Species Composition and New Records of Diatom Taxa on Phyllodictyon pulcherrimum (Chlorophyceae) from the Gulf of California

Round 1

Reviewer 1 Report

Figure 2: maybe it is the resolution of the image, but I do not see the Cocconeis. Perhaps an arrow to indicate an example specimen?

Discussion: While I cannot disagree with any statements made by the authors, I can’t help but feel that there is a missed opportunity here to increase the impact of this manuscript. The authors seem content to conclude that their study has yielded the greatest measured diversity of epiphytic diatoms on green seaweeds…but there is no speculation of why that might be. Is it geographic—were the other sampled green seaweeds also from similar latitudes? Is the increased diversity a function locality--the Gulf of California versus the open Pacific coast? How does the epiphytic diatom richness compare to other benthic substrates in the sampled area? Does the morphology of the seaweed matter—a “sheet” versus a branched morphology? What about differences in the diatom growth habit? Did the authors see as many flat, monoraphid diatoms (such as Cocconeis) in Caulerpa or Ulva versus their own collection? It would really help the impact and citation rate of this paper if the authors used the opportunity to propose some hypotheses about why the diatom species richness was so high on this seaweed. Of course, the caveat is always that N = 1 here, but there’s nothing preventing the authors from proposing a few ideas and providing at least some context for this study.

Flora: It would help if the Figures and Flora were in the same order.

Planktonic taxa—there are some taxa listed here which are very likely planktonic “by-catch” rather than benthic diatoms (Thalassiosira, Coscinodiscus, Chaetoceros). There aren’t enough of these taxa to suggest the extraordinary species richness is artificially inflated with the inclusion of planktonic taxa, but if one was to score diversity by number of genera, that would be more likely to introduce some statistical error.

Biddulphia: Figure 11a-b is not the same taxon as 11c or 11f. Pseudocellate elevations are structurally different (short and flattened in a-b and elongate and rounded in c, f). I’m not sure what taxon 11a-b represents, but it isn’t B. tridens.

Biddulphia toumeyii is a synonym of B. tridens (see Navarro 1990)

Biddulphia californica—check Rattray’s Pseudauliscus taxa, in particular P. ralfsii and P. peruvianus. The poration looks loculate and the position of the rimoportula to the ocelli is telling.

Biddulphia tridentata—I’m not convinced the pseudocelli are stalked as opposed to just broken. These look like valve views of B. biddulphiana to me (particularly with respect to the internal crosswalls and position of the rimoportula).

Odontella: see Sims et al. 2018 for a recent review of the Odontellaceae. The diatom shown in Fig. 12a-b does not conform to the type morphology of Odontella aurita. The slender ocelli suggest O. rostrata or O. atlantica.

Amphitetras—I’m unconvinced Fig. 15a and 15b are different taxa., nor that 15e is not conspecific with 15c-d. What valve characteristics are you suggesting differ between these?

Cyclotella and Cyclostephanos—also likely plankton (and Cyclostephanos is freshwater), so probably not epiphytic representatives.

Dimeregramma and Plagiogramma—see Li et al. 2015, 2020 for updated taxonomy (Fragilariophycideae rather than Triceratiales).

Plagiogramma interrupta—the apical grooves (parallel lines just below the valve apices) strongly suggest a Talaroneis rather than Plagiogramma.

Auricula—this is a raphid genus (note the fibulae visible in the raphe canal on the valve edge). Figure 37b-g are most likely an Undatella—note the stauros perpendicular to the raphe keels.

Tabularia parva—Fig. 20p,q look like there are rimoportula at both apices, and the areolar structure is wrong for a Tabularia. Perhaps a smaller Hyalosynedra (see Sabir et al. 2018)? Same with Synedra commutata (Fig. 20j).

Delphineis—I do not see much of the characteristic sternum for the genus present on Fig. 17k…perhaps a “staurosiroid” or “fragilarioid” araphid genus.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This study is a summary of epipgytic diatoms attached to green algae (macrophyta) inhabiting the Gulf of california.
1. The research content is suitable for the scope of the journal
2. It is an interesting result that reveals that a large number of diatom species are attached to marine plants.
3. However, if you can revise following something, hope this manuscript can be accepted for publication in DIVERSITY.

Specific comments
1. The formal research institute's identification number (holotype number or herbarium number) for all species identified in this study should be suggested.
2. More detailed explanation of unidentified species (sp.) is needed in this study. For example, Cyclostephanos sp.
3. Explain in detail the ecological characteristics of the collection site of macrophyta or diatoms.
4. The order of arrangement of the species and the related photos are inconsistent. For example, in text, Figure 42 is the last, and in the order of arrangement, Figure 46 is the last.

5. New high resolution pictures should be taken.
For example, fig 3-i and j, fig 4- c and d, fig 6- a and b, fig 9-c, fig 10-d, fig 19- f, g and i, fig 22-j and t , fig 31-l, fig 37-b and c, fig 38-b, i, j and p, fig 39-b and c, fig 41-d, fig 43-u, etc.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The following must be considered before publication.

1. This study is difficult to regard as a typical diatom taxonomy paper. In particular, since diatoms attached from a specific seaweed contain a lot of various freshwater and planktonic species, the expression is called epiphytic diatom. It is considered necessary to further comment on the ecological and geographic characteristics of seaweed locality.
2. The resolution of diatom pictures, irregular arrangement, deposition number of each holotype or picture, and figure arrangement in the plate are insufficient in completeness. In particular, I think the author's judgment that it is impossible to correct figures with low resolution is not correct. If so, I am curious about the significance of inserting photos into the paper. In addition, a clear explanation of unidentified species (sp.) (molecular analysis and SEM analysis in some cases) is required. Enough comparative analysis with other taxonomically similar species is exclusively required.
3. Finally, it is judged that it is not desirable to express that time and energy are unnecessary for revising the reviewer's recommendations. In conclusion, although this paper is an interesting study, but it requires additional efforts and responses from the authors.

Author Response

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Author Response File: Author Response.docx