Community dynamics and ecosystem simplification in a high-CO ₂ ocean

Abstract

Disturbances are natural features of ecosystems that promote variability in the community and ultimately maintain diversity. Although it is recognized that global change will affect environmental disturbance regimes, our understanding of the community dynamics governing ecosystem recovery and the maintenance of functional diversity in future scenarios is very limited. Here, we use one of the few ecosystems naturally exposed to future scenarios of environmental change to examine disturbance and recovery dynamics. We examine the recovery patterns of marine species from a physical disturbance across different acidification regimes caused by volcanic CO 2 vents. Plots of shallow rocky reef were cleared of all species in areas of ambient, low, and extreme low pH that correspond to near-future and extreme scenarios for ocean acidification. Our results illustrate how acidification decreases the variability of communities, resulting in homogenization and reduced functional diversity at a landscape scale. Whereas the recovery trajectories in ambient pH were highly variable and resulted in a diverse range of assemblages, recovery was more predictable with acidification and consistently resulted in very similar algaldominated assemblages. Furthermore, low pH zones had fewer signs of biological disturbance (primarily sea urchin grazing) and increased recovery rates of the dominant taxa (primarily fleshy algae). Together, our results highlight how environmental change can cause ecosystem simplification via environmentally mediated changes in community dynamics in the near future, with cascading impacts on functional diversity and ecosystem function.carbonate chemistry | habitat patchiness | resilience | emergent effects | species interaction

Decline in Coccolithophore Diversity and Impact on Coccolith Morphogenesis Along a Natural CO2 Gradient

“…Previous studies along pH gradients near Mediterranean volcanic seeps have demonstrated that although seawater acidification with CO 2 can benefit some organisms, such as heterokont algae, it is detrimental to most sessile calcified species and leads to a reduction in biodiversity (Porzio et al, 2011;Johnson et al, 2013;Kroeker et al, 2013b). Here we show that CO 2 seeps may also be useful for studying the effects of ocean acidification on plankton.…”

“…Natural CO 2 seeps are being used to examine the response of coastal ecosystems to ocean acidification (HallSpencer et al, 2008). Hundreds of benthic species have been investigated in these settings (Fabricius et al, 2011;Porzio et al 2011;Inoue et al, 2013;Kroeker et al, 2013b). Meroplanktonic calcified organisms such as juvenile gastropods and foraminifera are adversely affected as CO 2 levels increase (Cigliano et al, 2010), but carbon dioxide seeps have not so far been used for the study of ocean acidification on holoplankton.…”

“…High CO 2 concentrations affect the metabolism, growth, calcification, and behavior of many marine organisms (Rodolfo-Metalpa et al, 2011;Kroeker et al, 2013a). Some photosynthetic organisms benefit from increased levels of CO 2 , although many calcified species are adversely affected by corrosion or competition from non-calcified forms (Porzio et al, 2011;Johnson et al, 2013;Kroeker et al, 2013b).…”

The other ocean acidification problem: CO 2 as a resource among competitors for ecosystem dominance

“…However, in the projected near-future conditions presented in these analyses (figure 2), sea urchin densities are similar to control sites at tropical vents (K.E.F. 2013, unpublished data) and temperate vents [72,73]. In addition, the abundance of small mobile grazers (primarily gastropods) does not differ among the low pH and control sites at the temperate vents [74].…”

Twenty-first century climate change and submerged aquatic vegetation in a temperate estuary: the case of Chesapeake Bay

“…The great challenge of predicting the effects of acidification on SAV communities stems from the fact that indirect effects can be at least as important as the direct effects on individual plants, but are much more difficult to predict (Kroeker et al 2013a(Kroeker et al , 2013b. In the Chesapeake, we must consider the impacts of coastal acidification on the competitive balance between submerged vegetation and competing macroalgae and epiphytes.…”