Reviewing Introduction Histories, Pathways, Invasiveness, and Impact of Non-Indigenous Species in Danish Marine Waters

Round 1

Reviewer 1 Report

The paper is very interesting, well-written/well prepared and covers gaps of knowledge on NIS in Danish waters. 

However, several important publications regarding NIS in the Baltic Sea have been omitted and should be cited in the paper. These papers explain many aspects discussed in the paper: invasiveness and impact of NIS, scenarios for new NIS arrivals into the Baltic Sea:

e. g. Dobrzycka-Krahel A., Graca B., 2018. Effect of salinity on the distribution of Ponto–Caspian gammarids in a non-native area – environmental and experimental study. Marine Biology Research 14 (2): 183-190. 

Author Response

We have added the suggested reference plus 3 other references on NIS in the Baltic (Outinen et al. 2021. Biofouling 37: 984-997; Lehtiniemi et al. 2020. Journal of Environmental Management 267: 110608; Ojaveer et al. 2021. Science of the Total Environment 785: 147375) and made changes in the text accordingly (lines 426-428; 872-873; 986-988).

Reviewer 2 Report

Paper is an extensive report from the non indigenous species collected in Danish waters over last years. It contains very useful and well presented information with rich literature cited.

I have only two minor remarks

1) near the Danish waters there was a long term study on the NIS species inhabiting the Dutch waters, that demonstrated multiyear sequence of population growth and establishment of NIS species - phenomenon certainly valid for Danish waters as well - this paper shall be cited

Hummel H, Vijnhoven 2014 Long term patterns in the establishment... Marine Ecology 35, suppl. 1, 50-55pp

2) there was important paper showing that supposed Mnemiopsis in N. Baltic - next to the Danish Bornholm was in fact Mertensia - an N. Sea ctenophore and not an NIS - possible only to say with molecular methods - that problem shall be discussed - how sure are authors that observations of Mnemiopsis were correct ? - see the paper :

Gorokhova et al 2009 Molecular evidence for the occurrence of ctenophore Mertensia... Limnology an Oceanology 54, 6, 2025-2033 pp

 

 

Author Response

Ad 1). The paper from the Netherlands is certainly relevant for Danish waters and has been included with additions to the text to confirm that a similar pattern has been observed for some NIS in Danish waters, but unfortunately with no quantitative data (lines 1020-1025)

Ad 2) Thank you also for pointing out this paper. We have included it and added several lines of text (lines 599-602). However, we would like to point out that only adults have been included in the analyses presented here, and those cannot be confused with Mertensia ovum as this native species does not belong to the lobate ctenophores and has never been observed in the adult stage in the Baltic Sea - see Jaspers et al. 2013 JPR 35(3): 582-592 and Jaspers et al. 2012 Biol. Letters 8(5): 809-812.

 

Reviewer 3 Report

The authors systematically review the Non-Indigenous Species (NIS) in Danish marine waters, which provided comprehensive and useful information for the ecological scientist and local government. I suggest to accept it.

However, the following suggestions for the authors considering:

1. Because this is a very long review with so many information about the NIS. I strong suggest the authors provide an overall conclusion for the readers, including the list of NIS in Danish marine waters, the evaluation methods to marine MIS, pathway of NIS, the positive or negative effects of NIS, the current problem and changing trends of the NIS, and the measures should be taken for the precautions against the NIS in local waters.

2. The caption of figure 3 is not suitable.

Author Response

We thank this reviewer for suggesting a spell check - not that there were many spelling mistakes, but we did discover a few other language issues probably arising during the final stages of accepting and rejecting track-changes. We hope that all mistakes have now been corrected.

Ad 1. We have added some text to the conclusions about rate of new NIS arrivals, pathways, monitoring, evaluation and impacts. The total list of NIS (123 species plus information about first records etc.) is included as Supplementary Table 1, and we have added a reference to this in the conclusions. We do not think that proposing management measures is within the scope of the paper.

Ad 2. Caption to Figure 3 has been changed.