Phytoplankton Assemblages Research Articles

Fluorescence-based primary productivity estimates are influenced by non-photochemical quenching dynamics in Arctic phytoplankton.

Chlorophyll fluorescence-based estimates of primary productivity typically include dark or low-light pre-treatments to relax non-photochemical quenching (NPQ), a process that influences the relationship between PSII photochemistry and fluorescence yields. The time-scales of NPQ relaxation vary significantly between phytoplankton taxa and across environmental conditions, creating uncertainty in field-based productivity measurements derived from fluorescence. To address this practical challenge, we used fast repetition rate fluorometry to characterize NPQ relaxation kinetics in Arctic Ocean phytoplankton assemblages across a range of hydrographic regimes. Applying numerical fits to our data, we derived NPQ relaxation life times, and determined the relative contributions of various quenching components to the total NPQ signature across the different assemblages. Relaxation kinetics were best described as a combination of fast-, intermediate- and slow-relaxing processes, operating on time-scales of seconds, minutes, and hours, respectively. Across sampling locations and depths, total fluorescence quenching was dominated by the intermediate quenching component. Our results demonstrated an average NPQ relaxation life time of 20 ± 1.9 min, with faster relaxation among high light acclimated surface samples relative to lowlight acclimated sub-surface samples. We also used our results to examine the influence of NPQ relaxation on estimates of photosynthetic electron transport rates (ETR), testing the commonly held assumption that NPQ exerts proportional effects on light absorption (PSII functional absorption cross section, σPSII) and photochemical quantum efficiency (FV/FM). This assumption was violated in a number of phytoplankton assemblages that showed a significant decoupling of σPSII and FV/FM during NPQ relaxation, and an associated variability in ETR estimates. Decoupling of σPSII and FV/FM was most prevalent in samples displaying symptoms photoinhibition. Our results provide insights into the mechanisms and kinetics of NPQ in Arctic phytoplankton assemblages, with important implications for the use of FRRF to derive non-invasive, high-resolution estimates of photosynthetic activity in polar marine waters.

Phytoplankton assemblages under hydrochemical conditions of the Volga River Delta

In May 2021, comprehensive studies were conducted in the southeastern part of the Volga River avandelta (marine part of the delta). The work aimed to compare and identify the possible interaction of hydrochemical conditions and the structure of the phytoplankton community. Based on field observations, instrument measurements, and statistical analysis, three algaecoenoses were obtained (rapids, periphyton-pelagic, and marine), 4 types of environmental conditions identified by abiotic factors (oxygen-deficient, rapids, creak, and marine), and 2 types of biotopic conditions identified according to production-destructive characteristics (river with a prevalence of production, marine - production shifted towards equilibrium). For the marine part, an discrete phytopelagic community was identified, represented by benthopelagic aggregates with a complex trophic structure based on ribbon-like colonies of araphid diatom (Staurosira spp. и Staurosirella spp.). It is shown that such a community structure may serve as an indicator of water masses with significant destructive processes. Thus, an abiotic oxygen-deficient biotope located in the river part of the study area was characterized by a similar set of species. Both water areas were characterized by high AOU values, an increase in the contribution of mineral phosphorus to the Redfield ratio and a lack of nitrogen. At the same time, the water areas with a pronounced predominance of production processes over destructive ones were characterized by an abundance of centric diatoms. Thus, the selected groups of species can serve as indicators concerning certain biotopic conditions (in terms of production/destruction of organic matter).

In situ phytoplankton photosynthetic characteristics and their controlling factors in the eastern Indian Ocean

Photosynthesis is the most important bioenergy conversion process on Earth. Capturing instantaneous changes in in situ photosynthesis in open ocean ecosystems remains a major challenge. In this study, fast repetition rate fluorometry (FRRF), which can obtain nondestructive, real-time and in situ estimates of photosynthetic parameters, was used for the first time to continuously observe the spatial variation in in situ photosynthetic parameters in the eastern Indian Ocean (EIO). We further formulated new insights regarding abiotic and biotic factors of potential importance in determining photosynthetic performance. First, we found that the distributions of micro/nano- and picophytoplankton were opposite under the control of nutrient concentrations. Micro/nanophytoplankton had higher cell abundances in the nearshore and upwelling regions, while picophytoplankton had higher abundances in the open ocean, and Prochlorococcus was the dominant group. Second, based on the FRRF technology, we obtained the high-precision and high-density vertical profile map of photosynthetic parameters in the euphotic layer. It was observed that values of the maximum photochemical efficiency (Fv/Fm; 0.14–0.55, unitless) and the functional absorption cross-section of PSII (σPSII; 1.71–4.90 nm2 RCII−1) increased with increasing depth, while high values of the photosynthetic electron transfer rates (ETRRCII; 0.0019–17.0292 mol e− mol RCII−1 s−1) and the nonphotochemical quenching (NPQNSV; 0.35–7.26, unitless) occurred in the shallow 50 m layer, and the values decreased as the depth increased. Finally, we discussed limiting factors that regulated the distribution of photosynthetic parameters and concluded that optical properties varied significantly with changes in the ocean physico-chemical parameters and taxonomic composition of phytoplankton assemblages in the EIO. Picophytoplankton (especially cyanobacteria), rather than the micro/nanophytoplankton community, was the dominant factor influencing photosynthesis. Among abiotic factors, photosynthetically active radiation (PAR) was the proximal limiting factor affecting photosynthetic efficiency, followed by temperature and dissolved inorganic nitrogen (DIN). Consequently, phytoplankton photosynthetic parameters exhibited great variability, allowing rapid responses to environmental condition changes. In this study, we established the basis for detecting future changes in primary production in this oligotrophic area.

Phytoplankton functional groups as indicators of environmental changes in weir and non-weir sections of the lower Nakdong River, Republic of Korea

The Nakdong River underwent water impoundment after eight weirs were constructed as part of South Korea's Four Major River Restoration Project from 2009 to 2012. In this study, we aimed to confirm whether the assemblage of phytoplankton based on phytoplankton functional groups (PFGs), could indicate environmental changes in the weir section (WS) and non-weir section (NWS) of the lower Nakdong River after the construction of the weir. Thus, we examined the relationships between PFGs and gradients in environmental drivers, such as physicochemical, meteorological, and hydrological variables. Environmental gradients were observed between the WS and NWS in dissolved oxygen (DO), electric conductivity (EC), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), dissolved total nitrogen (DTN), dissolved total phosphorus (DTP), ammonia nitrogen (NH3–N), nitrate nitrogen (NO3–N), and phosphorus (PO4–P), which were relatively higher in the WS. Seventeen PFGs were identified (A, B, C, D, E, F, G, H1, J, LM, LO, MP, P, T, W1, X1, and X2).Additionally, the LM and P groups, preferring an enriched lentic system more than other groups, were found to be the dominant PFGs that led the succession of assemblages. Traditional nutrients (N, P) and organic pollutants (BOD, COD) primarily affected the autochthonous growth of the most dominant PFGs in the WS as HRT (hydraulic retention time) increased. Furthermore, the hydrological variables associated with meteorological conditions have a synergistic effect on the composition of the major PFGs and chemical and physical variables in the WS. In other words, the WS may be a new source of inoculum that primarily determines the occurrence and maintenance of phytoplankton in the immediate downstream region (NWS). In particular, group LM (mainly potentially toxic Microcystis) developing in the upper weir impoundment is transported downstream, resulting in a high inoculation effect on further growth in the NWS during the summer monsoon season.

Nitrogen enrichment ameliorates the stimulatory effects of reduced salinity on photosynthesis and growth of phytoplankton assemblages in the northern South China sea

Anthropogenic activities and climate change are exacerbating the occurrence of extreme rainfall that normally brings large amounts of nutrient-rich freshwater from the land to the sea, resulting in acute salinity decrease and nutrient increase. To evaluate the effects of such changes in salinity and nutrients, we tracked the changes in photosynthetic efficiency and growth of phytoplankton assemblages from the northern South China Sea at 5 salinity levels and at an intermediate salinity level with 3 or 4 nitrogen concentrations. The results showed that the reduction of salinity reduced the maximum photochemical quantum yield (FV/FM) of photosystem II of phytoplankton within a short-term cultivation (i.e. 24-72 h), followed by a stimulatory effect. The reducing effect of reduced salinity lasted longer in the nearshore area than in the offshore area, so the stimulatory effect occurred later in the former area. Nitrogen enrichment mitigated the negative effect of reduced salinity in short-term cultivation and showed a positive effect on FV/FM in long-term cultivation. Moreover, both reduced salinity and enriched nitrogen stimulated phytoplankton growth after an acclimation period. Our results suggest that the reduced salinity stresses phytoplankton in the short term, which is mitigated by nitrogen enrichment, but benefits them in the long term. This sheds light on how phytoplankton thrive and even flourish in coastal or estuarine environments where salinity and nutrients typically covary strongly after extreme rainfall.

Zooplankton-phytoplankton biomass and diversity relationships in the Great Lakes.

Quantifying the relationship between phytoplankton and zooplankton may offer insight into zooplankton sensitivity to shifting phytoplankton assemblages and the potential impacts of producer-consumer decoupling on the rest of the food web. We analyzed 18 years (2001-2018) of paired phytoplankton and zooplankton samples collected as part of the United States Environmental Protection Agency (U.S. EPA) Great Lakes Biology Monitoring Program to examine both the long-term and seasonal relationships between zooplankton and phytoplankton across all five Laurentian Great Lakes. We also analyzed effects of phytoplankton diversity on zooplankton biomass, diversity, and predator-prey (zooplanktivore/grazer) ratios. Across the Great Lakes, there was a weak positive correlation between total algal biovolume and zooplankton biomass in both spring and summer. The relationship was weaker and not consistently positive within individual lakes. These trends were consistent over time, providing no evidence of increasing decoupling over the study period. Zooplankton biomass was weakly negatively correlated with algal diversity across lakes, whereas zooplankton diversity was unaffected. These relationships did not change when we considered only the edible phytoplankton fraction, possibly due to the high correlation between total and edible phytoplankton biovolume in most of these lakes. Lack of strong coupling between these producer and consumer assemblages may be related to lagging responses by the consumers, top-down effects from higher-level consumers, or other confounding factors. These results underscore the difficulty in predicting higher trophic level responses, including zooplankton, from changes in phytoplankton assemblages.

Production of ice-nucleating particles (INPs) by fast-growing phytoplankton

Abstract. Sea spray aerosol contains ice-nucleating particles (INPs), which affect the formation and properties of clouds. Here, we show that aerosols emitted from fast-growing marine phytoplankton produce effective immersion INPs, which nucleate at temperatures significantly warmer than the atmospheric homogeneous freezing (−38.0 ∘C) of pure water. Aerosol sampled over phytoplankton cultures grown in a Marine Aerosol Reference Tank (MART) induced nucleation and freezing at temperatures as high as −15.0 ∘C during exponential phytoplankton growth. This was observed in monospecific cultures representative of two major groups of phytoplankton, namely a cyanobacterium (Synechococcus elongatus) and a diatom (Thalassiosira weissflogii). Ice nucleation occurred at colder temperatures (−28.5 ∘C and below), which were not different from the freezing temperatures of procedural blanks, when the cultures were in the stationary or death phases of growth. Ice nucleation at warmer temperatures was associated with relatively high values of the maximum quantum yield of photosystem II (ΦPSII), an indicator of the physiological status of phytoplankton. High values of ΦPSII indicate the presence of cells with efficient photochemistry and greater potential for photosynthesis. For comparison, field measurements in the North Atlantic Ocean showed that high net growth rates of natural phytoplankton assemblages were associated with marine aerosol that acted as effective immersion INPs at relatively warm temperatures. Data were collected over 4 d at a sampling station maintained in the same water mass as the water column stabilized after deep mixing by a storm. Phytoplankton biomass and net phytoplankton growth rate (0.56 d−1) were greatest over the 24 h preceding the warmest mean ice nucleation temperature (−25.5 ∘C). Collectively, our laboratory and field observations indicate that phytoplankton physiological status is a useful predictor of effective INPs and more reliable than biomass or taxonomic affiliation. Ocean regions associated with fast phytoplankton growth, such as the North Atlantic during the annual spring bloom, may be significant sources of atmospheric INPs.

Rooted floating-leaf macrophytes structure the coexistence of different phytoplankton assemblages within a shallow lake

Rooted floating-leaf macrophytes structure the coexistence of different phytoplankton assemblages within a shallow lake

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.

Seasonal dynamics of bacterial community and co-occurrence with eukaryotic phytoplankton in the Pearl River Estuary

In this study, we investigated the taxonomic composition of the bacteria and phytoplankton communities in the Pearl River Estuary (PRE) through Illumina sequencing of the V3–V4 region of the 16 S rRNA gene. Furthermore, their relationships as well as recorded environmental variables were explored by co-occurrence networks. Bacterial community composition was different in two size fractions, as well as along the salinity gradient across two seasons. Free-living (FL) communities were dominated by pico-sized Cyanobacteria (Synechococcus CC9902) while Exiguobacterium, Halomonas and Pseudomonas were predominantly associated with particle-associated (PA) lifestyle, and Cyanobium PCC-6307 exhibited seasonal shifts in lifestyles in different seasons. In wet season, bacterial community composition was characterized by abundance of Cyanobacteria, Actinobacteria, and Bacteroidetes, which were tightly linked with high riverine inflow. While in dry season, Proteobacteria increased in prevalence, especially for Psychrobacter, NOR5/OM60 clade and Pseudomonas, which were thrived in lower water temperature and higher salinity. Moreover, we discovered that differences between PA and FL composition were more significant in the wet season than in the dry season, which may be due to better nutritional conditions of particles (indicated by POC%) in the wet season and then attract more diverse PA populations. Based on the analysis of plastidial 16 S rRNA genes, abundant small-sized mixotrophic phytoplankton (Dinophyceae, Euglenida and Haptophyta) were identified in the PRE. The complexity of co-occurrence network increased from FL to PA fractions in both seasons, which suggested that suspended particles can provide ecological niches for particle-associated colonizers contributing to the maintenance of a more stable community structure. In addition, the majority of phytoplankton species exhibited positive co-occurrences with both other phytoplankton species and bacterial counterparts, indicating the mutual cooperation between phytoplankton assemblages and specific bacterial populations e likely benefited from phytoplankton-derived organic compounds. This study enhances our understanding of the seasonal and spatial dynamics of bacterial communities and their potential relationship with phytoplankton assembly in estuarine waters.

Environmental and spatial factors play different roles in phytoplankton community assembly in different hydrological seasons in Lake Wuchang, China

Lake phytoplankton communities are affected by environmental and spatial factors. We studied the relative importance of environmental and spatial factors on the phytoplankton community assembly in Lake Wuchang across three hydrological seasons, which were divided into dry (December to March), normal (April to June, October to November) and wet seasons (July to September) based on the water level and depth. Spatial and temporal patterns of environmental factors and phytoplankton community composition and diversity were studied using Kruskal–Wallis test, Wilcoxon test and NMDS. CCA, Mantel and partial Mantel tests, and PLS-PM were used to investigate the effects of environmental and spatial factors on phytoplankton community characteristics. Results showed that phytoplankton assemblages at the eight study sites were composed of totally 244 species belonging to 9 phyla, which changed from Bacillariophyta and Chlorophyta to Cyanophyta across the whole hydrological period. There was significantly higher abundance and biomass in the normal and wet seasons than that in the dry season. Phytoplankton alpha diversity exhibited uniform temporal distribution patterns with higher values in the dry season than in the normal and wet seasons. The Mantel and partial Mantel tests revealed that environmental (physicochemical conditions of lake water) and spatial factors (geographic distances among sites) jointly affected the phytoplankton community structure and beta diversity across the hydrological seasons, while spatial factors were more important in the wet season. Partial least squares path models showed that spatial factors exhibited a significant positive correlation with the phytoplankton diversity with the path coefficients of 0.53 and 0.71 in the normal and wet seasons, respectively. Phytoplankton composition had significant correlation with on phytoplankton diversity with the path coefficient of −0.75 and 0.61 in the normal and wet seasons, respectively. Our findings revealed that both environmental and spatial factors affected the phytoplankton community assembly in Lake Wuchang. Environmental factors played a more important role in the dry season, while spatial factors were more important in the wet season. With the exception of the abiotic factors (environmental and spatial), the impacts of biotic factors on phytoplankton community cannot be ignored. Therefore, it is also necessary to strengthen further research on the top-down control over phytoplankton communities in Lake Wuchang.

Long-term adjustment of phytoplankton structure to environmental traits at timescales during lifetime development and over generations

Long-term ecological research of deep Lake Mondsee covers over more than six decades of phytoplankton observation. According to our study, phytoplankton groups of various phenological traits are suitable to address the impact of two major environmental stressors: nutrient surplus by eutrophication from 1968 to 1998 and warming by climate change. Here, we focus on phytoplankton biovolume, phytoplankton assemblage structure, net changes rates, and phytoplankton biodiversity. Biweekly net change-dependent persistence of phytoplankton assemblages followed a dome-shaped relationship of observations. A short-term persistence of taxonomic traits along weeks is predominant and contributes to the structural stabilization of phytoplankton assemblages. This short-term persistence is interpreted by the benefit of lifetime adjustment of phytoplankton organisms. The long-term development phytoplankton structure is discussed as an alignment of organisms over generations. Single key taxa, as Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis &Komárek 1988, which are omnipotent players in phytoplankton assemblages and occur during different environmental scenarios in the long-term, are most suitable for long-term ecological research. Our findings interpret that phytoplankton taxa are excellent organisms to track the impact of environmental constraints due to their short generation time (1), their lifetime adjustment (2), and the re-occurrence in the long-term over generations (3).

Response of Phytoplankton Communities to Variation in Salinity in a Small Mediterranean Coastal Lagoon: Future Management and Foreseen Climate Change Consequences

Mediterranean coastal lagoons are particularly vulnerable to increasing direct anthropogenic threats and climate change. Understanding their potential responses to global and local changes is essential to develop management strategies adapted to these ecosystems. Salinity is a fundamental structuring factor for phytoplankton communities; however, its role under climate change is understudied. We hypothesized that salinity variations imposed by climate change and/or management actions could disturb Mediterranean lagoons’ phytoplankton communities. To test our hypothesis, we performed two 5-day microcosm experiments in which natural phytoplankton assemblages from the Santa Giulia lagoon (Corsica Island) were subjected to three increasing (53–63–73) and decreasing (33–26–20) levels of salinity, to mimic strong evaporation and flash flooding, respectively. Results indicate that over-salinization inhibited growth and modified the assemblages’ composition. Freshening, on the contrary, showed feeble effects, mainly boosting microphytoplankton abundance and depleting diversity at lowest salinity. In both experiments and under freshening in particular, initially rare species emerged, while photosynthetic activity was degraded by salinity increase only. We demonstrated that phytoplankton communities’ structure and metabolism are strongly altered by the predicted implications of climate change. Such impacts have to be considered for future management of coastal lagoons (control of sea exchanges and watershed fluxes). This work constitutes a priority step towards the proactive adapted management and conservation of such as-yet-neglected ecosystems in the context of climate change.

Cladophora as ecological engineer: A new test from the largest lake of Qinghai-Tibet plateau with filamentous algal blooms

Filamentous algae blooms (FABs) have been increasing globally in recent years, and their presence can have both harmful and beneficial effects on aquatic ecosystems. As one of the most common FABs, Cladophora blooms have been reported in the lakes of the Qinghai-Tibet Plateau during the past few years. However, there have been few studies focused on how FABs impact other aquatic organisms, especially in alpine lakes since these are at the forefront of responding to global climate change. In this study, the phytoplankton communities in different regions of Qinghai Lake were profiled in different seasons using meta-barcode sequencing. The phytoplankton assemblages in areas with Cladophora blooms were compared to those without Cladophora. The phytoplankton community structure correlated with physicochemical properties including water temperature, electrical conductivity, nitrate, and the presence or absence of Cladophora blooms. The relative abundance of Bacillariophytes was found to be higher in zones with Cladophora blooms than in other regions. Significant seasonal changes in phytoplankton biomass and β diversity were observed in zones with Cladophora blooms. Growth and microbial degradation of Cladophora can change the pH, dissolved oxygen, secchi depth, and nitrate. Together with seasonal temperature and electrical conductivity changes, Cladophora growth can significantly impact the phytoplankton biomass, community dissimilarity and assembly process. These results showed that Cladophora plays a key role in littoral aquatic ecosystem ecology.

Stress Response in Toxic Diatoms: The Effects of Abiotic Factors on Growth and RNA Content in Pseudo-nitzschia calliantha and in Pseudo-nitzschia multistriata

Pennate diatoms belonging to the genus Pseudo-nitzschia are important components of phytoplankton assemblages in aquatic environments. Among them, the bloom-forming species Pseudo-nitzschia calliantha and Pseudo-nitzschia multistriata are known as domoic acid producers, and are thus considered harmful for aquatic organisms and for human health. For these reasons, monitoring the abundance of such species, as well as identifying the growth conditions enhancing or inhibiting their growth, could help to predict eventual risks for aquatic communities and for humans by direct or indirect exposure to these toxic algae. In this work, we assessed the effects of different parameters (irradiance, temperature, salinity, and nutrients) on six Pseudo-nitzschia species by evaluating their specific growth rates and total RNA content. Our results—corroborated by statistical analyses of regression and correlation plots of control samples and samples exposed to stressful conditions, showed, as expected, a general decrease in growth rates under suboptimal levels of temperature, irradiance, salinity, and nutrient supply (especially under silicon depletion), that was usually accomplished by a general increase in RNA content inside cells. We hypothesized that increments in RNA levels in cells exposed to unfavorable conditions could be due to a relatively fast activation of the mechanisms of stress response.

EFFECT OF PIG FARMING EFFLUENTS ON LIMNOLOGICAL PARAMETERS AND PHYTOPLANKTON COMPOSITION

Pig farming plays an important role in the Brazilian economy, but it may trigger environmental issues, especially regarding the contamination of water resources. In this study, we evaluated the effects of the deposition of effluents from a pig farm on the phytoplankton assemblage composition and limnological parameters at different spots of the Divisa River - Fazenda São Luís, Aparecida de Minas/MG, Brazil. Over six months, we analyzed several variables at three different sampling sites on the surface of a coastal zone. We registered seventy-four phytoplankton genera, with Chlorophyceae and Cyanophyceae representing the most abundant classes, and Cryptophyceae and Cyanophyceae displaying the highest densities. The PERMANOVA analysis revealed dissimilarity between sampling sites P1 x P3 and P2 x P3, and the SIMPER analysis showed that Cryptophyceae and Cyanophyceae contributed to the observed dissimilarity. The correspondence canonical analysis (CCA) allowed the organization of sampled sites in three groups, in which the phytoplankton composition was distinguished according to trophic gradients. We concluded that pig farming effluents discharged without previous treatment into water bodies exert influences in both the phytoplankton community and the dynamics of its assemblage, by increasing total phosphorus and contributing for increased abundances of Cryptophyceae and Cyanophyceae in the last evaluated site (P3).

Environmental assessment of oyster beds in the northern Arabian Gulf Coast of the United Arab Emirates

The United Arab of Emirates (UAE) hosts valuable coastal and marine biodiversity, and oysters are one of the habitants of its marine ecosystem. Oysters play an essential role in the nearshore coasts where they work as an active filter. They filter nutrients, phytoplankton, sediments, heavy metals, and toxins out of the water, which improves the water quality. This is the first study that characterizes oyster bed habitats in the UAE by analyzing water quality parameters, polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs)and heavy metals in water, sediments and oyster samples collected from five locations along the coasts of Sharjah, Ajman, and Umm al Quwain. Oyster bed areas supported a diverse assemblage of benthic life including oysters, scallops, pen shells, hard corals, and macroalgae. Mobile species in these habitats included groupers, emperors, snappers, sea snakes, among others. The phytoplankton assemblages were dominated by diatoms, dinoflagellates, and small cryptophytes. Harmful diatom Pseudonitzschia was found in all locations. No detectable concentrations of PAHs and OCPs were reported in this study, and water quality parameters were within the acceptable levels for the region. On the other hand, water quality index was reported marginal, mostly due to the presence of higher than acceptable concentrations of chromium and mercury in all sites studied. Bioconcentration factors concluded that oysters were able to bioconcentrate metals such as arsenic, cadmium, chromium, and zinc, when compared to water. No detectable concentrations of lead and mercury were reported in oysters, suggesting higher depuration rates for those metals.

Integrated statistical analysis of calcareous nannofossil and elemental geochemistry of an outcrop from of the eastern Cenomanian Western Interior Seaway: Novel insights of shallow marine paleoceanography and nannoplankton paleoecology

Phytoplankton assemblages in shallow marine environments are being impacted by anthropogenic climate change, but long-term outcomes of these changes are uncertain. Investigation of past neritic calcareous nannoplankton can help us understand the fate these ecosystems face. In this study, a Canonical Correspondence Analysis (CCA) of calcareous nannofossils and X-ray fluorescence geochemistry was used to determine how past planktonic ecosystems were influenced by paleoenvironmental parameters on the eastern side of the Late Cretaceous Western Interior Seaway in the Cenomanian (ca. 95–93 Ma). Samples were collected every 10 cm from the Graneros Shale Greenhorn Formation at an outcrop in northwestern Iowa to determine high resolution changes in assemblages and paleoenvironments. Nannofossil diversity outside of a few small intervals ranges is high (generally 30–60 species) with abundant small Biscutum constans, confirming other publications that show elevated diversity in Cretaceous nearshore settings. The CCA results imply assemblages were most influenced by terrigenous influence, wet vs. dry climate, and changes in water mass source. Cretaceous nannofossil paleoecology was also revised based on the CCA results. Size differentiation of nannofossil taxa may highlight more complexity in environmental preferences that have been largely overlooked. After the initial transgression of the Greenhorn Sea into the region, the climate became wetter and terrigenous influence in the area was high. The peak of terrigenous influence corresponds with elevated nannofossil diversity but a lack of microfauna, which may indicate a similar oceanographic setting to the modern Gulf of Mexico nearshore dead zone. As sea level continued to rise above this point, nannoplankton assemblages indicate a potential shift to a higher productivity, stratified water column. As the muddy Graneros Shale transitioned to a further offshore chalky Greenhorn Formation, a normal marine, cosmopolitan nannofloral assemblage became established. Nannofossil and geochemical evidence indicates high productivity from upwelling might be related to the change of deposition to chalk in the Greenhorn Formation. While only a single outcrop was investigated, the novel use of an integrated micropaleontological and geochemical analysis has shed light on the dynamics of how phytoplankton ecosystems were established and modified in shallow marine environments of the Cretaceous and could have important implications on modern shallow marine settings.

Wind‐driven currents and water masses shape spring phytoplankton distribution and composition in hydrologically complex, productive shelf waters

AbstractThe Northern Patagonian shelf (35–42°S SW South Atlantic) is a transitional area between the subtropical and subantarctic domains, where the shelf shifts from source to sink of atmospheric CO2. In the southeast portion (39–42°S, 61–55°W) of this area, winds interact with different water masses and picture a complex circulation that supports two productive frontal systems: the Mid‐Shelf Front (MSF) and the Patagonian Shelf‐break Front. We combined remote sensing (e.g., monthly surface chlorophyll a over the period: September–December 2002–2021), reanalysis (winds and surface currents), and in situ measurements from three cross‐shelf cruises in spring 2016, 2017, and 2019, to assess the underlying drivers of phytoplankton distribution. The anomalous high chlorophyll concentration in the MSF in spring 2016 was related to enhanced water mass retention by N‐NE winds. Contrasting phytoplankton assemblages emerged related to stratified waters in the shelf influenced by the Patagonian Current and vertically mixed waters at the continental edge (Malvinas Current). Large diatoms prevailed in the outer shelf followed by dinoflagellates, while nanoflagellates and microzooplankton dominated in the mid‐shelf. Furthermore, thickness of the subsurface chlorophyll maximum was broader in the early spring than in a more advanced state of the bloom where the coccolithophore Emiliania huxleyi was abundant. We showed that different time‐scale physical processes—winds, surface currents and vertical mixing—are underpinning the development of spring blooms with different taxa composition in the Patagonian shelf, where different water masses define the hydrological complexity that led to patchy phytoplankton.

Summer Phytoplankton Assemblages and Harmful Cyanobacterial Blooms in Freshwaters of New Jersey

Summer Phytoplankton Assemblages and Harmful Cyanobacterial Blooms in Freshwaters of New Jersey