Inducible defenses in an estuarine bivalve do not alter predator handling times and are not affected by climate change

Abstract

Mussels use their shells for protection which they can thicken or grow in response to predator cues, commonly referred to as an inducible defense. Oceans are experiencing elevated pCO2 due to climate change. Elevated pCO2 can have negative effects on bivalve morphology and physiology, but we are still learning about the consequences of these effects on predator-prey interactions, a key motivation of this study. Using a 4 wk (short-term) laboratory experiment, we orthogonally manipulated 2 levels of pCO2 (ambient or elevated to predicted future conditions that mimicked diel variability) and 2 levels of predator presence (absent or present) of blue crabs Callinectes sapidus to determine their effects on the morphology and predator handling times on southern ribbed mussels Geukensia granosissima. Experimental results indicated that shell length and width increased in mussels in response to the predator cues, and these inducible defenses were not affected by elevated pCO2. Unexpectedly, mussels exposed to elevated pCO2 exhibited greater growth in shell depth independent of the predator treatment, resulting in shells with rounder shapes. These effects on mussel morphometrics did not affect average crab handling times, but mussels exposed to the presence of a predator under elevated pCO2 conditions had highly variable handling times. This work highlights the complexity of animal physiology, morphology, and interspecific interactions on predator-prey relationships in a changing ocean.