She’s got to be from out of town: Effects of a poleward range shift of the southern hiltoni on resident nudibranch Authors: Michael Brito, Kenzie Pollard, Samuel Walkes, Eric Sanford

Introduction Hypotheses A B • Warm water anomalies in the NE Pacific during 2014-2016 led to • When exposed to P. hiltoni cues, H. opalescens and F. poleward range shifts in many marine species along the trilineata will feed less and hide more often, and P. hiltoni California coast, including the nudibranch will not change its behavior. (Sanford et al., 2019). • When directly confronted by P. hiltoni, H. opalescens and iNaturalist.org • Earlier work suggests that this predator can cause declines in F. trilineata will recognize and avoid the threat of predation, Photo: resident species abundance and diversity (Goddard et al., 2011). H. crassicornis will fail to recognize the threat of predation, C D • This range shift may result in novel interactions between P. and P. hiltoni will have an aggressive response to the other P. hiltoni and H. crassicornis, which have not occupied the same hiltoni. region of the coast until now. • We tested whether the range expansion of P. hiltoni into Bodega Bay may be increasing competitive/predation pressures on three

Results Mitchell Kim Photo: Murphy Ryan Photo: resident nudibranchs ( opalescens, Flabellina • F. trilineata fed less frequently when exposed to P. hiltoni Figure 5: The range-shifting nudibranch (A) Phidiana hiltoni, and the three trilineata, and ), which could resident species: (B) Hermissenda opalescens, (C) Flabellina trilineata, (D) cues (Figure 3) and spent more time avoiding P. hiltoni when Hermissenda crassicornis. potentially lead to changes in species abundance and diversity. placed in proximity (Figure 4). Discussion Methods • In contrast, the other species displayed varying behaviors or did not show a strong response to the presence of P. hiltoni. • The resident F. trilineata feeds less and exhibits more escape • We collected nudibranchs at Dillon Beach, Miwok Beach, behaviors in the presence of P. hiltoni cues. F. trilineata may be and Pinnacle Gulch in July 2019. 80 less able to compete for food due to increased time spent • In the lab, we exposed F. trilineata, H. opalescens, and P. 70 avoiding this perceived threat. hiltoni individuals to water-borne cues from H. opalescens 60 50 • The other nudibranch species did not show a significant and P. hiltoni for 45 hours (Figure 1). At 9:00, 12:00, 15:00, 40 response to the cues of P. hiltoni. and 18:00 hours, we noted any sheltering, feeding, and 30 20 neutral behaviors. Afterwards, we calculated the amount of (mm2) 10 • A larger sample size of H. crassicornis individuals is necessary hydroid (Obelia sp.) consumed per individual. 0 to effectively examine the potential effects of the newly • Additionally, P. hiltoni individuals were paired with another overlapping range of H. crassicornis and P. hiltoni. Control Control Control Average Surface Area Change Change Area Surface Average nudibranch. During a 5-minute trial, we counted and hiltoni P. hiltoni P. hiltoni P. • Size appeared to be a good indication of how the nudibranch

observed behaviors for each individual (Figure 2). opalescens H. opalescens H. opalescens H. would react. F. trilineata were much smaller, and H. H. opalescens P. hiltoni F. trilineata opalescens, H. crassicornis, and P. hiltoni were all larger and of Figure 1) A component Treatment of the apparatus used. Figure 3: The average change in surface area of hydroid measured in millimeters for a similar size. The water-born cue each species and the corresponding treatment (Two-way ANOVA, F2,15 = 3.1502, • The observed trends warrant more research with larger sample H. opalescens P. hiltoni from P. hiltoni and H. p=0.072, error bars are +/- 1SD). opalescens was fed sizes to confirm statistical significance. F. trilineata H. opalescens through into each H. crassicornis • More research is needed to examine how poleward range shifts individual container 11% 6% may affect species interactions in coastal communities. (the colored squares) 13% containing a nudibranch 25% 19% (each color corresponds 13% 37% Acknowledgments to a species). Special thanks to Dr. Eric Sanford for his guidance and field assistance, and 33% Jackie Sones, Sam Walkes, Katie DuBois, and Anika Agrawal for aiding in the never- 56% 12% = F. trilineata = H. opalescens = P. hiltoni = Control 19% ending search for nudibranchs. Thank you to Erin de Leon Sanchez, Jenna Quan, and 31% 6% the BIS 124 (Coastal Marine Research) class for their support and feedback throughout 19% the project. Finally, I thank my research partner Kenzie Pollard for her brilliance and valuable insight that was an integral part of ensuring this project was carefully executed. Figure 2) An example of the direct No contact Withdrawal/change direction interaction trials. H. crassicornis withdrawal neutral References (left) and P. hiltoni (right) in 8cm repeated contact aggression/attack • Goddard J. et al. 2011. Impacts associated with the recent range shift of the aeolid nudibranch bowl. Phidiana hiltoni (, Opisthobranchia) in California. Marine Biology 5: 1095-1109. Figure 4: The percentage of each observed response of each nudibranch to the • Sanford E. et al. 2019. Widespread shifts in the coastal biota of northern California during the presence P. hiltoni 2014-2016 marine heatwaves. Scientific Reports 9, Article number: 4216.