The enhanced ability to direct sexual reproduction may lead to improved restoration outcomes for Acropora cervicornis. Gravid fragments of A. cervicornis were maintained in a laboratory for two sequential trials in the seven days prior to natural spawning in the Florida Keys. Ten replicates of five chemicals known to affect spawning in various invertebrate taxa were tested. Hydrogen peroxide at 2 mM (70%) and L-5-hydroxytryptophan (5-HTP) at 5 (40%) and 20 µM (30%) induced spawning within 15.4 h, 38.8 h and 26.9 h of dosing at or above the rate of release of the control (30%) within 14.6 h. Serotonin acetate monohydrate at 1 µM (20%) and 10 µM (20%), naloxone hydrochloride dihydrate at 0.01 µM (10%) and potassium phosphate monobasic at 0.25 µM (0%) induced spawning at rates less than the control. Although the greatest number of fragments spawned using hydrogen peroxide, it was with 100% mortality. There was a significantly higher induction rate closer to natural spawn (Trial 2) compared with Trial 1 and no genotype effect. Mechanisms of action causing gamete release were not elucidated. In Caribbean staghorn corals, 5-HTP shows promise as a spawning induction agent if administered within 72 h of natural spawn and it will not result in excessive mortality. Phosphate chemicals may inhibit spawning. This is the first study of its kind on Caribbean acroporid corals and may offer an important conservation tool for biologists currently charged with restoring the imperiled Acropora reefs of the Florida Keys.
Stony coral culture has recently been the focus of increasing interest and effort, with most production taking place by asexual reproduction through fragmentation. In corals grown for reef restoration, techniques for sexual propagation offer the potential to increase genetic diversity of species for which this is a concern. After decades of population decline, the Caribbean staghorn coral Acropora cervicornis was listed as threatened under the U.S. Endangered Species Act in 2006, along with its congener, elkhorn coral A. palmata. We used practical large‐scale, land‐based culture conditions with aquaria set up in a choice/no‐choice design to test three substrate properties for their influence on settlement and metamorphosis in staghorn coral planula larvae. This transitional life stage is critical for sexual reproduction and currently represents a culture bottleneck. A total of 999 live primary polyps were produced across all experimental substrates. Planula larvae showed significant preference for substrates that were biologically conditioned, top oriented, and rugose. Conditioning was essentially prerequisite for settlement and metamorphosis, with orientation and texture also affecting larval settling. Although the ideal combination of substrate properties produced lower settling and metamorphosis rates than those observed in smaller‐scale culture experiments with elkhorn coral, results are informative in the development of reliable aquaculture techniques for sexual propagation of Caribbean Acropora in land‐based systems.
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