Models of habitat suitability, size, and age-class structure for the deep-sea black coral Leiopathes glaberrima in the Gulf of Mexico

Abstract

Deep-sea corals are important components of the benthos in the Gulf of Mexico, because they provide structural complexity to associated species of fish and invertebrates, and they serve as proxies for environmental conditions on millennial time scales. In the Gulf of Mexico, large colonies of the black coral Leiopathes glaberrima have been estimated to be over 2000 years old. As such, they are vulnerable to disturbance and slow to recover from adverse interactions with anchors, fishing gear, sedimentation, oil and gas extraction, and sampling. There is a growing need for non-lethal scientific collections and new information on the distribution, ecology, and population connectivity of L. glaberrima aggregations to support management decisions. A large number of remotely operated vehicle (ROV) surveys have been conducted in the Gulf of Mexico deep sea since 2008, including telepresence cruises that broadcast live seafloor images to shore. Visual observations from these surveys were collated and geo-referenced in a regional database with national museum records in order to: (1) map the distribution of L. glaberrima throughout the U.S. Gulf of Mexico, (2) predict the distribution of L. glaberrima based upon environmental correlates using maximum entropy (MaxEnt) modeling, and (3) correlate the size-class structure to the age-class structure using growth rate estimates from previous radiocarbon studies. We found that L. glaberrima has a broad distribution in the U.S. Gulf of Mexico, with suitable habitat spanning depths between 200 and 1000 m that are concentrated near the Mississippi Canyon and along the West Florida Shelf. On average, L. glaberrima colonies had a height of 34.2 cm and a basal diameter of 0.42 cm, which correlates to an age of ~ 143 yrs. Future efforts should focus on calibrating the size and growth relationships of black corals and other corals, in order to add value to telepresence-based exploration and promote non-invasive sampling techniques.