Physiological and behavioural strategies of aquatic animals living in fluctuating environments

Abstract

Shallow or near-shore environments, such as ponds, estuaries and intertidal zones, are among the most physiologically challenging of all aquatic settings. Animals inhabiting these environments experience conditions that fluctuate markedly over relatively short temporal and spatial scales. Living in these habitats requires the ability to tolerate the physiological disturbances incurred by these environmental fluctuations. This tolerance is achieved through a suite of physiological and behavioural responses that allow animals to maintain homeostasis, including the ability to dynamically modulate their physiology through reversible phenotypic plasticity. However, maintaining the plasticity to adjust to some stresses in a dynamic environment may trade off with the capacity to deal with other stressors. This paper will explore studies on select fishes and invertebrates exposed to fluctuations in dissolved oxygen, salinity and pH. We assess the physiological mechanisms these species employ to achieve homeostasis, with a focus on the plasticity of their responses, and consider the resulting physiological trade-offs in function. Finally, we discuss additional factors that may influence organismal responses to fluctuating environments, such as the presence of multiple stressors, including parasites. We echo recent calls from experimental biologists to consider physiological responses to life in naturally fluctuating environments, not only because they are interesting in their own right but also because they can reveal mechanisms that may be crucial for living with increasing environmental instability as a consequence of climate change.

Ideas and perspectives. The fluctuating nature of oxygen shapes the ecology of aquatic habitats and their biogeochemical cycles: the aquatic oxyscape

“…In the design of experiments on the physiology of aquatic animals, oxygen is frequently treated as a fixed factor and maintained around the water saturation. However, organisms inhabiting aquatic environments experience ample diel oxygen fluctuations and are adapted to endure or respond to the experienced variation (Blewett et al, 2022;Morash et al, 2018). Oxygen may be systematically depleted at night and fully recovered during the day, changes that certainly have consequences on the tolerance to acute stressors such as hypoxia and warming.…”

Salinity stress in the black‐chinned tilapia Sarotherodon melanotheron

“…The use of fish transferred to different saline media and the subsequent mechanistic approaches using physiological, biochemical, and molecular analyses has brought major insights about the functionality of these exchanges with the external environment, especially at the gill level. Also, physiological tradeoffs, for example between osmoregulation and oxygen consumption (aka the osmorespiratory compromise), have been thoroughly studied (Blewett et al, 2022; Gilmour & Perry, 2018; Sardella & Brauner, 2007; Wood & Eom, 2021). For example, for the euryhaline Atlantic killifish ( Fundulus heteroclitus ), those acclimated to freshwater present, compared to those acclimated to brackish or marine conditions, a decrease in hypoxia tolerance associated with a reduced respiratory surface area in the gills and corresponding lower oxygen extraction efficiency (Giacomin et al, 2019).…”

Context-dependent antioxidant defense system (ADS)-based stress memory in response to recurrent environmental challenges in congeneric invasive species

“…Owing to global climate change and human activities, the increasing frequency and intensity of environmental changes pose an unprecedented threat to marine species, particularly sessile ones lacking behavioral choices to select optimal habitats (Hackerott et al 2021 ; Hughes et al 2018 ; Pickering et al 2013 ). In response to these environmental challenges, marine sessile organisms have to rapidly implement available strategies to mitigate the adverse effects of environmental stressors (Blewett et al 2022 ; Snell-Rood et al 2018 ; Somero 2022 ). Often, acute environmental challenges induce the redox imbalance and excessive accumulation of reactive oxygen species (ROS), leading to oxidative stresses and potential damages to organisms (Hofmann and Todgham 2010 ; Schieber and Chandel 2014 ; Sies 2019 ).…”