Spatial and Temporal Variability in Parrotfish Assemblages on Bahamian Coral Reefs

Round 1

Reviewer 1 Report

Diversity – 1778405 Reviewer

 

General comments

The work by Sherman and collaborators, “Spatial and temporal variability in parrotfish assemblages on Bahamian Coral Reefs,” analyzes a long-term (2011-2019) parrotfish data set from New Providence, Bahamas. Current (2019) fish community characteristics (e.g., heavily dominated by small parrotfish species, Scarus iserti) and low population density (below 20 ind. 100m^-2) are likely driven by overfishing (authors’ conclusion). The authors use the results to emphasize the urgency of science-based management strategies to protect these ecologically essential herbivores. The manuscript is well written and provides the necessary information to move forward with fisheries regulation in the Bahamas. However, the MN could benefit from some improvements I suggest here.

 

The Bahamas archipelago is large (700 islands and 2400 cays covering 13,878 km²). The fishing pressure varies across islands depending upon port proximity, habitat type, depth, and other factors (Harborne 2017, Sherman et al. 2018 cited on the MN). I suggest some title modification to indicate this is a work completed in New Providence, NOT other Bahamian reefs. I also propose to add a short description (probably at the end of the introduction section) of the fishing history around the Bahamas and New Providence specifically (the audience of this Journal is a bit broader compared to, for instance, “Coral Reefs” and they would probably need more context).

 

The materials and methods section would benefit from a better biological description of the reef types. Information on average coral cover, macroalgal abundance, and structural complexity could be helpful to interpret better the author’s findings (this could be obtained from benthic AGRRA surveys.

 

Given the informative value of “biomass g m^-2” and its extended use in most Fish Community AGRRA reports, I was surprised the authors did not use it. By NO means this observation minimizes the scientific value of this work or compromise its validity for publication, but I just wondered why they chose not to. Given that communities are dominated but small parrotfish (Scarus iserti), it may be worth exploring if biomass shows similar trends (food for thought).

 

In the discussion section, there are a few points I consider worth elaborating about:

1)    Is there any reason why East (higher density) and West (lower density) reef fish communities differ? Could it be a survey sample size effect?

2)    The results indicate larger individuals in deeper (forereef) areas. Could this also be an indication of overfishing? There is vast work on this topic showing deep reefs as a refuge from artisanal and commercial fishing (Tyler et al. 2009; Goetse et al. 2011; Petit et al. 2021)

https://www.academia.edu/532864/Evidence_for_a_depth_refuge_effect_in_artisanal_coral_reef_fisheries

https://onlinelibrary.wiley.com/doi/epdf/10.1002/aqc.3795?saml_referrer

https://link.springer.com/content/pdf/10.1007/s00338-011-0732-8.pdf

3)    It will be great to elaborate more on an integrative approach that combines the ecological role(s) of parrotfish in the studied reefs and the need for protection given the foreseeable threats in the region (The second to last paragraph (lines 353-366) will be a good place for it). For example, how effective is the current herbivory pressure given the practical absence of large species in the area? It may be worth relating it to macroalgal abundance in the area. Is the current fishing pressure pushing the system to its maximum resilience edge? Given the recent threats of another Caribbean-wide Diadema die-off, would existing herbivorous fishes be able to control macroalgae if this Diadema’s role is hampered, again?

4)    Lastly, it’ll be worth mentioning how representative is the study case for the Bahamas as a whole. Are fish communities of northern islands such as Abaco and Grand Bahama under the same fishing pressure? If not, would it be reasonable to propose differential fishing regulations for each region?

 

Specific comments

Line 25-28: I suggest splitting this sentence

Line 32: Eliminate “Specifically”

Line 40: Replace “can” with “is”

Line 53: Replace “correlated” with “associated with or related to”

Line 60: Replace “biodiversity” with “diversity”

Line 69: Eliminate “Specifically”

Line 271-274: I suggest splitting this topic sentence.

 

 

Figure 1. The figure could be confusing because it has two different scales in the same figure. I suggest modifications to delineate the large-scale location (upper right corner) and the detailed study sites.

 

Supplementary materials

Please, enlarge the font size of the axis and labels for all figures.

 

 

 

Author Response

 

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

 

General comments

The study provides contributions on the ecology of the parrotfish assemblages Bahamian Coral Reefs, with evidence of decline in fish abundances over time. The study contains a substantial amount of work and a great surveying effort. Also, the study provides a baseline for abundance values of parrotfishes around the islands of New Providence, which is a valuable information for extinction risk assessments. While I think the article is interesting, I feel that authors gave to much attention in describing spatial and temporal patterns of parrotfish assemblages at site level (e.g. Lines 146-155, section 3.1 and 3.2), which is not of great relevance for an international audience. I believe that analyses need to be improved to better describe spatiotemporal changes in fish assemblage structure for patch and forereefs. I think an interesting question is how fish assemblages of fore- and patch reefs are structured? Similarly, how fore- and patch reefs were distinctly affected by fisheries over time. Mean total densities as showed in Fig. 2b helped in attending these issues, but it is still lacking for species and family levels and for fish assemblage structure.  Authors decided to investigate spatial and temporal patterns separately, which is not incorrect but ignores interactions between sampling period and reef zones. There is not much evidence to state that parrotfish assemblages were more variable for patch reefs compared to forereefs. In general, most figures need to be improved, legends are too small.

 

Introduction

I believe that the introduction is okay. My only suggestion is better contextualizing the drives of parrotfish abundances (e.g. depth, wave exposure) which are important for spatial patterns.  

 

Study area

Most sites patch reef sites are placed at the East side of New Providence, while forereef sites are placed at West and North sides. Are there oceanographic and environmental differences between theses regions that may influence the spatial patterns of parrotfish assemblages? If so, I think it worth to be mentioned in this section.  A short description of the patch and forereef zones in terms of habitats, depth, wave exposure is also useful.

 

Results

Figure 3 and Figure 5-9 and Figures S1- S4 need to be improved. Letters are too small.

 

L. 183 – 185. I recommend to authors rewrite the results of nMDS. I can’t really see that parrotfish assemblages within forereef zone were more diverse. It seems to me that species codes are placed inside Ellipses where there are both patch and forereef samples. Also, what authors mean by “similar” in this sentence? Fore and patch reef samples of the periods 2011-12 and 2015-16 are clustered inside the smallest ellipse, so I can’t see that forereef samples were more similar compared to patch reefs as stated.

 

L. 186-187. The dispersion of 2019 samples are higher than those of 2011-2012 and 2015-2016. It means that species abundance/composition was more variable between samples of 2019 compared to the previous sampling periods. It is a common pattern for more depleted assemblages, so it is interesting to be highlighted. An approach such as Permutational analysis of multivariate dispersions (PERMDISP) can be useful here.

 

L. 187. “being primarily driven by mean densities of Sp. Viride” is quite vague and needs re-writing.

 

L. 201-224 (Temporal patterns). I think that describing temporal patterns for specific sites is valuable for local managers and can be maintained in the paper. However, I strongly suggest investigating temporal changes in fish assemblages at species and family levels for fore and patch reefs.  

 

Discussion

L. 282-284. Again, I can’t see how Fig. 5 and Fig. 7 show a high diverse parrotfish assemblage within the forereef zone.

L. 293-306. In my opinion, most of these sentences are quite general and should be better placed in the introduction section. In the discussion, authors should give more detail on which specific habitat and environmental differences may drive assemblage patterns of fore and patch reefs.  

L.307 – 317. What is the main fishing gear used in the Bahamas to catch parrotfishes (spearfishing, fishing nets, traps)? For example, depth may be inversely related to spearfishing pressure if it is only allowed to free-divers and parrotfishes of deeper areas, such as forereefs, may be less susceptible over time compared to patch reefs.

Spatial patterns may be driven by ontogenetic variability in habitat use but this issue was ignored in the discussion.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Overall this is a well written, well carried out piece of work. It reads very well and the introduction and conclusion have a good flow to them. Figures are generally well presented

 

Are the authors comfortable with stating that they “examine fine scale spatial and temporal patterns of parrotfish biodiversity”….based on this analysis? It seems to me to be slightly overstating what the analysis actually does. I know the data do have both a spatial and a temporal component to them…but these “fine-scale” aspects are more properties of the datset rather than the analysis.  I worry that this type of statement makes the reader expect something else  (e.g. analysis of spatial autocorrelation in parrotfish populations, or explicit clustering of sites based on a spatially analysis. Or for temporal an identification of different  temporal trends for individual sites). 

 

My genuine question to the authors: Is there a way of describing the dataset and analysis early on that strongly matches with the rest of the paper, so that the reader doesn’t detect any mis-match?

 

Line 25 to 26. The very first sentence doesn’t work/make sense 100% if read carefully. I suggest shortening or tweaking this to make it more punchy.

 

Line 60. fine scale spatial and temporal patterns of parrotfish biodiversity?

 

Line 121. A small point but 9999 permutations is often considered standard for permutation testing for rigorous statistical inference.

 

Line 185-188. This is a bit confusing/misleading as it seems the only clusters observed here (Fig 5) are  really the different survey years….which is temporal, not spatial. Yes fore and patch reef are differentiated, but these were assigned to sites at the beginning. There is no additional spatial insight into parrotfish populations around New Providence being presented here.

 

Line 208. There is a hypen rather than a en dash between 2011 and 2012

 

Line 314. “consumption by fishers is estimated to be ~63%”. This is not very clearly worded….I don’t think this means consumption (eating) but targeting or catching by fishers. Also 63% of what? Catch composition? Time spent fishing for?

 

Line 261. Is there some shading/highlighting of the sentences here that needs to be removed?

 

Line 338. Sentence on effect of size on parrotfish reducing macroalgal abundance….I suggest a recent highly relevant citation here: Lange, I. D., Perry, C. T., Morgan, K. M., Roche, R., Benkwitt, C. E., & Graham, N. A. (2020). Site-level variation in parrotfish grazing and bioerosion as a function of species-specific feeding metrics. Diversity, 12(10), 379.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper is well written and makes a valuable contribution to support fisheries management of parrotfish species in The Bahamas. Researchers conducted spatial and temporal analyses using transect surveys to assess the status of parrotfish species across different reefs and zones in the New Providence area. I recommend changes be made to the paper before publication, including: 

 

General Grammar:

1. Some of the text appears to be different colors (e.g. lines 59-64). 

2. There are unnecessarily large spacings between some words (e.g. line 82).

3. There are a few run-on sentences that need to be tended to(e.g. line 25-28).

 

Introduction: 

1. Include a paragraph on current management measures in place to protect parrotfish species. This verbiage is found in the discussion section, but could serve better in the introduction to stress the need for such measures, especially since there are no fishery regulations to protect these species in The Bahamas and this work indicates the species’ are doing worse off than historically thought.

Methods:

1. More detail is needed to describe the survey design, specifically:

1. How many surveys were conducted per temporal period. 

2. Which sites were assessed for temporal changes (this can easily be indicated in Table 1).

3. When during the year these surveys were conducted. 

2. If these surveys were not conducted during the same seasons across years, there may in fact be a seasonal effect, which should be investigated further and included in the temporal analysis and NMDS work. 

 

Results/Figures:

1. Based on the order in which each figure is referred to, Figure 3 (mean densities of parrotfish species across the three survey periods) should come after Figure 5 (NMDS results).

2. In Figure 3, explain the symbols above the bars seen in the species where a statistically significant change in mean density were found.

3. In Figure 5 it might help to include the arrows for each species. The lengths and direction of these arrows can help the reader visually interpret results that differences are primarily driven by mean densities of Sp. viride. 

4. As a comment, Figure 4 is a clever way of visualizing both spatial and temporal differences. 

5. It would be beneficial to identify and organize the survey sites along the x axis in Figure 6 and 7 spatially or by reef zone to help readers recognize differences in size frequency across reef zones. 

 

Discussion: 

 

1. I noted that you refer to the data as a “nine year dataset”, however it appears as though there are only 5 years of intermittent surveying between 2011 and 2019. By referring to it as a nine year dataset you are implying it is continuous and if that was the case time series analysis may have been the more appropriate temporal analysis methods. 

2. Given how much is included in the paper, it might be beneficial to organize the discussion into sections that reflect the results section (e.g. temporal analysis, spatial analysis, etc.) 

3. There should be more emphasis on the implications this study has on fisheries management, especially because no current management is in place for The Bahamas and this study shows such a significant decline in mean densities of parrotfish species. 

4. It may be beneficial to integrate the needed future research recognized in the paper with implications on management.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 5 Report

In my opinion, this is a good and interesting research, with findings contributing to the further understanding of the coral reef communities. The provided results have not only strictly academic interest but can be useful for the conservation purposes. I have only a few minor suggestions on how to improve the original version of this manuscript.

Abstract L17. “(≥21 cm TL)” – please avoid abbreviations in the Abstract or define them at the first appearance in the text.

M&Ms section. It remained unclear to me how fish species identifications were made during the surveys. Could you please clarify this? If these identifications were made during the surveys, using the naked eye approach, how taxonomically reliable could they be? The authors themselves acknowledge that even the experienced local fishermen can misidentify the species they catch (L316). Let me to cite the original text: only “subtle differences in markings differentiate Striped Parrotfish (Sc. iseri) from Princess Parrotfish (Sc. taeniopterus) in their initial and terminal phases”. A clear source of identification error! The same question holds for the total length determination. Was there a possibility of misidentifications and other factors able to bias the results (counting errors, for example)? All potential sources of bias must be acknowledged in the text, with estimates of their probable magnitude.

L271 “We used a nine-year data set” – actually the authors have analyzed a five-year data set (2011, 2012, 2015-2016, and 2019).

Supplementary file. As I observed, the legends for figures S1-S4 as well as the labels for the ox and oy axes are too small and difficult-to-read; please enlarge them.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The revised manuscript has improved and reflects the comments from reviewers. I have one suggestion, which is to add a sentence in the results describing temporal patterns in parrotfish assemblages across reef zones. I agree that this information is presented in some figures, but there is no reference of ‘reef zones’ in the section 3.2 (temporal patterns) of the results. I still think this is necessary, to better achieve the specific objective 1. Regarding the figures, my only specific suggestion in the first revision was to enlarge the fonts to allow an adequate visualization. Fonts are still quite small in some cases. To be more specific, I suggest:

Figure 3 - Enlarge the fonts of both scale values and names (years and mean density). Also, enlarge the fonts of species codes and letters of statistically significant differences.

Figure 8 and 9 (a) - Enlarge the fonts of: “size classes”, y axis title (Percentage of Parrotfishes and Percentage of SRV), y axis scale and zone codes (fore and patch).

Figure 8 and 9 (b) - Enlarge the fonts of the color scale and make the color bar slightly thicker.

Author Response

The revised manuscript has improved and reflects the comments from reviewers. I have one suggestion, which is to add a sentence in the results describing temporal patterns in parrotfish assemblages across reef zones. I agree that this information is presented in some figures, but there is no reference of ‘reef zones’ in the section 3.2 (temporal patterns) of the results. I still think this is necessary, to better achieve the specific objective 1. We have incorporated new sentences to this section and inserted reef types next to referenced sites for ease of reference. Regarding the figures, my only specific suggestion in the first revision was to enlarge the fonts to allow an adequate visualization. Fonts are still quite small in some cases. To be more specific, I suggest:

Figure 3 - Enlarge the fonts of both scale values and names (years and mean density). Also, enlarge the fonts of species codes and letters of statistically significant differences.

These changes have been made.

Figure 8 and 9 (a) - Enlarge the fonts of: “size classes”, y axis title (Percentage of Parrotfishes and Percentage of SRV), y axis scale and zone codes (fore and patch).

These changes have been made.

Figure 8 and 9 (b) - Enlarge the fonts of the color scale and make the color bar slightly thicker.

These changes have been made.