High Prevalence of Pea Crab in a Mussel Population (Mytilus edulis) of the Atlantic French Coast
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis study undertakes a survey of the prevalence of pea crabs in mussel populations on the Atlantic Coast of France.
The purpose of the study is not entirely clear from the abstract, although there is a concluding comment that mussel populations on this coast have been experiencing mass mortality events - is this the motivation for the study perhaps? The motivation for the study is much more clearly explained in the introduction, perhaps this could be worked into the abstract also.
Lines 81-85 says "Finally, we evaluated whether this parasite could contribute to the recurrent mussel mortality and population decline events reported in France over the past decade by comparing shell length and gonadal histology between infected and non-infected mussels as proxies to determine if growth and reproductive development are impaired." Frankly, I do not believe that examining the prevalence of pea crabs in samples from 9 populations at one time point would have any capacity whatsoever to shed light on this wider population process over the last decade. I would strongly suggest the authors revise the loftiness of their stated research aims.
Line 97 - how were mussels "randomly selected" - was a quadrat placed on the shore haphazardly and all mussels within it removed? People sampling mussels by selection tend to go for the largest mussels or more emergent mussels, so if this is the case it should be clearly stated. The issue here is that the size of mussels with and without pea crabs is compared and so if the sampling was not random it could result in bias.
Line 102 - was the sex and development stage of the crabs determined? And if mature females, they almost certainly would be carrying eggs - was this recorded?
Line 108 - was the sex of the mussels determined?
Line 140 - anyone who is familiar with mussel biology will know that size of mussels is definitely NOT a proxy for growth.
Line 140 - it is not clear if this analysis is being done for all 9 populations simultaneously or separately for each.
Line 142 - the assumptions outlined are not valid, because male pea crabs move around among mussels - I am surprised sex of the pea crabs was not recorded.
Line 147-148 - why a Monte Carlo simulation when this analyses should be done on the raw data with a goodness of fit test. A Monte Carlo simulation is inappropriate analyses for considering simple frequencies of occurance.
Lines 155-156 - give the actual numbers of crabs please so we know what the actual sample size is.
Lines 162-164 - what was the sex of the 48 mussels that were sampled? And how many pea crabs were in each sex? Was the sex of the pea crab related to the sex of the mussel?
Lines 167-168 - why were only 17 out of the 30 or more crabs genetically identified? How does this give you confidence about the identity of all the crabs?
Figure 1 - seems to have nothing to do with the research about pea crabs, and given only one of the presented sites is investigated in this study I am not sure why it is in the manuscript?
Lines 175-180 - what were the mean mussel shell lengths? Figure 3 - why is this a box plot when the data are parametric?
Lines 214-215 - how many female mussels were examined? Same with the males in the text that follows.
Lines 294 - 302 - is conjecture in the absence of high quality scientific observations which should have been undertaken in a study of this nature. Were the samples kept and can they be examined now to sort this important data out?
The discussion is lengthy and tends to go well beyond the scope of the data presented which is minimal.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsManuscript Number: Ecologies-3757578-peer-review-v1
Title: “High prevalence of pea crab in a mussel population (Mytilus edulis) of the Atlantic French coast”.
Authors: Sara Cobo-Arroyo, Sofia Blanco, Angel P. Diz, Paloma Moran
General Comments:
The present manuscript (Ecologies-3757578) reports on the incidence of the pea crab Pinnotheres pisum in a French mussel (Mytilus edulis) population to evaluate whether this parasite could contribute to population decline events and several episodes of mass mortality reported over the past decade. In my opinion the manuscript is well-written and supported by a thorough bibliographic search, but it could be more focused on the target guest - P. pisum. An adequate statistical analysis has been implemented. Some Results could be better explored. In my opinion Discussion section contains a proper interpretation of the Results.
Despite the relevance of this study, the main concerns I find in this manuscript stem from the fact that it covered only one season (Winter) and a very small number of individuals sampled (432 mussels – 48 mussels per site!), which I believe does not represent a sufficiently representative sample of each location. Therefore, it seems very ambitious to discuss the prevalence of Pinnotheres pisum based only on 48 individuals collected at each sampling site.
I believe that the manuscript contains valuable data for researchers involved in aquatic ecology, but as it stands does not meet the standards required for publication in an international journal such as Ecologies, reason why I think it should be rejected.
However, I have listed some suggestions and specific comments below, which might help the authors to make some changes/corrections and improve the overall quality of the manuscript. (I have not annotated any comments in the MS file).
Suggestions / Specific Comments:
Abstract
Line10: “… marine invertebrates, with a particularly notable …” by, for example “… marine invertebrates, in a particularly notable …”.
Line 12: “… can compromise aquaculture production …”. Are collection sites close to aquaculture facilities? Is the cultivated species the same as the wild species present in the rocky intertidal?
Keywords
Line 25: The authors should better explore these words. Some are already in the Title: “pea crabs”, “Mytilus”, “prevalence”.
Introduction
Line30: “… including polychaetes [1] and echinoderms [2] …”. But see de Gier and Becker for a review on the updated list of symbiont-host associations.
Lines 44-45: please replace: “… and Pinnotheres bicristatus Garcia Raso & Cuesta, 2019.…” by “… and Pinnotheres bicristatus Garcia Raso & Cuesta, 2019 in Cuesta, García Raso, Abelló, Marco-Herrero, Silva & Drake, 2019…”.
Lines 78, 81, 136, 138, 211, 379, 381: Avoid the use of “we”.
Material and methods
Lines 132-133: Replace “Diz & Skibinski (2024)” by “Diz and Skibinski (2024)”.
Results
What is the size range of mussels at each sampling site? What is their degree of maturity? Were they all mature? This could be summarized in a table.
Before carrying out genetics, pea crabs should have been analyzed morphologically and the hard and soft females and, within these, the ovate and non-ovate females should have been counted.
Line 163: “… (Fisher’s exact test, p = 0.618) …” italicize “p”, and throughout the text
Line 164: “… showing similar proportions”. Statistically similar proportions? (57.1% for females, and 70.3% for males).
Line 178: “… (Shapiro-Wilk test, p=0.765, p=0.531, p=0.606) …” by “… (Shapiro-Wilk test, p = 0.765, p = 0.531, p = 0.606) …”, and throughout the text, to be consistent.
Discussion
Lines 277 and 278: In my opinion, prevalence (despite being a different pea crab) only be compared with M. galloprovincialis from Bay of Cadiz (30.5%) (N ≈ 500 inds.), since in this study by Perez-Miguel et al., the other prevalences were due to organisms captured in more confined locations (muddy sandy beaches, estuaries or river mouths). On the other hand, in the work of Cuesta et al., despite the high prevalence, the authors are not studying intertidal populations, but subtidal ones (different pea crab and different host).
See also other bibliographic papers, for example:
- Haines et al. 1994. The pea crab, Pinnotheres pisum (Linnaeus, 1767), and its association with the common mussel, Mytilus edulis (Linnaeus, 1758), in the Solent (UK). Journal of Shellfish
Research 13,5–10.
- Lynch et al. 2014. The health status of mussels, Mytilus spp., in Ireland and Wales with the molecular identification of a previously undescribed haplosporidian. J. Invertebr. Pathol. 118, 59–65.
- Becker and Türkay 2017. Host specificity and feeding in European pea crabs (Brachyura, Pinnotheridae). Crustaceana 90, 819–844.
Lines 300-301: “When the bivalve hosted two crabs, one was large and one was smaller and darker in color, probably a male”. Hard females and males are morphologically different, so this sentence needs to be improved.
Lines 312-313: “… since a series of biological and environmental factors could be converging that have favored the infestation only in this population studied”. If the next paragraph attempts to explain these biological and environmental factors, do not make it a paragraph.
Line 339-341: “Furthermore, prevalence increases in intertidal zones where bivalves remain submerged for longer periods, increasing their exposure to parasitic larvae present in the water column”. (REFS!!!)
Line 356: “… pinnoterids…” by “… pinnotherids…”. Also in line 364.
References
Some inconsistencies: Please revise: italicize species names. The specific epithet is not capitalized. “sp.” is not capitalized or italicized.
Line 428: Please add the required information: 190(3), 359-366.
Line 438: Add page numbers.
Line 446: Add space before “Pinnotheres maculatus”.
Line 457: Backwater Clam Mmeretrix Casta. Please correct “Meretrix”.
Line 459: “1967” in bold.
Line 482: Replace “;” by “.”.
Line 502: “2020” in bold.
Line 506: Correct the spacing.
Line 514: Do not italicize “and”.
Line 528: Insert date and all the required information.
Line 540: Insert page numbers.
Line 551: Date in bold.
Figures captions
Do not italicize Figures and Tables captions (only the species names).
Figure 1: Please correct “Kerhihan”, “Arachon”,
Figures
Figure 3: use de same decimal places. Use the same font size as in Figure 2.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsReview for the paper submitted to “Ecologies”.
Title: High prevalence of pea crab in a mussel population (Mytilus edulis) of the Atlantic French coast
Authors: Sara Cobo-Arroyo, Sofia Blanco, Angel P. Diz, Paloma Moran
The authors focused on the interactions between pea crabs and bivalve mollusks. Their study examined mussel populations along the French Atlantic coast, revealing that pea crabs were found inhabiting the mantle cavity of Mytilus edulis, particularly in La Tranche-sur-Mer. The authors showed that these infestations were notably common, with a significant portion of mussels hosting one or more crabs. The authors found no significant differences in infestation rates between male and female bivalves. Genetic analysis confirmed the identification of the crab species as Pinnotheres pisum. Although the infestation levels were high, the authors reported no immediate negative effects on shell length or reproductive development in the infected mussels, suggesting that the relationship may not always lead to evident detrimental outcomes in the host.
The implications of the authors' work are as follows: First, understanding this parasitic relationship is crucial for aquaculture since high infestation rates could potentially impact mussel production levels, despite showing no immediate physical impairment. Second, the absence of observable growth or reproductive issues raises questions about the long-term physiological impacts of infestations, which may manifest in subtler ways over time.
Suggestions for improving the paper:
Introduction.
L 37. The authors should mention what pathogens were detected in pea crabs. Are these pathogens dangerous for consumers?
L 40. The authors should clarify specific instances of trade restrictions or market losses caused by pea crab infestations.
L 47. The authors should include the prevalence rate ranges observed across studied regions.
Materials and Methods.
L 89. The sampling method should be described in detail.
L 91-93. What was the period between sampling and placing the mussels into individual tanks? The authors should report the rearing conditions in the tanks and the equipment used to monitor water quality parameters.
Table 1. The authors should include the sampling depth.
L 143. The authors should clarify these assumptions more clearly. In particular, they should explain the methods used to confirm the similarity in age or cohort among the sampled mussels.
Results.
L 163-164. The authors should report the sex ratio of hosts in each population.
L 175. It would be useful to include a graph showing size-frequency distributions of mussels from the studied locations.
Figure 1 should be supplemented with a larger-scale map and a coordinate grid.
The authors should revise the data presentation on page 7: there is overlap between the caption for Figure 3 and the body of Figure 4.
Discussion.
L 268. The authors should report relevant environmental or ecological details about La Tranche-sur-Mer, such as water temperature, salinity, tidal exposure, or bivalve density, that might explain why this population was infested while no crabs were found at the other eight sites.
L 347. The authors' statement that "the prevalence increases in intertidal zones where bivalves remain submerged for longer periods" requires clarification. They should explain how tidal patterns at La Tranche-sur-Mer differ from those at the other eight sampled populations.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
