Earlier this summer, a massive mortality event occurred among multiple species at the East Flower Garden Bank. While cause remains unknown, the epicenter of the event was approximately 100m away from our shallow transplant site at East Bank. Understandable, we were eager to learn if the corals had survived. To learn more about this event and the work the Flower Gardens NMS is doing to unravel this mystery, please visit these report links: Initial Report, Response Update, and Investigation Continues. In addition, by the last week of September higher than average summer temperatures had caused a sustained increase in water temperatures above the bleaching threshold for most coral species. The sanctuary has conducted several survey cruises and estimate that bleaching is up to 50% of all corals on the shallow cap.
Unfortunately, at our shallow sites both the tagged control colonies and the transplanted colonies were not immune to the effects of above average water temperatures. All colonies in the study were observed with paling or bleaching, and the colonies that had been transplanted from mesophotic depths demonstrated greater bleaching severity than the shallow water controls. We observed coral tissue remaining on most of the study colonies, which provides some hope for recovery and survival. Sampling was conducted to assess bleaching responses, and should be useful in comparison to the samples of the same colonies during a relatively healthy period in May 2016. Our mesophotic transplant source sites appeared unaffected by this bleaching event, perhaps due to reduced thermal stress as indicated by the presence of strong thermoclines around 130ft. The next time these sites will be revisited is September 2017, and we hope to see recovery of our experimental and other reef corals. As cold fronts began to sweep across Texas and the Gulf of Mexico in October, we are hopeful that the bleached corals will be able to recover.
As a continued investigation of possible "depth-generalist" morphotypes identified in shallow and mesophotic M. cavernosa, we conducted four 25m transects at both shallow and mesophotic depths at East and West Banks. By video and macro photography of all M. cavernosa colonies found in the transects, we will be able to quantify the relative proportion of each morphotype in the populations. Additionally, at McGrail Bank, we conducted two 100m transects to complement previous ROV surveys. Finally at Bright Bank, the technical dive team collected nine additional coral samples to complete the sampling for population genetics analyses.
As always, we owe a special thank you to the crew of the R/V Manta, our volunteers and collaborators, and to Emma Hickerson, GP Schmahl, et al. for the outstanding support we receive from the FGBNMS. This year we were fortunate to have additional assistance from Dr. Matt Ajemian and Mike McCallister (FAU HBOI), Mike Dickson (UF), Jeff Beal (FWC), and Rachel Susen (Moody Gardens). Joshua Voss, Michael Studivan, and Patrick Gardner comprised the technical diving team, while Danielle Dodge and recent Voss lab alumna Jennifer Polinski took on primary responsibilities at the shallow sites. Thank you and well done to all involved.
Check out our Flickr album for more photos from this cruise!
MSS and JDV