Species interactions through ontogeny: Effects of size-selective predation by red grouper on Caribbean spiny lobster in solution holes of Florida Bay

Demographic size- or stage-structure can result in significant heterogeneity in species interactions within populations and ontogenetic shifts in the strength or type of these interactions have important consequences for populations. In the case of the Caribbean spiny lobster, Panulirus argus (Latreille, 1804), and red grouper, Epinephelus morio (Valenciennes, 1928), both are important fishery species commonly found co-occurring in Florida Bay habitats. Red grouper are known to prey upon juvenile lobsters but karst solution holes excavated by red grouper often host large groups of lobsters. A combination of experiments tested the effect of red grouper on different lobster size classes to determine how this interaction changes through lobster ontogeny: red grouper were excluded from solution holes to test the effect of grouper presence on the abundance of each lobster size class; artificial dens were constructed to test the avoidance behaviors of small lobsters to red grouper; and a tethering experiment tested how lobster survival varied across size classes. Lobster abundance in solution holes with red grouper increased more than in holes where the grouper was removed (126% versus 16.9%), but this effect was strongest on adult and large immature lobsters. Experiments with artificial dens showed no effect of caged grouper presence on the abundance of small lobsters. Survival of tethered lobsters was lowest for small juveniles but again differed significantly between size classes. Overall, the distribution of lobsters in solution holes appears to be driven primarily by asymmetrical predation risk from red grouper through lobster ontogeny. Shifts in this interaction across life stages may play an important role in structuring the Caribbean spiny lobster population in Florida Bay.