Effects of estuarine acidification on predator–prey interactions

Abstract

Short-term experiments exposing calcifying organisms to acidification have revealed altered growth and strength of their exoskeletons. We tested the hypothesis that multi-generational exposure to sustained estuarine acidification from runoff from acid sulphate soils (ASS) would: (1) reduce the shell strength of sessile or relatively immobile wild benthic invertebrates and (2) as a consequence render these invertebrates that rely on armour for anti-predator defence more susceptible to generalist benthic predators. First, we compared the force required to break the exoskeletons of Saccostrea glomerata, Bembicium auratum, and Heloecius cordiformis between replicate south-east Australian mangrove forests close to (acidified) and away from (reference) major ASS outflow drains. Second, we assessed differences in the susceptibility of oysters from acidified and reference forests to predation by the generalist muricid gastropod Morula marginalba. Mollusc shells were significantly weaker at ASS-affected than at reference sites, but the strength of crab carapaces was not influenced by acidification. Oysters from acidified sites were consumed by M. marginalba at a faster rate than oysters from reference sites in choice and nochoice experiments because M. marginalba required less time to drill through weaker shells. Many other predators such as crabs are generalist feeders that consume prey at rates inversely proportional to their shell strength. Hence, in the absence of effects of acidification on the ability of these predators to consume prey, molluscs at acidified sites may also be more susceptible to other such predators. This study highlights how human stressors can rapidly alter predator-prey interactions that have evolved over many years.

Ocean acidification increases the vulnerability of native oysters to predation by invasive snails

“…Previous work documented that Sydney rock oysters from sites with strongly acidified waters (pH , 7.0, driven by the run-off of acid sulfate soils) were consumed more quickly by predatory snails than oysters from control sites [40]. Although shell thickness and growth were not quantified in this particular study, oysters from the acidified sites had weaker shells that were crushed more easily.…”

“…Predatory snails drill through the shell of their prey using their radula to slowly rasp away shell material that is softened by acidic secretions produced by a specialized boring organ. Radular teeth are chitinous, rather than calcareous, and thus the drilling apparatus itself may not be influenced by decreased pH [40]. Although snails in our study were acclimated to the two CO 2 levels for two weeks, they were not raised for extended periods under these conditions.…”

Environmental salinity modulates the effects of elevated CO2 levels on juvenile hard shell clams, Mercenaria mercenaria

“…However, it is likely that at low Ω Arg levels dissolution plays a major role in the mass balance of the shells. Shell erosion may become a major factor affecting survival of bivalves in brackish coastal and estuarine waters by weakening the shells and making them more vulnerable to predators (Green et al, 2009;Amaral et al, 2012).…”

Ocean acidification through the lens of ecological theory

“…Nonspecialist predators, by contrast, may expand their dietary breadth or exclude a formerly preferred prey if the abundance or energetic value per individual of the prey declines. OA may also increase prey vulnerability (e.g., through impaired shell integrity; Gaylord et al 2011, Amaral et al 2012; see also Doropoulos et al 2012), or elevate the energetic needs of predators; such changes could further modulate the balance of energy intake vs. expenditure. Similar considerations apply to metabolic shifts deriving from CO 2 -induced warming, which could combine with or offset consequences of OA.…”