Theresa K. Hattenrath-Lehmann

Niche of harmful alga Aureococcus anophagefferens revealed through ecogenomics.

Harmful algal blooms (HABs) cause significant economic and ecological damage worldwide. Despite considerable efforts, a comprehensive understanding of the factors that promote these blooms has been lacking, because the biochemical pathways that facilitate their dominance relative to other phytoplankton within specific environments have not been identified. Here, biogeochemical measurements showed that the harmful alga Aureococcus anophagefferens outcompeted co-occurring phytoplankton in estuaries with elevated levels of dissolved organic matter and turbidity and low levels of dissolved inorganic nitrogen. We subsequently sequenced the genome of A. anophagefferens and compared its gene complement with those of six competing phytoplankton species identified through metaproteomics. Using an ecogenomic approach, we specifically focused on gene sets that may facilitate dominance within the environmental conditions present during blooms. A. anophagefferens possesses a larger genome (56 Mbp) and has more genes involved in light harvesting, organic carbon and nitrogen use, and encoding selenium- and metal-requiring enzymes than competing phytoplankton. Genes for the synthesis of microbial deterrents likely permit the proliferation of this species, with reduced mortality losses during blooms. Collectively, these findings suggest that anthropogenic activities resulting in elevated levels of turbidity, organic matter, and metals have opened a niche within coastal ecosystems that ideally suits the unique genetic capacity of A. anophagefferens and thus, has facilitated the proliferation of this and potentially other HABs.

Ocean warming since 1982 has expanded the niche of toxic algal blooms in the North Atlantic and North Pacific oceans.

Significance This study used high-resolution (daily, quarter-degree resolution) sea-surface temperature records to model trends in growth rates and bloom-season duration for two of the most toxic and widespread harmful algal bloom species indigenous to the North Atlantic and North Pacific oceans. Alexandrium fundyense synthesizes saxitoxin and Dinophysis acuminata synthesizes okadaic acid, which cause the human health syndromes paralytic and diarrhetic shellfish poisoning, respectively. The model provided hindcasts of harmful algal bloom (HAB) events that were consistent with in situ observations from long-term monitoring programs during the same time period. This study provides evidence that increasing ocean temperatures have already facilitated the intensification of these, and likely other, HABs and thus contribute to an expanding human health threat. Global ocean temperatures are rising, yet the impacts of such changes on harmful algal blooms (HABs) are not fully understood. Here we used high-resolution sea-surface temperature records (1982 to 2016) and temperature-dependent growth rates of two algae that produce potent biotoxins, Alexandrium fundyense and Dinophysis acuminata, to evaluate recent changes in these HABs. For both species, potential mean annual growth rates and duration of bloom seasons significantly increased within many coastal Atlantic regions between 40°N and 60°N, where incidents of these HABs have emerged and expanded in recent decades. Widespread trends were less evident across the North Pacific, although regions were identified across the Salish Sea and along the Alaskan coastline where blooms have recently emerged, and there have been significant increases in the potential growth rates and duration of these HAB events. We conclude that increasing ocean temperature is an important factor facilitating the intensification of these, and likely other, HABs and thus contributes to an expanding human health threat.

Vitamin B1 and B12 Uptake and Cycling by Plankton Communities in Coastal Ecosystems

While vitamin B12 has recently been shown to co-limit the growth of coastal phytoplankton assemblages, the cycling of B-vitamins in coastal ecosystems is poorly understood as planktonic uptake rates of vitamins B1 and B12 have never been quantified in tandem in any aquatic ecosystem. The goal of this study was to establish the relationships between plankton community composition, carbon fixation, and B-vitamin assimilation in two contrasting estuarine systems. We show that, although B-vitamin concentrations were low (pM), vitamin concentrations and uptake rates were higher within a more eutrophic estuary and that vitamin B12 uptake rates were significantly correlated with rates of primary production. Eutrophic sites hosted larger bacterial and picoplankton abundances with larger carbon normalized vitamin uptake rates. Although the >2 μm phytoplankton biomass was often dominated by groups with a high incidence of vitamin auxotrophy (dinoflagellates and diatoms), picoplankton (<2 μm) were always responsible for the majority of B12-vitamin uptake. Multiple lines of evidence suggest that heterotrophic bacteria were the primary users of vitamins among the picoplankton during this study. Nutrient/vitamin amendment experiments demonstrated that, in the Summer and Fall, vitamin B12 occasionally limited or co-limited the accumulation of phytoplankton biomass together with nitrogen. Combined with prior studies, these findings suggest that picoplankton are the primary producers and users of B-vitamins in some coastal ecosystems and that rapid uptake of B-vitamins by heterotrophic bacteria may sometimes deprive larger phytoplankton of these micronutrients and thus influence phytoplankton species succession.

Nitrogenous Nutrients Promote the Growth and Toxicity of Dinophysis acuminata during Estuarine Bloom Events

Diarrhetic Shellfish Poisoning (DSP) is a globally significant human health syndrome most commonly caused by dinoflagellates within the genus Dinophysis. While blooms of harmful algae have frequently been linked to excessive nutrient loading, Dinophysis is a mixotrophic alga whose growth is typically associated with prey availability. Consequently, field studies of Dinophysis and nutrients have been rare. Here, the temporal dynamics of Dinophysis acuminata blooms, DSP toxins, and nutrients (nitrate, ammonium, phosphate, silicate, organic compounds) were examined over four years within two New York estuaries (Meetinghouse Creek and Northport Bay). Further, changes in the abundance and toxicity of D. acuminata were assessed during a series of nutrient amendment experiments performed over a three year period. During the study, Dinophysis acuminata blooms exceeding one million cells L-1 were observed in both estuaries. Highly significant (p<0.001) forward stepwise multivariate regression models of ecosystem observations demonstrated that D. acuminata abundances were positively dependent on multiple environmental parameters including ammonium (p = 0.007) while cellular toxin content was positively dependent on ammonium (p = 0.002) but negatively dependent on nitrate (p<0.001). Nitrogen- (N) and phosphorus- (P) containing inorganic and organic nutrients significantly enhanced D. acuminata densities in nearly all (13 of 14) experiments performed. Ammonium significantly increased cell densities in 10 of 11 experiments, while glutamine significantly enhanced cellular DSP content in 4 of 5 experiments examining this compound. Nutrients may have directly or indirectly enhanced D. acuminata abundances as densities of this mixotroph during experiments were significantly correlated with multiple members of the planktonic community (phytoflagellates and Mesodinium). Collectively, this study demonstrates that nutrient loading and more specifically N-loading promotes the growth and toxicity of D. acuminata populations in coastal zones.

Mapping the Distribution of Cysts from the Toxic Dinoflagellate Cochlodinium polykrikoides in Bloom-Prone Estuaries by a Novel Fluorescence In Situ Hybridization Assay

ABSTRACT Cochlodinium polykrikoides is a cosmopolitan dinoflagellate that is notorious for causing fish-killing harmful algal blooms (HABs) across North America and Asia. While recent laboratory and ecosystem studies have definitively demonstrated that Cochlodinium forms resting cysts that may play a key role in the dynamics of its HABs, uncertainties regarding cyst morphology and detection have prohibited even a rudimentary understanding of the distribution of C. polykrikoides cysts in coastal ecosystems. Here, we report on the development of a fluorescence in situ hybridization (FISH) assay using oligonucleotide probes specific for the large subunit (LSU) ribosomal DNA (rDNA) of C. polykrikoides. The LSU rDNA-targeted FISH assay was used with epifluorescence microscopy and was iteratively refined to maximize the fluorescent reaction with C. polykrikoides and minimize cross-reactivity. The final LSU rDNA-targeted FISH assay was found to quantitatively recover cysts made by North American isolates of C. polykrikoides but not cysts formed by other common cyst-forming dinoflagellates. The method was then applied to identify and map C. polykrikoides cysts across bloom-prone estuaries. Annual cyst and vegetative cell surveys revealed that elevated densities of C. polykrikoides cysts (>100 cm−3) during the spring of a given year were spatially consistent with regions of dense blooms the prior summer. The identity of cysts in sediments was confirmed via independent amplification of C. polykrikoides rDNA. This study mapped C. polykrikoides cysts in a natural marine setting and indicates that the excystment of cysts formed by this harmful alga may play a key role in the development of HABs of this species.

Identification of unique microbiomes associated with harmful algal blooms caused by Alexandrium fundyense and Dinophysis acuminata

Biotic interactions dominate plankton communities, yet the microbial consortia associated with harmful algal blooms (HABs) have not been well-described. Here, high-throughput amplicon sequencing of ribosomal genes was used to quantify the dynamics of bacterial (16S) and phytoplankton assemblages (18S) associated with blooms and cultures of two harmful algae, Alexandrium fundyense and Dinophysis acuminata. Experiments were performed to assess changes in natural bacterial and phytoplankton communities in response to the filtrate from cultures of these two harmful algae. Analysis of prokaryotic sequences from ecosystems, experiments, and cultures revealed statistically unique bacterial associations with each HAB. The dinoflagellate, Alexandrium, was strongly associated with multiple genera of Flavobacteria including Owenweeksia spp., Maribacter spp., and individuals within the NS5 marine group. While Flavobacteria also dominated Dinophysis-associated communities, the relative abundance of Alteromonadales bacteria strongly co-varied with Dinophysis abundances during blooms and Ulvibacter spp. (Flavobacteriales) and Arenicella spp. (Gammaproteobacteria) were associated with cells in culture. Eukaryotic sequencing facilitated the discovery of the endosymbiotic, parasitic dinoflagellate, Amoebophrya spp., that had not been regionally described but represented up to 17% of sequences during Alexandrium blooms. The presence of Alexandrium in field samples and in experiments significantly altered the relative abundances of bacterial and phytoplankton by both suppressing and promoting different taxa, while this effect was weaker in Dinophysis. Experiments specifically revealed a negative feedback loop during blooms whereby Alexandrium filtrate promoted the abundance of the parasite, Amoebophrya spp. Collectively, this study demonstrates that HABs formed by Alexandrium and Dinophysis harbor unique prokaryotic and eukaryotic microbiomes that are likely to, in turn, influence the dynamics of these HABs.

The role of a PSP-producing Alexandrium bloom in an unprecedented diamondback terrapin (Malaclemys terrapin) mortality event in Flanders Bay, New York, USA

Abstract Diamondback terrapins (Malaclemys terrapin) are a threatened or endangered species in much of their range along the U.S. Atlantic and Gulf coasts. Over an approximately three‐week period from late April to mid‐May 2015, hundreds of adult diamondback terrapins were found dead on the shores of Flanders Bay, Long Island, New York, USA. Concurrent with the mortality event, elevated densities of the paralytic shellfish toxin (PST)‐producing dinoflagellate, Alexandrium fundyense (>104 cells L−1) and high levels of PST in bivalves (maximal levels = 540 &mgr;g STX eq. 100 g−1 shellfish tissue) were observed in the Flanders Bay region, resulting in shellfish bed closures in regional tributaries. Gross and histologic postmortem examinations of terrapins revealed no physical trauma to individuals or a common, underlying disease process to explain the deaths. PST compounds (0.2–12.5 &mgr;g STX eq. 100 g−1) were present in various M. terrapin tissues collected over the duration of the mortality event. High‐throughput sequencing revealed that the ribbed mussel (Geukensia demissa, a PST vector) was present in the gastrointestinal tracks of all terrapin samples tested. While the potential of PST to cause mortality in chelonians has not been well‐characterized, in the absence of other significant findings from necropsies and pathological analyses, we provide evidence that PST in shellfish was likely high enough to cause or contribute to the mortality in these small (<2.0 kg) animals. HighlightsFor the first time, a terrapin mortality event was associated with the saxitoxin producing dinoflagellate, Alexandrium.Saxitoxin was quantified within heart, kidney, liver, and brain tissues of terrapins.High‐throughput sequencing of gut contents revealed ribbed mussels as a likely PST vector.Mussels in the region had saxitoxin levels seven‐times above US federal closure limits.

Reply to Dees et al.: Ocean warming promotes species-specific increases in the cellular growth rates of harmful algal blooms

Recently, we (1) reported that, since 1982, several regions across the North Atlantic and North Pacific Oceans have experienced warming in specific seasons and locations that have significantly increased the potential cellular growth rates and bloom seasons of two harmful algae, Alexandrium fundyense and Dinophysis acuminata , and that new blooms caused by these species have emerged in these same regions. In their comment “Harmful algal blooms in the Eastern North Atlantic Ocean,” Dees et al. (2) examine the Continuous Plankton Recorder data from the North Eastern Atlantic and North Sea from 1982 to 2015 and find no relationship between Dinophysis spp. abundance and sea-surface temperature. This observation is consistent … [↵][1]1To whom correspondence should be addressed. Email: christopher.gobler{at}stonybrook.edu. [1]: #xref-corresp-1-1