the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Jan 2026
Environmental and habitat controls on non-marine ostracod distribution in Arctic lakes
Abstract. The Arctic is warming almost four times faster than the global average. Lakes in the Arctic are a prominent feature of the landscape and are consequently undergoing limnological and ecological change such as shifts in algal productivity, water column mixing depths, and ice persistence. Most recently, the nutrient-colour paradigm has been associated with extensive loss of benthic habitat. Ostracods (small aquatic crustaceans) are a significant contributor to the benthic biomass of shallow to mid-depth lakes (<20 m) and there is great potential to use fossil ostracods to reconstruct past environmental change and predict future ecosystem states in these lake-rich regions. However, relative to mid-latitude regions, little is known of the ecological traits of ostracods in the Arctic. Here we present the first systematic survey of ostracod species and ecological preferences for the Kangerlussuaq region of southwest Greenland, the largest ice-free margin of Greenland. Candona candida is a generalist species in the Kangerlussuaq region, being present in deeper lakes and at the higher end of the bioavailable soluble reactive phosphorus and nitrate gradients. These traits suggest that C. candida will become abundant in the Greenlandic ostracod fauna, and potentially across the Arctic. For some species, particularly Cypris pubera, bioavailable nutrient concentrations are a dominant control on distribution. Nutrient status of water appears to be a significant control on ostracod presence and abundance and should be included in future ecological studies globally.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-6147', Claude Meisch, 28 Jan 2026
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AC1: 'Reply on RC1', Lucy Roberts, 26 Feb 2026
We appreciate the positive comments on the manuscript. Comments 1-8 can be easily addressed in a revised manuscript.
Citation: https://doi.org/10.5194/egusphere-2025-6147-AC1
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AC1: 'Reply on RC1', Lucy Roberts, 26 Feb 2026
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RC2: 'Comment on egusphere-2025-6147', Steffen Mischke, 09 Feb 2026
This manuscript by Roberts et al. provides important and new information about the distribution of freshwater ostracods in Greenland and the ecological preferences of the recorded species. Such information is very relevant and needed in regions where lakes are affected most intensively by current climate warming.
The manuscript is generally well-structured, well-written and well-illustrated. The inferences are supported by the presented data.
I have only a single major concern:
The authors describe that ostracod specimens were collected alive and as those represented by empty carapaces and disarticulated valves. These different specimens were apparently carefully differentiated. Such dataset is very valuable because those specimens collected alive are directly linked to the measured environmental parameters. In addition, the timing of the occurrence of the specific species during the year’s seasons can be assessed based on such data. However, the authors did not make use or full use of this differentiation. In the discussion section, the different recorded species are discussed with respect to measured environmental parameters such as nutrients, apparently regardless whether actually specimens collected alive or as empty carapaces and disarticulated valves were recorded. I suggest to differentiate more clearly between those specimens collected alive on the one hand side, and those collected as empty carapaces and disarticulated valves.
Minor comments follow below. I added also some suggestions for improvements in an annotated pdf file.
The abstract
The abstract could provide some more detailed information. The authors state that ostracods from lakes in a specific region in Greenland were systematically investigated. How many lakes were sampled? What are the depth ranges for all these samples? Which ranges of conductivities or pH or alkalinities (or other important factors) were sampled?
Two species are mentioned in the abstract. How many species were recorded in general? Which are the three or five most abundant taxa?
Introduction
line (l) 57: The mentioned relationship between light penetration and changes in mixing depth is not very obvious and a short hint to explain this link here would be helpful.
2.1 Study area
The mean annual temperature is provided here but the seasonality is very important in such Arctic environment, and mean January and July temperatures should be added.
Anderson et al. (2012) is provided as reference for the climate data but this is apparently not the source of the original climate data. Is it possible to refer to the original source which is possibly some weather monitoring authority?
I suggest to add some information about the local geology in the catchments of the lakes. The authors mention the many lakes in the region and the potential to use lake-sediment records as climate archives. However, preservation of ostracod valves in cold-water lake deposits can be poor in regions with igneous crustal or volcanic rocks. Also, “geological weathering of the glacial bed” is mentioned in the discussion section but not very helpful without information of the local geology.
2.2 Field methods
The authors describe (l 140) that the top ~1 cm of sediment was sampled where submerged macrophytes were present. So, was the top sediment not generally sampled, and were therefore, empty carapaces and disarticulated valves mostly not included in the survey? Sampling with a net is surely very appropriate to collect specimens alive, but endobenthic taxa and those not present as larger instar or adult stages during the sampling period might not be included.
How were sediment samples collected at positions where macrophytes were present? Which type of grab or corer or dredge was used and how much sediment or which area was sampled?
Results
l 230
The authors describe that the electrical conductivity in these lakes ranged from 0.9 to 4.1 mS/cm but Table 3 includes lake 15 with a conductivity of 0.01 mS/cm and some more lakes with conductivities <0.9 mS/cm.
l 231
Water temperature data are provided here with two decimal positions. Is this precision justified? Are temperatures in the lakes laterally very stable, is the used device very accurate and are temporal changes insignificant to support this precision?
Figures
Fig. 1
A study-area map such as those shown in Fig. 1 should include coordinates.
Fig. 2
The caption should explain the abbreviations “LV” and “RV”.
Fig. 4
Abundances of ostracods are shown in Fig. 4 and the unit is “values per gram”. Are these values specimens collected alive, carapaces, disarticulated valves, or all together? It is important because some of the measured lake parameters may change seasonally and it can be useful to differentiate here specimens collected alive from empty carapaces and valves.
Tables
Table 2
Genera names should be written in italics.
Format, style
- The authors write about ostracod valves and shells in the text and figures. A consistent term should be used.
- Numerals and numbers are not used in a consistent way. A consistent format should be used to write about records from three lakes (or 3 lakes). In general, numerals are used for such items and numbers smaller than 11 or 13. Consistent use of numerals is important here to avoid confusion of “3 sites and lake 3”, for example.
- Italics are sometimes not used in tables and the text.
- The author refer to figures in two ways, for example “Fig 4” and “Fig. 4”.
- Two salinity classification terminologies were used, for example “oligosaline” and “oliogohaline”. The latter is part of the more commonly used Venice system for the salinity-related characterisation of waters.
- Literature references in the text are a bit inconsistent regarding the use of commas. Which format is needed: “Smith et al. 2000” or “Smith et al., 2000”? Same for papers authored by two persons.
- Units are inconsistently formatted such as “mS cm-1” and “μgL-1” (with and without space).
I tried to spot and mark issues 2 and 3.
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AC2: 'Reply on RC2', Lucy Roberts, 26 Feb 2026
We thank the reviewer for their detailed and positive review. Their main comments are addressed below.
- The issues surrounding soft parts, carapaces, disarticulated valves:
We agree that this point is important. Regular (e.g. monthly) sampling of both ostracods and physico-chemical variables would be the ideal strategy for determining controls on ostracod assemblages, but this is generally unfeasible in remote Arctic lakes. Our approach represents a compromise that is used in most such studies in remote regions. In these lakes it is not unreasonable to assume that all the specimens (living or dead) obtained from surface sediment samples are representative of the time-averaged "present day" living fauna. The reviewer’s comments can be addressed in a revised document by: 1) adding symbols to Figure 3 to highlight which species were collected with soft parts in which lakes; 2) updating figure captions to clarify when abundances are based on specimens collected alive, from empty carapaces and valves, or include all individuals collected; and 3) the addition of text in the discussion to highlight the assumptions made about sampling, including spatial and temporal variability, for ostracods and for physico-chemical data measurement. The count data (differentiated as collected alive, as carapaces, as valves) are also available in the supplementary information.
- The abstract:
Some of these details can been added to the abstract. Some details were not provided in an attempt to keep the abstract concise, but these comments can be added whilst still keeping the abstract short.
- The study area:
The possibility of obtaining historical data from the Kangerlussuaq Airport weather station and the PROMICE weather stations can be looked into when revising the manuscript. A sentence on the local geology can also easily be added.
- Field methods:
The methods to collect ostracods using the hand net can be clarified in the text. When sampling within submerged macrophytes, there was exposed lakebed. So even when sampling where there were submerged macrophytes, a sample of the surface sediment was always retrieved in the net.
- Results, figures, tables and formatting:
These comments are generally relating to typos and inconstancies in style, which can be easily addressed in a revised manuscript. We thank the reviewer for carefully identifying some of these inconsistencies.
Citation: https://doi.org/10.5194/egusphere-2025-6147-AC2
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Preliminary remark. This reviewer is not competent for the review of the statistical analysis in the manuscript.
In general: this is an excellent manuscript. The authors are to be congratulated for their extensive and important work on the non-marine ostracods of Greenland. The text has been carefully written. The figures are of excellent quality. The references are up to date. I agree with the identifications of the species recorded.
I have only a few comments and suggestions for improvement. I recommend publishing the ms after a minor revision.
Here are my comments:
a. References. The DOIs are given for 2 of them. I suggest adding them for all the references where available.
Claude Meisch