Coping with stress in a warming Gulf: the postlarval American lobster's cellular stress response under future warming scenarios.

The Gulf of the Maine (GoM) is one of the fastest warming bodies of water in the world, posing serious physiological challenges to its marine inhabitants. Marine organisms can cope with the cellular and molecular stresses created by climate change through changes in gene expression. We used transcriptomics to examine how exposure to current summer temperatures (16 °C) or temperature regimes reflective of projected moderate and severe warming conditions (18 °C and 22 °C, respectively) during larval development alters expression of transcripts affiliated with the cellular stress response (CSR) in postlarval American lobsters (Homarus americanus). We identified 26 significantly differentially expressed (DE) transcripts annotated to CSR proteins. Specifically, transcripts for proteins affiliated with heat shock, the ubiquitin family, DNA repair, and apoptosis were significantly over-expressed in lobsters reared at higher temperatures relative to current conditions. Substantial variation in the CSR expression between postlarvae reared at 18 °C and those reared at 22 °C suggests that postlarvae reared under severe warming may have a hindered ability to cope with the physiological and molecular challenges of ocean warming. These results highlight that postlarval American lobsters may experience significant heat stress as rapid warming in the GoM continues, potentially compromising their ability to prevent cellular damage and inhibiting the reallocation of cellular energy towards other physiological functions beyond activation of the CSR. Moreover, this study establishes additional American lobster stress markers and addresses various knowledge gaps in crustacean biology, where sufficient 'omics research is lacking.

Expected ocean warming conditions significantly alter the transcriptome of developing postlarval American lobsters (Homarus americanus): Implications for energetic trade-offs.

The American lobster (Homarus americanus) is one of the most iconic and economically valuable fishery species in the Northwestern Atlantic. Surface ocean temperatures are rapidly increasing across much of the species' range, raising concern about resiliency in the face of environmental change. Warmer temperatures accelerate rates of larval development and enhance survival to the postlarval stage, but the potential costs at the molecular level have rarely been addressed. We explored how exposure to current summer temperatures (16 °C) or temperature regimes mimicking projected moderate or extreme warming scenarios (18 °C and 22 °C, respectively) for the Gulf of Maine during development influences the postlarval lobster transcriptome. After de novo assembling the transcriptome, we identified 2542 differentially expressed (DE; adjusted p < 0.05) transcripts in postlarvae exposed to 16 °C vs. 22 °C, and 422 DE transcripts in postlarvae reared at 16 °C vs. 18 °C. Lobsters reared at 16 °C significantly over-expressed transcripts related to cuticle formation and the immune response up to 14.4- and 8.5-fold respectively, relative to those reared at both 18 °C and 22 °C. In contrast, the expression of transcripts affiliated with metabolism increased up to 7.1-fold as treatment temperature increased. These results suggest that lobsters exposed to projected warming scenarios during development experience a shift in the transcriptome that reflects a potential trade-off between maintaining immune defenses and sustaining increased physiological rates under a warming environment. This could have major implications for post-settlement survival through increased risk of mortality due to disease and/or starvation if energetic demands cannot be met.

Impedance Pneumography for Minimally Invasive Measurement of Heart Rate in Late Stage Invertebrates.

Temperatures in oceans are increasing rapidly as a consequence of widespread changes in world climates. As organismal physiology is heavily influenced by environmental temperature, this has the potential to alter thermal physiological performance in a variety of marine organisms. Using the American lobster (Homarus americanus) as a model organism, this protocol describes the use of impedance pneumography to understand how cardiac performance in late stage invertebrates changes under acute thermal stress. The protocol presents a minimally invasive technique that allows for real-time collection of heart rate during a temperature ramping experiment. Data are easily manipulated to generate an Arrhenius plot that is used to calculate Arrhenius break temperature (ABT), the temperature at which heart rate begins to decline with increasing temperatures. This technique can be used in a variety of late stage invertebrates (i.e., crabs, mussels, or shrimps). Although the protocol focuses solely on the impact of temperature on cardiac performance, it can be modified to understand the potential for additional stressors (e.g., hypoxia or hypercapnia) to interact with temperature to influence physiological performance. Thus, the method has potential for wide-ranging applications to further understand how marine invertebrates respond to acute changes in the environment.