Stability and decline in deep-sea coral biodiversity, Gulf of Mexico and US West Atlantic

Characterizing deep-sea coral biodiversity is essential to evaluate the current state of deep-sea ecosystems and to assess vulnerability to anthropogenic threats such as offshore drilling and ocean acidification. Thousands of deep-sea coral records from the past 6 decades are compiled in the publicly accessible NOAA database, but few large-scale analyses of deep-sea coral biodiversity through time have been conducted. This study provides the longest temporal analysis of deep-sea coral generic biodiversity (58 yr), and the first such study for US waters. To mitigate missing temporal and spatial data, a machine learning model was employed to simulate deep-sea coral occurrences. Patterns of deep-sea coral generic biodiversity were calculated for observed and simulated data from 1960 to 2018 in the US marine ecoregions of the Gulf Stream Slope, Carolinian Atlantic Shelf and Slope, South Florida/Bahamian Atlantic Shelf and Slope, and Northern Gulf of Mexico (NGOM) Shelf and Slope. There were statistically significant decreases in deep-sea coral generic biodiversity for all ecoregion/depth pairs in simulated data and most ecoregion/depth pairs in observed data. There was relative stability in biodiversity from 1960 to the mid-2000s, followed by generally rapid decreases between 2007 and 2011. Biodiversity stabilized after 2011, though it remains at the lowest average level in the past 58 yr. Most ecoregions and depths show the lowest generic richness during the most recent time interval (2010-2018) compared to the preceding 5 decades. The most persistent deep-sea coral genera from 1960 to 2018 vary based on ecoregion and depth. Rapid decreases in biodiversity support previous work showing deep-sea corals can undergo biodiversity loss in less than 4 yr, which is alarming given their slow growth and decadal recovery times. This analysis provides a robust temporal framework for future researchers to evaluate casual mechanisms affecting deep-sea coral biodiversity and inform on conservation strategies.