Ph.D. thesis by Dr Laura Falkenberg
Throughout my PhD, I assessed the conceptual model that while cross-scale abiotic stressors can combine to synergistically favour shifts in marine habitats from kelp forests to mats of turfing algae, management of local conditions can counter this change. My experimental manipulations found broad support for the hypotheses that; 1) cross-scale factors (i.e. local and global) can have interactive effects which increase the probability of expansion of turfs but not kelp and, 2) management of local conditions (e.g. maintaining intact forests, limiting nutrient enrichment) can dampen the effects of global change (e.g. forecasted carbon dioxide). I published the results from my thesis in four papers. In the first, I showed that experimental enrichment of CO2 and nutrients influence the biomass accumulation of turf and kelp differently, with turf responding positively to enrichment of both resources while kelp responded to enrichment of nutrients but not CO2. Given that such direct responses could be mediated by interactions with other taxa, in the second paper I considered a key competitive interaction and revealed that the presence of kelp can inhibit the synergistic positive effect of resource enrichment (i.e. CO2 and nutrients) on their turf competitors. Similarly, in the third paper I highlighted the importance of herbivory by showing that under enriched CO2 conditions rates of this process were increased to counter the expansion of turfs. Finally, in the fourth paper, I considered a scenario in which these biotic controls were absent and identified that where multiple resources had been enriched and prompted a synergistic response (i.e. the expansion of turf where CO2 and nutrients are modified), subsequent reduction of the locally-determined factor alone (i.e. nutrients) substantially slowed further expansion of turf algae, but that the legacy of nutrient enrichment was not entirely eradicated. Together, these results represent progress in ecological tests of hypotheses regarding global climate change as they incorporate comprehensive sets of abiotic and biotic community drivers.
You can access all of Laura’s publications from the University of Adelaide’s digital library, or email her for a copy.
In May 2013 the National Oceanic and Atmospheric Administration in the USA reported that the atmospheric concentration of CO2 at one of their recording stations topped 400 ppm for the first time. The media surrounding this event seems to have been very much based around the event itself with little comment on what it may mean.
We can be moderately confident of one thing however – increased CO2 in the atmosphere means that more will dissolve into the ocean, which means an increase in ocean acidification (this is classical chemistry!). Despite the recent efforts of some of the worlds best scientists, both here in Australia and overseas, we still have an incomplete picture of the likely biological and ecological effects of this ocean acidification. Unfortunately, as we enter a time of uncertainty for science funding in Australia, we may not develop this understanding until it’s too late.
Here is an opportunity for a winter escape to the gold Coast for the Australian Marine Science Association (AMSA http://www.amsa.asn.au/) Golden Jubilee conference, 7-11 July 2013. Abstracts are now being accepted, submission close on March 15.
Session topics of particular relevance to ocean acidification; Marine biota in a changing ocean; Resilience; Communicating Science
Thanks to Prof. Bradley Eyre, Southern Cross University for this communication
Check out the recently published ocean acidification theme section in Marine Ecology Progress Series (open access). Edited by Phillip Boyd NIWA, the section comprises 8 papers considering various impacts of OA in the context of Multiple Environmental Drivers (MED’s). http://www.int-res.com/articles/theme/m470_ThemeSection.pdf
Direct effects of ocean acidification (red) and ocean warming (blue) on Fe chemistry in seawater from Hoffmann et al.
1/ Understanding the responses of ocean biota to a complex matrix of cumulative anthropogenic change Boyd PW, Hutchins DA 2/ Environmental controls on coccolithophore calcification Raven JA, Crawfurd K 3/ Responses of marine primary producers to interactions between ocean acidification, solar radiation,and warming. Gao K, Helbling EW, Häder DP, Hutchins DA 4/ Influence of ocean warming and acidification on trace metal biogeochemistry. Hoffmann LJ, Breitbak E, Boyd PW, Hunter KA 5/ Global change and the future of harmful algal blooms in the ocean. Fu FX, Tatters AO, Hutchins DA [Does this mean we will have more of these???? http://www.heraldsun.com.au/news/national/red-tide-of-algae-strikes-10-more-sydney-beaches/story-fndo317g-1226526090204 ] 6/ Phytoplankton niches, traits and eco-evolutionary responses to global environmental change. Litchman E, Edwards KF, Klausmeier CA,Thomas MK 7/ The biological pump in a high CO2 world. Passow U, Carlson CA 8/ Integrating climate-related stressor effects on marine organisms: unifying principles linking molecule to ecosystem-level changes. Pörtner HO
Coral reefs are structurally complex and “cemented” together by Crustose Coralline Algae.
Unlike some of the media coverage, I’m not saying that coral reefs will be resistant to ocean acidification, and I’m certainly not saying that corals will be. There is some good news for the gloom of ocean acidification. Yet, the devil is in the detail!
Unknown to most people, Crustose Coralline Algae (known in the field as CCA to stop us tripping over the long name) are the pink algae which cement together the matrix of coral reefs the world over, effectively solidifying the structure that we know as “coral” reefs. These CCAs also form a dense, concrete like ridge on the exposed side of most reefs, protecting the more fragile corals from destructive wave energy. So, from a reef perspective they are very important.
Until now, most of the research into the future of CCAs under ocean acidification has demonstrated that they are likely to dissolve (e.g. Tropical species and temperate species). However, some colleagues and I have recently discovered two important things about these CCAs, (1) that they contain dolomite, a rather robust mineral that most people associate with mountains in Italy; and (2) that dolomite is quite resistant to pH which we are expecting in the world’s oceans in the next 100 years (link to the paper here).
What does this mean? Unfortunately it doesn’t mean that the world’s coral reefs are going to be saved from ocean acidification by dolomite-rich CCA. By all accounts the corals are still in trouble (though I still have my hopes for more adaptive capacity than we give them credit for!). However, there is some hope, because these CCA are likely to maintain their structure and thus continue to protect reefs from damage by waves.