Assessing Efficacy of “Eco-Friendly” and Traditional Copper-Based Antifouling Materials in a Highly Wave-Exposed Environment

Round 1

Reviewer 1 Report (Previous Reviewer 3)

The authors have taken action on my previous comments, and have generally improved the  manuscript. A few points remain:

The term "skin-like" for Micanti is not very descriptive. Skin is normally smooth, while this product is hairy. The first time it is mentioned in L23 you could say:  (i.e., a slow-copper release coating and a self-adhesive, fibre-covered, skin-like coating) .

The photos of the fouled plates provided in Table S2 are very useful. I would still like to see single images of the three main fouling organisms (referred to in L276-277).

L163-164 Consider a slight change in the wording to: The third and fourth materials we considered were two widely available copper-based AF paints that have not been designated eco-friendly...

L168. Define RMS (according to ASME B46.1, RMS is the root mean square average of the profile height deviations from the mean line measured). Note that the units are um, not um^2 as you have written. Also it is meaningless to give this average to four decimal places (the error will be large). It should be stated as: The steel surface roughness (RMS) was 6.6 μm.

L557 I suggest: The two copper-based, AF paints and the slow-release, “eco-friendly” copper-based paint all showed ...

Also some formatting (e.g. sub/superscripts) needs to be corrected.

Author Response

The authors have taken action on my previous comments, and have generally improved the  manuscript. A few points remain:

The term "skin-like" for Micanti is not very descriptive. Skin is normally smooth, while this product is hairy. The first time it is mentioned in L23 you could say:  (i.e., a slow-copper release coating and a self-adhesive, fibre-covered, skin-like coating).

R/. Thank you. We modified the Abstract. We changed: (i.e., a slow-copper release and a skin-like coating) --> (i.e., a slow-copper release coating and a self-adhesive, fiber-covered, skin-like coating).

The photos of the fouled plates provided in Table S2 are very useful. I would still like to see single images of the three main fouling organisms (referred to in L276-277).

R/. We add photos of the species Obelia geniculata, Austromegabalanus psittacus, and Pyura chilensis in Supplementary Material Table S2.

L163-164 Consider a slight change in the wording to: The third and fourth materials we considered were two widely available copper-based AF paints that have not been designated eco-friendly...

R/. Corrected, thank you.

L168. Define RMS (according to ASME B46.1, RMS is the root mean square average of the profile height deviations from the mean line measured). Note that the units are um, not um^2 as you have written. Also it is meaningless to give this average to four decimal places (the error will be large). It should be stated as: The steel surface roughness (RMS) was 6.6 μm.

R/. Corrected, thank you.

L557 I suggest: The two copper-based, AF paints and the slow-release, “eco-friendly” copper-based paint all showed ...

R/. Corrected, thank you.

Also some formatting (e.g. sub/superscripts) needs to be corrected.

R/. Thank you, we checked all the manuscript.  

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 1)

Recommende to accept the current version.

Author Response

Recommende to accept the current version.

R/. Thank you.

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Suggestions and comments to jmse-2041080:

The manuscript evaluated the antifouling property of eco-friendly and traditional copper-based antifouling coatings and materials in a highly wave-exposed environment. This long-term research is very meaningful and detailed. However, some suggestions need to be taken care before accepting:

（1）       The title is tedious. I suggest to change one. For example, “Antifouling evaluation of eco-friendly and traditional copper-based antifouling materials in a highly wave-exposed environment”

（2）       Please check English carefully, both in grammar and words. For example, two “we” appeared in line 477, the “farther” should be replaced by “further” in line 562.

（3）       The sentence “We showed biofouling biomass and cover gains through time are similar among all untreated materials and one the skin-like ecofriendly AF.” is confusing and need to be revised.

Author Response

Suggestions and comments to jmse-2041080:

The manuscript evaluated the antifouling property of eco-friendly and traditional copper-based antifouling coatings and materials in a highly wave-exposed environment. This long-term research is very meaningful and detailed. However, some suggestions need to be taken care before accepting:

（1）       The title is tedious. I suggest to change one. For example, “Antifouling evaluation of eco-friendly and traditional copper-based antifouling materials in a highly wave-exposed environment”

R/. We agree, we changed it to: “Assessing efficacy of “eco-friendly” and traditional copper-based antifouling materials in a highly wave-exposed environment”.

We have added quotation marks to eco-friendly to highlight this is a denomination based on the brand offering the product and a fully-tested true eco-friendly product.

（2）       Please check English carefully, both in grammar and words. For example, two “we” appeared in line 477, the “farther” should be replaced by “further” in line 562.

R/ Thanks. We revised the grammar and corrected several mistakes.

     Line 477: We corrected it. 

     Line 562: We corrected it.

（3）       The sentence “We showed biofouling biomass and cover gains through time are similar among all untreated materials and one the skin-like ecofriendly AF.” is confusing and need to be revised.

R/ The sentence was modified to: “ We showed that biofouling cover and biomass increased at similar rates over time among all untreated materials, including the skin-like AF”. 

Reviewer 2 Report

This paper investigates the effect of substratum and depth on marine biofouling in a high energy environment. Nontoxic surfaces, including a textured coating (Micanti) and three biocidal coatings, one of which is a mentioned as slow release formulation, were tested over a 15-month period with measurements of fouling at three time intervals.  The report includes the grazing effect of a mass recruitment of a sea urchin. 

I have a few minor questions regarding the design but overall, the study is well designed with appropriate statistical analysis of the results.  There is a substantial body of work but, unfortunately, I do not see that there is sufficient that is new to recommend publication.

I read this paper in conjunction with previously published studies (references 32 and 33) from the authors.  Given that the latter contain detailed observations of the fouling over comparable time periods at the same two depths, including on one of the antifouling coatings in the present study (Ocean Jet 33), my impression is that there is insufficient that is original in the present paper.  Essentially the paper, establishes that: 1) the biocidal antifouling coatings are effective over what is a comparatively short timeframe for commercial coatings designed for high energy environments (ships’ hulls), i.e. not surprising; 2) the nonbiocidal coatings are fouled by the expected community composition (based on prior studies in this region); 3) Micanti is ineffective, which is unsurprising given the lack of success of another ‘hairy’ coating SealCoat and the false premise that hairy marine organisms, such as seals are devoid of fouling (c.f. Joseph et al.(1986) J Mammal 67 (4), 772–772. doi: 10.2307/1381148); sea urchins are effective grazers of fouling, which the authors recognise is not new and cite the relevant literature.

Other comments:

It is unfortunate that Seavoyage 100 CDP is used in the context of an eco-friendly slow release paint.  As far as I am aware, this formulation contains diuron as a co-biocide to copper oxide.  Diuron has attracted significant concerns for its detrimental effects on the environment (see e,g, Egardt et al. (2017) Mar Poll Bull 125, 282-288) and human health (see e.g. https://www.epa.gov/pesticides/epa-seeks-public-comment-measures-address-human-health-and-ecological-risks-posed-diuron ).

There is no information on the release rates of copper from the coatings. Generally, SPCs contain less biocide and are less toxic than CDPs.

It is unclear from supplementary figure 1 whether coatings were positioned in the same pattern on the four moorings or whether they were randomised (I may have missed comment on this).

Were all coatings of the same color given that coating color can affect marine biofouling (e.g. Swain et al. (2006) Biofouling 22, 425-429)?

Suggest combine sections 3.2 and 3.3: as mentioned mean % cover by itself is not very enlightening, e.g. could be 100% Obelia versus 100% barnacle, which would be very different in terms of loading and drag-related impacts.

Minor edits:

Line 39: what does ‘unprocessed’ sea water mean?

Line 59: Cu₂O

Line 61: fouling-release not foul-release (industry generally refers to foul release but, of course, it is grammatically incorrect- fouling is released not foul).

Line 78: exercised not exerted

Line 90: within

Line 95: marine renewable energy (MRE) at first mention

Line 116: upwelling shadow?

Line 158: SeaVoyage is a registered trademark

Line 160: A/F-21

Line 240: Tukey

Line 255: sp. not sp.  but the species is identified in the SI table and prior publications.  Is it in doubt?

Line 294: replaced

Line 338 and elsewhere: although semester originally referred to 6 months (Latin derivation) that is no longer the case.

Line 475: urchin

Line 554: similar

Line 558: approaches

Author Response

This paper investigates the effect of substratum and depth on marine biofouling in a high energy environment. Nontoxic surfaces, including a textured coating (Micanti) and three biocidal coatings, one of which is a mentioned as slow-release formulation, were tested over a 15-month period with measurements of fouling at three time intervals.  The report includes the grazing effect of a mass recruitment of a sea urchin.  I have a few minor questions regarding the design but overall, the study is well designed with appropriate statistical analysis of the results. 

There is a substantial body of work but, unfortunately, I do not see that there is sufficient that is new to recommend publication I read this paper in conjunction with previously published studies (references 32 and 33) from the authors.  Given that the latter contain detailed observations of the fouling over comparable time periods at the same two depths, including on one of the antifouling coatings in the present study (Ocean Jet 33), my impression is that there is insufficient that is original in the present paper. 

Essentially the paper, establishes that:

1) the biocidal antifouling coatings are effective over what is a comparatively short timeframe for commercial coatings designed for high energy environments (ships’ hulls), i.e. not surprising;

2) the nonbiocidal coatings are fouled by the expected community composition (based on prior studies in this region);

3) Micanti is ineffective, which is unsurprising given the lack of success of another ‘hairy’ coating SealCoat and the false premise that hairy marine organisms, such as seals are devoid of fouling (c.f. Joseph et al.(1986) J Mammal 67 (4), 772–772. doi: 10.2307/1381148); sea urchins are effective grazers of fouling, which the authors recognise is not new and cite the relevant literature.

R/. The present contribution presents results of a new replicated field experiment that builds on our previous studies at the site. The 2019 paper describes biofouling composition and ecological succession for the first time in Chilean wave exposed environments. The 2020 assessed, in a separate replicated field experiment, the susceptibility of different materials against a traditional copper-based AF paint. In the current contribution we submitted to JMSE we maintain the comparison among different materials (3) and contrast two widely available AF paints in Chile commonly used in the shipping and aquaculture industries. A shortcoming of our previous studies was the arbitrary selection of just one traditional AF paint (OJ 33), among the few available in the market. We here show that the two most common ones have similar efficacy over a 1.5 year exposure to field conditions.  In addition, we tested the efficacy of two coatings sold as “eco-friendly” in the Chilean market. One of them is a slow-release AF paint which, as we discuss below and in the revised manuscript, does have biocide (toxic) compounds. The other one is a skin-like coating (Micanti) that is being promoted worldwide as eco-friendly and has been introduced in the Chilean market in recent years.  Our results show that the slow-release paint has similar efficacy to traditional ones in preventing biofouling accumulation over the same time span and environmental conditions, including grazing. They also show that the Micanti coating does not reduce biofouling. We want to stress that this contribution, and the previous two studies, are all supported by separate, replicated field experiments, i.e. they are completely independent studies at the same general study site.

We thus believe the results presented here, in addition to the serendipitous insights gained by massive sea urchin recruitment, are indeed novel and represent a very significant contribution to our understanding of anti-biofouling strategies in wave exposed environments, and that JMSE is the appropriate outlet to communicate them.

Finally, we probably did not highlight enough the insights gained by the settlement and growth of the common black sea urchin on suspended experimental plates. We are sure the reviewer did not want to imply that previous studies conducted in other places, with other (or the same) sea urchin species, in different habitats and experimental conditions, and with different fouling species, are sufficient to conclude that urchins can control biofouling biomass, particularly in high productive ecosystems. The critical observations we show are that Tetrapygus niger can massively settle, rapidly grow to juvenile sizes and graze on large sessile animals in suspended structures that are highly exposed to orbital currents and waves. At least for us this was surprising.  

Other comments:

It is unfortunate that Seavoyage 100 CDP is used in the context of an eco-friendly slow release paint.  As far as I am aware, this formulation contains diuron as a co-biocide to copper oxide.  Diuron has attracted significant concerns for its detrimental effects on the environment (see e,g, Egardt et al. (2017) Mar Poll Bull 125, 282-288) and human health (see e.g. https://www.epa.gov/pesticides/epa-seeks-public-comment-measures-address-human-health-and-ecological-risks-posed-diuron ).There is no information on the release rates of copper from the coatings. Generally, SPCs contain less biocide and are less toxic than CDPs.

R/. We agree with the reviewer that this presentation can be confusing and have made several changes in the manuscript, from the Title on,  to avoid misinterpretation by readers. Any coating with copper oxide can have detrimental effects on the environment. We used the denomination of “eco-friendly” in contrast to “traditional” (non-eco-friendly)  based on how these coatings are presented in the market. The “eco-friendly” formulation of the product was not tested here.

The Sherwin-Williams brand sells the SeaVoyage 100 CDP paint as a “eco-friendly” tin-free controlled wear polymer (CDP) with a predictable and stable wear rate achieved through a combination of hydrophobic and hydrophilic resin. Sherwin-Williams sells it because it has a long-term antifouling performance and with EPA registration number. Consequently, we called it "eco-friendly" because it was a commercial name. Similarly, the skin-like Micanti coating is presented worldwide as eco-friendly, including promotional videos.  While this material seems to be non-toxic to most marine organisms, it could have environmental effects since the skin can detach from moving structures and pollute the environment. 

We are now much more careful in the manuscript, and  we specified that these are commercial denominations, and that further studies should be done to test the environmental impact. Particularly the slow-release AF paint due to their similar efficacy with not eco-friendly brands over biofouling communities.

We made some modifications to the Title, Abstract, Introduction, Methods and Discussion :

Title:

Assessing efficacy of ‘eco-friendly’ and traditional copper-based antifouling materials in a highly wave-exposed environment

Abstract:

“Although the called ´eco-friendly´ slow-release technologies are not completely innocuous to the environment, we suggest this approach over the more environmentally aggressive traditional copper paints, which are largely the most widely used in aquaculture and shipping industries today. However, further research is needed to test whether their environmental impact is significantly lower in the long-term than traditional AF paints, and therefore the search for non-toxic coating must continue.”

Methods:

“Second, two antifounling strategies offered/denominated as ´eco-friendly´ in the market  were compared: d) a modified substrate surface coating commercially known as Micanti (Micanti). This is a nylon fiber and polyester film with furry texture and a two-component water-based adhesive marketed as an eco-friendly ‘hairy solution’ to the fouling problem, primarily for the shipping industry. It is advertised as suitable for all circumstances worldwide, moored or sailing. It is advertised as suitable for all circumstances worldwide, moored or sailing; and e) a slow-release antifouling paint, Seavoyage 100 CDP Sherwin-Williams (CDP), offered as ´eco-friendly´. This is a copper-based paint with slow-release technology (controlled wear polymer). As all copper-based paints it can pollute the environment in the mid- to long-term, but has gained the commercial denomination eco-friendly and it is the way we use it here. Third, we compared two non-ecofriendly copper-based AF paints widely available in the market: f) Seavoyage A/F-21 Sherwin-Williams (F21) and g) Ocean Jet 33 (OJ33). Treatment chemical characteristics, application, and manufacturer description are presented in Supplementary Material Table S1. Steel plates (A36) with antifouling were painted at San Antonio, Chile, following the same procedures used in ships. The steel surface roughness (RMS, µm²) was 6.6116 [32].

It is unclear from supplementary figure 1 whether coatings were positioned in the same pattern on the four moorings or whether they were randomised (I may have missed comment on this).

R/. No, they were randomized. We clarified this in the text: “A total of seven treatments were deployed randomly in testing frames at each depth and four moorings.”

Were all coatings of the same color given that coating color can affect marine biofouling (e.g. Swain et al. (2006) Biofouling 22, 425-429)?

R/. Thank you for calling our attention to this neat study. Please note that Swain et al.’s study assesses effects of black and white surfaces in very shallow waters (40 cm). But it is important to consider. We added to the discussion this text:

“It has been suggested that contrasting color  differences may impact the establishment of a biofouling communities, at least in short-term tests of AF coatings. [59], showed that fouling species exhibit significantly higher settlement by Ulva and spirorbis tube worms on black plastic surfaces compared to white plastic surfaces when exposed at shallow (ca. 40 cm) depths in comparatively short (14d) experimental trails. The mechanisms producing such differences are unclear and authors do not advance an explanation, but they may be related to differences in solar radiative heat gains or rugosity between black and white plates. Our study, compared three coatings with different colors: CDP and OJ33 color red and F21 color blue, in a highly wave-exposed environment and no differences were observed in cover or biomass at 5 and 15 m deep waters after a few weeks exposure. Together with previous studies with different materials [32,33], color does not seem to play any significant role in biofouling establishment and growth, at least not after few weeks and at waters depths beyond few centimeters.”

Suggest combine sections 3.2 and 3.3: as mentioned mean % cover by itself is not very enlightening, e.g. could be 100% Obelia versus 100% barnacle, which would be very different in terms of loading and drag-related impacts.

R/. Ok, done. Thank you.

Minor edits:

Line 39: what does ‘unprocessed’ sea water mean?

R/. "Unprocessed": Means untreated, but we agree that it is confusing. So, we removed it. Thank you.

Line 59: Cu₂O

R/. We corrected it.

Line 61: fouling-release not foul-release (industry generally refers to foul release but, of course, it is grammatically incorrect- fouling is released not foul).

R/. We corrected it.

Line 78: exercised not exerted

R/. We corrected it.

Line 90: within

R/. We corrected it.

Line 95: marine renewable energy (MRE) at first mention

R/. We corrected it.

Line 116: upwelling shadow?

R/. Upwelling shadows are high-temperature regions within coastal upwelling systems.

Line 158: SeaVoyage is a registered trademark

R/. We corrected it. We added Sherwin-Williams.

Line 160: A/F-21

R/. We corrected it.

Line 240: Tukey

R/. We corrected it.

Line 255: sp. not sp.  but the species is identified in the SI table and prior publications.  Is it in doubt?

R/. Yes, it is true. Thank you. We corrected it.

Line 294: replaced

R/. We corrected it.

Line 338 and elsewhere: although semester originally referred to 6 months (Latin derivation) that is no longer the case. 

R/. We clarified and explained this in the methods:

“To test for differences in the above treatment effects through ecological succession, three exposure time treatments were performed: a) exposure in the field for 6 months, during the first phase of the experiment (First six months (First6): October 2018- April 2019), b) exposure in the field for approximately 6 months during the second phase of the experiment (Second six months (Second6): April 2019-January 2020), and c) exposure for 15 continuous months (Yearly: October 2018- January 2020).”

Line 475: urchin

R/. We corrected it. Thank you.

Line 554: similar

R/. We corrected it.

Line 558: approaches

R/. We corrected it.

Reviewer 3 Report

This study set out to investigate the antifouling effects of three commercial coatings and a novel surface treatment (Micanti) compared to untreated materials in a highly wave-exposed marine environment. Unfortunately the test panels became colonised by omnivorous sea urchins halfway through the planned exposure period. The authors have discussed this potential set-back in a positive manner.
All three of the commercial coatings are copper-based, but two are described as non-ecofriendly, while the third (Seavoyage 100) is said to be eco-friendly. No reason for describing this copper-based coating as "eco-friendly" is given. This point is central to the work because the main conclusion to be drawn from the results is that the inert surfaces (acrylic, stainless steel) accumulate fouling as expected, while all three copper-based coatings prevent this. Accumulated fouling on the inert surfaces is reduced by sea urchin grazing (especially at the shallowest depth). The special coating Micanti fouls to a similar degree as the inert surfaces, and this fouling is not removed by sea urchins. The nature of Micanti as a "hairy" surface composed of polymer fibres needs to be described.
Section 2.4 describes the use of a precision balance (0.0001g) to measure wet fouled plates after draining for one minute. This is completely meaningless! I have personally weighed wet, heavily fouled plates after removal from the sea and you are lucky to get a result that is accurate to within (tens of ) grams. The amount of fouling quoted is very low, and puzzling. In Figs. 3 and 4 biomass amounts up to a maximum of only 0.7g /100 cm2 (i.e. the area of one sample plate) is quoted. This cannot be correct, as macro-fouling orgainsms had attached and the weight of e.g. one barnacle is more than this. In Fig. 2 and the supplementary graph S3 the weight of biomass is given in the units g/day/100 cm2. There seems to be some confusion in units. Quoting fouling accumulation rates as g/day/100 cm2 is not particulalry helpful, as rates will not be constant during the fouling period owing to changing sea temperature, etc. It would be preferable to give the actual amount of fouling recorded at the end of each exposure period.
Please provide photos of the fouled plates (these are missing from the Supplementary material). It would be very helpful to have photographs of the main fouling organisms and the sea urchins in the text, as readers in other countries may not be familiar with these species (especially Pyura chilensis).
In general, the claim that the copper-containing CDP paint is "eco-friendly" must be justified in detail. Otherwise, as stated above, the only conclusion is that copper-based paints prevent fouling. This is very-well known.

Some detail points are:
Please indicate the compass direction that the plates are facing in Fig. 1.
Give the manufacturer of the coatings in the text (Sherwin-Williams).
What plate material were the coatings applied to? What surface roughness was achieved by sanding the plates (L145)? This will influence fouling settlement. If you cannot give the surface roughness, at least quote the grade of sandpaper used.

Author Response

This study set out to investigate the antifouling effects of three commercial coatings and a novel surface treatment (Micanti) compared to untreated materials in a highly wave-exposed marine environment. Unfortunately, the test panels became colonized by omnivorous sea urchins halfway through the planned exposure period. The authors have discussed this potential set-back in a positive manner.

R/. Ok, thank you.

All three of the commercial coatings are copper-based, but two are described as non-ecofriendly, while the third (Seavoyage 100) is said to be eco-friendly. No reason for describing this copper-based coating as "eco-friendly" is given. This point is central to the work because the main conclusion to be drawn from the results is that the inert surfaces (acrylic, stainless steel) accumulate fouling as expected, while all three copper-based coatings prevent this.

R/. We agree with the reviewer that this presentation can be confusing and have made several changes in the manuscript, from the Title on,  to avoid misinterpretation by readers. Any coating with copper oxide can have detrimental effects on the environment. We used the denomination of “eco-friendly” in contrast to “traditional” (non-eco-friendly)  based on how these coatings are presented in the market. The “eco-friendly” formulation of the product was not tested here.

The Sherwin-Williams brand sells the SeaVoyage 100 CDP paint as a “eco-friendly” tin-free controlled wear polymer (CDP) with a predictable and stable wear rate achieved through a combination of hydrophobic and hydrophilic resin. Sherwin-Williams sells it because it has a long-term antifouling performance and with EPA registration number. Consequently, we called it "eco-friendly" because it was a commercial name. Similarly, the skin-like Micanti coating is presented worldwide as eco-friendly, including promotional videos.  While this material seems to be non-toxic to most marine organisms, it could have environmental effects since the skin can detach from moving structures and pollute the environment. 

We are now much more careful in the manuscript, and  we specified that these are commercial denominations, and that further studies should be done to test the environmental impact. Particularly the slow-release AF paint due to their similar efficacy with not eco-friendly brands over biofouling communities.

We made some modifications to the Title, Abstract, Introduction, Methods and Discussion :

Title:

Assessing efficacy of ‘eco-friendly’ and traditional copper-based antifouling materials in a highly wave-exposed environment

Abstract:

“Although the called ´eco-friendly´ slow-release technologies are not completely innocuous to the environment, we suggest this approach over the more environmentally aggressive traditional copper paints, which are largely the most widely used in aquaculture and shipping industries today. However, further research is needed to test whether their environmental impact is significantly lower in the long-term than traditional AF paints, and therefore the search for non-toxic coating must continue.”

Methods:

“Second, two antifounling strategies offered/denominated as ´eco-friendly´ in the market  were compared: d) a modified substrate surface coating commercially known as Micanti (Micanti). This is a nylon fiber and polyester film with furry texture and a two-component water-based adhesive marketed as an eco-friendly ‘hairy solution’ to the fouling problem, primarily for the shipping industry. It is advertised as suitable for all circumstances worldwide, moored or sailing. It is advertised as suitable for all circumstances worldwide, moored or sailing; and e) a slow-release antifouling paint, Seavoyage 100 CDP Sherwin-Williams (CDP), offered as ´eco-friendly´. This is a copper-based paint with slow-release technology (controlled wear polymer). As all copper-based paints it can pollute the environment in the mid- to long-term, but has gained the commercial denomination eco-friendly and it is the way we use it here. Third, we compared two non-ecofriendly copper-based AF paints widely available in the market: f) Seavoyage A/F-21 Sherwin-Williams (F21) and g) Ocean Jet 33 (OJ33). Treatment chemical characteristics, application, and manufacturer description are presented in Supplementary Material Table S1. Steel plates (A36) with antifouling were painted at San Antonio, Chile, following the same procedures used in ships. The steel surface roughness (RMS, µm²) was 6.6116.

Accumulated fouling on the inert surfaces is reduced by sea urchin grazing (especially at the shallowest depth). The special coating Micanti fouls to a similar degree as the inert surfaces, and this fouling is not removed by sea urchins. The nature of Micanti as a "hairy" surface composed of polymer fibres needs to be described.

R/. Yes, in the methods, we now described it as: “ This is a nylon fiber and polyester film with furry texture and a two-component water-based adhesive marketed as an eco-friendly ‘hairy solution’ to the fouling problem, primarily for the shipping industry. It is advertised as suitable for all circumstances worldwide, moored or sailing”

Section 2.4 describes the use of a precision balance (0.0001g) to measure wet fouled plates after draining for one minute. This is completely meaningless! I have personally weighed wet, heavily fouled plates after removal from the sea and you are lucky to get a result that is accurate to within (tens of ) grams.

R/. It is true. We eliminate the text “precision balance (0.0001g)”. Thank you.

The amount of fouling quoted is very low, and puzzling. In Figs. 3 and 4 biomass amounts up to a maximum of only 0.7g /100 cm2 (i.e. the area of one sample plate) is quoted. This cannot be correct, as macro-fouling orgainsms had attached and the weight of e.g. one barnacle is more than this.

R/. Thank you for noting this significant mistake in the units. The mean biomass accumulation is by the day of each plate at different moorings. We present rates of biomass accumulation as grams of biofouling per plate per day of exposure in the field (g/day/100 cm2). In this manner we can compare across different periods,  because plates were not exposed for exactly the same number of days. We corrected the title of the y-axis in Figure 3 and Figure 4. Thank you. 

In Fig. 2 and the supplementary graph S3 the weight of biomass is given in the units g/day/100 cm2. There seems to be some confusion in units. Quoting fouling accumulation rates as g/day/100 cm2 is not particulalry helpful, as rates will not be constant during the fouling period owing to changing sea temperature, etc. It would be preferable to give the actual amount of fouling recorded at the end of each exposure period.

R/. yes, there was a confusion of units. We apologize.  But we believe rates of biomass accumulation are more informative in this case, allowing for direct comparison across periods and treatments. We now give an indication of total mean biomass per plate in the text within the Results section.

Please provide photos of the fouled plates (these are missing from the Supplementary material). It would be very helpful to have photographs of the main fouling organisms and the sea urchins in the text, as readers in other countries may not be familiar with these species (especially Pyura chilensis).

R/. Yes, thank you. We added the photos to Supplementary Material, Table S2: Annual photos.

In general, the claim that the copper-containing CDP paint is "eco-friendly" must be justified in detail. Otherwise, as stated above, the only conclusion is that copper-based paints prevent fouling. This is very-well known.

R/. As we mention above, our paper aimed to compare “eco-friendly” and “non-eco-friendly” strategies as they are denominated and offered in the market. We made it clear in the manuscript. Please see above.

Some detail points are:
Please indicate the compass direction that the plates are facing in Fig. 1.
R/. Done. Thank you.

Give the manufacturer of the coatings in the text (Sherwin-Williams).
R/. Done. Thank you.

What plate material were the coatings applied to? What surface roughness was achieved by sanding the plates (L145)? This will influence fouling settlement. If you cannot give the surface roughness, at least quote the grade of sandpaper used.

R/. “Steel plates (A36) with antifouling were painted at San Antonio, Chile, following the same procedures used in ships. The steel surface roughness (RMS, µm²) was 6.6116. (Navarrete et al., 2020.The Journal of Ocean Technology)”

Round 2

Reviewer 2 Report

.