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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 overlap- Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 431: 243-254, 2011 244 fisheries move offshore (Koslow et al. 2000. Thus, locating both mature fish populations and spawning habitats essential to population stability are critical considerations for fisheries management (Coleman et al. 1996, Crowder et al. 2000. To alleviate fishing pressure on grouper aggregations during spawning, 2 marine reserves covering 200 n miles 2 were established in June 2000 on the shelf break (50-120 m deep) of the northeastern Gulf of Mexi co ( Fig. 1): Madison Swanson (29°06' N to 29°17' N, 85°38' W to 85°50' W) and Steamboat Lumps (28°03' N to 28°14' N, 84°37' W to 84°48' W) Marine Reserves (Coleman et al. 2004).Two important red grouper behaviors have been documented recently in these marine reserves: (1) sediment excavation (Scanlon et al. 2005) and (2) sound production (Montie et al. 2011). In the present study, we focused on sediment excavation in Steamboat Lumps Marine Reserve and the potential for the 2-dimensional spacing of the holes to be within the known acoustic communication range of red grouper.In continental shelf areas with a sedimentary bottom, red grouper excavate large (5 to 25 m diameter) depressions (or holes) that they use as home territories (Scanlon et al. 2005). Red grouper excavate by carrying mouthfuls of sediment from within a depression to a short distance away and then depositing the sediment by flushing it through their opercles (Scanlon et al. 2005. In Steamboat Lumps Marine Reserve, holes are mainly observed to be dug and maintained by males who use this habitat as their home territory where they will spawn. Further inshore, juvenile (female) red grouper also exhibit this behavior ). Hole excavation is mainly found in areas where relief such as rock outcroppings is not present . Excavation uncovers loose rocks such as cemented carbonate nodules, which provide an important source of substrate and refuge for organisms in areas where it was not previously available (Scanlon et al. 2005). Habitat preferences based on substrate composition influence the distribution of many marine organisms, especially benthic species (Day et al. 1989. Additionally, the probability of observing other species is higher at holes where red grouper are present (active sites) compared to those where red grouper are not present (inactive sites) .Holes can be observed using high-resolution acoustic sonar (e.g. side-scan or multibeam sonar) (Scan lon et al. 2005, Allee et al. in press; Fig. 2). In addition, the swim bladder in fish, including red grouper, can be detected with sonar because acou...

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