Dataset: Benthic invertebrate abundances associated with octocoral forests in St. John, US Virgin Islands from July 2019 to Jan 2020

This research was conducted from the University of the Virgin Islands Marine Station in Lameshur Bay St. John, U.S. Virgin Islands at depth ≤ 13 m during July – August 2019 and January 2020.

Methods & Sampling:

Benthic surveys of invertebrates and octocoral forests were conducted using the same quadrats (1 m2) on SCUBA during July – August of 2019 and in January of 2020 placed at ≤ 13-m depth. Quadrats were randomly placed along 20 m, non-overlapping transects that were positioned haphazardly along fringing reefs.Unitary organisms were recorded as individuals, and encrusting modular organisms were counted by the number of autonomous patches of biomass, with both expressed as organisms quadrat-1. Organisms were identified in situ or with reference photos (18.2 megapixels) using field guides (Humann et al., 2013), expert opinion (mostly for sponges), and an electronic reference catalog (Zea et al., 2014). Surveys were conducted at the Cabritte Horn, Tektite, and White Point study sites. Arborescent octocorals with their holdfasts present in the quadrat were measured and contributed to mean height, and density of octocoral canopy measurements. Octocoral height was quantified by measuring the distance from hold fast to to the most distal branch 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:

PVC Quadrats (1 m2)
Transect tapes
Measuring ribbons with mm graduations
GoPro Hero 3+ camera
Sony Cybershot DSC-WX300/B