The interactive influence of temperature and salinity on larval and juvenile growth in the gastropod Crepidula fornicata (L.)

• Larvae and juveniles of C. fornicata reared in various temperatures and salinities.
• Growth rates were determined as shell length and relative shell mass.
• Larvae and juveniles grew more slowly at lower salinity and temperatures.
• Larval exposure to low salinity affected juvenile growth in 4 of 6 treatments.
• Magnitude of effects depended on temperature–salinity interaction and parentage.

Sea surface temperatures have been rising and are predicted to continue rising in coming years because of global warming. In addition, salinity has been decreasing in high latitudes and is expected to continue decreasing due to altered precipitation patterns and glacial melting caused by climate change. Many marine organisms that are adapted to the present conditions may be drastically affected by these oceanic changes. Early life stages (larvae and juveniles) should be especially susceptible, since they do not yet have the fully developed morphological defenses of adults. This study investigated the effects of reduced salinity (20 compared to a control of 30) and altered temperature (15, 20, 25, and 29 °C) on the growth, percent inorganic content (representing shell calcification), and feeding rates of larvae and juveniles of the widespread coastal snail Crepidula fornicata. Both larval and juvenile growth rates were significantly depressed at low salinity and lower temperatures. In addition, the salinity that snails were exposed to as larvae significantly impacted their juvenile growth rates in 4 out of 6 treatments, an example of latent effects. The magnitude and direction of this effect were strongly impacted by temperature and parentage. Juvenile feeding rates were significantly depressed following a rapid change in salinity but then gradually recovered to near initial levels over 3 h. There was little difference in the percent inorganic content of juveniles but for larvae that had been reared at 20 °C, percent inorganic content was 27% lower for those reared at a salinity of 20 compared with those reared at 30. In conclusion, the early life stages of C. fornicata may experience more favorable conditions in a warmer future: growth rates will increase, probably making larvae and juveniles less vulnerable to size-specific predation. Conversely, in regions where salinity is decreasing, C. fornicata larvae and juveniles will likely grow more slowly, thereby increasing predation risk by forcing them to spend more time at more vulnerable smaller sizes. Thus, the future of C. fornicata and their potential to continue invading new habitats will depend greatly on the specific salinity and temperature conditions they will be exposed to throughout larval and juvenile development.