Regional variations in early life stages response to a temperature gradient in the northern shrimp Pandalus borealis and vulnerability of the populations to ocean warming

- Optimal survival temperatures in northern shrimp larvae varied for populations from cold and warm regions of the NW Atlantic.
- Northern shrimp larvae from cold regions (e.g., Labrador Shelf) could benefit from warmer surface water in spring.
- Northern shrimp larvae from an isolated population in the Lower St Lawrence Estuary (warm region) could be at risk from future warming.

In order to define the relative vulnerability of northern shrimp (Pandalus borealis) populations to the ongoing global warming, we compared the thermal performance curves for survival and growth in the first three pelagic larval stages from three populations of the Northwest Atlantic. Egg carrying females were obtained from different regions characterized by distinct sea surface temperature (SST) conditions for larval development in spring. Two independent experiments were conducted in two different years. In spring 2012, larvae from females captured in the Lower St Lawrence Estuary (LE) and in the Northeast Gulf of St Lawrence (GSL) were compared. In spring 2014, larvae from females captured in the LE and on the Labrador-Newfoundland Shelf (Northwest Atlantic, NWA) were used. The LE larvae were used both years and served as the reference population for comparisons. In 2012 and 2014, groups of 25 newly hatched northern shrimp larvae from each source population were incubated at six temperatures (0, 3, 6, 9, 12, and 15 °C) to monitor and compare survival and growth at moult. Northern shrimp larvae from the LE (warmer May-June SST) had a higher optimal temperature range for survival compared to larvae from the GSL and the NWA (colder May-June SST) populations. However, in 2012 growth performance at moult was reduced at higher temperatures for the LE population compared to the GSL population. The differences in thermal performance curves observed may suggest the presence of a certain level of local adaptation in response to the different regional SST regimes in spring-early summer. Northern shrimp larvae in the Northeast Gulf of St Lawrence and Northwest Atlantic shelf could benefit from warmer early-spring temperatures; however, larvae from the Lower Estuary may be closer to their upper tolerance limits and thus more likely at risk of negative impact of future warming of surface water masses.