In this study, Gymnodinium aeruginosum was exposed to polystyrene (PS) and polymethyl methacrylate (PMMA) of three particle sizes (0.1 μm, 1.0 μm and 100 μm) and two concentrations (10 mg/L and 75 mg/L) for 96 h. The density of algae cells, the endpoints that reactive oxygen species (ROS), total protein (TP), malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT), scanning and transmission electron microscopy (SEM and TEM) were used to explore the toxicity mechanism to the microalgae. At a concentration of 75 mg/L, the 96 h inhibition ratios (IR) with particle sizes of 0.1 μm, 1.0 μm and 100 μm on G. aeruginosum were 55.9%, 63.7% and 6.0% for PS, respectively, and 3.0%, 4.1% and ‐0.6% for PMMA, respectively. The most significant changes in ROS, TP, MDA, SOD and CAT were observed at 75 mg/L 1.0 μm of PS when treated for 96 h. When exposed to nanoplastics (NPs) and microplastics (MPs), the algae cells were damaged, and the antioxidant system was activated. Extracellular polymeric substance (EPS) could help to detoxify the algae. In general, PS was more toxic than PMMA. The toxicity of small MNPs (0.1 μm and 1.0 μm) was related to the concentrations, while large MNPs (100 μm) did not.

The effects of two harmful algal bloom (HAB) species Alexandrium tamarense and Gymnodinium catenatum on ecological quality status were studied using 14-day protozoan samples as test organisms. A fuzzy coding system with four traits and 11 categories of the test organisms was used for biological trait analysis. Five treatments were designed following the concentrations of 10⁰, 10², 10³, 10⁴ and 10⁵ cell ml‐¹ of each algal species. The community-weighted means were used to summarize the functioning process of the test organism assemblages. The community functioning of the protozoa showed a significant change in the treatments with high algal concentrations (10⁴ and 10⁵ cell ml⁻¹). The functional richness of the test organisms showed continuous increasing trend from 10² to 10⁴ cell ml⁻¹, and sharply dropped. These findings suggest that the BTA may be used as a useful tool for assessing the effects of HABs on ecological quality status in marine ecosystems.

The effects of two harmful algae Alexandrium tamarense and Gymnodinium catenatum on ecological quality status were identified using biofilm-dwelling ciliate assemblage as test organism communities. The body-size spectra of the test ciliates were observed at a gradient of cell concentrations of both algal species: 10⁰ (control), followed by10², 10³, 10⁴ and 10⁵ cells ml⁻¹. The test ciliates showed clear variations in body-size spectra along the concentration gradients of both algal species. In terms of probability density, the ciliates generally peaked at low levels of algal concentrations (10⁰–10⁴ cells ml⁻¹) in small size forms, followed by the forms with large sizes at the concentration of 10⁵ cells ml⁻¹ of both algal species. Bootstrapped-average analysis demonstrated a significant change in body-size spectrum when algal concentrations were higher than 10⁴ cells ml⁻¹. It is suggested that the body-size spectrum of the ciliates may be used to indicate the effects of harmful algal bloom.

Resting stages of plankton were sampled in the surficial sediments in the port of Haifa, Israel, on the eve of a major port enlargement project. We recorded the structure of the assemblages and examined their relationship with different environments within the port. Our findings reveal a remarkably high diversity coupled with low density and the highest number of oligotrich ciliate cyst types recorded from marine sediments. Near the eutrophic and highly polluted zone of the Kishon estuary ciliates were more abundant than elsewhere in the port, whereas dinoflagellates' abundance was reduced, and these trends held true both for full and empty cysts. Some harmful or potentially toxic species, such as Scrippsiella acuminata, were widespread in the port. The toxigenic species include Alexandrium minutum, Gymnodinium uncatenatum and Lingulodinium polyedrum. Active cells of the unarmoured, bloom-forming Akashiwo sanguinea were identified in the cultures obtained from the incubated sediments.

To understand how the marine copepod Tigriopus japonicus responds to the toxic marine dinoflagellate Gymnodinium catenatum, we assessed acute toxicity and investigated swimming behavior parameters (e.g., swimming speed, swimming path trajectory, and swimming distance) in response to G. catenatum exposure. In addition, the mRNA expression levels of detoxification-related genes (e.g., phase I cytochrome P450 [CYP] and phase II glutathione-S transferase [GST]) were measured in G. catenatum-exposed copepods. No significant change in survival was observed in response to G. catenatum, but swimming speed was significantly decreased (P < 0.05) at a high concentration of G. catenatum (600 cells/mL). Furthermore, the swimming distance was significantly decreased (P < 0.05) compared to that of the control at 600 cells/mL G. catenatum, while no significant change in swimming path trajectory was observed, suggesting that G. catenatum potentially has adverse effects on the swimming behavior of T. japonicus. In addition, the transcriptional regulation of T. japonicus CYPs and -GSTs were significantly upregulated and downregulated (P < 0.05), respectively, in response to G. catenatum. In particular, certain genes (e.g., CYPs [CYP307E1, CYP3041A1, and CYP3024A2] and GSTs [GST-kappa, GST-mu5, and GST-omega]) were significantly induced (P < 0.05) by G. catenatum, suggesting that these genes likely play a critical role in detoxification mechanisms and might be useful as potential molecular biomarkers in response to G. catenatum exposure. Overall, these results elucidate the potential impacts of the dinoflagellate G. catenatum on the swimming behavior and detoxification system of the marine copepod T. japonicus.

Previous studies conducted on Daya Bay implied that the bay had been undergoing potential phosphorus limitation. In this context, alkaline phosphatase activity (APA) and the associated microbes were investigated in three different seasons in Daya Bay, South China Sea. Both bulk-community (fractioned into dissolved and particulate) and single-cell assays of APA were used to estimate the P status of phytoplankton at the community and species level. Unexpected high potential APA (Vmax) was observed in Daya Bay. Bulk APA showed that the maximum value in the spring (mean 583.26 nM h−1) corresponded well to low phosphate concentration. Furthermore, particulate APA (P-APA) showed an inverse hyperbolic relationship with phosphate, implying the coexistence of both constitutive and inducible AP; meanwhile, a threshold phosphate concentration for the transition from high to low APA was found around 0.2 μM in our study. P-APA and dissolved APA (D-APA) exhibited a tight link with phytoplankton and bacteria, which indicated that both of them were two main carriers of the enzyme. During the spring cruise, we encountered a small-scaled bloom of Gymnodinium that was probably at a declining phase. Extreme high levels of bulk and D-APA were characterized at this spring bloom event, and we suspected that bacteria especially active bacteria played an important role in APA production and partitioning at the post-bloom phase. In Daya Bay, diatoms were the dominant phytoplankton groups and percentages of ELF (Enzyme Labelled Fluorescence) labelled diatoms followed the same seasonal fluctuation as bulk APA, which suggested that diatoms were responsible for major variations of the bulk AP activity except for the spring bloom. Taken together, we considered that phytoplankton may be experiencing more P stress in spring and that the mineralization of organic P via alkaline phosphatase may help phytoplankton overcome P deficiency.

We analyzed surface sediments from 23 northeast USA estuaries, from Maine to Delaware, and nine estuaries from Prince Edward Island (PEI, Canada), to determine how dinoflagellate cyst assemblages varied with nutrient loading. Overall the abundance of cysts of heterotrophic dinoflagellates correlates with modeled nitrogen loading, but there were also regional signals. On PEI cysts of Gymnodinium microreticulatum characterized estuaries with high nitrogen loading while the sediments of eutrophic Boston Harbor were characterized by high abundances of Spiniferites spp. In Delaware Bay and the Delaware Inland Bays Polysphaeridium zoharyi correlated with higher temperatures and nutrient loading. This is the first study to document the dinoflagellate cyst eutrophication signal at such a large geographic scale in estuaries, thus confirming their value as indicators of water quality change and anthropogenic impact.

The spatial distribution of dinoflagellate cysts was studied to understand the impact of industrial pollution on the surface sediment of Izmir Bay, Turkey. Forty two dinoflagellate cyst morphotypes belonging to 12 genera were identified and qualified at 12 sampling points. The cyst of Gymnodinium nolleri dominated the bay and had the highest abundance in most of the stations, following Spiniferites bulloideus and Lingulodinium machaerophorum. The highest cyst concentration was recorded in the inner part of the bay. Cyst concentration ranged between 384 and 9944cystg−1 dry weight of sediment in the sampling area. Sediment metal concentrations were determined. Heavy metal levels in Izmir Inner Bay were higher than the Middle and Outer Bay. L. machaerophorum, Dubridinium caperatum and Polykrikos kofoidii showed significant positive correlation with some metals (Cd, Pb, Cu, Zn) and organic carbon content. However, there was no significant correlation between dinoflagellate cyst abundance and sediment type.

Testing phytoplankton viability within ballast tanks and receiving waters of ballast water discharge remain understudied. Potentially harmful dinoflagellates and diatoms are transported via ballast water to Galveston Bay, Texas (USA), home to three major ports: Houston, Texas City and Galveston. Ballast water from vessels transiting the North Atlantic Ocean was inoculated into treatments representing low and high salinity conditions similar to the Ports of Houston and Galveston respectively. Phytoplankton in ballast water growout experiments were deemed viable and showed growth in low and mid salinities with nutrient enrichment. Molecular methods identified several genera: Dinophysis, Gymnodinium, Gyrodinium, Heterocapsa, Peridinium, Scrippsiella, Chaetoceros and Nitzschia. These phytoplankton genera were previously identified in Galveston Bay except Scrippsiella. Phytoplankton, including those capable of forming harmful algal blooms leading to fish and shellfish kills, are transported to Galveston Bay via ballast water, and are viable when introduced to similar salinity conditions found in Galveston Bay ports.

Suspended particles (SP) are increasing dramatically in Bohai Bay, China and may affect the growth and composition of phytoplankton assembly. To determine the effects of SP on the growth of two dominant phytoplankton species, Phaeodactylum tricornutum Bohlin and Gymnodinium sp., we cultured and tested their growth characteristics under SP concentrations ranging from 0gL−1 to 0.8gL−1. Our results show that the increase in the SP concentrations results in significant decrease in the maximum cell densities and the maximum specific growth rates of these two species. The half maximal inhibitory concentration (IC50) of SP to P. tricornutum and Gymnodinium sp. were 1.07gL−1 and 0.68gL−1 respectively, indicating the inhibitory effect of SP on Gymnodinium sp. was greater than on P. tricornutum. These results suggest that SP inhibits the growth of the two algal species and P. tricornutum is more tolerant to SP than Gymnodinium sp.