The annual gametogenic cycle in the blue mussel, Mytilus edulis L. was investigated from May 2010 to May 2011 in two locations in north-western Iceland. Food availability (chlorophyll-a) was high in early spring at both sites, with a summer maximum in July in Steingrimsfjördur but an autumn maximum in September in Patreksfjördur. Gonad development started in November at both sites, with ripe gametes still visible in the follicles, and continued throughout the year, except for a very short time prior to spawning in Steingrimsfjördur. Gametes developed mostly between November and May. Spawning was protracted, lasting from July to early winter at both sites. The main spawning events occurred from August (11.7°C) to October (9.4°C) in Patreksfjördur, but from July (9.8°C) to October (8.6°C) in Steingrimsfjördur
