After the paper: evidence given and courage gained.

For science, our conclusions are helping macroalgae to be recognized as huge contributors of oceanic carbon sequestration. For me, this article added a fancy journal to my list of publications and enhanced my scientific career.

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     Blue carbon refers to the global carbon stock accumulated on the ocean and in coastal ecosystems, both in the living form and within marine sediments. Through photosynthesis, marine primary producers convert carbon dioxide into living biomass that is further transferred through the food chain. Organic carbon from dead organisms can be delivered to marine sediments in coastal vegetated habitats or to the deep sea, and be sequestered there for long time scales.

     Similar to terrestrial forest, blue carbon is recognized as an incredible carbon sink and its protection is a key strategy to capture atmospheric carbon dioxide and mitigate the climate crisis. Nevertheless, not all blue carbon elements are equally recognized as important carbon sinks. This is the case of macroalgae that, contrary to seagrass, mangroves and saltmarshes, do not build sediments from organic carbon that can be measured. However, macroalgae are impressive primary producers that cannot be neglected from the blue carbon budget.

     Turtles and whales are tracked across the ocean with satellite tags attached to their body – not a practical method to track a fragment of seaweed. 

     Macroalgae do not have a proper root system to anchor in the substrate and to trap organic matter within the sediment. Therefore, macroalgae are ‘moving habitats’ adrift from the action of the wave. Before our publication, it was hypothesized that macroalgal biomass is exported from the coast to other habitats where the carbon can be sequestered in marine sediments. However, tracking macroalgal export remained a challenge. 

     Here comes the topic of my doctoral thesis. Speaking as a scientist, the project focused on the identification of marine plants in coastal vegetated sediments. Speaking in plain terms, I had to identify how much detritus from heavily degraded marine plants were trapped in the detritus of other heavily degraded organisms. The approach to be used was environmental DNA (eDNA). 

  Environmental DNA is the DNA shed by any organism in their surroundings. Using the eDNA approach, one can recover the organism’s DNA from the environment (such as from this sand sample).

    Following this idea, the fate of macroalgae could be tracked by using eDNA. The challenge was how to obtain environmental samples ranging from the coast to the open ocean, and from the surface to the bottom of the sea. Such sampling would require a global expedition. Luckily for us, several of such expeditions already exist and their metagenomic data are available online.

     To demonstrate the important contribution of macroalgae to oceanic carbon sequestration, the job required identification of macroalgal genes from hundreds of metagenomes. Once identifying those genes and their abundance, we observed a ubiquitous presence of macroalgae from the coast to the open ocean, and decreasing abundance of genes with increments in depth. This was quantitative evidence to prove the hypothesis that huge amounts of macroalgal biomass are exported from coastal habitats, making macroalgae important stocks in oceanic carbon pools.

     The article was published in Nature Geoscience and it seems I got beginners luck. This was my first publication submitted to a fancy journal and the overall process made me feel that publishing here was an easy task. The article was considered for review within days, and the peer reviews were positive. My advisor was very surprised after each editorial email received.

Macroalgae may be the best strategy to cut cattle enteric methane emissions. 

     Macroalgae are not only amazing because of the carbon they hold. Macroalgae play several ecological roles, and also can be harvested for economic purposes. Before the publication of the article, macroalgae have become trending and new natural solutions for climate change have been proposed. One of such solutions – and the focus of my postdoctoral research, is the use of Asparagopsis macroalgae to reduce ruminant enteric methane. 

     For science, our conclusions are already allowing macroalgae to be recognized as huge contributors of oceanic carbon sequestration. For me, this article added a fancy journal to my list of publications and definitively enhanced my scientific career. Thanks to my beginners’ luck, I feel the courage to attempt publication of my future articles in similar journals. I may be rejected this time. Or maybe the luck continues.

A. Ortega

Biologist, KAUST

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