate a maximum species richness in the challenging zone of the critical salinity 5–8, where the large-bodied bottom dwellers (macrozoobenthos, macroalgae and aquatic higher plants) experience large-scale salinity stress which leads to an impoverished diversity. We propose a new conceptual model to explain why the diversity of small, fast-developing, rapidly evolving unicellular plankton organisms benefits from relative vacancy of brackish-water ecological niches and impaired competitiveness therein. The ecotone theory, Hutchinson's Ecological Niche Concept, species–area relationships and the Intermediate Disturbance Hypothesis are considered as a theoretical framework for understanding extinctions, speciation and variations in the evolution rates of different aquatic species in ecosystems with the pronounced salinity gradient.
Recent climate warming is expected to affect phytoplankton biomass and diversity in marine ecosystems. Temperature can act directly on phytoplankton (e.g. rendering physiological processes) or indirectly due to changes in zooplankton grazing activity. We tested experimentally the impact of increased temperature on natural phytoplankton and zooplankton communities using indoor mesocosms and combined the results from different experimental years applying a meta-analytic approach. We divided our analysis into three bloom phases to define the strength of temperature and zooplankton impacts on phytoplankton in different stages of bloom development. Within the constraints of an experiment, our results suggest that increased temperature and zooplankton grazing have similar effects on phytoplankton diversity, which are most apparent in the post-bloom phase, when zooplankton abundances reach the highest values. Moreover, we observed changes in zooplankton composition in response to warming and initial conditions, which can additionally affect phytoplankton diversity, because changing feeding preferences of zooplankton can affect phytoplankton community structure. We conclude that phytoplankton diversity is indirectly affected by temperature in the post-bloom phase through changing zooplankton composition and grazing activities. Before and during the bloom, however, these effects seem to be overruled by temperature enhanced bottom-up processes such as phytoplankton nutrient uptake.
We present an analysis of the global impact of microplanktonic grazers on marine phytoplankton and its impli- cations for remineralization processes in the microbial community. The data were obtained by an extensive literature search that yielded 788 paired rate estimates of autotrophic growth (m) and microzooplankton grazing (m) from dilution experiments. From studies in which phytoplankton standing stock was measured in terms of carbon equiv- alents, we show that the production estimate from dilution experiments is a reasonable proxy (r 5 0.89) for production determined by the standard 14 C method. The ratio m :m, the proportion of primary production (PP) consumed by micrograzers, shows that microzooplankton consumption is the main source of phytoplankton mortality in the oceans, accounting for 67% of phytoplankton daily growth for the full data set. This ratio varies modestly among various marine habitats and regions, with data averages ranging from 60% for coastal and estuarine envi- ronments to 70% for the open oceans, and from ;59% for temperate-subpolar and polar systems to 75% for tropical-subtropical regions. Given estimates for the metabolic requirements of micrograzers and assuming they consume most bacterial production, regionally averaged estimates of the protistan respiration are 35-43% of daily PP for the first level of consumer or 49-59% of PP for three trophic transfers. The estimated contributions of microbial grazers to total community respiration are of the same magnitude as bacterial respiration. Consequently, potential ecosystem differences in micrograzer activity or trophic structure are a large uncertainty for biogeochemical models that seek to predict the microbial community role in carbon cycling from bacterial parameters alone.
Salinity varies widely in coastal areas that often have a high abundance of Pseudo-nitzschia H. Peragallo. Pseudo-nitzschia is abundant in Louisiana waters, and high cellular domoic acid has been observed in natural samples but no human illness has been reported. To assess the threat of amnesic shellfish poisoning (ASP), we examined the effect of salinity on Pseudo-nitzschia occurrence in the field and growth in the laboratory with special emphasis on the salinity range where oysters are harvested (10–20 psu). In Louisiana coastal waters, Pseudo-nitzschia spp. occurred over a salinity range of 1 to >35 psu, but they occurred more frequently at higher rather than lower salinities. Seven species were identified, including toxigenic species occurring at low salinities. In culture studies, seven clones of three species grew over a salinity range of 15 to 40 psu, some grew at salinities down to 6.25 psu, and most grew at salinities up to 45 psu. Tolerance of low salinities decreased from Pseudo-nitzschia delicatissima (Cleve) Heiden to P. multiseries (Hasle) Hasle to P. pseudodelicatissima (Hasle) Hasle emend. Lundholm, Hasle et Moestrup. In conclusion, although Pseudo-nitzschia was more prevalent in the field and grew better in the laboratory at higher salinities, it grew and has been observed at low salinities. Therefore, the probability of ASP from consumption of oysters harvested from the low salinity estuaries of the northern Gulf of Mexico is low but not zero; animal mortality events from toxin vectors other than oysters at higher salinity on the shelf are more likely.
ABSTRACT The literature on discriminant feeding by planktonic protozoans using geometric and nongeometric criteria is reviewed with emphasis on recent studies that indicate phagotrophic protists can use information other than particle size or shape to sort among potential prey. Sufficient data are available for ciliates, aplastidic microflagellates, and phagotrophic dinoflagellates. Numerous representative taxa of all three groups have chemosensory capabilities, either to specific chemicals or to prey exudates, that modify their motility patterns resulting in aggregation or dispersal. Representatives of all three groups also have specific prey preferences. These considerations imply, but do not prove, selectivity in feeding through use of chemical cues. Although prey geometry is clearly a first-order determinant of ingestion through passive mechanical selection, recent studies illustrate that planktonic ciliates and flagellates can use other criteria to discriminate among prey. the evidence clearly implicates use of chemical cues, most likely perceived through contact chemoreception. Filter feeders as well as raptors have such abilities indicating that feeding mechanisms per se do not imply limitations on feeding behavior. Evidence of considerable flexibility and complexity in chemoperceptive feeding suggests that we have only glimpsed the more detailed features of feeding behavior in aquatic protozoans.