Depth and water mass zonation and species associations of cold-water octocoral and stony coral communities in the southwestern Atlantic

Abstract

The Southwest Atlantic continental margin between latitudes 21 and 23° S comprises the Campos Basin area. Its continental shelf is some 100 km wide, with the slope starting between 80 and 130 m in depth. The slope is about 40 km wide, extending deeper to the south (2000 m) than to the north (1500 m). Water masses influencing the area include (1) surficial tropical water (TW), 250 to 300 m depth; (2) South Atlantic central water (SACW), below TW 300 to 550 m; (3) Antarctic inter- mediate water (AIW), between 550 and 1200 m depth; and (4) North Atlantic deep water (NADW), 1200 to 3500 m depth. Distributions of octocorals (25 genera, 32 species/morphotypes) and stony corals (27, 11) and associations among taxa and with water masses were analyzed. Different commu- nities were found over 3 depth ranges. Complete dissimilarity was observed between the continental shelf margin/upper slope and the middle-lower slope. The shallower depth range (52 to 760 m) was influenced by TW, SACW and the upper limit of AIW, while 11 species/morphotypes occurred exclu- sively in the middle depths (1000 to 1200 m), under the sole influence of AIW. No species were exclu- sive to the deepest depth range (1200 to 1605 m), which is bathed by NADW. Middle slope areas were distinct from one another, while lower slope areas were more homogeneous. Co-occurrences of spe- cies indicate the type of environment they live in, as soft or hard bottoms. One group of species indicative of cold-water coral communities includes Lophelia pertusa, Enallopsammia spp., Coral- lium niobe and Paragorgia johnsonii.