Many aquatic animals produce larvae that use complex swimming behaviors to locate settlement habitats. Microbes (Bacteria and Archaea) in the water column and on settlement surfaces may provide navigational information for animal larvae, however the role of microbes in each stage of the coral settlement process is not well understood. This project will use larvae from six Caribbean coral species to test a novel hypothesis about coral behavior, that coral larvae use waterborne microbial communities as navigational information and that they avoid adults of the same species. The study will: (1) determine how coral larvae navigate different reef microbial environments by quantifying their swimming behaviors using videoanalysis, (2) characterize microbial communities from part 1 using high-throughput DNA sequencing, (3) test for behavior, survivorship, and settlement effects in larvae exposed to individual bacterial species, and (4) observe whether patterns of coral settlement in the field are consistent with laboratory results.
Intellectual merit: Coral reefs create food, economic revenue, shoreline protection, and cultural pride, yet they are massively threatened by human activity. Meanwhile, coral recruitment rates continue to decline on Caribbean reefs. This project will advance knowledge of: the microbial cues key to successful coral recruitment, the conditions under which coral larvae can identify lower-mortality habitats, and the best approaches for helping threatened corals survive their most crucial life history stage.
Broader impacts: At a research site in Curaçao, we will continue to communicate our findings through the CARMABI Foundation nature education program and through CARMABI's broader outreach channels (news coverage, public lectures). We will continue to communicate with local scuba divers, nature resource managers, and government officials on Curaçao, and broadly through publications, presentations, photography exhibits, blogging, and podcasts. The project will support the training of one female postdoctoral researcher and two students.
Confirmation of Bacterial Isolate Bioactivity Bacterial isolates were shown to consistently induce behavioral changes, metamorphosis, and/or settlement in larvae of the coral Orbicella faveolata, which was recently listed as a threatened species under the U.S. Endangered Species Act. It was also found that adding small chips of coral skeleton to bacterial biofilm trials greatly increased the speed and total amount of larval settlement. Together, these results represent the fulfillment of the aims of the grant. These methods will be used to test new methods for reef restoration via the out-planting of sexually-produced coral larvae. Among the most effective settlement inducers in this study were strains of Bacillus, Tateyamaria, and Salinimicrobium bacteria. In the Pacific and elsewhere in the Caribbean, recent attention has been directly toward the metamorphic effect of Pseudoalteromonas bacteria. Therefore, we have found that multiple bacterial genera, not only bacteria of a single genus, are capable of inducing settlement and other behavioral effects in corals. These results are now being prepared for publication. Physiology and Behavior of Coral Larvae in Response to Symbionts We also studied the developmental and physiological effects of symbiont acquisition in the coral O. faveolata. Wecollected larvae with and without symbionts, in both total darkness and diurnal light regimes, in order to identify when and how symbionts alone or symbionts in the presence of light cause cellular stress to coral hosts, and to test whether light regime and symbiont infection also alter behavior, mortality, or settlement rate. Symbiont infection was found to significantly increase mortality, regardless of light regime, indicating that the presence of symbionts alone causes increased stress to coral hosts. Behavioral changes also occurred; symbiont infection together with total darkness caused a significant decrease in swimming behavior, and a slight increase in settlement rates as compared to the other treatments. Advances in Coral Reproductive Natural History Over three lunar cycles in two separate years, we attempted to determine the timing of spawning in the Pillar Coral Dendrogyra cylindrus, which was recently listed as a threatened species under the US Endangered Species Act. We confirmed that males of this species spawn before females. We collected gametes and successfully raised swimming larvae of this species. We also successfully raised settlers of this species for the first time. This represents an important achievement in natural history, which will allow for accelerated research and conservation of this rare species. Advancing development of a model system in the upside-down jellyfish Cassiopea xamachana – The Medina Lab is currently developing the upside-down jellyfish Cassiopea xamachana into a model system for studies of symbiosis and development. Concurrently, we have developed methods to work with C. xamachana embryos and larvae for studies of behavior and development. We successfully collected embryos and larvae from gravid female jellyfish, successfully reared and settled them in the laboratory. We also successfully kept adult jellyfish in the flow-through system at the Carmabi Field Station (feeding regularly with Artemia nauplii). Concurrently, lab members collected adult and juvenile samples for genetics studies as part of other research ongoing in the lab. These advancements will now allow larval settlement work in the Caribbean year round, including in the "coral larvae off season" from November to March.
