In hot water: sustained ocean warming reduces survival of a low-latitude coral reef fish

The influence of thermal extremes on coral reef fish behaviour in the Persian Gulf

“…Individuals were also observed to shift from a planktonic-based diet to a mixed planktonic and benthic diet during the Gulf’s extreme summer season. Our results show considerable scope for behavioural and trophic plasticity in P. trichrourus , which may allow this species to cope with seasonal variance in environmental conditions, including those that are above the mortality thresholds (Nilsson et al 2009; Munday et al 2009; Rummer et al 2014; Rodgers et al 2018) and below the optimum temperature of Indo-Pacific reef fish (Eme and Bennett 2008; Figueira and Booth 2010; Nakamura et al 2013).…”

“…The Gulf experiences the highest annual change in water temperature for coral reefs globally (winter: <15°C, summer: >35°C), with fishes persisting for several months in conditions that would be considered lethal to reef fishes in other parts of the world (Riegl and Purkis 2012; Vaughan et al 2019). Summer temperatures in the Gulf exceed the upper thermal limits of most tropical reef fishes (Nilsson et al 2009; Munday et al 2009; Rummer et al 2014; Rodgers et al 2018), while winter temperatures are well below the optimum temperatures reported for reef fish elsewhere in the Indo-Pacific (Eme and Bennett 2008; Figueira and Booth 2010; Nakamura et al 2013). Indeed, contemporary summer water temperatures in the Gulf are comparable to those predicted for tropical oceans at the end of this century (Riegl and Purkis 2012; IPCC 2014), while winter conditions can be so severe as to induce cold water coral bleaching (Shinn 1976; Coles et al 1991).…”

“…However, such strategies may not be sufficient to sustain prolonged periods (i.e. months) of extreme temperature (Rummer et al 2014; Rodgers et al 2018). For example, reductions in food intake and quality, coupled with low aerobic scope under extreme temperatures, can disrupt an ectothermic organism’s energy balance, with substantially less energy available for long-term maintenance, growth and reproduction (Gillooly et al 2001; Pörtner et al 2010; Neuheimer et al 2011), impacting individual fitness and potentially survival (Chase et al 2018).…”

“…The Gulf’s average SST is increasing twice as fast as the global average (Al-Rashidi et al 2009), with predictions of further increases of 0.5°C – 1.4°C by 2050, associated with hot salt brine discharge derived from local desalinisation plants (AGEDI 2016; Vaughan et al 2019). As P. trichrourus populations live for five months of the year above their predicted thermal optimum (Jun–Oct, mean SST >30°C) (Kaschner et al 2016), of which two months encompass temperatures above the mortality threshold of low latitude Indo-Pacific damselfish (July and August, mean SST ≥ 33°C) (Nilsson et al 2009; Munday et al 2009; Rummer et al 2014; Rodgers et al, 2018), Gulf populations may already be living close to their upper thermal limits; further increases in temperature are expected to pose a serious threat to population persistence. In addition, P. trichrourus populations in the Gulf are already considered endangered, associated with a fragmented distribution and strong dependence to diminishing coral habitat resources (Buchanan et al 2016; 2019).…”

“…Indeed, in addition to susceptibility to habitat loss (Pratchett et al 2018), coral reef fishes are also directly threatened by ocean warming due to their narrow thermal tolerance range (Tewksbury et al 2008; Sunday et al 2011). Experimental evidence suggests that coral reef fish may already be living close to their upper thermal limits (Rummer et al 2014) and that population structure may be directly impacted by increased variability in water temperature (Folguera et al 2011; Pratchett et al 2015; Rodgers et al 2018).…”