Predicting ecosystem shifts requires new approaches that integrate the effects of climate change across entire systems

Most studies that forecast the ecological consequences of climate change target a single species and a single life stage. Depending on climatic impacts on other life stages and on interacting species, however, the results from simple experiments may not translate into accurate predictions of future ecological change. Research needs to move beyond simple experimental studies and environmental envelope projections for single species towards identifying where ecosystem change is likely to occur and the drivers for this change. For this to happen, we advocate research directions that (i) identify the critical species within the target ecosystem, and the life stage(s) most susceptible to changing conditions and (ii) the key interactions between these species and components of their broader ecosystem. A combined approach using macroecology, experimentally derived data and modelling that incorporates energy budgets in life cycle models may identify critical abiotic conditions that disproportionately alter important ecological processes under forecasted climates.     

Antarctic echinoids and climate change: a major impact on the brooding forms

Ocean acidification (OA) and the accompanying changes to carbonate concentrations are predicted to have especially negative impacts in the Southern Ocean where, as a result of colder temperatures, there will be shallowing of both the aragonite (ASH) and calcite saturation horizons (CSH). Echinoids are a dominant group of the Antarctic macrofauna which, because of their high‐Mg calcite skeleton, are particularly susceptible to changes in the ASH. Using published information on the bathymetric distributions of Antarctic echinoids, we show that the majority of heavily calcified echinoids have their lower bathymetric limit above a depth of ca. 3000 m, approximately the current depth of the CSH. Echinoids whose depth range extends below 3000 m generally have thin, weakly calcified tests and include species from the Order Holasteroida, and the Families Cidaridae and Schizasteridae. Examination of the reproductive mode of Antarctic echinoids shows that brooding, where calcification of the young occurs in the same CaCO₃ environment as the mother, is primarily found at a depth above 3000 m. The predicted shallowing of the ASH and CSH under OA conditions is likely to negatively impact growth and reproduction of heavily calcified brooders in the Family Cidaridae, which may result in changes to bathymetric ranges, local population extinction, and associated losses in macrofaunal biodiversity. As with other calcified deep sea invertebrates, echinoids may be particularly vulnerable to the impacts of increased CO₂ and OA in the Southern Ocean.     

Marine biodiversity�Cecosystem functions under uncertain environmental futures

Anthropogenic activity is currently leading to dramatic transformations of ecosystems and losses of biodiversity. The recognition that these ecosystems provide services that are essential for human well-being has led to a major interest in the forms of the biodiversity–ecosystem functioning relationship. However, there is a lack of studies examining the impact of climate change on these relationships and it remains unclear how multiple climatic drivers may affect levels of ecosystem functioning. Here, we examine the roles of two important climate change variables, temperature and concentration of atmospheric carbon dioxide, on the relationship between invertebrate species richness and nutrient release in a model benthic estuarine system. We found a positive relationship between invertebrate species richness and the levels of release of NH₄-N into the water column, but no effect of species richness on the release of PO₄-P. Higher temperatures and greater concentrations of atmospheric carbon dioxide had a negative impact on nutrient release. Importantly, we found significant interactions between the climate variables, indicating that reliably predicting the effects of future climate change will not be straightforward as multiple drivers are unlikely to have purely additive effects, resulting in increased levels of uncertainty.     

Unshelled abalone and corrupted urchins: development of marine calcifiers in a changing ocean

The most fragile skeletons produced by benthic marine calcifiers are those that larvae and juveniles make to support their bodies. Ocean warming, acidification, decreased carbonate saturation and their interactive effects are likely to impair skeletogenesis. Failure to produce skeleton in a changing ocean has negative implications for a diversity of marine species. We examined the interactive effects of warming and acidification on an abalone (Haliotis coccoradiata) and a sea urchin (Heliocidaris erythrogramma) reared from fertilization in temperature and pH/pCO(2) treatments in a climatically and regionally relevant setting. Exposure of ectodermal (abalone) and mesodermal (echinoid) calcifying systems to warming (+2°C to 4°C) and acidification (pH 7.6-7.8) resulted in unshelled larvae and abnormal juveniles. Haliotis development was most sensitive with no interaction between stressors. For Heliocidaris, the percentage of normal juveniles decreased in response to both stressors, although a +2°C warming diminished the negative effect of low pH. The number of spines produced decreased with increasing acidification/pCO(2), and the interactive effect between stressors indicated that a +2°C warming reduced the negative effects of low pH. At +4°C, the developmental thermal tolerance was breached. Our results show that projected near-future climate change will have deleterious effects on development with differences in vulnerability in the two species.     

On the potential for ocean acidification to be a general cause of ancient reef crises

Anthropogenic rise in the carbon dioxide concentration in the atmosphere leads to global warming and acidification of the oceans. Ocean acidification (OA) is harmful to many organisms but especially to those that build massive skeletons of calcium carbonate, such as reef corals. Here, we test the recent suggestion that OA leads not only to declining calcification of reef corals and reduced growth rates of reefs but may also have been a trigger of ancient reef crises and mass extinctions in the sea. We analyse the fossil record of biogenic reefs and marine organisms to (1) assess the timing and intensity of ancient reef crises, (2) check which reef crises were concurrent with inferred pulses of carbon dioxide concentrations and (3) evaluate the correlation between reef crises and mass extinctions and their selectivity in terms of inferred physiological buffering. We conclude that four of five global metazoan reef crises in the last 500 Myr were probably at least partially governed by OA and rapid global warming. However, only two of the big five mass extinctions show geological evidence of OA.