Advances in Our Understanding of Pelagic\u2013Benthic Coupling

We synthesized our present understanding of pelagic\u2013benthic (P\u2013B) interactions in the northern Adriatic Sea (NAS) and Chesapeake Bay (CB) in a comparative analysis that builds on a prior comparison. We focus on primary production (PP) in the water column and benthos, the sedimentation and horizontal transport of particlulate organic matter (POM), and biogeochemical responses of the benthic community to sedimentation. Phytoplankton net PP (NPP) remains higher in CB (five times that in NAS) and rates of benthic respiration appear greater in CB (three times that in NAS). A lower fraction of phytoplankton NPP plus riverine inputs of POM is deposited to sediments in the NAS (23%) compared to CB (83%). A high percentage of organic matter inputs are respired by plankton and exported in the NAS and CB, and benthic communities respired a similar percentage of POM (86% in the NAS, 92% in CB). Net release of regenerated N from the benthos (0.2\u20130.3 mol N m 122 year 121) is also similar in both systems. At 0.53 mol N m 122 year 121, rates of benthic denitrification are higher in CB than in the NAS (0.3 mol N m 122 year 121), and the NAS appears to bury similar fractions of deposited N and P (N: 23% in NAS, 19% in CB; P: 50% in NAS, 45% in CB). To address the impacts of future climate\u2010driven warming and acceleration of the water cycle, we recommend a return to sustained monitoring combined with numerical simulations to allow improved understanding and predictions of changes in P\u2013B interactions

Diurnal transcript profiling of the diatom Seminavis robusta

Coastal regions contribute an estimated 20% of annual gross primary production in the oceans, despite occupying only 0.03% of their surface area. Diatoms frequently dominate coastal sediments, where they experience large variations in light regime resulting from the interplay of diurnal and tidal cycles. Here, we report on an extensive diurnal transcript profiling experiment of the motile benthic diatom Seminavis robusta. Nearly 90% (23 328) of expressed protein-coding genes and 66.9% (1124) of expressed long intergenic non-coding RNAs showed significant expression oscillations and are predominantly phasing at night with a periodicity of 24 h. Phylostratigraphic analysis found that rhythmic genes are enriched in highly conserved genes, while diatom-specific genes are predominantly associated with midnight expression. Integration of genetic and physiological cell cycle markers with silica depletion data revealed potential new silica cell wall-associated gene families specific to diatoms. Additionally, we observed 1752 genes with a remarkable semidiurnal (12-h) periodicity, while the expansion of putative circadian transcription factors may reflect adaptations to cope with highly unpredictable external conditions. Taken together, our results provide new insights into the adaptations of diatoms to the benthic environment and serve as a valuable resource for the study of diurnal regulation in photosynthetic eukaryotes