Strategies for biomass control are actively sought in response to proliferation of the introduced, suspension-feeding gastropod Crepidula fornicata along European coasts. Among these, dredging, crushing and on-site rejection may only be envisaged if the risk of further dissemination through the release of gametes and of excapsulated embryos/larvae is found to be nil or extremely low. This study evaluates such risk using three approaches: (1) determination of the periods of brood presence/absence, (2) external fertilizations of gametes obtained by gonad stripping, (3) cultures of mechanically-excapsulated embryos and larvae. A period of near- or total brood absence was observed between September 2006 and January 2007. The few zygotes (1.5% to 7.5%) obtained from external fertilizations did not proceed beyond the 4-cell stage. Excapsulated young embryos and mid-stages died in less than 4 days of culture. Despite their ability to swim, grow and feed, excapsulated veligers all died before metamorphosis. No juveniles were obtained from external fertilizations and excapsulated cultures, indicating that the release of crushed catches directly at sea could not present a dissemination risk from the standpoint of gamete or prematurely-excapsulated larval dispersal. Furthermore, by carrying out the crushing operations during the period of brood absence, the dissemination risk becomes nil. Negative ecological impact of such operations could be offset by attraction of motile predators, as yet unaccustomed to this introduced species, and their subsequent generalization to live slipper limpets and invasive feral Crassostrea gigas. At the very least, this biomass reduction approach would concentrate bottom habitat unavailability to restricted zones, freeing up the rest of the subtidal for other, formerly displaced species, as well as reducing the pressure on the trophic carrying capacity of affected habitats.

The egg capsules and larvae of Engina armillata (Reeve) (Gastropoda: Buccinidae) are described for the first time. Its general ecology in the Cape d'Aguilar Marine Reserve, Hong Kong, is also described, the species occurring under stable boulders with a community of encrusting species, notably sedentary tubicolous polychaetes. The diet of E. armillata at Cape d'Aguilar consists of serpulid and spirobid polychaetes. Of the four commonest such species, Hydroides elegans was preferred to Pomatoleios kraussi, Simplicaria pseudomilitaris and Spirorbis foraminosus. Consumption rates by E. armillata varied considerably amongst individuals, but generally ranged between 1.2 and 6.5% of predator dry weight day-1 during conditions wherein prey quantity was maintained. Such a figure is low when compared to other boring naticid and muricid predatory gastropods which spend much time and energy accessing their prey. The ready availability of easily accessible prey may account for the low consumption rate of E. armillata (as also seen in other non-boring predatory gastropods) and explain its apparent specialist feeding habits.