Publications

The global distribution of chromophoric dissolved organic matter (CDOM) in the euphotic layer of the Atlantic, Indian and Pacific oceans (between 35º N and 40º S) was analysed by absorption spectroscopy during the Malaspina 2010 circumnavigation. Absorption coefficients at 254 nm (a254) and 325 nm (a325), indices (a254/a365) and spectral slopes (between 275-295 nm, S275-295) were calculated from the dissolved fraction of the UV absorption spectra to describe the amount and quality of CDOM. Generalized additive models (GAMs) were applied to evaluate the relevance of physical and biogeochemical drivers of the variability of CDOM. Besides the low CDOM values, a first division of our data following the Longhurst's biogeographic classification showed significant differences in CDOM levels among provinces. The lowest values of a254 and a325 were found in the oligotrophic gyres, particularly in the Indian Ocean, and the highest in the upwelling areas, particularly in the Equatorial Pacific. Opposite distributions were obtained for S275-295 and a254/a365, indicative of higher photobleaching in the gyres. Within each province, whereas a254 was constant through the photic layer, a325 increased significantly with depth as a result of the dominance of photobleaching over biological production in the surface layer and the opposite at depth. The Pacific provinces, including the subtropical gyres, showed however significantly higher a325 values, indicative of lower photobleaching/higher biological production. The GAM analysis indicates that a254 and a325 were primarily related to chlorophyll a, exhibiting a significant positive linear response. Apparent oxygen utilization also contributed to explain the distributions of these absorption coefficients, being inversely related to a254 and directly related to a325. These results are consistent with the premise that a254 could be a proxy for the concentration of dissolved organic carbon and a325 for the aromatic by-products of biological degradation. The GAM analysis also shows that a254/a365 and S275-295 exhibited inverse relationships with solar radiation, indicating that the biological production of CDOM counteracts photodegradation as solar radiation increases. In summary, whereas photobleaching dictates the vertical distribution of CDOM, chlorophyll a explains the CDOM differences among the photic layer of the tropical and subtropical ocean provinces visited during the circumnavigation.

Black corals (Hexacorallia: Antipatharia) are a major component of mesophotic and deep marine ecosystems. Due to their preference for light deprived environments, black corals have historically been considered azooxanthellate, yet recent works have found them in association with dinoflagellates of the family Symbiodiniaceae down to 396 m depth. While corals and Symbiodiniaceae generally establish a symbiotic relationship in shallow water environments, the implications of this association is less well understood at deeper depths, where low light penetration cannot sustain efficient photosynthetic activity for the algae. However, Symbiodinaceae are not obligate autotrophs, and their capacity for heterotrophic feeding categorizes them as mixotrophs. In this study, we investigated the presence and diversity of Symbiodiniaceae associated with the deep-sea black coral Bathypathes thermophila (Antipatharia: Schizopathidae), collected from 204 to 655 m depth in the Saudi Arabian Red Sea. Using high-throughput sequencing of the ITS2 region, we report (1) the deepest record to date of Symbiodiniaceae associated with an anthozoan from 655 m, and (2) the first Red Sea record of Antipatharia in association with Symbiodiniaceae. Our analyses revealed that 14 out of 27 colonies of B. thermophila were associated with Symbiodiniaceae of the genera Cladocopium and Durusdinium . We unveiled 16 novel ITS2 type profiles, possibly unique to black corals and/or to these depths, along with seven profiles that were already known from shallow-water hard corals. No significant pattern was detected in terms of community diversity in relation to depth or sampling locality. Our study supports the existence of black corals-Symbiodiniaceae association and warrants further research to better understand the evolutionary processes and physiological mechanisms driving this association, specifically in light deprived environments.

Metabolite profiling of marine invertebrates, such as bivalve mollusks, may not only provide insights into the health state of an individual holobiont, but also the pollution levels of their environment Here, we combined 1 H nuclear magnetic responance (NMR) spectroscopy and mass spectrometry (MS)-based metabolomics techniques to investigate the organ-specific metabolomic profiles of Tridacna maxima giant clams. Clams were collected from across-shelf gradient in the Red Sea, from inshore to off-shore. We unequivocally profiled 306 metabolites and observed that the sampling location had minimal effects on metabolite composition. However, we observed significant differences in metabolite profiles among different organs (i.e., gills, mantle organ, and digestive system). Importantly, in addition to endogenous metabolites, we detected the presence of terephthalic acid and isophthalic acid, which likely originate from marine plastic ingestion. Collectively, our study opens opportunities for a deeper understanding of Tridacna maxima physiology through metabolomics, and illustrates the power of invertebrate metabolite profiling for monitoring plastic-related aquatic pollutants.

Seagrasses have been entwined with human culture for millennia, constituting a natural resource that has supported humanity throughout this history. Understanding the societal value of seagrass fosters appreciation of these ecosystems, encouraging conservation and restoration actions to counteract historic and predicted losses. This study overviews the plethora of seagrass use in human history, ranging from spiritual and ceremonial roles, direct and indirect food resources, medicines and raw materials, dating back more than 180 000 years. While many past uses have been abandoned in modern societies, others have persisted or are being rediscovered, and new applications are emerging. As these uses of seagrasses depend on harvesting, we also underscore the need for sustainable practices to (re)generate positive interactions between seagrasses and society. Our review contributes to revalue seagrass societal ecosystem services, highlighting ancient and more recent human and seagrass relationships to incentivize conservation and restoration actions.