Assessment of the Offshore Migration of Mussel Production Based on an Aquaculture Similarity Index (ASI)
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn general, the study is acceptable for publication. However, the unusual amount of data and (simple) calculations have resulted in the conclusion, which are rather obvious and the resulted areas of possible expansion of the aquaculture area may be proposed rather without these data and calculations. The Authors stress several times the global warming and other rapid changes in the world around us, but - as they also notice - their index does not contain any factor but the present ones. In my opinion the study should be published, but its significance is rather restricted. There are several suggested corrections I have marked in the file (please look at them). English should be corrected. perhaps the most important are figures - maps, whose markings ("a, b, c, ...) should be bigger and better visible. Some symbols are misused in the text.
Comments for author File: 
Comments.pdf
I am not a native speaker, but still I aam strongly suggesting the careful edition of the text by a native speaker. The English is, in general, not bad, but several statements should be rephrased (see the file). Especially several words are, in my opinion, misused.
Author Response
General comments:
In general, the study is acceptable for publication. However, the unusual amount of data and (simple) calculations have resulted in the conclusion, which are rather obvious and the resulted areas of possible expansion of the aquaculture area may be proposed rather without these data and calculations. The Authors stress several times the global warming and other rapid changes in the world around us, but - as they also notice - their index does not contain any factor but the present ones. In my opinion the study should be published, but its significance is rather restricted. There are several suggested corrections I have marked in the file (please look at them). English should be corrected. perhaps the most important are figures - maps, whose markings ("a, b, c, ...) should be bigger and better visible. Some symbols are misused in the text.
We thank the reviewer for their constructive evaluation and for considering the study suitable for publication. We acknowledge the reviewer’s concern that some of the conclusions may appear straightforward; however, we would like to emphasize that the novelty of this work lies in the methodological framework itself. The Aquaculture Suitability Similarity Index (ASI) integrates both environmental and technical factors into a spatially explicit, operational tool that evaluates similarity to historically successful cultivation sites. Unlike traditional suitability models, this approach offers a transferable and decision-oriented methodology that can be adapted to other regions and species, thereby supporting evidence-based aquaculture planning under current and future challenges.
Regarding the reviewer’s technical suggestions:
Markings in Figures 2, 3 and 4 have been enlarged to improve visibility.
All suggested corrections, including word choice and rephrasing, have been applied throughout the text to improve clarity and English style.
We apologize for the typographical error: the BGC index was mistakenly written as BQC in the original manuscript, and this has been corrected consistently in the revised version.
All revisions implemented in response to the reviewers’ comments are indicated in red throughout the manuscript.
Specific comments:
Comment 1. Line 38. Author and date related to the sentence “Mytilus galloprovincialis, is one of the most significant economic activities in the coastal region.
Response 1. References were added in the revised version of the manuscript.
Comment 2. The reviewer suggested changing “logistical constraints” to “logistic constraints” in some parts of the manuscript. We have carefully checked the usage and found that:
Response 2. Logistical constraints → preferred and standard in scientific and technical writing; refers to practical limitations related to logistics (e.g., transport, accessibility, infrastructure).
Logistic constraints → less common and can be confused with “logistic” in a mathematical sense (e.g., logistic regression or logistic curve).
Therefore, in the context of our study (aquaculture site selection, environmental conditions, etc.), “logistical constraints” is the correct and clearest phrasing.
Comment 3. Line 209. What are technical variables?
Response 3. We define technical variables as those related to practical constraints, such as water depth and distance to the nearest port. These variables are specified in the abstract.
Comment 4. Lines 242,243. 0.0036° × 0.0027° longitude or latitude? rather latitude, as constant, but this should be noted
Response 4. The values 0.0036° × 0.0027° correspond to longitude and latitude increments, respectively. The 0.0036° refers to the longitude grid spacing, and the 0.0027° refers to the latitude grid spacing. We acknowledge that the latitude spacing is effectively constant and have added a note in the manuscript to clarify this (lines 259-261).
Comment 5. Line 535. I cannot see BQC index in the figure.
Response 5. We apologize for the typographical error: the BGC index was mistakenly written as BQC in the original manuscript. This has been corrected throughout the revised text.
Comment 6. Line 612. Why not sessile organisms should be less sensitive? Surely, Mytilus cannot migrate to some other habitats, but its larvae can
Response 6. While mussels are sessile as adults and cannot relocate to avoid thermal stress, their larvae are planktonic and capable of dispersal. However, larval survival and successful recruitment are still strongly influenced by local environmental conditions, including temperature extremes and heatwaves. Therefore, both adult and larval stages remain vulnerable to climate change, justifying the need to explore alternative cultivation areas within the Rías Baixas that offer greater environmental resilience. This was added in the revision version of the manuscript (lines 630-636).
Comment 7. Lines from 619 to 623. it has already been stated above, more than one time.
Response 7. This part was removed following reviewer’s suggestion.
Comment 8. Line 736. New species in which sense?
Response 8. By “new species,” we refer to non-native species at a given location. This has been clarified in the revised version of the manuscript (lines 754-755).
Comment 9. Line 754. Water depth t is also an environmental factor
Response 9. We acknowledge that some technical factors, such as water depth, may also influence environmental conditions. However, in the ASI framework, these variables are classified as technical factors because they primarily relate to operational and logistical constraints rather than natural environmental variability.
Comment 10. Line 764. which is such a strategy?
Response 10. By “strategically,” we refer to a combination of site-specific planning, prioritization of areas with favorable environmental and logistical conditions, and the implementation of adaptive management practices to address operational challenges. This was better explained in this revised version of the manuscript (lines 794- 797).
Reviewer 2 Report
Comments and Suggestions for AuthorsReview of mussel production
1 – Line 25, abstract “exposure” to what? Not clear
2- Around line 70, It’s not clear if harmful algal blooms have occurred in the recent past. Is this a projection or a recurring problem. If blooms have occurred what species are involved – are the algae toxic to humans or mussels, and do they reduce the crop or make the mussels inedible?
3 – Has increased stratification already occurred and is there evidence for recently elevated temperatures or is this a future project only. In the region where this reviewer works, coastal bays are already experiencing temperature changes, and increased stratification. Is this the case in Spain?
4 – circa line 207, did the author’s develop the ASI entirely themselves or did they use models from other regions - there is no citation in the introduction to the methods to indicate the authors utilized other sources – is there no previous work along this line?
5 – The information supplied concerning the construction of the model and the data sources utilized is very detailed, and the process appears to consider the likely major environmental factors influencing mussel production.
6 – lines 663-664, when citing an author or paper as the subject of a sentence, it is better to use the senior author’s name and date, rather than just the citation number
7 – A potential use of this model is to determine which locales would be the best suited for expansion of mussel operations, considering not just the physical environment but also travel distance from existing docks, location of shipping lanes, barriers to permitting, spacing rafts to reduce local eutrophication, and the potential longevity of the relocated mussel operations. Although the mussel cultures can be moved over a wide area – and the consumer demand is likely to continue or grow – which strategy would be best – particularly to avoid eutrophication and conflicts with other fisheries or maritime trades? It would be worthwhile to address the next phase of model use in the discussion.
8 – The English is very professional and the paper is well written.
9 - This paper should briefly discuss trends in mussel sales and prices.
10 - There is no concrete discussion of a timeline for shifting mussel culture. When should this process start and where should it initially go?
The two requested improvements are to clarify current documented changes in the physical environment and water quality, and to briefly discuss how best to determine the sites for future mussel operations,,
Author Response
General comments
All revisions implemented in response to the reviewers’ comments are indicated in red throughout the manuscript.
Specific comments
Comment 1. – Line 25, abstract “exposure” to what? Not clear
Response 1. This part of the abstract was rewritten to make it clearer (lines 25, 26).
Comment 2. Around line 70, It’s not clear if harmful algal blooms have occurred in the recent past. Is this a projection or a recurring problem. If blooms have occurred what species are involved – are the algae toxic to humans or mussels, and do they reduce the crop or make the mussels inedible?
Response 2. Harmful algal blooms are a recurrent problem in the Rías Baixas and have been extensively studied, as described in reference [5]. Phytoplankton blooms can, under certain conditions, develop into seawater discolorations (commonly referred to as “red tides”). While many of these events are harmless, some evolve into high-biomass harmful algal blooms (HABs), which include toxin-producing species. These HABs do not usually kill mussels directly but can make them unsafe for human consumption, leading to harvesting closures and significant economic losses for the aquaculture sector. Lines (86-90).
Comment 3. Has increased stratification already occurred and is there evidence for recently elevated temperatures or is this a future project only. In the region where this reviewer works, coastal bays are already experiencing temperature changes, and increased stratification. Is this the case in Spain?
Response 3. Yes, the reviewer is correct — the Rías Baixas (Spain) are already experiencing temperature changes, as documented in [7, 10] and the references therein. To make this clearer, the fourth paragraph of the introduction has been rewritten to emphasize not only projected but also ongoing changes in sea surface temperature and stratification. For instance, Des et al. (2022) reported historical and future warming trends along the Galician coast in the context of aquaculture species, while Román et al. (2025) provided experimental evidence of the impacts of recent atmospheric heatwaves on intertidal shellfish beds in northwestern Spain. These findings support the view that elevated temperatures and increased stratification are already affecting the region and not merely a future projection.
Des, M.; Gomez-Gesteira, J.L.; deCastro, M.; Iglesias, D.; Sousa, M.C.; ElSerafy, G.; Gomez-Gesteira, M. Historical and Future Naturalization of Magallana Gigas in the Galician Coast in a Context of Climate Change. Sci. Total Environ. 2022, 838, pp. 156437. https://doi.org/10.1016/j.scitotenv.2022.156437.
Román, S.; Vázquez, E.; Román, M.; Viejo, R.M.; Weidberg, N.; Troncoso, J.S.; Woodin, S.A.;Wethey, D.S.; Olabarria, C. Understanding the effects of recent atmospheric heatwaves on seagrass-inhabited intertidal shellfish beds: a mesocosm experiment. Mar. Environ. Res. 2025, 212, pp. 107547 https://doi.org/10.1016/j.marenvres.2025.107547.
Comment 4. circa line 207, did the author’s develop the ASI entirely themselves or did they use models from other regions - there is no citation in the introduction to the methods to indicate the authors utilized other sources – is there no previous work along this line?
Response 4. There are different environmental suitability indices in the literature, most of them rely in already known limits of tolerance of the species under analysis. This approach is preferred when those limits are well defined. The ASI was developed entirely by us, as we recognized that the tolerance limits for mussels reported in the literature do not adequately reflect the specific characteristics of our study area.
Comment 5. The information supplied concerning the construction of the model and the data sources utilized is very detailed, and the process appears to consider the likely major environmental factors influencing mussel production.
Response 5. Thank you for your kind comment.
Comment 6. lines 663-664, when citing an author or paper as the subject of a sentence, it is better to use the senior author’s name and date, rather than just the citation number.
Response 6. This was changed through the revised version of the manuscript.
Comment 7. A potential use of this model is to determine which locales would be the best suited for expansion of mussel operations, considering not just the physical environment but also travel distance from existing docks, location of shipping lanes, barriers to permitting, spacing rafts to reduce local eutrophication, and the potential longevity of the relocated mussel operations. Although the mussel cultures can be moved over a wide area – and the consumer demand is likely to continue or grow – which strategy would be best – particularly to avoid eutrophication and conflicts with other fisheries or maritime trades? It would be worthwhile to address the next phase of model use in the discussion.
Response 7. We appreciate this insightful suggestion. As the reviewer correctly notes, the ASI framework was designed primarily to integrate key environmental and technical variables, serving as a first-order tool to identify areas with conditions similar to existing successful farms. Following the ASI calculation, however, we did not consider areas where potential conflicts with maritime traffic, navigation safety, or water quality preservation were likely. Specifically, ASI results were excluded from navigation zones, port vicinities, maritime transit corridors, vessel maneuvering areas, and coastal zones designated for tourism or recreation. Likewise, we excluded areas reserved for traditional and artisanal fisheries in order to safeguard fishery resources and avoid conflicts. In the Rías Baixas, the extent of such excluded zones is expected to increase under stricter regulatory frameworks, further underscoring the need to explore cultivation sites in more exposed offshore areas.
Looking ahead, the next phase of model development should extend beyond the physical environment to explicitly incorporate technological advances, which may represent a key dimension in guiding ASI applications. One promising direction is the use of hybrid offshore platforms that integrate aquaculture facilities with wave energy converters (WECs). Such platforms could attenuate wave energy, thereby reducing structural stress on mussel rafts, while simultaneously supplying renewable energy for farm operations such as monitoring and product handling. By embedding both these broader regulatory and socio-ecological constraints and the potential of technological innovations into the ASI framework, future applications could provide a more holistic basis for identifying sustainable expansion areas, balancing environmental suitability with operational resilience and long-term viability. A new paragraph was added at the end of the discussion section to address these issues (lines 766-778)
Comment 8. The English is very professional and the paper is well written.
Response 8. Thank you for comment.
Comment 9. This paper should briefly discuss trends in mussel sales and prices.
Response 9. We thank the reviewer for this suggestion. The second paragraph of the introduction has been revised to address this point. The Spain mussel farming market was valued at approximately USD 432.34 million in 2018, increased to USD 616.18 million in 2024, and is projected to reach USD 997.68 million by 2032, reflecting a compound annual growth rate (CAGR) of 5.78% during the forecast period (2025–2032) (https://www.credenceresearch.com/report/spain-mussel-farming-market?utm_source=chatgpt.com#summary). Remarkably, the autonomous region of Galicia produces 97% of Spain’s mussels, with production almost entirely concentrated in the Rías Baixas, highly productive embayments along the Atlantic coast [1, 2]. Mussel production in Galicia has maintained strong market demand, with relatively stable prices over recent years, reflecting the sector’s economic resilience and continued significance both domestically and internationally [1]. Prices exhibit some seasonal variation due to harvest cycles, and a substantial portion of production is exported, emphasizing Galicia’s key role in global mussel markets. These points have been incorporated into the introduction to provide context on the socio-economic relevance of mussel aquaculture.
Comment 10. There is no concrete discussion of a timeline for shifting mussel culture. When should this process start and where should it initially go?
Response 10. We appreciate the reviewer’s comment. At present, it is not possible to define a precise timeline for shifting mussel culture toward more external areas of the rías, since this process depends on multiple factors and the decisions of administrative authorities. Key determinants include the development of technological solutions (e.g., offshore platforms and anchoring systems), evolving regulatory frameworks, and the balance of interactions with other maritime activities such as fisheries, tourism, and transport.
What is already clear, however, is the growing need to anticipate this shift in the near future. Mussel aquaculture in the Rías Baixas is increasingly exposed to pressures such as anthropogenic stress, stricter environmental regulations, rising sea temperatures, stronger stratification, and more frequent extreme precipitation events that reduce salinity in the inner rías. These factors have already impacted the productivity of several species in the area.
In this context, the ASI developed in this study is not intended to prescribe exact timelines but rather to provide a decision-support tool that helps managers and stakeholders identify suitable future areas for relocation. By doing so, it contributes to advancing proactive strategies to maintain sustainable mussel production under changing environmental and socio-economic conditions.
Comment 11. The two requested improvements are to clarify current documented changes in the physical environment and water quality, and to briefly discuss how best to determine the sites for future mussel operations.
Response 11. We thank the reviewer for their valuable feedback. All suggested corrections have been carefully applied throughout the manuscript, and we believe that the revised version now addresses the two requested improvements.
