Kendra Hayashi

Marine phytoplankton temperature versus growth responses from polar to tropical waters – outcome of a scientific community-wide study

“It takes a village to finish (marine) science these days” Paraphrased from Curtis Huttenhower (the Human Microbiome project) The rapidity and complexity of climate change and its potential effects on ocean biota are challenging how ocean scientists conduct research. One way in which we can begin to better tackle these challenges is to conduct community-wide scientific studies. This study provides physiological datasets fundamental to understanding functional responses of phytoplankton growth rates to temperature. While physiological experiments are not new, our experiments were conducted in many laboratories using agreed upon protocols and 25 strains of eukaryotic and prokaryotic phytoplankton isolated across a wide range of marine environments from polar to tropical, and from nearshore waters to the open ocean. This community-wide approach provides both comprehensive and internally consistent datasets produced over considerably shorter time scales than conventional individual and often uncoordinated lab efforts. Such datasets can be used to parameterise global ocean model projections of environmental change and to provide initial insights into the magnitude of regional biogeographic change in ocean biota in the coming decades. Here, we compare our datasets with a compilation of literature data on phytoplankton growth responses to temperature. A comparison with prior published data suggests that the optimal temperatures of individual species and, to a lesser degree, thermal niches were similar across studies. However, a comparison of the maximum growth rate across studies revealed significant departures between this and previously collected datasets, which may be due to differences in the cultured isolates, temporal changes in the clonal isolates in cultures, and/or differences in culture conditions. Such methodological differences mean that using particular trait measurements from the prior literature might introduce unknown errors and bias into modelling projections. Using our community-wide approach we can reduce such protocol-driven variability in culture studies, and can begin to address more complex issues such as the effect of multiple environmental drivers on ocean biota.

QUANTITATIVE REAL-TIME POLYMERASE CHAIN REACTION FOR COCHLODINIUM FULVESCENS (DINOPHYCEAE), A HARMFUL DINOFLAGELLATE FROM CALIFORNIA COASTAL WATERS 1

Harmful blooms formed by species of the dinoflagellate Cochlodinium have caused massive fish kills and substantial economic losses in the Pacific Ocean. Recently, prominent blooms of Cochlodinium have occurred in central and southern California (2004–2008), and Cochlodinium cells are now routinely observed in microscopical analysis of algal assemblages from Californian coastal waters. The first documented economic loss due to a Cochlodinium bloom in California occurred in Monterey Bay and resulted in the mortality of commercially farmed abalone. Increasing occurrences of Cochlodinium blooms, the fact that these cells preserve poorly using standard techniques, and the difficulty of identifying preserved specimens using morphological criteria make Cochlodinium species prime candidates for the development of a quantitative real‐time polymerase chain reaction (qPCR) approach. The 18S rDNA gene sequenced from Cochlodinium cells obtained from California coastal waters, as well as GenBank sequences of Cochlodinium, were used to design and test a Molecular Beacon® approach. The qPCR method developed in this study is species specific, sensitive for the detection of C. fulvescens that has given rise to the recent blooms in the eastern Pacific Ocean, and spans a dynamic abundance range of seven orders of magnitude. Initial application of the method to archived field samples collected during blooms in Monterey Bay revealed no statistically significant correlations between gene copy number and environmental parameters. However, the onset of Cochlodinium blooms in central California was consistent with previously reported findings of correlations to decreased surface temperature and increased inputs of nitrogenous nutrients.

Microcystin Prevalence throughout Lentic Waterbodies in Coastal Southern California

Toxin producing cyanobacterial blooms have increased globally in recent decades in both frequency and intensity. Despite the recognition of this growing risk, the extent and magnitude of cyanobacterial blooms and cyanotoxin prevalence is poorly characterized in the heavily populated region of southern California. Recent assessments of lentic waterbodies (depressional wetlands, lakes, reservoirs and coastal lagoons) determined the prevalence of microcystins and, in some cases, additional cyanotoxins. Microcystins were present in all waterbody types surveyed although toxin concentrations were generally low across most habitats, as only a small number of sites exceeded California’s recreational health thresholds for acute toxicity. Results from passive samplers (Solid Phase Adsorption Toxin Tracking (SPATT)) indicated microcystins were prevalent throughout lentic waterbodies and that traditional discrete samples underestimated the presence of microcystins. Multiple cyanotoxins were detected simultaneously in some systems, indicating multiple stressors, the risk of which is uncertain since health thresholds are based on exposures to single toxins. Anatoxin-a was detected for the first time from lakes in southern California. The persistence of detectable microcystins across years and seasons indicates a low-level, chronic risk through both direct and indirect exposure. The influence of toxic cyanobacterial blooms is a more complex stressor than presently recognized and should be included in water quality monitoring programs.

Pseudo-nitzschia species composition varies concurrently with domoic acid concentrations during two different bloom events in the Southern California Bight

The San Pedro Shelf (SPS) region of the Southern California Bight has witnessed an increase of Pseudo-nitzschia spp. blooms during the past decade, although the domoic acid (DA) concentrations observed during these events have varied considerably. This study compared the extent, timing and environmental controls of Pseudo-nitzschia blooms that were observed in two consecutive years on the SPS. Environmental conditions were characterized during shipboard surveys during spring 2013 and 2014 along an onshore–offshore transect at surface and subsurface depths. A Pseudo-nitzschia bloom of similar cell abundances was observed during each year, yet maximal DA concentrations differed by nearly two orders of magnitude. Environmental parameters were favorable for Pseudo-nitzschia spp. growth in both years, but few factors could be identified that specifically pertained to DA, with the exception that toxicity correlated negatively with dissolved silicic acid concentrations. Automated ribosomal intergenic spacer analysis for Pseudo-nitzschia species indicated that the relative abundance of toxin-producing species had a strong influence on DA concentrations between years, with high-DA concentrations corresponding to Pseudo-nitzschia communities dominated by P. australis/P. seriata. Factors explaining the preferential growth of particular Pseudo-nitzschia species remain enigmatic but are important for predicting toxic events attributable to these taxa.

Variation in growth rate, carbon assimilation, and photosynthetic efficiency in response to nitrogen source and concentration in phytoplankton isolated from upper San Francisco Bay

Six species of phytoplankton recently isolated from upper San Francisco Bay were tested for their sensitivity to growth inhibition by ammonium (NH4+), and for differences in growth rates according to inorganic nitrogen (N) growth source. The quantum yield of photosystem II (Fv/Fm) was a sensitive indicator of NH4+ toxicity, manifested by a suppression of Fv/Fm in a dose‐dependent manner. Two chlorophytes were the least sensitive to NH4+ inhibition, at concentrations of >3,000 μmoles NH4+ · L−1, followed by two estuarine diatoms that were sensitive at concentrations >1,000 μmoles NH4+ · L−1, followed lastly by two freshwater diatoms that were sensitive at concentrations between 200 and 500 μmoles NH4+ · L−1. At non‐inhibiting concentrations of NH4+, the freshwater diatom species grew fastest, followed by the estuarine diatoms, while the chlorophytes grew slowest. Variations in growth rates with N source did not follow taxonomic divisions. Of the two chlorophytes, one grew significantly faster on nitrate (NO3−), whereas the other grew significantly faster on NH4+. All four diatoms tested grew faster on NH4+ compared with NO3−. We showed that in cases where growth rates were faster on NH4+ than they were on NO3−, the difference was not larger for chlorophytes compared with diatoms. This holds true for comparisons across a number of culture investigations suggesting that diatoms as a group will not be at a competitive disadvantage under natural conditions when NH4+ dominates the total N pool and they will also not have a growth advantage when NO3− is dominant, as long as N concentrations are sufficient.

Diversity and toxicity of Pseudo-nitzschia species in Monterey Bay: Perspectives from targeted and adaptive sampling

Monterey Bay, California experiences near-annual blooms of Pseudo-nitzschia that can affect marine animal health and the economy, including impacts to tourism and commercial/recreational fisheries. One species in particular, P. australis, has been implicated in the most toxic of events, however other species within the genus can contribute to widespread variability in community structure and associated toxicity across years. Current monitoring methods are limited in their spatial coverage as well as their ability to capture the full suite of species present, thereby hindering understanding of HAB events and limiting predictive accuracy. An integrated deployment of multiple in situ platforms, some with autonomous adaptive sampling capabilities, occurred during two divergent bloom years in the bay, and uncovered detailed aspects of population and toxicity dynamics. A bloom in 2013 was characterized by spatial differences in Pseudo-nitzschia populations, with the low-toxin producer P. fraudulenta dominating the inshore community and toxic P. australis dominating the offshore community. An exceptionally toxic bloom in 2015 developed as a diverse Pseudo-nitzschia community abruptly transitioned into a bloom of highly toxic P. australis within the time frame of a week. Increases in cell density and proliferation coincided with strong upwelling of nutrients. High toxicity was driven by silicate limitation of the dense bloom. This temporal shift in species composition mirrored the shift observed further north in the California Current System off Oregon and Washington. The broad scope of sampling and unique platform capabilities employed during these studies revealed important patterns in bloom formation and persistence for Pseudo-nitzschia. Results underscore the benefit of expanded biological observing capabilities and targeted sampling methods to capture more comprehensive spatial and temporal scales for studying and predicting future events.