About the Tropicalization of the Spanish Mediterranean Waters: Effects on Fish Communities

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review of: About the tropicalization of the Spanish Mediterranean waters

This study is concerned with a comparison of the tolerance  temperature ranges of native fish in the Spanish Mediterranean waters with those of fish that were first reported after 2017 in the same location. A previous study had based their tolerance values on data from the global range of all species of fish that were native to the Spanish Mediterranean. The current study determined the tolerance ranges for the same native fish using  only temperature data from the Spanish Mediterranean waters. The study found that the new values for native fish using only Spanish Mediterranean data were higher than those using an international data base. This finding modified the conclusion of the previous study.

            In my opinion the authors proved their point that it was important to base temperature tolerances of fish species on data from the Mediterranean waters rather than an international data base.

            I found this was a very difficult paper to follow.  It took me several hours to understand the methods and results. A part of my problem was geographic. I work in another part of the world and do not have a detailed knowledge of the regions under study.  I would like to see maps that specifically show the following locations:

Strait of Gibraltar and Alboran Sea (ESAL)

Levantine-Balearic regions (LEBA)

Figure 4. From the figures themselves and the legend itself, I found it hard to know the two regions under consideration. To describe parts A and B the figure uses terms like Strait-Alboran Sea Climatology and Levantine-Balearic sea Climatology. The legend uses terms like Alboran Sea and Balearic Sea. The legend also uses ESAL while the text (Lines 263-264) refers to the regions in that figure as ESAL and LEBA. This is very confusing to the reader. Consistenacy is needed. Don’t use different names for the same thing.

There is a. similar problem with the multiple ways that temperature tolerances can be referred to. We have maximum, minimum and mean tolerance values in two different regions. For example the median temperature  tolerance is found for the native fish species in international waters and in the Mediterranean. Likewise for the new species of fish found in the Mediterranean since 2017, we have median tolerance values for those fish in international waters and in the Mediterranean. In the text it is not always clear what group is being referred to; For example in the abstract (Line 30-32) it states “a surprising result: the Mediterranean species recorded in LFBA up to 2017 exhibit higher thermal preferences than those reported after this year, a difference that exceeds what had been observed in previous analyses.” I could not understand where this conclusion came from and what data set was being used.

Author Response

Please, find below my answers in bold (and also in the attached word document).

Review of: About the tropicalization of the Spanish Mediterranean waters

First of all we would like to sincerely thank the reviewer for this constructive review.

This study is concerned with a comparison of the tolerance  temperature ranges of native fish in the Spanish Mediterranean waters with those of fish that were first reported after 2017 in the same location. A previous study had based their tolerance values on data from the global range of all species of fish that were native to the Spanish Mediterranean. The current study determined the tolerance ranges for the same native fish using  only temperature data from the Spanish Mediterranean waters. The study found that the new values for native fish using only Spanish Mediterranean data were higher than those using an international data base. This finding modified the conclusion of the previous study.

            In my opinion the authors proved their point that it was important to base temperature tolerances of fish species on data from the Mediterranean waters rather than an international data base.

            I found this was a very difficult paper to follow.  It took me several hours to understand the methods and results. A part of my problem was geographic. I work in another part of the world and do not have a detailed knowledge of the regions under study.  I would like to see maps that specifically show the following locations:

Strait of Gibraltar and Alboran Sea (ESAL)

Levantine-Balearic regions (LEBA)

We fully agree with the reviewer. This is a common mistake that we make. We erroneously think that everybody works in the Mediterranean Sea. We have added a new Figure 1 situating the Mediterranean in a broader geographical context (Fig. 1A), and then a more detailed map showing the location and definition of ESAL and LEBA regions. Beside this, we have tried to use these terms (ESAL and LEBA) throughout the text.

Figure 4. From the figures themselves and the legend itself, I found it hard to know the two regions under consideration. To describe parts A and B the figure uses terms like Strait-Alboran Sea Climatology and Levantine-Balearic sea Climatology. The legend uses terms like Alboran Sea and Balearic Sea. The legend also uses ESAL while the text (Lines 263-264) refers to the regions in that figure as ESAL and LEBA. This is very confusing to the reader. Consistenacy is needed. Don’t use different names for the same thing.

The reviewer is right. We had used ESAL and LEBA in the old Figure 2 (now Figure 3) and in lines 200 to 203, but we accept that we had mixed different terminologies in the caption of Figure 3 (now Figure 4). We have corrected this and now we use ESAL and LEBA regions throughout the whole manuscript (there is one single exception in the discussion).

There is a. similar problem with the multiple ways that temperature tolerances can be referred to. We have maximum, minimum and mean tolerance values in two different regions. For example the median temperature  tolerance is found for the native fish species in international waters and in the Mediterranean. Likewise for the new species of fish found in the Mediterranean since 2017, we have median tolerance values for those fish in international waters and in the Mediterranean. In the text it is not always clear what group is being referred to; For example in the abstract (Line 30-32) it states “a surprising result: the Mediterranean species recorded in LFBA up to 2017 exhibit higher thermal preferences than those reported after this year, a difference that exceeds what had been observed in previous analyses.” I could not understand where this conclusion came from and what data set was being used.

Once again, the reviewer is right. We use three types of temperature data as already explain in the manuscript. FishBase values for new records, FishBase values for native Mediterranean species in the previous manuscript (and in the present one just for comparison), and temperature values from a Mediterranean climatology for Mediterranean native species. Following the reviewer’s suggestion, we have clarified in lines 485-487 what data we are talking abouit. We have also added some lines in the abstract for making more clear our point.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript entitled “About the tropicalization of the Spanish Mediterranean waters” deals with the “tropicalization hypothesis” which  refers to the idea that warming oceans are causing temperate marine ecosystems to become more “tropical-like” in structure and function. In other words, as sea temperatures rise due to climate change, tropical species expand their ranges poleward, while temperate or cold-water species decline or retreat, leading to a gradual shift in community composition toward tropical assemblages. The Poleward expansion of tropical species is composed of many tropical fish, invertebrates, and algae move into subtropical and temperate regions as previously cooler waters become warm enough to sustain them.

In the case of this manuscript just focused on fish, I suggest rephrasing the title to be adequate on fish topicalization

The study is dedicated to documenting the tropicalization of the Mediterranean Sea by recording fish that were not present before 2017. The study attempts to demonstrate the tropicalization of fish species through the thermal preferences of the collected fish.

The authors look forward to explaining what is happening in Spanish water of Mediterranean Sea with fish assemblage at two places: the Strait of Gibraltar Alboran Sea and the Levantine–Balearic Sea. The study considered the hypothesis of global warming that is affecting the sea temperature starting with the idea that in marine ecosystems, water temperature is widely regarded as the most significant environmental variable influencing species distribution and community structure within fish assemblages. The hypothesis is linked with the other idea that global warming is triggering shifts in the distribution of marine species. Particularly is assumed to be a northward migration of tropical fishes.

The study will be more strength if it considers reproduction: Species adapted to cooler waters often experience stress, reduced reproduction, or mortality as temperatures exceed their tolerance limits.

The manuscript entitled “About the tropicalization of the Spanish Mediterranean waters” deals with the “tropicalization hypothesis” which  refers to the idea that warming oceans are causing temperate marine ecosystems to become more “tropical-like” in structure and function. In other words, as sea temperatures rise due to climate change, tropical species expand their ranges poleward, while temperate or cold-water species decline or retreat, leading to a gradual shift in community composition toward tropical assemblages. The Poleward expansion of tropical species is composed of many tropical fish, invertebrates, and algae move into subtropical and temperate regions as previously cooler waters become warm enough to sustain them.

In the case of this manuscript just focused on fish, I suggest rephrasing the title to be adequate on fish topicalization

The study is dedicated to documenting the tropicalization of the Mediterranean Sea by recording fish that were not present before 2017. The study attempts to demonstrate the tropicalization of fish species through the thermal preferences of the collected fish.

The authors look forward to explaining what is happening in Spanish water of Mediterranean Sea with fish assemblage at two places: the Strait of Gibraltar Alboran Sea and the Levantine–Balearic Sea. The study considered the hypothesis of global warming that is affecting the sea temperature starting with the idea that in marine ecosystems, water temperature is widely regarded as the most significant environmental variable influencing species distribution and community structure within fish assemblages. The hypothesis is linked with the other idea that global warming is triggering shifts in the distribution of marine species. Particularly is assumed to be a northward migration of tropical fishes.

The study will be more strength if it considers reproduction: Species adapted to cooler waters often experience stress, reduced reproduction, or mortality as temperatures exceed their tolerance limits.

 

Author Response

We sincerely thank the reviewer for this constructive review.

The manuscript entitled “About the tropicalization of the Spanish Mediterranean waters” deals with the “tropicalization hypothesis” which  refers to the idea that warming oceans are causing temperate marine ecosystems to become more “tropical-like” in structure and function. In other words, as sea temperatures rise due to climate change, tropical species expand their ranges poleward, while temperate or cold-water species decline or retreat, leading to a gradual shift in community composition toward tropical assemblages. The Poleward expansion of tropical species is composed of many tropical fish, invertebrates, and algae move into subtropical and temperate regions as previously cooler waters become warm enough to sustain them. In the case of this manuscript just focused on fish, I suggest rephrasing the title to be adequate on fish topicalization

We agree with the reviewer and following this suggestion, we have changed the title, indicating that this work is focused on fish populations.

The study is dedicated to documenting the tropicalization of the Mediterranean Sea by recording fish that were not present before 2017. The study attempts to demonstrate the tropicalization of fish species through the thermal preferences of the collected fish.

The authors look forward to explaining what is happening in Spanish water of Mediterranean Sea with fish assemblage at two places: the Strait of Gibraltar Alboran Sea and the Levantine–Balearic Sea. The study considered the hypothesis of global warming that is affecting the sea temperature starting with the idea that in marine ecosystems, water temperature is widely regarded as the most significant environmental variable influencing species distribution and community structure within fish assemblages. The hypothesis is linked with the other idea that global warming is triggering shifts in the distribution of marine species. Particularly is assumed to be a northward migration of tropical fishes.

The study will be more strength if it considers reproduction: Species adapted to cooler waters often experience stress, reduced reproduction, or mortality as temperatures exceed their tolerance limits.

We also agree with this comment. In fact, at the end of the discussion and conclusions sections, we had already explain that a very important point was to discern if the species newly recorded had been naturalized or not. The truth is that we do not have reproduction data, or icthyoplankton data where we could identify eggs and/or larvae of these new species, showing that reproduction was occurring. Beside this, reproduction studies could show changes in the native species. As we say, we do not have these data. However, we have added some lines at the end of the work in order to emphasize this idea suggested by the reviewer and the importance of carrying out that kind of studies in the future.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revision has answered my questions.