Does Seawater Nitrogen Better Predict the Baseline Farmed Yield for Sugar Kelp (Saccharina latissima) Rather than the Final Yield?
, Charles Yarish 3,4, Matthew C. Rogers 5 and Schery Umanzor 1Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
GENERAL COMMENTS
The authors present interesting data to support that nitrogen contents of kelp growth sites may only be important to a threshold requirement for growth, but not necessarily well descriptive of realized biomass relative to other factors such as line spacing. The analysis is presented using data collected in both the northeastern US and Alaska. Sample collection was not well controlled or described for water quality or kelp tissue samples, and there are many uncontrolled variables between sites that limit data interpretation. Greater description of analytical methods are also needed. Specific comments follow.
1. More details are needed on sampling procedures. It is not possible to identify the specific number of water and tissue samples taken on each farm and how they coincided with the kelp growth cycle. As written (page 5), sampling started in March and was completed once each 4 weeks. It may be possible then that in Rhode Island, only two water samples were collected (March and April [harvest occurred in April]). This would differ from Alaska where kelp was harvested in June. Presumably, lines were deployed in Alaska later in the calendar year than those deployed in Rhode Island. Therefore, the timing between water quality measurement within the growth cycles may be different between sites. That can and should be reported.
2. The analytical instrumentation for water nitrogen measurement, elemental C and N, and isotopic C and N were provided, but not the methods used for measurement. Can the authors please report a method of analysis for each analyte in the study?
3. There are no details on how water samples were preserved and shipped between collection in northeastern US states and analytical lab in Alaska. Holding times from collection to analysis should also be reported.
4. The authors use the term “haphazardly” frequently in describing their sample collection procedures (i.e., see page 6, lines 108, 125 and 126; page 7 line 133; page 18, line 315). Haphazard implies poorly designed or potentially improperly executed, such as potentially biased selection of kelp tissues, non-random selection of water quality sampling sites within the kelp farm, or potentially biased selection of segments of grow line for biomass quantification at each farm that may be different from one aquaculture site to another. Poor quality data reduces confidence in the analysis provided. For example, in the context of temperature on page 18, the authors report that the haphazard collection of temperature data “resulted in an incomplete dataset that restricted proper inclusion in analysis.” Why then is the haphazard collection of kelp tissue samples and water quality samples sufficient for analysis? Please either use a more specific description of the sampling procedure used or describe in the discussion limitations in data interpretation that may be brought about by haphazard collection of samples.
5. On pages 6-7, lines 128-129, the authors report that biomass production rates were measured after water was drained from bagged samples from 50 cm grow line. It is unclear whether or how kelp was further dried to compare biomass production rates. Differences in kelp water content (how long the bags were draining, for example) between sites and seasons may affect interpretation of biomass production rate.
6. Page 20, lines 364-365: do the authors mean to report the minimum line spacing as 5-m or 10-m (flow dependent)? This would be more consistent with the practice as they reported previously (page 12, line 220).
Comments on the Quality of English Language
EDITORIAL COMMENTS
Minor editorial comments include the following:
Page 5, Lines 95-96: “Maine (ME), and”
Page 12, line 206: “p=0.036”
Page 12, line 210: change ”strongest” to “stronger”
Author Response
Please see the attached word document.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for Authors
The Stephens et al. (2023) study examines the function of seawater nitrogen in forecasting the initial and ultimate output of sugar kelp (Saccharina latissima) at five commercial farms located in the United States. Given the increased interest in kelp farming, the study is pertinent and timely. Still, there are a few problems in the manuscript that need to be fixed.
Lines 21–37 of the abstract are devoid of a specific hypothesis. It outlines the goal and some of the findings, but readers would be better served by a more focused hypothesis or study question.
The introduction (lines 39–78) gives a thorough overview of the history of nitrogen's function in kelp growth. But there's not much of a link to the study's goals. A stronger connection between the study's specific research topics and the body of existing literature would strengthen the introduction.
Important sources, such Redfield (1958) and Lüning and Neushul (1978), are cited to highlight the significance of nitrogen. Though these are basic research, there may be more context and support available in more recent literature.
Explain why the study is important and reduce the number of in-text citations to improve readability.
Instead of controlled experimental circumstances, the study's design is limited by the utilization of commercial procedures (lines 98–101). This adds unpredictability, which could skew the findings. The impact of this constraint on the findings and the measures taken to alleviate these concerns should be more clearly addressed in the text.
Provide a clearer timeline of the sampling process. Detail the specific tools or techniques used for sampling (lines 91-105).
Lines 170-179: If you wish that this manuscript to be practical considerations for sugar kelp farmers, highlight the main results without excessive details and use simpler language where possible for readability.
Line 301-310: Discuss the practical applications of the findings provide clear recommendations for future research or practices. The current opening is too abrupt and lacks a broader context. Begin with a brief summary of the main findings and their importance.
Lines 308-310: "The weak correlation between seawater nitrogen and kelp biomass highlights the need for a multifaceted approach to site selection and farm management that goes beyond nitrogen levels." Provide specific examples of other factors that were found to be important.
There's no direct comparison with previous studies. The discussion lacks a concluding paragraph that synthesizes the findings and their broader impact.
Author Response
Please see the attached Word document.
Author Response File: Author Response.docx
Reviewer 3 Report
Comments and Suggestions for Authors
The manuscript of Stephens et al., investigated the effect of nitrogen and line spacing on the yield of sugar kelp in 5 seaweed farms over a 2 year period in the US. The cultivation of seaweed is a widely studied topic that is highly relevant, especially in today’s global situation (potential climate mitigating feedstock). Therefore this paper deserves recognition in this field of research. The approach of the authors is well performed, the article is well written and the applied methodology merits publication in Phycology. However, after reading the manuscript I have some minor comments which ought to be addressed before publication:
- Please introduce some references for statements made in Lines 52-56.
- The authors mention that nitrogen level varies across seasons, with maxima in winter and minima in summer. However, what is the minimal amount kelp would need to grow? From what concentrations does nitrogen impact the growth of kelp ? Please add some numbers to the introduction section.
- Please add some more information regarding the Farm sites. What was the farming method? Long lines? How far away from the coast? Is there any multi-aquaculture present in (some of) the seaweed farms? What was the size of the farms? Were they all equal in size? What is the depth of the growth lines? Please elaborate sufficiently in the text.
- Lines 140-142: is the following statement correct? “The samples were screened upon arrival to ensure the absence of fungal development and oven-dried at 40 °C for 60 min, which was sufficient to dry the tissues to a constant weight considering the small biomass and thin blades.” 60 min seems incredibly short.
- Please mind the sub- and superscripts of chemical formula’s in Table 1, 2 and 3.
- What is meant with “C” in table 1 and 2? Should this not be C:N?
- How is the following statement possible as the only difference between Total N and nitrate is ammonium and that according to the authors there is no relationship with ammonium: “kelp biomass (kg /m) correlated strongest with Total N than it did with NO3- there was no relationship with NH4+ (see correlative values for month of harvest, above).”.
- Please also convert to metric units in the conclusion section.
Author Response
Please see the attached Word document.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
Thank you for your time addressing the comments on first review and for providing the additional details required for improved clarity. The revised manuscript should provide readership with interesting insight into factors that are meaningful for siting kelp operations, and limitations thereof.
Reviewer 2 Report
Comments and Suggestions for Authors
The Authors did the work to improve the manuscript. I have no further comments.
