Habitat Manipulation by Grouper in South Florida

Red grouper (Epinephelus morio) and goliath grouper (Epinephelus itajara) in south Florida has each been observed manipulating habitat through sediment and debris removal.  Red grouper excavate sediment filled limestone solution holes by scooping sediment and debris into their gullar cavity and ejecting it away from the hole.  Goliath grouper use their caudal fin to fan out crevices under natural and artificial reefs.  In both cases, we have observed higher diversity of organisms associated with manipulated habitats compared to when groupers are absent. 

During the summers of 2010 and 2011, juvenile red grouper excavations in Florida Bay were investigated.  Excavating activity by red grouper creates complex benthic habitat where little otherwise exists.  Exposed holes are colonized by numerous fishes and invertebrates, including economically important species like the Caribbean spiny lobster (Panulirus argus) multiple species of snapper (Genus Lutjanus).  At three locations north of Marathon, FL, we enumerated the abundance and diversity of motile fauna, sessile invertebrates, and benthic cover at each active excavation.  When compared to other complex structure found at the same locations, both the abundance and diversity of organisms was higher at active red grouper excavations.  Experimental manipulations of excavation associated communities conducted during summer 2011 will quantify the strengths of interactions between community members and begin to describe the mechanism that regulates these faunal communities. 

The diversity and abundance of reef fishes at reefs with goliath grouper showed a significant positive correlation with goliath grouper density.  Although we have yet to show that habitat manipulation by goliath groupers is the mechanism driving this pattern, we suspect that goliath groupers play an active role in the creation of heterogenous habitat which in turn positively influences local species richness.  Further study into the patterns of abundance and distribution shown here are imperative for understanding the mechanisms which regulate marine faunal communities.