Is the Dilution Technique Underestimating the Picophytoplankton Growth Measurements?
Round 1
Reviewer 1 Report
This article meets the requirements of the journal. It is of scientific interest and can be published without correction.
Reviewer 2 Report
This is an interesting paper addressing the dilution technique after a 24 h incubation period, a common technique used on marine and freshwater systems to measure phytoplankton growth and grazing mortality rates.
The authors prove that this technique underestimates the true phytoplankton growth and grazing mortality rates of picophytoplankton. Improvement of the techniques used are always welcome, and so the paper is novel and very interesting.
The paper is also simple and straightforward, clearly presented, with clear results and conclusions.
Although the paper is rather limited in the results presented. Because only one experiment was performed, during one sampling period, I believe that the trend found must be further explored in other experiments, and in other phytoplankton groups.
This should be a short paper, presenting very preliminary results, but it may be published with minor revision.
Specific comments are made below to improve the document:
The title could be more appealing. Maybe: Is the dilution technique underestimating the picophytoplankton growth measurements?
The abstract needs revision as the sentences are not in sequence with each other. Also, prior to the results a reference to the methods used is required, so the reader can understand the results.
- Material and Methods
Line 65. Explain further how you sampled Synechococcus and picoeucaryotes separately.
Did the authors identify which groups of organisms were present in the picoeucaryotes group: green algae, haptophytes, stramenopiles, dinoflagellates?
Line 82: dis the author measure light intensity? State water temperature.
Equations 4 and 5 – the 4/3 is awkward and needs to be presented better.
Explain how the authors get to equations 4 and 5.
Figure 1 – caption – the 3 h interval measurements, for field (natural) samples, is missing (squares).
Table 1 – authors should refer which results are statistically different.
Author Response
Please see the attached file.
Author Response File: 
Author Response.doc
Reviewer 3 Report
Ho et al. have performed a diel variation study where they show that by performing a dilution technique for 24-hour period one can greatly underestimate the growth of picophytoplankton. They suggest that estimates based on 24h sampling may not actually reflect the true growth of these population. This study is interesting and the experimental study is well performed. The authors have taken well into account of mortality processes including viral lysis. Such study could be of interest to aquatic ecologists. Overall the manuscript is well written and I don’t have any concern regarding the use of English language. I have some concerns regarding the text in the manuscript which I would like the authors to clarify or modify.
Specific comments
In the abstract the authors should indicate the possible underestimation (percentahe) that one can make in performing such studies.
L23: Size of picoeukaryotes can be upto 3µm? Size can depend upon the species present in the given study area.
L62: 12 & 13 June??
L82: provide in situ temperature and irradiance levels in brackets
L127: avoid providing references in the results
Fig.1: were the experiment done in replicates? Provide SD or SE for the data in the figure. Modify X-axis for better understanding. 19 pm should be either 7pm or 19hrs
Change filled area to “grey area” daytime and nighttime can be changed to day and night respectively
Table 1: provide SD or SE. Since it is an experiment, replicates are important to validate your results
nd? Not done or not detected
Author Response
Please see the attached file.
Author Response File: Author Response.docx
