Benthic Modification and Biotic Associations at Natural and Artificial Habitats Excavated by Red Grouper (Epinephelus morio) and Red Snapper (Lutjanus campechanus).

Munnelly, Ryan¹, Brett Pittinger², Sean Keenan², Theodore Switzer², ¹Coonamessett Farm Foundation, West Falmouth, MA, ²Fish and Wildlife Research Institute, Saint Petersburg, FL

Pockmarks are abundant seafloor features worldwide and, in West Florida Shelf waters <110 m deep, are thought to be sites of sediment excavation primarily by red grouper (Epinephelus morio), although red snapper (Lutjanus campechanus) also excavate sediment. During 2014–2017 side-scan sonar (445 kHz) was used to locate and deploy stereo-baited remote underwater video arrays within view of 202 such excavations in waters 17–110 m deep on the West Florida Shelf off the Florida Panhandle and Peninsula. Three excavation habitat classes included 73 isolated excavations on open sand, 74 associated with low-relief hard bottom, and 55 associated with artificial reefs. Physical characteristics of excavations varied between regions, among habitats, and with depth; mean diameter (± 1 SE) was 9.9 ± 0.3 m (3–24.6 m). Excavations not around artificial reefs contained 6.9 ± 0.5 m² (0–27.7 m²) of exposed rock, and epibenthic growth covered 33 ± 2% of the interiors. Members of 99 fish genera were encountered at excavations. Fish abundance was greatest at isolated excavations which showed similar evenness to excavated artificial reefs; diversity was higher at excavated low-relief hard bottom. Lutjanus campechanus was much more common in Panhandle waters, especially at excavated artificial reefs which had subsided 0.8 ± 0.1 vertical m below the seafloor (i.e. 48% ± 4% of the structure). These biotic and abiotic characteristics of excavations highlight the importance of E. morio’s ecosystem-engineering services and provide new insight on contributions of L. campechanus in creating or maintaining excavations at natural and anthropogenic habitats.