Dataset: Identity and heights of Octocoral species found on transects at 6 sites on the south shore of St John, U.S. Virgin Islands in 2021 and 2022

To investigate community dynamics of octocorals on Caribbean coral reefs, transect surveys were conducted at 6 sites on the south shore of St John, within the Virgin Islands National Park during the summers of 2021 and 2022.  Depending on the site, 3 to 6 transects were established. All sites were located at 6 to 9 meters depth and samples were collected by SCUBA from small boats. The identity and heights of all arborescent octocorals greater than or equal to 5 centimeters were recorded from 1 square meter quadrats on the transects.  The position of colonies relative to the site, meter on the transect, and side of the quadrat are included.

Censuses at sites Grootpan, Europa, and Tektite were based on 50-meter x 10-meter areas that were arbitrarily selected and permanently marked with stainless steel eyebolts at the corners of the sites. A total of six transect lines, also marked with eyebolts, were laid out at 10 m intervals. At Booby Rock, a 50-meter line running parallel to the approximately 7-meter depth contour was established, and survey transects (3 in 2021 and 6 in 2022) were positioned at random points along the line.  All octocorals present in 1 x 1-meter quadrats along the 10-meter long transects were identified and their heights were measured. Small branch tip samples were collected from colonies that could not be identified in the field.  Sclerites were digested from those colonies with a commercial bleach solution and sclerites were observed with a compound scope for identification. Octocoral adults were defined as individuals greater than or equal to 5 centimeters in height, with height determined to the nearest centimeter.