Review of 'Light pollution: A landscape-scale issue requiring cross-realm consideration'

Mayer-Pinto and colleagues submitted a review paper entitled « Light pollution: A landscape-scale issue requiring cross-realm consideration ». This work deals with a subject of great interest, the impacts of artificial light at night (ALAN) on organisms and ecosystems. This subject is the matter of intensive research and several original and review papers have been published the last years on this topic, as a result from an increasing awareness that ALAN induces dramatic negative effects on species, populations and ecosystems, and that politics of mitigation must be implemented in order to reduce the effects of ALAN. The originality of this submission lies in the fact that it considers mainly the effects resulting from the interactions in between aquatic and terrestrial realms, with the help of case studies.

The paper is well written and of interest for a general audience. I believe however that some aspects could be treated more in depth, in the light of recent publications on the matter. My comments follow.

-L60. Isn’t it, at the start, a key driver of biological (molecular and cellular) processes?

-L86-88. Most of the studies today indicate that on the long term ALAN affects dramatically and durably population abundance and richness, and ultimately ecosystems. Thus the term “might” (L86) sounds weak to me. Same comment for the use of “may” L136.

-L111. Since daily and seasonal are terms that refer to cyclic/periodic variations, please specify what “…or cyclic movement of…” refers to.

-L176-180. Is this useful?

-L194. I do not understand the meaning of “…associated with human populations…” here.

-L294-296. This has already been said before.

-The paper is based on the choice of 4 case studies. Since the salmon is one of these cases, perhaps the authors could refer to a previous recent review in which a whole section is dedicated to the impact of ALAN and other factors on the migrating Atlantic salmon. In this review paper examples of ALAN impacts on riparian systems are also provided and discussed in light of the literature available (see: Falcón et al., Frontiers in Neuroscience 2020; 10.3389/fnins2020.602796).

-In the review paper cited above, it is also emphasized that ALAN is not the only factor affecting populations and ecosystems and that the addition of anthropogenic threats, including ALAN, should also be considered when studying solutions to mitigate the effects of ALAN. Perhaps this could also be discussed in this MS, particularly at the end, in the part dealing with the challenges and practical solutions? On site studies prospective studies should consider the existence of 'multifactotial effects' whether positive (sometimes) or negative (most of the times).

-L320. Vertical migration refers to the LD synchronized movement, up and down the water column. Thus here I would write "vertical movement" or more simply "migration to the surface".

-L391-393. I do not see why they should be more sensitive; isn’t this the case for all the living? Or perhaps I am missing something here?

-L435-440. Indeed. Starting from the observation that ALAN is not “a natural environment” it would seem reasonable to believe it is per se a polluting factor; not mentioning that the absence of effect on the short term does not mean there will be no effect on the long term (as previous studies have shown). And not mentioning that the presence or absence of other harmful factors (depending on the area investigated) might interact with ALAN to promote effects not observable with ALAN alone.

L451-453. I disagree with this assumption; many studies now include this aspect; see the review paper referenced above (which discusses this extensively); and, the authors write later (L513-514) “…any light that is not natural in its origin is likely to interfere with ecological process”. I agree 100% with this.

-L493-496. I do not understand this sentence here. Aren’t all species important for the maintenance of an ecosystem?

-L500. What is an acceptable threshold?

-L547. There is more information available than suggested from the sentence. See Falcón et al, 2020, in which this is discussed.

-The reference list should be checked, as some references appear incomplete (e.g., lines 847, 883, 893, 967, 989, 1067, 1078,…).