Review of Methods to Repair and Maintain Lithophilic Fish Spawning Habitat

Round 1

Reviewer 1 Report

Article is well written and touch the most important topic for the coral reef habitat future.

Despite I’m a sceptic in term of real possibilities of the reef fish protection using humans resources by producing artificial reefs, the efforts needs toward this direction are unquestionable. However we need to acknowledge that the scale of actions needed is way bigger than human race capabilities, and as such, these actions can only mitigate small, local issues in the reef's ecosystems.

The article has well written abstract, very well written introduction and good discussion part. As for methods, I will suggest enlarging searching terms with the phrase: “river renaturation”. As for the spawning ground, artificial or natural, the primary protection from sedimentation is producing meander like river beds, thus sediment will be mostly deposited on its curves, protecting part of the river beds from being covered with sediment. As for the ocean coral reefs, a similar role can take artificial forewalls of the actual artificial reefs. River renaturation projects are usually combined with efforts to produce and maintain spawning grounds in the river's bed. Therefore I consider it worth to include in the review. However, since literature cited in the present manuscript already reach the number 230, if authors will find usefull mention this aspect it could be a part of the paragraph in the line: 523-547

Apart from that other suggestion is to illustrate Figure 1, but not mandatory.

Also, check the literature:

No 18, 35, 42, 51, 52, 53, 58

No 55 – lack of issue and pages number

No 96 – same issue

No 106, 107, 111, 113 – not sure is the anding punctuation correct – please recheck

No 122, 135, 142, 143 why is so much italic?

No 156 – check italic and ending punctuation.

No 172, 173, 175, 176, 178, 198, 202, 203, 204, 225,   – ending punctuation.

Check your Zotero database for possible issues.

I found this article important and valuable and I have hopes that might help in the crucial area of the artificial reef maintenance.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

I found the manuscript to be well written, and an interesting discussion topic. While a little parochial it does not detract from the overall review. I have made some very minor comments on the pdf version. I found Table 1 to be rather long, and suggest that it is somewhat condensed, or discussed in the manuscript.

Other than the comments added, I think it is a valuable review. Well done.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

This study is a review of published remediation methods for enhancing rocky reef spawning habitat. The authors identify and review 55 projects/papers, categorize the types of habitats involved, the remediation methods, and other information. The authors conclude by recommending a couple of other remediation approaches from other disciplines. The study may be useful to those considering or implementing various options for rocky reef remediation projects. Overall, I found the manuscript very clearly written and readable.

A few areas are in need of improvement before this material may be suitable for publication.

First, Table 1 would benefit from some additional organization. What order are are entries in this table? More importantly, the spatial scale of each project is important to recognize. Some techniques can only be implemented in very small locations (e.g. hand tools to clean a few meters of substrate) whereas others can address much larger reef areas. Add a column that notes spatial scale of the study.

Also missing, but crucial when deciding among mitigating techniques is the effectiveness of the approach. Again categorizing and summarizing this information based on degree of success as its own column would be very useful information. If no post restoration monitoring was conducting, that is good to document as well.

Similarly, the cost of the technique is important to know when choosing among techniques. Likely, this is not reported for some studies or will be difficult to convert to comparable numbers when it is available. Never-the-less, some effort to at least categorize the costs involved would be very useful.

On the topic of costs- Solving the underlying cause of the ongoing degradation (e.g., sedimentation, excessive nutrients) is preferable to undertaking repeated maintenance cleaning. This is inherently a cost/benefit analysis. Is it more expensive to fix the source of the mess, or repeatedly clean it up? This idea comes into the manuscript strangely in the first paragraph of the Discussion around line 219. This issue should be moved to the introduction to limit the scope of the paper. It is recognized that in some cases it is just not feasible to solve the problem at the source- and it is in those cases where this literature review is focused. 

There is also some grey area in what constitutes remediation. Some activities that have been shown to be effective at reducing the problems such a sedimentation, such as widening and re-vegetating riparian buffers seem oddly absent. While not directly at the site of the rocky bottom habitat being cleaned, neither are some of the upstream sediment traps that were discussed. Either include the riparian buffer solution to sedimentation or perhaps limit the scope to only those actions that directly clean the substrate. 

A similar bit of scope mis-match is in the removal of mobile biota. The crayfish removal studies seem an especially poor fit with the rest of the material. This has nothing to do with the actual habitat per se, like the rest of the studies. This could be removed to keep the focus on actual improvements to habitat. Sure, egg predation occurs at the spawning habitat but predator removal does not deal with the physical properties of habitat degradation like all the other studies in the review.

Another curious omission was the lack of marine studies in the search results. Has no one attempted this sort of remediation in the marine realm? Kelp forests (affixed to rocky substrate) come to mind as an extensively studied habitat. Rocky coasts of New England or the Pacific Northwest also have a rich research history. This is only touched on very late in the manuscript around line 609. In fact, I had assumed that the scope was limited to freshwater only until this point. This should be clarified up front, that the literature was reviewed for FW only or it was not. This would be useful to clarify in the section where the search terms are conveyed around line 129. Limiting the scope to only FW studies explicitly seems the best course at this stage.

In the list of search terms it wasn't clear how the results were limited to "rock reefs" versus "coral reefs" which have their own rich restoration literature. It is fine to exclude them, given that coral reefs are living/growing structure compared to rocks and therefore a fundamentally different problem. Although limiting the scope to only rock reefs is fine, it still may be useful to consider at least some of the remediation techniques for coral reefs in the section about "novel approaches". For example, enhancing the populations of biological controls on algal overgrowth of reefs by promoting herbivores (i.e. parrotfish and urchins) may have a freshwater analogue (snails or other surface grazers). 

A few additional comments on the manuscript by line number:

32. The concluding clause of the abstract is correct, but wasn't really a conclusion or outcome of the review material per se. For this- a comparison between the costs/success of fixing the problem at the sources (not really included in the review) versus maintenance cleaning (the subject of the manuscript) would have to be included.

95 change "post-project completion" to "after installation".

96 clarify "reef maturation"

110 This paragraph loses focus at this line, please reorganize.

118 Change "this" to "that"

123 Some overlap in these objectives, can they be made more mutually exclusive?

182 Table 2 needs some horizontal lines separating the groups. It is hard to tell which types of degradation go with what remediations and considerations. Also, is altered flow regime a type of physical disturbance? More or less flow, or different pulse events what formerly maintained habitat that don't take place any more? e.g., periodic flooding to flush fine sediment is prevented because people don't like floods. Under considerations, I would think "downstream sedimentation" would be a major concern for all stream and river applications. Sort of covered under non-target impacts, but the scope is so vastly different than others perhaps deserves explicit mention.

208. This figure seems less useful and could be omitted without a better justification. In any case- text notes that Other = 2 but other = 30 in the fig. Probably a Salmonid labeling discrepancy.

224. This paragraph seems out of place. Conducting the remediation in the right spot is important to minimize the need for maintenance, yes. But this decision comes before the need to remediate. Perhaps move this to the introduction to limit the scope?

228. Reword by moving the opening clause of this sentence after "degradation".

254. Doesn't this have to do with sediment settling on the eggs after they have been laid in addition to them sitting in a bed of sed. The sediment in the water upstream would have to be solved in addition to removing the sediment on the substrate.

257. No mention of riparian buffers farther upstream to solve the source problem?

267 Change "fines" to " fine sediment"

276 This sort of "application scale" would be very valuable to know for as many techniques as possible.

339 This is why it is important to note the actual or at least the potential scale for all techniques in table 1. 

353 Indeed ALL options require a cost benefit analysis

562 The Environmental Impact Statements (EIS) and National Envirnmental Policy Act (NEPA) alternative actions analysis literature may be a really good source of grey lit. Those are supposed to consider the costs an benefits of alternative actions. Not suggesting that those be surveyed here, but its worth mention that this sort of study would benefit development of those documents in the US and they probably have analogous paperwork in other countries. 

601. Replace the first "and" with the beginning of a new sentence. 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Provide estimates of spatial (1) scale and (2) cost for the relative categories added in Table 2. It is understood that these may consist of very broad ranges, but a least some sense of size and funding needed can be devised.  These ranges can be given as a footnote to the table or in the caption.

Table one formatting was ruined in the creation of the pdf, so unfortunately it could not be re-evaluated. 

The crayfish and egg predator text still does not belong with the rest of the material. It is not restoring the habitat per se like the rest of the studies. If things such as that are included I would expect to see things like urchin removal from rocky/kelp reefs to also be included. There is a much more direct link to improving the habitat in those systems. I did a google search of "rocky reef restoration" and these two links were among the first results. Come to think of it, better clarify why "rock" or "rocky reef" was not part of the original search terms

https://www.montroserestoration.noaa.gov/restoration/fish-habitat/kelp-forests-and-rocky-reef/

https://www.oxy.edu/academics/vantuna-research-group/palos-verdes-reef

The expertise of the authors and the papers reviewed do represent a bias toward freshwater systems. There are examples of rocky reef habitats in the marine realm that seem left out. If a major conclusion is that there are few rocky reef restoration studies in the marine realm compared to freshwater, that should be highlighted as a major gap in research, even in the abstract. 

If few studies measure the actual success of restoration- it is also worth noting that lack as a major finding and gap in research. Without knowing at least something about the possible scale, cost, and success of the various approaches it is difficult to know which are useful. 

Author Response

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Author Response File: Author Response.pdf