The effect of rearing temperature on the survival and growth of early juvenile Atlantic surfclams (Spisula solidissima)

The Atlantic surfclam (Spisula solidissima) is not currently cultivated on commercial scales, but it represents a potentially beneficial target species for crop diversification in the Northeast region of the United States. Surfclams are native to the region and rapid growth gives this species the potential to reach marketable sizes within 12 to 18 months. Since heating and chilling seawater are major operating costs for bivalve seed production, a thorough understanding of how temperature influences juvenile surfclam survival and growth during the nursery phase - the period between metamorphosis and out-planting - must be determined before mainstream production can occur. We assessed early juvenile rearing temperature by conducting a month-long study where post-metamorphic surfclams (initial shell length approximate to 0.7 mm) were exposed to one of five temperature treatments (18.0, 20.2, 23.2, 24.4, and 26.3 degrees C.). Survival was approximately twice as high at 18 degrees C compared to 26 degrees C. Growth was maximized at intermediate temperatures between 20 and 24 degrees C. Additionally, we monitored the survival and growth of juvenile surfclams for 20 weeks during the Northeast's typical bivalve nursery operating season. Surfclams (initial shell length approximate to 1.5 mm) were reared at a commercial-scale using flow-through upwelling systems, supplied with ambient seawater from the Cape May Canal. Surfclam seed survival after the 20-week study was 52%, with most mortality occurring after the temperature peaked around 27 degrees C. The average growth rate over this study was 0.049mm d(-1). Our results suggest that juvenile surfclams should be reared in temperatures close to 20 degrees C for the duration of the nursery phase. Colder temperatures increase survival but tend to slow growth. Prolonged exposure to warm temperatures can cause severe mortality, yet juvenile surfclams seem to have the ability to tolerate short-term exposures to unfavorably warm temperatures. Across the Northeast, the ambient seawater should be sufficient for surfclam seed production at commercial scales.