Ocean acidification and rising temperatures may increase biofilm primary productivity but decrease grazer consumption

Abstract

Climate change may cause ecosystems to become trophically restructured as a result of primary producers and consumers responding differently to increasing CO 2 and temperature. This study used an integrative approach using a controlled microcosm experiment to investigate the combined effects of CO 2 and temperature on key components of the intertidal system in the UK, biofilms and their consumers ( Littorina littorea ). In addition, to identify whether pre-exposure to experimental conditions can alter experimental outcomes we explicitly tested for differential effects on L. littorea pre-exposed to experimental conditions for two weeks and five months. In contrast to predictions based on metabolic theory, the combination of elevated temperature and CO 2 over a five-week period caused a decrease in the amount of primary productivity consumed by grazers, while the abundance of biofilms increased. However, long-term pre-exposure to experimental conditions (five months) altered this effect, with grazing rates in these animals being greater than in animals exposed only for two weeks. We suggest that the structure of future ecosystems may not be predictable using short-term laboratory experiments alone owing to potentially confounding effects of exposure time and effects of being held in an artificial environment over prolonged time periods. A combination of laboratory (physiology responses) and large, long-term experiments (ecosystem responses) may therefore be necessary to adequately predict the complex and interactive effects of climate change as organisms may acclimate to conditions over the longer term.

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

“…Other climatic changes expected on the California coast during this century, including increases in air temperature [46], may generate complex interactive effects [47] that also influence intertidal oysters and their predators. Predicting the net effect of environmental changes on the dynamics of a predator -prey interaction is complex, because both species might be impacted [21,22,42]. For example, lowered pH can alter both prey detection and predator avoidance in coral reef fishes through effects on olfactory pathways [23,24,48].…”

“…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. We selected snails that were all within a narrow size range for these experiments and did not test whether long-term exposure to elevated CO 2 might impact the growth or performance of these calcifying predators [41,42]. Many predator -prey interactions are sizestructured, and reductions in the growth rate of predators might have important consequences for prey population dynamics [36,39,43].…”

Emiliania huxleyi increases calcification but not expression of calcification-related genes in long-term exposure to elevated temperature and p CO 2

“…The response of coccolithophores to elevated pCO 2 must be considered in the context of other oceanic variables such as temperature [17,19,20], light availability and nutrient concentrations, all of which are expected to change in the future and hence could have interactive effects on E. huxleyi. While there have been tests of E. huxleyi responses to multiple variables [14,[21][22][23], only one study has tested the effect of multiple environmental factors in long-term experiments [24] and found a synergistic effect of pCO 2 and nitrogen source on carbon partitioning in E. huxleyi.…”

Ocean acidification and climate change: advances in ecology and evolution

“…In the second contribution to this issue, Russell et al [55] introduce the importance of longer-term species acclimatization for distinguishing the confounding effects of exposure length from the effects of being held in an artificial environment over prolonged time periods. They show that primary producers (algal biofilm) and consumers (Littorina littorea) are likely to respond differently to one another under increasing [CO 2 ] and warming and that species acclimatization is fundamental if trophic shifts in response to changing species metabolic demands are to be avoided.…”