Posts Tagged 'predation'

Context-dependent effects of ocean acidification on the interaction between a crab predator and its oyster prey

Ocean acidification affects the fitness of species in coastal and estuarine systems, although interactions among species may alleviate or elevate the responses. Acidification effects on predator-prey interactions were evaluated between the blue crab Callinectes sapidus and eastern oyster Crassostrea virginica. Animals were exposed to 5 pH treatments: (1) control (pH ~8.00), constant pH at (2) 7.10 and (3) 6.75, and cycling pH from (4) 7.10 and (5) 6.75 to ~8.00, respectively. Crab foraging behavior, oyster size, and their defensive response against crabs (i.e. shell thickening) were compared among pH treatments. Results showed that predation rates of crabs tended to decrease with pH and from cycling to constant conditions, though statistical differences were only found at the lowest pH value and when consuming the larger oysters offered. Also, crab interest in oysters decreased with decreasing pH. In contrast, prey handling times and foraging motivation triggered by an odor stimulus were not affected by pH. In oysters, size metrics decreased with pH and also from cycling to constant conditions. Additionally, shells were thicker in the presence of predators, although the defensive strategy of oysters was weakened at the lowest pH level examined. Results indicate that although impaired foraging behavior of blue crabs may compensate for the negative effects on oysters under extreme acidification conditions, net effects are difficult to predict depending on the conditions to which animals are exposed and the size and behavioral variables considered.

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The effect of ocean acidification on the escape behaviour of the sea star Parvulastra exigua to its sea star predator Meridiastra calcar

Ocean acidification (OA) driven by sea water uptake of anthropogenic atmospheric CO2 has broad deleterious effects on marine species including modified behavioural interactions such as between predators and prey. Predatory sea stars are key species in many marine ecosystems and often elicit defensive responses in their prey. This study investigated the effect of elevated CO2 on the escape response of the sea star Parvulastra exigua to its sea star predator Meridiastra calcar. In response to touch by M. calcarP. exigua exhibits a distinct fleeing response. The escape response of P. exigua with respect to velocity and escape trajectory was investigated after both species were acclimated in OA conditions. At pHT 7.6 and 7.8 velocity and escape trajectory of the fleeing response of P. exigua did not differ from that seen in the ambient treatment. However, there was a delay in the time that P. exigua started to flee with the initiation time being 2.8 times slower (10 vs 28 s) at pHT 7.6. This delay may increase the vulnerability of P. exigua to predation by M. calcar and have ecological effects with respect to the role of this species as an algal grazer on rocky shores of southeast Australia where these sea star species co-occur.

Continue reading ‘The effect of ocean acidification on the escape behaviour of the sea star Parvulastra exigua to its sea star predator Meridiastra calcar’

Marine gastropods at higher trophic level show stronger tolerance to ocean acidification

Climate change and anthropogenic activities are producing a range of new selection pressures, both abiotic and biotic, on marine organisms. Although it is known that climate change can differentially affect fitness-related traits at different trophic levels of the food web, it is not clear if different trophic levels will respond via phenotypic plasticity in the form of maintenance of phenotypes in the face of abiotic and biotic environmental stress similarly. To answer this question, we combined a mesocosm experiment (120 days) using a food web comprising three gastropod species from two trophic levels (grazers and meso-predators) and a meta-analysis including 38 studies to address whether different trophic levels exhibit similar phenotypic responses to abiotic and biotic variables. Abiotic (ocean acidification) and biotic (predation) stress significantly influenced body mass, shell mass, shell thickness and shell strength in both grazers and meso-predators in the mesocosm experiment, with the magnitude of OA effects greater on the meso-predator than the grazers; a result supported by the meta-analysis. In contrast, both mesocosm experiment and meta-analysis found that predation risk induced stronger responses in shell morphology for grazers compared to meso-predators. Together, our findings indicate that higher trophic level species are better able to maintain aspects of their phenotype under OA, suggesting that they may show greater tolerance to climate change effects in general, while lower trophic levels express higher levels of plastic inducible defences to maintain function when under threat of predation. By using marine snails as a model, our study provides new knowledge for understanding how changing environmental conditions may alter biological interactions, and increases our understanding of how climate change may affect ecological communities in which gastropods play a key role.

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