Diversity and Abundance of Deep Sea Corals and Sponges in the Steep Bathyal Terrain of West Florida Escarpment

Despite considerable improvement in technology over the past decade, still very little is known of deep sea ecosystems, especially at extreme depths around 1500 m or more in the Gulf of Mexico (GOM). This study characterizes the coral and sponge ecosystems found below 1500 meters on the West Florida Escarpment using video survey data collected by the NOAA ship Okeanos Explorer. Eight ROV dives were evaluated from the 2017 and 2018 GOM expeditions, ranging from 1500 to 3000 meters in depth. Each dive was divided into segments based on geological characteristics and distance traveled. Corals and sponges observed in each segment were then identified to lowest practical level and counted from periodic screen captures. Overall, the most common coral taxa observed were octocorals in families Isididae and Plexauridae and black corals in families Antipathidae and Schizopathidae. Of the sponges, glass sponges were the predominant group, including Euplectelidae and Hyalonematidae. All segments were assigned values for substrate, seafloor slope, and depth. The study compared diversity and abundance for categories within these factors using univariate and multivariate statistics. Diversity and abundance were significantly different between depth zones 1500-2000 and 2500-3000 m and between the hard and soft substrate categories. Variation was expected on different substrates, as most sessile benthic organisms have adapted to anchor on either hard or soft substrate. However, the differences in diversity and abundance among depth categories was not expected, because all segments were extremely deep. Also not expected was the similarity between remote dive sites in the northern and southern latitude categories. Overall, this study offers an initial habitat characterization of deep sea ecosystems on the West Florida Escarpment, and raises several questions as to the causes in variation in diversity and abundance throughout the range.