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  • The initial submission of this article was received on June 5th, 2019 and was peer-reviewed by 2 reviewers and the Academic Editor.
  • The Academic Editor made their initial decision on July 4th, 2019.
  • The first revision was submitted on September 17th, 2019 and was reviewed by 1 reviewer and the Academic Editor.
  • A further revision was submitted on October 22nd, 2019 and was reviewed by the Academic Editor.
  • The article was Accepted by the Academic Editor on October 23rd, 2019.

Version 0.3 (accepted)

· Oct 23, 2019 · Academic Editor


Thanks for making the final edits.

[# PeerJ Staff Note - this decision was reviewed and approved by James Reimer, a PeerJ Section Editor covering this Section #]

Version 0.2

· Oct 10, 2019 · Academic Editor

Minor Revisions

Thank you for your thorough response to the reviewers' comments on the original MS. I noticed a few minor things that still need addressing:

335: change 'moves' to 'movements'
344: two spaces required: min–1inS. intermedius
494: change 'overcome' to 'move'
Figs 8 & 9: change the spacing of increments on the X axes to reflect variation between sample times – the increments currently represent 4 hours at each end of the graphs but only 1 hour in the centre.

I'll be happy to accept the MS once those are attended to.

Reviewer 2 ·

Basic reporting

The improvements that you made in the revision of the MS were great and improved how easy it was to follow the story throughout the MS and tables and figures.

Experimental design

The improvements that you made in the revision of the MS were great and improved how easy it was to follow the story throughout the MS and tables and figures.

Validity of the findings

The improvements that you made in the revision of the MS were great and I think the conclusions you now make are all fully supported by the data you present and add novel information to the literature.

Additional comments

Great work on the revision of the MS. I think this was a great study and should be published as is.

Version 0.1 (original submission)

· Jul 4, 2019 · Academic Editor

Major Revisions

As you can see below the two reviewers both found your manuscript interesting, but differed on its suitability for publication. I believe that it can be made suitable for publication in PeerJ following revision that takes into account the reviewers' comments. In particular the Methods section would benefit from clarification, including subheadings that map onto those in the Results.

Reviewer 1 ·

Basic reporting

1. Basic Reporting
• Writing could use some additional editing from someone whose first language is English; this is an editor's job, not a reviewer's.
• The Results section is overly verbose with an over-abundance of descriptive observations.

Experimental design

2. Experimental design
• The experimental design of this study is frankly a mess. Its structure is difficult to discern, but appears to be an intertwined collection of observations of urchin behavior at 4- 5 sites under varying natural conditions, interspersed with periodic intrusions of manipulations (adding food, adding predator or crushed conspecific cues, etc.). Thus, the design lacks structure making analysis of the data a problem. Tables 1 and 2 suggest that nearly all of the data were analyzed with simple 2-sample t-tests or their non-parametric equivalent. However, these observations are not independent of one another and therefore the use of multiple t-tests on the same study is inappropriate and greatly inflates the probability of a type 1 error (i.e., concluding a significant difference when none exists). In reality, there seem to be 4 or 5 independent observational periods - those are represented by the observations made at the separate locations. Therefore, each of those should be considered a replicate. One analysis approach would be to use a general linear model to examine the effect of different time periods elapsed since certain events (kelp additions, storms, predators added, conspecifics crushed) on the various response variables measured.

• Nighttime recordings were made under illumination of a "lantern"; that term in English usually refers to a very specific type of camping light - probably not what these authors used. I'm assuming they used an underwater light of some type and they mention an "impulse duration of 1 s", so I'm guessing its a flash strobe. What do the authors know about the response of urchins to flashes of light at night from a light source of this particular wavelength range and intensity? They don't have image forming eyes, but they do have photosensors and this type of night-time disturbance could potentially be a problem.

Validity of the findings

3. Validity of the findings
• The results as currently presented can not be trusted because the statistical analyses are incorrect given the convoluted experimental design.

Additional comments

4. General comments
• In general, the study has some interesting aspects - particularly the long term nature of the observations which allows assessment of how long certain attractive/alarm cues persist. Doing the study in the field using the video technology is also innovative. But the overall subject matter (sea urchin behavior) is likely to be interesting to only a small audience, so the manuscript is perhaps better suited to a more specialized journal (e.g., Journal of Shellfish Research). Unfortunately, the work as it now stands is not publishable because the experimental design is poorly conceived and the statistical analyses of the resultant data completely inadequate. The experimental design issues can not be fixed unless the whole study were conducted again. But a reanalysis of the data in line more with what I suggest can salvage the study to some extent.

Reviewer 2 ·

Basic reporting

This was a very interesting manuscript and I commend the authors for taking the time to collect all this novel video data in the field, and for the many hours it took to analyze the data.

Below are a number of notes on the Figures which I believe would improve the clarity of the results and the overall readability of the manuscript. They are listed by line number below. Other small wording and editing suggestions are listed in the General Comments Section below.

Some notes on the Figures and Tables Presented:
• Overall I think the figures were well done and fully supported the results presented and the conclusions made.
• I think a better use of colour should be made across all the figures. As there are many figures in this manuscript, and some are very complicated, I think it would be very helpful if all the results relating to one urchin species was always in one colour, and all the results relating to the other was in a different colour. This way it will be easier to read the figures as in every one the urchin species will have its distinct colour.
o Figure 1 – Colour for urchin species would be very helpful here (rather than the black and white) as it will be easier to tell apart the urchin patterns. Also on the other figures you used colour for the symbols (triangles, etc), that would be helpful in this figure.
o Figure 2 – The three different colours is distracting. I think if you used one colour for A (one urchin species) and another for B, it would be a lot clearer. Labels could just be used on the x axis instead of the three colours.
o Figure 2 – Why is during the storm in panel A “bc”? As the other two are “a” shouldn’t it just be “b”?
o Figure 4 – Why are relative numbers of urchins plotted instead of actual numbers? Why is a trendline not drawn through the data and tested for fit (regression)?
o Figure 6 - Why are relative numbers of urchins plotted instead of actual numbers? Why is a trendline not drawn through the data and tested for fit (regression)? The x axis should be labeled and the colours removed. All points should be in the colour for M. nudus to match all other figures.
o Figure 10 – Why does this Figure not include a panel B (Response to crushed M. nudus) to match Figures 8 and 9?

Experimental design

Generally, the methods for the study are well described, which is excellent considering the number of different analyses within the manuscript. Below are a number of questions and changes which I believe would improve the clarity of the methods and the overall readability of the manuscript. They are listed by line number below. Small wording and editing suggestions are listed in the General Comments Section below.

• Line 119 – 129 – This paragraph is focused on methods, and I think the manuscript would read better if this was moved from the end of the introduction to the first section of the methods section. The intro would then end at Line 118, which would work well. The paragraph would fit well at the current Line 162.
• Line 137 – 141 – Was there is a reason for the different substrate types and depths between the two bays? Or is it just characteristic of each bay?
• Line 135 – Is there any tidal influence on water depth within these two bays?
• Line 142 – 144 – The two urchin species are already described in the intro. This first sentence can be removed and the urchin species names could just be added into the second sentence.
• Line 145 – 147 – Why was this completed? Was it to balance the density of the species in the study areas?
• Line 154 – How high were the frames?
• Line 199 – I know it is far too late now, but why were M. nudus crushed to simulate predator attack, but S. intermedius were not crushed?
• Line 206 – is the word “sonde” correct? I have not heard of this term
• Line 207 – “every” should be added so it reads “….measured the sea level every 10 min…”
• Line 211 – How were the 10 sea urchins selected if there were more than 10 in the frame? Randomly?
• Line 275 – I really enjoy the Procedural Controls section. Great work!

Validity of the findings

Below are a few questions about the results you present:
• Line 402 – You describe that after the crushed urchins experiment it took a while (7-19 days) before urchins returned. Was the food source continually changed over this time period, or was it left untouched? Could the absence of food, or disturbance during food changing have influenced this time to return?
• Line 438 – What does this statement refer to. It is unclear.
• Line 440 – 441 – You mention that there was a significant linear trend in the data, why was a trendline not shown on the corresponding figure?
There were a couple statements that were made that I believe are a bit too far reaching for the data presented.
• Line 533 – While an interesting statement about the prevention of disease, I think it is a bit of a leap from the study results to this statement and should be removed or downplayed.
• Line 634 – 638 – While interesting, I think this paragraph, particularly the last sentence is a very strong statement based on the limited data presented in this manuscript. “…are likely more stable than all known chemical cues emitted by other aquatic animals”, this is a very wide reaching statement and I believe should be removed or downplayed quite a lot. This comes up in the conclusion again, and I think it should be removed from there. While perhaps an interesting discussion point (making the suggestion), it certainly wasn’t a major finding of this study in my opinion, as it is not based on a strong amount of evidence.

Additional comments

• The second sentence of the results paragraph includes two separate statements and should be split into two sentences. I think “…speed and distance travelled whereas S. intermedius…” would read better as “… speed and distance travelled. Furthermore, S. intermedius....”
• The sentence in the results paragraph where the alarm response is noted “…90 and 20 h for starfish attacks….” I assume this is 90 h and 20 h? It should be clarified.
• Line 64/65 – A reference to support this statement, or some additional wording around where the poisonous species reside, might be helpful.
• Line 71 – Change “caused” to “can cause”
• Line 72 – I suggest changing the wording of the first item in this list to match the others. It would then read “ ‘cryptic behavior’, i.e. hiding in a crack or hole”. The other two behaviors should then also have single quotes around them to match ‘associative behavior’ and ‘dispersion behavior’
• Line 75 – “vice versa” can be removed
• Line 80 – “may not present” I think would read better as “these behaviors may not occur”
• Line 82 – 85 – This sentence is confusing to read and should be reworded or split into two sentences in order to be clearer to the reader. The point you are making is very good, it is just difficult to get there at the moment.

• Line 190 – remove “during”
• Line 310 – 311 – The names and dates after the species names should be in brackets in order to match the style in the rest of the manuscript. Same with Lines 380 – 381.
• Line 321 – “During approximately the day after the storm” does not read well.
• Line 324 – This entire sentence can be removed as it does not add any information into the manuscript. “They performed moves of different length interrupted by stops of different duration”.
• Line 328 – This sentence can be removed as it doesn’t add in new information, just the opposite information from the sentence above.
• Line 329 – “As well” should be changed to “whereas”
• Line 332 – “length of one move” should be changed to “step length” for clarity.
• Line 336 – Should this read as “The average locomotion speeds during storm conditions were…..”?
• Line 439 – “not such obvious” should be changed to “not very obvious”
• Line 473 – Add “in the field” after video recording.
• Line 486 – Should read as “…resulting in higher distances traversed”
• Line 488 – Wording suggestion – “….S. intermedius would be able to average…”
• Line 697 - The sentence where the alarm response is noted “…90 and 20 h for starfish attacks….” I assume this is 90 h and 20 h? It should be clarified.

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