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Density-dependent coral recruitment displays divergent
responses during distinct early life-history stages
Christopher Doropoulos, Nicolas R. Evensen, Luis A. Gómez-Lemos and Russell C.
Babcock
Article citation details
R. Soc. open sci. 4: 170082.
http://dx.doi.org/10.1098/rsos.170082
Review timeline
Original submission:
Revised submission:
Final acceptance:
31 January 2017
20 April 2017
20 April 2017
Note: Reports are unedited and appear as
submitted by the referee. The review history
appears in chronological order.
Note: This manuscript was transferred from another Royal Society journal with peer review.
Review History
RSOS-170082.R0 (Original submission)
Review form: Reviewer 1 (Margaret Miller)
Is the manuscript scientifically sound in its present form?
Yes
Are the interpretations and conclusions justified by the results?
Yes
Is the language acceptable?
Yes
Is it clear how to access all supporting data?
Yes
Do you have any ethical concerns with this paper?
No
© 2017 The Authors. Published by the Royal Society under the terms of the Creative Commons
Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use,
provided the original author and source are credited
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2
Have you any concerns about statistical analyses in this paper?
Yes
Recommendation?
Accept with minor revision (please list in comments)
Comments to the Author(s)
This paper describes three experiments spanning different life history processes, though the three
are very distinct and testing very different things (physiological survival vs. behavior, vs.
ecological survival). Given that the parameters being tested in the different experiments are
inherently different, I feel that the title’s attribution of these responses to ‘divergent densitydependence’ between stages is not the best characterization of the study. Nonetheless, the
experiments are interesting and useful (though the larval survivorship one is less so for reasons
given below) and I recommend publication with minor revisions.
The ‘larval survivorship’ experiment in fact did not address the larval period when density
dependence might be expected (i.e. the first 2.5 days). This point is glossed over a bit in various
places in the paper. In addition to lower survivorship in the early days, I would imagine that
density dependence would have little relevance after general dispersal and loss of buoyancy
disperse the larvae throughout the water column. I would expect any density dependence in the
larval phases to be discernable in the earliest phases. This statement in Abstract should be revised
(Larval survival was exceptionally high (>80%) and density-independent for 12 days following
spawning; Ln27-28; also ln 306-307 in Disc) and the point acknowledged more generally in the
paper.
Some specific suggestions:
Methods: Of what material were the 20 ml experimental containers?
Ln 139: how were dead vs. live larvae distinguished under the microscope? Do they look
qualitatively different?
Ln 200: it says that survivors were scored in situ . . . I take it this means in the field and not under
a microscope? Were recruits confidently visible to the naked eye at one month post settlement?
Relatedly, had no settlers budded over one month?
Ln 229: refers to ‘initial analyses’ showing interaction (reported in Table 1), but it does not
articulate what these ‘initial analyses’ were exactly.
Ln 260: This sentence equates ‘gregarious’ with positive density dependence which I don’t think
is true (and your third experiment parses them as separate factors). This word should be
removed.
Ln 260-265: Did the larvae settle entirely on the CCA chip provided or on the container, or both?
Consider the possibility that ‘density dependence’ at settlement would be invoked according to
the AREA available for settlement, not the volume of the container. Were the CCA chips
standardized very closely (or possibly measured and could be tested as a covariate)?
Ln 356: it says ‘non-linear increase’ in settlement with larval density . .but didn’t results show at
best a linear relationship?
Fig 3 D and E: Legend refers to ‘thick’ and ‘thin’ lines but what I see are red and blue lines (which
implies that they refer to the exposed and crevice habitats, respectively). Does this mean that the
significant models only related to crevice habitats (i.e. blue)? Also, I am not clear what
importance the ‘non-significant model fits’ have and why they are depicted at all. This legend
should be clarified.
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3
Fig 3 E: Is turf cover here depicted for the whole tile? Or within each microhabitat? Similarly for
Fig 3D, is this x-axis density just the density in the respective microhabitat? (it says ‘per tile’
which sounds like the density pooled for both microhabitats)
Review form: Reviewer 2 (Yimnang Golbuu)
Is the manuscript scientifically sound in its present form?
Yes
Are the interpretations and conclusions justified by the results?
Yes
Is the language acceptable?
Yes
Is it clear how to access all supporting data?
Yes
Do you have any ethical concerns with this paper?
No
Have you any concerns about statistical analyses in this paper?
I do not feel qualified to assess the statistics
Recommendation?
Accept with minor revision (please list in comments)
Comments to the Author(s)
I think the authors have done a good job in addressing the concerns raised by the previous
reviews,
My only issue is the experiments on density dependent settlement. I am not sure of the relevance
of density dependent settlement in the field. In the lab experiments, when density was high,
there was a positive relationship. But for lower density, it was much variable. I think in the field,
the density are much lower because there are more space, therefore, settlement is much variable
in the field and it is not density dependent. I disagree that ultimately, space is limited for coral
recruits. So while the lab experiment was interesting, it had no relevance in field condition.
On line 89, there seem to be a word missing.
Line 89-90 is not clear, maybe better to re-write.
I also have question on line 353, whether conspecifics induced settlement has been shown for A.
millepora.
Yimnang Golbuu
Palau International Coral Reef Center
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4
Decision letter (RSOS-170082)
18-Apr-2017
Dear Dr Doropoulos
On behalf of the Editors, I am pleased to inform you that your Manuscript RSOS-170082 entitled
"Density-dependent coral recruitment displays divergent responses during distinct early lifehistory stages" has been accepted for publication in Royal Society Open Science subject to minor
revision in accordance with the referee suggestions. Please find the referees' comments at the end
of this email.
The reviewers and handling editors have recommended publication, but also suggest some minor
revisions to your manuscript. Therefore, I invite you to respond to the comments and revise your
manuscript.
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5
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6
Once again, thank you for submitting your manuscript to Royal Society Open Science and I look
forward to receiving your revision. If you have any questions at all, please do not hesitate to get
in touch.
Kind regards,
Dr Kevin Padian
Subject Editor, Royal Society Open Science
[email protected]
Reviewer comments to Author:
Reviewer: 1
Comments to the Author(s)
This paper describes three experiments spanning different life history processes, though the three
are very distinct and testing very different things (physiological survival vs. behavior, vs.
ecological survival). Given that the parameters being tested in the different experiments are
inherently different, I feel that the title’s attribution of these responses to ‘divergent densitydependence’ between stages is not the best characterization of the study. Nonetheless, the
experiments are interesting and useful (though the larval survivorship one is less so for reasons
given below) and I recommend publication with minor revisions.
The ‘larval survivorship’ experiment in fact did not address the larval period when density
dependence might be expected (i.e. the first 2.5 days). This point is glossed over a bit in various
places in the paper. In addition to lower survivorship in the early days, I would imagine that
density dependence would have little relevance after general dispersal and loss of buoyancy
disperse the larvae throughout the water column. I would expect any density dependence in the
larval phases to be discernable in the earliest phases. This statement in Abstract should be revised
(Larval survival was exceptionally high (>80%) and density-independent for 12 days following
spawning; Ln27-28; also ln 306-307 in Disc) and the point acknowledged more generally in the
paper.
Some specific suggestions:
Methods: Of what material were the 20 ml experimental containers?
Ln 139: how were dead vs. live larvae distinguished under the microscope? Do they look
qualitatively different?
Ln 200: it says that survivors were scored in situ . . . I take it this means in the field and not under
a microscope? Were recruits confidently visible to the naked eye at one month post settlement?
Relatedly, had no settlers budded over one month?
Ln 229: refers to ‘initial analyses’ showing interaction (reported in Table 1), but it does not
articulate what these ‘initial analyses’ were exactly.
Ln 260: This sentence equates ‘gregarious’ with positive density dependence which I don’t think
is true (and your third experiment parses them as separate factors). This word should be
removed.
Ln 260-265: Did the larvae settle entirely on the CCA chip provided or on the container, or both?
Consider the possibility that ‘density dependence’ at settlement would be invoked according to
the AREA available for settlement, not the volume of the container. Were the CCA chips
standardized very closely (or possibly measured and could be tested as a covariate)?
Ln 356: it says ‘non-linear increase’ in settlement with larval density . .but didn’t results show at
best a linear relationship?
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7
Fig 3 D and E: Legend refers to ‘thick’ and ‘thin’ lines but what I see are red and blue lines (which
implies that they refer to the exposed and crevice habitats, respectively). Does this mean that the
significant models only related to crevice habitats (i.e. blue)? Also, I am not clear what
importance the ‘non-significant model fits’ have and why they are depicted at all. This legend
should be clarified.
Fig 3 E: Is turf cover here depicted for the whole tile? Or within each microhabitat? Similarly for
Fig 3D, is this x-axis density just the density in the respective microhabitat? (it says ‘per tile’
which sounds like the density pooled for both microhabitats)
Reviewer: 2
Comments to the Author(s)
I think the authors have done a good job in addressing the concerns raised by the previous
reviews,
My only issue is the experiments on density dependent settlement. I am not sure of the relevance
of density dependent settlement in the field. In the lab experiments, when density was high,
there was a positive relationship. But for lower density, it was much variable. I think in the field,
the density are much lower because there are more space, therefore, settlement is much variable
in the field and it is not density dependent. I disagree that ultimately, space is limited for coral
recruits. So while the lab experiment was interesting, it had no relevance in field condition.
On line 89, there seem to be a word missing.
Line 89-90 is not clear, maybe better to re-write.
I also have question on line 353, whether conspecifics induced settlement has been shown for A.
millepora.
Yimnang Golbuu
Palau International Coral Reef Center
Author's Response to Decision Letter for (RSOS-170082)
See Appendix A.
Decision letter (RSOS-170082.R1)
20-Apr-2017
Dear Dr Doropoulos,
I am pleased to inform you that your manuscript entitled "Density-dependent coral recruitment
displays divergent responses during distinct early life-history stages" is now accepted for
publication in Royal Society Open Science.
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8
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Appendix A
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OCEANS AND ATMOSHPERE
Christopher Doropoulos | PhD
41 Boggo Road, Dutton Park, QLD, 4102, Australia
T +61 7 3833 5652
E [email protected]
20 April 2017
RE: RSOS-170082
Dear Dr Kevin Padian,
Please find the completed revision for our manuscript entitled “Density-dependent coral recruitment
displays divergent responses during distinct early life-history stages” for resubmission to the Royal Society
Open Science.
We appreciate the input of both Reviewers and have responded to all minor revisions suggested.
We hope the manuscript is now ready for publication in the Royal Society Open Science. Please feel free to
contact me immediately if you have any questions regarding the study.
On behalf of all the authors,
Christopher Doropoulos
All comments from each Reviewer are copied in full in italicised black font. Our responses are indicated in
regular blue font, and new insertions are boldfaced and in black font. Line numbers refer to the new
submission of the
Manuscript.
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from http://rsos.royalsocietypublishing.org/ on June 17, 2017
Reviewer comments to Author:
Reviewer: 1
Comments to the Author(s)
This paper describes three experiments spanning different life history processes, though the three are very
distinct and testing very different things (physiological survival vs. behavior, vs. ecological survival). Given
that the parameters being tested in the different experiments are inherently different, I feel that the title’s
attribution of these responses to ‘divergent density-dependence’ between stages is not the best
characterization of the study. Nonetheless, the experiments are interesting and useful (though the larval
survivorship one is less so for reasons given below) and I recommend publication with minor revisions.
We believe that the Title is a fair representation of the study because at three distinct early-life history
stages the corals showed different density-dependent responses.
The ‘larval survivorship’ experiment in fact did not address the larval period when density dependence might
be expected (i.e. the first 2.5 days). This point is glossed over a bit in various places in the paper. In addition
to lower survivorship in the early days, I would imagine that density dependence would have little relevance
after general dispersal and loss of buoyancy disperse the larvae throughout the water column. I would
expect any density dependence in the larval phases to be discernable in the earliest phases. This statement
in Abstract should be revised (Larval survival was exceptionally high (>80%) and density-independent for 12
days following spawning; Ln27-28; also ln 306-307 in Disc) and the point acknowledged more generally in
the paper.
This is a valid point that density-dependent effects on larval survival may occur in the earliest stages
following spawning when the eggs are undergoing embryogenesis and developing into larvae. During this
time many are still on the surface in spawning slicks and definitely at their highest density. We have made
alterations where relevant.
As an aside, it also needs to be considered when does a spawned egg become a ‘larvae/planulae’? Most
coral biologists would probably define that as the time when the cilia develop and the larvae begins
swimming. This typically occurs at ~24-48 hours in Acropora and Faviidae (e.g. Babcock and Mundy 1986
Coral Reefs), prior to which the egg is still undergoing embryogenesis and described as a ‘prawn chip’.
Abstract
- Lines 27 to 28: “Larval survival was exceptionally high (>80%) and density-independent
from 2.5 to 12 days following spawning.”
Already described in the M&M
- Lines 130 to 131: “We began an experiment to examine the effect of larval density on larval
survival once the coral larvae had developed into swimming planulae, 60 hours following
spawning.”
Already described in the M&M
- Lines 135 to 137: “Previous work has shown that coral larvae are found at maximum
densities of ~5 individuals per 20 ml in multispecies spawning slicks [40], so we chose
densities that ranged below and above this maximum.”
Results
- Lines 256 to 257: “No relationship was observed between initial larval density and larval
survival from 2.5 to 12 days following the spawning of the Acropora millepora (Fig. 1, Fig.
S2, Table
1a).” from http://rsos.royalsocietypublishing.org/ on June 17, 2017
Downloaded
Discussion
- Lines 307 to 309: “Larval survival in the experimental arena free of competitors, predators,
or microbes, was extremely high and density-independent from 2.5 days until 12 days
following spawning.”
- Lines 324 to 328: “Apart from the current study where we found extremely high and density-
independent survival of Acropora larvae (>80%) from 2.5 days until 12 days following
spawning, only one previous study has addressed the relationship between coral larval
density and survival and found strong density-dependent survival of Montipora larvae from
2 days to 7.5 days following spawning [35].”
- Lines 337 to 340: “In addition, density-dependent responses may occur in the earliest
stages following spawning when positively buoyant developing embryos are distributed
predominantly on the water surface in the highest densities in spawning slicks.”
Already described in the Figure 1 legend
- Line 595: “Experiment began 60 hours following spawning.”
Some specific suggestions:
Methods: Of what material were the 20 ml experimental containers?
The containers used for the larval survival experiment are made of glass.
- Lines 134 to 135: “Swimming and healthy coral larvae were sampled and placed into sterile
20 ml glass containers (scintillation vials) with filtered seawater (0.2 µm and UV).”
The containers used for the larval settlement experiment are made of polystyrene.
- Lines 161 to 163: “Swimming and healthy planulae that were searching and testing the
substrata for settlement were sampled and placed into sterile 20 ml polystyrene cell culture
wells with filtered seawater (0.2 µm and UV).”
Ln 139: how were dead vs. live larvae distinguished under the microscope? Do they look qualitatively
different?
Dead and live larvae are qualitatively different. Firstly, live larvae always swim. Sometimes it appears they
are not moving but on close inspection they are always slightly moving. Secondly, dead larvae are often
deformed and irregular. Not long following death they undergo lysis (i.e., they explode).
Ln 200: it says that survivors were scored in situ . . . I take it this means in the field and not under a
microscope? Were recruits confidently visible to the naked eye at one month post settlement? Relatedly,
had no settlers budded over one month?
That’s correct, survival was scored in the field and not under a microscope. Recruits are confidently visible
in situ to the naked eye one month post settlement because every individual is mapped onto underwater
paper when they settle using a microscope. This map of settlers is then taken underwater so each
individual can be relocated. The tiles used also have a natural grid so it is ‘easy’ to sample the ‘rows’ and
‘columns’. Each tile takes approximately 15 minutes to score in situ. Magnification also occurs underwater
and that aids in identifying the recruits. At one month following settlement the average size of individual
Acropora millepora recruits is 1 mm in maximum diameter, with few growing in size since settlement
because most of the energy is allocated to calcification prior to the acquisition of zooxanthellae. That
contrasts brooded
Pocillopora
settlers that grow in
Downloaded
from damicornis
http://rsos.royalsocietypublishing.org/
on size
June rapidly
17, 2017 following settlement, for which I
have used the same technique (e.g. Doropoulos et al. 2016 Ecological Monographs).
Ln 229: refers to ‘initial analyses’ showing interaction (reported in Table 1), but it does not articulate what
these ‘initial analyses’ were exactly.
The initial analyses are described.
- Lines 230 to 232: “Initial analyses showed significant interactions between microhabitats x
gregariousness and microhabitats x density on coral post-settlement survival.”
Ln 260: This sentence equates ‘gregarious’ with positive density dependence which I don’t think is true (and
your third experiment parses them as separate factors). This word should be removed.
As suggested by the Reviewer the sentence has been rewritten with the word ‘gregarious’ removed.
- Lines 262 to 263: “There was a positive relationship between the initial density of A.
millepora and the probability of settlement (Fig. 2).”
Ln 260-265: Did the larvae settle entirely on the CCA chip provided or on the container, or both? Consider
the possibility that ‘density dependence’ at settlement would be invoked according to the AREA available for
settlement, not the volume of the container. Were the CCA chips standardized very closely (or possibly
measured and could be tested as a covariate)?
The larvae did settle on the CCA chip and on the walls of the container. The size of the chips was
standardised very closely at 5 x 5 mm (refer to line 164) so alterations in CCA chip size would not potentially
confound the experiment. That is, the settlement of the larvae is only a response to initial larval density
because everything else (container size, water volume, CCA chip size) were all equal.
- Lines 167 to 169: “Upmost care was taken to standardise the CCA chip size to 5 x 5 mm
to remove any potential confounding interaction between larval density and CCA chip
size.”
- Lines 172 to 174: “Settlement was then scored by directly counting all larvae that had
attached and metamorphosed in each well on the CCA chip and container surfaces under
a dissecting microscope.”
Ln 356: it says ‘non-linear increase’ in settlement with larval density, but didn’t results show at best a linear
relationship?
The Reviewer is correct that the results (depicted in Fig. 2) show a linear increase in the probability of
settlement with increased larval density. This results in a non-linear increase in settlement abundance. This
is described previously in the paragraph:
- Lines 347 to 349: “To illustrate, settlement rates were 50% at 20 larvae per 20 ml (and no
different to the lower larval densities), but 75% at 50 larvae per 20 ml, resulting in a nonlinear increase in the abundance of settlers at the highest density.”
Fig 3 D and E: Legend refers to ‘thick’ and ‘thin’ lines but what I see are red and blue lines (which implies
that they refer to the exposed and crevice habitats, respectively). Does this mean that the significant models
only related to crevice habitats (i.e. blue)? Also, I am not clear what importance the ‘non-significant model
fits’ have and why they are depicted at all. This legend should be clarified.
Downloaded from http://rsos.royalsocietypublishing.org/ on June 17, 2017
The Reviewer is correct that the lines are red and blue in 3d and 3e, referring to exposed and crevice
microhabitats respectively. Additionally, we have used different line thickness to indicate the nonsignificant and significant model fits for the exposed and crevice microhabitats respectively. The nonsignificant model fits of the exposed microhabitat have been depicted so the differences in slope between
the microhabitats is obvious. We prefer to leave these non-significant fits. If the Handling Editor would like
us to remove them we can. The legend has been altered to provide further clarification.
- Lines 607 to 610: “Bars with different letters above them in a, b, and c were significantly
different, and solid lines in d and e represent the mean prediction of significant (thick and
blue) and non-significant (thin and red) model fits.”
Fig 3 E: Is turf cover here depicted for the whole tile? Or within each microhabitat? Similarly for Fig 3D, is
this x-axis density just the density in the respective microhabitat? (it says ‘per tile’ which sounds like the
density pooled for both microhabitats)
As noted by the Reviewer, the labels on the x-axes of Fig. 3d and 3e were incorrect. Both have been
changed by deleting the words ‘per tile’ because it refers to within each microhabitat, which are depicted
by the different colours.
Reviewer: 2
Comments to the Author(s)
I think the authors have done a good job in addressing the concerns raised by the previous reviews.
We thank Yimnang for his positive feedback.
My only issue is the experiments on density dependent settlement. I am not sure of the relevance of density
dependent settlement in the field. In the lab experiments, when density was high, there was a positive
relationship. But for lower density, it was much variable. I think in the field, the density are much lower
because there are more space, therefore, settlement is much variable in the field and it is not density
dependent. I disagree that ultimately, space is limited for coral recruits. So while the lab experiment was
interesting, it had no relevance in field condition.
We agree that in many systems settlement space on the benthos is not a limiting factor. However, in
degraded systems, for example with high sedimentation or turf algae, settlement space could be a limiting
factor. Moreover, combined with low larval supply, the effect would dampen recovery because of limited
settlement space plus highly variable settlement probability because of low larval density.
- Lines 390 to 392: “Within the context of coral reef degradation [e.g. 30], low larval supply
causing recruitment limitation from bottlenecks at settlement appear the first risk to coral
recovery.”
Additionally, we agree that the density of larvae in the field needed for successful recruitment remains
elusive and needs further investigation. However, laboratory experiments are important in establishing
some kind of first principle to build upon. We highlight this in the Discussion.
- Lines 390 to 392: “Propagule supply is the key first step to population recovery, and for coral
reefs the supply of coral larvae is critical for habitat recovery following disturbances. Due to
their minute size, direct estimates of the actual supply of coral larvae and larval survival
remain a mystery on reefs [49]. Hence, density-dependent thresholds for ecologically
relevant abundances of coral larvae that can contribute to recruitment on reefs are unknown,
but laboratory experiments can partly provide the information necessary for application to
predictive
modelling
[e.g. 50, 51].”
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from http://rsos.royalsocietypublishing.org/
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- Lines 395 to 398: “Thus, while successful coral recruitment and population recovery are
likely to be optimal with consistent supplies of larvae to disturbed patches of reef without
space limitation, the density threshold that enhances recruitment success remains elusive
and requires further investigation.”
On line 89, there seem to be a word missing. Line 89-90 is not clear, maybe better to re-write.
The sentence has been adjusted for clarification.
- Lines 86 to 92: “Patterns reveal that: (1) larval survival is negatively related to density in
Montipora capitata [35]; (2) larval settlement increases with larval density using mass in
situ culturing with gametes collected from spawning slicks [36], Acropora digitifera [37],
and A. muricata and A. tenuis [38]; larval settlement of Siderastrea radians is (3)
positively related to crustose coralline algae but negatively related to turf algae cover [12];
and, (4) the relationship between coral settlers and recruits is density-dependent so that
increasing settlement density does not improve recruit densities in Acropora spp. [37, 38].”
I also have question on line 353, whether conspecifics induced settlement has been shown for A. millepora.
Aggregative settlement in experimental studies has previously been shown in Acropora millepora recruits
by Puill-Stephan et al. 2012 Proc Roy Soc B: Biol Sci. The work is already referred to in the manuscript, but
we have now also included it in the relevant location in the Discussion.
- Lines 355 to 358: “High settlement variability at lower larval densities is expected
considering that invertebrate settlement is facilitated by positive chemical cues derived from
conspecifics [18], and aggregative settlement of Acropora millepora has previously been
shown in experimental studies [28].”
Yimnang Golbuu
Palau International Coral Reef Center