Chronic warm exposure impairs growth performance and reduces thermal safety margins in the common triplefin fish (Forsterygion lapillum)

Abstract

Intertidal fish species face gradual chronic changes in temperature and greater extremes of acute thermal exposure through climate-induced warming. As sea temperatures rise, it has been proposed that whole-animal performance will be impaired through oxygen and capacity limited thermal tolerance [OCLTT; reduced aerobic metabolic scope (MS)] and, on acute exposure to high temperatures, thermal safety margins may be reduced because of constrained acclimation capacity of upper thermal limits. Using the New Zealand triplefin fish (), this study addressed how performance in terms of growth and metabolism (MS) and upper thermal tolerance limits would be affected by chronic exposure to elevated temperature. Growth was measured in fish acclimated (12 weeks) to present and predicted future temperatures and metabolic rates were then determined in fish at acclimation temperatures and with acute thermal ramping. In agreement with the OCLTT hypothesis, chronic exposure to elevated temperature significantly reduced growth performance and MS. However, despite the prospect of impaired growth performance under warmer future summertime conditions, an annual growth model revealed that elevated temperatures may only shift the timing of high growth potential and not the overall annual growth rate. While the upper thermal tolerance (i.e. critical thermal maxima) increased with exposure to warmer temperatures and was associated with depressed metabolic rates during acute thermal ramping, upper thermal tolerance did not differ between present and predicted future summertime temperatures. This suggests that warming may progressively decrease thermal safety margins for hardy generalist species and could limit the available habitat range of intertidal populations.

Hyperoxia increases maximum oxygen consumption and aerobic scope of intertidal fish facing acutely high temperatures

“…1A). These temperatures are close to the upper thermal tolerance limit (U TL , 31.4°C) of F. lapillum (McArley et al, 2017), suggesting that, in at least some rock pools, this species would face temperatures close to its tolerable limit. While the exclusively intertidal triplefin [Bellapiscis medius (Günther 1861)] also appears to live close to its thermal limits (Hilton et al, 2008), the upper thermal limit of this species is unknown.…”

“…Although the MS of at least one triplefin species appears constrained at higher temperatures (McArley et al, 2017), these findings were determined under normoxia (100% of air saturation) and this is not always the setting within rock pools. Thermal ramping in rock pools generally occurs on hot sunny days when rates of algal photosynthesis are high and rock pool water can become hyperoxic at this time (see Fig.…”

“…ṀO 2,max (21°C) was taken as the highest ṀO 2 value recorded in any measurement cycle, which was in all cases the first cycle following exhaustive exercise. A 5 min exhaustive exercise protocol has previously been used to elicit ṀO 2,max values in triplefins (Khan et al, 2014a;McArley et al, 2017) and is suitable for assessment of ṀO 2,max in benthic species which will not continuously swim in a flume (Clark et al, 2013;Norin and Clark, 2016). The fish were then left undisturbed in respirometers for a period of ∼16 h under conditions of constant temperature (∼21°C) and water oxygen content (normoxia or hyperoxia), and ṀO 2 was measured in repeating 10 min cycles (∼100 individual ṀO 2 measurements).…”

“…These higher energetic demands are reflected in the profound influence of temperature on aerobic metabolism where rates of oxygen consumption typically increase exponentially under acute thermal ramping (e.g. Healy and Schulte, 2012b;McArley et al, 2017). The aerobic metabolic response to thermal ramping has been well characterised in fish but there is a lack of studies investigating the role of aerobic metabolism in thermal tolerance in intertidal fish species, which are routinely exposed to acute high temperatures.…”

Temperature-and sex-specific grazing rate of a tropical copepod Pseudodiaptomus annandalei to food availability: Implications for live feed in aquaculture

“…| 3869 (Angilletta, 2009;Angilletta, Niewiarowski, & Navas, 2002;Grote et al, 2015;Hirche, 1987). A strong reduction in the pellet production at 35°C may be a result of physiological depression, that has been observed in aquatic taxa in shallow water bodies exposed to extreme temperatures, for example, damselfly (Dinh, Janssens, & Stoks, 2016), intertidal species (Dong, Yu, Wang, & Dong, 2011;McArley, Hickey, & Herbert, 2017) and copepods (Low et al, 2018…”