3D Particle Tracking to Analyze Predator-Prey Interactions in Mnemiopsis leidyi

Meeting Abstract

P3.134  Monday, Jan. 6 15:30  3D Particle Tracking to Analyze Predator-Prey Interactions in Mnemiopsis leidyi MACPHERSON, R.S.*; COLIN, S.P.; GEMMELL, B; COSTELLO, J; University of California, Berkeley rmacpherson@berkeley.edu

Mnemiopsis leidyi is a species of lobate ctenophore that has recently expanded its habitat to areas including the Black and Mediterranean Seas. This has piqued interest in the identification of environmental factors that can encourage or discourage its invasion of a region. Our lab is interested in the effects of low-level turbulence in the water, which can induce higher swimming speeds, on the fluid flow inside and around Mnemiopsis and on its prey capture efficiency. We define prey capture efficiency as the ratio of prey captured to prey encountered at the lobes. Because of the bilateral symmetry of Mnemiopsis, 2D techniques to image fluid flow are not reliable; unlike an organism with radial symmetry, the fluid flow in one plane will likely be very different from that in another plane. Therefore we developed a technique using specialized mirror tanks to take recordings with two orthogonal views in the same video. We then developed software in MATLAB allowing us to extract the x, y, and z information of objects in the tanks. This allowed us to reliably track particles and small organisms in and around Mnemiopsis in three dimensions. Once the technique was developed, we used the mirror method to analyze the variation of Mnemiopsis’ prey capture efficiency with swimming speed by monitoring encounters between Mnemiopsis and Artemia, small brine shrimp that are typical prey for the ctenophore. It was found that capture efficiency did not change with higher swimming speeds, showing that Mnemiopsis in areas with low level turbulence in the water will be just as effective at catching their prey as the same organisms in areas with still water. Video of the fluid flow inside Mnemiopsis taken at different swimming speeds might elucidate the reason for this.

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