Exoskeletal predator defenses of juvenile California spiny lobsters (Panulirus interruptus) are affected by fluctuating ocean acidification

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.