This study constructed a model to trace the bioaccumulation of MeHg within the Mediterranean Sea food web in the Bay of Villefranche. The model initially enabled assessing the levels of iHg and MeHg accumulating in LMA sponges. The model was also used to assess the differences in MeHg bioaccumulation in fish in a setup with and without sponges to see if sponges influence the MeHg bioaccumulation in fish. Although an advanced model was developed and the design of scenarios was ingenious in this study, the article reads rather obscure. Many paragraphs are suggested to be refined, and the logicality should be simultaneously increased. Major revision is needed and some comments are shown as follows.

(1) Line 85: The sentence “This is proposed in (Amptmeijer et al., 2025b), which is a……” is confused. Please rewrite the sentence.

(2) Section 2.1: A map is needed for the model domain in the main text.

(3) For the subtitles of sections 2.1, 2.2, 2.3, and 2.3.2, dashes are better than semicolons. And capitalize the first letter of “semi-labile” in Section 2.6.

(4) Section 3.4: In my opinion, the observations of Hg and MeHg in the study domain are too few to support the model evaluation. I suggest more observations particularly for various environments and functional groups.

(5) All the figures should be improved due to their rough presentation.

(6) Section 4.2: What’s the underlying mechanisms for low MeHg due to DOM consumption in HMA sponges? I only see the results of model scenarios. However, the mechanistic inference is more meaningful.

(7) For model studies, uncertainty analysis is necessary to explain the credibility of the model results. I recommend the supplement of uncertainty analysis.

The manuscript addresses a significant and persistent anomaly in marine ecotoxicology: the observation that marine sponges, particularly those with high microbial abundance, accumulate high concentrations of inorganic Hg while maintaining unexpectedly low levels of MeHg. The authors employ a coupled 1D hydrodynamic-biogeochemical model to test the hypothesis that trophic dilution via DOM consumption, rather than microbial mediated MeHg demethylation, drives these patterns. Furthermore, the study posits a potentially massive ecosystem service, suggesting that sponge grounds could reduce MeHg bioaccumulation in benthic fish by up to 45%. The overall manuscript is well organized, and a minor revision is needed. My specific comments are as below:

1. Title: MeHg demethylation
2. Abstract: The second sentence is too long. The complex role of sponges and their significance should be more clearly emphasized.
3. Line 6: demethylation of MeHg
4. Line 11-12: This conclusion is overly speculative and requires additional supporting evidence.
5. Lines 17-24: Links between sponges Hg and fish Hg are needed here.
6. Line 36: ?
7. Lines 33-43: This section is overly general and would benefit from greater conciseness.
8. Lines 45-48: In the case of inorganic mercury (iHg), iHg-DOM binding determines the bioavailability of iHg for methylation.
9. Section2:In this section, the role of sponges in Hg cycling and MeHg accumulation in biota should be clearly highlighted. This is important and helps readers understand the significance of this study.
10. Section 1.3: Why DOM consumption can result in low MeHg concentrations?
11. Lines 567-570: Yes, The validation of the model relies on a limited sample sizes (n=4 for HMA and n=6 for LMA sponges). The use of Kolmogorov-Smirnov (KS) tests on such sparse data provides a misleading sense of statistical robustness, as the test lacks the power to reject the null hypothesis, thereby creating a "false positive" agreement between model and observation. The author should strengthen the discussion by explicitly addressing how the limited sample size may influence the validity and generalizability of the findings, rather than simply noting the limitation.