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.
Highlights
Predator−prey interactions are complex and can be affected by both biotic and abiotic conditions (Connell 1961, Hughes & Seed 1981, Blundon & Kennedy 1982, Kishida et al 2010, Gestoso et al 2015)
Elevated pCO2 and associated changes in water chemistry caused by ocean acidification can be detrimental to calcareous organisms since it causes dissolution of the current calcareous structure and disrupts the formation of new calcified material needed for inducible defenses
Under elevated pCO2 conditions, handling times were significantly more variable for mussels exposed to the presence of a predator than those in the control group
Summary
Predator−prey interactions are complex and can be affected by both biotic and abiotic conditions (Connell 1961, Hughes & Seed 1981, Blundon & Kennedy 1982, Kishida et al 2010, Gestoso et al 2015). Corals invested more energy for calcification to prevent decreased growth and skeletal density when exposed to elevated pCO2 (Hoegh-Guldberg et al 2007). As a consequence, they had less energy to heal wounds inflicted by corallivorous fishes, potentially leading to further population declines (Rice et al 2019). Despite the examples of negative effects of elevated pCO2 on some calcareous organisms, responses are equivocal, with evidence of both null effects and the ability to adapt to future ocean acidification conditions. Theoretical predictions and even empirical evidence for how future ocean conditions may affect predator−prey interactions often come from studies that maintain static environmental conditions of elevated pCO2, which may not fully capture the environmental and ecological reality for many organisms living in dynamic coastal habitats
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