Risk assessment of nitrate and petroleum-derived hydrocarbon addition on Contricriba weissflogii biomass, lifetime, and nutritional value

Different responses of marine microalgae Phaeodactylum tricornutum upon exposures to WAF and CEWAF of crude oil: A case study coupled with stable isotopic signatures

Increasing use of chemical dispersants for oil spills highlights the need to understand their adverse effects on marine microalgae and nutrient assimilation because the toxic components of crude oil can be more bioavailable. We employed the crude oil water-accommodated fraction (WAF) and chemically enhanced WAF (CEWAF) to compare different responses in marine microalgae (Phaeodactylum tricornutum) coupled with stable isotopic signatures. The concentration and proportion of high-molecular-weight polycyclic aromatic hydrocarbons (HMW PAHs), which are key toxic components in crude oil, increased after dispersant addition. CEWAF exposure caused higher percent growth inhibition and a lower chlorophyll-a level of microalgae than those after WAF exposure. Compared with WAF exposure, CEWAF led to an enhancement in the self-defense mechanism of P. tricornutum, accompanied by an increased content of extracellular polymeric substances. 13C-depletion and carbon assimilation were altered in P. tricornutum, suggesting more HMW PAHs could be utilized as carbon sources by microalgae under CEWAF. CEWAF had no significant effects on the isotopic fractionation or assimilation of nitrogen in P. tricornutum. Our study unveiled the impact on the growth, physiological response, and nutrient assimilation of microalgae upon WAF and CEWAF exposures. Our data provide new insights into the ecological effects of dispersant applications for coastal oil spills.

Carbon sequestration reduced by the interference of nanoplastics on copper bioavailability

Microplastics (MPs) have been recognized as a serious new pollutant, especially nanoplastics (NPs) pose a greater threat to marine ecosystem than larger MPs. Within these ecosystems, phytoplankton serve as the foundational primary producers, playing a critical role in carbon sequestration. Copper (Cu), a vital cofactor for both photosynthesis and respiration in phytoplankton, directly influences their capacity to regulate atmospheric carbon. Therefore, we assessed the impact of NPs on Cu bioavailability and carbon sequestration capacity. The results showed that polystyrene nanoplastics (PS-NPs) could inhibit the growth of Thalassiosira weissflogii (a commonly used model marine diatom) and Chlorella pyrenoidosa (a standard strain of green algae). The concentration of Cu uptake by algae has a significant negative correlation with COPT1 (a Cu uptake protein), but positive with P-ATPase (a Cu efflux protein). Interestingly, PS-NPs exposure could reduce Cu uptake and carbon Cu sequestration capacity of algae, i.e., when the concentration of PS-NPs increases by 1 mg/L, the concentration of fixed carbon dioxide decreases by 0.0023 ppm. This provides a new perspective to reveal the influence mechanisms of PS-NPs on the relationship between Cu biogeochemical cycling and carbon source and sink.

Different biological responses of Skeletonema costatum and Prorocentrum donghaiense to polymetallic nodules from seawaters

The negative impacts of polymetallic nodules mining on deep-sea benthic organisms have been widely established, but there is still a lack of understanding of the environmental impact on the surface ocean scenario. Phytoplankton growth experiment was conducted to determine the biological effect of polymetallic nodules on Prorocentrum donghaiense and Skeletonema costatum. The results showed that regardless of concentration and particle size, polymetallic nodules show a promoting effect on P. donghaiense (p < 0.05), the cell density in the experimental group increased by 35.2%-46.5% compared to the control at the end of the experiment. While fine particles significantly inhibited the growth of S. costatum (p < 0.05), the maximum inhibition rate on cell density reached 63.1%. Polymetallic nodules significantly enhance the Fv/Fm and the maximum electron transport rate of photosystem II in P. donghaiense, thereby increasing its growth rate. However, polymetallic nodules particles stimulated the antioxidant activity and extracellular polymeric substances secretion of S. costatum, resulting in phytoplankton flocculation and sedimentation, which inhibits its growth. Thus, these discriminatory impacts may cause alterations in biomass and community structure, ultimately affecting the ecological function.

The interference of marine accidental and persistent petroleum hydrocarbons pollution on primary biomass and trace elements sink

More than 80 % of the primary biomass in marine environments is provided by phytoplankton. The primary mechanism in the trace element sink is the absorption of trace elements by phytoplankton. Because of their difficult degradability and bioaccumulation, petroleum hydrocarbons are one of the most significant and priority organic contaminants in the marine environment. This study chose Chlorella pyrenoidosa as the model alga to be exposed to short and medium-term petroleum hydrocarbons. The ecological risk of accidental and persistent petroleum hydrocarbon contamination was thoroughly assessed. The interaction and intergenerational transmission of phytoplankton physiological markers and trace element absorption were explored to reflect the change in primary biomass and trace element sink. C. pyrenoidosa could produce a large number of reactive oxygen species stimulated by the concentration and exposure time of pollutants, which activated their antioxidant activity (superoxide dismutase (SOD) activity, β-carotene synthesis, antioxidant trace elements uptake) and peroxides production (hydroxyl radicals and malondialdehyde). The influence of the growth phase on SOD activity, copper absorption, and manganese adsorption in both persistent and accidental pollution was significant (p < 0.05, F > Fα). Adsorption of manganese and selenium positively connected with SOD, malondialdehyde, and Chlorophyl-a (p < 0.01). These findings convincingly indicate that petroleum hydrocarbon contamination can interfere with primary biomass and trace element sinks.

Nutrient Alteration Drives the Impacts of Seawater Acidification on the Bloom-Forming Dinoflagellate Karenia mikimotoi

Seawater acidification and nutrient alteration are two dominant environmental factors in coastal environments that influence the dynamics and succession of marine microalgae. However, the impacts of their combination have seldom been recorded. A simulated experimental system was set up to mimic the effects of elevated acidification on a bloom-forming dinoflagellate, Karenia mikimotoi, exposed to different nutrient conditions, and the possible mechanism was discussed. The results showed that acidification at different pH levels of 7.6 or 7.4 significantly influenced microalgal growth (p<0.05) compared with the control at pH 8.0. Mitochondria, the key sites of aerobic respiration and energy production, were impaired in a pH-dependent manner, and a simultaneous alteration of reactive oxygen species (ROS) production occurred. Cytochrome c oxidase (COX) and citrate synthase (CS), two mitochondrial metabolism-related enzymes, were actively induced with acidification exposure, suggesting the involvement of the mitochondrial pathway in coping with acidification. Moreover, different nutrient statuses indicated by various N:P ratios of 7:1 (N limitation) and 52:1 (P limitation) dramatically altered the impacts of acidification compared with those exposed to an N:P ratio of 17:1 (control), microalgal growth at pH 7.4 was obviously accelerated with the elevation of the nutrient ratio compared to that at pH 8.1 (p<0.05), and nutrient limitations seemed beneficial for growth in acidifying conditions. The production of alkaline phosphatase (AP) and acid phosphatase (AcP), an effective index indicating the microalgal growth status, significantly increased at the same time (p<0.05), which further supported this speculation. However, nitrate reductase (NR) was slightly inhibited. Hemolytic toxin production showed an obvious increase as the N:P ratio increased when exposed to acidification. Taken together, mitochondrial metabolism was suspected to be involved in the process of coping with acidification, and nutrient alterations, especially P limitation, could effectively alleviate the negative impacts induced by acidification. The obtained results might be a possible explanation for the competitive fitness of K. mikimotoi during bloom development.

Relationship between plankton-based β-carotene and biodegradable adaptablity to petroleum-derived hydrocarbon

Coastal environment are often stress from petroleum-derived hydrocarbon pollution. However, petroleum-derived hydrocarbon is persistent organic pollutants and their biodegradation by phytoplankton is little known. Five species of marine phytoplankton, including Dunaliella salina, Chlorella sp., Conticribra weissflogii, Phaeodactylum tricornutum Bohlin, and Prorocentrum donghaiense, have been used to test their tolerance to petroleum hydrocarbon contamination. D.salina and Chlorella sp can survive in high levels of No. 0 diesel oils water-soluble fractions (WSFs, 5.0 mg L^-1), furthermore, petroleum hydrocarbon could be biodegraded effectively by them (Fig. 2). The content of β-carotene in these two species of phytoplankton has significant correlation with degradation rate of WSFs concentrations (Fig. 4), petroleum hydrocarbons could be biodegraded effectively by algae. Meanwhile, the ·OH in seawater can be removed by β-carotene effectively so that algal cells could be protected by the β-carotene for its strong antioxidant capacity. Therefore, β-carotene as a coin has two sides on the degradation of WSFs. Here we explore the relationship between plankton-based β-carotene and biodegradable adaptabllity to petroleum-derived hydrocarbon, which offers a green technology for petroleum-derived hydrocarbon treatment.

Influence of acidification and eutrophication on physiological functions of Conticribra weissflogii and Prorocentrum donghaiense

Eutrophication and acidification have been the most concerned environmental problems in coastal ecosystem. However, their combined effect on coastal ecosystem function was unknown. Both diatom (Conticribra weissflogii) and dinoflagellate (Prorocentrum donghaiense) are used as coastal algal model. Seven parameters were determined for physiological function assessment, including cell density, chlorophyll a (Chl a), protein, malonaldehyde (MDA), superoxide dismutase, carbonic anhydrase (CA), and nitrate reductase (NR). The influence of nitrate (N) and phosphate (P) on MDA and CA in C. weissflogii was significant, and that on Chl a and protein in P. donghaiense were also significant. However, the influence of acidification on physiological functions was not significant. The effect of acidification could be intensified by coastal eutrophication. More importantly, the coexist influence of acidification and eutrophication on CA, NR and protein in C. weissflogii and MDA in P. donghaiense was significant. Both NR activity and Chl a content in P. donghaiense were positively correlated to N and P concentration when pH were 7.9 and 7.8, respectively. With simultaneous worsening of acidification and eutrophication, the cell growth of P. Donghaiense was accelerated more obviously than C. weissflogii, i.e., dinoflagellate was more adaptable than diatom, thus algal species distribution and abundance could be changed.

Effect of nitrate enrichment and diatoms on the bioavailability of Fe(III) oxyhydroxide colloids in seawater

The photoconversion of colloidal iron oxyhydroxides was a significant source of bioavailable iron in coastal systems. Diatoms dominate phytoplankton communities in coastal and upwelling regions. Diatoms are often exposed to eutrophication. We investigated the effects of different species of diatom, cell density, illumination period, and nitrate additions on the bioavailability of Fe(III) oxy-hydroxide colloids in seawaters. With the increase of illumination period from 1 to 4 h, the ratios of concentrations of total dissolved Fe (DFe) to colloidal iron oxyhydroxides and Fe(II) to DFe increased up to 24.3% and 23.9% for seawater without coastal diatoms, 45.6% and 30.2% for Skeletonema costatum, 44.3% and 29.7% for Thalassiosira weissflogii, respectively. The photochemical activity of coastal diatoms themselves (excluding the dissolved organic matter secreted by algae) on the species transformation of iron in seawater (including the light-induced dissolution of Fe(III) oxyhydroxide colloids and the photo-reduction of Fe(III) into Fe(II)) was confirmed for the first time. There was no significant difference of the ability of S. costatum and Thalassiosira weissflogii on the photoconversion of colloidal iron oxyhydroxides. The photoproduction of dissolved Fe(II) and DFe in the seawater with or without diatoms could be depressed by the nitrate addition.

Effect of excessive CO2 on physiological functions in coastal diatom

Rising dissolution of anthropogenic CO₂ in seawater may directly/indirectly cause ocean acidification and desalination. However, little is known about coastal physiological functions sensitivity to these processes. Here we show some links between ocean acidification/desalination and physiological functions in Thalassiosira weissflogii. Cell density (CD), protein, chlorophyll a (Chl a), malonaldehyde (MDA), superoxide dismutase (SOD), and carbonic anhydrase (CAs) were determined for the assessment of algal biomass, nutritional value, photosynthesis and respiration, lipid peroxidation, antioxidant capacity, and carbon sequestration ability. The influence of pH on the algal Chl a and MDA were extremely significant (P < 0.01). Salinity (S) on cell density and acidity (pH) on protein was significant (0.01 < P < 0.05). Additionally, a significant negative-correlation was observed between cell density and CAs. CAs and SOD had negatively correlations with CD, Chl a, protein, and MDA under pH or S influence, but positive correlation between themselves. Coastal physiological functions were affected by increasing order was acidification < acidification + desalination < desalination for Chl a and protein, desalination < acidification + desalination < acidification for SOD and CAs. Thus, the ongoing excessive CO₂-driven ocean acidification and desalination should be of high attention when assessing the risks of climate change on coastal phytoplankton.

Influence of dissolved organic nitrogen on Ni bioavailability in Prorocentrum donghaiense and Skeletonema costatum

Dissolved organic nitrogen (DON) is an important nutrient in the aquatic environment. This study examined the influence of DON addition on the adsorption, absorption, and distribution in macromolecular forms of environmentally deleterious trace metal (Ni) in Prorocentrum donghaiense and Skeletonema costatum over eight days. Ni adsorption and absorption of two species increased with the addition of urea, while Ni adsorption and absorption of two species in the presence of humic substances (HS) decreased. Meanwhile, Ni adsorption and absorption of P. donghaiense were higher than that of S. costatum. Furthermore, Ni contents in the protein fraction of the cells, both in P. donghaiense and S. costatum, were increased with both urea and HS addition. Thus, urea and HS input could impact Ni biogeochemistry and bioavailability, and then affect the biodynamics thereafter.

Effect of coastal eutrophication on heavy metal bioaccumulation and oral bioavailability in the razor clam, Sinonovacula constricta

As traditional seafoods, the razor clams are widely distributed from tropical to temperate areas. Coastal razor clams are often exposed to eutrophication. Heavy metal contamination is critical for seafood safety. However, how eutrophication affects bioaccumulation and oral bioavailability of heavy metals in the razor clams is unknown. After a four-month field experimental cultivation, heavy metals (Fe, Cu, Ni, V, As, and Pb) could be bioaccumulated by the razor clams (Sinonovacula constricta) through exposure to metals present in water and sediments or in the food chain, and then transferred to human via consumption of razor clams. Bionic gastrointestinal digestion and monolayer liposome extraction are used for metal oral bioavailability (OBA) assessment. The influence of eutrophication on OBA is decreased for Fe and Pb and increased for V. A significant positive linear correlation was observed between the bioaccumulation factors of Fe, Ni, V, and As in razor clams and the coastal eutrophication. These results may be due to the effect of eutrophication on metal species transformation in coastal seawater and subcellular distribution in razor clams. The maximum allowable daily intakes of razor clams are controlled by eutrophication status and the concentration of affinity-liposome As in razor clams.