We collected images from three UCH sites and surrounding coral reefs in Palau (Micronesia, western Pacific). Sites were selected based on accessibility, depth (≤ 6 m), and proximity to naturally-occurring coral reefs. All UCH dated from WWII, meaning that at the time of sampling, structures had rested on the seafloor for approximately 80 years. In May 2022, we collected images from two World War II shipwrecks: the “Fish N Fins shipwreck” (henceforth FNF) was located near a dive shop by the same name, and the “Taoch shipwreck” was located in the Taoch region of Palau’s Rock Island Southern Lagoon. Unfortunately, the identity of these two shipwrecks is unknown. In November 2022, we collected images from an Aichi E13A “Jake” sea plane wreck (henceforth Plane) near Ngermid.
We collected images of the sessile invertebrate fauna at each site using a Nikon D850 camera with a wide-angle lens, a GoPro Hero 7 with a wide-angle lens, and two Olympus TG-6 cameras. Wide-angle photography was used to record adult corals or other sessile invertebrates (≤ 5 cm diameter) in quadrats (0.34 ± 0.01 m2, mean ± SE). Olympus cameras were used for macro photography of young coral recruits (< 5 cm diameter), with each recruit being photographed individually to enable identification. A size scale was included in images to show colony size and quadrat area.
Images were recorded in transects at each site. The FNF shipwreck was oriented in an upright position, was 30 m long, and stretched from the seafloor (4 m depth) to above the sea surface. Images were recorded in three transects on the starboard hull (4, 3, and 2 m depth), one transect along the starboard gunnel (1 m depth), one transect on the port side (2 - 4 m depth), and one transect on the deck of the ship (2 m depth). Each transect stretched the length of the ship, ~30 m. A coral reef interspersed with sandy sediment surrounded the FNF shipwreck on both sides. Coral heads and coral rubble occurred on the seafloor within 1 m of the shipwreck, so there was almost no gap between the shipwreck and the adjacent natural reef. Quadrats were recorded from the coral reef (4 m depth) in three transects, each 20 – 30 m in length: near the starboard side, near the port side, and near the bow of the shipwreck.
The Taoch shipwreck was oriented on its side and 30 m long. It rested on the seafloor at 6 m depth and stretched to 1 m depth. Images were collected in transects that stretched the length of the ship: three transects on the hull (6 m, 3 m, 1 m depth) and 2 transects on the deck (6 m, 4 m depth). The seafloor on the deck side of the shipwreck was blanketed by sand and punctuated by sparse coral heads. On the hull side of the wreck, there was an area of sand ~2–5 m wide, and then a dense coral reef sloped upward to shore. Quadrats were recorded from this sloping coral reef in transects running the length of the ship: two transects (6 m, 3 m) on the hull side of the shipwreck and one transect (6 m depth) on the deck side of the shipwreck.
The seaplane rested approximately in flight orientation on the seafloor at 2 m depth. Quadrats from this aircraft were photographed in 2 transects: along the fuselage (12 m long), and along the wings (15 m). A coral reef covered the limestone walls of the U-shaped bay where the plane wreck rested, with a gap of 1 – 5 m from the airplane. This surrounding coral reef was photographed in a single transect stretching around the tail of the aircraft (~20 m long, 2 m depth).
