Cascading effects of thermally-induced anemone bleaching on associated anemonefish hormonal stress response and reproduction

Abstract

Organisms can behaviorally, physiologically, and morphologically adjust to environmental variation via integrative hormonal mechanisms, ultimately allowing animals to cope with environmental change. The stress response to environmental and social changes commonly promotes survival at the expense of reproduction. However, despite climate change impacts on population declines and diversity loss, few studies have attributed hormonal stress responses, or their regulatory effects, to climate change in the wild. Here, we report hormonal and fitness responses of individual wild fish to a recent large-scale sea warming event that caused widespread bleaching on coral reefs. This 14-month monitoring study shows a strong correlation between anemone bleaching (zooxanthellae loss), anemonefish stress response, and reproductive hormones that decreased fecundity by 73%. These findings suggest that hormone stress responses play a crucial role in changes to population demography following climate change and plasticity in hormonal responsiveness may be a key mechanism enabling individual acclimation to climate change.

Anemonefish facilitate bleaching recovery in a host sea anemone

“…The total chlorophyll was considerably higher in the sea anemones occupied by fish by the end of our experiment. Although horizontal endosymbiont repopulation was not possible due to filtered and UV sterilised seawater used in this experiment, our findings are comparable to the rates observed for H. magnifica hosting A. chrysopterus in Moorea, French Polynesia 38 . In contrast, only partial recovery was recorded 2–4 months following bleaching of occupied Stichodactyla haddoni and H. crispa in Bootless Bay, Papua New Guinea, and E. quadricolor remained bleached after 6 months at Lizard Island, Australia, despite hosting anemonefish 32 , 36 .…”

“…Depending on the severity, sublethal impacts can occur to the sea anemones, such as oxidative stress and decreased size 33 , 35 . Bleached sea anemone habitat has cascading consequences for anemonefishes, including decreased fecundity, increased metabolic demand, increased stress hormones, and vulnerability to predators due to behavioural changes 36 – 38 .…”

Near-future ocean warming and acidification alter foraging behaviour, locomotion, and metabolic rate in a keystone marine mollusc

“…This may reflect metabolic adaptation to a fluctuating temperature regime in intertidal and shallow water habitats as previously found in other molluscs 62 , and similar fluctuating conditions are found in Mo' orea (temperatures recorded from 2007-2016: min = 25.1 °C in October 2015; max = 30.8 °C in April 2016; see ref. 63 ).…”

Cophylogenetic analysis of the relationship between anemonefish Amphiprion (Perciformes: Pomacentridae) and their symbiotic host anemones (Anthozoa: Actiniaria)

“…In contrast, low toxicity anemones do not appear to confer protective benefits to the fish. For example, fish associated with bleached host anemones have shown lower fitness in terms of decreased fecundity and spawning frequency (Saenz-Agudelo et al 2011;Beldade et al 2017). Fish also have increased oxygen consumption and metabolic rates when residing in bleached host anemones (Norin et al 2018).…”