UC San Diego

The physiology, development, behavior and survival of the early life history stages

of marine fish are challenged by increasing carbon dioxide concentrations in the ocean,

known as ocean acidification. A widespread effect of elevated pCO2 on fish larvae is

increased otolith size. To understand the functional consequences of larger otoliths on the

vestibular system of fish larvae, Chapter 2 investigated the vestibulo-ocular reflex (VOR)

of white seabass (Atractoscion nobilis) larvae reared at 2500 μatm pCO2. The VOR is

an otolith-dependent response in fish that stabilizes vision during body movement. Larvae

reared at high pCO2 possessed saccular and utricular otoliths that were 17% and 38% larger in size. Despite the increased otolith size, the gain of the VOR, which describes the

ratio of eye to head amplitude, was not statistically different between treatment (0.39 +-

0.05, n = 28) and control (0.30 +- 0.03, n = 20) larvae.

Fish spawning habitat and survival of offspring are greatly influenced by environmental

conditions. In Chapter 3, the effects of pCO2 on the spawning habitat of Anchoveta

(Engraulis ringens) and mortality of eggs and early stage larvae were investigated. Eggs,

larvae, and oceanographic data, were collected across an onshore-offshore gradient in pCO2 that ranged from 167-1392 μatm. pCO2 was statistically significant in explaining egg presence. The abundance of eggs and relative absence of larvae at high pCO2 suggests that Anchoveta preferentially spawned at high pCO2 (>800 μatm) and that these eggs had lower survival.

Fish living in a high-pCO2 world may have to spend more energy on acid-base

balance. Chapter 4 explores the effects of elevated pCO2 on the oxygen consumption rate

(OCR) and abundance of Na+-K+-ATPase (NKA) proteins in white seabass larvae reared at 2000 μatm pCO2. OCR, a proxy for aerobic metabolic rate, did not differ significantly

between larvae reared at present-day (0.18 +- 0.03 μL O2 individual-1 h-1, n = 80) and future (0.19 +- 0.03 μL O2 individual-1 h-1, n = 80) pCO2. Consistent with this finding, the relative abundance of NKA proteins that fuel important ion exchangers for acid-base balance did not differ between control and treatment larvae in Western blot and immunohistochemistry analyses. Mass and length were also unchanged at high pCO2, suggesting larvae were physiologically robust in these variables to ocean acidification conditions.