Dallas Lafont1, Nick Shears1
1 Institute of Marine Science, University of Auckland, Auckland, New Zealand
Understanding the relative importance of different anthropogenic stressors in driving habitat loss is key to developing management strategies aimed at conserving and restoring marine ecosystems. Long-term declines in kelp forests on rocky reefs in Queen Charlotte Sound, New Zealand, have been suggested to be due several anthropogenic stressors including warming coastal waters, turbidity associated with land-use, and fisheries-driven trophic cascades. Examining how the extent and depth distribution of remaining kelp forests varies across environmental gradients can provide valuable insights into the key stressors influencing kelp distribution. Drop-camera surveys were carried out at 102 reefs across Queen Charlotte Sound. Habitat types within each survey photo were classified and used to examine how the depth distribution and prevalence of kelp forests (Ecklonia radiata and Carpophyllum spp.) related to seawater temperature, turbidity, wave exposure and urchin density. Kelp forests were most prevalent in areas with high water motion and higher turbidity, but urchin barrens dominated more sheltered areas, covering >65% of the reef on average. The prevalence and lower depth limit of kelp was negatively related to urchin density, and positively related to wave exposure. Our results indicated that sea urchins were the most significant stressor limiting kelp forests, and their influence on kelp was moderated by water motion. A sea urchin removal experiment is currently underway to test if sea urchin grazing is the primary factor limiting kelp recovery across the Sound or whether future kelp forest restoration will need to employ more active restoration approaches.