Abstract Summary
Hurricanes play a fundamental role in shaping coral reef benthic and fish communities. Long-term degradation and loss of ecosystem persistence and resilience may drive reefs into a permanent state of mediocrity. Mediocre reefs are characterized by slow but progressive homogenization, which may involve declining biodiversity, carbonate budget, accretion rate, and productivity. This may drive the system into often irreversible regime shifts and a compromised ability to recover from disturbance. The increasing recurrence of stochastic events (e.g. coral bleaching, coral mortality events, catastrophic hurricanes, extreme rainfall/runoff) can further drive the system towards homogenization characterized by reef flattening, shrinking food web, collapsing fish assemblages, and declining ecological functions. These factors represent a major management challenge and a threat for coral survival and achieving long-term benefits of ecological restoration. A case study from Culebra Island, Puerto Rico is discussed. Category five Hurricanes Irma and María caused significant devastation of restored assemblages of ESA-listed Staghorn coral (Acropora cervicornis) in 2017. Fish censuses were conducted within control and impact sites before and after out-planting for three years, within and outside a no-take reserve. There were highly significant (PERMANOVA, p< 0.05) increases in fish species richness, abundance, and biomass within restored plots, particularly, within the reserve. Restored thickets with larger corals sustained higher fish biomass and abundance. But hurricanes with waves exceeding 6-10 m eliminated 99.9% of out-planted coral cohorts. There was a significant collapse in coral thickets, in benthic spatial relief, and in fish assemblages. This was similar to observations made on collapsed natural reefs, with stochastic coral colony fragmentation dislodging, flattening and formation of extensive rubble fields. This was followed in 2018 by a mid to late summer Acroporid coral mortality event coinciding with sea surface temperature exceeding 29°C, a mesoscale eddy with a 5-fold increase in chlorophyll-a concentration, and with high concentrations of dissolved organic carbon across the eastern Puerto Rico shelf. Changes in the dynamics of hurricanes and mesoscale eddies can significantly influence the benefits of long-term reef restoration and must be accounted in any modeled projection of restoration outcomes and success.
