Life on the edge: thermal optima for aerobic scope of equatorial reef fishes are close to current day temperatures

Abstract

Equatorial populations of marine species are predicted to be most impacted by global warming because they could be adapted to a narrow range of temperatures in their local environment. We investigated the thermal range at which aerobic metabolic performance is optimum in equatorial populations of coral reef fish in northern Papua New Guinea. Four species of damsel fishes and two species of cardinal fishes were held for 14d at 29, 31, 33, and 34°C, which incorporated their existing thermal range (29–31°C) as well as projected increases in ocean surface temperatures of up to 3°C by the end of this century. Resting and maximum oxygen consumption rates were measured for each species at each temperature and used to calculate the thermal reaction norm of aerobic scope. Our results indicate that one of the six species, Chromisatripectoralis, is already living above its thermal optimum of 29°C. The other five species appeared to be living close to their thermal optima (approximately 31°C). Aerobic scope was significantly reduced in all species, and approached zero for two species at 3°C above current-day temperatures. One species was unable to survive even short-term exposure to 34°C. Our results indicate that low-latitude reef fish populations are living close to their thermal optima and may be more sensitive to ocean warming than higher-latitude populations. Even relatively small temperature increases (2–3°C) could result in population declines and potentially redistribution of equatorial species to higher latitudes if adaptation cannot keep pace.

Molecular processes of transgenerational acclimation to a warming ocean

“…Reduced aerobic scope (the capacity for oxygen uptake above resting 45 metabolic rate) at higher temperatures can affect vital functions such as growth, swimming 46 performance, reproduction and competitive ability [10][11][12][13][14] . In reef fishes, aerobic scope declines at temperatures just a few degrees above the summer average, within the range projected 48 to occur as a result of climate change 9,12,15 . However, aerobic capacity can be fully restored 49 transgenerationally, when parents and their offspring both experience the same elevated 50 temperatures (transgenerational acclimation) 1 .…”

Communities and change in the anthropocene: understanding social-ecological vulnerability and planning adaptations to multiple interacting exposures

“…Increasing evidence suggests that many reef fish species are already living close to their thermal optima (Rummer et al 2014), meaning that that higher ocean temperatures will lead to reduced fitness or mortality (Munday et al 2008). Many marine species, ranging from turtles to phytoplankton, have altered their distributions in response to warming waters in order to maintain their optimal thermal range (Polovina et al 2008;Pike 2014).…”

DIVING IN A WARMING WORLD: Thermal constraints on the diving capacity of estuarine crocodiles (Crocodylus porosus)

“…Ectotherm performance is optimised within a limited range of body temperatures (i.e. thermal performance breadth) and ongoing climate warming will likely drive temperatures beyond sustainable limits (Rummer et al, 2014). Body temperatures surpassing thermal performance optima are generally accompanied by a marked decline in fitnessrelated traits such as locomotor capacity (Johansen and Jones, 2011), developmental rates/growth (McLeod et al, 2013), immune competence (Yu et al, 2009) and survival (Rohr and Palmer, 2013).…”

“…A narrowed aerobic scope is thought to translate into a reduced capacity for activities including growth, movement, digestion and reproduction (Pörtner, 2002), and the thermal effects on individuals may scale up to affect population and community dynamics (Pörtner and Peck, 2010). A narrowed aerobic scope at high temperatures has been demonstrated in a number of tropical ectotherms Johansen and Jones, 2011;Rummer et al, 2014); however the OCLTT hypothesis is not universal Ern et al, 2014;Norin et al, 2014;Ern et al, 2015;Ern et al, 2016). Many ectotherms experience compromised performance at temperatures below those affecting aerobic scope (Norin et al, 2014), suggesting the mechanistic explanation may be multi-faceted and thus remains unresolved in many taxa.…”

“…For example, AAS can narrow at thermal extremes Nilsson et al, 2009;Johansen and Jones., 2011;Rummer et al, 2014), continually increase with rising temperature up to lethal limits (Norin et al, 2014), or be thermally independent (Ern et al, 2014;Verhille et al, 2016;Poletto et al, 2017). Likewise, the thermal plasticity of metabolism can differ within a species depending on level of assessment (i.e.…”