A wide range of natural phenomena — cyclones, severe storms, hot weather, disease outbreaks, sediment movements — can remove resident plants and animals, creating gaps or patches. These gaps provide opportunities for colonists to arrive, replenishing populations affected by disturbance, but also allow opportunities for other species to arrive. Human activities also act as disturbances: the seabed is disturbed by fishing gear, nutrients and pollutants are released into the water, and new species are introduced and become pests.
A primary aim of our research was to understand the direct effects of human disturbances, particularly those that recur, and to compare them with natural disturbances. In the intertidal zone, we examined the effects of recreational activities, particularly pedestrian traffic and the removal of animals for food or bait. In the subtidal zone, we examined the effects of pollutants — particularly heavy metals and nutrients — and of invasive species.
Outcomes
- Recurrent disturbances from pedestrian traffic could act as independent disturbance-recovery cycles at one location, while at nearby locations several disturbances acted synergistically to produce major change. These findings provided valuable guidance to Australian natural resource managers.
- We showed that the standard laboratory-based approach to predicting pollutant effects is flawed. Brief pulses of toxic metals occurring at intervals of 4–8 weeks produced severe impacts on key species not predicted by current laboratory approaches.
- We documented a range of indirect effects, including shifts in dominant species on rocky shores following removal of habitat-forming seaweeds by intense trampling, and increases in weakly competitive species after pulses of pollutants.
Resilience
Our later research focused on developing a deeper understanding of resilience in temperate marine environments — specifically the factors that influence the capacity of a system to return to its original state following disturbance, rather than flipping to alternative community states. This included:
- Resilience of the intertidal alga Hormosira banksii, examining recovery rates at a regional scale along the Victorian coast and latitudinally from New South Wales to Tasmania, and testing whether harvesting of intertidal snails affects recovery rates.
- Responses of sessile invertebrate communities to disturbance — whether heavily invaded communities are less resilient, and whether removal of invaders allows native species to retain space.
Keough Lab 