Recovery of Seamount Precious Coral Beds From Heavy Trawling Disturbance

Resilience and the related concept of recovery provide insights into ecosystem function, connectivity, and succession. Most marine resilience studies have focused on shallow-water ecosystems. However, increasing anthropogenic impacts in the deep sea make studies of resilience and recovery in the deep sea time-critical, with deep-sea hard-substrate habitats and large-scale disturbances having received the least attention. Ironically one of the key anthropogenic impacts to the seafloor, trawling, provides an ideal experimental design to understand processes of recovery from large-scale disturbance in the deep sea.

Seamount hard-substrate habitats in particular are thought to have low resilience due to the slow growth rates and recruitment limitations of key structure-forming taxa. The goal of our project is to test the hypothesis of low resilience by examining a series of locations in the far Northwestern Hawaiian Islands and the Emperor Seamount Chain. These sites have had some of the heaviest trawl impacts in the world, from both fish and precious coral fisheries, and include sites that are still trawled as well as ones that have been protected since the establishment of the US Exclusive Economic Zone in 1977. We compare these to untrawled sites as part of a three “treatment” design. During two cruises in 2014 and 2015 we used the AUV Sentry to image nine features (three per treatment). CTD data were also collected. Images were analyzed for all visible megafauna as well as substrate parameters (rugosity, slope, composition, relief). Yuryaku, in the “still trawled” treatment was characterized by extensive areas of bare substrate with abundant trawl scars. This feature also had lower diversity and lower abundance of megafauna compared to the recovering and never trawled locations. Preliminary data suggest recovering and never trawled features have overlapping species, but not in comparable abundances.