In numerous studies, researchers have explored the interactions between fungi and their hosting biota in terrestrial systems, while much less attention has been paid to the counterpart interactions ...in aquatic, and particularly marine, ecosystems. Despite the growing recognition of the potential functions of fungi in structuring phytoplankton communities, the current insights were mostly derived from phytoplankton hosts, such as diatoms, green microalgae, and cyanobacteria. Dinoflagellates are the second most abundant group of phytoplankton in coastal marine ecosystems, and they are notorious for causing harmful algal blooms (HABs). In this study, we used high-throughput amplicon sequencing to capture global snapshots of specific fungal assemblages associated with laboratory-cultured marine dinoflagellate. We investigated a total of 13 clonal cultures of the dinoflagellate
that were previously isolated from 5 geographic origins and have been maintained in our laboratory from several months to more than 14 years. The total recovered fungal microbiome, which consisted of 349 ASVs (amplicon sequencing variants, sequences clustered at a 100% sequence identity), could be assigned to 4 phyla, 18 classes, 37 orders, 65 families, 97 genera, and 131 species. The fungal consortium displayed high diversity and was dominated by filamentous fungi and ascomycetous and basidiomycetous yeasts. A core set of three genera among all the detected fungi was constitutively present in the
strains isolated from geographically distant regions, with the top two most abundant genera,
and
, capable of using hydrocarbons as the sole or major source of carbon and energy. In addition, fungal taxa previously documented as endophytes in other hosts were also found in all tested strains of
. Because host-endophyte interactions are highly variable and strongly case-dependent, these fungal taxa were not necessarily genuine endosymbionts of
; instead, it raised the possibility that dinoflagellates could potentially serve as an alternative ecological niche for the colonization of fungal endophytes. Our findings lay the foundation for further investigations into the potential roles or functions of fungi in the regulation of the growth dynamics and HABs of marine dinoflagellates in the field.
The genus Gymnodinium contains more than 230 extant species, approximately 30% of which have not been reported since their original description. Approximately eight Gymnodinium species have been ...reported or described in the coastal waters of China. This work reports the presence of Gymnodinium trapeziforme from Jiaozhou Bay, China, in 2020, and its morphological and phylogenetic characterization by using light and scanning electron microscopy and systematic analysis based on partial LSU rDNA sequences. We observed the typical diagnostic features of G. trapeziforme, including a small size, biconical to ovoid shape, and a sulcal extension intruded to the epicone and connected to the horseshoe-shaped apical structure complex (ASC). Additionally, we firstly observed that the ASC consisted of three parallel series of vesicles, with the central one possessing knobs, and having more than 10 amphiesmal vesicles within the ASC. The nucleus was cucurbit-shaped, and the amphiesmal vesicles covering the cell surface, which would be peeled off for the cells in stress. While our molecular phylogeny inferred with the maximum likelihood (ML) and Bayesian inference (BI) confirmed the conspecificity of our isolate with the holotype G. trapeziforme (accession No. EF192414), we found a difference of 14 bases in the D1–D6 domains of the LSU rDNA sequences between the two entities, which indicates a detectable speciation of the two populations. Our work provides a detailed morphological and molecular characterization of G. trapeziforme that was isolated from the coastal water of China, which also broadens the geographical distribution of this 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.
► Cochlodinium polykrikoides cultures grew faster on glutamic acid than nitrate, ammonium, and urea. ► Nitrogen (N) enrichment enhanced cellular growth and photosynthesis of C. polykrikoides during ...blooms. ► Bloom populations assimilated nitrate in eutrophic tributaries but organic nitrogen in open, estuarine waters. ► C. polykrikoides blooms are strongly influenced by N and are nutritionally flexible, capable of adapting to differing nitrogen regimes.
The harmful dinoflagellate Cochlodinium polykrikoides is well known for forming ichthyotoxic blooms around the world, but the nutritional factors supporting and promoting these blooms have not been well studied. To better understand the nitrogen (N) nutritional ecology of C. polykrikoides, the temporal and spatial dynamics of nutrients, C. polykrikoides cells, and co-occurring phytoplankton were monitored within multiple NY (USA) estuaries over a three-year period. Uptake rates of bicarbonate and various N compounds were assessed during blooms and the growth responses of C. polykrikoides relative to co-occurring phytoplankton were quantified during N enrichment bioassays. Finally, the growth kinetics of C. polykrikoides were examined using clonal cultures grown on four N sources (ammonium, glutamic acid, nitrate, urea). Blooms of C. polykrikoides occurred when concentrations of nitrate and ammonium were <2μM but dissolved organic N levels were high (>20μM). During blooms, the addition of N compounds (ammonium, glutamic acid, nitrate, or urea) significantly enhanced primary productivity among microphytoplankton (>20μm; p<0.05) and significantly increased the net growth of C. polykrikoides relative to other phytoplankton groups (p<0.05), suggesting blooms were N-limited. The dominant N compounds assimilated by communities dominated by C. polykrikoides (90% of cells) within eutrophic tributaries were nitrate and nitrite while in mesotrophic, open estuarine regions, urea and glutamic acid dominated N uptake. Finally, C. polykrikoides cultures grown on glutamic acid displayed significantly faster growth rates than cultures grown on urea, ammonium, and nitrate (p<0.05). The sum of these observations indicate that N strongly influences C. polykrikoides blooms and that this alga is nutritionally flexible, capable of adapting to differing nutrient regimes and utilizing a variety of N compounds over a range of concentrations to form blooms.
The genus Gymnodinium includes many morphologically similar species, but molecular phylogenies show that it is polyphyletic. Eight strains of Gymnodinium impudicum, Gymnodinium dorsalisulcum and a ...novel Gymnodinium‐like species from Chinese and Malaysian waters and the Mediterranean Sea were established. All of these strains were examined with light microscopy, scanning electron microscopy and transmission electron microscopy. SSU, LSU and internal transcribed spacers rDNA sequences were obtained. A new genus, Wangodinium, was erected to incorporate strains with a loop‐shaped apical structure complex (ASC) comprising two rows of amphiesmal vesicles, here referred to as a new type of ASC. The chloroplasts of Wangodinium sinense are enveloped by two membranes. Pigment analysis shows that peridinin is the main accessory pigment in W. sinense. Wangodinium differs from other genera mainly in its unique ASC, and additionally differs from Gymnodinium in the absence of nuclear chambers, and from Lepidodinium in the absence of Chl b and nuclear chambers. New morphological information was provided for G. dorsalisulcum and G. impudicum, e.g., a short sulcal intrusion in G. dorsalisulcum; nuclear chambers in G. impudicum and G. dorsalisulcum; and a chloroplast enveloped by two membranes in G. impudicum. Molecular phylogeny was inferred using maximum likelihood and Bayesian inference with independent SSU and LSU rDNA sequences. Our results support the classification of Wangodinium within the Gymnodiniales sensu stricto clade and it is close to Lepidodinium. Our results also support the close relationship among G. dorsalisulcum, G. impudicum, and Barrufeta. Further research is needed to assign these Gymnodinium species to Barrufeta or to erect new genera.
We present experiments that examined the grazing and survivorship of zooplankton native (Acartia tonsa) and non-native (Artemia salina) to NY (USA) estuaries when exposed to blooms and cultures of ...the three harmful algae native to NY, Alexandrium fundyense, Aureococcus anophagefferens (strains CCMP 1850 and CCMP 1984) and Cochlodinium polykrikoides. During experiments with cultures of A. anophagefferens, clearance rates (CR) of A. salina were significantly greater than those of A. tonsa for both algal strains examined. A. salina fed on cultures of C. polykrikoides at higher rates than all phytoplankton species examined, including the control diet (Rhodomonas salina), and faster than rates of A. tonsa fed C. polykrikoides. During experiments with A. fundyense, A. salina actively grazed all cell concentrations (250–1500 cells ml−1) while A. tonsa did not feed at any concentration. Percent mortality of A. salina and A. tonsa fed A. fundyense for 48 h were 43 ± 7.7% and 72 ± 7.8%, respectively, percentages significantly higher than those of individuals fed all other algal diets. During 25 field experiments using natural blooms of the three HAB species performed across six NY estuaries, A. salina significantly (p < 0.05) reduced cell densities of A. anophagefferens, C. polykrikoides, and A. fundyense relative to the control treatments in all but one experiment. The sum of these findings demonstrates that a failure to graze these HABs by the indigenous copepod, A. tonsa, may permit blooms to occur. In addition, the ability of A. salina to graze these HABs at densities that were inhibitory to A. tonsa suggests that A. salina could, in some circumstances, be considered as a part of mitigation strategy for these events.
Blooms of
Phaeocystis globosa
have been frequently reported in Chinese coastal waters, causing serious damage to marine ecosystems. To better understand the ecological characteristics of
P. globosa
...in Chinese coastal waters that facilitate its rapid expansion, the effects of temperature, salinity and irradiance on the growth of
P. globosa
from the South China Sea were examined in the laboratory. The saturating irradiance for the growth of
P. globosa
(
I
s
) was 60 μmol/(m
2
∙s), which was lower than those of other harmful algal species (70–114 μmol/(m
2
∙s)). A moderate growth rate of 0.22/d was observed at 2 μmol/(m
2
∙s) (the minimum irradiance in the experiment), and photo-inhibition did not occur at 230 μmol/(m
2
∙s) (the maximum irradiance in the experiment). Exposed to 42 different combinations of temperatures (10–31°C) and salinities (10–40) under saturating irradiance, P. globosa exhibited its maximum specific growth rate of 0.80/d at the combinations of 24°C and 35, and 27°C and 40. The optimum growth rates (>0.80/d) were observed at temperatures ranging from 24 to 27°C and salinities from 35 to 40. While
P. globosa
was able to grow well at temperatures from 20°C to 31°C and salinities from 20 to 40, it could not grow at temperatures lower than 15°C or salinities lower than 15. Factorial analysis revealed that temperature and salinity has similar influences on the growth of this species. This strain of
P. globosa
not only prefers higher temperatures and higher salinity, but also possesses a flexible nutrient competing strategy, adapted to lower irradiance. Therefore, the
P. globosa
population from South China Sea should belong to a new ecotype. There is also a potentially high risk of blooms developing in this area throughout the year.
We report on the emergence of
Cochlodinium polykrikoides blooms in the Peconic Estuary and Shinnecock Bay, NY, USA, during 2002–2006. Blooms occurred during late summer when temperatures and ...salinities ranged from 20 to 25
°C and 22 to 30
ppt, respectively. Bloom patches achieved cell densities exceeding 10
5
ml
−1 and chlorophyll
a levels exceeding 100
μg
l
−1, while background bloom densities were typically 10
3–10
4 cells
ml
−1. Light, scanning electron and ultrathin-section transmission electron microscopy suggested that cells isolated from blooms displayed characteristics of
C. polykrikoides and provide the first clear documentation of the fine structure for this species. Sequencing of a hypervariable region of the large subunit rDNA confirmed this finding, displaying 100% similarity to other North American
C. polykrikoides strains, but a lower similarity to strains from Southeast Asia (88–90%). Bioassay experiments demonstrated that 24
h exposure to bloom waters (>5
×
10
4
cells
ml
−1) killed 100% of multiple fish species (1-week-old
Cyprinodon variegates, adult
Fundulus majalis, adult
Menidia menidia) and 80% of adult
Fundulus heteroclitus. Microscopic evaluation of the gills of moribund fish revealed epithelial proliferation with focal areas of fusion of gill lamellae, suggesting impairment of gill function (e.g. respiration, nitrogen excretion, ion balance). Lower fish mortality was observed at intermediate
C. polykrikoides densities (10
3–10
4
cells
ml
−1), while fish survived for 48
h at cell densities below 1
×
10
3
cells
ml
−1. The inability of frozen and thawed-, or filtered (0.2
μm)-bloom water to cause fish mortality suggested that the thick polysaccharide layer associated with cell membranes and/or a toxin principle within this layer may be responsible for fish mortality. Juvenile bay scallops (
Argopecten irradians) and American oysters (
Crassostrea virginica) experienced elevated mortality compared to control treatments during a 9-day exposure to bloom water (∼5
×
10
4
cells
ml
−1). Surviving scallops exposed to bloom water also experienced significantly reduced growth rates. Moribund shellfish displayed hyperplasia, hemorrhaging, squamation, and apoptosis in gill and digestive tissues with gill inflammation specifically associated with areas containing
C. polykrikoides cells. In summary, our results indicate
C. polykrikoides blooms have become annual events on eastern Long Island and that bloom waters are capable of causing rapid mortality in multiple species of finfish and shellfish.
The impacts of harmful algal blooms (HABs) on economies, public health, ecosystems, and aquaculture across the globe have all increased in recent decades, and this has been acutely the case in China. ...Here, we review the history of HABs and HABs research in China, as well as recent trends in HABs and future prospects of HAB science in China. The most updated analyses demonstrated that the number of HAB events, the number of HAB species, the aerial coverage of HABs, and the impacts of HABs in Chinese waters during the 21st century were all higher than that during the last two decades of the 20th century. The increase in the number of HABs in China has been significantly correlated with the increased discharge of ammonium and total phosphorus into coastal waters (p < 0.01 for both). Notable newly recognized events this century have included chronic HABs caused by Prorocentrum donghaiense and Karenia mikimotoi, a paralytic shellfish poisoning event caused by Gymnodinium catenatum that sickened 80 people, brown tides caused by Aureococcus anophagefferens, green tides caused by Ulva prolifera, golden tides caused by Sargassum horneri, and the disruption of a nuclear power plant caused by a bloom of Phaeocystis globosa. A series of key discoveries regarding HABs has been made this century including documentation of nearly all known HAB toxins in Chinese waters, discovery of novel cyst-formation and/or life stages of multiple HABs-causing species, identification of the chemical and physical oceanographic drivers of multiple HABs including those formed by P. donghaiense, K. mikimotoi, and U. prolifera, and the successful mitigation of HABs via the use of modified clay approaches. Future research prospects highlighted include the use of macroalgae as a means to prevent, mitigate, and control (PCM) HABs and the process by which multi-disciplinary studies involving molecular approaches (omics), remote in situ detection, artificial intelligence, and mega-data analyses might be used to develop refined and realistic HAB forecasting platforms. Collectively, this review demonstrates the significant evolution of HAB science since the 20th century in China and demonstrates that while HABs in China are complex and widespread, recent and on-going discoveries make the development of detailed understanding and effective measures to mitigate the negative effects of HABs a hopeful outcome in the coming years.
While harmful algal blooms (HABs) have become a threat to fisheries, environmental and public health, and economies worldwide, most of the approaches under investigations for prevention, control, and ...mitigation (PCM) of HABs are limited by high cost and possible secondary pollution. This study reports our laboratory and field experiments demonstrating effective growth-inhibiting effects of the widely cultivated seaweed
Gracilaria lemaneiformis
on phytoplankton possibly forming HABs. Laboratory experiments demonstrated significant growth-inhibiting effects of fresh
G. lemaneiformis
thalli in a dose-response manner on four of six test microalgae commonly observed in the seaweed cultivation area (
Scrippsiella trochoidea
,
Prorocentrum micans
,
Skeletonema costatum
,
Dunaliella salina
) and on the natural phytoplankton assemblage in seawater. Significant inhibiting effects were also observed from in situ bottle (1.0 L) and mesocosm (50 and 1000 L) experiments on the harmful alga
Phaeocystis globosa
during its blooms. Based on a large-scale field survey, the phytoplankton abundance in the areas with
Gracilaria
cultivation was demonstrated to be significantly lower than that in the areas without
Gracilaria
. Collectively, our results showed that large-scale cultivation of
G. lemaneiformis
is an effective approach to prevent HABs in coastal waters, as an added value to the economically viable industry of
Gracilaria
cultivation.
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