The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve

Young, Craig S.; Gobler, Christopher J.

doi:https://doi.org/10.5194/bg-15-6167-2018

Articles | Volume 15, issue 20

https://doi.org/10.5194/bg-15-6167-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-15-6167-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 15, issue 20

Research article

|

23 Oct 2018

Research article |

| 23 Oct 2018

The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve

Craig S. Young and Christopher J. Gobler

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Final revised paper (published on 23 Oct 2018)
Supplement to the final revised paper
Preprint (discussion started on 29 Mar 2018)
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: 'Comment on “The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve” by Young and Gobler', Anonymous Referee #1, 15 May 2018
- AC1: 'Response to Reviewer #1', Christopher Gobler, 13 Jun 2018
RC2: 'Review bg-2018-115 Young & Gobler', Anonymous Referee #2, 21 May 2018
- AC2: 'Response to Reviewer #2', Christopher Gobler, 13 Jun 2018

Peer-review completion

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

ED: Reconsider after major revisions (14 Jun 2018) by Clare Woulds

AR by Christopher Gobler on behalf of the Authors (15 Jul 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (07 Aug 2018) by Clare Woulds

RR by Anonymous Referee #1 (09 Aug 2018)

Suggestions for revision or reasons for rejection

Response to revised manuscript bg-2018-115

The authors have addressed most of my concerns, but it seems the main issue is still not resolved. The data do not show that the increase in growth of bivalves in treatments with Ulva is due to changes in saturation state.
The authors provided new regression analyses showing that growth is correlated to saturation state. The figure is not shown, but after reproducing the data, it appears these regressions pool all the data within an experiment, without addressing the specific effect of Ulva. This analysis does not contribute anything new and does not address my original comment, which was: “…a statistically significant difference in a carbonate chemistry parameter across treatments does not mean that it is biologically relevant. The authors do not discuss if the magnitude of change in growth is realistic for a 0.04 change in saturation state.”

To clarify my point, I extracted data from all their figures and plotted shell weight growth (mg/day) by aragonite saturation state (example for Fig. 1 attached, Mercenaria). The CO2/Ulva treatment only increased saturation state by a very small amount (0.03). Assuming a linear correlation between growth and saturation state (as identified by the authors), in the absence of Ulva, one would need a saturation state >1.5 to achieve the same increase in shell weight growth that was observed in the CO2/Ulva treatment (red arrows).
This same pattern is observed for the data in Fig. 2 (Mercenaria), Fig. 5, and Fig. 6 (Agropectin). This pattern does not hold for Fig. 3 and 4 (Crassostrea). The fact that growth increased in Fig. 7 (Mytilus) in Ulva treatments, despite the unexpected effect of saturation state (i.e., pCO2 effect), again suggests that Ulva provides a positive effect on growth, but this affect cannot be explained by changes in aragonite saturation state.

My conclusion from this data is that the presence of Ulva in a closed experimental system provided an unknown positive affect on shell growth for 3 of the 4 tested species. The change is growth is much greater than what can be expected from the observed Ulva-induced changes in aragonite saturation state alone.
The emphasis on saturation state throughout the Results and Discussion ignores this aspect of the data, leading to the incorrect conclusion that the increased saturation state by Ulva caused an increase in shell growth. Saturation state alone does not explain the observed biological response. Therefore, I suggested that the authors provide alternative hypotheses.

Referee Report: PDF

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RR by Anonymous Referee #3 (17 Aug 2018)

ED: Publish subject to minor revisions (review by editor) (07 Sep 2018) by Clare Woulds

AR by Christopher Gobler on behalf of the Authors (17 Sep 2018) Author's response Manuscript

ED: Publish as is (09 Oct 2018) by Clare Woulds

AR by Christopher Gobler on behalf of the Authors (10 Oct 2018) Author's response Manuscript

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Short summary

Photosynthetic activity and/or nitrate assimilation by the macroalgae Ulva buffered carbonate chemistry and yielded enhanced growth of bivalves by mitigating the harmful effects of elevated CO₂ levels. This benefit was not limited to acidified conditions, as evidenced by increased bivalve growth in the presence of Ulva within ambient CO₂ treatments. The ability of macroalgae to buffer carbonate chemistry may be increasingly important for calcifying organisms vulnerable to ocean acidification.