Little is known about the biology of the softshell clam in Europe, despite it being identified as a potential species to culture for food in the future. Monthly samples of the softshell clam, Mya arenaria, were collected intertidally from Co. Wexford, Ireland, over a period of sixteen months. The mean weight of sampled individuals was 7 4 ± 4 . 9 ？g and mean length was 8 . 2 ± 0 . 2 ？cm. Histological examination revealed a female-to-male ratio of 1？:？1.15. In 2010, M. arenaria at this site matured over the summer months, with both sexes either ripe or spawning by August. A single spawning event was recorded in 2010, completed by November. Two unusually cold winters, followed by a warmer-than-average spring, appear to have affected M. arenaria gametogenesis in this area, potentially affecting the time of spawning, fertilisation success, and recruitment of this species. No hermaphrodites were observed in the samples collected, nor were any pathogens observed. Timing of development and spawning is compared with the coasts of eastern North America and with other European coasts. 1. Introduction The softshell clam, Mya arenaria, is widely distributed in coastal and intertidal soft substrates in boreal waters and is often a dominant species in benthic communities [1]. Mya arenaria currently occupies a wide geographical range in the northern hemisphere, on the east and west coasts of North America, where it is commercially important for fisheries and aquaculture [2, 3]. In 2008 alone, the National Marine Fisheries Service of USA reported approximately 1.73 million kg of M. arenaria harvested, worth in excess of €16 million [4]. The present European distribution of M. arenaria ranges from Northern Norway to Portugal, including the Black Sea [5–7], with recent reports of its introduction to the Mediterranean Sea [4]. Mya arenaria is rarely collected for food or bait in European waters, but it is an ecologically important food source for fish such as plaice (Pleuronectes platessa) and flounder (Platichtys flesus) [6], shrimp, sandworms, crabs, and wading birds such as oystercatchers (Haematopus ostralegus) and curlew (Numenius arquata) [8]. Due to the softshell clams’ ability to survive and reproduce in a variety of differing areas such as mud and gravel, it could be an ideal species to culture in European waters in the future. Mya arenaria are widespread around all Irish and British coasts [9, 10], but little information is currently available on reproductive biology in these areas. Previous work in the United States has revealed that the sexes of M. arenaria
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