We examined the response of multiple structures used for predator defense in the California spiny lobster, Panulirus interruptus, to a series of ocean acidification-like conditions. Lobsters were collected by modified commercial traps offshore La Jolla, CA (in the area around 32.8534193, -117.2687516) in October 2016 and held at ambient conditions (pH 7.97, 16.5°C) before exposure to stable or diurnally fluctuating reduced pH conditions established by bubbling CO2 and as measured using best practices (ambient pH/stable, 7.97, 16.5°C; reduced pH/stable 7.67, 16.6°C; reduced pH with low fluctuations, 7.67 ± 0.05, 16.4°C; reduced pH with high fluctuations, 7.67 ± 0.10, 16.4°C). After three months, we examined the composition (wt. % and concentration of Ca and Mg), ultrastructure (cuticle and thickness of exocuticle ), and mechanical properties (hardness and stiffness). Layer thickness (µm) and wt. % mineralization were determined using a scanning electron microscope (SEM) equipped with electron-dispersive x-ray spectroscopy (EDX). Concentration of elements (µmol/mg sample) was measured using inductively-coupled x-ray spectrometry (ICP-MS), while material properties (GPa) were measured using a nanoindenter with a Berkovitch diamond tip.