Abstract
Recovery of the elkhorn coral Acropora palmata is critical to reversing coral reef ecosystem collapse in the western Atlantic, but the species is severely threatened. To gauge potential for the species’ restoration in Florida, USA, we conducted an assisted migration experiment where 50 coral fragments of 5 nursery-raised genetic strains (genets) from the upper Florida Keys were moved to 5 sites across 350 km of the offshore reef. Additionally, 4 fragments from the 1 remaining colony of A. palmata in Dry Tortugas National Park (DRTO) were added to the 2 DRTO experimental sites to test for local adaptation. To measure coral performance, we tracked coral survival, calcification, growth, and condition from May 2018 to October 2019. All 24 corals relocated to the DRTO sites survived and calcified ~85% faster than the fewer surviving corals transplanted to the 2 upper Keys sites. While coral survival across the entire experiment did not depend on genet, there was a weak but statistically significant genetic effect on calcification rate among the corals relocated to DRTO. The DRTO native genet was among the fastest growing genets, but it was not the fastest, suggesting a lack of local adaptation at this scale. Our results indicate that DRTO, a remote reef system inhabited by the species during the Holocene and located at the nexus of major ocean currents, may be a prime location for reestablishing A. palmata. Assisted migration of A. palmata to DRTO could restore a sexually reproducing population in <10 yr, thereby promoting the species’ regional recovery.
Highlights
The global loss of species is perhaps the greatest challenge in addressing ecosystem collapse because it is irreversible
The rate of colony height extension was statistically higher at the 2 Dry Tortugas National Park (DRTO) sites, averaging 4.8 cm yr−1, compared to rates at the 3 main Keys sites, where they averaged 1.5 cm yr−1
Our experiment demonstrated that 5 Acropora palmata genets sourced from the upper Florida Keys survived and flourished when transplanted to the Dry Tortugas reef system, 300 km away
Summary
The global loss of species is perhaps the greatest challenge in addressing ecosystem collapse because it is irreversible. Of the 2 species, A. palmata is arguably the more important ecosystem engineer (Macintyre & Glynn 1976), with some exceptional locations where A. cervicornis built thick Holocene reefs (Macintyre et al 1977, Aronson et al 2002). While both species suffered dramatic population declines from a disease pandemic in the late 1970s (Gladfelter 1982, Aronson & Precht 2001), the decrease in A. palmata is arguably more consequential for reef morphology. The results of reef degradation and flattening include loss of ecosystem services such as coastal protection from storms, food security from important fisheries, and economic returns from tourism (Costanza et al 1997, 2014, Spalding et al 2017, Storlazzi et al 2019)
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