Mr Dan Crossett1,2, Prof David Schiel2, Dr Robyn Dunmore1,3
1Cawthron Institute, Nelson, New Zealand, 2MERG @ University of Canterbury, Christchurch, New Zealand, 3SLR Consulting NZ LTD., Richmond, New Zealand
Anthropogenic stressors on rocky reefs include coastal runoff and warming oceans. Light availability and species distributions are two important factors affected by these stressors. In combination with anthropogenic pressure, 130km of the coastline was greatly affected by the Mw 7.8 Kaikōura earthquake. Sedimentation from coastal erosion and storm runoff increased along the coastline, smothering recovering algae and causing poor growth of already stressed individuals. An intense marine heatwave a year later caused further ecological disruption. Recruitment of subtidal large brown algal species were tracked for several years following the earthquake to determine the recovery trajectory of this system, and controlled laboratory experiments were run to disentangle the response of early life stage algae to temperature, sediments, and variable light. A local source of algal propagules, inferred through adult macroalgae density, significantly increased recruitment but refuge within a canopy did not increase the number of recruits. Landsburgia quercifolia had the greatest recruitment in areas that experienced the most intensive impacts from the earthquake, and their germlings were found to be resilient to increasing seawater temperature, increasing sediment, and decreasing light. Warmer seawater temperature (>4°C above austral winter) significantly decreased survival and growth of Durvillaea antarctica, and Lessonia variegata germlings. A reduction in light also had a significant negative effect on survival and growth of these species, however, addition of fine sediment generally had a greater negative effect on germling growth and survival. Furthermore, the combination of elevated seawater temperature and high sediment had an even greater negative effect on both D. antarctica, and L. variegata. It seems clear that a combination of factors, their interactions, reef erosion, continual inputs from the catchment, and elevated temperatures are causing significant delays in the recovery of the earthquake-affected ecosystem.
Presentation Slides – Dan Crossett
