Kim Walker

Kim Walker

Former Graduate Student

M.S. Biology 2016

Former graduate AND undergraduate student

B.S. Biological Science 2009, M.S. Biology 2016

The light’s on but nobody’s home:  Negative phototactic response of Kelletia kelletii larvae to light intensity and wavelength

Kim’s undergraduate research in the Zacherl lab involved exploring the behavior of Kellet’s Whelk (Kelletia kelletii) larvae. Many marine invertebrate larvae control their vertical position in the water column, potentially influencing dispersal outcomes. Previous laboratory studies with marine gastropod Kelletia kelletii larvae revealed that this species exhibits diel vertical migration (DVM) that is partially controlled by light. She explored light intensity and wavelength as potential cues initiating downward swimming and verified that DVM occurs in the field with plankton tows. She varied full-spectrum light intensity (ranging from 2.5 to 126 micromol·m-2·sec-1) in six replicate 10 cm diameter X 125 cm tall columns each containing 100 one-week old dark-adapted larvae and determined their vertical positions after 2 hrs light exposure. As light intensity decreased, significantly fewer larvae descended (ANOVA, p = <0.0001). At 2.5 micromol·m-2·sec-1 the percent larvae at the top of columns was similar to that in the dark control (p<0.05). The effect of wavelength was tested by comparing blue/green light (450-550 nm) at 14 micromol·m-2·sec- to full spectrum light (380-740 nm) of equivalent intensity. The proportion of descending larvae was significantly different (ANOVA, p=0.0006) indicating that K. kelletii larvae respond differentially to varying wavelengths of light. Surface plankton tows (n=5) were conducted at 1200 h and 2400 h off the coast of Palos Verdes, CA to examine whether laboratory findings were consistent with field vertical distributions of larvae. As predicted by lab studies, there were significantly more larvae at the surface at 2400 hr versus 1200 hr (t-test, p=0.0008).

As an undergraduate, Kim presented these data at the Western Society of Naturalists meeting, and some of her data were incorporated into a paper published in Journal of Marine Biology in 2012.

Romero MR*, Walker KM, Cortez CJ*, Sanchez Y*, Nelson KJ*, Ortega DC*, Smick SL*, Hoese WJ, and D C Zacherl. 2012. Larval Diel Vertical Migration of the Marine Gastropod Kelletia kelletii (Forbes, 1850). Journal of Marine Biology. doi:10.1155/2012/386575.

EFFECTS OF OLYMPIA OYSTER (OSTREA LURIDA) RESTORATION TECHNIQUES ON INVERTEBRATE COMMUNITY COMPOSITION

As  a graduate student, Kim studied the effects of Olympia oyster restoration on epifaunal and infaunal community composition. Ostrea lurida’s potential role as a foundation species has not been explored, so little is understood about whether any ecosystem services will be produced by ongoing restoration efforts for the United States’ only native oyster species on the west coast. Further, the effectiveness of different techniques for restoring Olympia oyster beds has not been systematically evaluated. The most common technique is augmenting available habitat by adding dead shell onto mudflats and allowing remnant oysters to seed the shell with spat; shell has been added at varying thicknesses, either consolidated in bags or simply placed loose onto the mudflat. Kim explored the effects of different combinations of Olympia oyster restoration techniques (varying the thickness of constructed shell beds using loose versus bagged oyster shell) on epifaunal and infaunal abundance, diversity, and community composition. Twenty-five oyster beds were established in Newport Bay, Orange County, California in June 2010. Five beds were not augmented with any shell and were used as control plots. The other twenty beds were randomly assigned to be constructed using dead oyster shell at thicknesses of 12 cm or 4 cm using shell bagged in jute or loose shell (n= 5 replicates per treatment). Visual inspection of MDS plots and results from ANOSIM indicated a significantly different shift in community composition of the oyster beds versus the control plots, with trends in differences of the thick beds and thin-bagged beds. Amphipods, polychaetes and oligochaetes all declined significantly over the study period, but not because of shell enhancements. Bivalves, gastropods and isopods all increased over the study period with observable trends towards increases on the thicker beds and thin-bagged beds, although insignificant. Results could inform future restoration efforts for this species and establish ecosystem services provided by O. lurida as a foundation species.

Kim presented results from her thesis research at Southern California Academy of Sciences. These data will get worked into a manuscript to be written in 2016-2017.

Kim is currently working for California Department of Fish and Wildlife as an Environmental Scientist on the Fisheries Research and Management Project. She conducts research and manages saltwater sportfishing species in southern California.