Troubles Never Come Alone: Outcome of Multiple Pressures on a Temperate Rocky Reef

Round 1

Reviewer 1 Report

The paper by Azzola et al.  aims at evaluating short-term changes undergone by a Mediterranean rocky reef communities when different stressors  and a major disturbance came in action contemporaneously. The topic is interesting and the study is rightly conducted, thus data are to be published but several changes are needed to improve the paper. A list of comments/suggestions is reported below:

Introduction

Lines 66-68 and lines 72-73: these part should be eliminated; references could be added to the sentence of lines 81-85

Methods

Line 143: a list of OTUs could be added in supplementary. Moreover, can the authors report one or more references about the use of OTUs?

Results

The results are not clearly presented. For a reader it is difficult  to separate the cause and the effects of changes. I agree with the authors that  “Distinguishing the outcome of every single affector, even excluding natural variability, is difficult” but further information could be done. Only the effect of storm on the communities is showed in table 3 and figure 6. What about changes in community structure between June and October?  The authors report that at 20 m “The algal species that exhibited the greatest variation were Jania spp. and Padina pavonica, more abundant in October”, but what are the seasonal taxa responsible to  the decrease of the cover at 10 m? Also, the authors said that “The cumulative effect of the four affectors peaked at 20 m depth, where the greatest changes in the rocky reef community were documented” but the changes are not clearly described. Thus, I suggest to better highlight the changes in the community structure, especially between June and October, clearly separating the temporal variations of affectors and those of the assemblages.

The authors did not consider the diversity of the assemblages, but it could be an interesting aspect to test regardless of the result.

Discussion

A comparisons between the observed changes in community structures and the effects of the single considered affectors reported in literature  could be interesting.

Also, the authors investigated about the occurrence of thermal anomalies; however, this aspect is not considered in the discussion. The short-term effects of thermal anomalies are not easy to be evaluated but some comments should be added to justify the study. For examples, a comparison between the observed changes in community structures and those reported in literature in relation to the occurrence of thermal anomalies (e.g. Ceccherelli et al Scientific Reports (2020) 10:17332) could be made.

Supplementary

Table S1 and S2: I suggest to separate taxa/OTUs between phyla, maintaining the alphabetic order within each phylum. Moreover, bare rock, mucilage and sediment should be reported separately. Finally, what is the meaning to separate Encrusting dark sponges and  Encrusting white sponges? In absence of a specific significance they could be grouped in encrusting undetermined sponges. Spirastrella cuncatrix should be in italic.

Author Response

Reviewer: The paper by Azzola et al. aims at evaluating short-term changes undergone by a Mediterranean rocky reef communities when different stressors and a major disturbance came in action contemporaneously. The topic is interesting and the study is rightly conducted, thus data are to be published but several changes are needed to improve the paper. A list of comments/suggestions is reported below:

Authors: We thank the Reviewer for the words of appreciation and for the suggestions and comments aimed at improving our paper. We did our best to make the changes requested.

Reviewer: Introduction - Lines 66-68 and lines 72-73: these part should be eliminated; references could be added to the sentence of lines 81-85

Authors: The two parts have been reworded and partially eliminated to make the sentences more general, not mentioning the example of the Portofino MPA (lines 72-74, lines 75-77).

Reviewer: Methods - Line 143: a list of OTUs could be added in supplementary. Moreover, can the authors report one or more references about the use of OTUs?

Authors: Table S1 and Table S2 of the Supplementary materials already list the descriptors including all the species as well as OTUs. As 'OTU' we consider the non-taxonomic categories (e.g., turf, rock, sediment) and the organisms for which taxonomic identification was not possible (lines 144-146). For example, in the above-mentioned tables 'encrusting corallines' and 'encrusting sponge' are OTUs. However, we reorganized the two tables as suggested, to also answer the last question of the Reviewer. We added two references in the text about the use of OTUs (line 146).

Reviewer:  Results - The results are not clearly presented. For a reader it is difficult to separate the cause and the effects of changes. I agree with the authors that  “Distinguishing the outcome of every single affector, even excluding natural variability, is difficult” but further information could be done.

Authors: We did our best to better present our results, adding new analyses (lines 179-184), new figures (Figure 5, 6 and 9) and improving the Discussion (lines 438-470).

Reviewer:  Only the effect of storm on the communities is showed in table 3 and figure 6. What about changes in community structure between June and October?  

Authors: The previous Table 3 reported not only the species indicating the effects of the storm, but also the descriptors 'mucilage' and 'Caulerpa cylindracea'. Table 3 shows the descriptors that mostly contributed to the similarity (SIMPER analysis results) not only between October-December, but also between June-October. To make it clearer a sentence has been added to the table caption (line 298). Moreover, to better explore changes between June and October seasonal species have been added to the new Table 3. 

The previous Figure 6 (new Figure 8) shows the descriptors indicating the effects of the storm, as the change in cover of seasonal species, mucilage and Caulerpa cylindracea are reported in the previous Figure 5 (new Figure 7).

Following the Reviewer suggestion to better explore changes in community composition due to the other dominant species (cover >5%) a new Figure 5 has been added showing the compositional change of the communities in the three time periods at the four depths investigated (lines 179-182, lines 273-276).

Reviewer:  The authors report that at 20 m “The algal species that exhibited the greatest variation were Jania spp. and Padina pavonica, more abundant in October”, but what are the seasonal taxa responsible to the decrease of the cover at 10 m?

Authors: The Reviewer is right, this sentence was not clear: the species Jania spp. and Padina pavonicaexhibited the greatest variation at both 10 m and 20 m depth. We reworded the sentence (lines 317-319).

In addition, the new Figure 5 shows the seasonal species that contributed most to the variation at all depths investigated and as mentioned above, seasonal species have been added to the new Table 3 (SIMPER analysis results).

Reviewer: Also, the authors said that “The cumulative effect of the four affectors peaked at 20 m depth, where the greatest changes in the rocky reef community were documented” but the changes are not clearly described. Thus, I suggest to better highlight the changes in the community structure, especially between June and October, clearly separating the temporal variations of affectors and those of the assemblages.

Authors: In the Results we have already highlighted that at 20 m depth the cover of seasonal species changed significantly over the time, which was not appended at 30 m and 40 m depth (lines 315-317, new Figure 7); the mucilage decreased significantly from June to October and no significant changed occurred at 10 m and 30 m depth (lines 325-326, new Figure 7); Caulerpa cylindracea showed its maximum peak at this depth, while no significant cover and changes were observed for all the other depths (lines 333-335, new Figure 7); lastly three of the four descriptors indicating the effects of the storm showed significant changes at this depth (lines 357-361, new Figure 8). These results are consistent with the major changes observed at 20 m depth obtained by analysing time-trajectories (lines 257-262, Figure 4). We hope that with the new Figure 5 the Reviewer can consider our analyses more complete. Moreover, a new Figure 9 has been added to better display the level of pressures of seasonality and affectors at the four depths investigated.

Reviewer: The authors did not consider the diversity of the assemblages, but it could be an interesting aspect to test regardless of the result.

Authors: Following the Reviewer suggestion we applied the Shannon diversity index to analyse the community structure (diversity) over the three time periods at the four depths investigated (lines 182-184; lines 277-279, new Figure 6).

Reviewer: Discussion - A comparisons between the observed changes in community structures and the effects of the single considered affectors reported in literature could be interesting.

Authors: We agree with the Reviewer that a comparison of our results with the effects of the single considered affectors reported in literature could be interesting. For this reason we have improved the Discussions by better questioning the effects of each affector considered (lines 438-470). However, unfortunately, our study at a short time scale does not fully allow us to assess the effects of individual affectors on the community and species for which further studies would be necessary (e.g., reduction in the number of species in a given community due to thermal anomalies could be more adequately observed at long time scales and with constant monitoring activities over time).

Reviewer: Also, the authors investigated about the occurrence of thermal anomalies; however, this aspect is not considered in the discussion. The short-term effects of thermal anomalies are not easy to be evaluated but some comments should be added to justify the study. For examples, a comparison between the observed changes in community structures and those reported in literature in relation to the occurrence of thermal anomalies (e.g. Ceccherelli et al Scientific Reports (2020) 10:17332) could be made.

Authors: We thank the Reviewer for this suggestion, it is true that comments about analyses on thermal anomalies was necessary. We improve our Discussion by comparing our results with the suggested study (lines 438-445). 

Reviewer:  Supplementary - Table S1 and S2: I suggest to separate taxa/OTUs between phyla, maintaining the alphabetic order within each phylum. Moreover, bare rock, mucilage and sediment should be reported separately. Finally, what is the meaning to separate Encrusting dark sponges and  Encrusting white sponges? In absence of a specific significance they could be grouped in encrusting undetermined sponges. Spirastrella cuncatrix should be in italic.

Authors: To make the Table S1 and S2 more readable, we have separated the species/OUTs between phyla. In addition, we have grouped all 'encrusting sponges' into 'undetermined encrusting sponges'. The species name Spirastrella cunctatrix has been corrected.

Reviewer 2 Report

Author Response

Reviewer: A very interesting job

Authors: We are pleased that our job was appreciated by the Reviewer, whom we thank for the positive feedback.

Reviewer 3 Report

This manuscript by Azzola et al. follow the effects of a thermal anomaly, the seasonal dominance of a invasive macroalgae Caulerpa cylindracea, a mucilage event derived from this species and the aftereffect of a big storm event on the subtidal rocky community in the Ligurian Sea, Italy.

The document is well structured with a pertinent Introduction, correct and well explained field methods, data handling and statistical approach. The results are well presented with nicely done figures and tables.

I recommend this manuscript for publication but I'd like the authors to improved two main points:

First, I had some trouble with the term "affector" which is an unusual word in the ecology area as I was struggling to understand why more common words as "stressors" or "variables" weren't being used.
After reading the manuscript, I understood that the authors are trying to push their recently minted term 'affector' (as originally published by Montefalcone et al. 2011) but the usage of this word (considering its intended definition in Ecology) is still very restricted, being mostly employed by the authors' nearest circles.
I do not have much problem with the new term although I had somewhat some difficulty to differentiate it from a most commonly used term in Ecology such as stressor. I also noticed this issue in some parts of this manuscript as the term 'stressor' is employed to refer to the same thing as previously called 'affector'. Given that, I think the authors must try to make the meaning of the term "affector" more solid and define its differentiation from "stressor" more clearly, as well the usage of the word in the text.
Now, leaving aside any criticism on the term,  I think that, considering that you aim to reach broader audiences worldwide and usage by scientific community, the explicit definition of the term should be included in the body of the text of the present article (and future ones as well) so a wider audience can be acquainted and, in consequence, more comfortable with its use in Ecology.

The Discussion is some what lacking given the amount of work and data the authors have been through. I felt that the authors fell in a generalization of "multivariate approach" are hard to analyze and to pinpoint the "one main factor controlling the biological communities" - which is true for most articles dealing with such approach -  and I agree with it.
Nevertheless, I think the authors could explore with more details the biological and ecological aspects on the species relations in the area and region (Mediterranean Sea). How individual species responded to such and such affector and to each other (specially to Caulerpa cylindracea expansion and the mucilage). I think that this could informative to other authors and also enrich this section of the manuscript.

To the last, I congratulate the authors for the good work and well presented manuscript.

Comments for author File: Comments.pdf

Author Response

Reviewer: This manuscript by Azzola et al. follow the effects of a thermal anomaly, the seasonal dominance of a invasive macroalgae Caulerpa cylindracea, a mucilage event derived from this species and the aftereffect of a big storm event on the subtidal rocky community in the Ligurian Sea, Italy. The document is well structured with a pertinent Introduction, correct and well explained field methods, data handling and statistical approach. The results are well presented with nicely done figures and tables. I recommend this manuscript for publication but I'd like the authors to improved two main points:

Authors: We would like to thank the Reviewer for the positive comments on our manuscript. We did our best to improve it following the Reviewer suggestions.

Reviewer: First, I had some trouble with the term "affector" which is an unusual word in the ecology area as I was struggling to understand why more common words as "stressors" or "variables" weren't being used. After reading the manuscript, I understood that the authors are trying to push their recently minted term 'affector' (as originally published by Montefalcone et al. 2011) but the usage of this word (considering its intended definition in Ecology) is still very restricted, being mostly employed by the authors' nearest circles. I do not have much problem with the new term although I had somewhat some difficulty to differentiate it from a most commonly used term in Ecology such as stressor. I also noticed this issue in some parts of this manuscript as the term 'stressor' is employed to refer to the same thing as previously called 'affector'. Given that, I think the authors must try to make the meaning of the term "affector" more solid and define its differentiation from "stressor" more clearly, as well the usage of the word in the text. Now, leaving aside any criticism on the term, I think that, considering that you aim to reach broader audiences worldwide and usage by scientific community, the explicit definition of the term should be included in the body of the text of the present article (and future ones as well) so a wider audience can be acquainted and, in consequence, more comfortable with its use in Ecology.

Authors: We understand the Reviewer troubles with the term ‘affector’, which is not widely used in Ecology, as rightly stated. However, we do believe that the use of the term ‘stressor’ to refer to both stress and disturbance is incorrect as they have different ecological meaning (Grime, 1977). For this reason, the authors Montefalcone et al. (2011) introduced the term ‘affector’ into the ecological literature to embrace both stressors and disturbances. We agree with the Reviewer that an explicit definition was needed to reach broader audience and, following this suggestion, we improved the first part of our Introduction (lines 36-47). Moreover, in the Abstract we have replaced the term ‘affector’ with ‘pressure’ (lines 19, 26), as a definition in this section might be overly discursive.

Reviewer: The Discussion is some what lacking given the amount of work and data the authors have been through. I felt that the authors fell in a generalization of "multivariate approach" are hard to analyze and to pinpoint the "one main factor controlling the biological communities" - which is true for most articles dealing with such approach -  and I agree with it. Nevertheless, I think the authors could explore with more details the biological and ecological aspects on the species relations in the area and region (Mediterranean Sea). How individual species responded to such and such affector and to each other (specially to Caulerpa cylindraceaexpansion and the mucilage). I think that this could informative to other authors and also enrich this section of the manuscript.

Authors: We thank the Reviewer for this suggestion aimed at improving our ms. Unfortunately, a detailed analysis of how individual species respond to each affector is not possible as our work focused on the community structure from the beginning and did not include surveys targeting individual species. However, we tried to follow the Reviewer suggestion to better explore biological and ecological aspects. With this porpoise two new analyses have been conducted: i) to assess relative importance of dominant species (cover >5%) in determining changes in community structure and composition (lines 179-182; lines 273-276) a graphical display of community composition was added (new Figure 5); ii) to correlate change in community composition and structure Shannon-Wiener diversity index was applied (lines 182-184; lines 277-279; new Figure 6).  In the Discussion a sentence about these new aspects has been then added (lines 391-394).   

Reviewer: To the last, I congratulate the authors for the good work and well presented manuscript.

Authors: We are glad to know that Reviewer appreciated our work.

Round 2

Reviewer 1 Report

The authors improved the paper following suggestions. In my opinion, the paper is now suitable to be pubilshed