What caused H. akashiwo to bloom into a red tide frenzy in San Francisco Bay last summer?  Another bloom like that one could wipe out the remaining Bay-Delta population of White Sturgeon.  We must understand this organism … before next summer! 

1. Recent Red Tide History in San Francisco Bay.

H. akashiwo bloomed twice in SF Bay over the past 20 years.

The previous recent red tide bloom of H. akashiwo occurred in Richardson Bay in the summer and autumn of 2002.  That bloom eventually extended around the Tiburon Peninsula and across the central Bay to the Berkeley shores.  The bloom’s impact on fishes is unknown.  (See: Herndon, Cochlan, and Horner (2003) Heterosigma akashiwo, a raphidophyte, in Richardson Bay https://www.researchgate.net/publication/313203374_Heterosigma_akashiwo_blooms_in_San_Francisco_Bay  )

The H. akashiwo bloom of 2022 was first spotted in Seaplane Lagoon, Alameda on July 16^th.  That bloom quickly spread around Alameda Island, into Lake Merritt, and across central SF Bay.  And, as we all know, it was a significant fish-killer. 

(BTW:  To clear up any confusion, a red tide bloom in 2004 was caused by a different organism with a similar-sounding name.  That creature was a dinoflagellate called Akashiwo sanguinea.  – The word “akashiwo” means “red tide” in Japanese. – The A. sanguinea bloom did not result in any fish kill. See: Akashiwo sanguinea, a dinoflagellate, in Central Bay (see Cloern, Schraga, and Lopez (2005) Heat Wave Brings an Unprecedented Red Tide to San Francisco Bay  https://www.usgs.gov/publications/heat-wave-brings-unprecedented-red-tide-san-francisco-bay
PDF is here: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/eost2005EO07  )

The red tide bloom of 2022 was first observed in Seaplane Lagoon, Alameda on July 16^th by Luis from LASPHOTOS. 

Luis knows Seaplane Lagoon very well.  For most of his life, he has worked near the lagoon and observed it on a near weekly basis.

• Over most of the past 20 years, Luis has seen small red tide blooms form in the northeast corner of Seaplane Lagoon in late summer.
• By July 16^th, Luis noticed that this bloom was much larger. It spread into the adjacent ship docking basin just to the south.  Not long after that, the bloom expanded into waters surrounding Alameda Island.
• Luis confirmed by microscopic examination that Heterosigma akashiwo was the culprit in 2022. He posted his report here: https://www.youtube.com/watch?v=QCtiRyo58tc

A slide by Damon Tighe from his mid-September presentation to the Lake Merritt Rotary Nature Center Friends. 

Damon Tighe, a volunteer naturalist around Lake Merritt, next documented the spread of H. akashiwo outward from Alameda Island.  (Damon’s presentation is posted here:  https://www.youtube.com/watch?v=-COM00KIWo4)

• Dark reddish-brown water was reported in the Alameda Channel and as far north as Treasure Island by August 2^nd and south to San Leandro Marina by August 9^th.
• This phytoplankton bloom eventually spread west to Hunters Point, north into San Pablo Bay, and south past the Dumbarton Bridge.

Another slide by Damon Tighe from his mid-September presentation. 

Fish began dying a few weeks later. 

• The first fish kills were first reported in Central Bay on August 21^st and 22^nd.
• A week later on August 28^th through the 30^th, both Damon Tighe and Katie Noonan reported dead fish in Lake Merritt: dozens of striped bass and bat rays along with thousands of gobies and some clams and mussels.
• Between 400 to 600 white sturgeon carcasses and perhaps 20 to 30 dead green sturgeon were counted along the shores around the wider area of north and south San Francisco Bay.

2. Investigating the Habitat at Ground Zero: Seaplane Lagoon & Alameda Island.

Some lifeforms in Seaplane Lagoon where the red tide first blossomed.

Luis has studied and documented flora and fauna in Seaplane Lagoon for decades.  He gave me a tour on November 10th. 

• Seaplane Lagoon has robust subtidal habitat. However, shoreline marsh habitat is limited to non-existent in this engineered seaplane and ship docking basin.
• According to Luis: The sides of Seaplane lagoon have consisted of rip rap for at least 50 years since the Naval Air Station days.  However, from the tideline down, the lagoon has up to 12 species of seaweed and seagrass.  The lagoon also has a wide assortment of native and invasive invertebrates along with fish and birds. 

More examples of lifeforms in Seaplane Lagoon.

Marsh habitat around the southern shore of Alameda Island is minimal.

Marsh habitat around the shores of Alameda Island is similarly minimal.  The area has long history of urbanization and human disturbance.  Habitat along the shoreline varies from up to a 10-20 meter strip of pickleweed and spartina fringing marsh (photo B) to less than 1 meter of non-native ice plant (photo c), to only a seawall with no marsh (photo D).

As discussed in a previous blog post, some research suggests that seaweeds (macroalgae) and seagrasses provide natural control over red tide blooms.  https://www.ogfishlab.com/2022/09/28/fish-in-the-bay-september-2022-part-2-seaweed-seagrass-beds-inhibit-red-tides/

Whether true or not, it is worth noting that both seaweeds and seagrasses are present in Seaplane Lagoon where H. akashiwo first bloomed in 2022.  It is equally noteworthy, that both Seaplane Lagoon and the shores around Alameda Island where the H. akashiwo red tide quickly spread have been highly disturbed in the past and provide very little marsh habitat.

…

Many questions remain!  What is this creature?  Why does it bloom?  What does it want?  

(In the discussion below, editorial comments are shown in red font.) 

3. Mind-meld with H. akashiwo.

Spock mind-melding with the Horta. Image from the Star Trek website.  https://www.startrek.com/videos/watch-star-trek-history-the-devil-in-the-dark

Horta via Spock:  “Go out … to the Chamber of the Ages.  Walk carefully in the vault of tomorrow. … Sorrow for the murdered children …” 

LESSON 1: Many types of phytos are Mixotrophic. They are both photosynthetic AND also hunt prey!  

L V Il’iash (2002) Relationship between photosynthetic activity and assimilation of organic matter in marine plankton mixotrophic algae–the possibility of different metabolic strategies https://pubmed.ncbi.nlm.nih.gov/12395752/ Abstract. The relationship between photosynthetic and heterotrophic activities of plankton mixotrophic algae is characterized by the type of metabolic strategy.

• Algae with a primary photoautotrophic strategy grow at the expense of photosynthesis without uptake of organic substrates when inorganic and organic nutrients are available. They assimilate only organic substrates when inorganic nutrients are in shortage, while heterotrophic activity supports photosynthesis under conditions of inorganic nutrients deficiency.
• Algae with a primary heterotrophic strategy grow heterotrophically under repletion of inorganic and organic nutrients. Photosynthesis occurs only when organic substrates are depleted.
• The most mixotrophic algae combine the features of a primary photoautotrophic and a primary heterotrophic strategies. The varieties of metabolic types of mixotrophic algae form a continuum with a primary photoautotrophic strategy on the one end and a primary heterotrophic strategy on the other.
• The natural conditions allowing mixotrophic algae to use one or other metabolic strategy are determined by the dynamic of inorganic and organic nutrients.

Crane and Grover (2010)  Coexistence of mixotrophs, autotrophs, and heterotrophs in planktonic microbial communities  https://pubmed.ncbi.nlm.nih.gov/19878684/   Abstract.  We examine what circumstances allow the coexistence of microorganisms following different nutritional strategies, using a mathematical model. This model incorporates four nutritional types commonly found in planktonic ecosystems:

• heterotrophic bacteria that consume dissolved organic matter and are prey to some of the other organisms;
• heterotrophic zooflagellates that depend entirely on bacterial prey;
• phototrophic algae that depend only on light and inorganic nutrients, and
• mixotrophs that photosynthesize, take up inorganic nutrients, and consume bacterial prey.

Mixotrophs are characterized by a parameter representing proportional mixing of phototrophic and heterotrophic nutritional strategies. Varying this parameter, a range of mixotrophic strategies was examined in hypothetical habitats differing in supplies of light, dissolved organic carbon, and dissolved inorganic phosphorous. Mixotrophs expressing a wide range of mixotrophic strategies persisted in model habitats with low phosphorus supply, but only those with a strategy that is mostly autotrophic persisted with high nutrient supply, and then only when light supply was also high.

Organisms representing all four nutritional strategies were predicted to coexist in habitats with high phosphorus and light supplies. Coexistence involves predation by zooflagellates and mixotrophs balancing the high competitive ability of bacteria for phosphorus, the partitioning of partially overlapping resources between all populations, and possibly nonequilibrium dynamics. In most habitats, the strategy predicted to maximize the abundance of mixotrophs is to be mostly photosynthetic and supplement nutritional needs by consuming bacteria.

Ward et al (2011) Biophysical aspects of resource acquisition and competition in algal mixotrophs  https://pubmed.ncbi.nlm.nih.gov/21670581/  Abstract.  Mixotrophic organisms combine autotrophic and heterotrophic nutrition and are abundant in both freshwater and marine environments. Recent observations indicate that mixotrophs constitute a large fraction of the biomass, bacterivory, and primary production in oligotrophic environments. While mixotrophy allows greater flexibility in terms of resource acquisition, any advantage must be traded off against an associated increase in metabolic costs, which appear to make mixotrophs uncompetitive relative to obligate autotrophs and heterotrophs.

… At low resource concentrations, when the uptake of nutrients is limited by diffusion toward the cell, the investment in cell membrane transporters can be minimized. In this situation, mixotrophs can acquire limiting elements in both organic and inorganic forms, outcompeting their specialist competitors that can utilize only one of these forms. This advantage can be enough to offset as much as a twofold increase in additional metabolic costs incurred by mixotrophs.

Jeong, Yeong, Park, and Jae (2005) Feeding by phototrophic red-tide dinoflagellates: Five species newly revealed and six species previously known to be mixotrophic https://www.researchgate.net/publication/280008906_Feeding_by_phototrophic_red-tide_dinoflagellates_Five_species_newly_revealed_and_six_species_previously_known_to_be_mixotrophic   Abstract. … 5 red-tide dinoflagellates (Gymnodinium catenatum, G. impudicum, Lingulodinium polyedrum, Prorocentrum donghaiense, and P. triestinum) which had been previously thought to be exclusively autotrophic dinoflagellates are mixotrophic species.

We investigated the feeding behaviors, the kinds of prey species that 11 mixotrophic red-tide dinoflagellates (Akashiwo sanguines, Alexandrium tamarense, G. catenatum, G. impudicum, Heterocapsa triquetra, L. polyedrum, P. donghaiense, P. micans, P. minimum, P. triestinum, and Scrippsiella trochoidea) fed on, and the effects of the prey concentration on the growth and ingestion rates of P. donghaiense, H. triquetra, P. micans, and L. polyedrum when feeding on algal prey. …

All algal predators tested in the present study ingested small phytoplankton species that had equivalent spherical diameters (ESDs) < 12 μm. A. sanguinea and L. polyedrum were able to ingest large phytoplankton species such as H. triquetra, S. trochoidea, and A. tamarense. Prorocentrum spp. fed on prey by engulfing the prey cell through body sutures, while S. trochoidea engulfed prey through the apical horn as well as through the sulcus. … The results of the present study suggest that the algal predators sometimes have a potentially considerable grazing impact on populations of the algal prey.

H. akashiwo is also prey!  It is a small, unarmored, and nutritious cell that is highly susceptible to predation by larger dinoflagellates, cilliates, and copepods.  

Demir et al (2007)  Assessment of Microzooplankton Grazing on Heterosigma akashiwo Using a Species- Specific Approach Combining Quantitative Real-Time PCR (QPCR) and Dilution Methods  https://link.springer.com/article/10.1007/s00248-007-9263-9  Abstract. Delaware’s Inland Bays (DIB) are subject to numerous mixed blooms of harmful raphidophytes each year, and Heterosigma akashiwo is one of the consistently occurring species. … In this study, microzooplankton grazing pressure was assessed as a top–down control mechanism on H. akashiwo populations in mixed communities. …

We detected grazing on H. akashiwo using QPCR in samples where chl a analyses indicated little or no grazing on the total phytoplankton community. Overall, specific microzooplankton grazing pressure on H. akashiwo ranged from 0.88 to 1.88 day−1 at various sites. Experiments conducted on larger sympatric raphidophytes (Chattonella subsalsa, Chattonella cf. verruculosa and Fibrocapsa japonica) demonstrated no significant microzooplankton grazing on these species. Grazing pressure on H. akashiwo may provide a competitive advantage to other raphidophytes such as Chattonella spp. that are too large to be consumed at high rates by microzooplankton and help to shape the dynamics of this harmful algal bloom consortium. …

• Interesting related fact: Noctiluca scintillans (aka “Sea Sparkle”) is a large dinoflagellate that feeds on H akashiwo and diatoms.  And, it also causes red tides.  https://en.wikipedia.org/wiki/Noctiluca_scintillans 
• N scintillans is also a very beneficial link in the food web as long as populations do not explode and go red. http://en.citizendium.org/wiki/Noctiluca_scintillans 
• Video of N scintillans attempting to feed on H akashiwo on a microscope slide. https://www.youtube.com/watch?v=NK7S-Ni0zb4&list=PLJKbCf7cKjR9nG3-DPxVxrb0EJW1ZnvcU&index=9 

LESSON 2.  Diel Vertical Migration.  Flagellated phytos, like H. akashiwo, migrate up and down in the water column.

Hall and Pearl (2011) Vertical migration patterns of phytoflagellates in relation to light and nutrient availability in a shallow microtidal estuary  https://www.researchgate.net/publication/270039494_Vertical_migration_patterns_of_phytoflagellates_in_relation_to_light_and_nutrient_availability_in_a_shallow_microtidal_estuary  Abstract  … Two diel field studies were conducted during June and July 2001 to establish how the composition and productivity of the phytoplankton are influenced by the vertical water column structure within the shallow, eutrophic, microtidal Neuse River Estuary, North Carolina, USA.

During both studies, an upper photic mixed layer with low dissolved inorganic nitrogen (DIN) (∼1 μM) lay above a sub-halocline, aphotic region with elevated DIN (̃2 to 5 μM). Phytoflagellates were dominant and observed diel vertical migration (DVM) patterns are likely an important reason for their success in this N-limited system characterized by strong vertical separation of light and DIN resources. Integrated water column primary productivities during June and July were 15 and 113% greater, respectively, than expected for a vertically homogenous phytoplankton community. … Displacements of flagellate populations during DVM were positively correlated with cell size, exposing larger cells to higher light and nutrient levels over the diel period. …

H. akashiwo performs its own Diel Vertical Migration: it swims upward toward the surface after first light and then down again as darkness approaches.

Tamara Brown (2015) To the surface and back: determining the photobiology of the toxic Raphidophyte Heterosigma akashiwo with emphasis on its diel migration in Departure Bay, British Columbia, Canada   https://www.researchgate.net/publication/343084955_To_the_surface_and_back_determining_the_photobiology_of_the_toxic_Raphidophyte_Heterosigma_akashiwo_with_emphasis_on_its_diel_migration_in_Departure_Bay_British_Columbia_Canada  Abstract.  Heterosigma, and other ichthyotoxic Raphidophytes have been described as exhibiting a vertical migration pattern known as diel vertical migration (DVM), … A significant diel migration of Heterosigma was observed in Departure Bay at 95% confidence … however, salinity and temperature data showed that a subsurface wave occurred during the bloom which caused Heterosigma cells to be advected towards the surface, away from their regular evening migration pattern.

Bearon, Grunbaum, and Cattolico (2004) Relating cell-level swimming behaviors to vertical population distributions in Heterosigma akashiwo (Raphidophyceae), a harmful alga  https://www.researchgate.net/publication/250392606_Relating_cell-level_swimming_behaviors_to_vertical_population_distributions_in_Heterosigma_akashiwo_Raphidophyceae_a_harmful_alga   Abstract. Cell motility may facilitate the formation of harmful algal blooms (HABs) by enabling algal cells to swim to favorable microenvironments that support explosive growth. … Heterosigma cells are capable of rapid changes between at least two active swimming modes, distinguishable by the magnitude of the oscillatory component of motion. Swimming direction varied during a diurnal photoperiod, with swimming direction changing from random to upward directed shortly after the start of the light phase.

Motility assays performed 6-8 h into the light phase showed that two Heterosigma strains from geographically distant locations differed significantly in gross swimming speeds, … Propensity to form toxic surface slicks, and therefore frequency and severity of HAB impacts, may vary substantially among Heterosigma strains, mediated by differences in cell-level motility.

Stratification of the water column may help enable H. akashiwo cells to concentrate quickly at the surface.

Bearon, Grunbaum, and Cattolico (2006) Effects of salinity structure on swimming behavior and harmful algal bloom formation in Heterosigma akashiwo, a toxic raphidophyte  https://www.researchgate.net/publication/250218522_Effects_of_salinity_structure_on_swimming_behavior_and_harmful_algal_bloom_formation_in_Heterosigma_akashiwo_a_toxic_raphidophyte   Abstract. The formation of toxic surface blooms of the motile raphidophyte Heterosigma akashiwo often occurs too quickly to be attributed to cell reproduction. Rapid appearance of surface blooms is more consistent with the hypothesis that a dispersed cell population aggregates at the surface due to a combination of physical factors and swimming behavior. Because of the frequent association of Heterosigma bloom formation with a decrease in surface salinity, we hypothesize that a layer of low-salinity water over a high-salinity layer will suppress near-surface vertical mixing and this halocline will enable up-swimming cells to rapidly aggregate at the surface. … upward swimming speed was unchanged in cells encountering a salinity jump from 28 to 16 parts per thousand. We used observed swimming behaviors to parameterize a model of a 2-layer stratified water column in which vertical mixing is suppressed at the halocline and modeled by eddy diffusivity within each layer. The model predicts rapid aggregation of cells to the surface layer.

H. akashiwo migrates to the bottom at night to gather and store polyphosphates. It then exploits phosphorus depleted surface waters during daylight.

Watanabe, Kohata, and Kunugi (2008) Phosphate accumulation and metabolism by Heterosigma akashiwo (Raphodophycea) during diel vertical migration in a stratified microcosm https://www.researchgate.net/publication/229450665_Phospahte_accumulation_and_metabolism_by_Heterosigma_akashiwo_Raphodophycea_during_diel_vertical_migration_in_astratified_microcosm  Abstract.  Diel vertical migration by Heterosigma akashiwo (Hada) Hada (Raphidophyceae) was monitored in a 1.5 in tall microcosm. Vertical stratification, with low salinity and low orthophosphate (Pi) concentration in the upper layer and high salinity and high Pi concentration in the lower layer, was simulated in the tank, analogous to summer stratification in the Seto Inland Sea. The phosphate metabolism of H. akashiwo during this vertical migration was studied using 31P-NMR spectroscopy. At night this species migrated to the lower phosphate-rich layer and took up inorganic phosphate (Pi) which then was accumulated as polyphosphate (PPi) by an increase in the chain length of PPi During the daytime this species migrated to the phosphate-depleted surface water and utilized the accumulated PPi for photophosphorylation by decreasing the chain length of PPi During the first night after the phosphorus was introduced to the previously impoverished waters, the cells took up inorganic phosphate, accumulating the new phosphorus nutrient internally as Pi But the cells did not convert Pi to PPi presumably due to their lack of ATP. After the second day of the experiment, conversion of Pi to PPi at night was much more rapid than on the first day, presumably due to increased ATP availability. Then the cycle continued, with uptake of Pi and conversion to PPi at night at the bottom and its utilization during the day at the surface. These data suggest that the role of PPi in the metabolism of this species appears to be as a phosphate pool which regulates the level of Pi and ATP in the cell. Diel vertical migration allows this red tide species to shuttle between the phosphate-rich lower layer and the photic upper layer in stratified waters. …

LESSON 3.  Nitrogen & H. akashiwo.

H. akashiwo grows fastest when nitrogen (N) is available as Ammonium (NH4+) versus Urea or Nitrate (NO3-) … but grows well enough on all three types.

Ji et al (2020) Utilization of various forms of nitrogen and expression regulation of transporters in the harmful alga Heterosigma akashiwo (Raphidophyceae)    https://pubmed.ncbi.nlm.nih.gov/32113589/  Abstract.  Nitrogen (N) is an essential nutrient for phytoplankton growth. There is ample evidence that N enrichment promotes harmful algae blooms (HABs) but molecular mechanisms regulating N-nutrient uptake and metabolism are not so clear, especially for the raphidophyte Heterosigma akashiwo, which forms ichthyotoxic HABs in many coastal waters. In this study, the utilization of three different chemical forms of N (nitrate, ammonium, and urea) by H. akashiwo CCMA 369 was investigated in batch culture conditions. Results showed that H. akashiwo grew well on all three N compounds, and the highest cell yield occurred in the NH4+ culture group. …

Compared with the co-occurring immobile diatom Skeletonema costatum, the high expression of AMT [Ammonium Transporter] in dark period in H. akashiwo is consistent with its diel vertical migration behavior, which may promote N-nutrient acquisition from deeper layers and give advantages for H. akashiwo to form blooms.

Herndon and Cochlan (2007) Nitrogen utilization by the raphidophyte Heterosigma akashiwo … https://www.sciencedirect.com/science/article/abs/pii/S1568988306001065?via%3Dihub
Abstract. The nitrogen uptake and growth capabilities of the potentially harmful, raphidophycean flagellate Heterosigma akashiwo (Hada) Sournia were examined in unialgal batch cultures (strain CCMP 1912). Growth rates as a function of three nitrogen substrates (ammonium, nitrate and urea) were determined at saturating and sub-saturating photosynthetic photon flux densities (PPFDs). At saturating PPFD (110 μE m−2 s−1), the growth rate of H. akashiwo was slightly greater for cells grown on NH4+ (0.89 d−1) compared to cells grown on NO3− or urea, which had identical growth rates (0.82 d−1). At sub-saturating PPFD (40 μE m−2 s−1), both urea- and NH4+-grown cells grew faster than NO3−-grown cells (0.61, 0.57 and 0.46 d−1, respectively). … These laboratory results demonstrate that at both saturating and sub-saturating N concentrations, N uptake preference follows the order: NH4+ > NO3− > urea, and suggests that natural blooms of H. akashiwo may be initiated or maintained by any of the three nitrogen substrates examined.

More generally, Ammonium (NH4+) encourages dinoflagellates and cryptophytes.  Nitrate (NO3-) encourages diatom growth.

Kang and Kang (2022) Reduced forms of nitrogen control the spatial distribution of phytoplankton communities: The functional winner, dinoflagellates in an anthropogenically polluted estuary  https://www.sciencedirect.com/science/article/abs/pii/S0025326X22002107    Abstract.  The effects of reduced forms of nitrogen (NH4+ and dissolved organic nitrogen (DON)) on the spatial distribution of diatoms and dinoflagellates in an estuarine-coastal water continuum were investigated from 2015 to 2019. The proportion of non-DIN in total nitrogen was utilized as an indicator of DON along with direct measurements of DON. While NO3− originated from Seomjin River, the abundant NH4+ and DON occurred from Gwangyang Bay through Namhae. Diatoms were mostly confined to the upper estuarine system and dinoflagellates dominated in the regions with high levels of NH4+ and DON. Generalized additive models also presented the different responses of diatoms and dinoflagellates to increases in NH4+ and DON. Thus, our results highlight that diatoms dominate in NO3−-replete water with full access to the source and dinoflagellates take over the ecologically open niche in an anthropogenically polluted estuary with full access to reduced forms of nitrogen.

Moon et al (2021) Water Quality Improvement Shifts the Dominant Phytoplankton Group From Cryptophytes to Diatoms in a Coastal Ecosystem.  https://www.researchgate.net/publication/353846314_Water_Quality_Improvement_Shifts_the_Dominant_Phytoplankton_Group_From_Cryptophytes_to_Diatoms_in_a_Coastal_Ecosystem  Abstract. We investigated long-term variations in the dominant phytoplankton groups with improvements in water quality over 11 years in the Yeongil Bay on the southeastern coast of Korea. River discharge declined during the study period but TN from river discharge remained stable, indicating the input of enriched nutrients to the bay was fairly consistent. NH 4 ⁺ levels decreased with a decrease in TN from the POSCO industrial complex.

While the study region was characterized by the P-limited and deficient environment, cryptophytes dominated with the intensified P-limitations. The relative abundance of cryptophytes declined from 70% in 2010 to 10% in 2016, but that of diatoms increased from 70% in 2009 to 90% in 2016. Correlation analysis showed a positive correlation of cryptophytes with NH 4 ⁺ and a negative correlation with photic depth. Generalized additive models also exhibited an increase in diatom dominance and a decrease in cryptophyte dominance with an increase in water quality, indicating that a decrease in NH 4 ⁺ and increase in light favored the diatom growth but suppressed the cryptophyte growth. Thus, water quality improvements shift the dominant group in the coastal ecological niche from cryptophytes to diatoms.

LESSON 4.  Phosphorus & H. akashiwo.

H. akashiwo specializes in phosphorus uptake as concentrations decline.

Yang et al (2021) Growth and Nutrient Uptake Characteristics of Heterosigma akashiwo (Raphidophyceae) under Nitrogen and Phosphorus Concentrations in the East China Sea  https://pdfs.semanticscholar.org/9277/42caa3bfdc5f3843146654e31b2db7bd7acc.pdf
…  H. akashiwo may have a competitive advantage over many other phytoplankton species, particularly in low-nutrient and oligotrophic seawater. It has been shown to grow in low-nutrient environments (0.2 µmol L−1 for PO4 3− and 0.3 µmol L−1 for NO3 −) [11], respond rapidly to nutrient additions [10], and even become the dominant species [17]. However, its growth rate does not increase when phosphorus is supplied to a nitrogen-deficient system [17]. …

Nutrient Uptake Dynamics.  Some marine phytoplankton species can store DIP and utilize DOP as coping strategies to periodical P limitation [28–30]. H. akashiwo also shows coping strategies in response to P deficiency [14,15,31]. In general, P is deficient in the upper layer of stratified waters but sufficient in the lower layer. Owing to its motility, H. akashiwo is able to vertically migrate at night to P-rich depths to accumulate P and store it as polyphosphate. It then returns to the upper layer in the daytime to perform photosynthesis by using the accumulated polyphosphate.

Ji et al (2022) Transcriptomic response of the harmful algae Heterosigma akashiwo to polyphosphate utilization and phosphate stress https://www.sciencedirect.com/science/article/abs/pii/S1568988322000956  Abstract. Phosphorus (P) is one of the major macronutrients necessary for phytoplankton growth. In some parts of the ocean, however, P is frequently scarce, hence, there is limited phytoplankton growth. …

Here, we examined the physiological and molecular responses of the widely present harmful algal bloom (HAB) species, Heterosigma akashiwo in polyP utilization, and in coping with P-deficiency. … our results indicate that polyP is bioavailable to H. akashiwo, and this HAB species have evolved a comprehensive strategy to cope with P deficiency.

H. akashiwo metabolism changes throughout the diurnal cycle.

Ji et al (2018) Metatranscriptome analysis reveals environmental and diel regulation of a Heterosigma akashiwo (raphidophyceae) bloom   https://pubmed.ncbi.nlm.nih.gov/29345115/  Abstract ... Here, we investigated a bloom of the raphidophyte Heterosigma akashiwo in the East China Sea in 2014 using metabarcode (18S rDNA) and metatranscriptome sequencing.

Based on 18S rDNA analyses, the phytoplankton community shifted from high diversity in the pre-bloom stage to H. akashiwo predominance during the bloom. A sharp decrease in ambient dissolved inorganic phosphate and strong up-regulation of phosphate and dissolved organic phosphorus (DOP) uptake genes, including the rarely documented (ppGpp)ase, in H. akashiwo from pre-bloom to bloom was indicative of rapid phosphorus uptake and efficient utilization of DOP that might be a driver of the H. akashiwo bloom. Furthermore, observed up-regulated expression of mixotrophy-related genes suggests potential contribution of mixotrophy to the bloom. Accelerating photosynthetic carbon fixation was also implied by the up-regulation of carbonic anhydrase genes during the bloom. Notably, we also observed a strong morning-to-afternoon shift in the expression of many genes. …

Raphidophytes, in general, are adapted to thrive under P limitation.  Larger Chattonella cells are better adapted at storing Phosphorus than H. akashiwo.

Wang and Liang (2015)  Growth and alkaline phosphatase activity of Chattonella marina and Heterosigma akashiwo in response to phosphorus limitation https://pubmed.ncbi.nlm.nih.gov/25662231/  Abstract. The growth and alkaline phosphatase activity (APA) of two raphidophyceae species Chattonella marina and Heterosigma akashiwo were investigated in response to P-limitation and subsequent addition of dissolved inorganic phosphorus (DIP, NaH2PO4) and two dissolved organic phosphorus (DOP) compounds: guanosine 5-monophosphate (GMP) and triethyl phosphate (TEP). APA levels increased greatly after P-starvation as the decrease of the cellular phosphorus quotes (Qp). C. marina responded to P-limitation quickly and strongly, with 10-fold increase in APA within 24 hr after P-starvation. The larger difference between maximal and minimal QP values in C. marina indicated its high capacity in P storage. APA of H. akashiwo was maximally enlarged about 2.5 times at 48 hr of P-starvation. After the addition of nutrients, cell numbers of Chattonella marina increased in all treatments including the P-free culture, demonstrating the higher endurance of C. marina to P-limitation. However, those of H. akashiwo increased only in DIP and GMP cultures. APA increased only after the addition of the monophosphate ester GMP.

The results suggest that quick responses of C. marina to P-limitation, high capacity in P storage as well as endurance for P-depletion provide this species an ecological advantage in phytoplankton community competition under DIP-limited conditions.

H. akashiwo blooms under low P conditions, then Alexandrium, Chattonella, and/or perhaps Prorocentrum eventually may take over after P is near depleted.

Wang, Liang and Kang (2011) Utilization of dissolved organic phorphorus by different groups of phytoplankton taxa https://www.sciencedirect.com/science/article/abs/pii/S1568988311001107 Abstract.  The utilization of nine dissolved organic phosphorus (DOP) compounds by five bloom-causing phytoplankton species was studied under batch culture conditions. The DOP compounds included were adenosine 5-triphosphate (ATP), adenosine 5-monophosphate (AMP), cytidine 5-monophosphate (CMP), guanosine 5-monophosphate (GMP), uridine 5-monophosphate (UMP), glucose-6-phosphate (G6P), sodium glycerophosphate (GYP), 4-nitrophenyl phosphate (NPP), and triethyl phosphate (TEP), and the phytoplankton taxa were Skeletonema costatum, Prorocentrum micans, Alexandrium tamarense, Chattonella marina, and Heterosigma akashiwo.

The four flagellate taxa, P. micans, A. tamarense, C. marina, and H. akashiwo, grew well under various DOP regimes. P. micans and C. marina were the most capable of using DOP compounds, sustaining better growth on a majority of nucleotides (ATP, AMP, CMP, GMP, and UMP) and phosphomonoesters (G6P and GYP) than in inorganic phosphorus (P) controls. A. tamarense and H. akashiwo showed equivalent growth in most organic and inorganic P cultures, while the diatom species, S. costatum, could only utilize AMP and GMP. Furthermore, A. tamarense and C. marina could endure N, P-depleted conditions. Among the nine DOP compounds tested, the nucleotide compounds had the highest nutritional value for algal cell growth, while TEP could not sustain growth as the sole source of P. These results suggest that enhanced DOP utilization and the endurance of nutrient-limitation by harmful flagellate taxa offer their competitive advantages, which may account for the frequent occurrence of their blooms in coastal waters.

Zhang et al (2019) Functional Differences in the Blooming Phytoplankton Heterosigma akashiwo and Prorocentrum donghaiense Revealed by Comparative Metaproteomics  https://pubmed.ncbi.nlm.nih.gov/31375486/  Abstract. Phytoplankton blooms are natural phenomena in the ocean, which are the results of rapid cell growth of some phytoplankton species in a unique environment. However, little is known about the molecular events occurring during the bloom. Here, we compared metaproteomes of two phytoplankton Heterosigma akashiwo and Prorocentrum donghaiense in the coastal East China Sea. H. akashiwo and P. donghaiense accounted for 7.82% and 4.74% of the phytoplankton community protein abundances in the non–bloom sample, whereas they contributed to 60.13% and 78.09%, respectively, in their individual blooming samples. Compared with P. donghaiense, H. akashiwo possessed a significantly higher abundance of light-harvesting complex proteins, carbonic anhydrasem and RuBisCO. The blooming H. akashiwo cells expressed more proteins related to external nutrient acquisition, such as bicarbonate transporter SLC4, ammonium transporter, nitrite transporter, and alkaline phosphatase, while the blooming P. donghaiense cells highly expressed proteins related to extra- and intracellular organic nutrient utilization, such as amino acid transporter, 5′-nucleotidase, acid phosphatase, and tripeptidyl-peptidase. The strong capabilities of light harvesting, as well as acquisition and assimilation of inorganic carbon, nitrogen, and phosphorus, facilitated the formation of the H. akashiwo bloom under the high turbidity and inorganic nutrient-sufficient condition, whereas the competitive advantages in organic nutrient acquisition and reallocation guaranteed the occurrence of the P. donghaiense bloom under the inorganic nutrient-insufficient condition. … Metaproteomics was applied in this study to reveal the adaptive and responsive strategies of two coexisting phytoplankton species, H. akashiwo and P. donghaiense, during their bloom periods. Metabolic features and niche divergence in light harvesting, as well as carbon, nitrogen, and phosphorus acquisition and assimilation likely promoted the bloom occurrence under different environments.

LESSON 5.  Raphidophytes & many Dinoflagellates exude toxins in red tide mode.

H. akashiwo cells become more toxic as they age and particularly as they sink during diel vertical migration. (Perhaps energy absorbed during daylight enables cells to charge up small peroxide jolts of toxicity needed for the nighttime bacterial hunt near the bottom?)

Creed and Trick (2011)  Sinking of Heterosigma akashiwo results in increased toxicity of this harmful algal bloom species  https://www.researchgate.net/publication/251694363_Sinking_of_Heterosigma_akashiwo_results_in_increased_toxicity_of_this_harmful_algal_bloom_species

Abstract.  Notable physiological responses such as toxicity and sinking rates of the red tide forming raphidophyte Heterosigma akashiwo are correlated with high levels of macronutrient stress. … It was hypothesized that there is variability in the rates of sinking within cell cultures and that sinking cells are more toxic than the neutrally buoyant or floating cells. … Sinking and floating rates were significantly higher during the late stationary growth phase for all isolates. For two H. akashiwo isolates, sinking populations were significantly more toxic than those that were positively buoyant. A similar trend was observed in a third strain, however the relationship was not significant. Differences in adaptive ecophysiology among the different strain likely caused the variation. It is suggested that the most toxic cells within a bloom are those found at the lower depths, potentially interacting with the benthic community or ensuring that subsequent bloom propagation contains cells with the potential for toxicity.

Nutrient deficiency during massive blooms may stimulate Raphidophytes to produce reactive ROS ‘superoxides’ that are toxic to fishes.

Yuasa et al (2020) Nutrient deficiency stimulates the production of superoxide in the noxious red-tide-forming raphidophyte Chattonella antiqua  https://pubmed.ncbi.nlm.nih.gov/33218451/    Abstract. The raphidophyte Chattonella antiqua is a single-celled alga that forms ‘red tides’ in coastal areas. C. antiqua produces superoxide anions (O2-), the excessive production of which has been associated with fish mortality. It is suggested that putative NADPH oxidase in the outer membrane oxidizes intracellular NADPH to produce O2- and secrete it externally. Earlier studies revealed that photosynthetic electron transport, a major producer of NADPH in photosynthetic organisms, is involved in the production of O2- in C. antiqua but the details of the O2- production mechanism have yet to be elucidated. Since nutrient deficiency adversely affects the formation of blooms of C. antiqua, in this study, we examined the effects of nutrient deficiency on O2- production in C. antiqua.

When cells were grown under nitrogen (N)- or phosphorus (P)-deficient conditions, the production of O2- was stimulated. In particular, the extracellular levels of O2- under N- or P-deficient conditions were high during the dark period when photosynthetic activities in terms of actual quantum efficiency and photochemical quenching were low. The extracellular levels of O2- under the nutrient-deficient conditions were unaffected by the presence of 3-(3,4-dichlorophenyl)-1,1‑dimethylurea (DCMU), an inhibitor of photosynthetic electron transport, but decreased when the nutrients were present. Furthermore, the intracellular ratio of NADPH to NADP+ under N- or P-deficient conditions was higher than that under nutrient-replete conditions. These observations suggest that another metabolic pathway, independent of photosynthesis, provides NADPH for the production of O2- under nutrient deficiency.

Cho et al. (2022)  Generation of Reactive Oxygen Species (ROS) by Harmful Algal Bloom (HAB)-Forming Phytoplankton and Their Potential Impact on Surrounding Living Organisms  https://pubmed.ncbi.nlm.nih.gov/35204089/   Abstract.  Most marine phytoplankton with relatively high ROS generation rates are categorized as harmful algal bloom (HAB)-forming species, among which Chattonella genera is the highest ROS-producing phytoplankton.

In this review, we examined marine microalgae with ROS-producing activities, with focus on Chattonella genera. Several studies suggest that Chattonella produces superoxide via the activities of an enzyme similar to NADPH oxidase located on glycocalyx, a cell surface structure, while hydrogen peroxide is generated inside the cell by different pathways. Additionally, hydroxyl radical has been detected in Chattonella cell suspension. By the physical stimulation, such as passing through between the gill lamellas of fish, the glycocalyx is easily discharged from the flagellate cells and attached on the gill surface, where ROS are continuously produced, which might cause gill tissue damage and fish death. Comparative studies using several strains of Chattonella showed that ROS production rate and ichthyotoxicity of Chattonella is well correlated. Furthermore, significant levels of ROS have been reported in other raphidophytes and dinoflagellates, such as Cochlodinium polykrikoides and Karenia mikimotoi.  …

4. Summary.

Lessons learned from H. akashiwo.

Captain Kirk confronts the Horta.  From Star Trek: Original Series episode “The Devil in the Dark”

Spock: “… In my brief contact with the creature’s mind, I discovered it is a highly intelligent, extremely sophisticated animal.”
Kirk: “A Horta.  A Horta!  Mister Spock, … you must re-establish communications with it.”

… To be continued. 

Fun facts about this Star Trek episode: https://en.wikipedia.org/wiki/The_Devil_in_the_Dark:

• This was William Shatner’s favorite episode. …
• The episode also marks the first appearance of Doctor McCoy’s catchphrase, “I’m a doctor, not a …!” In this case, the line is, “I’m a doctor, not a bricklayer!”, said by McCoy when Kirk orders him to heal the Horta.

• HORTA — a backronym used in the mining industry, based on the Horta in this Star Trek episode