Red snapper excavate sediments around artificial reefs: observations of ecosystem-engineering behavior by a widely distributed lutjanid

Abstract

Hard substrate and vertical relief are limited habitat resources for reef-associated species in many regions. On the West Florida Shelf (WFS) of the Gulf of Mexico, red grouper Epinephelus morio act as ecosystem engineers by excavating sediments to expose limestone bedrock. Excavations can exceed 25 m in diameter and 2 m in depth and are among the most abundant WFS seafloor features at depths between 40 and 110 m. As part of a survey of hard-bottom habitats and associated reef fish assemblages, 1203 excavations were identified in WFS waters along the Florida Panhandle between 2014 and 2019. These excavations often contained subsided artificial reef material within their interior and infrequently included E. morio among observed fishes. We video-identified red snapper Lutjanus campechanus excavating sediments around 2 subsided artificial reefs in 2015 and 2017 for a total of approximately 56 min of excavation activity. A total of 24 excavation events were documented around a tire pile in 2015, and 5 were documented around a pyramid-shaped reef module in 2017. These observations help to explain the subsidence of artificial reefs and apparent excavation around their bases despite the scarcity of previously known excavating species. This suggests that L. campechanus might be ecosystem engineers on the WFS.