Exposure to elevated temperature reduces effects of acidification on inducible defenses in the blue mussel, Mytilus edulis, and on predation rate and predator efficiency of the green crab, Carcinas maenas

Chair: Ana Queiros

Aaron Honig (1)*, Ron Etter (1) and Robyn Hannigan (2)

1 Biology Department, University of Massachusetts, Boston, MA, USA
2 School for the Environment, University of Massachusetts, Boston, MA USA

Background
Increased temperature, pCO2 and reduced ΩArag under anticipated marine climate change may require greater energetic investment during calcification in the blue mussel, Mytilus edulis. Such energetic investment may result in metabolic trade-offs, limiting inducible defenses during exposure to crab predators. Elevated temperatures may ameliorate deleterious effects of reduced pCO2 conditions. Consequently, to assess effects of climate change on predation vulnerability, we quantified the effects of high temperature and pCO2 on inducible defenses in blue mussel prey and crab predator efficiency.

Methods
Mussels were acclimatized to treatment conditions (12, 15, 18 °C; 380, 500, 1000 ppmv) using a CO2-dosing ocean acidification aquaria system. Juvenile mussels (< 5 cm) were exposed to a single green crab (Carcinus maenas) separated by mesh. Mean number and diameter of byssal threads per mussel were counted. Surviving mussels were exposed to a single crab predator. Predation rate (# mussels consumed/tank), and predator efficiency (ht: handling time, bt: breaking time, et: eating time; efficiency = ((ht + bt + et)/estimated mg dry tissue weight) were recorded within experimental aquaria.

Findings
Byssal number, diameter and strength in juveniles exposed to crab predators were all reduced under elevated pCO2 conditions at low temperature compared to those under elevated temperature and pCO2. Similarly, predation rate and predator efficiency on mussels were significantly greater in juveniles exposed to elevated pCO2 conditions at low temperature than those exposed to elevated temperature and pCO2.

Conclusions
Study results support previous experimental results suggesting reduced effects of ocean acidification on inducible defenses, limiting predation rate and predation efficiency, under elevated temperatures, possibly due to increased metabolic investment, specifically while maintaining energetically-costly shell calcification under adverse conditions. Quantifying how anticipated shifts in environmental conditions may affect prey vulnerability in calcifying organisms is vital to understanding potential climate-driven shifts in community ecology within intertidal habitats.