Validating cumulative impact methods in marine systems

Mr Jackson Stockbridge1, Dr Alice  Jones2, Prof Bronwyn Gillanders3

1The University Of Adelaide, Adelaide, Australia, 2The University of Adelaide, Adelaide, Australia, 3The University of Adelaide, Adelaide, Australia

Marine ecosystems are under threat from multiple stressors arising from human activities. When considered in isolation, the effects of human activities such as overfishing, pollution, climate change, invasive species and physical degradation can be measured and quantified to give an estimate of impact. However, these stressors rarely act in isolation, and as such an estimate of the cumulative impact is needed. The most commonly applied methods for assessing cumulative impacts involve mapping threats and using expert knowledge to determine vulnerability of a system to different threats. These methods rely on many assumptions and incorporate expert knowledge in the place of empirical data. To assess whether spatial cumulative impact maps correlate with actual impact, we used data from a seagrass condition survey. We assessed the relationship between measured seagrass condition and previously published cumulative impact scores for a study area in northern Spencer Gulf, South Australia. The results show that there is little correspondence between modelled cumulative impact scores and measured seagrass condition at 31 sites throughout northern Spencer Gulf. Using seagrass as a case study, we have highlighted that the current approach to assessing cumulative impacts in marine ecosystems does not adequately capture the actual impacts of human activities on marine ecosystems. This is likely to be the result of a lack of empirical data to support many of the assumptions used in cumulative impact assessment methods. The outcomes highlight the need to develop more robust approaches to cumulative impact assessment in marine ecosystems.


I completed my Bachelor of Science  with Honours was completed at The University of Adelaide under the supervision of Prof Bronwyn Gillanders and Dr Alice Jones. My Honours project aimed to quantify the condition of mangroves around South Australia in order to promote their status as important areas of carbon sequestration.

Now into my second year as a PhD candidate with the same supervisor, i am looking at how we model cumulative impacts in marine ecosystems.

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