Characterization of Marine Teleost Ionocytes in the Gill, Skin, and Inner Ear Epithelia and their Implications for Ocean Acidification

Ionocytes are specialized epithelial cells that excrete or absorb ions across an epithelium to regulate ionic, osmotic and acid-base levels in internal fluids. These ionocytes perform a wide range of functions (e.g. osmoregulation, pH regulation, and calcification) across various organs (e.g. gill, skin, inner ear). As atmospheric CO2 levels rise and oceanic pH levels fall, teleosts may increase their investment on ionocytes to survive in future ocean conditions. But generally speaking, the gill, skin, and inner ear ionocytes within marine teleost are not well characterized. This dissertation contains research spanning five southern Californian teleosts: the Blacksmith Chromis punctipinnis, the Yellowfin Tuna Thunnus albacares, the White Seabass Atractoscion nobilis, the Pacific Mackerel Scomber japonicus, and the Splitnose Rockfish Sebastes diploproa. In Chapter II, I investigated the individual and group behavioral responses of the Blacksmith, a temperate damselfish, after exposure to CO2-induced low-pH conditions. In Chapter III, I describe a novel technique used to quantify skin ionocytes in larval fishes. In Chapter IV, I applied the Chapter III’s technique to document developmental patterns in the skin and gill ionocytes of larval Yellowfin Tuna. In Chapter V, I investigated larval White Seabass response to hypercapnia by monitoring oxygen consumption rate and quantifying ionocyte abundance and relative ionocyte area across development. In Chapter VI, I characterized two types of inner ear ionocytes responsible for otolith calcification in the Pacific Mackerel. In Chapter VII, I investigated whether future CO2 /pH conditions would affect the gill and inner ear ionocytes of Splitnose Rockfish. Altogether, this work across the multiple teleosts demonstrates that ionocytes 1) have the plasticity to respond to external pH stress, 2) are sufficient to maintain internal homeostasis despite significant differences in CO2/pH levels, and 3) differ greatly in protein, morphology, and function depending on the tissue in question