PREDICTING ZOOPLANKTON'S VULNERABILITY TO CLIMATE WARMING: UPPER THERMAL LIMITS AND ACCLIMATION PLASTICITY

• Main Author: Spyrou, Marios
• Format: Thesis
• Language: English
• Published: 2014
• Subjects: Climate change; Upper thermal limits; Acclimation plasticity; Survival; Reproduction; Distribution; Calanus finmarchicus; North Atlantic; Copepods
• Online Access: http://hdl.handle.net/10026.2/2567

The upper thermal limits (CTmax) of several crustacean planktonic species were investigated with a dynamic method in an attempt to predict their vulnerability to climate warming. The species were maintained at two acclimation temperatures (13 °C and 22.5 °C) before exposure to acute thermal stress to measure their acclimatory ability (i.e. phenotypic plasticity). The results showed that both cold and warm acclimated crab and shrimp larvae had significantly higher CTmax (p < 0.001) compared to the copepod species, suggesting that these taxa may be less susceptible to future climate warming. The high acclimation temperature increased significantly the CTmax of all the species (p < 0.001) and affected the between taxa differences in thermal limits. The CTmax of the warm acclimated copepods were not significantly different and ranged from 33.24 to 33.74 °C (± 0.23). The rest of the study was focused on Calanus finmarchicus and Calanus helgolandicus, whose responses to chronic thermal stress were also tested with a static method. No significant differences were found in the egg production rates (EPR) or hatching success (HS) for the two species. In contrast, 26.67 % (± 11.82) of cold acclimated C. helgolandicus adults survived at 25 °C, while C. finmarchicus survival rates reached 0 % at 24.5 °C. This suggests that C. helgolandicus has a higher affinity for warm temperatures. C. helgolandicus and C. finmarchicus nauplii had low CTmax in the dynamic method but higher tolerances in the static method compared to the adult stages, as 3.77 % ± 2.6 managed to survive at 26 °C and 11.11 % ± 7.62 at 25 °C (respectively). This sets new boundaries on the existing literature which considers nauplii as the most sensitive stage. Warm acclimated C. helgolandicus had higher survival rates than the cold acclimated ones, as 6.67 % ± 4.63 adults and 7.69 % ± 7.69 nauplii managed to survive at 27 °C. However, organismal adaptation to the high temperature probably led to the significant decline in EP observed (i.e. trade-off). Overall, the current study shows that C. finmarchicus has lower thermal tolerance compared to C. helgolandicus, which renders it more vulnerable to climate warming. The results could partially explain C. finmarchicus decreased abundance in the North Atlantic, but predictions are very hard to make since the two species had no differences in the vital for future recruitment and distribution processes of EPR and HS. In collaboration with Sir Alister Hardy Foundation for Ocean Science & Marine Biological Association