Are seamounts refuge areas for fauna from polymetallic nodule fields?

Cuvelier, Daphne; Ribeiro, Pedro A.; Ramalho, Sofia P.; Kersken, Daniel; Martinez Arbizu, Pedro; Colaço, Ana

doi:https://doi.org/10.5194/bg-17-2657-2020

Articles | Volume 17, issue 9

Biogeosciences, 17, 2657–2680, 2020

https://doi.org/10.5194/bg-17-2657-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue: Assessing environmental impacts of deep-sea mining...

Biogeosciences, 17, 2657–2680, 2020

https://doi.org/10.5194/bg-17-2657-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 9

Research article 15 May 2020

Research article | 15 May 2020

Are seamounts refuge areas for fauna from polymetallic nodule fields?

Daphne Cuvelier et al.

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Final revised paper (published on 15 May 2020)
Preprint (discussion started on 12 Aug 2019)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Evaluation of Cuvelier et al: Are seamounts refuge areas for fauna from polymetallic nodule fields?', Anonymous Referee #1, 02 Oct 2019
- AC1: 'Replies to Reviewer 1', Daphne Cuvelier, 31 Oct 2019
RC2: 'Manuscript review', Anonymous Referee #2, 10 Oct 2019
- AC2: 'Replies to Reviewer 2', Daphne Cuvelier, 31 Oct 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (05 Dec 2019) by Matthias Haeckel

Dear authors,

2 reviewer comments have been received for your manuscript that you have both responded to.
Both reviewers have made substantial comments that need to be addressed and incorporated during the revision of your manuscript. This should be possible considering your replies.

A few additional comments (in addition to the reviewer's comments) from my side are:
I agree with the reviewers that Figure S1 presents essential information on the size of seamounts, water depths and locations of the transects. Therefore it should be moved into the article. However, important information is not accessible from the current figure, because axes and color code labels are not readable (even if zooming into the PDF) due to too low resolution of the figure.
During the revision, please take care to significantly improve the quality of all figures (Fig.7 has a similar problem) that labels and annotations become readable.
It may be useful to add a table in the supplement containing specific information for each seamount raised by R#1 (i.e. size, summit and base depth, average slopes at sampling/video depths and average current direction/velocity (e.g. sampling site upstream or downstream), etc).

R#1, comment 3: The distance between the ROV laser spots on the videos (I believe it is 50 cm for the parallel beams, but please confirm with the ROV team of Kiel6000) should enable estimating the width of the visual field and hence allow providing an area for the transects, i.e. ind/m2. This would increase comparability.

R#1, comment L.288-295: This is an important point and I agree with the reviewer that more discussion on possible reasons would be helpful. For example, the seafloor POC flux in APEI3 seems to be reduced by ~30% compared to the investigated license areas (see biogeochemistry paper of Volz et al. (2018) Deep-Sea Research I 140).

R#2, comment 3: Where is Fig. R1 you mention in your reply?

Kind regards, Matthias Haeckel

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AR by Daphne Cuvelier on behalf of the Authors (09 Jan 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (31 Jan 2020) by Matthias Haeckel

RR by Anonymous Referee #1 (14 Feb 2020)

Suggestions for revision or reasons for rejection

Evaluation of bg-2019-304-manuscript-version3

Cuvelier et al: Are seamounts refuge areas for fauna from polymetallic nodule fields?

General evaluation

The authors did a good job in improving the manuscript and considered most of my concerns regarding the original manuscript, and I am happy to see that the abundances presented in the text and Tab. 1 have been corrected. There are only a few issues left, which are listed below and should be considered carefully before publication of the the paper.

Methods
Lines 96 ff: I agree that the method for quantification of the samples may be suitable for the comparisons made in this study, provided that the variations in altitude and camera angle were comparable between transects (but I guess that keeping the target altitude on the flat plain was much easier than at the seamounts?). My only concern is the statement that "altitudes >10 m were omitted", meaning that, the other way round, all altitudes between <2 m and 10 m were considered? Since the area correlates with the square of the distance, the area observed could vary by a factor of >25 between sections, which would introduce a substantial bias.
Further, although the standardisation to section transect length is perfectly suitable for the comparisons within the study, it would be helpful to include some information on the approximate field of view of the camera, e.g. at the target altitude with a standard pan and tilt setting, in order to get at least some feeling when comparing this study with others.

The authors should also include the information given in their rebuttal, that specimens samples were also used for identifications when possible.

Results, Discussion

Line 202: delete "#".
Lines 252ff (original 220): the modified statement is still not correct. The majority of the ophiuroids were not morphospecies 5, but Ophiuroidea indet.
Line 333: should read "…showed that an asymptote was reached neither …."
Line 339: should read "1000 m"

Figures and tables

Fig. 3: I am still not quite happy with this figure, because rare taxa are hardly comparable, despite modifying the axes, and I still suggest to sum up the less abundant morphospecies.

Apart from this, the x-axis labels are incomplete; should read: "Density (ind/100 m)". Negative density values for the seamounts are strange; the minus sign should be deleted. In panel (B), the scaling of the x-axis is not clear; only "-12" is given for the left hand part. I suggest to include a finer scaling here, such as 0.5, 1.0, 1.5 etc. Similar in panel (c).

Caption: what does #4 and #5 mean - number of video transects? Rather write "4 transects" or "N=4".

Fig. 4: Y-axis labels. In panels a and c: "Number of species" (with capital N). And what does "Species" in panels b and c mean? I guess it should also be "Number of species"?

Fig. 6: my previous comment is still valid, the y-axis label is incomplete and should comprise quantity and unit; in this case: "Density (ind/100 m)"

Tab. A1: include sums for higher taxa; e.g., Cnidaria, Anthozoa, Ceriantharia etc.

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ED: Publish subject to minor revisions (review by editor) (25 Feb 2020) by Matthias Haeckel

AR by Daphne Cuvelier on behalf of the Authors (09 Mar 2020) Author's response Manuscript

ED: Publish as is (20 Mar 2020) by Matthias Haeckel

ED: Publish as is (23 Mar 2020) by Jack Middelburg(Co-Editor-in-Chief)

Short summary

Polymetallic nodule mining will remove hard substrata from the abyssal deep-sea floor. The only neighbouring ecosystems featuring hard substratum are seamounts, and their inhabiting fauna could aid in recovery post-mining. Nevertheless, first observations of seamount megafauna were very different from nodule-associated megafauna and showed little overlap. The possible uniqueness of these ecosystems implies that they should be included in management plans for the conservation of biodiversity.