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The raphidophyte Chattonella marina complex (hereafter Chattonella) consists of noxious red-tide-forming algae that are damaging to fish farms. Chattonella produces and secretes large amounts of the superoxide anion (•O 2 - ), and the production of extracellular •O 2 - has been associated with fish mortality. We reported previously that photosynthetic electron transport is correlated with the production of •O 2 - in the genus Chattonella. However, the physiological roles of the production of extracellular •O 2 - remain to be clarified. In the present study, we examined the effects of the production of extracellular •O 2 - on photosynthesis and cell proliferation in two strains of Chattonella, namely, Ago03, a highly toxic strain that produces large amounts of •O 2 - externally, and Ago04, a low-toxicity strain that produces very small amounts of •O 2 - . Both the growth rate and the net photosynthetic activity of Ago04 were higher than those of Ago03. In Ago04, levels of Rubisco and 3-phosphoglycerate, the product of the reaction catalyzed by Rubisco, were 4-fold higher than those in Ago03, suggesting the higher photosynthetic activity of Ago04. In the presence of glycolaldehyde, a specific inhibitor of the Calvin-Benson cycle, the levels of NADP + and the photosynthetic parameter qP declined under strong light in Ago04. By contrast, levels of NADP + and qP in Ago03 changed less significantly than those in Ago04. Given that •O 2 - is produced by a putative NADPH oxidase that converts O 2 to •O 2 - in Chattonella, it seems likely that the production of •O 2 - might play a role not only in the elimination of excess reducing power of NADPH from the cell, via •O 2 - , but also in the regeneration of NADP + , as a result of the action of NADPH oxidase, which oxidizes NADPH, to maintain photosynthetic electron transport., Competing Interests: Declaration of competing interest The authors know of no conflict of interest associated with this publication., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Brown tides caused by Aureococcus anophagefferens occur frequently worldwide and have contributed to the collapse of Mercenaria mercenaria farming in the United States. This economically valuable hard clam has been used in China for more than 20 years. To date, it has remained unknown whether A. anophagefferens Chinese strain has an impact on hard clam cultivation in the coastal areas of China or other sea areas worldwide if it enters through ship ballast water and other ways. In this study, a Chinese strain of A. anophagefferens isolated from the brown tide waters of Bohai Bay, China, was selected to explore its influence on the feedback of hard clams. After being fed with A. anophagefferens, hard clams showed characteristics similar to starvation. The reduced feeding efficiency of hard clams leads to reduced energy intake. However, the immune response and oxidative stress, result in increased energy consumption. An imbalance in the energy budget may be an important reason for hard clam starvation. This study has described the response characteristics of the A. anophagefferens Chinese strain to M. mercenaria, explored the reasons for the negative impact of A. anophagefferens on hard clams, and provides ideas for reducing shellfish aquaculture caused by brown tides., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Harmful algal blooms (HABs) have affected salmon farms in Chile since the early 1970's, causing massive losses in fish. Two large HABs occurred in 2002 and 2009, during which Alexandrium catenella blooms killed tons of salmon over an extended geographic area in southern Chile. At the beginning of 2016, high and persistent densities of Pseudochattonella cf. verruculosa and A. catenella were detected in the estuarine and marine ecosystems of southern Chile. Mortality for this latter event reached 27 million salmon and trout (i.e. 39,000 tons). Unfortunately, the threshold concentrations of algae that could be harmful to the health of farmed salmon in southern Chile have not yet been quantified. Here, to protect fish farms from HABs, critical concentration levels, i.e. thresholds at which the behavior of farmed Salmo salar is affected by harmful algae were quantified using generalized linear mixed models (GLMM). An extensive database from southern Chile covering the period from 1989 to 2016 was analyzed. The database included salmon behavior, cell abundance of microalgae and oceanographic factors. For both species analyzed, the higher the cell abundance, the greater the probability of detecting anomalous behavior. A threshold of 397 cells/mL was estimated for A. catenella, although it can increase up to ca. >975 cells/mL at a Secchi depth >6 m and up to 874 cells/mL during flood tide. A threshold value <1 cell/mL for Pseudochattonella cf. verruculosa was found to be associated with anomalous salmon behavior, which significantly increased at a water temperature of 11 °C. Evidence for a relationship between fish behavior and mortality is provided., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The potential for toxic contaminants and nutrient pollution to alter natural cycles of estuarine phytoplankton blooms is well known, yet few studies have examined how these combined stressors affect harmful algal species. Here, a robust testing protocol was developed to enable an ecotoxicological assessment of responses to commonly co-occurring estuarine contaminants by harmful algal bloom species. The population growth and toxicity (as cell density and hemolytic activity, respectively) of a cultured strain of the toxigenic raphidiophycean, Chattonella subsalsa, were assessed in two experiments (duration 10 days and 28 days) across a gradient of atrazine concentrations and N:P ratios simulating nutrient-rich versus nutrient-depleted regimes. The response of this large-celled, slowly growing alga to atrazine × nutrients depended on growth phase; atrazine was most inhibitory during early exponential population growth (day 10), whereas nutrient regime was a more important influence during later phases of growth (day 28). Without atrazine, toxicity toward fish was highest in low-P cultures. At atrazine levels >25 μg L -1 , hemolytic activity was highest in low-N cultures, and increased with increasing atrazine concentration in all nutrient-limited cultures. Hemolytic activity varied inversely with atrazine concentration in N,P-replete conditions. Overall, atrazine inhibitory effects on population growth of this C. subsalsa strain depended on the growth phase and the nutrient regime; hemolytic activity was higher and further enhanced by atrazine in low N-P regimes; and atrazine inhibited hemolytic activity in nutrient-replete conditions. The data suggest that, depending on the growth phase and nutrient regime, atrazine can help promote toxic C. subsalsa blooms., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The algicidal and growth-inhibiting bacteria associated with seagrasses and macroalgae were characterized during the summer of 2012 and 2013 throughout Puget Sound, WA, USA. In 2012, Heterosigma akashiwo-killing bacteria were observed in concentrations of 2.8×10 6 CFUg -1 wet in the outer organic layer (biofilm) on the common eelgrass (Zostera marina) in north Padilla Bay. Bacteria that inhibited the growth of Alexandrium tamarense were detected within the biofilm formed on the eelgrass canopy at Dumas Bay and North Bay at densities of ∼10 8 CFUg -1 wet weight. Additionally, up to 4100CFUmL -1 of algicidal and growth-inhibiting bacteria affecting both A. tamarense and H. akashiwo were detected in seawater adjacent to seven different eelgrass beds. In 2013, H. akashiwo-killing bacteria were found on Z. marina and Ulva lactuca with the highest densities of ∼10 8 CFUg -1 wet weight at Shallow Bay, Sucia Island. Bacteria that inhibited the growth of H. akashiwo and A. tamarense were also detected on Z. marina and Z. japonica at central Padilla Bay. Heterosigma akashiwo cysts were detected at a concentration of 3400cystsg -1 wet weight in the sediment from Westcott Bay (northern San Juan Island), a location where eelgrass disappeared in 2002. These findings provide new insights on the ecology of algicidal and growth-inhibiting bacteria, and suggest that seagrass and macroalgae provide an environment that may influence the abundance of harmful algae in this region. This work highlights the importance of protection and restoration of native seagrasses and macroalgae in nearshore environments, in particular those regions where shellfish restoration initiatives are in place to satisfy a growing demand for seafood., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The inimical effects of the ichthyotoxic harmful algal bloom (HAB)-forming raphidophytes Heterosigma akashiwo, Chattonella marina, and Chattonella antiqua on the early-life stages of the Japanese pearl oyster Pinctada fucata martensii were studied. Fertilized eggs and developing embryos were not affected following exposure to the harmful raphidophytes; however, all three algal species severely affected trochophores and D-larvae, early-stage D-larvae, and late-stage pre-settling larvae. Exposure to C. marina (5×10 2 cellsml -1 ), C. antiqua (10 3 cellsml -1 ), and H. akashiwo (5×10 3 cellsml -1 ) resulted in decreased success of metamorphosis to the trochophore stage. A complete inhibition of trochophore metamorphosis was observed following exposure to C. antiqua at 5×10 3 cellsml -1 and C. marina at 8×10 3 cellsml -1 . In all experiments, more than 80% of newly formed trochophores were anomalous, and in the case of exposure to H. akashiwo at 10 5 cellsml -1 more than 70% of D-larvae were anomalous. The activity rates of D-larvae (1-day-old) were significantly reduced following exposure to C. antiqua (8×10 3 cellsml -1 , 24h), C. marina (8×10 3 cellsml -1 , 24h), and H. akashiwo (10 4 cellsml -1 , 24h). The activity rates of pre-settling larvae (21-day-old) were also significantly reduced following exposure to C. antiqua (10 3 cellsml -1 , 24h),C. marina (8×10 3 cellsml -1 , 24h), and H. akashiwo (5×10 4 cellsml -1 , 24h). Significant mortalities of both larval stages were induced by all three raphidophytes, with higher mortality rates registered for pre-settling larvae than D-larvae, especially following exposure to C. marina (5×10 2 -8×10 3 cellsml -1 , 48-86h) and C. antiqua (10 3 -8×10 3 cellsml -1 , 72-86h). Contact between raphidophyte cells and newly metamorphosed trochophores and D-larvae, 1-day-old D-larvae, and 21-day-old larvae resulted in microscopic changes in the raphidophytes, and then, in the motile early-life stages of pearl oysters. Upon contact and physical disturbance of their cells by larval cilia, H. akashiwo, C. marina and C. antiqua became immotile and shed their glycocalyx. The trochophores and larvae were observed trapped in a conglomerate of glycocalyx and mucus, most probably a mixture of larval mucous and raphidophyte tricosyts and mucocytes. All motile stages of pearl oyster larvae showed a typical escape behavior translating into increased swimming in an effort to release themselves from the sticky mucous traps. The larvae subsequently became exhausted, entrapped in more heavy mucous, lost their larval cilia, sank, become immotile, and died. Although other toxic mediators could have been involved, the results of the present study indicate that all three raphidophytes were harmful only for motile stages of pearl oysters, and that the physical disturbance of their cells upon contact with the ciliary structures of pearl oyster larvae initiated the harmful mechanism. The present study is the first report of lethal effects of harmful Chattonella spp. towards larvae of a bivalve mollusc. Blooms of H. akashiwo, C. antiqua and C. marina occur in all major cultivation areas of P. fucata martensii during the developmental period of their larvae. Therefore, exposure of the motile early-life stages of Japanese pearl oysters could adversely affect their population recruitment. In addition, the present study shows that further research with early-life development of pearl oysters and other bivalves could contribute to improving the understanding of the controversial harmful mechanisms of raphidophytes in marine organisms., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The marine genus Pseudochattonella is a recent addition to the list of fish killing microalgae. Currently two species are recognised (viz. P. verruculosa and P. farcimen) which both form recurrent coastal blooms sometimes overlapping in space and time. These events and their ecological and economic consequences have resulted in great interest and concern from marine biologists and the aquaculture industry. Since the first recorded blooms in Japanese (late 1980s), Scandinavian (1993) and Chilean (2004) waters numerous studies have focused on understanding the causative means of the fish killing. Mortality is probably due to Pseudochattonella discharging mucocysts that cause gill irritation and damage to the fish fills. Here, a review is provided of the literature on Pseudochattonella that covers the last ca. 25 years and focus on a number of topics relevant to understanding the general biology of the genus including ways to distinguish the two species. The literature addressing biogeography and known harmful events is evaluated and based on these findings an updated distribution map is proposed. P. farcimen is presently restricted to North European waters. Despite being very difficult to delineate based on morphology alone the two Pseudochattonella species seem to have separate growth optima. In laboratory experiments P. verruculosa consistently has higher temperature growth optima compared to P. farcimen though periods of overlap have been noted in the field. The review ends by proposing five areas with knowledge gaps and each of these could form the basis of future studies., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A number of marine and freshwater harmful algal bloom (HAB) species have colonized new areas and expanded their habitat range in recent years. Nevertheless it is notoriously difficult to establish when colonization first occurred, what the dispersal routes are, and to separate recent invasion from increases in existent but small populations. The freshwater raphidophyte Gonyostomum semen is a nuisance species that has expanded its habitat range and increased in abundance in northern Europe during the past decades. To evaluate to what extent sediments can be used for determining historic occurrence of G. semen, a quantitative real-time PCR method for detecting cysts of this algae was developed. This paper presents a qPCR protocol with a set of primers that are specific to Gonyostomum and with PCR conditions optimized for sediment samples from humic lakes, which are the common habitat of G. semen. With this sensitive method as few as 1.6 cysts per PCR reaction could be reliably quantified, corresponding to 320 cysts per g wet weight sediment. Cysts were present in sediments with ages ranging from years to decades and their persistence allows detection of historic populations up to at least 50 years old. With this qPCR assay it will be possible to trace the presence of G. semen in environments prior to the onset of algae-specific monitoring programs as well as for quantification in water column samples., (Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.)

Several studies on various Chattonella species have reported that bacteria may play an important role in Chattonella bloom initiation, however, no studies have described how these bacteria promote the growth of C. marina. The interaction between C. marina and bacteria was investigated for identification and characterization of potential growth-promoting bacteria. In preliminary tests, the growth promoting effect of Pseudomonas species (25 strains) was investigated and P. asplenii (≥2.27) was determined as a growth-promoting bacteria for both C. marina strains (CCMP 2049 and 2050). This bacterium exerted optimal growth-promoting effects on C. marina, causing an increase in the initial density of P. asplenii to approximately 1×10 7 cellsmL -1 , which was used as the initial density in this study. To determine whether the growth-promoting activity was direct or indirect, P. asplenii was incubated in the algal media and then a filtrate of this culture was added to both C. marina strains. The P. asplenii filtrate stimulated the growth of C. marina and maintained the growth-promoting effects after high temperature (121°C for 20min) and pressure (15psi) treatment. Thus, P. asplenii is able to promote C. marina growth through the release of a heat-resistant substance, such as inorganic nutrients. A nutrient analysis indicated that this bacterium elevated the phosphate concentration. Interestingly, P. asplenii was unable to survive in phosphate-limited media but could grow in phosphate-limited media incubating C. marina. Moreover, this bacterium could secrete significantly more phosphate in the presence of C. marina (p<0.0001). These results suggested that P. asplenii and C. marina may have a mutualistic interaction., (Copyright © 2016 Elsevier B.V. All rights reserved.)