Reply on RC2

We would like to thank you for your comments, we have addressed them accordingly. We revised large sections of the manuscript, including an improved separation of the results and discussion. We have also added statistical testing of the 2018 and 2020 coverage and thickness data and put more emphasis on the observations done within this study. Finally, we have included a species list as a supplementary table. Below are responses to the specific comments:


Dear reviewer,
We would like to thank you for your comments, we have addressed them accordingly. We revised large sections of the manuscript, including an improved separation of the results and discussion. We have also added statistical testing of the 2018 and 2020 coverage and thickness data and put more emphasis on the observations done within this study. Finally, we have included a species list as a supplementary 86 colonization refer to a process -shouldn´t it be more specific like "coverage" or "state of colonization?
Updated to "initial coverage estimate". 93 please explain why nudibranchs and gastropods were excluded how did you overall selected your list and what was the rationale?
The text has been revised. It was eggs of nudibranchs and gastropods that were excluded. 97-98 wasn´t the data secured such that the same person could compare and analyze the data later to insure more comparable data in 2018 and 2020?
Unfortunately it was not feasible to have the 2018 data re-evaluated by the structural inspectors present during the 2020 survey.
I would like to see the species list! I failed to find it in results or reference to an appendix! A species list is now available as a supplementary table.
Same as above "different species of crustacean"! A species list is now available as a supplementary table.
I would think the term "percent coverage" is better Amended.
Although -tidal depth ranges are well-defined terms I find it a little bit odd to use these depth categories in relation to floating structures where indeed the organisms do not experience the consequences of tides (e.g. the Kelp is not exposed to diurnal desiccation, changing light levels etc.) I Suggest to use depth ranges in meters instead The structures are anchored to the seabed using suction anchors and are attached to these by heavy chains. This results in an intertidal zone. However, intertidal zone is likely reduced as compared to a non-floating structure.
130 Laminaria belong to the group of Phaeohyceae -should maybe be "Laminaria and other Phaeophyceae" Amended.
144 "no significant differences were noted on the mooring lines…" This is a statement that should certainly be substantiated with additional information. What parameter did you look at (e.g. communities, coverage, biomass, individual species, biodiversity indices…)? What was your data format? test used … etc. "Significant" has been replaced by "clear".
168-172. This part is not clear. The part about the coverage is clear but information on how you have distinguished between soft and hard fauna is missing (what species belongs to which groups) especially since the 2018 survey was performed by nonspecialist. How was thickness determined from the underwater video film? Again bear in mind, that although this can easily be done by non-specialist, data is still subjective and the data quality could therefore be improved if the same person did both year (whether specialist or not). Legends on figure 7 an 8 missing information about the years and how changes is defied (2018 vs 2020?). This section has been revised accordingly. New figures have been introduced and now include a T-test, conducted on the coverage and thickness data. Details on specific taxonomic groups with regards to hard and soft growth, respectively, are now included.
175. Subheading should rather be "identification of species" as no non-indigenous species in fact was determined with certainty Amended. . 193 -197 This is a potential important finding, due to the threatened status of Desmophyllum, and I would recommend to contact external experts as you did with the Barnacles. A strong group I located just around the corner at Edinburg University.

Amended
Advised experts agree that the colony is likely D. pertusum, but due to the small size and uncharacteristic appearance a positive identification would require close up imagery of the calyx using a stills camera. The text has been amended. 215-216. If diversity "is lacking" there is either 0 or 1 species present! Better to write whether there was fauna at all. Did you quantify species richness or diversity at all? In case this should be described under methods and results. Better to delete this sentence The sentence has been revised.
224 similar in what way?
In regard to species composition and distribution. This text has been revised.
What do you mean by "not significant enough" if no statistical analysis was performed write instead "differences was not clear" Amended.
235 Different I what way?
The text has been revised.
239-241 How can you conclude the species succession follow the same trend as you have stated in the material and methods that only a few phyla was recorded by the nonspecialists. Species succession implies that the relative contribution species to the community changes over time.
The section has been revised, and together with the new section regarding changes in taxonomic composition between 2018 and 2020. We do believe that we can say that Hywind FOWF seems to follow the same pattern as other offshore structures in the North Sea. However, the limited taxonomical resolution should of course be considered. 251 the information about the uncertain due to lack of consistent methodology should (as mentioned in the above several times) should be flagged up front in MS and it also concerns the above comments on succession.
Information regarding inconsistencies between the years has been included in the Methodology section, as well as briefly in the Discussion section.