Climate change is expected to affect ocean biodiversity and play a major role in future changes in the structure of marine communities. Indeed, marine species are directly impacted by changes in ocean temperature and acidity, which can alter their abundance, diversity, distribution, feeding patterns, development and reproduction. Biodiversity measures are therefore commonly used in studies that monitor and assess the effects of climate change on marine communities.
However, it is difficult for scientists to predict exactly how changes in ocean acidification and temperature will influence marine communities in the future due to the complex nature of marine ecosystems and insufficient laboratory conditions or mesocosm (external laboratory) to reproduce this complexity. Previous experimental research has used different methods to assess potential effects and has produced conflicting results.
To improve understanding of the effects of climate on marine communities, scientists from the University of Adelaide have now reviewed 58 studies of community responses around volcanic CO2 vents in temperate reef, coral reef and seagrass ecosystems. CO2 that bubbles up from the ocean floor in these areas acidifies the seawater and this affects the surrounding biological communities. Scientists use these conditions as a proxy to provide information on what may happen to biological communities in the face of ocean acidification.
The researchers also reviewed the results of 23 studies conducted in outdoor experimental environments (mesocosms) or laboratories to determine whether these conditions can adequately represent the changes that occur in marine communities. Their objective was to test the prevalence of global and widespread biodiversity responses and community-level changes to the stresses of acidification and warming in natural and man-made sites. Their results are published in the journal Biology of global change.
Previous research studies have typically used measures of species diversity to track changes in communities. This means that they counted the number of different species present and their abundance in communities subject to changing environmental conditions. Overall, the University of Adelaide researchers found this to be the wrong measure to use, as both increases and decreases in species richness were recorded, reversing any global trends. Instead, there was a community replacement pattern, meaning that while some species declined or disappeared from the community, others moved in and became established.
“The belief that climate change will alter global marine biodiversity is one of the most widely accepted,” said Professor Ivan Nagelkerken of the University of Adelaide’s Institute of Environment and Ecology Laboratories of the South Seas, who was the first author of the study. “Commonly used biodiversity measures do not detect the reorganization of marine communities due to ocean acidification, as new species replace species that are lost. [This means that] little or no change in biodiversity is detected when one community of marine species is replaced by another, even when there is significant loss of habitat.
Instead, the researchers detected globally repeated patterns of species replacements and community “reshuffles” in CO studies.2 vent communities. In particular, these communities showed decreased cover by calcareous algae, crustacean coral algae, and filter feeders that have calcified shells or tubes. All of these organisms contain calcium carbonate which would dissolve under acidic conditions. In contrast, there was increased coverage by fleshy algae, turf algae, and biofilm in the CO2 vent communities. The authors believe that these measures of community change are more useful than simply determining species diversity.
Moreover, outdoor laboratory studies of marine communities were even less sensitive in detecting species replacements, community reshuffling, or biodiversity changes than natural systems, either to ocean acidification or warming. or a combination of the two. This lower sensitivity is not unexpected because community structure is often influenced by ecological processes that operate on significantly larger spatial and temporal scales than those tested in outside laboratories.
“Lab experiments are weak at detecting changes in biodiversity, so natural systems experiencing advanced ocean acidification are emerging as an innovative way to study biodiversity responses,” said Professor Sean Connell, co -author and professor at the University of Adelaide Institute of Environment and South Seas Ecology Laboratories. “No ecological study, whether in the laboratory or in the field, can fully replicate the complex ecological interactions that exist in nature across the temporal and spatial scales relevant to climate change.”
The authors conclude that there are detectable and generalizable changes that occur in marine communities in response to environmental changes in acidity and temperature, but that these are not accurately tracked by considering biodiversity changes alone. Instead, ecologists should monitor species shifts and community reorganization, particularly in terms of important functional groups, if they wish to detect the effects of climate change on marine communities.
“Future projections of ecosystem change and stability will be more meaningful if they focus on detections of species replacements and changes in species abundance rather than testing for signs of habitat loss or loss of biodiversity. in itself,said Professor Nagelkerken.
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By Alison Bosman, Terre.com Personal editor
