Location:
Yawzi Point and East Cabritte sites along the south shore of St. John, U.S. Virgin Islands at ~8–9-m depth
Research conducted from the University of the Virgin Islands Marine Station in Lameshur Bay during March 2019.
Methods & Sampling:
Quadrats (1m2) were placed such that the light logger was at its center. Octocorals were counted and measured if their holdfasts were present within the quadrat. Height was measured as the distance from the holdfast to the most distal branch relatively perpendicular to the benthos.
Canopy closure was quantified using a modified method from (Jennings et. al. 1999) whereby a GoPro Hero 3+ camera with a 130° field of view (manufacturer’s specification, Go-Pro., Inc. San Mateo, CA) was used to record still images in the center, and at each of the four corners, of quadrats, with all five images quadrat-1 recorded within < 5 minutes. To avoid biases in estimating canopy closure caused by adjacent non-living substrata (e.g., boulders and rock walls), images were excluded when they included these features. Images were analyzed using ImageJ software (v1.52a, Schneider et al., 2012), in which 300 randomly located dots (~ 0.5 pixel in diameter) were superimposed on each image. The number of dots on the octocoral canopy were counted and expressed as a percentage of the dot population. This metric was used to quantify canopy closure, and the results from the five images quadrat-1 were averaged to characterize each quadrat.
Instruments:
Quadrat (1m2)
Ribbon Tape with mm graduations
GoPro Hero 3+
©2020 Biological and Chemical Oceanography Data Management Office.