|Evaluation of bg-2019-304-manuscript-version3|
Cuvelier et al: Are seamounts refuge areas for fauna from polymetallic nodule fields?
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.
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.
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.