Meeting Abstract

P1.45  Saturday, Jan. 4 15:30  Effects of low tide conditions on susceptibility to herbivory in the kelp Saccharina sessilis PINEDA, J.R.*; HENDERSON, S.Y.; BURNAFORD, J.L.; University of Washington Friday Harbor Laboratories; Cerritos College; California State University Fullerton jpineda@skidmore.edu

Conditions in the intertidal zone differ at high and low tide. One potential low-tide stressor is wind, which can cause desiccation. Algae, unable to escape stressful conditions, accumulate damage over repeated low tides. We investigated whether damage from desiccation alters susceptibility to herbivory in the low intertidal canopy-forming kelp Saccharina sessilis. We assessed overall herbivory risk in the field by counting S. sessilis and three major consumers (the chiton Katharina tunicata, the isopod Idotea wosnesenskii, and the snail Lacuna spp.) in 0.25m² quadrats. We assessed the effects of desiccation on herbivory in the laboratory. We collected S. sessilis blades and cut two 25cm² samples from each. For 90 minutes once a day for three days, one sample from the pair experienced a “no-wind” simulated low tide while the other member of the pair experienced a “windy” low tide with airflow of 1 m/s. Before and after each low tide we measured area, wet weight, and the amount of visible damage on the kelp. After the third day, we placed paired kelp samples into a container either with or without herbivores. We conducted separate trials with K. tunicata and I. wosnesenskii. Once ~50% of the S. sessilis tissue in a herbivore container was consumed, we terminated the trial for a pair of herbivore and non-herbivore containers. Trials lasted 1 to 5 days. Our results showed that herbivore distribution in the field was patchy, and preference for damaged vs. undamaged tissue differed between herbivores. Overall, susceptibility to herbivory likely varies among individuals in the field due to differences in low-tide damage and the varying abundance of herbivores with different preferences.