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Sendai Bay in northern Japan suffered serious damage from massive tsunamis generated by the 2011 off the Pacific coast of Tohoku earthquake. The physical disturbance caused by a tsunami may affect the coastal ecosystem, including the planktonic diatom community. We investigated seasonal changes in the diatom community structure at a coastal and an offshore station in Sendai Bay, from June 2011 (3 months after the tsunami) to April 2014. Diatom abundance increased at both stations during the spring. Sporadic increases were also recorded at the coastal station during the summer because of silicate input from river discharge. Seasonal succession of the diatom communities was similar at both the coastal and offshore stations. The onset of the spring bloom consisted mainly of Chaetoceros spp. when water temperatures were low. Subsequently, species such as Skeletonema costatum s.l. became dominant as salinity and nutrient concentrations decreased. Cell density decreased from summer into early winter. Leptocylindrus danicus became dominant in the summer, but was replaced by Thalassiosira cf. mala from autumn into winter. Redundancy analysis (RDA) showed that most of the variation in the diatom community could be explained by temperature, salinity, NO 3 − , NO 2 − , PO 4 3− , and SiO 2 . In addition, the occurrence of diatom species before the tsunami showed a similar pattern to that after the tsunami, suggesting that the tsunami did not have a serious impact on the diatom community in Sendai Bay.

The genus Skeletonema includes phytoplankton species that are important primary producers in marine food chains. Brackish waters have been reported to be one of the important habitats of some species of Skeletonema . To elucidate the species diversity of Skeletonema in brackish waters, we investigated three Japanese brackish bodies of water: the coastal waters of Toyama Bay, a tidal area of the Chikugo River, and a constructed reservoir in Isahaya Bay. We used molecular analysis based on large subunit rDNA and fine morphological structure to identify species. Skeletonema costatum s.s. (sensu stricto) was isolated at salinities as low as 0.6, but Skeletonema dohrnii , Skeletonema subsalsum , and Skeletonema tropicum were not found at salinities below 11.0. S. costatum s.s. could survive transfer from a medium with a salinity of 15 to a salinity of 2, but S. dohrnii did not survive in the same experiment. Only S. costatum s.s. germinated from the sediment of a reservoir in which the salinity was 0.1–1.4; incubation conditions included temperatures of 10, 15, 20, 25, and 30 °C and salinities of 5 and 30. Skeletonema costatum s.s. was identified as the species most adaptable to low-level salinity variations throughout its lifecycle.

Intraspecific variation in diatoms has been shown to play a key role in species' responses to several important environmental factors such as light, salinity, temperature and nutrients. Furthermore, modelling efforts indicate that this variation within species extends bloom periods, and likely provides sufficient variability in competitive interactions between species under hydrographically variable conditions. The intraspecific variation most likely corresponds to optimal fitness in temporary microhabitats and may help to explain the paradox of the plankton. Here, we examine the implications of intraspecific variation for the ecology and success of diatoms in general and emphasize the potential implications for our understanding of carbon metabolism in these important organisms. Additionally, data from palaeoecological studies have the potential for evaluating genetic variation through past climate changes, going thousands of years back in time. We suggest pathways for future research including the adoption of multiple strains of individual species into studies of diatom carbon metabolism, to refine our understanding of the variation within and between species, and the inclusion of experimental evolution as a tool for understanding potential evolutionary responses of diatom carbon metabolism to climate change. This article is part of the themed issue ‘The peculiar carbon metabolism in diatoms’.

Temporal variation in the wintertime diatom community structure in Tokyo Bay was investigated from 1981 to 2000 with respect to possible environmental influences. A previous study found that rapid industrialization around the 1960s altered the diatom community. We found that a similar eutrophic-type community with low species diversity dominated by Skeletonema costatum sensu lato (s.l.) still prevailed in 2000, despite recent relaxation of eutrophic conditions. When the cell density and carbon biomass of S. costatum s.l. declined from the mid 1980s to the late 1990s, diatom communities dominated by various species occurred sequentially and species diversity increased. Principal components analysis on environmental factors revealed that S. costatum s.l. favored typical wintertime conditions in the Tokyo district, sunny (less rain) and cold. In contrast, cloudy and warm conditions from the mid 1980s to the mid 1990s were responsible for the decline in S. costatum s.l., allowing other diatom species to grow. The second most important species, Eucampia zodiacus, favored windy years, presumably with strong advection and vertical mixing. The interannual variation of S. costatum s.l. and E. zodiacus populations was out of phase, suggesting that these species had responded to different climatic forcing at different temporal scales.

Ocean acidification (OA), which is a major environmental change caused by increasing atmospheric CO2, has considerable influences on marine phytoplankton. But few studies have investigated interactions of OA and seasonal changes in temperature and photoperiod on marine diatoms. In the present study, a marine diatom Skeletonema costatum was cultured under two different CO2 levels (LC, 400 µatm; HC, 1000 µatm) and three different combinations of temperature and photoperiod length (8:16 L:D with 5 ∘C, 12:12 L:D with 15 ∘C, 16:8 L:D with 25 ∘C), simulating different seasons in typical temperate oceans, to investigate the combined effects of these factors. The results showed that specific growth rate of S. costatum increased with increasing temperature and day length. However, OA showed contrasting effects on growth and photosynthesis under different combinations of temperature and day length: while positive effects of OA were observed under spring and autumn conditions, it significantly decreased growth (11 %) and photosynthesis (21 %) in winter. In addition, OA alleviated the negative effect of low temperature and short day length on the abundance of RbcL and key photosystem II (PSII) proteins (D1 and D2). These data indicated that future ocean acidification may show differential effects on diatoms in different clusters of other factors.

Incubation experiments with axenic cultures of four common phytoplankton species of the genera Chaetoceros, Skeletonema, Prorocentrum, and Micromonas were performed to test for the production of fluorescent dissolved organic matter (FDOM) by marine phytoplankton. Our results prove that the four species exuded both fluorescent protein-like and marine humic—like materials in variable amounts, with more production by the diatoms Chaetoceros sp. and Skeletonema costatum and less by Prorocentrum minimum. Whereas the exudation of protein-like substances by healthy phytoplankton cells has been recognized, the in sity production of marine humic-like substances is still a matter of debate. Using axenic cultures, we demonstrate unequivocally that phytoplankton can directly contribute to the autochthonous production of colored humic-like substances in the ocean. Extrapolation of these findings to the field indicates that about 20% of the marine humic—like substances produced in the highly productive coastal upwelling system of the Ría de Vigo could originate from growing phytoplankton. Therefore, the exudation of FDOM by marine phytoplankton should be considered in future studies of the dynamics of colored DOM in marine systems.

Cyanobacteria are found globally due to their adaptation to various environments. The occurrence of cyanobacterial blooms is not a new phenomenon. The bloom-forming and toxin-producing species have been a persistent nuisance all over the world over the last decades. Evidence suggests that this trend might be attributed to a complex interplay of direct and indirect anthropogenic influences. To control cyanobacterial blooms, various strategies, including physical, chemical, and biological methods have been proposed. Nevertheless, the use of those strategies is usually not effective. The isolation of natural compounds from many aquatic and terrestrial plants and seaweeds has become an alternative approach for controlling harmful algae in aquatic systems. Seaweeds have received attention from scientists because of their bioactive compounds with antibacterial, antifungal, anti-microalgae, and antioxidant properties. The undesirable effects of cyanobacteria proliferations and potential control methods are here reviewed, focusing on the use of potent bioactive compounds, isolated from seaweeds, against microalgae and cyanobacteria growth.

In this paper, the acute toxicity test were used to study the effects of different concentrations of suspended solids on the growth of Skeletonema costatum . The research result showed that the effects of different concentration of suspended solids on the growth of Skeletonema costatum were very significantly (P <0.01);The relationship between concentration of suspended solids and the inhibition rate of Skeletonema costatum growth was linear, the half inhibition concentration of Skeletonema costatum 48h-EC50 was 1.58g/L,r =0.9769,96 h-EC50 was 2.82g/L, r=0.9927.

A comparative assessment of phytoplankton dynamics during low tide (LT) and high tide (HT) was conducted from February 2022 to January 2023 in a tropical mesotidal creek, Manori, Mumbai, India. In total, 124 phytoplankton species were recorded. The HT resulted in greater species richness (124 species) and diversity indices (Shannon–Wiener’s index) than the LT (102 species). The Pielou’s e venness ( Jʹ ) and Simpson’s dominance index ( 1-D ) did not show significant fluctuations with the tides due to the marine phytoplankton species moving rhythmically in and out of the creek with the tides. Overall, the seasonal abundance was maximum during pre-monsoon at HT (5.79 × 10 3 u/L) and lowest in monsoon at LT (0.45 × 10 3 u/L), whereas spatial abundance was maximum at S1 (HT- 4.04 × 10 3 u/L) at HT and lowest at S3 (LT- 0.75 × 10 3 u/L) at LT. The diatoms dominated in their abundance (1.83 × 10 3 u/L and 3.82 × 10 3 u/L in HT) and diversity (77 in LT and 92 in HT). The species such as Coscinodiscus centralis , Coscinodiscus granii, Coscinodiscus radiatus, Triops furca, Melosira varians, Nitzchsia palea, Chaetoceros affinis , Skeletonema marinoi, Stephanocyclus meneghinianus, Planktoniella sol and Skeletonema costatum  were the dominant native residents in the creek. SIMPER analysis revealed that the maximum similarity was during the monsoon (47.65%), and the minimum was during the pre-monsoon (38.10%) at LT. However, in HT, the maximum similarity of phytoplankton shifted to post-monsoon (63.85%) and the minimum during the pre-monsoon (46.71%). The mean value of richness ( dʹ ) and Shannon’s diversity ( Hʹ ) showed a moderate phytoplankton diversity in the system. The environmental parameters (water temperature > pH > nitrate > salinity > DO > Alk > silicate) have a greater influence on the distribution of the phytoplankton community with tides as revealed by the Canonical correspondence analysis. Therefore, it has been found that tides play a significant role in the distribution and abundance of the phytoplankton community in a mesotidal creek environment.

Background Diatoms contribute 20% of the global primary production and are adaptable in dynamic environments. Diatoms always bloom earlier in the annual phytoplankton succession instead of dinoflagellates. However, how diatoms acclimate to a dynamic environment, especially under changing light conditions, remains unclear. Results We compared the growth and photosynthesis under fluctuating light conditions of red tide diatom Skeletonema costatum , red tide dinoflagellate Amphidinium carterae , Prorocentrum donghaiense , Karenia mikimotoi , model diatom Phaeodactylum tricornutum , Thalassiosira pseudonana and model dinoflagellate Dinophycae Symbiodinium . Diatoms grew faster and maintained a consistently higher level of photosynthesis. Diatoms were sensitive to the specific inhibitor of Proton Gradient Regulation 5 (PGR5) depending photosynthetic electron flow, which is a crucial mechanism to protect their photosynthetic apparatus under fluctuating light. In contrast, the dinoflagellates were not sensitive to this inhibitor. Therefore, we investigate how PGR5 functions under light fluctuations in the model diatom P. tricornutum by knocking down and overexpressing PGR5. Overexpression of PGR5 reduced the photosystem I acceptor side limitation (Y (NA)) and increased growth rate under severely fluctuating light in contrast to the knockdown of PGR5 . Conclusion Diatoms acclimatize to fluctuating light conditions better than dinoflagellates. PGR5 in diatoms can regulate their photosynthetic electron flow and accelerate their growth under severe light fluctuation, supporting fast biomass accumulation under dynamic environments in pioneer blooms.