Sutherland Lab

Plankton-fluid interactions
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Research
Our research relates to interactions between marine plankton and the fluid environment with the goal of exploring two major themes:

1) Trophic interactions and the cycling of organic material in the ocean

2) Biological propulsion

To explore these themes, we primarily work with zooplankton (especially jelly-plankton) using a variety of in situ and experimental techniques.


Current projects:

Trophic interactions between jellyfish and ichthyoplankton at biological hot spots off the Oregon coast

Interactions between marine picoplankton and mucous-net filter feeders

Influence of organism-scale turbulence on the predatory impacts of a suite of cnidarian medusae



Past projects:

Ctenophore swimming and feeding in turbulence

Ostracod swimming behavior in flow

Low-Reynolds number filtration of submicrometer particles

Jet propulsion by salps

An in situ technique for measuring filtration rates

Jellyfish swimming behavior in shear flow

NCEAS working group on global jellyfish blooms



Trophic interactions between jellyfish and ichthyoplankton at biological hot spots off the Oregon coast

Collaborators: Ric Brodeur, Elizabeth Daly
Student: Sam Zeman
Funding: Oregon Sea Grant
, UO Office for Research and Innovation

The Northern California Current (NCC), off the Oregon coast, sustains a biologically rich ecosystem.  Periodic upwelling produces pulses in primary and secondary productivity which support a large fisheries biomass.  Large cnidarian jellyfish, primarily Chrysaora fuscescens, Aurelia aurita and Aequorea sp., are seasonally abundant in the NCC and a key component of food webs but are typically not included in food web models due to uncertainties in the predator-prey relationships. 

Frontal regions are key physical and biological features off of the Oregon coast and are predominantly produced by wind-driven coastal upwelling and river plumes.  These regions are characterized by sharp spatial gradients in hydrographic properties— including temperature, salinity and nutrients— as well as velocity gradients.  These regions have been characterized as ‘biological hotspots’ because elevated diversity and biomass are predictably found there.

The goal of this project is to characterize fine-scale distributions of large medusae and their zooplankton prey off the Oregon coast.  This goal is being addressed through a combination of field video surveys, stratified net sampling and diet studies.  


Chysaora



Interactions between marine picoplankton and mucous-net filter feeders

Collaborators: Gitai Yahel, Fabien Lombard, Yaron Tikochinski
Student: Keats Conley
Funding: United States- Israel Binational Science Foundation

The upper ocean is dominated by micron and submicron cells and these microorganisms are central in biogeochemical cycling. Chordate, mucous-net filter feeders, including salps, doliolids and appendicularians, have high individual filtration rates and specialize in filtering and retaining these minute particles, using highly sophisticated, mucus based, filtration apparatae.  Contrary to the current understanding that filtration is non-selective by these filter-feeders, our preliminary data show that particle selection can be non-uniform, even for similarly sized cells.  Surprisingly, bacteria of the SAR 11 clade, the most abundant organism in the upper ocean, are not retained by some ascidians while similar sized bacteria (e.g., Prochlorococcus) are retained with close to 100% efficiency.

This project relies on novel in situ sampling methods, next generation molecular techniques and visualizations of particle-mesh interactions to address three fundamental questions:

1) What are the differential retention patterns for different picoplanktonic phylotypes by pelagic tunicates?

2) How do selection preferences and selection mechanisms vary among pelagic filter feeders and how does this variation relate to the filtration apparatus geometry and hydrodynamics?

3) What are the mechanisms of particle retention (or lack of it) for different cell types, focusing in particular on salps and their interaction with SAR 11 bacteria?

SALPATRON     SalpSampling      Salpatron    
Underwater sampling at Villefranche-sur-mer, France, to investigate particle selection by appendicaularians and salps.


Influence of organism-scale turbulence on the predatory impacts of a suite of cnidarian medusae

Collaborators: Sean Colin, Jack Costello
Students (undergraduates):
Susan Brush, Clare Chisholm, Aaron Nelson, Alex Poje
Funding:
National Science Foundation

Turbulence is known to influence plankton behavior, ingestion rates and vertical distributions and can therefore profoundly modify the flow of material through pelagic ecosystems; but organism-scale effects of turbulence are not understood and field studies have been rare. A detailed understanding of effects of turbulence on organism-scale predator-prey interactions, as well as a broader view of how trophic exchanges shift in turbulence, are critical to predicting current and future food-web interactions.

Using a suite of cnidarian hydromedusae with unique morphologies, fluid signatures and prey selection patterns from Friday Harbor labs, WA, we are investigating the influence of turbulence on predator-prey interactions. 

Angles

Swimming behavior in still water and turbulence: 

Compass plots of swimming direction from swimming angle data measured in still water (A-D) and in turbulence (E-H). (A, E) Aeqourea, (B, F) Mitrocoma, (C, G) Stomotoca, (D, H) Aglantha.  Black vectors show mean direction for each individual and red vector shows overall mean direction, which is listed in the bottom right-hand corner.



Ctenophore swimming and feeding in turbulence

(with John Dabiri, Jack Costello and Sean Colin)

In the ocean, predator-prey interactions occur in moving fluid, yet studies of prey capture are often conducted in still-water tanks.  Currently, I am working to understand how environmental  turbulence influences the mechanics of prey capture.  Our target organism, the invasive comb jelly Mnemiopsis leidyi , is of particular interest because it can exert a strong trophic impact in both its native environment (Atlantic Coast of N. and S. America) and areas where it has been introduced (Black, Caspian, Baltic and Mediterranean Seas).

Turb
        Tank



Ostracod swimming behavior in flow

(with John Dabiri and Mimi Koehl)

Simultaneous, in situ measurements of zooplankton behavior and the background fluid motion are rare, and little is known in general about the swimming behavior of ostracods, which are ubiquitous in benthic marine environments.  Working under a dock in Kanehoe Bay, Hawaii, we collected Particle Image Velocimetry (PIV) measurements and ostracod swimming tracks using a Self Contained Underwater Velocimetry Device (SCUVA).  In slow flows (Urms ~0.4  cm s-1), ostracod swimming tracks were more tortuous, and encounters with bottom-dwelling organisms and with other ostracods were more frequent than in higher velocity wave-driven flows (Urms ~3.5  cm s-1), indicating that foraging and mating activities may be curtailed when ambient water flow is too rapid or variable.


Ostracod_tracks



Low-Reynolds number filtration of submicrometer particles

(with Larry Madin and Roman Stocker)

Though salps are centimeters in length and swim at speeds of ~1-10 cm s-1, filtration occurs on a fine, mucous mesh (fiber diameter ~0.1 μm) at low velocity (1.6 cm s1) and is thus a low Reynolds number (Re ~103) process.  A model of particle capture efficiency by a rectangular mesh was used to estimate particle capture rates on the salp filtering mesh based on realistic oceanic particle concentrations.  Particle feeding experiments using 0.5, 1 and 3 µm fluorescent polystyrene microspheres were then performed to test the theoretical model.  Results from both the model and from experiments showed that smaller particles are captured at considerably higher rates than larger particles.  Though particles smaller than mesh openings (1.4 µm) are expected to supply substantially less carbon than larger particles, they can still completely satisfy salp energetic needs.  By removing different sized particles with nonuniform efficiency and packaging them into fast-sinking fecal pellets, salps have the potential to structure oceanic particle size spectra.


Low-Re
          biofiltration


Link to publication in Proceedings of the National Academy of Sciences
Link to popular article in Oceanus magazine




Jet propulsion by salps

(with Larry Madin)

Salps are barrel-shaped marine organisms that are common in the open ocean and swim using a pulsed jet.  Among salp species, there are a variety of body shapes and swimming styles that correspond to differences in ecological function.  Dye visualization via bluewater SCUBA techniques and laboratory Digital Particle Image Velocimetry (DPIV) were used to describe jet wake structure and swimming performance variables including thrust, drag and propulsive efficiency among three salp species (Pegea confoederata, Weelia (Salpa) cylindrica, Cyclosalpa sp.).  Locomotion by each species was achieved using vortex ring ring propulsion.   Different combinations of swimming speed and hydrodynamic efficiency were observed and can be considered in light of metabolic constraints and ecological roles.  Though nature does not strive for optimality, this work shows the value of a comparative approach for understanding how underlying structure and mechanism influence performance.


salp_jets


Link to publication in the Journal of Experimental Biology
Link to popular article in Oceanus magazine

 


An in situ technique for measuring filtration rates

(with Larry Madin)

Accurately measuring filtration rates poses a challenge because salps are delicate, difficult to collect and maintain, and may not behave normally in the laboratory. Morphometric analysis of salps swimming in situ provides a way to measure the volume of fluid passing through the mucous filtering mesh. High definition video sequences collected by SCUBA divers were digitized to measure time-varying swimming kinematics and body volume over a pulse cycle. This non-invasive method produced higher feeding rates than other methods and revealed that body volume, pulse frequency and degree of contraction are important factors for determining volume filtered. The convergence of different species with diverse morphologies on similar normalized filtration suggests a tendency towards a flow optimum.


Volume_flow_rate


Link to publication in Marine Biology

 


Jellyfish swimming behavior in shear flow

(with Monty Graham)

For my MSc work, I used a combination of in situ observations from a towed optical instrument, JellyCam, and laboratory experiments in kreisel tanks to show that moon jellyfish (Aurelia aurita) respond to velocity gradients by swimming asymmetrically.  This asymmetrical swimming helps to explain a behavioral component to aggregations of jellyfish  at density discontinuities (i.e., vertical and horizontal fronts) where velocity gradients are steep.





Link to publication in Limnology and Oceanography