Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Appendicularians were obtained from the above culture facility.

Experiments with 5-day old Oikopleura dioica were conducted at the Michael Sars Centre in Bergen, Norway in October 2022 and 2023. Individual animals (15-24 replicates) were removed from their culture chamber, probed to abandon their house, and placed in a staging beaker containing 0.22 µm filtered seawater (FSW) to build fresh houses. Up to 12 actively pumping animals were then transferred from the staging beaker to an incubation chamber. Feeding incubations were carried out in a 12˚C water table with a motorized stir paddle to maintain suspension for 10 minutes. Following the 10-minute incubation, 3-8 animals were individually pipetted into watch glasses and probed to abandon houses so that the appendicularian and house could be preserved separately. Appendicularians were fixed by pipetting animal in 1 mL FSW into a 1.8 mL cryovial with 5 µl 25% microscopy grade glutaraldehyde (0.125% final concentration) to stop digestion. Houses were pipetted into cryovials in a volume of 100 µl without fixative.

Laboratory feeding incubations were carried out on two occasions with two experimental designs. One with all particle sizes (1.0 and 2.0 µm) available in equal concentration to appendicularians. The other with particle sizes (0.5, 1.0 and 3.0 µm) simulated environmental conditions with smaller particles available in higher concentration. For each particle size, two different microsphere types were used with different functionalized surfaces (carboxylate- and amine-modified).

Fixed animals were removed and placed on a slide with 10 µl of 100 ug/ml of recombinant PCR grade proteinase K solution from Pichia pastoris (Conley and Sutherland 2017) to chemically digest tissue. Samples were then gently compressed between the glass slide and cover slip. Photos were taken of animal guts using a 40x objective and a Nikon D850 camera. We directly counted all particles with both surface modifications for our experiment where particles were available in equal concentration using the CY3 filter cube. 

NSF Award Abstract:
Marine microorganisms are among the most abundant life forms on the planet, playing a key role in ocean nutrient cycling. Though predation on these microorganisms is critical to nutrient cycling, little is known about their interactions with predators - specifically the direct interaction between microorganism cell surfaces and predator capture surfaces. This project examines how cell surfaces may influence the predation of marine microorganisms. Cell surface modification is a recognized strategy for predator avoidance among terrestrial microorganisms, but its application in the ocean is largely unexplored. By examining microbial prey with varying surface characteristics and predators with a range of feeding strategies, this research is providing foundational knowledge for future ocean food web models. This project engages public audiences through exhibits and workshops at museums (e.g., Oregon Museum of Science and Industry) and coastal aquariums with a focus on predator-prey interactions in the ocean from small microbial prey to larger predators. A large-scale art installment emphasizes these food web interactions. These 'Eco Murals' focus on ocean ecosystems and involve participation from community members, especially underrepresented minorities. This project is training the next generation of scientists by involving graduate and undergraduate students in research, professional development, and scientific communication. This research includes independent graduate student research as well as capstone projects in Bioinformatics and Genomics. Undergraduate students participate in this research following the previously successful NSF REU Exploration of Marine Biology on the Oregon Coast model. Finally, by leveraging initiatives aimed at promoting the persistence of historically underrepresented and underserved populations in STEM fields, this project recruits, supports, and retains female, first-generation, and underrepresented minority students.

The differential selection and rejection of microbial prey alters our understanding of carbon fate and nutrient cycling in the ocean. This project directly tests the effects of microbial surface properties on particle selection by globally abundant suspension feeders. Cell surface properties are known to be a fundamental aspect of predation avoidance in terrestrial microbes, but the role of microbial surface properties in avoiding or enhancing predation is a research frontier in ocean science. This knowledge gap limits understanding of microbial mortality, microbial loop function, and prediction of ecosystem response to future climate scenarios. This research links specific particle properties with ecologically-relevant trophic interactions through experiments with widespread suspension feeders representing major feeding strategies by copepod nauplii, pteropods, appendicularians, and echinoderm larvae. First, this project quantifies the surface properties of major marine microbial groups to inform feeding incubations with artificial prey. Second, artificial microspheres with varying surface properties are used in controlled laboratory feeding incubations to determine selectivity and third, to quantify particle fate from released fecal pellets and pseudofeces. Finally, the major marine microbial taxa in the guts of wild-caught suspension feeders are quantified using qPCR. This research forms an integrative approach, yet the results of each objective have scientific impact which can be applied to diverse fields beyond the ocean.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.