First record of the predatory snail Acanthinucella spirata (Blainville, 1832) north of its known range

Abstract

Background: Rapidly changing marine environments have increased the need to document the expansion of organismal ranges into new, previously undocumented regions. Such range expansions can shed light on the ecological factors that promote successful spread and establishment of species in new areas, and the evolutionary processes that may lead to adaptations. Acanthinucella spirata (Blainville, 1832) is a muricid gastropod that has expanded its range northward along the California coast since the Pleistocene. Its previously documented range was from Tomales Bay, California (38.2°N), to Punta Baja, Baja California (22.9°N). Here we report the first record of A. spirata north of its previously defined range, along the Californian coast of North America. Methods: Populations of reproducing muricid gastropods were found during a survey of the high intertidal zone of a moderately wave-protected boulder field on Cape Mendocino, CA (Latitude 40.396°N Longitude-124.378°W) on 17 June 2017. A sample of 65 individual snails were haphazardly collected and digitally photographed, weighed, and measured. Photos and morphological data were used to key individuals to species, and we used shell shape to compare collected snails to suspected Acanthinucella species and with potential source populations. Results: Snails were positively identified as A. spirata, roughly 431 km north of this species' previously defined northern range limit. Snails had a mean shell length of 28.32 mm (± 3.0 s.d.) and a mean mass of 4.23 g (± 1.1 s.d.). Discussion: Due to A. spirata's non-planktonic larval stage, hitchhiking on avian hosts or rafting are the likely causes for the northward non-contiguous dispersal of the species, especially because populations have not been reported between new and previously defined range boundaries. Such stratified range expansions, which occur via a combination of both contiguous and non-contiguous dispersal, are consistent with several recent studies documenting present-day range expansions.