Location: Lameshur Bay St. John, U.S. Virgin Islands at ~ 7.0 ± 0.5-m depth
Research conducted from the University of the Virgin Islands Marine Station in Lameshure Bay during July – August 2019.

Methods & Sampling:

At each site (White Point, Tektite, Cabritte Horn) corals were haphazardly selected and categorized as within "dense" or "sparse" octocoral canopies. Colonies were categorized as within dense canopies if they were shaded by at least one octocoral colony ≥ 25 cm tall when it flexed in routine oscillatory water flow. Preliminary surveys showed that colonies of Porites astreoides (urn:lsid:marinespecies.org:taxname:288889) met this criterion when the distance from the nearest tall octocoral was less than half the height of the octocoral colony. The distance between P. astreoides colonies and the nearest octocoral was measured to categorize colonies of P. astreoides as within or outside the understory habitat. A single induction curve was performed on each P. astreoides on one of 16 days during July and August 2019. Sampled colonies were > 4 cm in diameter to provide space on the colony surface for the placement of the fiber-optic probe (5 mm diameter) attached to the Diving Pulse Amplitude-Modulation (PAM) fluorometer (Heinz Walz, GmbH) that was used to measure induction time. To standardize the light environment of samples all induction curves were performed between 09:00 and 11:00 hrs on clear cloudless days. In this study actinic light from the Diving PAM was set to 896 µmol photons m-2 s-1 during the induction protocol. There was a two-minute rest period between the first saturation pulse assessing Fm and the initiation of actinic light. Once turned-on, actinic light was continuously delivered for 17 minutes with a total of 13 saturating pulses being delivered one every 1.4 minutes.

Instruments:

PVC Quadrats (1 m2)
Transect tapes
Measuring ribbons with mm graduations
Underwater Fluorometer Diving-PAM (Heinz Walz GmbH)