Integrity of crustacean predator defenses under ocean acidification and warming conditions
Crustaceans are a diverse group of species, but all rely on an exoskeleton that is shed and formed anew throughout their lifetime. Exoskeletons perform a wide range of functions, sometimes acting as armor, a means to produce sound, a tool to crush hard prey, or even a window to facilitate transparency. The exoskeleton and its functions, however, are likely vulnerable to ocean acidification and ocean warming, which may alter its composition and the energy allocated towards its production. I investigated the effects of these future ocean conditions on two southern Californian crustaceans, the California spiny lobster Panulirus interruptus and the grass shrimp Hippolyte californiensis, which rely on their exoskeleton for different predator defenses. P. interruptus is an iconic feature of southern California’s kelp forest ecosystem but also a potential prey item for many of its large predators. Spiny lobsters use their antennae, mandibles, carapace, and horns to avoid predation. Each of these structures is specialized for a certain defense, displaying differences in composition, structure, and material properties that allow the antennae, for example, to remain flexible to avoid breaking when pushing predators away while imbuing hardness in crushing structures like the mandible (Chapter 1). Juvenile lobsters exposed to ocean acidification-like conditions largely maintained their predator defenses, displaying some differences in the composition across the exoskeleton but no strong effects to defense functionality, including the non-exoskeletal defenses of detecting chemical cues and the tail-flip escape response (Chapter 3). Additionally, larval P. interruptus, exposed to both ocean acidification and warming conditions, grew slightly smaller in reduced pH but maintained their transparency in both conditions (Chapter 2). In contrast, H. californiensis resides in eelgrass meadows where a primary defense strategy is cryptic colouration, accomplished via a transparent exoskeleton with underlying pigment. When exposed to both ocean acidification and ocean warming-like conditions, shrimp maintained their transparency and did not respond negatively to either condition (Chapter 4). Together, this work on both species demonstrates that a diversity of predator defenses in temperate crustaceans, included those afforded by the exoskeleton, appear to be relatively resilient to both future ocean acidification and ocean warming conditions.