Effects of high temperatures on threatened estuarine fishes during periods of extreme drought

Abstract

Climate change and associated increases in water temperatures may impact physiological performance in ectotherms and exacerbate endangered species declines. We used an integrative approach to assess the impact of elevated water temperature on two fishes of immediate conservation concern in a large estuary system, the threatened longfin smelt (Spirinchus thaleichthys) and endangered delta smelt (Hypomesus transpacificus). Abundances have reached record lows in California, USA, and these populations are at imminent risk of extirpation. California is currently impacted by a severe drought, resulting in high water temperatures, conditions that will become more common as a result of climate change. We exposed fish to environmentally relevant temperatures (14°C and 20°C) and used RNA sequencing to examine the transcriptome-wide responses to elevated water temperature in both species. Consistent with having a lower temperature tolerance, longfin smelt exhibited a pronounced cellular stress response, with an upregulation of heat shock proteins, after exposure to 20°C that was not observed in delta smelt. We detected an increase in metabolic rate in delta smelt at 20°C and increased expression of genes involved in metabolic processes and protein synthesis, patterns not observed in longfin smelt. Through examination of responses across multiple levels of biological organization, and by linking these responses to habitat distributions in the wild, we demonstrate that longfin smelt may be more susceptible than delta smelt to increases in temperatures, and they have little room to tolerate future warming in California. Understanding the species-specific physiological responses of sensitive species to environmental stressors is crucial for conservation efforts and managing aquatic systems globally.

Understanding imperfect detection in a San Francisco Estuary long‐term larval and juvenile fish monitoring programme

“…Although both smelt species seem to be associated with lower temperature, longfin smelt occupancy at higher temperatures is predicted to be lower relative to delta smelt at higher temperature (Figure ). This suggests that juvenile longfin smelt may be less tolerant of high temperatures than delta smelt, a result consistent with laboratory studies (Jeffries et al., ).…”

Unusual aerobic performance at high temperatures in juvenile Chinook salmon,Oncorhynchus tshawytscha

“…Moyle and Leidy, 1992; Moyle et al ., 2011; Quiñones and Moyle, 2014) and management becomes more crucial for population persistence, knowledge of thermal limits, optimal thermal ranges, and a mechanistic understanding of how key physiological processes, such as metabolic rate, change in response to environmental variables become more important (Beitinger et al ., 2000; Pörtner, 2001; Niklitschek and Secor, 2005; Horodysky et al ., 2015; Martin et al ., 2015; Jeffries et al ., 2016; Komoroske et al ., 2016). Therefore, our objective was to estimate the aerobic scope of juvenile Chinook salmon ( Oncorhynchus tshawytscha ) acclimated to two different rearing temperatures (15 or 19°C) and tested over a range of acute temperature changes (12–26°C).…”

Transcriptomic responses to environmental change in fishes: Insights from RNA sequencing

“…As with osmoregulatory stress, the effect of heat stress on metabolic processes varied among species (Table 1). Notably, metabolism was strongly upregulated in the heat-stressed catfish ) and delta smelt (Hypomesus transpacificus; Jeffries et al 2016), species known for their high thermal tolerance, whereas a lack of metabolic response was observed in P. borchgrevinki (Bilyk and Cheng 2014). Such evidence of contrasting responses to heat stress in cold-and warm-adapted fishes sheds light on how adaptive divergence can alter the contents of the genomic tool kits with which species can respond to contemporary thermal stress.…”