Physiological impacts of elevated carbon dioxide and ocean acidification on fish

Abstract

Most fish studied to date efficiently compensate for a hypercapnic acid-base disturbance; however, many recent studies examining the effects of ocean acidification on fish have documented impacts at CO2 levels predicted to occur before the end of this century. Notable impacts on neurosensory and behavioral endpoints, otolith growth, mitochondrial function, and metabolic rate demonstrate an unexpected sensitivity to current-day and near-future CO2 levels. Most explanations for these effects seem to center on increases in Pco2 and HCO3- that occur in the body during pH compensation for acid-base balance; however, few studies have measured these parameters at environmentally relevant CO2 levels or directly related them to reported negative endpoints. This compensatory response is well documented, but noted variation in dynamic regulation of acid-base transport pathways across species, exposure levels, and exposure duration suggests that multiple strategies may be utilized to cope with hypercapnia. Understanding this regulation and changes in ion gradients in extracellular and intracellular compartments during CO2 exposure could provide a basis for predicting sensitivity and explaining interspecies variation. Based on analysis of the existing literature, the present review presents a clear message that ocean acidification may cause significant effects on fish across multiple physiological systems, suggesting that pH compensation does not necessarily confer tolerance as downstream consequences and tradeoffs occur. It remains difficult to assess if acclimation responses during abrupt CO2 exposures will translate to fitness impacts over longer timescales. Nonetheless, identifying mechanisms and processes that may be subject to selective pressure could be one of many important components of assessing adaptive capacity.

Otolith size and the vestibulo-ocular reflex of larvae of white seabass Atractoscion nobilis at high pCO2

“…Behavioral effects may not manifest until the later larval stages, after the development of gills and acid−base regulation. The many negative effects of elevated pCO 2 on the sensory systems and behavior of tropical reef fish larvae has been attributed to the disruption of the GABA and GABA A neurotransmitter and receptors (Nilsson et al 2012, Hamilton et al 2014, Heuer & Grosell 2014. The resiliency of the VOR to elevated pCO 2 despite the role of GABA as the primary inhibitory neurotransmitter (Spencer & Baker 1992) suggests that white seabass larvae, and perhaps the larvae of other fish, may utilize Na Subtle changes in the VOR were discernible in our experiments.…”

“…The effects of OA on marine fish are diverse (see review by Heuer & Grosell 2014), variable and most severe during the early life-history stages (Rombough 1988, Tseng et al 2013. The dynamics of these stages are critical in determining future population size and recruitment success (Houde 1997).…”

Novel and potential physiological roles of vacuolar-type H+-ATPase in marine organisms

“…A few studies have reported downregulation of VHA mRNA in gills from fish exposed to OA (e.g. Esbaugh et al, 2012;Tseng et al, 2013), which, as pointed out in a recent review (Heuer and Grosell, 2014), was most likely due to downregulation of branchial HCO 3 − secretion to seawater and H + reabsorption into the blood.…”

Acid–base physiology, neurobiology and behaviour in relation to CO2-induced ocean acidification

“…This has also been referred to as a 'switch' in GABA A R action in other studies (see Tyzio et al, 2006). Nilsson et al (2012) sparked a flurry of studies in which gabazine was applied to a variety of animals that were exposed to elevated CO 2 and subjected to diverse tests ( gabazine reversed the effects of elevated CO 2 (reviewed in Heuer and Grosell, 2014;Nilsson and Lefevre, 2016). One of those studies using gabazine was our own ; working on the California splitnose rockfish (Sebastes diploproa), we found increased anxiety-like behaviour in fish exposed to ∼1100 µatm CO 2 ( pH 7.75) for 7 days and subjected to the light/dark preference test .…”