Reef recovery and resilience: interpreting abiotic effects on critical early life stages of large brown algae

Abstract

Rocky reefs throughout the temperate zone are dominated by large brown algae, which are major foundation species and ecosystem engineers. There is usually an ecological bottleneck at the early life stage of such algae when they are vulnerable to a wide range of stressors. A large earthquake that affected the coastline of southern New Zealand highlighted the combined effects of sudden changes to multiple stressors on large algal assemblages. In particular, the regime of temperature, sediment and light suddenly changed as the coastal platform was lifted, and sediments from the catchment occluded the light environment of nearshore waters. Here we tested the effects of these stressors on early survival and growth of 3 formerly dominant species—the fucoids Landsburgia quercifolia and Durvillaea antarctica and the laminarian Lessonia variegata—over 100 d using a culture laboratory. After 42 d, interactive effects were found for growth of all species. Decreasing light and increasing temperature had the greatest negative effect on L. variegata and D. antarctica growth. Growth was minimal at the lowest light treatment (PAR: 16 µmol m-2 s-1) for all species, but often least growth was found at the highest sediment treatment (PAR: 32 µmol m-2 s-1). L. quercifolia was resilient to increasing temperature, whereas survival and growth decreased with increasing temperature for D. antarctica and L. variegata. These results are highly suggestive of the coincident influences of major stressors on the post-earthquake marine ecosystem. These results also highlight that recovery of large brown algae following disturbance events is likely to be slow due to an increase in coastal sedimentation and extreme water temperature.