The veined rapa whelk (Rapana venosa) invasion of the Chesapeake Bay in the United States was first observed in 1998. Chesapeake Bay rapa whelk population demographics, age-at-length relationships, and invasion progression (temporal, spatial) from 1998 to 2009 are described. Between June 1998 and November 2009, 27,624 rapa whelks, ranging from 11- to 195-mm shell length (SL), were collected fromthe lower Bay.Using a Von Bertalanffy age-at-length model (R2 = 0.99), the 195-mm-SL whelk collected in 2007 was 26 y old, making 1981 the estimated year of first introduction. Age-frequency distributions for Ocean View, Hampton Bar, and the lower James River showed increased whelk numbers per age class and consistent representation of Age 2–3 through Age 7–8 whelks throughout the time series indicating recruitment and establishment. Whelk range expansion into James River oyster habitats began in 2004 and continued through 2009. Whelks occupy shallow areas during warmer months, move into deeper habitats during cooler months, and annually reinvade shallow areas as temperatures warm seasonally. Channels act as salinity refugia and conduits between foraging habitats. Salinity tolerances allow rapa whelk use of epifaunal habitats bounded by the 10–12 isohalines formerly used by native oyster drills [Urosalpinx cinerea (Say, 1822); Eupleura caudata (Say, 1822)] as juveniles and infaunal habitats with salinities of 15–25 that do not overlap with native whelks (Busycotypus canaliculatus, Busycon carica) as adults. Establishment was facilitated by local disturbance of native species distributions by Tropical Storm Agnes (1972).
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Vol. 35 • No. 4