Putting It To Work: New Study Looks at Spawning Aggregation Population Genetics

The largest known spawning aggregation of Nassau Grouper in the Caribbean, found in the Cayman Islands, is the focus of REEF's Grouper Moon Project. Photo by Jim Hellemn.

A new publication in the scientific journal, Coral Reefs, evaluates population genetics of spawning aggregations and the role of juvenile recruitment, from both local and external sources, in sustaining and increasing local aggregations. The study included information from REEF's Grouper Moon Project in the Cayman Islands.

Like many places throughout the Caribbean, Nassau Grouper spawning aggregations in the US Virgin Islands were overfished until their disappearance in the 1970s and 1980s. In the early 2000s, however, Nassau Grouper were found gathering at Grammanik Bank, USVI, a mesophotic coral reef adjacent to one of the extinct aggregation sites, and regulatory protective measures were implemented to protect this fledgling aggregation. The authors of this study addressed two objectives: 1) which factors (local vs. external recruitment) are important in shaping recovery of the USVI spawning aggregations, and 2) the impact of severe past overfishing on the genetic structure of the Gremmanik Bank aggregation. For this second objective, REEF Grouper Moon Project scientists provided genetic samples from individual Nassau Grouper taken from the Little Cayman spawning aggregation, a much larger and less impacted aggregation.

No population structure was detected between the USVI and Cayman spawning aggregations. Additionally, the USVI spawning population showed signs of a genetic bottleneck, typical of greatly reduced populations. These collective results suggest that external recruitment is an important driver of the USVI spawning aggregation recovery. These findings also provide a baseline for future genetic monitoring of the spawning aggregations. The paper, titled "The ups and downs of coral reef fishes: the genetic characteristics of a formerly severely overfished but currently recovering Nassau grouper fish spawning aggregation", was published earlier this month in the March 2016 issue of Coral Reefs. Grouper Moon scientist, Dr. Brice Semmens, was a co-author on the paper. To find out more about this study and to see a list of all publications that have included REEF projects, visit www.REEF.org/db/publications.

Design by Joanne Kidd, development by Ben Weintraub