Physiological implications of ocean acidification for marine fish: emerging patterns and new insights

Abstract

Ocean acidification (OA) is an impending environmental stress facing all marine life, and as such has been a topic of intense research interest in recent years. Numerous detrimental effects have been documented in marine fish, ranging from reduced mortality to neurosensory impairment, and the prevailing opinions state that these effects are largely the downstream consequences of altered blood carbon dioxide chemistry caused by respiratory acid-base disturbances. While the respiratory acid-base disturbances are consistent responses to OA across tested fish species, it is becoming increasingly clear that there is wide variability in the degree of downstream impairments between species. This can also be extended to intraspecies variability, whereby some individuals have tolerant physiological traits, while others succumb to the effects of OA. This review will synthesize relevant literature on marine fish to highlight consistent trends of impairment, as well as observed interspecies variability in the responses to OA, and the potential routes of physiological acclimation. In all cases, whole animal responses are linked to demonstrated or proposed physiological impairments. Major topics of focus include: (1) respiratory acid-base disturbances; (2) early life survival and growth; (3) the implications for metabolic performance, activity, and reproduction; and (4) emerging physiological theories pertaining to neurosensory impairment and the role of GABA receptors. Particular emphasis is placed on the importance of understanding the underlying physiological traits that confer inter- and intraspecies tolerance, as the abundance of these traits will decide the long-term outlook of marine fish.

Early Development of the Threespine Stickleback in Relation to Water pH

“…The juveniles reside in caves with high night-time fluctuations in CO 2 ; the young experience natural fluctuation in pH as photosynthesis is increasing during the day and respiration during the night in the reef matrix. Melzner et al (2011) showed that hypercapnia increases during food limitation, suggesting that some responses measured in laboratory experiments during CO 2 stress can be masked if fish are fed ad libitum (Esbaugh, 2017), as is the case in the present work.…”

“…Recently, Esbaugh (2017) reviewed the observed effects of elevated CO 2 on early life stage survival in a variety of marine teleost species. The responses ranged from high (Baumann et al, 2012) to low mortality (Lonthair et al, 2017), or even no observed changes in high CO 2 conditions (Frommel et al, 2013).…”

“…The current ocean acidification and change in the equilibrium of the seawater chemistry are so rapid that they will most likely lead to major changes in marine ecosystems and impact marine life (Pelejero et al, 2010). For more than a decade, the biological responses of phytoplankton (Lohbeck et al, 2012), foraminifera (Bijma et al, 2002), pteropods (Bednaršek et al, 2017), bivalves (Jansson et al, 2013), crustaceans (Vehmaa et al, 2013) and fish (reviewed by Clements and Hunt, 2015;Esbaugh, 2017) have been studied under different ocean acidification scenarios. Research suggests that mobile species, such as crustaceans and fish are less sensitive to acidification than sessile species, possibly due to their high metabolic rates and active regulation of internal pH (reviewed by Kroeker et al, 2013).…”

Living in a high CO2 world: a global meta‐analysis shows multiple trait‐mediated fish responses to ocean acidification

“…We documented varying adverse responses when examining specific fish traits. These are important results as, in addition to identifying the direction and quantifying the magnitude of these responses, we were able to show that, if fish traits are not taken into account, consequences of ocean acidification on marine animals might not be detected as in some cases species‐specific responses could be antagonistic (Esbaugh ). Our study adds on previous evidence showing that larvae are the most sensitive life stage (Melzner et al.…”

Effects of ocean acidification on salinity tolerance and seawater growth of Atlantic salmon Salmo salar smolts

“…Since there was no difference in cortisol between the OA and control groups, cortisol is unlikely to be involved in the higher growth seen in the 1010 μatm CO 2 exposed fish. Haematocrit of S. salar smolts was also unaffected by OA conditions, consistent with previous studies on marine teleosts (Esbaugh, ) and indicative that at least this variable of respiratory physiology is consistently unaltered by OA conditions. It would be of value to measure other metabolic parameters associated with the transition to seawater under OA conditions.…”