Under a watchful eye, the coral reefs of Flower Garden Banks National Marine Sanctuary show signs of resilience
By Dr. Michelle Johnston and Elizabeth Weinberg
Conducting fieldwork 100 miles offshore can be a challenging task when coordinating people, equipment, and boat operations in a remote location – but this is exactly what Flower Garden Banks National Marine Sanctuary scientists do each year to monitor the health of the coral reef in the national marine sanctuary. Since 1989, scientists have analyzed photographs and water quality, tracked stressors on the environment, and evaluated how management techniques are supporting the health of sanctuary ecosystems through annual monitoring expeditions.
2016 was an unprecedented season, with a localized coral and invertebrate mortality event as well as a coral bleaching event occurring within the sanctuary. A Conservation Series report from the NOAA Office of National Marine Sanctuaries summarizes fish and seafloor observations and water quality data from long-term monitoring study sites and deep monitoring sites within Flower Garden Banks National Marine Sanctuary at East Flower Garden Bank and West Flower Garden Bank. The data shed light on the mortality and bleaching events and show that on the whole, coral communities remain healthy.
Monitoring sanctuary conditions
Despite global coral reef decline in recent decades, East Flower Garden Bank and West Flower Garden Bank have long been recognized as some of the healthiest coral reef communities in the world. These areas have suffered minimally from hurricanes, coral bleaching, and disease, while supporting a relatively diverse and abundant populations of marine animals.
The report summarizes fish and seafloor community observations and water quality data from 2016, as well as historical data resulting from 27 years of nearly continuous monitoring. Monitoring has shown that coral continues to dominate the seafloor community in both study sites. The primary species of coral found at the study sites is Orbicella franksi, or boulder star coral, which is listed as a threatened species under the Endangered Species Act.
Monitoring sanctuary threats
In July 2016, a localized mortality event occurred at East Flower Garden Bank. Scientists found coral, bivalves, sea urchins, brittle stars, crustaceans, and other invertebrates dead and covered in bacterial mats across a 6.5 acre area on the shallow coral cap. Response cruises on board the R/V Manta helped scientists document the event and collect samples for analysis.
While the exact cause is uncertain, decreased salinity from heavy rainfall, high seawater temperatures, and low oxygen levels may have been contributing factors to the event. Flower Garden Banks National Marine Sanctuary scientists and research partners will be gathering for a symposium in early 2018 to compile data and bring together hypotheses from various experts.
Due to elevated seawater temperatures in excess of 30°C (86°F) in 2016, corals around the world, most notably the Great Barrier Reef, were also affected by a severe bleaching event. At East and West Flower Garden Banks, coral bleaching began in late September on the heels of the localized mortality event, and peaked in October. Sanctuary scientists conducted bleaching response cruises off the R/V Manta, photographing corals in repetitive monitoring stations to document the event. Approximately 46 percent of the coral colonies within East Flower Garden Bank monitoring stations and 24 percent of the coral colonies in West Flower Garden Bank monitoring stations exhibited signs of bleaching stress. This was the worst bleaching event on record at the sanctuary.
Most of the coral colonies recovered from the coral bleaching event. After assessing data taken in January 2017 at East Flower Garden Bank, only four percent of the coral colonies within the study sites were still exhibiting signs of bleaching or paling. Most of the corals on the reef that had been impacted by bleaching had survived. Although sites within West Flower Garden Bank were not photographed in early 2017 due to time and weather constraints, a similar recovery there was confirmed by diver observations.
Building partnerships for a strong sanctuary
Regular, comprehensive monitoring of an offshore sanctuary like Flower Garden Banks requires collaboration. In order to study coral health, fish populations, and changes in water quality, sanctuary divers work with partners from the Bureau of Ocean Energy Management, as well as volunteer scientific divers. Working off the R/V Manta, the sanctuary’s 83-foot, high-speed catamaran, researchers are able to undertake extensive dive operations. In 2016, Manta supported 15 research cruises and expeditions, several of which supported the annual monitoring effort and report. The sanctuary continues to support annual research in the Flower Garden Banks: 24 cruises, funded through partners, took place in 2017.
Through these collaborative monitoring efforts, we are able to ensure that the ecosystems the sanctuary protects remain healthy. Despite global coral cover decline on most coral reefs in recent decades, mean coral cover at East and West Flower Garden Banks remains high (50 to 60 percent) compared to many other shallow reefs in the Caribbean region.
Until recently, it was apparent that problems affecting coral reefs throughout the southeast U.S. and Caribbean region, including land-based sources of pollution and bleaching, have not had a major impact at the banks, partially due to their relative isolation and depth. However, in 2016, effects from increasing seawater temperatures and the mortality event are reasons for concern and increased vigilance. All are signs that intensifying regional environmental stressors may be reducing the protection that the isolation of the banks might have previously afforded. Continued monitoring and the access to research platforms such as the R/V Manta in order to respond to severe events will be critical to ensure data are available to understand and distinguish the drivers of ecosystem change in the northwestern Gulf of Mexico.
Dr. Michelle Johnston is the research ecologist at Flower Garden Banks National Marine Sanctuary. Elizabeth Weinberg is the social media coordinator and editor/writer for NOAA’s Office of National Marine Sanctuaries.