MEPS 431:243-254 (2011)  -  DOI: https://doi.org/10.3354/meps09167

ABSTRACT: Red grouper Epinephelus morio act as ecosystem engineers by excavating depressions (or holes) in areas of flat sandy bottom, which provide suitable habitat for themselves and numerous other species. To understand the spatial extent of the holes, which serve as spawning habitat, and determine how that habitat changes, high-resolution multibeam sonar data were collected in overlapping areas in 2006 and 2009 within Steamboat Lumps Marine Reserve. This marine reserve was established in 2000 and is located in the eastern Gulf of Mexico. Vertical profiles of the holes visually identified from the multibeam data were extracted to characterize hole shape and determine changes in the height, width, and slope of each hole over time and space. Results from this analysis indicated an increase in hole density from 110 to 141 holes km^–2 from 2006 to 2009, respectively, with 181 holes detected in 2006 and 231 holes detected in 2009. Height and slope also increased between 2006 and 2009. The shape changes present in the 151 holes identified in the same location between the 2 survey years suggest that while hole shape varies due to red grouper maintenance, holes are constructed and maintained over time. The communication network determined from calculating a 70 m limit to red grouper acoustic communication showed an increase in communication overlap from 2006 to 2009, with over 95% of holes located within 70 m of their nearest neighbor. The increase in number and density of holes from 2006 to 2009 demonstrates that multiyear habitat mapping using active acoustic sonar is an effective method to monitor the presence and extent of red grouper spawning populations.

KEY WORDS: Red grouper · Epinephelus · Multibeam sonar · Marine reserves · Holes · Habitat engineer · Gulf of Mexico