Effect of a fluctuating thermal regime on adult and larval reef corals

Abstract

We compared responses of adults and larvae of the brooding corals Pocillopora damicornis and Seriatopora hystrix to 12-h exposures to constant temperature treatments (211C, 281C, or 301C) and a treatment in which temperature fluctuated from 281 to 211C, simulating daily temperature variation generated by tidally driven upwelling in their natural habitat (Nanwan Bay, southern Taiwan). In all treatments, the maximum dark-adapted quantum yield of photosystem II (F V /F M ) of the larvae was B49% lower than that of adult corals; F V /F M in the larvae also differed among temperature treatments, with the highest values in the fluctuating treatment. These results show that the larvae of at least P. damicornis are more sensitive to temperature than adults, and suggest that larvae are physiologically well suited to fluctuating temperature regimes. To assess whether the timing of larval release affected their performance, larvae of P. damicornis were compared among release days within a single reproductive event. Groups of larvae released on nine consecutive days differed significantly in size, Symbiodinium content, and F V /F M . This demonstration of functional differences among coral larvae that are released on different dates within a single reproductive event creates the potential for advantages to accrue from the coincidence of larval phenotypes with temporally varying conditions. Adult colonies may experience selective advantages by producing broods of functionally variable larvae, in order to match extreme phenotypes to unusual environmental conditions.

Large-amplitude internal waves sustain coral health during thermal stress

“…Most studies, however, concentrate on the influence of increased temperatures (e.g., Brown et al 2000;Oliver and Palumbi 2011;Barshis et al 2013). Yet studies on corals influenced by cold water fluctuations have indicated that these corals exhibit enhanced heat resistance due to supposed acclimations to recurring stress (Putnam et al 2010;Mayfield et al 2013). This study concords with this hypothesis, since LAIW-exposed corals used to large short-term variations in temperature were less affected by variations from longterm average temperatures than sheltered corals (see also McClanahan et al 2007a;Oliver and Palumbi 2011).…”

Impact of diurnal temperature fluctuations on larval settlement and growth of the reef coral <i>Pocillopora damicornis</i>

“…Q m , an indicator of the excitation pressure over PSII, was reduced in fluctuating treatments, reflecting a stronger competitiveness of photochemical process for reaction centers over non-photochemical quenching (Iglesias-Prieto et al, 2004). The higher F /F m and lowered Q m under fluctuating conditions suggest that the diel temperature oscillations could relieve heat stress on corals and corroborate previous findings that temperature fluctuations are favorable to the photo-physiology of corals (Mayfield et al, 2012;Putnam et al, 2010). The positive effect of exposure to fluctuating temperatures on these photophysiological metrics may be associated with the cooling overnight and upregulation of the genes related to photosynthesis (Mayfield et al, 2012).…”

“…For instance, the photo-physiology in larval and adult pocilloporid corals is more adapted to fluctuating temperatures (Putnam et al, 2010;Mayfield et al, 2012). Conversely, significant reductions in photochemical efficiency, symbiont density and aerobic respiration were found in corals exposed to fluctuating temperatures compared to those in constant temperatures Edmunds, 2008, 2011).…”

“…Successful larval settlement, post-settlement survival and growth are of paramount importance to population persistence as well as the recovery of degraded reefs (Ritson-Williams et al, 2009;Penin and Adjeroud, 2013). Mounting evidence suggests that ocean warming poses a serious threat to these early processes (reviewed in Keshavmurthy et al, 2014), but most previous experiments utilized steady temperature treatments, neglecting the temporal variations of in situ temperature (but see Putnam et al, 2010). To date, there is a paucity of knowledge regarding the influence of dynamic temperatures on these crucial early stages of reef corals.…”

“…These studies have demonstrated that temperature fluctuations can either speed up or retard early development and growth, depending upon the mean temperatures and amplitude of the fluctuations. However, few studies have explored this thermodynamic effect on corals which routinely experience temperature oscillations in nature (e.g., Putnam et al, 2010;Mayfield et al, 2012).…”