Possible Population Growth of Astrospartus mediterraneus (Risso, 1826) (Ophiuroidea, Gorgonocephalidae) in the Mediterranean Sea

Round 1

Reviewer 1 Report

This study reports the historical presence of A. mediterraneus in the Mediterranean Basin, as well as it population trends in the Ligurian Sea at a multiannual scale, the later by means of ROV. The work here presented is of interest to the scientific community as, while characteristic of the Mediterranean waters, said species remains largely unknown, with scant to no information on its ecology prior to this study. Moreover, the article deals with the implications of long term fluctuations in Mediterranean echinoderms, which is rarely done, less with long (over 10 years) time series. Overall, the manuscript if of high quality, well-structured and easy to read.

However, despite dealing with an interesting topic there are some minor issues that need to be address prior to publication, mostly regarding the methodology, which could be more detailed. Additionally, in order to support some of the conclusions further discussion might be advisable. Following are the comments and suggestions that, in my opinion, should be addressed before publication.

 

Introduction

Lines 33. Change “This basket star” for “The basket star”.

Lines 31-45. I’d suggest the authors to reorganize this section of the introduction has follows: Lines 31 to 33, then 39-45, and end with 33-37. This way it

Lines 39-45. This section just reads as a list of locations where the species has been found, with little added information. I’d suggest the authors to mention the whole distribution extent of the species, including the Atlantic and then focusing on the Mediterranean, while adding developing a bit more on the geographical information already available (e.g. develop on the distribution on a West vs. East / North vs. South basin approach and/or tackle a bit more on the historical trend of said records.

Line 54. Delate Moreover.

Lines 54-57. Perhaps this section is a bit succinct. I’d recommend the authors to expand a bit on the importance of ROV based exploration in the Mediterranean mesophotic environments, which have been long-neglected in the Mediterranean Sea in comparison to deeper and shallower areas.

 

Material and Methods

Line 67-77. The methods for your bibliographic literature review are not fully explained. For the systematic literature search was it conducted using the biographic database like WoS, OBIS or WoRMS? Which key search terms were used? did the authors set years limits to their search? did they exclusively used published articles, or included grey literature (e.g. conference papers)?

Additionally, the authors also mention and use data from citizen science initiatives, but their precedence is never clarified. Similarly, the authors should provide a rationale on which citizen science initiatives were used, and a rationale on which how they were chosen. Finally, in the results the collected data should be presented in a table similar to table 1, containing the relevant information for each observation (location, abundance, depth, substrate, etc.), as in Table 1. Similarly, a table should be provided in the supplementary where these observations of this new table can be linked to specific citizen science databases, reports, etc. as done with the observations from scientific articles.

Table 1. The authors mention that the density of Astrospartus is given as ind/m², but just taking the values from hard substrate areas. As such, it should be advisable for the authors to include the total length and the percentage of hard substrate present on each transect. Without said information comparison between transect in the table is hindered, as it is impossible to distinguish transects with an absence of A. mediterraneus on hard substrates from those on other substrate types. Also, two decimals should be enough for the density values.

Line 78-94. The authors cover a considerable time span (2012-2022) with ROV footage coming from different projects across said period, and refer the reader to Enrichetti et al. (2019b) for “Further technical specifics of ROVs, tracks and video analysis”.  Nevertheless, said article only has data for transect filmed between 2015-2016. Authors should provide in the text the number of transects filmed per survey and the R/V in which they were carried, as well as the technical specifications of the ROVs used in each survey. Redirecting the reader to Enrichetti et al. (2019b) should be limited for an in-depth characterization of the studied areas, which is currently missing from the article.

Lines 98-113. The authors should explain how the correlations were performed, which software was used, etc. as well as the model used. Although it is clear from the figures that a linear model was selected, it should be briefly explained along the text.

Supplementary material. While it is just a suggestion, a large proportion of the references used in Sup. Mat. 1 are not mentioned along the reference list, but the reader is redirected to Zibrowius (1978), whom had already compiled all known observations of the species to that date. Given the lack of any major updates on the topic until the present work, I’d suggests the authors to complete the reference list with those already mentioned in Zibrowius (1978), just for a sense of completion and having them all listed altogether.

 

Results

Fig. 2. The image is blurry, being it impossible read the inner legend in panel C. Also the red dots are supposed to be scaled based on the density of the points, but given their blurriness, it is difficult to properly appreciate the size differences. Please, provide the image with higher quality.

Fig. 3. Similarly to Figure 2, the axes legends are blurry and cannot be properly understood. Please, provide the image with higher quality.

Fig. 5. Please, provide a scale bar for the images when possible.

Figs. 4 and 6, 7 and 8. While the images can be fully understood, they are all a bit blurry.

Lines 138-139. This line “The species is cited for the Aegean Sea without any information about the 138 locality or coordinates (Table S1).” is almost identical to lines 41-42 of the introduction, please delate it.

 

Discussion

In my opinion, while the article is interesting and provides much needed information on long-term observations of rare fauna, it overreaches on its conclusions when it affirms that “In conclusion, this study allowed to depict for A. mediterraneus a general trend of expansion at a pluriannual scale”.

The authors mention the ‘high abundances observed in this study for the Ligurian coast’ (e.g. line 237) of A. mediterraneus as partial support to conclude that A. mediterraneus has been on the rise on the Mediterranean Sea on the past decades. Nevertheless, if we take the data from Table 1 we can see that only 1 A. mediterraneus sighting has an average density above 0.5 ind/m² (Portofino Cape, Jul. 2020, with 0.79 ± 0.45 ind/m²) while 9 other sightings have between 0.1-0.5 ind/m², and the remaining 32 sightings with A. mediterraneus have less than 0.1 ind/m² each. Also, if you take a look at Fig. 7(a), you see that in the explored 10-year window A. mediterraneus densities were rather stable at ca. 0.25 ind/m², with a single outlier in Jul. 2020. Hence, with the given data it rather appears that A. mediterraneus densities in the studied area have remained stable for over a decade and that, while punctual peaks in density might occur after certain triggers (e.g. rainfall values), they rapidly recover to the average values of ca. 0.25 ind/m² once the event has passed.

While an increase in sightings across the basin could indeed indicate higher abundances, A. mediterraneus apparently mainly occurs in a rather unexplored habitat, hence this increase in sightings might just reflect an increase in sampling in said environments (as the authors already acknowledge, lines 224-241), but does not necessarily imply an increase on its abundance or density over time.  In fact, and based on the author’s own data, it appears that in the studied site the population has been relatively stable for at least a decade, as it is acknowledged along the text (Lines 275-277). Finally, while the authors do mention outbreaks in another Mediterranean area, they do not compare density values with previous observations. Also, they mention an increase in reported outbreaks for the species by citizen science initiatives, but give no data nor reference to support such claims. Thus, it is currently difficult to interpret whether or not their observed values are indeed higher than those reported in other areas or in previous decades while, according to the time series data, the species appears to be rather stable on the studied site. Hence,

Given the existing uncertainty on the topic to conclude that “a general trend of expansion at a pluriannual scale” has been observed, it might perhaps be an overstatement. I would recommend to expand and strengthen the comparison of their own data at a Mediterranean label, specifically with those records which might have provided quantitative and qualitative data for A. mediterraneus populations, and further develop and incorporate the data coming from citizen science initiatives. They should also further discuss the apparent stability of their observed population in this context, as the fact that the population has maintained stable for almost a decade would rather contradict the vision of it being on the rise.

Finally, I’d like to congratulate the authors on the quality of their work, and hope they will continue working on the topic in the near future.

Author Response

We would like to thank the Reviewer for the comments and suggestions. You can find the response here below.

Comments and Suggestions for Authors

 

This study reports the historical presence of A. mediterraneus in the Mediterranean Basin, as well as it population trends in the Ligurian Sea at a multiannual scale, the later by means of ROV. The work here presented is of interest to the scientific community as, while characteristic of the Mediterranean waters, said species remains largely unknown, with scant to no information on its ecology prior to this study. Moreover, the article deals with the implications of long term fluctuations in Mediterranean echinoderms, which is rarely done, less with long (over 10 years) time series. Overall, the manuscript if of high quality, well-structured and easy to read.

However, despite dealing with an interesting topic there are some minor issues that need to be address prior to publication, mostly regarding the methodology, which could be more detailed. Additionally, in order to support some of the conclusions further discussion might be advisable. Following are the comments and suggestions that, in my opinion, should be addressed before publication.

Introduction

Lines 33. Change “This basket star” for “The basket star”.

ANSWER: done

Lines 31-45. I’d suggest the authors to reorganize this section of the introduction has follows: Lines 31 to 33, then 39-45, and end with 33-37. This way it

ANSWER: rewritten accordingly.

Lines 39-45. This section just reads as a list of locations where the species has been found, with little added information. I’d suggest the authors to mention the whole distribution extent of the species, including the Atlantic and then focusing on the Mediterranean, while adding developing a bit more on the geographical information already available (e.g. develop on the distribution on a West vs. East / North vs. South basin approach and/or tackle a bit more on the historical trend of said records.

ANSWER: the section was improved with the requested details.

Line 54. Delate Moreover.

ANSWER: ok.

Lines 54-57. Perhaps this section is a bit succinct. I’d recommend the authors to expand a bit on the importance of ROV based exploration in the Mediterranean mesophotic environments, which have been long-neglected in the Mediterranean Sea in comparison to deeper and shallower areas.

ANSWER: the section was improved as suggested.

Material and Methods

Line 67-77. The methods for your bibliographic literature review are not fully explained. For the systematic literature search was it conducted using the biographic database like WoS, OBIS or WoRMS? Which key search terms were used? did the authors set years limits to their search? did they exclusively used published articles, or included grey literature (e.g. conference papers)?

ANSWER: major details were added to the material and methods part.

Additionally, the authors also mention and use data from citizen science initiatives, but their precedence is never clarified. Similarly, the authors should provide a rationale on which citizen science initiatives were used, and a rationale on which how they were chosen. Finally, in the results the collected data should be presented in a table similar to table 1, containing the relevant information for each observation (location, abundance, depth, substrate, etc.), as in Table 1. Similarly, a table should be provided in the supplementary where these observations of this new table can be linked to specific citizen science databases, reports, etc. as done with the observations from scientific articles.

ANSWER: we decided to not present data derived by citizen science because they are already available at the online platforms reported in the text. If the Editor think that this material is necessary for us is not a problem so supply a further table.

Table 1. The authors mention that the density of Astrospartus is given as ind/m², but just taking the values from hard substrate areas. As such, it should be advisable for the authors to include the total length and the percentage of hard substrate present on each transect. Without said information comparison between transect in the table is hindered, as it is impossible to distinguish transects with an absence of A. mediterraneus on hard substrates from those on other substrate types. Also, two decimals should be enough for the density values.

ANSWER: we added this information in Table 1 and reduced the number of decimal.

Line 78-94. The authors cover a considerable time span (2012-2022) with ROV footage coming from different projects across said period, and refer the reader to Enrichetti et al. (2019b) for “Further technical specifics of ROVs, tracks and video analysis”. Nevertheless, said article only has data for transect filmed between 2015-2016. Authors should provide in the text the number of transects filmed per survey and the R/V in which they were carried, as well as the technical specifications of the ROVs used in each survey. Redirecting the reader to Enrichetti et al. (2019b) should be limited for an in-depth characterization of the studied areas, which is currently missing from the article.

ANSWER: We have clarified that all the transect were carried out with the same methology present in the reference. Moreover, we added in the Table 1 the mean percentage of hard substrate per transect.

Lines 98-113. The authors should explain how the correlations were performed, which software was used, etc. as well as the model used. Although it is clear from the figures that a linear model was selected, it should be briefly explained along the text.

ANSWER: some details were added.

Supplementary material. While it is just a suggestion, a large proportion of the references used in Sup. Mat. 1 are not mentioned along the reference list, but the reader is redirected to Zibrowius (1978), whom had already compiled all known observations of the species to that date. Given the lack of any major updates on the topic until the present work, I’d suggests the authors to complete the reference list with those already mentioned in Zibrowius (1978), just for a sense of completion and having them all listed altogether.

ANSWER: done.

Results

Fig. 2. The image is blurry, being it impossible read the inner legend in panel C. Also the red dots are supposed to be scaled based on the density of the points, but given their blurriness, it is difficult to properly appreciate the size differences. Please, provide the image with higher quality.

ANSWER: all the images were attached separately in high quality format (330 dpi).

Fig. 3. Similarly to Figure 2, the axes legends are blurry and cannot be properly understood. Please, provide the image with higher quality.

ANSWER: all the images were attached separately in high quality format (330 dpi). The font size of x axes legend was set at 10.

Fig. 5. Please, provide a scale bar for the images when possible.

ANSWER: ok.

Figs. 4 and 6, 7 and 8. While the images can be fully understood, they are all a bit blurry.

ANSWER: all the images were attached separately in high quality format (330 dpi).

Lines 138-139. This line “The species is cited for the Aegean Sea without any information about the locality or coordinates (Table S1).” is almost identical to lines 41-42 of the introduction, please delate it.

ANSWER: removed.

Discussion

In my opinion, while the article is interesting and provides much needed information on long-term observations of rare fauna, it overreaches on its conclusions when it affirms that “In conclusion, this study allowed to depict for A. mediterraneus a general trend of expansion at a pluriannual scale”.

ANSWER: We agree, the text was correct accordingly

The authors mention the ‘high abundances observed in this study for the Ligurian coast’ (e.g. line 237) of A. mediterraneus as partial support to conclude that A. mediterraneus has been on the rise on the Mediterranean Sea on the past decades. Nevertheless, if we take the data from Table 1 we can see that only 1 A. mediterraneus sighting has an average density above 0.5 ind/m² (Portofino Cape, Jul. 2020, with 0.79 ± 0.45 ind/m²) while 9 other sightings have between 0.1-0.5 ind/m², and the remaining 32 sightings with A. mediterraneus have less than 0.1 ind/m² each. Also, if you take a look at Fig. 7(a), you see that in the explored 10-year window A. mediterraneus densities were rather stable at ca. 0.25 ind/m², with a single outlier in Jul. 2020. Hence, with the given data it rather appears that A. mediterraneus densities in the studied area have remained stable for over a decade and that, while punctual peaks in density might occur after certain triggers (e.g. rainfall values), they rapidly recover to the average values of ca. 0.25 ind/m² once the event has passed.

While an increase in sightings across the basin could indeed indicate higher abundances, A. mediterraneus apparently mainly occurs in a rather unexplored habitat, hence this increase in sightings might just reflect an increase in sampling in said environments (as the authors already acknowledge, lines 224-241), but does not necessarily imply an increase on its abundance or density over time.  In fact, and based on the author’s own data, it appears that in the studied site the population has been relatively stable for at least a decade, as it is acknowledged along the text (Lines 275-277). Finally, while the authors do mention outbreaks in another Mediterranean area, they do not compare density values with previous observations. Also, they mention an increase in reported outbreaks for the species by citizen science initiatives, but give no data nor reference to support such claims. Thus, it is currently difficult to interpret whether or not their observed values are indeed higher than those reported in other areas or in previous decades while, according to the time series data, the species appears to be rather stable on the studied site.

ANSWER: details were added in the text.

Given the existing uncertainty on the topic to conclude that “a general trend of expansion at a pluriannual scale” has been observed, it might perhaps be an overstatement. I would recommend to expand and strengthen the comparison of their own data at a Mediterranean label, specifically with those records which might have provided quantitative and qualitative data for A. mediterraneus populations, and further develop and incorporate the data coming from citizen science initiatives. They should also further discuss the apparent stability of their observed population in this context, as the fact that the population has maintained stable for almost a decade would rather contradict the vision of it being on the rise.

ANSWER: We have better discussed these points

Finally, I’d like to congratulate the authors on the quality of their work, and hope they will continue working on the topic in the near future.

Reviewer 2 Report

This paper is of interest to Mediterranean workers who research on echinoderms, benthic ecology and the effects of sea change on these. An extensive set of data has been compiled and the analysis is well executed. The conclusions are reasonable and based on the data without too much extrapolation or speculation. The only substantive comments I have on the science are:

1. The authors refer several times to an 'outbreak' (which I take to mean a population bloom) of A. mediterraneus but it is not always clear from the text whether this is the event that started in 2016 and reported in the dissertation by Montasell Bartres (2020) or to events reported on in the present study, or both; also, is the point 07/2 in Fig. 7(a) such a population bloom? It would be less ambiguous to give the actual date of the 'outbreak' when this is mentioned.

2. There is indeed a strong correlation between mean density of the brittlestar and rainfall (as in Fig. 7b right) but I note that this is due to the point at the extreme right of the graph with an exceptional rainfall of >300mm. Without this one point the correlation between density and rainfall would be less strong. Can the authors comment on this?

In general the paper is well written but it would benefit from a linguistic review by a native English speaker since while not incorrect, some sentence constructions are awkward. I have not made any extensive linguistic revision but I have made suggestions for improvement of particular words that do not seem to convey the meaning intended by the authors and of sentences where the construction is not really good English. I have also indicated those instance where I could not understand exactly what it was that the authors wanted to say.

You will find my suggestions and comments in the attached file. The following are the more significant ones:

Throughout the text, the author use 'average' but in scientific writing the term 'mean' is preferred as it is more exact whereas 'average' has other meanings.

In line 82, the authors refer to 'colonies'; if they are meaning Astrospartus, this species forms aggregates, not colonies.

The symbols in Fig 2 are hardly distinguishable because of the low resolution of the maps.

The labels of the x-axis in Fig. 3 are difficult to read.

The images in Fig. 5 are of low resolution and consequently not clear.

In Fig. 7, state what the error bars are.

In Fig. 9, the Petronio arrow is hardly visible because of the black outline.

 

Comments for author File: Comments.pdf

Author Response

We would like to thank the Reviewer for the comments and suggestions. Please find the response here below and in the attached PDF.

Comments and Suggestions for Authors

This paper is of interest to Mediterranean workers who research on echinoderms, benthic ecology and the effects of sea change on these. An extensive set of data has been compiled and the analysis is well executed. The conclusions are reasonable and based on the data without too much extrapolation or speculation. The only substantive comments I have on the science are:

1. The authors refer several times to an 'outbreak' (which I take to mean a population bloom) of A. mediterraneus but it is not always clear from the text whether this is the event that started in 2016 and reported in the dissertation by Montasell Bartres (2020) or to events reported on in the present study, or both; also, is the point 07/2 in Fig. 7(a) such a population bloom? It would be less ambiguous to give the actual date of the 'outbreak' when this is mentioned.

OK, the text was correct accordingly

2. There is indeed a strong correlation between mean density of the brittlestar and rainfall (as in Fig. 7b right) but I note that this is due to the point at the extreme right of the graph with an exceptional rainfall of >300mm. Without this one point the correlation between density and rainfall would be less strong. Can the authors comment on this?

Correct, the highest values strongly drive the correlations. Nevertheless, the correlations are significant also without considering these values.

In general the paper is well written but it would benefit from a linguistic review by a native English speaker since while not incorrect, some sentence constructions are awkward. I have not made any extensive linguistic revision but I have made suggestions for improvement of particular words that do not seem to convey the meaning intended by the authors and of sentences where the construction is not really good English. I have also indicated those instance where I could not understand exactly what it was that the authors wanted to say.

You will find my suggestions and comments in the attached file. The following are the more significant ones:

Throughout the text, the author use 'average' but in scientific writing the term 'mean' is preferred as it is more exact whereas 'average' has other meanings.

Answer: we have corrected through the text.

In line 82, the authors refer to 'colonies'; if they are meaning Astrospartus, this species forms aggregates, not colonies.

Answer: we corrected with specimens.

The symbols in Fig 2 are hardly distinguishable because of the low resolution of the maps.

Answer: the maps and the other figures are provided in TIFF with higher resolution (330 dpi).

The labels of the x-axis in Fig. 3 are difficult to read.

Answer: the font size was increased (10).

The images in Fig. 5 are of low resolution and consequently not clear.

Answer: all the figures are provided in high resolution (330 dpi). Images were modified accordingly.

In Fig. 7, state what the error bars are.

Answer: we added that bars are SE in the caption.

In Fig. 9, the Petronio arrow is hardly visible because of the black outline.

Answer: the outline was reduced.

Author Response File: Author Response.pdf

Reviewer 3 Report

This goal of this study was to test the recently perceived increase in abundance and distribution of the Mediterranean brittle star Astrospartus mediterraneus. Data have been extracted from the literature and from 10 years of ROV surveillance, as well as from citizen science observations. The authors critically evaluate the data and conclude that the species does expand over a longer time span. One explanation is increased food supply after rainfall that is suposed to promote reproduction.

I think that this analysis could be improved by considering the life-style and biology of these animals.

1. This is a large species that probably doesn't grow to its adult size in a single year, but data on its ontogeny are scarce. I wonder, what size where the reported animals? Has any recruitment of small (postmetamorphic) stages been observed? It is supposed to have some of the largest oocytes among all ophiuroids, up to 1.5 mm in diameter (Hendler 1991), which strongly suggests direct development, which in turn suggests limited dispersal capabilities of larvae. If environmental changes (rainfall) indeed promote reproduction events, we should see the effects in terms of "outbreaks" years after the rainfall. Thus, this argumentation rests on loose grounds.

2. Ophiuroids are mobile, but not very fast. Did you consider the feasible distance that the adults might move to colonize a new area? How fast can they respond to locally improved food conditions? The fan coral that they often live on have a patchy distribution. Can they move between patches of coral? The study mentioned that the brittle stars show host fidelity for years.

3. I would have liked to see information on the distribution and abundance of the host species. The fan coral have been found to be more widely distributed than previously thought, but in discontinuous patches. If the hosts have also been underreported, we may only have missed both host and epibiont by udersampling. Or perhaps the host species increased in abundance due to unknown factors, allowing the ophiuroids to increase in abundance as a response. There should be a time difference between both events of course.

4. The so called "outbreak" of A. mediterraneus that impeded the artisan fishermen is fascinating. Was this a one-time event or is the local population still large and continues to impede the fishery? Did the fishermen recently move to these areas or have they been fishing there with the same methods and intensity for many years before the outbreak?

5. Is the life-span of this species known? Short-lived species of brittle star can colonize a new area with a recruitment event triggered by favourable conditions. All members of the population then have the same age and when they dy, the population can go extinct if no additional recruitment event has happened. We don't know if this species reproduces every year or only when conditions are very good and so we don't know if age cohorts come and go.

6. How does this species compare to the population dynamics of other gorgoncephalids? Could it possibly be a normal pattern for these animals to increase and decrease in abundance depending on environmental conditions (food, host availability etc)?

The English is excellent and I only have a couple of comments.

On line 226, "addressed to ...causes", I'm not sure that "addressed" is the correct term. They could have different causes.

On line 232 add "a" species.

On line 255, "echinoderms" should be "echinoderm"

On line 260, rephrase as "with higher temperatures usually being triggers..."

On line 269, "stars" should be "star"

Supplementary materials, should the title have been written out?

Author Response

We wold like to thank the Reviewer for the comments and suggestions. The response is here below:

Comments and Suggestions for Authors

This goal of this study was to test the recently perceived increase in abundance and distribution of the Mediterranean brittle star Astrospartus mediterraneus. Data have been extracted from the literature and from 10 years of ROV surveillance, as well as from citizen science observations. The authors critically evaluate the data and conclude that the species does expand over a longer time span. One explanation is increased food supply after rainfall that is suposed to promote reproduction.

In our opinion (but it is a matter of hypothesis), the increases in food supply in a specific site enhance the aggregation of basket stars. Also, the general geographic distribution of the species seems driven by food supply. All these points were better explicated in the discussion that was deeply re-organized.

I think that this analysis could be improved by considering the life-style and biology of these animals.

1. This is a large species that probably doesn't grow to its adult size in a single year, but data on its ontogeny are scarce. I wonder, what size where the reported animals? Has any recruitment of small (postmetamorphic) stages been observed? It is supposed to have some of the largest oocytes among all ophiuroids, up to 1.5 mm in diameter (Hendler 1991), which strongly suggests direct development, which in turn suggests limited dispersal capabilities of larvae. If environmental changes (rainfall) indeed promote reproduction events, we should see the effects in terms of "outbreaks" years after the rainfall. Thus, this argumentation rests on loose grounds.

Some details were added

2. Ophiuroids are mobile, but not very fast. Did you consider the feasible distance that the adults might move to colonize a new area? How fast can they respond to locally improved food conditions? The fan coral that they often live on have a patchy distribution. Can they move between patches of coral? The study mentioned that the brittle stars show host fidelity for years.

Some details were added

3. I would have liked to see information on the distribution and abundance of the host species. The fan coral have been found to be more widely distributed than previously thought, but in discontinuous patches. If the hosts have also been underreported, we may only have missed both host and epibiont by udersampling. Or perhaps the host species increased in abundance due to unknown factors, allowing the ophiuroids to increase in abundance as a response. There should be a time difference between both events of course.

This point was deeply discussed

4. The so called "outbreak" of A. mediterraneus that impeded the artisan fishermen is fascinating. Was this a one-time event or is the local population still large and continues to impede the fishery? Did the fishermen recently move to these areas or have they been fishing there with the same methods and intensity for many years before the outbreak?

We have clarified this point

5. Is the life-span of this species known? Short-lived species of brittle star can colonize a new area with a recruitment event triggered by favourable conditions. All members of the population then have the same age and when they dy, the population can go extinct if no additional recruitment event has happened. We don't know if this species reproduces every year or only when conditions are very good and so we don't know if age cohorts come and go.

Some details were added

6. How does this species compare to the population dynamics of other gorgoncephalids? Could it possibly be a normal pattern for these animals to increase and decrease in abundance depending on environmental conditions (food, host availability etc)?

Some details were added. Unfortunately, to our knowledge, there are no studies regarding the population dynamics of other gorgonocephalids. Obviously, there are data about other brittle stars, but the ecology of Astrospartus is so peculiar that we believe no true comparisons are possible.

The English is excellent and I only have a couple of comments.

On line 226, "addressed to ...causes", I'm not sure that "addressed" is the correct term. They could have different causes.

Answer: we rephrased the sentence.

On line 232 add "a" species.

Answer: added.

On line 255, "echinoderms" should be "echinoderm"

Answer: here the term refers to general characteristics of this phylum.

On line 260, rephrase as "with higher temperatures usually being triggers..."

Answer: rephrased.

On line 269, "stars" should be "star"

Answer: corrected.

Supplementary materials, should the title have been written out?

Answer: Supplementary materials are available as Canessa at al., 2022.

Round 2

Reviewer 1 Report

The authors have thoroughly applied all changes suggested, and covered all issues pointed out during the first review. Hence, I do not see any need for an additional one. My sincere congratulations on their work.

The only thing I'd like to point out again is the figure's quality, as they are considerably blurry again. Yet, I'm inclined to believe this might be an issue with the generated pdf rather than the original files, so disregard this comment if that is the case.

Author Response

The authors have thoroughly applied all changes suggested, and covered all issues pointed out during the first review. Hence, I do not see any need for an additional one. My sincere congratulations on their work.

We are pleased to have been able to respond to comments and suggestions appropriately according to the Reviewer. We would like to thank you again for your help in the manuscript improvement. We uploaded the TIFF images in high quality separately.

Reviewer 3 Report

Thank you for considering my original comments. The manuscript is much clearer now. I still wonder how the brittle stars move so quickly in response to rainfall, and reproduction takes much longer time than the observed density changes, but I know that there is no answer at this point. The study is a valuable contribution to better understanding the ecology of this species and its hosts.

I spotted a typo in the caption of table S1: "gorgenocephale" should be gorgoncephale. There may be others, but the tracked changes that split letters from words made it hard to spot errors. 

Author Response

Thank you for considering my original comments. The manuscript is much clearer now. I still wonder how the brittle stars move so quickly in response to rainfall, and reproduction takes much longer time than the observed density changes, but I know that there is no answer at this point. The study is a valuable contribution to better understanding the ecology of this species and its hosts.

We would like to thank you again for your help in improving the manuscript, as all your comments were very useful and appreciated.

I spotted a typo in the caption of table S1: "gorgenocephale" should be gorgoncephale. There may be others, but the tracked changes that split letters from words made it hard to spot errors. 

We have checked through the file the presence of other errors, thank you.