Summary of Abstract Submission

Abstract Submission No. IO50-03-0033PresentationOral

INFLUENCE OF NATURAL ENVIRONMENTAL GRADIENTS AND ANTHROPOGENIC EFFLUENTS ON CORAL REEFS IN THE RED SEA

Benjamin Kurten*1, Saskia Kurten2, Reny P. Devassy3, Mohsen M. El-Sherbiny4, Ulrich Sommer1, Ulrich Struck5, Ali M. Al-Aidaroos3

1 GEOMAR Helmholtz Centre for Ocean Research Kiel, Marine Ecology, DusternbrookerWeg 20, 24105 Kiel, Germany
2 King Abdullah University of Science and Technology, Red Sea Research Center, Thuwal 23955-6900 , Kingdom of Saudi Arabia
3 King Abdulaziz University, Faculty of Marine Sciences, Department of Marine Biology, P.O. Box 80207, Jeddah 21589, Kingdom of Saudi Arabia
4 Suez Canal University, Faculty of Science, Department of Marine Science, Ismailia 41522, Egypt
5 Leibniz Institute for Research on Evolution and Biodiversity, Museum fürNaturkunde, Invalidenstrasse 43, 10115 Berlin, Germany

ABSTRACT :

An integral concept of ecological research is the constraint of biodiversity along latitudinal and environmental gradients. The Red Sea features a natural environmental gradient characterized by increasing water temperature, nutrient richness,and Chla concentrations from North to South. The aim of this study was to assess the relationships between ecohydrography, plankton biodiversity and coral reef biota by means of carbon (d13C) and nitrogen (d15N) stable isotopes.Environmental samples (nutrients, Chl a), oceanographic data (salinity, temperature), particulate organic matter (POM) and biota (phytoplankton, zooplankton, bivalves, soft corals, fishes) were collected at nine coral reefs over ~1500 km distance along the Red Sea coast of Saudi Arabia.The trophic state of ambient waters, as indicated by Chl a, changed from strong oligotrophy in the north to mesotrophy in the south and was associated with increasing biomasses of diatoms, picoeukaryotes and Synechococcus as indicated by pigment fingerprinting (CHEMTAX) and flow cytometry.Several potentially harmful algae, including Dinophysis miles and Gonyaulaxspinifera (Dinophyceae), as well as copepodites,veligers (Gastropoda larvae) and Chaetognatha were encountered in larger numbers in the vicinity of an aquaculture facility at Al Lith. A Trichodesmium surface bloom was observed on the Farasan Banks, and together with ubiquitous diatom-Cyanobacteria symbioses (Rhizosolenia-Richielia) form potentially important N sources. Biota guilds separated in d13C and d15N isotopic niche spaces and were significantly correlated with environmental factors at latitudinal scale. Both d15N and relative trophic positions (RTPs) of biota tend to increase southwards, but urban runoff offsets the natural environmental gradient in the central region of the Red Sea toward higher d15N and RTPs. The present study reveals that Red Sea coral reefs are influenced primarily by the latitudinal environmentalgradient and localized urban runoff.