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Many studies have demonstrated that some macroalgae (including the widely cultivated red alga Gracilaria lemaneiformis) can inhibit the growth of microalgae via allelopathy and resource competition, with the former as the major contributor. However, little is known currently about whether or not and how microalgae react as a feedback to the inhibitory effects or, more generally, the interactions between seaweed and microalgae in their co-culturing system. Here, we report a laboratory-based study on the interactions between the seaweed Gracilaria lemaneiformis and the common harmful algal blooms (HABs)-forming dinoflagellate Akashiwo sanguinea. We found that while both the fresh thalli of G. lemaneiformis and the extracts of fresh and dried G. lemaneiformis could significantly inhibit the growth of A. sanguinea, the dead cells of A. sanguinea “revenged” G. lemaneiformis via promoting the growth of bacteria and consequently slowed the growth of G. lemaneiformis, which was evidenced by the lowered pH, slowed nutrients consumption in the cultures, the elevated counts of bacteria, and the reduced biomass of G. lemaneiformis. Collectively, our results showed that while G. lemaneiformis could inhibit the growth of microalgae with allelopathy as a major contributor, the death of allelopathy-affected microalgae could promote bacterial growth, which sequentially inhibits the growth of G. lemaneiformis as a feedback.

A study was conducted in the marine finfish cage culture area in Sungai Udang, Penang, at the northern part of the Malacca Straits to examine the phytoplankton composition and abundance especially for potentially harmful phytoplankton. Monthly sampling were taken from March 2016 to January 2017 at nine sampling stations. Physio-chemical parameters of surface seawater such as pH, dissolved oxygen, temperature, salinity, total suspended solids, and nutrients (nitrate, nitrite, ammonium, phosphate and silicate) were also measured. A total of 54 phytoplankton taxa were recorded, with 37 genera belonged to diatoms, 15 of dinoflagellates, and 2 of cyanobacteria. The composition of phytoplankton was dominated by diatoms (>85%) at all sampling stations throughout the sampling period. The phytoplankton abundance ranged between 2.6×103 cells L-1 and 5.8×106 cells L-1. The potentially harmful toxic phytoplankton observed throughout the sampling period are dinoflagellates Alexandrium spp., Prorocentrum micans and Dinophysis caudata and diatoms, Pseudo-nitzchia spp but in low cell density. A total of six bloom-forming phytoplankton that can potentially trigger mass mortality of cultured fish such as Akashiwo sanguinea, Chaetoceros spp., Ceratium furca, Ceratium fusus, Margalefidinium spp. and Karlodinium spp. recorded at this area were relatively low in cell densities. Furthermore, no fish kill incident was reported in the area from blooms of phytoplankton during the period of study. Even though potentially harmful phytoplankton present were in low densities, they may pose significant risks to aquaculture activity if there is a sudden bloom. Hence, a monitoring program should be implemented to provide early warning of harmful algae blooms and safeguard the aquaculture industry in Sungai Udang, Penang.

A natural compound with the algicidal effect was isolated from the culture medium of Aspergillus sp. SCSIOW2 and was identified as malformin C, which was based on the data of 1H-NMR, 13C-NMR, and ESI-MS. Malformin C exhibited dose-dependent algicidal activities against two strains of noxious red tide algae, Akashiwo sanguinea and Chattonella marina. The activity against A. sanguinea was stronger than that against C. marina (the algicidal activity of 58 and 36% at 50 μM treatment for 2 h, respectively). Morphology changes including perforation, plasmolysis, and fragmentation of algal cells were observed. Malformin C induced a significant increase in ROS level, caused the damage of SOD activity, and led to the massive generation of MDA contents in algae cells. To our knowledge, this is the first report of the cyclic peptide described as an algicidal compound against HABs.

Background Phytoplankton blooms are frequent events in coastal areas and increase the production of organic matter that initially shapes the growth of opportunistic heterotrophic bacteria. However, it is unclear how these opportunists are involved in the transformation of dissolved organic matter (DOM) when blooms occur and the subsequent impacts on biogeochemical cycles. Results We used a combination of genomic, proteomic, and metabolomic approaches to study bacterial diversity, genome traits, and metabolic responses to assess the source and lability of DOM in a spring coastal bloom of Akashiwo sanguinea. We identified molecules that significantly increased during bloom development, predominantly belonging to amino acids, dipeptides, lipids, nucleotides, and nucleosides. The opportunistic members of the bacterial genera Polaribacter, Lentibacter, and Litoricola represented a significant proportion of the free-living and particle-associated bacterial assemblages during the stationary phase of the bloom. Polaribacter marinivivus, Lentibacter algarum, and Litoricola marina were isolated and their genomes exhibited streamlining characterized by small genome size and low GC content and non-coding densities, as well as a smaller number of transporters and peptidases compared to closely related species. However, the core proteomes identified house-keeping functions, such as various substrate transporters, peptidases, motility, chemotaxis, and antioxidants, in response to bloom-derived DOM. We observed a unique metabolic signature for the three species in the utilization of multiple dissolved organic nitrogen compounds. The metabolomic data showed that amino acids and dipeptides (such as isoleucine and proline) were preferentially taken up by P. marinivivus and L. algarum, whereas nucleotides and nucleosides (such as adenosine and purine) were preferentially selected by L. marina. Conclusions The results suggest that the enriched DOM in stationary phase of phytoplankton bloom is a result of ammonium depletion. This environment drives genomic streamlining of opportunistic bacteria to exploit their preferred nitrogen-containing compounds and maintain nutrient cycling.

Blooms of Akashiwo sanguinea frequently break out around the world, causing huge economic losses to the aquaculture industry and seriously damaging coastal ecosystems. However, the formation mechanisms of A. sanguinea blooms remain unclear. We investigated the allelopathic effects of A. sanguinea on multiple phytoplankton species, explored the mode of allelochemicals action and the way of nutrient factors regulation of the allelopathic activity. Results show that strains of A. sanguinea could inhibit the growth of co-occurring phytoplankton including Scrippsiella trochoidea, Phaeocystis globosa, and Rhodomonas salina, but inhibition of Prorocentrum micans was not obvious. The inhibition rates on phytoplankton were positively correlated with the cell densities of A. sanguinea. The highest inhibition rate of 94% on R. salina was for A. sanguinea CCMA256 culture of 2 000 cells/mL at 72 h. We observed that cells of S. trochoidea, Ph. globosa, and R. salina were lysed when co-cultured with A. sanguinea, with the shortest time for S. trochoidea. Additionally, the growth rates of A. sanguinea were promoted by co-culturing with S. trochoidea, Ph. globosa, and R. salina. Four components of A. sanguinea culture were all able to inhibit growth of R. salina: the strongest inhibitory effect was found in the sonicated culture, followed by whole-cell culture, filtrates of sonicated culture, and filtrate culture. The crude extract of A. sanguinea culture also lysed cells of R. salina, and the inhibition rates on R. salina increased with the increasing dose of crude extract. It was shown that both nutrient enrichment and nitrogen:phosphorus ratio imbalance enhanced remarkably the allelopathic activity of A. sanguinea. The highest inhibition rate on R. salina of 70% occurred in A. sanguinea JX13 treatment at 2 000 cells/mL under high nutrient condition in 48 h. In JX14 treatment at 2 000 cells/mL for N:P of 10:1, the inhibition rate increased by 1.7 times of that for N:P of 20:1. In addition, the allelopathy of A. sanguinea could not only be a competitive strategy but also a nutrition strategy, playing an important role in formation and/or maintenance of blooms of the mixotrophic dinoflagellate A. sanguinea.

Akashiwo sanguinea, a cosmopolitan red tide-forming dinoflagellate, is reported for the first time as a bloom from the Cochin estuary along the South Eastern Arabian Sea. Monthly sampling showed the continuous presence of A. sanguinea with occasional blooms. Blooms of A. sanguinea with the highest abundance of 2.8 × 105 cells l−1 were observed during the monsoon season (June 2019) with chlorophyll a of 17.2 mg m−3. The bloom period was characterized by higher concentrations of nitrate (26 μmol l−1) and phosphate (3.8 μmol l−1). Routine monitoring of the bloom region showed the survival of the Akashiwo sanguinea population in the temperature (26 to 30°C) and salinity (22 to 24 PSU) range indicating its eurythermal and euryhaline characteristics.

Characterizing ecological relationships between viruses, bacteria and phytoplankton in the ocean is critical to understanding the ecosystem; however, these relationships are infrequently investigated together. To understand the dynamics of microbial communities and environmental factors in harmful algal blooms (HABs), we examined the environmental factors and microbial communities during Akashiwo sanguinea HABs in the Jangmok coastal waters of South Korea by metagenomics. Specific bacterial species showed complex synergistic and antagonistic relationships with the A. sanguinea bloom. The endoparasitic dinoflagellate Amoebophrya sp. 1 controlled the bloom dynamics and correlated with HAB decline. Among nucleocytoplasmic large DNA viruses (NCLDVs), two Pandoraviruses and six Phycodnaviruses were strongly and positively correlated with the HABs. Operational taxonomic units of microbial communities and environmental factors associated with A. sanguinea were visualized by network analysis: A. sanguinea–Amoebophrya sp. 1 (r = .59, time lag: 2 days) and A. sanguinea–Ectocarpus siliculosus virus 1 in Phycodnaviridae (0.50, 4 days) relationships showed close associations. The relationship between A. sanguinea and dissolved inorganic phosphorus relationship also showed a very close correlation (0.74, 0 day). Microbial communities and the environment changed dynamically during the A. sanguinea bloom, and the rapid turnover of microorganisms responded to ecological interactions. A. sanguinea bloom dramatically changes the environments by exuding dissolved carbohydrates via autotrophic processes, followed by changes in microbial communities involving host‐specific viruses, bacteria and parasitoids. Thus, the microbial communities in HAB are composed of various organisms that interact in a complex manner.

No presente trabalho apresentamos a caracterização da assembleia microfitoplanctônica na Baía de Todos os Santos, considerando as condições abióticas locais, em uma curta série temporal, com o objetivo de ampliar o conhecimento sobre os padrões de composição, diversidade e distribuição do fitoplâncton na baía. Foram realizadas amostragens em três dias consecutivos, no mês de setembro 2016, em cinco pontos distribuídos no setor nordeste da baía. Foram medidos in situ a temperatura, salinidade, oxigênio dissolvido e transparência da água. Amostras foram coletadas utilizando-se garrafa de Van Dorn (1L), em subsuperfície (~0,5m), para análises quantitativas do microfitoplâncton. Amostras de 20mL foram coletadas por meio de arrastos horizontais de rede de plâncton de 20μm de abertura de malha, para análises de composição da comunidade. Os taxa foram identificados com base em literatura especializada e as análises quantitativas foram realizadas segundo o método de Utermöhl. As variáveis abióticas evidenciaram um ambiente homogêneo, com uma massa d’água quente e salina, tipicamente marinha. Foram identificados 104 táxons e as diatomáceas apresentaram a maior riqueza e abundância de espécies, demonstrando um padrão típico encontrado em sistemas estuarinos tropicais. Considerando a importância da composição e estrutura da comunidade fitoplanctônica para o equilíbrio ecológico da baía e manutenção dos serviços ecossistêmicos, destacamos a ocorrência de espécies potencialmente nocivas, capazes de provocar danos ao sistema em caso de florações, a exemplo do que já ocorreu na ocasião da floração de Akashiwo sanguinea no ano de 2007.

Oxygen minimum zones (OMZs) are characterized by enhanced carbon dioxide (CO2) levels and low pH and are being further acidified by uptake of anthropogenic atmospheric CO2. With ongoing intensification and expansion of OMZs due to global warming, carbonate chemistry conditions may become more variable and extreme, particularly in the eastern boundary upwelling systems. In austral summer (February–April) 2017, a large-scale mesocosm experiment was conducted in the coastal upwelling area off Callao (Peru) to investigate the impacts of ongoing ocean deoxygenation on biogeochemical processes, coinciding with a rare coastal El Niño event. Here we report on the temporal dynamics of carbonate chemistry in the mesocosms and surrounding Pacific waters over a continuous period of 50 d with high-temporal-resolution observations (every second day). The mesocosm experiment simulated an upwelling event in the mesocosms by addition of nitrogen (N)-deficient and CO2-enriched OMZ water. Surface water in the mesocosms was acidified by the OMZ water addition, with pHT lowered by 0.1–0.2 and pCO2 elevated to above 900 µatm. Thereafter, surface pCO2 quickly dropped to near or below the atmospheric level (405.22 µatm in 2017; Dlugokencky and Tans, 2021; NOAA/Global Monitoring Laboratory (GML)) mainly due to enhanced phytoplankton production with rapid CO2 consumption. Further observations revealed that the dominance of the dinoflagellate Akashiwo sanguinea and contamination of bird excrements played important roles in the dynamics of carbonate chemistry in the mesocosms. Compared to the simulated upwelling, natural upwelling events in the surrounding Pacific waters occurred more frequently with sea-to-air CO2 fluxes of 4.2–14.0 mmol C m−2 d−1. The positive CO2 fluxes indicated our site was a local CO2 source during our study, which may have been impacted by the coastal El Niño. However, our observations of dissolved inorganic carbon (DIC) drawdown in the mesocosms suggest that CO2 fluxes to the atmosphere can be largely dampened by biological processes. Overall, our study characterized carbonate chemistry in nearshore Pacific waters that are rarely sampled in such a temporal resolution and hence provided unique insights into the CO2 dynamics during a rare coastal El Niño event.

Harmful algal blooms (HABs), caused by the overgrowth of certain phytoplankton species, have negative effects on marine environments and coastal fisheries. In addition to cell-counting methods using phytoplankton nets, a hydroacoustic technique based on acoustic backscattering has been proposed for the detection of phytoplankton blooms. However, little is known of the acoustic properties of HAB species. In this study, as essential data to support this technique, we measured the acoustic properties of two HAB species, Akashiwo sanguinea and Alexandrium affine, which occur in the South Sea off the coast of Korea. Due to the small size of the target, we used ultrasound for the measurements. Experiments were conducted under laboratory and field conditions. In the laboratory experiment, the acoustic signal re]from each species was directly proportional to the cell abundance. We derived a relationship between the cell abundance and acoustic signal re]for each species. The measured signals were compared to predictions of a fluid sphere scattering model. When A. sanguinea blooms appeared at an abundance greater than 3 500 cells/mL, the acoustic signals varied with cell abundance, showing a good correlation. These results confirm that acoustic measurements can be used to detect HAB species.

The dinoflagellate Cochlodinium geminatum can form near-monospecific blooms which have occurred at the same location in the South China Sea repeatedly in the last decade. Here, we demonstrate the allelopathic effects of C. geminatum isolated from the bloom waters of the Pearl River Estuary, South China Sea, in August 2011, which inhibited four of six co-occurring phytoplankton species tested. Inhibition increased with rising cell density and reached a maximum in the declining growth stage. Four different C. geminatum culture components negatively affected growth of Akashiwo sanguinea in order of decreasing percent inhibition: sonicated culture, filtrate of sonicated culture, whole-cell culture and filtrate of whole-cell culture. The highest inhibition was at 25 °С and salinities of 30 PSU and light intensities of 100 μmol photons m−2 s−1. Overall, our study showed that C. geminatum could inhibit growth of phytoplankton competitors during succession of phytoplankton community, achieving nearly monospecific blooms, and the allelopathic effects were regulated by environmental factors.

Carbonyl compounds, especially polyunsaturated aldehydes (PUAs), are increasingly reported as teratogenic to grazers and deleterious to phytoplankton. While PUAs have been considered to be mainly produced by diatoms after cell wounding, little is known about whether microalgae other than diatoms, particularly harmful algal bloom (HAB)-forming species, produce carbonyl compounds. In this study, we analyzed the carbonyl compounds from eight common HAB-forming species (Akashiwo sanguinea, Karenia mikimotoi, Karlodinium veneficum, Margalefidinium polykrikoides, Prorocentrum donghaiense, P. minimum, Scrippsiella trochoidea, and Heterosigma akashiwo) using gas chromatography-mass spectrometry in full scan and selected ion monitoring (SIM) modes. Our results show a ubiquitous presence of carbonyl compounds in both dissolved and particulate forms in all species we examined. In the full scan mode, 133 chromatographic peaks were detected from 51 samples altogether. Both the varieties of carbonyl compounds and their quantities were algal species dependent, although most of the carbonyl compounds could not be fully identified according to the mass spectral database only due to the unavailability of enough standards for all analytes. Aided with nine standards in SIM mode, we further identified and quantified all nine aldehydes (2-methyl-2-pentenal, trans-2-nonenal, cis-6-nonenal, 2,6-dimethyl-5-heptenal, trans-2-hexenal, trans-2-decenal, 2,4-heptadienal, trans-trans-2,4-octadienal, and trans-trans-2,4-decadienal). Four of these nine aldehydes were detected in particulate form, which confirmed that trans-2-nonenal could be produced by K. mikimotoi, Karl. veneficum, P. donghaiense, P. minimum, S. trochoidea, and H. akashiwo, 2,4-heptadienal and trans-trans-2,4-decadienal by A. sanguinea, M. polykrikoides, and S. trochoidea, and trans, trans-2,4-octadienal by S. trochoidea, respectively. We proved that some dinoflagellate and raphidophyte species could contribute to the pool of carbonyl compounds including PUAs in a marine ecosystem. Some carbonyl compounds, particularly those in high cell quota and/or dissolved concentration, may be related to fish-killing or allelopathy which needs further identification and quantification.

The dinoflagellate Karlodinium veneficum blooms kill fish by the production of karlotoxins. We investigated the allelopathy (Akashiwo sanguinea as the target species) and toxicity (Oryzias melastigma, Artemia salina and Brachionus plicatilis as test animals) of four strains of K. veneficum isolated from coastal waters of China and the USA to explore the ecological implications of allelopathy and toxicity. In general, all four strains of K. veneficum at high cell densities (>100 000 cellsmL(-1)) significantly inhibited the growth of A. sanguinea to different extents, but they exhibited either positive or negative allelopathy at lower densities. The toxicity of the four strains showed a decreasing order coinciding with their culture histories in the laboratory, suggesting K. veneficum may have gradually lost toxicity during laboratory culturing. The allelopathic and toxic potencies among K. veneficum strains were not perfectly parallel, indicating that either the allelochemicals and toxins of K. veneficum may be different chemicals, or the same chemicals functioned in different modes. Moreover, we found A. salina avoided feeding on more toxic strains. These results together suggest that toxins provide an advantage for K. veneficum via avoiding predation, but allelopathy may not play an important role in initiating blooms of K. veneficum.

Algicidal bacteria offer an eco-friendly and promising approach for controlling harmful algae blooms (HABs). In this study, repeated batch fermentation of immobilized algicidal bacterium Vibrio brasiliensis H115 was preformed to enhance the productivity of the algicidal compounds. The highest algicidal efficiency of the fermentation products against Akashiwo sanguinea (100%) was achieved when the fermentation time was decreased from 24 to 14 h. The cell-free fermentation broth was then spray-dried and floating microcapsules were prepared from the dried powder. The optimum preparation conditions for floating microcapsules were: sodium alginate (SA), 3%; CaCO3: SA (mass ratio), 3:4; CaCl2, 3%; citric acid, 4%; ethylcellulose, 2%; crosslinking time, 30 min. Under the optimal conditions, the floating microcapsules displayed efficient A. sanguinea cell lysis ability and the algicidal efficiency increased from 10.62% (4 h) to 100% (24 h). These results suggest that the floating microcapsules could potentially be practically used for controlling the outbreaks of A. sanguinea.

Akashiwo sanguinea is closely linked to the healthy growth of Labrenzia sp. PO1. Herein, PO1 and SY1 strains of Labrenzia sp. were isolated from A. sanguinea to investigate their growth. A total of 6067 genes in the Labrenzia sp SY1 and 6067 genes in Labrenzia sp PO1 were identified by RNA sequencing. Totally, 2402 genes out of 6067 were found as differentially expressed genes (DEGs). PO1 strain, 595 with decreased transcript abundance, and 1807 increase transcript abundance. Total 2320 DEGs, 766 with decreased transcript abundance, and 1554 increase transcript abundance were found in the SY1 strain. Transcriptome analysis divulged that DEGs were enriched with regulating metabolic processes, biological processes, and binding activities and may play critical roles in Labrenzia sp. PO1 growth. The ABC transporter pathway was also enriched in PO1 with 23 genes encoding ABC transporters with increased transcript abundance only in this strain. ABC transporter transcript levels and Labrenzia sp. PO1 growth was highest at 32 h, indicating that transporter-encoding genes may be involved in PO1 growth through nutrient transport. Moreover, their low expression in SY1 may be related to its slower growth. This study of Labrenzia sp. PO1 and SY1 transcriptomes may be used as a foundation for future research on the biofilm formation phenomenon of Labrenzia sp. PO1, as the formation was observed only in PO1.

Dinoflagellate blooms currently caused serious environmental problems in different areas of the world. Recent studies revealed close relationship between dinoflagellate blooms and microbial community dynamics, while less attention has been paid on the bacterial culturability change associated with the bloom. Here, we investigated the temporal variation of microbial community composition and culturability during the decline stage of an Akashiwo sanguinea bloom occurred in Shenzhen, China. The daily microbial community phylogenetic structures in water samples collected during a four-day period after the bloom peak were assessed through 16S rRNA gene amplicons sequencing on the MiSeq (Illumina) platform. The environmental parameters, Chlorophyll a concentrations, and total viable and culturable bacterial densities were also measured. Our results showed that Gamma-proteobacteria comprising mostly of Pseudoalteromonadaceae and Vibrionaceae was the predominant microbial class in the post-bloom samples, except for the second day. During that day, the represented groups switched to Alpha-proteobacteria (Rhizobiales) and Beta-proteobacteria (Comamonadaceae), with the microbial culturability decreased. Total viable bacterial densities reached the maximum value on the third day, with Gamma-proteobacteria regained the dominance till the fourth day. The dramatic microbial community succession and culturability variation observed in this study indicated the complication of algae-bacteria interactions during dinoflagellate bloom.

We investigated the dynamics of the bacterial composition and metabolic function within Akashiwo sanguinea bloom using a 100-L indoor microcosm and metagenomic next-generation sequencing. We found that the bacterial community was classified into three groups at 54% similarity. Group I was associated with “during the A. sanguinea bloom stage” and mainly consisted of Alphaproteobacteria, Flavobacteriia and Gammaproteobacteria. Meanwhile, groups II and III were associated with the “late bloom/decline stage to post-bloom stage” with decreased Flavobacteriia and Gammaproteobacteria in these stages. Upon the termination of the A. sanguinea bloom, the concentrations of inorganic nutrients (particularly PO43−, NH4+ and dissolved organic carbon) increased rapidly and then decreased. From the network analysis, we found that the A. sanguinea node is associated with certain bacteria. After the bloom, the specific increases in NH4+ and PO43− nodes are associated with other bacterial taxa. The changes in the functional groups of the bacterial community from chemoheterotrophy to nitrogen association metabolisms were consistent with the environmental impacts during and after A. sanguinea bloom. Consequently, certain bacterial communities and the environments dynamically changed during and after harmful algal blooms and a rapid turnover within the bacterial community and their function can respond to ecological interactions.

The studies on the species diversity, distribution, environmental implications, and molecular basis of resting cysts (stages) of dinoflagellates and a few species of other groups conducted in China during the last three decades are reviewed. The major achievements are summarized as the following five aspects: 1) The continual efforts in detecting the species diversity of resting cysts (spores) in dinoflagellates and other classes using either morphological or molecular approaches, or both, in the four seas of China, which led to identifications of 106 species of dinoflagellate resting cysts and 4 species of resting stages from other groups of microalgae, with a total of 64 species of dinoflagellate cysts and the resting stage of the brown tide-causing Aureococcus anophagefferens being unequivocally identified via molecular approaches from the sediments of Chinese coastal waters; 2) The well-known toxic and HABs-causing dinoflagellates Karenia mikimotoi, Karlodinium veneficum, Akashiwo sanguinea and the pelagophyte A. anophagefferens were proven to be resting cyst (stage) producers via laboratory studies on their life cycles and field detections of resting cysts (resting stage cells). And, via germination experiment and subsequent characterization of vegetative cells, numerous dinoflagellate species that had never been described or found to form cysts were discovered and characterized; 3) The distributions of the resting cysts of Alexandrium catenella, A. pacificum, Gymnodinium catenatum, K. mikimotoi, K. veneficum and Azadinium poporum and the resting stage cells of A. anophagefferens were morphologically and molecularly mapped in all four seas of China, with A. anophagefferens proven to have been present in the Bohai Sea for at least 1,500 years; 4) Obtaining important insights into the ‘indicator’ values of the dinoflagellate cyst assemblages in sediment cores for tracking eutrophication, environmental pollution and other anthropological influences in coastal waters; 5) Studies on the cyst-pertinent processes and genetic basis (transcriptomics together with physiological and chemical measurements) of resting cyst dormancy not only revealed the regulating patterns of some environmental factors in cyst formation and germination, but also identified many characteristically active or inactive metabolic pathways, differentially expressed genes, and the possibly vital regulating function of the phytohormone abscisic acid and a group of molecular chaperones in resting cysts. We also identified seven issues and three themes that should be addressed and explored by Chinese scientists working in the area in the future.

The objective of this study was to evaluate variations in the composition and abundance of the phytoplankton community after an exceptional harmful bloom of Akashiwo sanguinea that occurred in Todos os Santos Bay (BTS) in early March, 2007. Samples were collected every ten days, between April, 2007 and March, 2008, from the estuarine gradient of the Paraguacu River to BTS. The physical and chemical variables were measured in situ using a multiparameter sensor. Water samples were collected for analysis of the dissolved inorganic nutrient concentrations and for the study of composition and abundance of the microphytoplankton. Overall, 135 taxa were identified, with a higher richness of diatoms. The total cell density ranged from 2.92 × 103 to 1.16 × 107 (5.47 × 105 ± 1.69 × 106) cells L−1, with higher values in the freshwater zone than in the marine area. Five species showed peaks of abundance throughout the study, forming small blooms. Four of these blooms occurred in the rainy season, formed by the species Guinardia striata (April, 2007), Scrippsiella cf. acuminata (August, 2007), Euglena gracilis (August, 2007), and Skeletonema cf. costatum (September, 2007), while a new bloom of the species Akashiwo sanguinea occurred during the dry season (December, 2007). The environment was typically oligotrophic, with low spatiotemporal variation in the concentrations of dissolved nutrients. Even so, we observed short-term variations in the structure and composition of the phytoplankton community, demonstrated by rapid bloom events, followed by an increase in the total abundance of microphytoplankton, especially during the rainy season. The blooms did not cause any notable changes in the water column and did not present any harmful effects on the system.

Understanding aspects of the biology of early life stages of marine fish is critical if one hopes to reveal the factors and processes that impact the survival and recruitment (year class) strength. The Peruvian anchovy (Engraulis ringens) is a key species in the Humboldt current system, and the present study provides the first description of the embryonic and larval development of this species reared in captivity. Embryonic and early exogenous feeding stages of larvae were illustrated in detail at 18.5°C. Hatching was completed within 42 and 48 h post-fertilization at 18.5 and 14.5°C, respectively. Mean ± 95% C.I. standard length (LS) at hatch (3.40 ± 0.10 mm at 18.5°C and 2.76 ± 0.34 mm at 14.5°C) was significantly different between the two temperatures. Larval behaviour was assessed at 18.5°C; at the onset of exogenous feeding [3 days post-hatch (dph)], larvae were fed small, motile dinoflagellates, Akashiwo sanguinea. At 7 dph, larvae started to feed almost exclusively on zooplankton (rotifers and Artemia nauplii). Larval activity increased with age, and the first sign of schooling was noted at 31 dph (18.56 mm LS) at 18.5°C. Temperature had a significant effect on size-at-age, but not on body shape (depth to LS ratio). The size-at-age data for larvae (this study) was used to parameterize a temperature-corrected von Bertalanffy growth function for Peruvian anchovy, the accuracy of which was assessed for juveniles and adults (literature values).

Arenibacter sp. strain 6A1 was isolated from seawater during an Akashiwo sanguinea bloom in Shenzhen, China. Here, we present its 4,666,208-bp genome sequence, consisting of 3,623 coding sequences with a G+C content of 38.95%.

Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organic matter cycling in the coastal Peruvian upwelling system. Eight mesocosms, each with a volume of ∼55 m3, were deployed for 50 d ∼6 km off Callao (12∘ S) during austral summer 2017, coinciding with a coastal El Niño phase. After mesocosm deployment, we collected subsurface waters at two different locations in the regional oxygen minimum zone (OMZ) and injected these into four mesocosms (mixing ratio ≈1.5 : 1 mesocosm: OMZ water). The focus of this paper is on temporal developments of organic matter production, export, and stoichiometry in the individual mesocosms. The mesocosm phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift coincided with a short-term increase in production during the A. sanguinea bloom, which left a pronounced imprint on organic matter C : N : P stoichiometry. However, C, N, and P export fluxes did not increase because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, export fluxes during the study were decoupled from surface production and sustained by the remaining plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant for most of the experiment. We explain this constancy by light limitation through self-shading by phytoplankton and by inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes remained balanced and there were few opportunities for blooms, which represents an event where the system becomes unbalanced. Overall, our mesocosm study revealed some key links between ecological and biogeochemical processes for one of the most economically important regions in the oceans.

Resting cysts represent the dormant life stage produced by sexual reproduction of dinoflagellates; it generally maintain a limited level of metabolic activities. In the present study, changes in the photosynthetic apparatus of Akashiwo sanguinea during the encystment process in different nitrogen (N) conditions were characterized, and the transcriptional responses of nine photosynthesis genes were further evaluated. The photochemical efficiency decreased with elevation of N deprivation and growth of algae, and the resting cysts maintained limited photosynthetic activity. Meanwhile, the transcription of photosystem II genes (psbA and psbD) were down-regulated, especially the levels of the psbA gene, suggesting the inactivation of photosystem II under N limitation. Moreover, genes involved in cytochrome f (petA) and ATP synthase (atpA, atpB) were also transcribed at low levels in N-deprivation cultures. In contrast, the transcription of the RubisCO large subunit gene (rbcL) was up-regulated, indicating the maintenance of carbon fixation in N-limited conditions. The transcription levels of photosystem I genes (psaA and psaB) showed no significant correlation with the N condition. Further, most of the photosynthesis genes were down-regulated in the resting cysts, which was coincided with the inactive physiological status of the dormant stage. The results demonstrated that photosynthesis genes are differentially regulated in response to varying N conditions and life cycles. The findings will provide fundamental knowledge for better understanding the physiological characteristics and molecular regulation mechanisms in the developmental life cycle of marine dinoflagellates.

Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The high productivity in surface waters is facilitated by upwelling of nutrient-rich deep waters, with high light availability enabling fast phytoplankton growth and nutrient utilization. However, there are numerous biotic and abiotic factors modifying productivity and biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions on their future functioning requires understanding of the mechanisms driving biogeochemical cycles therein. In this study, we used in situ mesocosms to obtain mechanistic understanding of processes controlling productivity, organic matter export, and particulate matter stoichiometry in the coastal Peruvian upwelling system. Therefore, eight mesocosm units with a volume of ~50 m3 were deployed for 50 days ~6 km off Callao during austral summer 2017, coinciding with a coastal El Niño event. To compare how upwelling of different water bodies influences plankton succession patterns, we collected two subsurface waters at different locations in the regional oxygen minimum zone (OMZ) and injected these into four replicate mesocosms, respectively (mixing ratio ≈ 1.5:1 mesocosm: OMZ water). The differences in nutrient concentrations between the collected water bodies were relatively small, and therefore we do not consider treatment differences in the present paper. The phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic harmful dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift resulted in a major short-term increase in productivity during A. sanguinea growth which left a pronounced imprint on organic matter C:N:P stoichiometry. However, C, N, and P export fluxes were not affected by this ecological regime shift because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, ongoing export fluxes during the study were maintained mainly by a remaining “background” plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant in between the ecological regime shifts. We explain this constancy by light limitation through self-shading by phytoplankton and inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes seemed to be relatively well balanced and there was little opportunity for blooms, which represents an event where the system becomes unbalanced. The mesocosm study revealed key links between ecological and biogeochemical processes for one of the economically most important regions in the oceans.