Dataset: Bleaching Moorea 2019

Bleaching prevalence in Pocillopora spp. corals was quantified from photoquadrats (0.5 × 0.5m) taken on the fore reef in March and May 2019. Photoquadrats to quantify bleaching were recorded at 10 m depth at two sites on the fore reef of the north shore of Moorea (38 from Site 1 and 40 from Site 2). Photoquadrats were recorded at locations that initially were randomly selected along a ~50 m transect in 2005, but were resampled thereafter. The transect and photoquadrat placement was the same as that for the permanent sites used for annual sampling of the coral community by the MCR-LTER program and were marked with rebar. A total of 1043 Pocillopora spp. colonies in these quadrats in March, and 1023 corals in May, were assigned to one of four bleaching severity categories: 0 = no bleaching, 1 = partial bleaching (many pale branch tips), 2 = moderate bleaching (white branch tips, bleaching extends down the branch), 3 = severe bleaching (whole colonies white). We also assigned corals as not bleached (category 0) vs bleached (category 1-3 combined).

Colony size was quantified as the diameter (in centimeters) along the longest axis of the coral in planar view from the photoquadrat images. The size of a colony was not recorded if the colony was only partially in the frame and the longest axis could not be identified. As a result, size was measured for 641 out of 1023 (62%) colonies assigned to a bleaching category in May 2019, and 1125 out of 1186 (95%) of colonies observed in February 2019 and categorized as alive or dead in August 2019. Size was estimated using ImageJ software. Each photograph included a reference scale with which each image was individually size-calibrated. The smallest colony size detectable in the images was ~ 2 cm.