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1. The Possession of Coccoliths Fails to Deter Microzooplankton Grazers

   https://doi.org/10.3389/fmars.2020.569896  

   Mayers, Kyle M.; Poulton, Alex J.; Bidle, Kay; Thamatrakoln, Kimberlee; Schieler, Brittany; Giering, Sarah L.; Wells, Seona R.; Tarran, Glen A.; Mayor, Dan; Johnson, Matthew; et al (December 2020, Frontiers in Marine Science)

   Phytoplankton play a central role in the regulation of global carbon and nutrient cycles, forming the basis of the marine food webs. A group of biogeochemically important phytoplankton, the coccolithophores, produce calcium carbonate scales that have been hypothesized to deter or reduce grazing by microzooplankton. Here, a meta-analysis of mesocosm-based experiments demonstrates that calcification of the cosmopolitan coccolithophore, Emiliania huxleyi , fails to deter microzooplankton grazing. The median grazing to growth ratio for E. huxleyi (0.56 ± 0.40) was not significantly different among non-calcified nano- or picoeukaryotes (0.71 ± 0.31 and 0.55 ± 0.34, respectively). Additionally, the environmental concentration of E. huxleyi did not drive preferential grazing of non-calcified groups. These results strongly suggest that the possession of coccoliths does not provide E. huxleyi effective protection from microzooplankton grazing. Such indiscriminate consumption has implications for the dissolution and fate of CaCO 3 in the ocean, and the evolution of coccoliths. 

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2. Global Trends in the Distribution of Biogenic Minerals in the Ocean

   https://doi.org/10.1029/2022JC019470  

   Subhas, Adam V.; Pavia, Frank J.; Dong, Sijia; Lam, Phoebe J. (February 2023, Journal of Geophysical Research: Oceans)

   Abstract The cycling of marine particulate matter is critical for sequestering carbon in the deep ocean and in marine sediments. Biogenic minerals such as calcium carbonate (CaCO₃) and opal add density to more buoyant organic material, facilitating particle sinking and export. Here, we compile and analyze a global data set of particulate organic carbon (POC), particulate inorganic carbon (PIC, or CaCO₃), and biogenic silica (bSi, or opal) concentrations collected using large volume pumps (LVPs). We analyze the distribution of all three biogenic phases in the small (1–53 μm) and large (>53 μm) size classes. Over the entire water column 76% of POC exists in the small size fraction. Similarly, the small size class contains 82% of PIC, indicating the importance of small‐sized coccolithophores to the PIC budget of the ocean. In contrast, 50% of bSi exists in the large size fraction, reflecting the larger size of diatoms and radiolarians compared with coccolithophores. We use PIC:POC and bSi:POC ratios in the upper ocean to document a consistent signal of shallow mineral dissolution, likely linked to biologically mediated processes. Sediment trap PIC:POC and bSi:POC are elevated with respect to LVP samples and increase strongly with depth, indicating the concentration of mineral phases and/or a deficit of POC in large sinking particles. We suggest that future sampling campaigns pair LVPs with sediment traps to capture the full particulate field, especially the large aggregates that contribute to mineral‐rich deep ocean fluxes, and may be missed by LVPs. 

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3. Trophic flows to mesozooplankton support the conventional paradigm of pelagic food web structure in ocean ecosystems

   https://doi.org/10.1093/icesjms/fsae131  

   Landry, Michael R; Décima, Moira; Stukel, Michael R; Gutiérrez-Rodríguez, Andrés (September 2024, ICES Journal of Marine Science)

   Andersen, Ken (Ed.)

   Abstract The current conventional paradigm of ocean food web structure inserts one full level or more of microzooplankton heterotrophic consumption, a substantial energy drop, between phytoplankton and mesozooplankton. Using a dataset with contemporaneous measurements of primary production (PP), size-fractioned mesozooplankton biomass, and micro- and mesozooplankton grazing rates from 10 tropical to temperate ocean ecosystems, we examined whether the structural inefficiencies in this paradigm allow sufficient energy transfer to support active metabolism and growth of observed zooplankton standing stocks. Zooplankton carbon requirements (ZCR) were determined from allometric equations that account for ecosystem differences in temperature and size structure. ZCRs were relatively low (∼30% of PP or less) for both oligotrophic systems and bloom biomass accumulation in eutrophic coastal waters. Higher relative ZCRs (>30% PP) were associated with elevated mesozooplankton grazing scenarios (bloom declines, abundant salps), advective subsidies, and open-ocean upwelling systems. Microzooplankton generally dominated as grazers of PP but were equal or secondary to direct herbivory as nutritional support for mesozooplankton in five of eight regional studies. All systems were able to satisfy ZCR within the conventional food-web interpretation, but balanced open-ocean upwelling systems required the most efficient alignments of contributions from microzooplankton grazing, direct herbivory, and carnivory to do so. 

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4. Monitoring Coral Reef Metabolism Under Changing Oceans–Novel Insights From Seawater Stable Carbon Isotopes

   https://doi.org/10.1029/2025JG009416  

   Bolden, Isaiah W; Timmerman, Amanda_H V; Clark, David R; Belanger, Bryce K; Oster, Jessica L; Salas‐Saavedra, Marcos; Niespolo, Elizabeth M (April 2026, Journal of Geophysical Research: Biogeosciences)

   Abstract Mounting environmental stressors are driving Caribbean reefs from coral to sponge and macroalgae dominance, necessitating a need for more nuanced metrics of reef metabolism under trophic transitions. Drawing upon four seasonally replicated field campaigns to Curaçao, we reveal highly variable net ecosystem productivity (−243 ± 69 C m⁻² day⁻¹to 216 ± 36 mmol C m⁻² day⁻¹) and calcification (−143 ± 42 mmol CaCO₃m⁻² day⁻¹to 140 ± 21 mmol CaCO₃m⁻² day⁻¹). We observe periods of intense net ecosystem dissolution that fall significantly below previously reported global averages. We offer two additional metabolic insights by integrating measurements of the stable carbon isotope composition of dissolved inorganic carbon (δ¹³C_DIC). First, Keeling plots of water column DIC and δ¹³C_DICmeasurements suggest that zooplankton grazing may be a significant source of respired carbon to the reef ecosystem, even during periods of net autotrophy. This suggests that heterotrophic feeding by corals or other consumers is a primary energy pathway that may provide the mixotrophic coral community with a stable food source and bolster its resilience to periods of symbiont stress. Second, by isolating photosynthetic fractionation factors, we reveal a potential carbonate chemistry dependence on algal community photosynthetic plasticity. This provides an important fingerprint of how the dominant primary producers physiologically respond to changing ocean conditions, which is essential for forecasting future shifts in the community and its metabolic function. These findings suggest that integrating stable isotopes into reef biogeochemical toolkits offers unprecedented insights into community interactions in a changing ocean. 

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5. Pelagic calcium carbonate production and shallow dissolution in the North Pacific Ocean

   https://doi.org/10.1038/s41467-023-36177-w  

   Ziveri, Patrizia; Gray, William Robert; Anglada-Ortiz, Griselda; Manno, Clara; Grelaud, Michael; Incarbona, Alessandro; Rae, James William; Subhas, Adam V.; Pallacks, Sven; White, Angelicque; et al (December 2023, Nature Communications)

   Abstract Planktonic calcifying organisms play a key role in regulating ocean carbonate chemistry and atmospheric CO 2 . Surprisingly, references to the absolute and relative contribution of these organisms to calcium carbonate production are lacking. Here we report quantification of pelagic calcium carbonate production in the North Pacific, providing new insights on the contribution of the three main planktonic calcifying groups. Our results show that coccolithophores dominate the living calcium carbonate (CaCO 3 ) standing stock, with coccolithophore calcite comprising ~90% of total CaCO 3 production, and pteropods and foraminifera playing a secondary role. We show that pelagic CaCO 3 production is higher than the sinking flux of CaCO 3 at 150 and 200 m at ocean stations ALOHA and PAPA, implying that a large portion of pelagic calcium carbonate is remineralised within the photic zone; this extensive shallow dissolution explains the apparent discrepancy between previous estimates of CaCO 3 production derived from satellite observations/biogeochemical modeling versus estimates from shallow sediment traps. We suggest future changes in the CaCO 3 cycle and its impact on atmospheric CO 2 will largely depend on how the poorly-understood processes that determine whether CaCO 3 is remineralised in the photic zone or exported to depth respond to anthropogenic warming and acidification. 

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