Long sediment-laden algal turf likely impairs coral recovery on Florida’s coral reefs

Abstract

Coral reefs in the Florida Reef Tract have seen protracted loss of coral over the past several decades due to a variety of disturbances from marine heat waves, cold snaps, and disease events. Corals have not recovered despite abundant herbivorous fishes and relatively low macroalgal cover, two factors thought to facilitate resilience of corals. Thus, factors affecting the replenishment of coral populations may be hindering the recovery of corals. To study the potential factors affecting coral recovery in reefs of the Florida Reef Tract, we assessed benthic abiotic variables (substrate slope, depth, structural complexity, and abundance of sediment), fish assemblages, and benthic composition in three different reef habitats (groove, spur wall, spur top) located on three low-relief reefs and three high-relief spur-and-groove reefs. Herbivorous fish biomass ranged (44.7–107 g m⁻²), which is above average for the Caribbean. Yet there was low coral cover (~ 1%) and low density (~ 1 coral m²) of small adult corals, which likely reflects the cumulative effects of years of disturbances. The presence and density of juvenile corals were negatively correlated with the depth of the sediment layer trapped within long, sediment-laden algal turfs (LSAT), which are particularly abundant (> 50% cover) in low complexity reef habitats (low-relief groove, low-relief spur top, and high-relief groove). Our results indicate that current unsuitable habitat conditions (high sediment load) for early life stage corals may be an important factor preventing coral recovery. Consequently, the abundance of herbivorous fishes and coral cover trajectories appear decoupled in the region, and additional management initiatives considering LSAT composition are required to aid reef resilience.