Abstract

Active restoration began at Laughing Bird Caye National Park (LBCNP) in 2006 and six in-situ nurseries were established in 2009 to scale up the effort. Host and symbiont genetics were analyzed on 23 acroporids. Corals housing Symbiodinium Clade D spp. purportedly have high resistance to what are now semi-regular bleaching events. Because this thermal tolerance is thought to come with a trade-off of reduced growth rates, experiments in 2012 compared growth rates between multiple Acropora cervicornis genets housing Clade A3 or S. trenchii (D1a) cultured on ropes in two nurseries. The corals harboring S. trenchii (D1a) symbionts (n = 61) grew an averaged 2.8 cm/month +/- 0.08 cm/month; corals harboring A3 symbionts (n = 61) averaged 2.4cm/month growth +/-0.07cm/month; t(60) = -3.15, p < 0.0025. Growth rate experiments using Total Linear Extension (TLE) were repeated in 2013, using only two distinct geno-types of A. cervicornis harboring either symbionts A3 or S. trenchii, in two nursery locations. There were significant differences in growth rates when the two host-symbiont combinations were compared. The corals housing S. trenchii (D1a) (n = 60) averaged 19.3 cm/month +/- 1.2cm/month and the corals housing A3 (n = 55) averaged 13.9 cm/month +/- 1.0 cm/month; t(54) = -5.44, p < 0.0001. When growth rates between two nursery sites, one at 2m, one at 5m, were compared independent of clade, there were also significant differences, with all corals growing faster at the shallow nursery. These results suggest that there are few trade-offs in growth for colonies of A. cervicornis harboring populations of stress-tolerant Symbiodinium trenchii, in these in-situ nursery conditions in southern Belize, and that here, shallow nurseries promote faster growth than deeper sites.

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