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

Abstract

Environmentally-induced changes in fitness are mediated by direct effects on physiology and behaviour, which are tightly linked. We investigated how predicted ocean warming (OW) and acidification (OA) affect key ecological behaviours (locomotion speed and foraging success) and metabolic rate of a keystone marine mollusc, the sea hare Stylocheilus striatus, a specialist grazer of the toxic cyanobacterium Lyngbya majuscula. We acclimated sea hares to OW and/or OA across three developmental stages (metamorphic, juvenile, and adult) or as adults only, and compare these to sea hares maintained under current-day conditions. Generally, locomotion speed and time to locate food were reduced ~1.5-to 2-fold when the stressors (OW or OA) were experienced in isolation, but reduced ~3-fold when combined. Decision-making was also severely altered, with correct foraging choice nearly 40% lower under combined stressors. Metabolic rate appeared to acclimate to the stressors in isolation, but was significantly elevated under combined stressors. Overall, sea hares that developed under OW and/or OA exhibited a less severe impact, indicating beneficial phenotypic plasticity. Reduced foraging success coupled with increased metabolic demands may impact fitness in this species and highlight potentially large ecological consequences under unabated OW and OA, namely in regulating toxic cyanobacteria blooms on coral reefs. Rising atmospheric carbon dioxide (CO 2) levels may lead to continued and accelerated global warming over the coming century 1. The resulting elevated sea surface temperature (SST) (i.e. ocean warming; OW) is accompanied by increased partial pressure of CO 2 (pCO 2) in the ocean, thus rapidly changing the marine environment by increasing acidity (i.e. ocean acidification; OA) at unprecedented rates 2. The Intergovernmental Panel on Climate Change (IPCC) has indicated that, by year 2100, global mean SST will increase by 2-4 °C and seawater pH decrease by 0.14-0.43 units 3 , with concomitant effects on marine ecosystems. Marine invertebrates are critical

Marine heatwaves of different magnitudes have contrasting effects on herbivore behaviour

“…While behavioural effects of MHW magnitude were apparent, survival and oxygen consumption rates were largely unaffected by MHW magnitude both in the heatwave and recovery periods, indicating the likelihood of continued species survival and physiological functioning after short-term events such as those simulated here. The lack of change in these traits under different temperatures may reflect an adaptation of our experimental animals to a fluctuating thermal environment, as previously found for other mollusc species 2 , 23 . Further, decoupling of behaviour-physiology thermal performance is a recognised response of organisms to stress (e.g., 25 ).…”

Linking observed changes in pelagic catches to temperature and oxygen in the Eastern Tropical Pacific

“…Large pelagic fishes caught in the Eastern Tropical Pacific warm pool (Guatemala, El Salvador, Nicaragua, Costa Rica) had a small scope between oxygen demand and supply, indicating warming may be affecting the physiological performance of species via a higher oxygen demand. Species in these warmer EEZs may be particularly vulnerable to additional factors that cause physiological stress and limit organisms' aerobic scope, such as ocean acidification, overfishing and declining habitat quality (Horwitz et al, 2020; Laubenstein et al, 2018). Consequently, this region may be less resilient to El Niño events that can drive temperatures above the physiological tolerance limits of many species (Smale et al, 2019).…”

Marine heatwaves of differing intensities lead to distinct patterns in seafloor functioning

“…This can lead to changes in activity and feeding choice (e.g. [ 16 , 17 ]). For example, Lohrer et al .…”

“…This can lead to changes in activity and feeding choice (e.g. [16,17]). For example, Lohrer et al [18] showed that warming in McMurdo Sound, Antarctica, during 2010-2017 resulted in higher sediment primary production, which increased sediment metabolism and shifted benthic community composition.…”