According to a recent published report, by Benjamin Halpern and his colleagues at UCSB's National Center for Ecological Analysis and Synthesis, over 40% of the world's oceans are heavily impacted by anthropogenic activities. Only a few, "if any", areas are unaffected.
The report have taken four years to compile and resulted in 17 models of the earth. Each of the different models shows the damage caused by human activities such as pollution and fishing. The different models have then been merged into one showing the global effect (see image).
Benjamin Halpern explains, on the UCSB website, the process he and his colleagues followed to make the composite map:
"1. We gathered or created maps (with global coverage) of all types of human activities that directly or indirectly have an impact on the ecological communities in the ocean's ecosystems. In total, we used maps for 17 different activities in categories like fishing, climate change, and pollution. We also gathered maps for 14 distinct marine ecosystems and modeled the distribution of 6 others.
2. To estimate the ecological consequences of these activities, we created an approach to quantify the vulnerability of different marine ecosystems (e.g., mangroves, coral reefs, or seamounts) to each of these activities, published in Conservation Biology, October 2007. For example, fertilizer runoff has been shown to have a large effect on coral reefs but a much smaller one on kelp forests.
3. We then created the cumulative impact map by overlaying the 17 threat maps onto the ecosystems, and using the vulnerability scores to translate the threats into a metric of ecological impact.
4. Finally, using global estimates of the condition of marine ecosystems from previous studies, we were able to ground-truth their impact scores."