Biological responses of sharks to ocean acidification

Abstract

Sharks play a key role in the structure of marine food webs, but are facing major threats due to overfishing and habitat degradation. Although sharks are also assumed to be at relatively high risk from climate change due to a low intrinsic rate of population growth and slow rates of evolution, ocean acidification (OA) has not, until recently, been considered a direct threat. New studies have been evaluating the potential effects of end-of-century elevated CO 2 levels on sharks and their relatives' early development, physiology and behaviour. Here, we review those findings and use a meta-analysis approach to quantify the overall direction and magnitude of biological responses to OA in the species of sharks that have been investigated to date. While embryo survival and development time are mostly unaffected by elevated CO 2 , there are clear effects on body condition, growth, aerobic potential and behaviour (e.g. lateralization, hunting and prey detection). Furthermore, studies to date suggest that the effects of OA could be as substantial as those due to warming in some species. A major limitation is that all past studies have involved relatively sedentary, benthic sharks that are capable of buccal ventilation—no studies have investigated pelagic sharks that depend on ram ventilation. Future research should focus on species with different life strategies (e.g. pelagic, ram ventilators), climate zones (e.g. polar regions), habitats (e.g. open ocean), and distinct phases of ontogeny in order to fully predict how OA and climate change will impact higher-order predators and therefore marine ecosystem dynamics.

A triple trophic boost: How carbon emissions indirectly change a marine food chain

“…How ocean communities respond to CO 2 enrichment will not only depend on how it affects species directly, but, more importantly, how it affects species indirectly (Wootton, ). Numerous laboratory experiments suggest that CO 2 enrichment, and the resultant changes in seawater chemistry, will have a direct negative impact on marine species (e.g., herbivores, Parker, Ross, & O'connor, Pörtner, Scanes, Wright, , apex predators, Rosa, Rummer, & Munday, ). Yet, these experiments, do not incorporate indirect effects and the ecological and evolutionary complexity which can buffer or exacerbate the effects of change (e.g., Goldenberg et al, ).…”

Port Jackson Shark Growth Is Sensitive to Temperature Change

“…While this study explored the relationship between temperature and shark growth in isolation, experiments demonstrate that multiple parameters interact to affect shark growth; e.g., temperature and ocean acidification (Di Santo, 2015;Pistevos et al, 2015). Therefore, as species approach physiological temperature thresholds, growth will likely also be influenced by synergistic ocean acidification effects (Pistevos et al, 2015) and shifts in other biological and phenotypic processes; e.g., metabolism, reproductive timing, and/or juvenile survival (e.g., Rosa et al, 2014;Di Santo, 2015Rosa et al, 2017). Given the logistical challenges of working with elasmobranchs in situ, few of these biological parameters are captured and thus, linkages between changing environmental conditions and biological processes are not well understood.…”

Aggressive communication in aquatic environments

“…Both studies highlight that chemical pollutants bear the potential to interfere with the natural agonistic behaviours of aquatic species. Furthermore, increased atmospheric CO2 levels lead to ocean acidification and increases in water temperature, and both have been shown to influence animal behaviour and communication (Briffa, de la Haye, & Munday, ; Cattano, Claudet, Domenici, & Milazzo, ; Clements & Hunt, ; Rosa, Rummer, & Munday, ). However, thus far, knowledge on the influence of increasing CO2 levels on aggressive behaviour is scarce.…”