The diversity of microbial plankton has received limited attention in the main basin of the Red Sea. This study investigates changes in the community composition and structure of prokaryotes and eukaryotes at the extremes of the Red Sea along cross-shelf gradients and between the surface and deep chlorophyll maximum. Using molecular methods to target both the 16S and 18S rRNA genes, it was observed that the dominant prokaryotic classes were Acidimicrobiia, Alphaproteobacteria and Cyanobacteria, regardless of the region and depth. The eukaryotes Syndiniophyceae and Dinophyceae between them dominated in the north, with Bacillariophyceae and Mamiellophyceae more prominent in the southern region. Significant differences were observed for prokaryotes and eukaryotes for region, depth and distance from shore. Similarly, it was noticed that communities became less similar with increasing distance from the shore. Canonical correspondence analysis at the class level showed that Mamiellophyceae and Bacillariophyceae correlated with increased nutrients and chlorophyll a found in the southern region, which is influenced by the input of Gulf of Aden Intermediate Water.

Please cite this article as: Kürten, B., Al-Aidaroos, A.M., Kürten, S., El-Sherbiny, M.M., Devassy, R.P., Struck, U., Zarokanellos, N., Jones, B.H., Hansen, T., Bruss, G., Sommer, U., Carbon and nitrogen stable isotope ratios of pelagic zooplankton elucidate ecohydrographic features in the oligotrophic Red Sea, Progress in Oceanography (2015), doi: http://dx.doi.org/10.1016/j.pocean. 2015.11.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. only by the thermohaline circulation, but also by mesoscale activities that transports nutrients to the upper water layers and interact with the general circulation pattern. Ecohydrographic features of the Red Sea, therefore, aid in explaining the observed configurations of isoscapes at the macroecological scale.

The diversity of coral reef and soft sediment ecosystems in the Red Sea has to date received limited scientific attention. This study investigates changes in the community composition of both reef and macrobenthic communities along a cross shelf gradient. Coral reef assemblages differed significantly in species composition and structure with location and depth. Inner shelf reefs harbored less abundant and less diverse coral assemblages with higher percentage macroalgae cover. Nutrient availability and distance from the shoreline were significantly related to changes in coral composition and structure. This study also observed a clear inshore offshore pattern for soft sediment communities. In contrast to the coral reef patterns the highest diversity and abundance of soft sediment communities were recorded at the inshore sites, which were characterized by a higher number of opportunistic polychaete species and bivalves indicative of mild disturbance. Sediment grain size and nutrient enrichment were important variables explaining the variability. This study aims to contribute to our understanding of ecosystem processes and biodiversity in the Red Sea region in an area that also has the potential to provide insight into pressing topics, such as the capacity of reef systems and benthic macrofaunal organisms to adapt to global climate change.