the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Physiological and ecological tipping points caused by ocean acidification
Abstract. Ocean acidification is predicted to cause profound shifts in many marine ecosystems by impairing the ability of calcareous taxa to calcify and grow, and by influencing the photo-physiology of many others. In both calcifying and non-calcifying taxa, ocean acidification could further impair the ability of marine life to regulate internal pH, and thus metabolic function and/or behaviour. Identifying tipping points at which these effects will occur for different taxa due to the direct impacts of ocean acidification on organism physiology is difficult and they have not adequately been determined for most taxa, nor for ecosystems at higher levels. This is due to the presence of both resistant and sensitive species within most taxa. However, calcifying taxa such as coralline algae, corals, molluscs, and sea urchins appear to be most sensitive to ocean acidification. Conversely, non-calcareous seaweeds, seagrasses, diatoms, cephalopods, and fish tend to be more resistant, or even benefit from the direct effects of ocean acidification. While physiological tipping points of the effects of ocean acidification either do not exist or are not well defined, their direct effects on organism physiology will have flow on indirect effects. These indirect effects will cause ecologically tipping points in the future through changes in competition, herbivory and predation. Evidence for indirect effects and ecological change is mostly taken from benthic ecosystems in warm temperate–tropical locations in situ that have elevated CO2. Species abundances at these locations indicate a shift away from calcifying taxa and towards non-calcareous at high CO2 concentrations. For example, lower abundance of corals and coralline algae, and higher covers of non-calcareous macroalgae, often turfing species, at elevated CO2. However, there are some locations where only minor changes, or no detectable change occurs. Where ecological tipping points do occur, it is usually at locations with naturally elevated pCO2 concentrations of 500 μatm or more, which also corresponds to just under that concentrations where the direct physiological impacts of ocean acidification are detectable on the most sensitive taxa in laboratory research (coralline algae and corals). Collectively, the available data support the concern that ocean acidification will most likely cause ecological change in the near future in most benthic marine ecosystems, with tipping points in some ecosystems at as low as 500 μatm pCO2. However, much more further research is required to more adequately quantify and model the extent of these impacts in order to accurately project future marine ecosystem tipping points under ocean acidification.
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RC1: 'Comment on esd-2023-24', Anonymous Referee #1, 06 Oct 2023
This manuscript is ambitious and seeks to connect “Physiological and ecological tipping points caused by ocean acidification,” as its title indicates. To my knowledge, this question has never been explored in ocean acidification research field and is of crucial importance for understanding the occurrence of tipping points and their consequences for ecosystem and global earth system functioning. This review addresses research requirements highlighted in the latest International Pannel on Climate Change’s reports and is of major interest for the scientific community. By connecting tipping points in the biosphere to those occurring in the ecosphere, this study is perfectly in the scope of the journal “Earth System Dynamics”.
However, despite the critical interest of its research question, this article requires major revisions before being considered for publication. First, despite its title, the article fails to discuss the link between physiological tipping points and their ecological counterpart. To address this problem, efforts must be made to connect the second part, “direct impact on key physiological processes”, and the third part, “changes at naturally high CO2 locations”. Key concepts discussed in the article (physiological tipping point, ecological tipping point, reaction norms) are not defined in the introduction, which threatens the understanding of the entire article. There is a lack of a whole body of literature (see references in the supplement file) on physiological tipping points to ocean acidification, particularly for molluscs, echinoderms, and pteropods. Discussion of tipping points is almost absent in parts 2.2 and 2.3, which contrasts with the title of the manuscript. Part 3 on “Ecological Tipping Points” lacks important concepts such as “engineer species” to effectively link with Part 2 on “Physiological Tipping Points”. A figure is missing to help readers understand the ecological concepts described in Part 3. Finally, despite its crucial interest for the study, Table 1 is not really discussed even if it could help to resolve some of the problems mentioned above.
If significant revision work is done, I believe this review could be of great interest to readers of “Earth System Dynamics” and to the scientific community working on climate change in general.
Please find suggestions for improving the manuscript in the supplement file.
- AC1: 'Reply on RC1', Christopher Cornwall, 14 Dec 2023
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AC3: 'New figure', Christopher Cornwall, 17 Dec 2023
Attached is also the new figure to assist the readers in understanding discussed material.
Legend:
Figure 2: Conceptual diagram demonstrating the need for understanding both physiological and ecological responses when inferring the impacts of OA on future marine ecosystems. Species that have negative (A; solid line, tipping point; dashed line, linear), neutral (B), or positive (C) physiological responses to elevated pCO2 conditions in isolation, may not demonstrate the same response in terms of their ecological response (D) when considered in terms of the whole community (solid line, negative response species with tipping point; dashed line, negative response species with linear response). For example, a species may physiologically have neutral responses but still show reduced relative abundance under elevated pCO2 conditions due to alterations in their ecological interactions with other species. Subsequently, ecological shifts in dominance (ecological tipping points) may occur sooner than physiological thresholds are exceeded (E).
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RC2: 'Comment on esd-2023-24', Anonymous Referee #2, 01 Nov 2023
This work presents a great depiction of the current state of understanding of the impact of OA on organisms and community structure. The text is generally direct and clearly written. The text generally suggests that identifying tipping points caused by OA is difficult and there are other factors to be considered. My major concern is that the paper reads more as a summary of the impact of OA rather than an assessment of how tipping point can be caused by OA.
The first parts (section 2) have some paragraphs that are a bit clearer about the difficulty of identifying tipping points from a physiological perspective only and translating this to any broader ecological processes.
From my point of view, the other parts however seem mainly about changes/shifts and do not touch enough on how these changes are likely to occur; gradual (linear) vs abrupt (tipping point/bi-phasic).
Another consideration is whether tipping points are likely to be caused by CO2 alone, or influenced primarily by interactions with other parameters/stressors?
Are there shifts in community structure or simplification of food web occurring through a tipping point or are they more gradual shifts along the spatial/temporal gradient of pCO2? No doubt that a shift in community structure/habitat forming species and so on are likely, and in fact shown in some areas (e.g., CO2 seep having different communities). However, can a proper sudden change in stable state be identified at a given range of pCO2 or are these occurring mostly gradually or randomly at different sites based on the site’s own characteristics? I think it is important here to clearly differentiate between gradual shift vs a sudden tipping point, or maybe the lack of appropriate data/studies to properly infer tipping points.
There is also a lack of more concrete direction on how to look properly into identifying actual sudden change in stable state in natural systems, for example, or thresholds in pCO2, especially in the concluding section.
Nonetheless, in my point of view, this can be a nice addition to the literature and provide some nice insights given it revised carefully and a little restructuring. In its current state, it feels a little as a summary to the impact of OA, to which some inferences about tipping points have been made. I hope that these comments help improve the paper.
Please see attached file for more detailed review comments.
- AC2: 'Reply on RC2', Christopher Cornwall, 14 Dec 2023
Status: closed
-
RC1: 'Comment on esd-2023-24', Anonymous Referee #1, 06 Oct 2023
This manuscript is ambitious and seeks to connect “Physiological and ecological tipping points caused by ocean acidification,” as its title indicates. To my knowledge, this question has never been explored in ocean acidification research field and is of crucial importance for understanding the occurrence of tipping points and their consequences for ecosystem and global earth system functioning. This review addresses research requirements highlighted in the latest International Pannel on Climate Change’s reports and is of major interest for the scientific community. By connecting tipping points in the biosphere to those occurring in the ecosphere, this study is perfectly in the scope of the journal “Earth System Dynamics”.
However, despite the critical interest of its research question, this article requires major revisions before being considered for publication. First, despite its title, the article fails to discuss the link between physiological tipping points and their ecological counterpart. To address this problem, efforts must be made to connect the second part, “direct impact on key physiological processes”, and the third part, “changes at naturally high CO2 locations”. Key concepts discussed in the article (physiological tipping point, ecological tipping point, reaction norms) are not defined in the introduction, which threatens the understanding of the entire article. There is a lack of a whole body of literature (see references in the supplement file) on physiological tipping points to ocean acidification, particularly for molluscs, echinoderms, and pteropods. Discussion of tipping points is almost absent in parts 2.2 and 2.3, which contrasts with the title of the manuscript. Part 3 on “Ecological Tipping Points” lacks important concepts such as “engineer species” to effectively link with Part 2 on “Physiological Tipping Points”. A figure is missing to help readers understand the ecological concepts described in Part 3. Finally, despite its crucial interest for the study, Table 1 is not really discussed even if it could help to resolve some of the problems mentioned above.
If significant revision work is done, I believe this review could be of great interest to readers of “Earth System Dynamics” and to the scientific community working on climate change in general.
Please find suggestions for improving the manuscript in the supplement file.
- AC1: 'Reply on RC1', Christopher Cornwall, 14 Dec 2023
-
AC3: 'New figure', Christopher Cornwall, 17 Dec 2023
Attached is also the new figure to assist the readers in understanding discussed material.
Legend:
Figure 2: Conceptual diagram demonstrating the need for understanding both physiological and ecological responses when inferring the impacts of OA on future marine ecosystems. Species that have negative (A; solid line, tipping point; dashed line, linear), neutral (B), or positive (C) physiological responses to elevated pCO2 conditions in isolation, may not demonstrate the same response in terms of their ecological response (D) when considered in terms of the whole community (solid line, negative response species with tipping point; dashed line, negative response species with linear response). For example, a species may physiologically have neutral responses but still show reduced relative abundance under elevated pCO2 conditions due to alterations in their ecological interactions with other species. Subsequently, ecological shifts in dominance (ecological tipping points) may occur sooner than physiological thresholds are exceeded (E).
-
RC2: 'Comment on esd-2023-24', Anonymous Referee #2, 01 Nov 2023
This work presents a great depiction of the current state of understanding of the impact of OA on organisms and community structure. The text is generally direct and clearly written. The text generally suggests that identifying tipping points caused by OA is difficult and there are other factors to be considered. My major concern is that the paper reads more as a summary of the impact of OA rather than an assessment of how tipping point can be caused by OA.
The first parts (section 2) have some paragraphs that are a bit clearer about the difficulty of identifying tipping points from a physiological perspective only and translating this to any broader ecological processes.
From my point of view, the other parts however seem mainly about changes/shifts and do not touch enough on how these changes are likely to occur; gradual (linear) vs abrupt (tipping point/bi-phasic).
Another consideration is whether tipping points are likely to be caused by CO2 alone, or influenced primarily by interactions with other parameters/stressors?
Are there shifts in community structure or simplification of food web occurring through a tipping point or are they more gradual shifts along the spatial/temporal gradient of pCO2? No doubt that a shift in community structure/habitat forming species and so on are likely, and in fact shown in some areas (e.g., CO2 seep having different communities). However, can a proper sudden change in stable state be identified at a given range of pCO2 or are these occurring mostly gradually or randomly at different sites based on the site’s own characteristics? I think it is important here to clearly differentiate between gradual shift vs a sudden tipping point, or maybe the lack of appropriate data/studies to properly infer tipping points.
There is also a lack of more concrete direction on how to look properly into identifying actual sudden change in stable state in natural systems, for example, or thresholds in pCO2, especially in the concluding section.
Nonetheless, in my point of view, this can be a nice addition to the literature and provide some nice insights given it revised carefully and a little restructuring. In its current state, it feels a little as a summary to the impact of OA, to which some inferences about tipping points have been made. I hope that these comments help improve the paper.
Please see attached file for more detailed review comments.
- AC2: 'Reply on RC2', Christopher Cornwall, 14 Dec 2023
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