Over six working days on Carrie Bow Caye, Michael Studivan and Amanda Alker conducted eighteen SCUBA dives, fourteen of which were to 130ft. During those dives, we collected 45 samples from the tagged shallow colonies, and 45 samples from additional mesophotic coral colonies along the walls between 100-125ft. As per Smithsonian regulations, we were diving using air as a breathing gas and following profiles within no-decompression limits. At 130ft, that allows eight minutes of time, which severely constricts the workload and number of samples able to be collected. In this regard, the team was extremely successful in finding and sampling the target number of corals.
By balancing the number of samples between shallow and mesophotic zones across all three sites, a comparison of population structure and analysis of gene expression across depths is possible. As we begin to process these samples, these data generated from this project will be used to compare genetic connectivity and gene expression across the Gulf of Mexico and Caribbean for Michael's dissertation research. Additionally, this will be the first study examining basal gene expression profiles of shallow corals through time in the Caribbean.
Check out all of the photos from the trip on our lab Flickr. While the photos speak for themselves and provide a better picture of the the structure of the Belizean barrier reef system, it is necessary to provide some closing thoughts as we prepare for our travels back home. These sites are typical of some mesophotic reef habitats in the Caribbean, where the shallow reef crest falls off in a vertical wall. Light levels at even 100ft are greatly diminished, causing relatively low coral growth compared to shallower reefs. Most colonies below 100ft were much smaller than their shallow conspecifics and were found in plating and encrusting morphologies rather than the usual mounding growth form. However, we noticed a diverse array of coral color morphotypes, some of which (red fluorescent, see photo slideshow above) are suspected to benefit from nitrogen fixation and light absorption at different wavelengths, due to bacterial symbionts.
Signs of human disturbance were also common on some of the reefs, namely overfishing and macroalgal overgrowth. We saw few if any large fish, including predators and herbivorous reef fish. There were some larger invertebrates including some commercially-important species such as spiny lobster and slipper lobster. Most of the larger critters were spotted at dusk, when the reef really comes alive.
We are extremely fortunate to have been able to revisit these sites and continue a monitoring project over the past two years. Perhaps future research will bring us back to Carrie Bow, which is truly a research island in paradise!