PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, No. 3, pp. 107-131, 13 figs., 2 tables September 28, 2018 
Heterobranch Sea Slug Range Shifts in the Northeast Pacific 
Ocean associated with the 2015-16 El Nino 
Jeffrey H. R. Goddard ’, Nancy Treneman 2 , Tara Prestholdt 3 , Craig Hoover 4 , 
Brenna Green 5 , William E. Pence 6 , Douglas E. Mason 7 , Phillip Dobry 8 , 
Jacqueline L. Sones 9 , Eric Sanford 10 , Robin Agarwal n , Gary R. McDonald 12 , 
Rebecca F. Johnson 5 , Terrence M. Gosliner 5 
1 Marine Science Institute, University of California, Santa Barbara, CA 93106-6150; email: 
jeffg@ucsb.edu._f Oregon Institute of Marine Biology, University of Oregon, Charleston, OR 97420. 
3 Department of Biology, The University of Portland, 5000 N Willamette Blvd, Portland, Oregon 97203. 
4 Department of Biological Sciences, California State Polytechnic University, 3801 W. Temple Ave., 
Pomona, California 91768-4032. 5 Department of Invertebrate Zoology and Geology, California 
Academy of Sciences, 55 Music Concourse Dr., Golden Gate Park, San Francisco, CA 94118-4503. 
6 25 Tarabrook Dr., Orinda, CA 94563. 7 Science Department, California High School, San Ramon, CA 
94583. 8 33 Petar Place, San Ramon, CA 94583. 9 Bodega Marine Reserve, University of California, 
Davis, PO. Box 247, Bodega Bay, CA 94923. 10 Department of Evolution and Ecology, University 
of California, Davis, Bodega Marine Laboratory, PO. Box 247, Bodega Bay, CA 94923. 
11 3114 Flowers Lane, Palo Alto, CA 94306. 12 Long Marine Lab, University of California 
Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 96050 
The strong 2015-16 El Nino comprised the second part of the unprecedented 2014- 
17 marine heat wave in the Northeast Pacific Ocean. From late 2015 through 2017 
we sampled mostly intertidal sites from La Paz, Baja California Sur to northern 
Oregon for benthic heterobranch sea slugs outside of their normal ranges. Combined 
with records obtained from colleagues and internet sources, we document northern 
range shifts for 37 species, including 21 ( Berthella strongi, Okenia angelensis, Acan- 
thodoris rhodoceras , Crimora coneja, Limacia mcdonaldi , Polycera atra , Triopha mac- 
ulata, Carminodoris bramale, Doris cf. pickensi, Thordisa rubescens, Cadlina sparsa, 
Doriopsilla albopunctata, Doriopsilla fulva, Doriopsilla gemela, Tritonia myrakeenae, 
Doto lancei, Doto form A of Goddard (1996), Flabellina bertschi, Hermosita hakuna- 
matata, Noumeaella rubrofasciata, Phidiana hiltoni) from new northernmost locali¬ 
ties. The average range extension of these 21, plus Hermissenda opalescens and 
Dirona picta reported by Merlo et al. (2018) from the west coast of Vancouver Island 
was 270 km (SD = 201 km, n = 23). Significantly, no species were observed south of 
their usual ranges during the 2014-17 marine heat wave. Combined with the results 
of Goddard et al. (2016) for the 2014 warm anomaly, the 2014-17 marine heat wave 
in the Northeast Pacific drove range shifts in at least 52 species of benthic hetero- 
branchs, approximately one quarter of the species known from the region. These 
numbers appear to be unprecedented in the historical record and point to global 
warming as a contributing factor, likely acting through a series of steps leading to 
increased poleward transport of coastal waters in the region, as well as elevated sea- 
surface temperatures. 
Keywords: Range shifts, heterobranch sea slugs, nudibranchs, Northeast Pacific Ocean, 
marine heat wave, El Nino, global wanning 
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