GODDARD ET AL.: EL NINO IMPACT ON HETEROBRANCH SEA SLUG RANGES 125 
heterobranchs such as Okenia rosacea, Doriopsilla fulva, and Hermissenda opalescens in Oregon 
and Phidiana hiltoni in northern California by keeping open thermal windows conducive to 
growth, reproduction and development. 
At Naples, an outer coast site in the northern part of the Southern California Bight, Bulla goul- 
diana was present for about one year after first appearing (Figure 4), while to the north at Morro 
Bay, B. gouldiana continues to be present after at least two years. Southern species may persist 
longer in embayments compared to nearby outer coast sites, owing to elevated summer tempera¬ 
tures on the one hand, and increased potential for larval retention and local recruitment on the 
other, thus allowing for reproduction and completion of life cycles in the bays. With the return to 
ENSO-neutral conditions and more normal sea-surface temperatures in the NE Pacific Ocean, it 
will be interesting to see how long southern species like Bulla gouldiana, Aplysia californica, 
A. vaccaria, and Doriopsilla fulva persist in northern embayments. 
Site-specific topography aside, with global ocean temperatures steadily increasing in the back¬ 
ground, recently settled southern species are likely to persist longer in their recently expanded 
northern ranges, especially compared to historically more ephemeral ENSO-driven range shifts 
(reviewed by Lluch-Belda et al. 2005). So far this appears to be the case for Okenia rosacea, 
Doriopsilla fulva, D. gemela, Felimida macfarlandi, Doto form A, Janolus anulatus, and 
Fla-bellina cooperi, all of which were found in 2017 at or near range limits reached a year or two 
earlier (Goddard et al. 2016; present study). However, other range shifts documented by Goddard 
et al. (2016) appear to have been short-lived, with no northern sightings since 2015 of Placida 
brookae McCarthy, Krug and Valdes 2017 (formerly P. cremoniana ), Trapania velox, Hancockia 
californica MacFarland, 1923, Anteaeolidiella chromosoma (Cockerell and Eliot, 1905), and 
Emarcusia morroensis Roller, 1972. Phidiana hiltoni, which has been taking smaller geographic 
steps with its lecithotrophic larvae, has yet to retreat from any new range acquired since 1977 and 
remains the best documented example of a permanent northern range shift among Northeast Pacif¬ 
ic heterobranchs (Goddard et al. 2011; present study; King et al. in prep). 
In central California southward range shifts by nudibranchs with more northern distributions 
were last observed during the strong La Nina events of 2007-08 and 2010-11 (e.g., Aldisa albo- 
marginata Millen in Millen and Gosliner, 1985, Aldisa cooperi, Robilliard and Baba, 1972, Diaul- 
ula lentiginosa (Millen, 1982), and Doris odhneri (MacFarland, 1966) subtidally off the Monterey 
Peninsula [see records at <http://www.baue. 0 rg/images/galleries/v/FieldGuide/Opistho 
branchs/>\, and Janolus fuscus (O’Donoghue, 1924) intertidally in San Luis Obispo Co. [JG 
personal observations, CASIZ 186479]). We did not observe any southern range shifts during the 
2014-17 marine heat wave, and the only record of a more northerly species penetrating central 
California we are aware of during this period is of Dirona albolineata MacFarland in Cockerell and 
Eliot, 1905 at Pillar Point (< https://www.inaturalist.org/observations/1727582 >). The last time 
D. albolineata was recorded farther south was during the 2009-10 La Nina, by GM at Carmel 
Point, on the Monterey Peninsula (for image see <https://www.inaturalist.org/observations/ 
834800 ). 
As the oceans continue to warm we expect more poleward range shifts by heterobranchs to 
become permanent, and likely lead to complex and unexpected changes in shallow-water benthic 
encrusting and fouling communities. 
Acknowledgments 
For assistance in the field we thank Will and Ziggy Goddard, Katy Kennedy, Sawyer Reid, 
Zach Taylor, Kara Termulo, Spencer Dybdahl-Riffle, Hans Bertsch, and Josh Hallas. JG thanks 
