Optimising recruitment in habitat creation for the native European oyster (Ostrea edulis): implications of temporal and spatial variability in larval abundance

European oyster (Ostrea edulis) restoration often requires the timely deployment of shell habitat for larval settlement. To inform this increasingly popular process, the present study investigated temporal and spatial abundance patterns of O. edulis larvae in a rare commercial fishery (Loch Ryan, Scotland, UK). Patterns in larval abundance were analysed against variability in temperature, salinity, chlorophyll, oxygen, tidal/moon phase, light, date, and location. ‘Temperature sum’ (sum total of degrees per day above 7 °C) was the most significant seasonal predictor of larval abundance; with a peak at 617 degree-days. Oyster larval abundance did not significantly vary between oyster bed and non-bed habitats but was significantly higher in the mid and near-surface part of the water column. The findings are discussed in the context of emerging international restoration initiatives and have implications for: where habitat restoration would be successful; the prediction of larval connectivity between sites; and a transferable indicator to optimise shell-habitat deployment timing.