Leigh Tait1, Christopher Battershill3, Frankie Thoral3, Toni Falconer2, David R. Schiel2
1National Institute of Water and Atmospheric research (NIWA), New Zealand - 2 University of Canterbury, New Zealand - 3University of Waikato, New Zealand
Marine autotrophs primarily require light, water, CO2, and nutrients to flourish. However, the role of light limitation as a driver of kelp bed decline has occurred in relatively few studies. In regions where extreme events (e.g., extreme rainfall/cyclones) or cumulative changes to land-based erosion have altered sediment regimes, the consequences to nearshore rocky reef can be dramatic. Here we show detailed patterns of kelp and photosynthetic assemblages to depths beyond 50m and across gradients of exposure to land-derived sediments. To do this we use Remote Operated Vehicles (ROV) and detailed photogrammetric reconstructions to quantify benthic communities, as well as in situ light measurements and modelling of light at the seabed. We assess the light thresholds that result in substantial changes in ecological trends and identify these transitions across depths and sedimentation regimes. Finally, we extrapolate these trends across satellite derived estimates of light availability and assess potential trajectories associated with changes to land-use and extreme events.