February 23-28, 2014

Phytoplankton in Red Sea coral reefs: temporal and spatial dynamic and potential impacts on the Benthic community

Cornelia Roder1, Maren Ziegler2, Daniel L. Roelke3, Jay Walton4, Christian R. Voolstra1

1Red Sea Research Center, King Abdullah University of Science and Technology, Saudi Arabia 2Senckenberg Research Institute, LOEWE Biodiversity and Climate Research Centre, Germany 3Department of Wildlife and Fisheries Sciences, Texas A&M University, USA 4Department of Mathematics, Texas A&M University, USA

Abstract 

Coral reef associated phytoplankton contributes to nitrogen and carbon fixation and may serve as an important energy source for the prevailing benthic community. While its abundance is usually controlled by the oligotrophic nature of pristine reef water, eutrophication results in phytoplankton biomass proliferation and diversity shifts. Consequently, shading, smothering, or contamination can threaten the light dependent coral population and may ultimately cause the deterioration of the whole ecosystem. Red Sea coral reefs have naturally been exposed to only little inorganic nutrient input. However, coastal development is rapidly progressing with yet unexplored effects on the ocean’s fringing reefs. Here, we apply mixed field and computational approaches to investigate phytoplankton assemblages in the central Red Sea. Based on pigment ratios we calculate phytoplankton diversities and use empirically derived data to identify key physico-chemical factors driving the community’s dynamics. Next to strong seasonal impacts, spatial patterns play an important role. We show that reefs closer to shore harbor a distinct phytoplankton community that has the potential to alter water quality and hence reef condition.

 

Quality not Quantity: multiple drivers may influence the light field incident upon coral based on shifts in phytoplankton biomass and composition 

Frances Withrow1, Daniel L. Roelke1, Jay Walton2, Cornelia Roder3, Christian R. Voolstra3

1Department of Wildlife and Fisheries Sciences, Texas A&M University, USA 2Department of Mathematics, Texas A&M University, USA 3Red Sea Research Center, King Abdullah University of Science and Technology, Saudi Arabia

Abstract 

Coral reefs of the Red Sea are among the few remaining pristine reef systems on Earth. But human development of coastal zones neighboring the Red Sea and potential changes in climate may influence water quality. This could impact phytoplankton communities, which in turn may influence the quality of the underwater light field. Health of coral reefs is affected by the spectral quality of light. We investigate through computational simulation how changes in phytoplankton biomass and composition influence the spectral quality of light incident upon corals.  We develop a mathematical model for a one dimensional water column with spectral light of diminishing intensity with depth, a nutrient source from advection, and a nutrient source from a land inflow.  Nutrient loading to the system and stratification are controlled parameters, and phytoplankton biomass and composition are response variables.  To the model output, taxon specific absorption spectra are used to predict underwater light fields. As it stands, spectral shifts in the underwater light field with changing nutrient loading and different levels of stratification degrade spectral quality.