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Molecular identification of two species of the carnivorous sea slug Philine, invaders of the US west coast

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Abstract

Open-coast and deep-water ecosystems have been less disrupted by invasion than estuaries, but a notable exception is the establishment of multiple species of the sea slug genus Philine in the northeastern Pacific. These large slugs spread from San Francisco Bay to the whole of the US west coast in 5 years during the 1990s, and are abundant from intertidal mudflats to soft-sediment bottoms >300 m deep along the open coast. Voracious predators that secrete acid, Philine spp. have few natural enemies and substantial impacts on native bivalve communities. Despite their ecological significance, the identity and number of invasive Philine spp. in the US has remained controversial. Here, we adopt a molecular approach to identify the species commonly found along the US west coast. We compared mitochondrial 16S gene sequences of reference specimens from the native range of seven possible invaders against sequences of 66 specimens collected from southern California to Oregon from intertidal and subtidal habitats. All slugs from southern California and Oregon were confirmed as P. auriformis, and most shared haplotypes with samples from New Zealand. Larger slugs from San Francisco, Tomales Bay and Bodega Harbor, believed to represent 3–4 species, were all identified as P. orientalis. Molecular data support a recent morphological analysis that erected two proposed species, P. paucipapillata from Hong Kong and P. quadripartita from Europe, which are genetically distinct from anatomically similar species. For taxonomically challenging groups like sea slugs, genetic data can illuminate cryptic invasions and provide a backdrop for further studies of the ecological impacts of introduced marine species.

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Acknowledgments

We thank R. Willan, B. Pernet, Y. Ralph, H. Weiskel and J. Goddard for collecting and sharing specimens, R. Portela Miguez for assistance with loaned material from the Natural History Museum of London, and C. Stepien and an anonymous reviewer for suggestions that greatly improved the manuscript. This study was supported by awards to PJK from the US National Science Foundation (OCE 06-48606 and 11-30072, DEB 08-17084), a faculty-student collaborative grant from the California State University Program for Education and Research in Biotechnology (CSUPERB), and an NSF GK-12 fellowship to J. Asif.

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Authors and Affiliations

  1. Department of Biological Sciences, California State University, Los Angeles, CA, 90032-8201, USA

    Patrick J. Krug, Jamal H. Asif & Isabel Baeza

  2. Auckland War Memorial Museum, Auckland, New Zealand

    Margaret S. Morley & Wilma M. Blom

  3. California Academy of Sciences, Golden Gate Park, San Francisco, CA, 94118, USA

    Terry M. Gosliner

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  1. Patrick J. Krug
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Correspondence to Patrick J. Krug.

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Krug, P.J., Asif, J.H., Baeza, I. et al. Molecular identification of two species of the carnivorous sea slug Philine, invaders of the US west coast. Biol Invasions 14, 2447–2459 (2012). https://doi.org/10.1007/s10530-012-0242-9

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