Survivorship and growth in staghorn coral (Acropora cervicornis) outplanting projects in the Florida Keys National Marine Sanctuary

Abstract

Significant population declines in Acropora cervicornis and A. palmata began in the 1970s and now exceed over 90%. The losses were caused by a combination of coral disease and bleaching, with possible contributions from other stressors, including pollution and predation. Reproduction in the wild by fragment regeneration and sexual recruitment is inadequate to offset population declines. Starting in 2007, the Coral Restoration Foundation™ evaluated the feasibility of outplanting A. cervicornis colonies to reefs in the Florida Keys to restore populations at sites where the species was previously abundant. Reported here are the results of 20 coral outplanting projects with each project defined as a cohort of colonies outplanted at the same time and location. Photogrammetric analysis and in situ monitoring (2007 to 2015) measured survivorship, growth, and condition of 2419 colonies. Survivorship was initially high but generally decreased after two years. Survivorship among projects based on colony counts ranged from 4% to 89% for seven cohorts monitored at least five years. Weibull survival models were used to estimate survivorship beyond the duration of the projects and ranged from approximately 0% to over 35% after five years and 0% to 10% after seven years. Growth rate averaged 10 cm/year during the first two years then plateaued in subsequent years. After four years, approximately one-third of surviving colonies were � 50 cm in maximum diameter. Projects used three to sixteen different genotypes and significant differences did not occur in survivorship, condition, or growth. Restoration times for three reefs were calculated based on NOAA Recovery Plan (NRP) metrics (colony abundance and size) and the findings from projects reported here. Results support NRP conclusions that reducing stressors is required before significant population growth and recovery will occur. Until then, outplanting protects against local extinction and helps to maintain genetic diversity in the wild.

Parasitic ‘Candidatus Aquarickettsia rohweri’ is a marker of disease susceptibility in Acropora cervicornis but is lost during thermal stress

“…Aquarickettsia' abundance as a metric of host potential for disease susceptibility Acropora cervicornis has declined precipitously over the last 50 years and is now the primary species used for large-scale coral restoration efforts throughout the Florida reef tract. However, disturbances such as chronic disease events limit long-term population recovery (Miller et al, 2014;Ware et al, 2020). As bleaching events become increasingly frequent worldwide, the extent of coral disease may also increase as bleaching reduces disease resistance (Muller et al, 2018).…”

“…These changes in microbiome ecological state (e.g, community composition or variability) may be driven by and exacerbate stress from environmental change (Lewis et al ., 2015; Zaneveld et al ., 2017). It is suggested, therefore, that microbial dysbiosis may contribute to problems plaguing threatened species such as scleractinian corals and should be considered when developing strategies to preserve these foundational species (Lesser et al ., 2007; West et al ., 2019; Ware et al ., 2020).…”

Differential survival of nursery‐reared Acropora cervicornis outplants along the Florida reef tract

“…To facilitate the recovery of acroporid populations, coral restoration programs have expanded along the Florida reef tract over the last 15 years (Johnson et al 2011; Schopmeyer et al 2012; Young et al 2012). These restoration programs have focused particularly on restoring populations of A. cervicornis (Goergen et al 2019; Ware et al 2020). Although coral restoration may be a useful option to increase coral populations, strategies to optimize survival of nursery‐reared outplants are still in their infancy.…”

Habitat complexity influences selection of thermal environment in a common coral reef fish

“…There are many obstacles to successful reef restoration (i.e. cost, small spatial scale, high coral mortality; Bellwood et al 2019 ; Ware et al , 2020 ), and even if strategies are successful, they may be unable to support associated fish assemblages if the local temperatures exceed the fish species’ preferred thermal temperatures. Further, the trade-off at lower temperatures may influence the poleward range extensions of some fishes.…”