Global-scale surveys of plankton communities using “omics” techniques have revolutionized our understanding of the ocean. Lipidomics has demonstrated the potential to add further essential insights on ocean ecosystem function but has yet to be applied on a global scale. We analyzed 930 lipid samples across the global ocean using a uniform high-resolution accurate-mass mass spectrometry analytical workflow, revealing previously unknown characteristics of ocean planktonic lipidomes. Focusing on 10 molecularly diverse glycerolipid classes, we identified 1151 distinct lipid species, finding that fatty acid unsaturation (i.e., number of carbon-carbon double bonds) is fundamentally constrained by temperature. We predict substantial declines in the essential fatty acid eicosapentaenoic acid over the next century, which are likely to have serious deleterious effects on economically critical fisheries.

Approximately 30% of the ocean's surface is subject to phytoplankton iron (Fe) limitation, especially in the Equatorial Pacific and Southern Oceans where upwelling provides a large flux of nitrate (NO 3 − ) and other nutrients (Moore et al., 2001(Moore et al., , 2013. Elsewhere, stratification of the upper ocean leads to depletion of NO 3 − , ammonia, and other bioavailable forms of nitrogen. In stratified oligotrophic gyres, shallow mixed layers also act to concentrate Fe deposited at the ocean's surface by atmospheric sources (Boyle et al., 2005;Sedwick et al., 2005). The large flux of Fe relative to NO 3 − in these ecosystems results in nitrogen limitation of photosynthesis and selects for phytoplankton like the cyanobacterium Prochlorococcus (Ward et al., 2013;Wu et al., 2000), whose small size allows them to outcompete other phytoplankton for recycled nitrogen species found at nanomolar concentrations (Morel et al., 1991).However, the same stratification that leads to Fe-rich conditions in the surface ocean can also impede Fe supply to the subsurface. Shallow mixed layers ensure that Fe derived from dust deposition does not reach the entirety of the euphotic zone, which can extend below 100 m in subtropical gyres. Stratification also limits the supply of regenerated Fe from below the euphotic zone. Indeed, a common feature of dFe profiles within subtropical gyres is a concentration minimum between 75 and 150 m (Bruland et al., 1994;Fitzsimmons et al., 2015;Sedwick et al., 2005). This subsurface dFe minimum often coincides with the deep chlorophyll maximum (DCM), a unique habitat where low irradiance drives phytoplankton photo-acclimation, increasing chlorophyll per cell to improve photosynthetic light capture (Letelier et al., 2004). Theoretical arguments suggest the increases in chlorophyll per cell should be matched by an equivalent increase in the number of Fe-bearing photosynthetic reaction

Microbial relationships are critical to coral health, and changes in microbiomes are often exhibited following environmental disturbance. However, the dynamics of coral-microbial composition and external factors that govern coral microbiome assembly and response to disturbance remain largely uncharacterized. Here, we investigated how antibiotic-induced disturbance affects the coral mucus microbiota in the facultatively symbiotic temperate coral Astrangia poculata, which occurs naturally with high (symbiotic) or low (aposymbiotic) densities of the endosymbiotic dinoflagellate Breviolum psygmophilum. We also explored how differences in the mucus microbiome of natural and disturbed A. poculata colonies affected levels of extracellular superoxide, a reactive oxygen species thought to have both beneficial and detrimental effects on coral health. Using a bacterial and archaeal small-subunit (SSU) rRNA gene sequencing approach, we found that antibiotic exposure significantly altered the composition of the mucus microbiota but that it did not influence superoxide levels, suggesting that superoxide production in A. poculata is not influenced by the mucus microbiota. In antibiotic-treated A. poculata exposed to ambient seawater, mucus microbiota recovered to its initial state within 2 weeks following exposure, and six bacterial taxa played a prominent role in this reassembly. Microbial composition among symbiotic colonies was more similar throughout the 2-week recovery period than that among aposymbiotic colonies, whose microbiota exhibited significantly more interindividual variability after antibiotic treatment and during recovery. This work suggests that the A. poculata mucus microbiome can rapidly reestablish itself and that the presence of B. psygmophilum, perhaps by supplying nutrients, photosynthate, or other signaling molecules, exerts influence on this process. IMPORTANCE Corals are animals whose health is often maintained by symbiotic microalgae and other microorganisms, yet they are highly susceptible to environmental-related disturbances. Here, we used a known disruptor, antibiotics, to understand how the coral mucus microbial community reassembles itself following disturbance. We show that the Astrangia poculata microbiome can recover from this disturbance and that individuals with algal symbionts reestablish their microbiomes in a more consistent manner compared to corals lacking symbionts. This work is important because it suggests that this coral may be able to recover its mucus microbiome following disturbance, it identifies specific microbes that may be important to reassembly, and it demonstrates that algal symbionts may play a previously undocumented role in microbial recovery and resilience to environmental change.

Approximately 30% of the ocean's surface is subject to phytoplankton iron (Fe) limitation, especially in the Equatorial Pacific and Southern Oceans where upwelling provides a large flux of nitrate (NO 3 − ) and other nutrients (Moore et al., 2001(Moore et al., , 2013. Elsewhere, stratification of the upper ocean leads to depletion of NO 3 − , ammonia, and other bioavailable forms of nitrogen. In stratified oligotrophic gyres, shallow mixed layers also act to concentrate Fe deposited at the ocean's surface by atmospheric sources (Boyle et al., 2005;Sedwick et al., 2005). The large flux of Fe relative to NO 3 − in these ecosystems results in nitrogen limitation of photosynthesis and selects for phytoplankton like the cyanobacterium Prochlorococcus (Ward et al., 2013;Wu et al., 2000), whose small size allows them to outcompete other phytoplankton for recycled nitrogen species found at nanomolar concentrations (Morel et al., 1991).However, the same stratification that leads to Fe-rich conditions in the surface ocean can also impede Fe supply to the subsurface. Shallow mixed layers ensure that Fe derived from dust deposition does not reach the entirety of the euphotic zone, which can extend below 100 m in subtropical gyres. Stratification also limits the supply of regenerated Fe from below the euphotic zone. Indeed, a common feature of dFe profiles within subtropical gyres is a concentration minimum between 75 and 150 m (Bruland et al., 1994;Fitzsimmons et al., 2015;Sedwick et al., 2005). This subsurface dFe minimum often coincides with the deep chlorophyll maximum (DCM), a unique habitat where low irradiance drives phytoplankton photo-acclimation, increasing chlorophyll per cell to improve photosynthetic light capture (Letelier et al., 2004). Theoretical arguments suggest the increases in chlorophyll per cell should be matched by an equivalent increase in the number of Fe-bearing photosynthetic reaction