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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC Santa Barbara Electronic Theses and Dissertations (2020)

As human induced climate change continues to alter the world’s oceans, it becomes

increasingly important to hone the predictive power of models to understand the ecosystem

level changes and challenges that the coming decades will bring. However, models are only

as robust as the data upon which they are formulated, and the experimentation required to

inform them must be based on an interconnected and concomitantly changing set of

conditions. Phytoplankton, specifically diatoms, are a worthy focus group as they are

particularly ecologically successful—and responsible for approximately 40% of marine

primary production. By scrutinizing the potential effects of climate change on

phytoplankton, the base of the marine food web, researchers can obtain crucial information

upon which to build predictions for entire ecosystems.

This series of experiments was designed to investigate the combined effects of

temperature and light on the growth and photophysiology of two strains (one coastal and one

open-ocean) of the diatom Thalassiosira pseudonana. The goal in producing this data-set is

to add to the growing body of multi-stressor research which will aid in understanding the

response of phytoplankton to future ocean conditions. This set of experiments takes

advantage of advances in culturing techniques and utilizes a bioreactor (multicultivator

Z160-OD) containing individual treatment vessels, thus allowing for the easy cultivation of

diatoms under eight different light regimes at the same temperature. Through the use of

higher treatment numbers across a gradient of conditions, we exploit the opportunity to

detect and quantify potential non-linear response patterns.

Our results show that the response of T. pseudonana to simultaneous changes in

temperature and irradiance is dependent on the measured response trait, which suggests that

interpretation of performance curves requires clear identification of all conditions under

which they were generated. Our data also suggest subtle differences between the two strains

in the response of growth rate at suboptimal irradiances. Over the range of temperatures

tested in these experiments where growth was possible, temperature proved unimportant to

the growth rate of the open ocean strain (CCMP 1014) at suboptimal light levels. Whereas

the coastal strain (CCMP 1335) demonstrated an interactive relationship between light and

temperature at suboptimal irradiances. As temperatures were pushed above the optimal, the

cellular characteristics of carbon content and size of the open ocean strain exhibit a clear

split based upon irradiance; with high light leading to large carbon-poor cells and low light

resulting in small, carbon-dense cells. Our findings also support the idea that the relationship

between growth rate and cellular carbon content, while complex and non-linear, is likely

predictable. The “choices” and energy trade-offs employed by this species of diatom under

the simplified set of experimental conditions in this study, highlight the importance of

having clear understandings of the mechanisms driving these changes before they are

incorporated into models, as hypothetical outcomes could be missed if only values obtained

under specific ranges are used for prediction.

    Cover page: A tale of two drivers: exploring the response of the marine diatom, Thalassiosira pseudonana to changes in temperature and irradiance
    • Article
    • Peer Reviewed
    UC Santa Barbara Previously Published Works (2017)
    Factors that affect the removal of organic carbon by heterotrophic bacterioplankton can impact the rate and magnitude of organic carbon loss in the ocean through the conversion of a portion of consumed organic carbon to CO2. Through enhanced rates of consumption, surface bacterioplankton communities can also reduce the amount of dissolved organic carbon (DOC) available for export from the surface ocean. The present study investigated the direct effects of elevated pCO2 on bacterioplankton removal of several forms of DOC ranging from glucose to complex phytoplankton exudate and lysate, and naturally occurring DOC. Elevated pCO2 (1000-1500 ppm) enhanced both the rate and magnitude of organic carbon removal by bacterioplankton communities compared to low (pre-industrial and ambient) pCO2 (250 -~400 ppm). The increased removal was largely due to enhanced respiration, rather than enhanced production of bacterioplankton biomass. The results suggest that elevated pCO2 can increase DOC consumption and decrease bacterioplankton growth efficiency, ultimately decreasing the amount of DOC available for vertical export and increasing the production of CO2 in the surface ocean.
      Cover page: Elevated pCO2 enhances bacterioplankton removal of organic carbon
      • Article
      • Peer Reviewed
      UC Santa Barbara Previously Published Works (2023)
      Periodic blooms of salps (pelagic tunicates) can result in high export of organic matter, leading to an outsized role in the oceans biological carbon pump (BCP). However, due to their episodic and patchy nature, salp blooms often go undetected and are rarely included in measurements or models of the BCP. We quantified salp-mediated export processes in the northeast subarctic Pacific Ocean in summer of 2018 during a bloom of Salpa aspera. Salps migrated from 300 to 750 m during the day into the upper 100 m at night. Salp fecal pellet production comprised up to 82% of the particulate organic carbon (POC) produced as fecal pellets by the entire epipelagic zooplankton community. Rapid sinking velocities of salp pellets (400-1,200 m d-1) and low microbial respiration rates on pellets (<1% of pellet C respired day-1) led to high salp pellet POC export from the euphotic zone-up to 48% of total sinking POC across the 100 m depth horizon. Salp active transport of carbon by diel vertical migration and carbon export from sinking salp carcasses was usually <10% of the total sinking POC flux. Salp-mediated export markedly increased BCP efficiency, increasing by 1.5-fold the proportion of net primary production exported as POC across the base of the euphotic zone and by 2.6-fold the proportion of this POC flux persisting 100 m below the euphotic zone. Salps have unique and important effects on ocean biogeochemistry and, especially in low flux settings, can dramatically increase BCP efficiency and thus carbon sequestration.
        Cover page: The Outsized Role of Salps in Carbon Export in the Subarctic Northeast Pacific Ocean.
        • Article
        • Peer Reviewed
        UC Santa Cruz Previously Published Works (2013)
        "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.
          Cover page: Marine Phytoplankton Temperature versus Growth Responses from Polar to Tropical Waters – Outcome of a Scientific Community-Wide Study
          • Article
          • Peer Reviewed
          UC Santa Cruz Previously Published Works (2015)
          Oceanic and coastal waters are acidifying due to processes dominated in the open ocean by increasing atmospheric CO2 and dominated in estuaries and some coastal waters by nutrient-fueled respiration. The patterns and severity of acidification, as well as its effects, are modified by the host of stressors related to human activities that also influence these habitats. Temperature, deoxygenation, and changes in food webs are particularly important co-stressors because they are pervasive, and both their causes and effects are often mechanistically linked to acidification. Development of a theoretical underpinning to multiple stressor research that considers physiological, ecological, and evolutionary perspectives is needed because testing all combinations of stressors and stressor intensities experimentally is impossible. Nevertheless, use of a wide variety of research approaches is a logical and promising strategy for improving understanding of acidification and its effects. Future research that focuses on spatial and temporal patterns of stressor interactions and on identifying mechanisms by which multiple stressors affect individuals, populations, and ecosystems is critical. It is also necessary to incorporate consideration of multiple stressors into management, mitigation, and adaptation to acidification and to increase public and policy recognition of the importance of addressing acidification in the context of the suite of other stressors with which it potentially interacts.
            Cover page: And on Top of All That… Coping with Ocean Acidification in the Midst of Many Stressors
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