Quantifying spatiotemporal variability in zooplankton dynamics in the Gulf of Mexico with a physical–biogeochemical model

Shropshire, Taylor A.; Morey, Steven L.; Chassignet, Eric P.; Bozec, Alexandra; Coles, Victoria J.; Landry, Michael R.; Swalethorp, Rasmus; Zapfe, Glenn; Stukel, Michael R.

doi:https://doi.org/10.5194/bg-17-3385-2020

Articles | Volume 17, issue 13

https://doi.org/10.5194/bg-17-3385-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-17-3385-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 13

Research article

|

05 Jul 2020

Research article |

| 05 Jul 2020

Quantifying spatiotemporal variability in zooplankton dynamics in the Gulf of Mexico with a physical–biogeochemical model

Taylor A. Shropshire, Steven L. Morey, Eric P. Chassignet, Alexandra Bozec, Victoria J. Coles, Michael R. Landry, Rasmus Swalethorp, Glenn Zapfe, and Michael R. Stukel

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Final revised paper (published on 05 Jul 2020)
Supplement to the final revised paper
Preprint (discussion started on 09 Dec 2019)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of “Quantifying spatiotemporal variability in zooplankton dynamics in the Gulf of Mexico with a physical-biogeochemical model” by Shropshire et al.', Anonymous Referee #1, 05 Jan 2020
- AC1: 'Response to referees comments', Taylor Shropshire, 06 Feb 2020
RC2: 'Review of Shropshire et al "Quantifying spatiotemporal variability in zooplankton dynamics in the Gulf of Mexico with a physical-biogeochemical model"', Anonymous Referee #2, 09 Jan 2020
- AC2: 'Response to referees comments', Taylor Shropshire, 06 Feb 2020
RC3: 'Review of Shropshire et al. paper', Anonymous Referee #3, 09 Jan 2020
- AC3: 'Response to referees comments', Taylor Shropshire, 06 Feb 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (10 Feb 2020) by Katja Fennel

AR by Taylor Shropshire on behalf of the Authors (17 Mar 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (19 Mar 2020) by Katja Fennel

RR by Anonymous Referee #3 (30 Mar 2020)

RR by Anonymous Referee #1 (04 Apr 2020)

Suggestions for revision or reasons for rejection

Review of revised manuscript “Quantifying spatiotemporal variability in zooplankton dynamics in the Gulf of Mexico with a physical-biogeochemical model”, by Shropshire et al.

The authors have provided a thorough and thoughtful response to my initial review. The changes they made address all of points I raised, and I recommend that this version be accepted for publication. However, there are three issues (listed below) about which I suggest they consider making a stronger statement in order to maximize the likelihood that their recommendations are followed.

1. Uncertainty in C:Chl ratios. On line 778, they say “Without these observations, it is difficult to gauge mismatches between model and [data]”. It is true that more in situ measurements would enable refinement of this component of the model, but there are two additional aspects that warrant mention.
(a) The range of realistic values of C:Chl is high (e.g. 25-250). Therefore, a poorly modeled C:Chl ratio could result in a large misfit even when the modeled nitrogen/carbon-based ecosystem dynamics was excellent. Thus, modelers could be motivated to change their ecological model in an effort to better fit the Chl, thereby degrading the ecological model and misleading their conclusions. I would argue it is not just “difficult to gauge”, it is critical for us to understand these ratios if we are using Chl for validation, and effort should be made to also collect data on carbon/nitrogen, even if such data is hard to get. We are hampered without them.
b) Quantifying uncertainty can be addressed in the absence of observations simply by conducting sensitivity tests on the components of the C:Chl submodel. The authors should advocate that future studies conduct such tests to examine the effects on the simulated Chl, and whether alteration of the parameterization of that subcomponent alone could explain or introduce a mismatch.

Relatedly: Line 806-810 “Higher phytoplankton biomass would be expected to support higher mesozooplankton grazing rates and secondary production... the surface Chl model-data mismatch may lead to an overestimation of secondary production for this region.”. This illustrates my point above, in that Chl and C-biomass are different and overestimate of Chl doesn’t necessitate there being an overestimate in phytoplankton biomass or associated secondary production. The authors should be good role models and examine whether their modeled phytoplankton biomass (i.e. in carbon ) is high.

2. I had apparently misread their text about vertical diffusivity being constant, not realizing that this situation was restricted to their parameter tuning exercise (Although I do wonder if that had an effect on their resulting parameters, but that is not something to investigate at this point). While they satisfactorily addressed the light attenuation issue, they did not discuss some of the physical factors that make simulating vertical distributions challenging. I suggest they reference some of the problems with accuracy in modelled vertical diffusivities and currents that I mentioned in my original review. Even when the processes may be dominated by plankton physiology, if the vertical transport is incorrect, it will be virtually impossible for the ecosystem model to reproduce observations. Ecosystem moders need to realize this when they are trying to use coupled models to study issues related to vertical profiles, including DCMs.

3. While on Lines 870-873, they now state “Future in situ grazing measurements are needed...that shed light on prey selectivity would be useful for parameterizing PBMs with multiple mesozooplankton functional groups.”. This point cannot be overemphasized, as our ignorance about how to characterize grazing hampers our ability to model zooplankton – rectification of which is a major objective of this work. They could add a couple of sentences to justify this point, by reminding the reader that modeling diet composition and secondary production relies entirely on the modeled prey selectivity formulation. They may also want to expand on this point to say that there exist a wide array of published multiple prey responses that have the potential to predict very different consumption rates. They should advocate for modeling studies that assess the implications of these different formulae to simulating secondary production.

Line 236. Extra parentheses

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ED: Publish subject to minor revisions (review by editor) (13 Apr 2020) by Katja Fennel

AR by Taylor Shropshire on behalf of the Authors (27 Apr 2020) Author's response Manuscript

ED: Publish as is (11 May 2020) by Katja Fennel

AR by Taylor Shropshire on behalf of the Authors (20 May 2020) Manuscript

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Short summary

Zooplankton are the smallest animals in the ocean and important food for fish. Despite their importance, zooplankton have been relatively undersampled. To better understand the zooplankton community in the Gulf of Mexico (GoM), we developed a model to simulate their dynamics. We found that heterotrophic protists are important for supporting mesozooplankton, which are the primary prey of larval fish. The model developed in this study has the potential to improve fisheries management in the GoM.