Chl-a Ratios Research Articles

A negative biological Indian Ocean dipole event in 2022

The biological dipole mode index (BDMI) showed a negative biological Indian Ocean dipole (BIOD) event occurred in the Equatorial Indian Ocean with the corresponding BIOD index BDMI(Ratio) at − 0.31 in October 2022. The chlorophyll-a (Chl-a) ratio (or Chl-a anomaly) between Chl-a in October 2022 and October Chl-a climatology from the Visible Infrared Imaging Radiometer Suite (VIIRS) showed negative dipolar features with the depressed and enhanced Chl-a in the east and west IOD zones, respectively. During this negative BIOD event, Chl-a ratio dropped to ~ 0.4–0.5 in the offshore region of the west Sumatra Coast in the east IOD zone, while it increased to ~ 1.5–1.6 in the northern west IOD zone. Temporal variations of the longitudinal averaged Chl-a ratio and the 20 °C isothermal (ISO20) depth anomaly generally coincided and collocated with each other. The positive and negative BIOD events in 2019 and 2022, respectively, were attributed to the nutrient dynamics driven by the physical dynamics in these two phases of IOD events. In the negative BIOD event in 2022, the depressed Chl-a in the east IOD zone was attributed to low sea surface nutrient levels due to dampened upwelling and deepened thermocline, while anomalously high Chl-a in the west IOD zone were driven by higher sea surface nutrient concentrations caused by the surface water divergence and shoaling thermocline.

Supplemental light quality affects optimal seeding density of microgreens

AbstractHigher seeding densities can negatively affect the yield of microgreens. We quantified the effects of supplemental light quality and seeding density on the yield of microgreens. Seeds of red beet (Beta vulgaris L. ssp. esculenta) were grown in a greenhouse and provided with a narrow‐spectrum (or “purple”) and broad‐spectrum (or “white”) supplemental lighting at nighttime. Purple spectrum contained 90% red, 0% green, 10% blue, and 0% far‐red (R90: G0: B10: FR0) light, and white spectrum had 35% red, 42% green, 23% blue, and 0% far‐red light (R35: G42: B23: FR0). Each light quality treatment contained seeding densities of 50, 150, 300, and 450 g m−2. We measured fresh weight (FW) and dry weight (DW) on days 8, 10, 12, and 14 after sowing, relative growth rate (RGR), canopy area (CA), and chlorophyll (chl)a, chlb, betacyanin, and betaxanthin pigments. The optimal seeding density in the white treatment was 300 g m−2, whereas FW increased even at the seeding density of 450 g·m−2 in the purple treatment. The RGR of seedlings decreased with increasing seeding density but was higher by 27.8% in the purple than white treatment. The slope of the relationship between DW and CA (related to photosynthetic efficiency) was higher for the purple than white treatment (0.012 vs. 0.008 g cm−2). The ratio of chla to chlb (related to photosynthetic reaction center activity) increased by 15% in the purple than white treatment. Therefore, higher optimal density in the purple than white light quality treatment is likely due to increased photosynthetic efficiency of seedlings.

MWCNTs Alleviated saline-alkali stress by optimizing photosynthesis and sucrose metabolism in rice seedling

ABSTRACTSaline and alkali stress affects the growth and development, survival rate, and final yield of rice, while new nano materials can have a positive effect on rice growth. In order to investing the effects of carboxymethyl multi walled carbon nanotubes (MWCNTs) on the growth and development of rice seedlings under salt alkali stress, rice seedlings were cultured using rice variety “Songjing 3” using nutrient solution water culture method. The effects of MWCNTs on water absorption capacity, leaf photosynthesis, and sucrose metabolism of rice seedlings under 50 mmol/L saline-alkali stress (1NaCl: 9Na2SO4: 9NaHCO3: 1Na2CO3) conditions were investigated. The results showed that MWCNTs can improve the water use ability of roots and leaves, especially the water absorption ability of roots, which provides a guarantee for the improvement of rice biomass and the enhancement of leaf photosynthetic capacity under adverse conditions. After treatment with MWCNTs, the photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (Tr) of leaves increased significantly, and the photochemical quenching value (qP), photochemical quantum efficiency value (Fv/Fm), and electron transfer rate value (ETR) of chlorophyll fluorescence parameters increased significantly, which is beneficial to the improvement of the PSII photosynthetic system. MWCNTs treatment promoted the increase of photosynthetic pigment content in leaves under salt and alkali stress, improved the ratio of Chla and Chlb parameters, increased the activities of key photosynthetic enzymes (RUBPCase and PEPCase) in leaves, increased the value of total lutein cycle pool (VAZ), and significantly enhanced the deepoxidation effect of lutein cycle (DEPS), which can effectively alleviate the stomatal and non stomatal constraints on leaf photosynthesis caused by salt and alkali stress. MWCNTs treatment significantly enhanced the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS) under salt and alkali stress, and decreased the activities of soluble acid invertase (SAInv) and alkaline/neutral invertase (A/N-Inv), indicating that MWCNTs promoted sucrose synthesis while inhibiting sucrose decomposition, thereby promoting sucrose accumulation in rice leaves. This study can provide theoretical and experimental basis for the application of MWCNTs to the production of rice under salt and alkali stress, and can find a new way for rice production in saline and alkaline lands.

Spatial distributions and environmentally-mediated factors of dimethylsulfoxide off the northern Antarctic Peninsula in summer

Spatial distributions of dissolved and particulate dimethylsulfoxide (DMSOd and DMSOp) were investigated off the northern Antarctic Peninsula during the austral summer of 2018, an ecologically and climatically important region of the world. In the upper waters, DMSOd was concentrated in the ice-melt zone because DMSO functions physiologically as an intracellular osmolyte and cryoprotectant. DMSOd concentrations had a weak positive correlation with temperature but a negative correlation with nutrients. This highlighted the importance of temperature-dependent biological activities and photolysis in DMSOd production and the important role of the intracellular antioxidation system in phytoplankton cells. The decrease of average DMSOp:Chl-a ratios in upper waters from west to east, along with decreasing temperatures and increasing diatoms proportions in the phytoplankton, illustrates how seawater DMSO production capacities depend on ambient temperatures and the composition of phytoplankton assemblages. DMSOp were accumulated in deep waters through bio-debris accumulation and microbial activity.

The N:Chl-a ratio defines the optimal physiological state in marine microalgae

Several factors may influence the growth of microalgae and their biochemical composition. Thus, bioassays can contribute to understanding how the environment influences the chemical element:chlorophyll-a ratio and the metabolic processes in different microalgae. The objective of this study, under laboratory conditions, was to study the variation in the Carbon-to-Chlorophyll-a (C:Chl-a), Nitrogen-to-Chlorophyll-a (N:Chl-a), and Hydrogen-to-Chlorophyll-a (H:Chl-a) ratios as indicators of the physiological state of species representative of different functional groups of phytoplankton: Isochrysis galbana, Chaetoceros calcitrans, and Dunaliella tertiolecta. The results suggest that changes in the content of intracellular pigments can be directly attributed to maximizing phytoplankton growth through the metabolic requirements, where Nitrogen and Carbon uptake and assimilation are critical drivers related to their physiological needs rather than their photosynthesis processes per se. Our observations documented the behavior of phytoplanktonic microalgae, where I. galbana showed the lowest Chl-a values associated with metabolic processes to produce complex molecules for storage and as reserve compounds. In C. calcitrans, metabolic processes are mainly addressed to generate complex compounds of Carbon and Nitrogen inside the cell rather than for population increase. Finally, D. tertiolecta showed that these elements are used gradually but progressively, generating more photosynthetic units during the exponential growth phase. This work provides new evidence to understand metabolic mechanisms between different groups of phytoplankton, essential knowledge to produce macromolecules and bioactive metabolites with different applications.

Short-term warming and N deposition alter the photosynthetic pigments trade-off in leaves of Leymus secalinus growing in different alpine grassland habitats on Qinghai-Tibetan plateau.

Warming and N (nitrogen) deposition are the two main driving factors of global change. We examined the effects of increased N deposition (8 kg ha-1 year-1) and warming, as well as their combined effect on the leaf photosynthetic pigments of Leymus secalinus, which is one of the key alpine plants growing in different grassland habitats on Qinghai-Tibetan plateau. In 2014, the experiments were established in 12 plots (2×5m) of three types of habitats including alpinemeadow (AM), alpine steppe (AS), and cultivated grassland (CG) with the following treatments: CK (control treatment), N (only N deposition), W (only warming), and W&N (warming combined with N deposition). Results showed that the effects of warming and N deposition on photosynthetic pigments of Leymus secalinus varied with different grassland habitat types. In three grassland types, warming led to no significant effects on the total chlorophyllcontent of L.secalinus, while N deposition alone only significantly enhanced total chlorophyllcontent in alpine meadow and cultivated grassland. N deposition combined with warming only significantly enhanced total chlorophyllcontent of L.secalinus in alpine steppe and cultivated grassland. Chla content plays an important role in determining the variation of total chlorophyll content. Chla/Chlb ratioof L.secalinus was more stable in alpine meadow compared with that of L. secalinus in the other two grassland types. Car/Chl ratioof L.secalinus was not prone to be affected by warming and N deposition in all grassland types. Leaf N content was obviously positively correlated with photosynthetic pigments, especially Chla content. Warming and N deposition all affected photosynthetic pigment dynamics and tended to increase Chla by enhancing its weight. Our results highlighted that both warming and N deposition as well as their combination can alter the trade-off of photosynthetic pigments through enhancing the Chla ratio in L. secalinus. In addition, growing habitats should be within consideration when studying alpine plants adaptation mechanism to global change in the future.

Effects of nitrogen and phosphorus on chlorophyll a in lakes of China: a meta-analysis

Whether or not chlorophyll a (Chla) is limited by nitrogen (N) or phosphorus (P), or both, remains highly debated. In part this is due to the lack of a robust statistical rarely considered using a statistical method in studies of peer-review research of lakes. Individual studies only used the use of the relationship between Chla and nutrients to judge the effects of N and P, ignoring the spatial heterogeneity of the ecological environment. Here, we evaluated the effects of nitrogen and phosphorus on Chla via a meta-analysis. The dataset consists of 1024 observations from 34 lakes in China. The results show that Chla is one of the most important indicators of water eutrophication, both nutrients were related Chla trophic state, and that TP plays an important role over TN, especially in the hypereutrophic Chla conditions. With the increase of TN/TP, Chla concentration is decreased, which may be the co-limited of TN and TP. These three values largely explained the increment of eutrophication Chla, although the relative effects differed across nutrients, with changes in the TN total contributing 5.2% of the increment in Chla, while the TP change contributed 272.0% of the increment in Chla. At spatial scales, logarithm-transformed response ratio () of Chla indicated that the lake shifts from N limitation (64.0% > 28.0%) in oligo-mesotrophic to P limitation (170.0% > 99.0%) in eutrophic and co-limitation (66.0% and 46.0%) by N & P in hypereutrophic. These results demonstrate that TP reduction can mitigate eutrophication in most large lakes but a dual TN and TP reduction may be needed in eutrophic lakes, especially in hypereutrophic states. This study highlights the differential effects of the three factors concentration, which may offer important implications for better management of the response of the eutrophication lakes to nutrients (N and P) in the future.

Chlorophyll-nutrient relationship changes with lake type, season and small-bodied zooplankton in a set of subtropical shallow lakes

Phytoplankton biomass is generally measured as chlorophyll-a concentration (Chla), and is well known to be sensitive to nutrients and large zooplankton. However, whether nutrient was still be a better predictor of Chla when potential affecting variables were taken together, and whether the critical TN:TP (total nitrogen: total phosphorus, by mass) threshold for classifying nutrient limitation varied with lake type remain uncertain. Furthermore, it remains largely unknown to what extent small zooplankton (SZ) can affect the nutrients-Chla relationships. Here, an investigation on how Chla responded to abiotic factors and SZ dynamics was performed in 21 subtropical shallow lakes along the lower reach of Chinese Yangtze River. These lakes were subdivided into two lake types including urban lakes featured by a low water exchange rate, and suburban lakes with hydrological connectivity. Chla and TP:Chla ratio were generally higher and lower in urban lakes than those in suburban lakes, respectively. Various analyses revealed that TP and water temperature were the key factors regulating Chla in urban and suburban lakes, respectively. Across urban lakes, TP accounted for >50% of the Chla variances in spring, autumn, and winter, but only explained 28% of summer Chla. However, if the sampling sites where SZ density was >17.5 times higher than that in spring were removed, the determination coefficient (R2) in the linear regression analysis between TP and summer Chla increased (from 0.28 to 0.57), and the Akaike Information Criterion decreased. Furthermore, TP:Chla was positively correlated with SZ in urban lakes in spring when the highest density of SZ (HSZ): the lowest density of SZ (LSZ) ratio was 456 (>17.5), while that interrelationship was not found in summer with the HSZ:LSZ ratio of 17.5. Therefore, the weak TP-summer Chla relationship in urban lakes was primarily caused by SZ when their density exceeded a 17.5-fold increase, i.e. small zooplankton could adopt “quantity-driven” strategy for phytoplankton control. For further strengthening the eutrophication management and remediation in subtropical urban lakes, it is critical to recover aquatic vegetation that can not only absorb P directly but provide refuge for zooplankton instead of dredging the sediments completely. In addition, we recommended that TN:TP ratio exceeding 20.0 could be the threshold identifying P-limitation in urban lakes rather than suburban lakes, and transparency can be used as rough indicators for measuring TP and Chla concentrations (<25 μm) in urban lakes.

Complementary Approaches to Assess Phytoplankton Groups and Size Classes on a Long Transect in the Atlantic Ocean

Phytoplankton biomass, through its proxy, Chlorophylla, has been assessed at synoptic temporal and spatial scales with satellite remote sensing (RS) for over two decades. Also, RS algorithms to monitor relative size classes abundance are widely used; however, differentiating functional types from RS, as well as the assessment of phytoplankton structure, in terms of carbon remains a challenge. Hence, the main motivation of this work it to discuss the links between size classes and phytoplankton groups, in order to foster the capability of assessing phytoplankton community structure and phytoplankton size fractionated carbon budgets. To accomplish our goal, we used data (on nutrients, photosynthetic pigments concentration and cell numbers per taxa) collected in surface samples along a transect on the Atlantic Ocean, during the 25th Atlantic Meridional Transect cruise (AMT25) between 50° N and 50° S, from nutrient-rich high latitudes to the oligotrophic gyres. We compared phytoplankton size classes from two methodological approaches: (i) using the concentration of diagnostic photosynthetic pigments, and assessing the abundance of the three size classes, micro-, nano-, and picoplankton, and (ii) identifying and enumerating phytoplankton taxa by microscopy or by flow cytometry, converting into carbon, and dividing the community into five size classes, according to their cell carbon content. The distribution of phytoplankton community in the different oceanographic regions is presented in terms of size classes, taxonomic groups and functional types, and discussed in relation to the environmental oceanographic conditions. The distribution of seven functional types along the transect showed the dominance of picoautotrophs in the Atlantic gyres and high biomass of diatoms and autotrophic dinoflagellates (ADinos) in higher northern and southern latitudes, where larger cells constituted the major component of the biomass. Total carbon ranged from 65 to 4 mg carbon m–3, at latitudes 45° S and 27° N, respectively. The pigment and cell carbon approaches gave good consistency for picoplankton and microplankton size classes, but nanoplankton size class was overestimated by the pigment-based approach. The limitation of enumerating methods to accurately resolve cells between 5 and 10 μm might be cause of this mismatch, and is highlighted as a knowledge gap. Finally, the three-component model of Brewin et al. was fitted to the Chlorophylla(Chla) data and, for the first time, to the carbon data, to extract the biomass of three size classes of phytoplankton. The general pattern of the model fitted to the carbon data was in accordance with the fits to Chladata. The ratio of the parameter representing the asymptotic maximum biomass gave reasonable values for Carbon:Chlaratios, with an overall median of 112, but with higher values for picoplankton (170) than for combined pico-nanoplankton (36). The approach may be useful for inferring size-fractionated carbon from Earth Observation.

Satellite-based observation of particulate organic carbon in the northern Bay of Bengal

Particulate organic carbon (POC) plays a vital role in the ocean carbon cycle and is related to many important ocean biogeochemical processes. This study investigates the annual and seasonal variability of POC and its relationship with sea surface temperature (SST), chlorophyll-a (Chl-a), and wind vector in the northern Bay of Bengal (BoB) of Bangladesh and validates satellite data with in situ measurement data. Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite level-3 data of POC, Chl-a, and SST were used in this study. Wind vector data were obtained from WindSat Polarimetric Radiometer satellite. Annual average of 18-year (2002–2019) surface POC concentration in the northern BoB ranged from 126.83 mg m−3 to 180.58 mg m−3 (average of 153.84±11.17 mg m−3) with a declining rate of -1.12 mg m−3 year−1. The POC was highest (181.80±22.34 mg m−³) during the northeast-monsoon (December–February) and lowest (136.56±36.24 mg m−³) in the pre-monsoon (March-May). Statistically significant (F3,202 =18.09; p<0.05) difference of POC was found amongst the seasons. A very weak inverse relationship was observed between the SST and POC seasonally and annually, whereas POC and Chl-a showed a strong positive relation in the northern BoB. POC was observed to be very prominent with northeasterly wind in northeast and post-monsoon and low with southwesterly wind in southwest and pre-monsoon. POC variability was influenced mainly by Chl-a, followed by SST and wind speed for BoB. The POC:Chl-a ratio in the northern BoB were ranged from 240.91 to 294.68, which shows a strong influence of biological processes on POC composition. Additional mechanisms responsible for the seasonal POC variability are also addressed in this study. A significantly (p<0.001) moderate correlation (r=0.75) was found between the MODIS Aqua satellite data and in situ observation. Further detailed investigation is needed to observe the role of POC variability in biogeochemical processes of the northern BoB.

Drivers of the variability of dimethylsulfonioproprionate (DMSP) and dimethylsulfoxide (DMSO) in the Southern North Sea

The influence of abiotic and biotic factors on the concentration of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) was investigated and compared during two annual cycles in 2016 and 2018 in the Belgian coastal zone (BCZ) in the southern North Sea at five fixed stations. These stations covered a near-offshore gradient from stations close to the mouth of the Scheldt estuary to most offshore stations. Significant differences of Chlorophyll-a (Chl-a) concentrations were observed between the two years with higher values in early spring 2018 (due to better light and nutrient conditions coupled to colder temperatures) and in summer 2018 (due to warmer conditions) compared to 2016. Nevertheless, the seasonal and spatial DMSP and DMSO (DMS(P,O)) patterns, as well as the yearly average were nearly identical in 2016 and 2018. This can be explained by the fact that the phytoplankton groups responsible for the large differences in Chl-a in 2018 and 2016 were low DMSP-producers characterized by several diatom and dinoflagellate species, occurring in early spring and summer. Further, the Prymnesiophyceae Phaeocystis globosa, occurring in late spring and responsible of most of DMS(P,O) measured in the area, reached similar biomass both years. The DMSP:Chl-a ratio obtained from the field measurements were similar to those previously published for the main observed phytoplankton groups, but more differences were observed for the DMSO:Chl-a ratio. DMS(P,O) estimations based on Chl-a linear regressions for the whole dataset need to account on two relationships discriminating the low and high-DMSP producing species.

Daily Variation of Chlorophyll-A Concentration Increased by Typhoon Activity

The chlorophyll-a (Chla) concentration product of the Himawari-8 geostationary meteorological satellite is used to show the temporal variation of Chla owing to the passage of typhoons, namely, tropical cyclones in the western North Pacific Ocean. The daily Chla variation shows that Chla usually increases along the paths of typhoons, whereas the same observations are almost impossible when using the data of polar-orbiting satellites as shown in previous studies. This is because the temporal resolution of Himawari-8 is ten times more than that of polar-orbiting satellites, and the daily Chla distribution contains a few disturbances attributed to clouds after compositing cloud-free data. Chla usually increases on the day of typhoon arrival, but mostly, the ratio of Chla increased by a typhoon to the background Chla, R Chla HIMA , is less than 2. Only a few typhoons considerably increased Chla. As a whole, R Chla HIMA is proportional to the maximum 10-min sustained wind speed up to 85 knots (44 m s−1), namely, 0.01 mg m−3 knot−1 (0.019 mg s m−4). However, there is no clear dependence between Chla and the wind speed in seas with higher Chla, such as the South China Sea. The result that typhoons are usually cultivating the ocean is important for studies of primary ocean productivity and carbon flux between the atmosphere and ocean.

Estimation of the Particulate Organic Carbon to Chlorophyll-a Ratio Using MODIS-Aqua in the East/Japan Sea, South Korea

In recent years, the change of marine environment due to climate change and declining primary productivity have been big concerns in the East/Japan Sea, Korea. However, the main causes for the recent changes are still not revealed clearly. The particulate organic carbon (POC) to chlorophyll-a (chl-a) ratio (POC:chl-a) could be a useful indicator for ecological and physiological conditions of phytoplankton communities and thus help us to understand the recent reduction of primary productivity in the East/Japan Sea. To derive the POC in the East/Japan Sea from a satellite dataset, the new regional POC algorithm was empirically derived with in-situ measured POC concentrations. A strong positive linear relationship (R2 = 0.6579) was observed between the estimated and in-situ measured POC concentrations. Our new POC algorithm proved a better performance in the East/Japan Sea compared to the previous one for the global ocean. Based on the new algorithm, long-term POC:chl-a ratios were obtained in the entire East/Japan Sea from 2003 to 2018. The POC:chl-a showed a strong seasonal variability in the East/Japan Sea. The spring and fall blooms of phytoplankton mainly driven by the growth of large diatoms seem to be a major factor for the seasonal variability in the POC:chl-a. Our new regional POC algorithm modified for the East/Japan Sea could potentially contribute to long-term monitoring for the climate-associated ecosystem changes in the East/Japan Sea. Although the new regional POC algorithm shows a good correspondence with in-situ observed POC concentrations, the algorithm should be further improved with continuous field surveys.

Size-fractionated biomass and primary productivity of Sargasso Sea phytoplankton

The size structure of phytoplankton communities greatly influences the function of pelagic food webs and, ultimately, the flux of material from the surface ocean to the deep sea. While the biomass and taxonomic composition of organisms in a specific size class are important characteristics of a food web, the activity of that size fraction is more directly relevant to trophic dynamics and biogeochemical cycling. Even if a size class dominates cell abundance or biomass, does it necessarily contribute the most to total primary productivity (PP)? We asked this question for phytoplankton communities from the Sargasso Sea. The picophytoplankton (0.7–2 μm) accounted for 53–85% of the total integrated chl-a and 46–99% or more of the total integrated PP. The microphytoplankton (20–200 μm) were responsible for up to 38% of the total PP, but accounted for no more than 22% of total chl-a. Variations in the picophytoplankton size-class explained 84% of the variance in total integrated chl-a and 87% of the variance in total PP. Size-dependent relative contributions to chl-a versus PP varied with depth, with differences generally driven by vertical variations in C:chl-a ratios and chl-specific rates of PP. Use of the relative contributions of picophytoplankton to biomass as a predictor of their contributions to total primary productivity resulted in an average underestimate of ~7%.

Comparison of Particulate Organic Carbon to Chlorophyll-a Ratio Based on the Ocean Color Satellite Data at the Ieodo and Socheongcho Ocean Research Stations

Lee, D.; Jeong, J.-Y.; Jang, H.K.; Min, J.-O.; Kim, M.J.; Youn, S.H.; Lee, T., and Lee, S.H., 2019. Comparison of particulate organic carbon to chlorophyll-a ratio based on the ocean color satellite data at the Ieodo and Socheongcho ocean research stations. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 267-271. Coconut Creek (Florida), ISSN 0749-0208.The Ieodo ocean research station (IORS) and the Socheongcho ocean research station (SORS) have been operated in South Korea to carry out a research across multiple disciplines. The IORS and the SORS are affected by various water masses such as Tsushima Warm Current (TWC), Yellow Sea Warm Current (YSWC) and Changjiang Diluted Water (CDW). Therefore, the IORS and the SORS are suitable for the research on the physio-ecological response of phytoplankton to environmental changes. The particulate organic carbon to chlorophyll-a ratio (POC:Chl-a) has been widely used for an indicator of the ecological and physiological conditions of the phytoplankton. The purpose of this study is to investigate the POC:Chl-a ratio and its controlling factors at the IORS and the SORS by using satellite dataset. At the IORS, POC:Chl-a ratio ranged from 166.16 to 431.20, and the average was 322.14 ± 46.35. On the other hand, at the SORS, POC:Chl-a ratio ranged from 131.92 to 703.98, and the average was 385.05 ± 123.95. The POC:Chl-a ratio was higher at the SORS from autumn to winter. However, POC:Chl-a ratio in the IORS showed similar ranges in every month. The difference in POC:Chl-a ratio between the IORS and the SORS appear to be caused by differences of environmental conditions such as light intensity, temperature, and nutrients. However, to reveal the detailed relationship between environmental conditions and POC:Chl-a ratio, a further study on seasonal variations of the phytoplankton community structure and several environmental parameters would be warrant.

Benthic-pelagic coupling of carbon and nitrogen along a tropical estuarine gradient (Gulf of Nicoya, Costa Rica)

Tropical estuaries are very little studied compared to temperate ones, despite their generally high primary production rate and hence potential contribution to global carbon and nitrogen budgets. The Gulf of Nicoya (northwest Costa Rica Pacific coast) is one of the most productive estuaries worldwide. However, how changes in benthopelagic coupling affect biogeochemical cycling of carbon and nitrogen over seasons and along the estuarine gradient is not known for this and, in general, other tropical estuaries. For this purpose, we performed two sampling campaigns during the rainy and dry seasons to investigate the contribution of the pelagic and benthic compartments to the carbon and nutrient pools and dynamics of organic matter remineralization in the estuary. Areal concentrations of chlorophyll a (Chla), organic carbon (C) and total nitrogen (N) integrated along the water column photic layer and in the surface sediment generally reached maximum concentrations in the middle of the estuary. Although, integrated Chla in the water column and sediment were in the same range, integrated C and N in the surface sediment (5 cm) were 2–10 times higher than in the water column. The C:Chla and N:Chla ratios in the suspended particulate matter were much higher than those typical of phytoplankton indicating a strong contribution of allochthonous organic matter. However, the C:N ratio in the water column was frequently lower than the Redfield ratio suggesting an important contribution of particulate inorganic N, particularly in the rainy season. Diffusive O2 sediment uptake rate and the O2 penetration depth within the sediment correlated with the organic carbon content in the sediment. In contrast, total oxygen utilization and total CO2 fluxes showed higher variability along the estuary but no significant statistical correlations with any other sediment biogeochemical variables. Organic carbon flux (JC) to the sediment was highly variable along the estuary and between seasons. Despite differences in absolute terms, the fraction of JC accumulated within the sediment for the whole inner part of the Gulf of Nicoya was about 60% in both seasons. Total C burial in the inner part of the gulf was 390 and 813 Tn C d−1 in the rainy and dry seasons, respectively, representing 1.8 and 3.8% of the daily Costa Rica CO2 emissions.

Uncoupling of Seasonal Variations Between Phytoplankton Chlorophyll a and Production in the East China Sea

AbstractPhytoplankton chlorophyll a (Chla), primary production (PP), and nutrient uptake rates are fundamental and important parameters in marine biogeochemical studies. However, the relationships between them are associated with much uncertainty that reflects gaps in basic understanding of ecosystem dynamic. In this study, we simultaneously measured PP and nitrate assimilation (NA) along with estimated concentrations of nutrients, particulate organic carbon concentrations, phytoplankton Chla, pigments, and carbon biomass in the dynamic shelf ecosystems of the East China Sea (ECS) on four cruises during different seasons. There were large spatial gradients of these parameters, and seasonal patterns of phytoplankton Chla and PP varied between water masses. The results of this study and previous work indicated that seasonal variations of Chla and PP were similar in coastal waters but opposite in off‐shelf waters. During summer in off‐shelf waters, there were patches of high PP and NA associated with low Chla concentrations; this pattern was reversed in the winter. We suggest that there is a global tendency for PP and Chla patterns to be out of phase. This asynchrony is reflected mainly in the seasonal variations of C:Chla ratios driven by the combined influences of light, temperature, and nutrients. Stronger grazing pressure by microzooplankton in summer likely contributed to the high production but low biomass in the ECS. The significant correlation between PP and NA suggested that variations of PP in the ECS were driven largely by nitrate uptake, which may be inhibited by high ammonium concentrations in the Changjiang River plume.

Stress tolerance and photoadaptation to solar radiation in Rhodymenia pseudopalmata (Rhodophyta) through mycosporine-like amino acids, phenolic compounds, and pigments in an Integrated Multi-Trophic Aquaculture system

Rhodymenia pseudopalmata lives in the intertidal zone receiving high doses of solar radiation, including the potentially harmful UVR. Previous studies proved it ability to adapt to different artificial light intensities and salinity concentrations. The aim of this study was to describe the differences on the Mycosporine-like amino acids (MAAs), phenolic compounds, and pigments of R. pseudopalmata due to exposure to high solar radiation. Vegetative thalli were exposed to solar radiation using a Solar Exposure Chambers System (SECS) under an Integrated Multi-Trophic Aquaculture (IMTA) approach with marine fish culture. Samples from natural populations in Playa de Carmen, Mexico were included as reference. The biosynthesis of MAAs, and phenolic compounds were stimulated as a response to the stress caused by the exposure to high solar irradiation. Liquid Chromatography-Mass Spectrometry (LC-MS) revealed seven MAAs and their precursor deoxygadusol. Five MAAs were partially characterized through MS2 and fragmentation patterns suggested a common fragmentation pattern pathway. After seven days (D7), the MAAs total content was significant five-fold higher compared to wild populations (0.26 ± 0.1 mg g−1 DW). The Individual composition increased from four MAAs at D0, up to eight at D7, including deoxygadusol, palythene and usujirene, MAAs with high antioxidant activity. At D7, phenolic compounds increased up to 20%, and the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant activity reduced the IC50 to 4.0 ± 0.6 mg mL−1. The pigment content, Phycoerythrin (PE):Chl-a, and MAAs:Chl-a ratios might confer a unique photoprotection role from PE and MAAs to Chl-a. Similarly, Fv/Fm which was adapted to the variations of Photosynthetic Active Radiation (PAR) indicated a process of dynamic photoinhibition. Overall, our results evidenced the ability of this species to tolerate the stress to high solar irradiance and suggested the photoadaptation of the thalli. Farming possibilities, expected MAAs productivity, potential applications of MAAs and ecological considerations are also discussed.

Patterns of nutrient limitation on periphyton in a tropical black-water lake depend on the relative contribution of autotrophic and heterotrophic components

ABSTRACTThis study addressed the occurrence of resource co-limitation of periphytic communities in a tropical black-water lake. We performed a field experiment using nutrient diffusing substrates to create treatments with nitrogen (N) and phosphorus (P) amendments. Two light levels were considered: high light (near the water surface) and low light (near the lake bottom). Periphyton nutritional limitation was also assessed using available literature on optimal stoichiometric ratios. Based on the stoichiometric ratios, we found that the periphytic autotrophic community was mostly N-limited. However, we observed higher values of total biomass (carbon [C]: mg m−2) in treatments with N and P joint addition and lower values of carbon to chlorophyll a (C:Chl-a) ratio in treatments with only N addition. We concluded that N limitation primarily affected the the algal periphytic community, and the N and P co-limitation primarily affected the total periphytic biomass, which also includes heterotrophic organisms. Our results of stoichiometry and periphyton development support the occurrence of N and P co-limitation at the community scale. Our results ultimately support the primacy of co-limitation as hierarchical levels of organization increase in biological systems, such as periphytic communities composed of diverse taxa.

Distribution of epipelic algae and related environmental nutrients in Taihu Lake, revealed by HPLC analysis

Epipelic algal biomass and composition (determined by HPLC pigment analysis) and related environmental nutrients were investigated in a phytoplankton-dominated area (Meiliang Bay), a macrophyte-dominated area (East Taihu Lake) and a transition zones (Gonghu Bay) in a shallow eutrophic freshwater lake (Taihu Lake, eastern China). Surface sediment samples were collected at 11 sampling sites in April and August 2016. Average epipelic algal biomass for Meiliang Bay, Gonghu Bay and East Taihu Lake was 6.5, 4.9 and 4.6μg chlorophyll (Chl)-ag–1 sediment respectively in April, and 3.8, 7.4 and 2.7μg Chl-ag–1 sediment respectively in August. The maximum biomass of epipelic algae appeared at the G1 sampling site (9.6μg Chl-ag–1 sediment) in August, whereas the minimum biomass of epipelic algae appeared at the E4 sampling site (1.7μg Chl-ag–1 sediment). Pigment (fucoxanthin, zeaxanthin and Chl-b) to Chl-a ratios indicated that epipelic algae were primarily diatoms, secondarily cyanobacteria and lastly green algae in Taihu Lake. Epipelic algae were significantly correlated with total nitrogen in the water and total phosphorus in the sediment (P&amp;lt;0.05), except for green algae. In general, using pigment as an indicator revealed that the epiphytic algal community varied over time and space. The distribution of variations in epipelic algae was related to the heterogeneity of environmental factors.