First visual record of rare purple dogwhelks (Nucella lapillus) on the Atlantic coast of Nova Scotia, Canada

Abstract

The dogwhelk Nucella lapillus is a rocky intertidal gastropod of the North Atlantic coast. Individual shell color varies. Common colors range between white and brown, with darker dogwhelks being more affected by heat stress than lighter-colored conspecifics. Other reported shell colors are black, mauve, pink, yellow, and orange from European coasts, red and grey from the Bay of Fundy coast of New Brunswick and Nova Scotia (Canada), and purple, black, gray, yellow, and orange from the coasts of Maine and Massachusetts (USA), with purple being considered as a rare color. On the Atlantic coast of Nova Scotia, dogwhelks are active from April until November, but information on dogwhelk shell color is missing for this coast. On 16 June 2016, we found two purple dogwhelks in the mid-to-high intertidal zone of a moderately wave-exposed rocky shore near Duncans Cove, on the Atlantic coast of Nova Scotia while collecting dogwhelks (n= 1000) for manipulative field experiments. All other dogwhelks collected on that day were of common white and brown colors. During earlier dogwhelk collections in Atlantic Nova Scotia (between 2011-2013) and field surveys in Duncans Cove (between 2014-2016), we did not find any purple dogwhelks, indicating the rareness of this color in that region. Interestingly, the purple dogwhelks were detected on a relatively cool day (12.3 ± 0.4 °C, mean ± se, n= 96 temperature measurements) compared to the intertidal temperatures of all other survey days (≥ 18.2 ± 0.5 °C), suggesting that purple dogwhelks may find it less thermally stressful to venture out of crevices and macroalgal cover under relatively cool temperatures. Our observations provide the first visual record of rare purple dogwhelks on the Atlantic coast of Nova Scotia, Canada.