The Heatwave of Summer 2022 in the North-Western Mediterranean Sea: Some Species Were Winners

Round 1

Reviewer 1 Report

General comment:

 This work, following the MHV event occurred in 2022, discusses the positive impact observed on three species that in the current context of climate change can be considered winners: Microdictyon umbilicatum, Penicillus capitatus and Posidonia oceanica.

The work provides empirical information "based on the opportunistic observations of the authors, spread across the entire studied area" and the results presented allow us to generate hypotheses and open new lines of research. The conclusion that "Extreme events always induce extreme reactions (also at the scientific level)" is remarkable and also gives food for thought that the scientific dependence on the search for maximum academic impact can generate important biases in knowledge.

 The paper is well presented and written, with good bibliographic support. Therefore, I believe it is publishable as it is. However, I suggest the authors improve or clarify some aspects that I will explain below.

 Introduction section:

 In line 86 the authors explain that there is a correlation between summer rainfall and the abundance of Astrospartus mediterraneus to hypothesize that this species is a possible "global change winner". In my opinion, it would be of interest to explain very briefly why this phenomenon of summer rainfall can be linked to climate change.

 Material and methods section

 It is emphasized that this work is based on "the opportunistic observations of the authors". More information on these observations should be given in this section to demonstrate to the reader that the empirical basis is consistent.

 Section Results and discussion

 In lines 157-158: "In contrast, the paintbrush stage is quite uncommon and localized at a very few sites, especially in the north-western Mediterranean" it is not clear whether this "Paintrbrush stage" is rare but somewhat more frequent in warm areas and therefore even more localized in the "north-western Mediterranean" areas. I would rewrite the sentence to make it clearer.

 A graphic representation (on a map) of what is known about the Mediterranean distribution of M. umbilicatum and P. capitatus would perhaps make it easier for the reader to quickly have a visual representation of this distribution (including the huge information gaps).

 In lines 215-216 it is emphasized that the flowering of P. oceanica is autumnal like other Mediterranean terrestrial phanerogams. However, no citation is provided nor is the hypothesis of the possible relationship between the two patterns as the authors seem to suggest.

In lines 242-245 it is stated that P. oceanica has withstood several events in the Mediterranean including the Messinian crises. However, no papers are cited in this regard although the consensus on the possibility that this species is a "Tethyan relict" is not absolute.

Conclusion section:

Some of the structural changes linked to possible climate change in the Mediterranean Sea are discussed. However, the example of the Lessepsian invasion of the genus Siganus in the Eastern Mediterranean and the changes it is generating at the community level may also be a consequence of the pre-existing thermal conditions in this eastern basin (or much of it), and this should also be discussed. Perhaps the authors can also look for other reported examples where changes in distribution and structure may be, less ambiguously, a product of warming (as the very expansion of Siganus and other thermophilic species in more northern and western parts of the Mediterranean).

 The pattern, also scientific and not only media, of exaggerating the destruction caused by extreme events such as MHV's is made explicit. In this sense, I believe that the authors could also look for some more literature, apart from citation 144, that justifies the underestimated resilience of these communities and their rather localized spatial and temporal impact through MHV's events. In lines 354-56 it is mentioned that "these species have high dispersal capacities via planktonic larvae, and connectivity between populations is maintained since it is rare that all of the individuals are killed", however, it is not specified to which type of organisms they refer and despite of the fact that there are many circalittoral foundation species (such as Paramuricea clavata) with lecithotrophic larvae and rather low interpopulation connectivity. Therefore, it would be necessary to provide concrete examples with their respective citations.

Author Response

Reviewer 1

Response to Reviewer 1

Many thanks for these valuable suggestions.

Comment. In line 86 the authors explain that there is a correlation between summer rainfall and the abundance of Astrospartus mediterraneus to hypothesize that this species is a possible "global change winner". In my opinion, it would be of interest to explain very briefly why this phenomenon of summer rainfall can be linked to climate change.

Response. We have just reported the authors’ assertion (Canessa, M.; Betti, F.; Bo, M.; Enrichetti, F.; Toma, M.; Bavestrello, G. Possible population growth of Astrospartus mediterraneus (Risso, 1826) (Ophiuroidea, Gorgonocephalidae) in the Mediterranean Sea. Diversity 2023, 15(122), 1-16).

Comment. It is emphasized that this work is based on "the opportunistic observations of the authors". More information on these observations should be given in this section to demonstrate to the reader that the empirical basis is consistent.

Response. We have given more details in the Materials and Methods section.

Comment. In lines 157-158: "In contrast, the paintbrush stage is quite uncommon and localized at a very few sites, especially in the north-western Mediterranean" it is not clear whether this "Paintrbrush stage" is rare but somewhat more frequent in warm areas and therefore even more localized in the "north-western Mediterranean" areas. I would rewrite the sentence to make it clearer.

Response. The sentence has been rewritten to make it clearer

Comment. A graphic representation (on a map) of what is known about the Mediterranean distribution of M. umbilicatum and P. capitatus would perhaps make it easier for the reader to quickly have a visual representation of this distribution (including the huge information gaps).

Response. The distribution of Penicillus capitatus (paintbrush stage) is given in the text. As far as Microdictyon is concerned, we have added a map.

Comment. In lines 242-245 it is stated that P. oceanica has withstood several events in the Mediterranean including the Messinian crises. However, no papers are cited in this regard although the consensus on the possibility that this species is a "Tethyan relict" is not absolute.

Response. Very relevant remark! We added this sentence and references: ‘As to how P. oceanica possibly survived the Messinian crises, the debate remains open (Taviani, 2002: Boudouresque, 2004; Bianchi et al., 2012): its presence in the Mediterranean is only formally attested by fossils after these crises (Moissette et al., 2007; Koskeridou et al., 2019).

Comment. The example of the Lessepsian invasion of the genus Siganus in the Eastern Mediterranean and the changes it is generating at the community level may also be a consequence of the pre-existing thermal conditions in this eastern basin (or much of it), and this should also be discussed.

Response. A sentence has been added

Comment. Perhaps the authors can also look for other reported examples where changes in distribution and structure may be, less ambiguously, a product of warming (as the very expansion of Siganus and other thermophilic species in more northern and western parts of the Mediterranean).

Response. Other examples have been added.

Comment. I believe that the authors could also look for some more literature, apart from citation 144, that justifies the underestimated resilience of these communities and their rather localized spatial and temporal impact through MHV's events. In lines 354-56 it is mentioned that "these species have high dispersal capacities via planktonic larvae, and connectivity between populations is maintained since it is rare that all of the individuals are killed", however, it is not specified to which type of organisms they refer and despite of the fact that there are many circalittoral foundation species (such as Paramuricea clavata) with lecithotrophic larvae and rather low interpopulation connectivity. Therefore, it would be necessary to provide concrete examples with their respective citations.

Response. References have been added and species specified. A sentence has been added about inter-individual and inter-populational variability.

Author Response File: Author Response.pdf

Reviewer 2 Report

I would like to congratulate the authors for this original and thoughtful work. As mentioned in the manuscripts, most of the current literature in the context of climate change and assessment of mass mortality events is focused on the “loser species” and it is only now that the scientific community start to focus on the “winner species”. We need more articles like this manuscript collecting information about winner species distribution patterns and expansion dynamics.

The article was an interesting reading although I think I would benefit from a quick read by a native English speaker to enhance the readability of some sections. I think leave below my suggestions and comments:

Line 24: the abbreviation of marine heat wave in English is MHW, please correct from the abstract and along the manuscript (Line 26, 108, ). In addition, a MHW is defined as a defined period, that in some cases can last for months. Therefore, I would suggest rephrasing “short-period” or adding relative.

Line 27: I would consider to add species to “winner”.

Line 31: If it was simply caught by fishing nets it is ok as it is. If because of the abundance of the algae, this interfered with the fishing activities I would consider to use the term “clog” the nets.

Line 34-35: the phrase is not quite clear, I would rephrase it.

Line 41-44: it is a long phrase that it too many commas. I would consider to shorten it.

Line 53: MHWs.

Line 54-56: Great statement. I completely agree with the authors.

Line 60 and 360: MHWs

Line 63-79: I would consider rewrite this full paragraph in more fluent way to increase readability.

Line 70: “non-indigenous species native to warm seas” is a bit confusing. Could it be rephrased to non-indigenous thermophilic species?

Line 76-79: the structure of these 3 phrases seems not right. Moreover, there is a opened parenthesis that was never closed.

Line 82-88: I would better connect the “it was considered as rare” to the beginning of the paragraph. In addition, although all facts around the basket star paragraph back up the idea of considering it a “winner species” I would suggest to better connect the different facts to increase readability.

Line 90-91: no comma in “depth range, of sessile invertebrates”. Also, I would consider to add “e.g.,” when including example species for gorgonians and sponges.

Line 118-122: I would better explain the fact developed here. To avoid repetitions and confusions, I would firstly avoid the use of “negative anomaly of wind episodes” and explain the lack of strong local winds that usually contribute to the upper layer mixing processes that would have helped preventing the documented extreme thermal event. I addition, the last phrase is not so clear.

Line 139 196 and 347: fishermen.

Figure 1: just some aesthetic comments: I would suggest some minor color correction and white balance to the pictures provided. Moreover, the scale could be added as the one in figure 1, leaving the metric reference out of the frame to homogenize the figures.

Figure 2: I would avoid to avoid too much repetition between the information showed in the legend of the figure and the caption. I would retake the “screen capture” to avoid the office markers to reshape/reorientate the legend. In addition, I would consider to put together Figure 2 and 3 vertically (also to homogenize format with Fig.1).

Line 245: reorder words to “Little Ice Age”.

Line 346-348: I would revisit the structure of this phrase.

Line 350-355: It is a very interesting discourse the one presented between the part in 350-355 and the second one in the last part of this paragraph. I missed a better connection/linker among them.

Line 363: I would add [58] as well.

Line 366: others.

 I think I would benefit from a quick read by a native English speaker to enhance the readability of some sections.

Author Response

Responses to Reviewer 2

Many thanks for these valuable suggestions.

I had a problem: the line numbering used by the reviewer did not correspond to that of my manuscript. In most cases, I was nevertheless able to identify the paragraph in question, but not always.

Author Response File: Author Response.pdf