Multi-year coral recruitment study across the Florida Reef Tract reveals boom-or-bust pattern among broadcast spawners and consistency among brooders

Abstract

Scleractinian coral populations are in global decline, and successful recruitment is fundamental to community persistence and recovery, but recruitment may vary by coral reproductive mode. Using settlement tiles, we assessed coral recruitment over 3 consecutive years across 4 regions (~300 km) of the Florida Reef Tract (FRT) to determine whether spatio-temporal variation differs between brooding and broadcast spawning corals and whether coral recruit distributions correlate with adult coral live tissue area, site temperature, or depth. We deployed 32 tiles to each of 30 sites with depths ranging from 2 to 18 m; tiles were retrieved and replaced annually. From 2016-2018, we counted 11633 scleractinian coral recruits, most of which belonged to the Siderastreidae, Agariciidae, Poritidae, and Faviidae families. Faviid recruits were rare (<1%). While recruitment of brooding agariciids and poritids was relatively stable across the 3 yr, recruitment of broadcast spawning siderastreids increased an unprecedented 70.7-fold from 2017 to 2018, in a boom that spanned 19 sites across the FRT. Elevated temperature during the preceding reproductive season was a significant predictor of low recruitment for all groups except siderastreids and faviids, and recruitment of brooding taxa was positively linked to adult confamilial live tissue area. For siderastreids, adult live tissue area was also related to recruitment, but the direction of the relationship differed by year and region. The unprecedented high recruitment of siderastreids in Florida, preceded by 2 yr of comparatively low recruitment, demonstrates that broadcast-spawning scleractinians are among the marine taxa capable of employing boom-and-bust recruitment cycles over geographically widespread areas.