Mitigating the Impact of Harmful Algal Blooms on Aquaculture Using Technological Interventions: Case Study on a South African Farm

Round 1

Reviewer 1 Report (Previous Reviewer 1)

no comments 

Author Response

We appreciate Reviewer 1 in checking the manuscript and submitting their report.

Reviewer 2 Report (Previous Reviewer 3)

This paper is a revision of a previously submitted paper. It appears that the authors have addressed most of the issues that I previously identified, although it is impossible to know for certain because they don’t provide a specific response to each major comment. Instead, they provide a very generic paragraph, which is insufficient for most journals. The paper still has a number of grammatical issues, despite being proofread (one example: “data” is sometimes treated as a plural and sometimes as a singular word—please be consistent). While I personally find that unfortunate, it is possible that the editors do not see that as a major issue.

Here are a few remaining issues:

46-48: it is not clear if these mechanisms are related to toxin production or mineralization of organic matter (not related to toxicity) that depletes DO.  I think it is important to clearly distinguish whether the impact of HABs is due to direct toxicity or some other mechanism, as this will influence the impact on the aquaculture industry. Direct toxicity has human health implications, whereas hypoxic or anoxic conditions from respiration associated with organic matter mineralization may kill off the cultured organisms but would not impact human health. This is a key differentiator, yet is not addressed explicitly at all. See final comment.

235: define “R” – presumably the Rand, but not all international readers will know that. 

274: could turbidity also be caused by inorganic, suspended matter? How do you differentiate between the organic plankton vs the inorganic suspended matter?

294: why not measure chlorophyll a in ug/L, which is a much more common and intuitive unit than QSU?  Is there a universal conversion factor?

388: One of my biggest question marks is why doesn’t the early warning system also include bloom toxicity?  Is it a huge issue if the bloom is forming but it is not toxic? In that case, assuming the system is normally in a flow-through mode, the non-toxic algae would either be ingested as food or leave the system, but not actually be “harmful”.  However, if it is toxic, then taking the measures outlined makes sense. I may be missing something here, but if so, it suggests other readers will also be missing it. This point needs to be addressed. 

As noted above, additional proofing is needed to meet appropriate standards. 

Author Response

This paper is a revision of a previously submitted paper. It appears that the authors have addressed most of the issues that I previously identified, although it is impossible to know for certain because they don’t provide a specific response to each major comment. Instead, they provide a very generic paragraph, which is insufficient for most journals. The paper still has a number of grammatical issues, despite being proofread (one example: “data” is sometimes treated as a plural and sometimes as a singular word—please be consistent). While I personally find that unfortunate, it is possible that the editors do not see that as a major issue.

We thank reviewer 2 for taking time to review the article thoroughly. Suggested changes related to use of data have now been made in the article, all changes are tracked. For the remaining issues, please find answers below.

Here are a few remaining issues:

46-48: it is not clear if these mechanisms are related to toxin production or mineralization of organic matter (not related to toxicity) that depletes DO.  I think it is important to clearly distinguish whether the impact of HABs is due to direct toxicity or some other mechanism, as this will influence the impact on the aquaculture industry. Direct toxicity has human health implications, whereas hypoxic or anoxic conditions from respiration associated with organic matter mineralization may kill off the cultured organisms but would not impact human health. This is a key differentiator, yet is not addressed explicitly at all. See final comment.

We thank reviewer 2 for his comment. There is mechanical damage (spiked HABs that damage gills etc of animals), toxin production and depletion of DO - different HABs have different effects on different species. Direct toxicity can have human health implications. The reviewer has requested a whole different topic for this paper of which none of us have the required expertise and is beyond the scope of the paper. There are multitudes of levels to harmful algal blooms with a range of different effects.  However, we do appreciate the point and have now added more text in rows 47-60 with two additional references.

235: define “R” – presumably the Rand, but not all international readers will know that. 

We thank reviewer 2 for this comment, this is now addressed in article.

274: could turbidity also be caused by inorganic, suspended matter? How do you differentiate between the organic plankton vs the inorganic suspended matter?

We thank reviewer 2 for his comment.

Turbidity can be caused by inorganic, suspended matter which is why turbidity is a very rudimentary way to measure blooms and would need to be confirmed by taking direct samples which allows you to differentiate between contributing factors. In most cases high turbidity is accompanied by high energy seas, in which HABs are highly unlikely and the risk of effect is low.

294: why not measure chlorophyll a in ug/L, which is a much more common and intuitive unit than QSU?  Is there a universal conversion factor?

We thank reviewer 2 for his comment. This is the setting of the instrument used. However, absolute values are not needed in this study.

388: One of my biggest question marks is why doesn’t the early warning system also include bloom toxicity?  Is it a huge issue if the bloom is forming but it is not toxic? In that case, assuming the system is normally in a flow-through mode, the non-toxic algae would either be ingested as food or leave the system, but not actually be “harmful”.  However, if it is toxic, then taking the measures outlined makes sense. I may be missing something here, but if so, it suggests other readers will also be missing it. This point needs to be addressed. 

We thank reviewer 2 for his comments. Bloom toxicity takes at least a full day if not weeks to test for and tests are done when species of concern are noted, tests are also expensive- there are currently no cost-effective probes for measuring toxicity. The point of a early warning system is to fast-track mitigating actions, the 2017 bloom occurred within an afternoon and stayed in the bay for weeks. The text in rows 45-58 aims to illustrate that a harmful algal bloom does not necessarily mean a toxic alga, but other resulting conditions can result in mortality.

We have added further clarification in lines 405-408 to emphasise that model suggested here relates to algal biomass and not to the toxicity of the HAB.

Author Response File: Author Response.docx

Reviewer 3 Report (New Reviewer)

Dear Authors

The presented article contains a very interesting way to solve the problem of early warning of algal blooms and protection of food production.

However, I propose to make a few corrections:

1. Table No. 3 should be included in the additional materials because the results contained therein are included in Chart No. 3.

2. In table No. 4, it is enough to provide the values of the correlation coefficient with an accuracy of 4 significant numbers.

3. I lack information linking the abundance of phytoplankton with its toxicity to Haliotis midae.

Best regards

Reviewer

Author Response

The presented article contains a very interesting way to solve the problem of early warning of algal blooms and protection of food production.

We thank reviewer 3 for their constructive comments.

However, I propose to make a few corrections:

Table No. 3 should be included in the additional materials because the results contained therein are included in Chart No. 3.

We thank reviewer for their careful review of the article. However, we feel the table gives a sense of the measurements being taken. Two means of presenting same data are included to ensure clarity for all the readers. 

2. In table No. 4, it is enough to provide the values of the correlation coefficient with an accuracy of 4 significant numbers.

We thank reviewer for their careful review, this is an excellent point and now the tables are corrected to show values upto 4 significant figures.

3. I lack information linking the abundance of phytoplankton with its toxicity to Haliotis midae.

We thank reviewer for their careful review of article. This presented models relate to algal biomass or abundance of phytoplankton. Such an early warning system would trigger some more tests. The point of a early warning system is to fast action, the 2017 bloom occurred within an afternoon and stayed in the bay for weeks.  

Bloom toxicity takes at least a full day if not weeks to test for and tests are done when species of concern are noted, tests are also expensive- there are currently no cost-effective probes for measuring toxicity. 

Two more lines are added 405-408 to emphasise this.

Author Response File: Author Response.docx

Reviewer 4 Report (New Reviewer)

Article

Mitigating the impact of Harmful Algal Blooms on Aquaculture using technological interventions. Abagold: A Case study

Authors

Tahmina Ajmal *  , Fazeel Mohammed  , Martin Scott Goodchild  , Jipsy Sudarsanan Vinu Padman  , Sarah Halse

General comments on the manuscript are as follows:

Introduction:

Materials and working methods Chapter:

Chapter 2. Harmful Algal Bloom Mitigation Technologies, we believe should be reworded in its entirety to be as clear as the Materials and Methods chapter.

Also chapters 3 and 4 must be reconsidered so that both the observations, the case study: Abagold Limited-A Case Study, manage to express much better the scientific observations made in order to judge and validate the final results regarding Mitigating the impact of Harmful Algal Blooms on Aquaculture using technological interventions.

References:

References are appropriate.

The paper is well balanced with technical and scientific data. 

Author Response

Abstract: We believe that the abstract should be revised in order to present as well as possible both the observations resulting from the research analysis and especially the results obtained. 

Authors thank reviewers for their comment. We have now updated the abstract to include main findings. Please see rows 20-23

Introduction:

In the introduction, all the technical and scientific elements that form the basis of the work are presented in a concise and clear manner.  

Authors thank the reviewer for their positive feedback.

Materials and working methods Chapter:

Chapter 2. Harmful Algal Bloom Mitigation Technologies, we believe should be reworded in its entirety to be as clear as the Materials and Methods chapter.

Authors thank the reviewer for their time. Authors have made corrections where necessary to make this section clearer now.

Results and Discussions Chapter:

Also chapters 3 and 4 must be reconsidered so that both the observations, the case study: Abagold Limited-A Case Study, manage to express much better the scientific observations made in order to judge and validate the final results regarding Mitigating the impact of Harmful Algal Blooms on Aquaculture using technological interventions.

Authors thank the reviewer for their comments. We have now updated section 4 by adding more details about Abagold. Please see lines 253-263.

For a better and clear understanding, the Results and Discussions Chapter should be slightly revised in order to emphasize the presentation of the results of the research undertaken based on the relevant observations.

Authors thank the reviewer for their time. Additional changes have been made to emphasize the results. All changes are tracked for ease of clarity.

References:

References are appropriate.

The paper is well balanced with technical and scientific data. 

Authors thank reviewer for their time and positive feedback.

Author Response File: Author Response.docx

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

It is recommended that the data presented on the prediction of the mathematical model indicate which program was used for statistical analysis. On the other hand, why were those months chosen for measurement instead of conducting it throughout the entire year?

Author Response

It is recommended that the data presented on the prediction of the mathematical model indicate which program was used for statistical analysis.

Thanks for your comment, Microsoft Excel was used for initial statistical analysis presented here and MATLAB was used for data filling and cleaning. This is also included in the paper in lines 318-320

On the other hand, why were those months chosen for measurement instead of conducting it throughout the entire year?

Thanks for your comment. As South Africa is in southern hemisphere, so these months are the peak months for the occurrence of HABs. An additional line is inserted in 292-295.

Author Response File: Author Response.pdf

Reviewer 2 Report

Review Manuscript ID: sustainability-2849874

 Mitigating the Impact of Harmful Algal Blooms on Aquaculture. Abagold: A Case Study.

 General:

This document addressed a very important topic for aquaculture: the impact of algal blooms on aquaculture. Few studies have addressed it; as time passes, more and more harmful events occur. The fact that the study focuses on a particular site makes the example even more relevant. The title must be changed since the entire document focuses on measurements and detection techniques. However, no emphasis on mitigation measures is observed. The document focuses on developing an early warning system; this is one of the steps, but the title implies mitigation measures.

 Title:

The title does not reflect the topics addressed in this paper. It must be modified.

 Abstract

It is concise and covers the essential results and conclusions.

 Harmful Algal Bloom Mitigation Technologies

This section contains several methods and equipment for monitoring, quantification, or identification of algal blooms. However, I do not see any method for mitigating HABs.

The major topics regarding algal bloom measurements are addressed; however, an explanation of the basis for using CHL1 and CHL2 as the major indicators is required since dinoflagellates and monoflagellates contain other pigments.

Statistical Analyses

The methods used are correct, but the tables must be improved.

 Conclusions

This section is well organized; it focuses on the model that allows early forecasting of algal blooms.

 More details are required to explain when an algal bloom becomes harmful.

Author Response

General:

This document addressed a very important topic for aquaculture: the impact of algal blooms on aquaculture. Few studies have addressed it; as time passes, more and more harmful events occur. The fact that the study focuses on a particular site makes the example even more relevant. The title must be changed since the entire document focuses on measurements and detection techniques. However, no emphasis on mitigation measures is observed. The document focuses on developing an early warning system; this is one of the steps, but the title implies mitigation measures.

 Title:

The title does not reflect the topics addressed in this paper. It must be modified.

Thanks for your comment. Title has now been changed to Mitigating the impact of Harmful Algal Blooms on Aquaculture using technological interventions. Abagold: A Case study

 Abstract

It is concise and covers the essential results and conclusions.

Thankyou

 Harmful Algal Bloom Mitigation Technologies

This section contains several methods and equipment for monitoring, quantification, or identification of algal blooms. However, I do not see any method for mitigating HABs.

The major topics regarding algal bloom measurements are addressed; however, an explanation of the basis for using CHL1 and CHL2 as the major indicators is required since dinoflagellates and monoflagellates contain other pigments.

Thanks for your comments. We agree that Chlorophyll and Phycoerythrin do not cover all the algal pigments. These are used here to relate to algal biomass in the absence of more specific sensors.

Statistical Analyses

The methods used are correct, but the tables must be improved.

Thanks for your comment. A figure is now inserted to better represent the data.

 Conclusions

This section is well organized; it focuses on the model that allows early forecasting of algal blooms.

 More details are required to explain when an algal bloom becomes harmful.

Thanks for your comment, this is already included in Introduction line 33-39. Also, as we reported to your previous remark, in this study we are not identifying toxins or specific algae. Our methods are based on detecting algal biomass.

Author Response File: Author Response.pdf

Reviewer 3 Report

Please see my comments on the manuscript.  This paper is a hybrid that involves a brief and somewhat superficial overview of monitoring approaches for HABs, and how they can be applied to a case study of an aquaculture facility in South Africa. 

The ANN is addressed in a very abbreviated way--more as an introduction to the concept than a rigorous analysis of its validity, although providing an example of an early warning system is clearly of value. The lack of detail in the EWS may be appropriate for a casual reader but will likely leave a researcher wanting more. While the EWS is certainly not novel, its application shown here may be considered a useful, albeit cursory, example for readers who would then need to delve deeper to determine its utility elsewhere.   

Comments for author File: Comments.pdf

There are numerous typographical errors that need correction, as well as a few substantive errors that definitely need to be addressed. I identify some of the typos but ultimately, there are too many for an ad hoc reviewer to point out. A rigorous proofreading is needed of the revision.  

Author Response

Thanks for your time in reviewing the article and detailed feedback. This is much appreciated. We have made attempt to address all your suggestions and corrections. The article has now also been proofread thoroughly.

Author Response File: Author Response.pdf