Density and Gorgonian Host-occupation Patterns by Flamingo Tongue Snails (Cyphoma gibbosum) in the Florida Keys

Abstract

A large-scale assessment of the density and gorgonian host-occupation patterns of the ovulid gastropod Cyphoma gibbosum L. was conducted at 63 shallow (< 7 m), low-relief hard-bottom and spur and groove sites in the Florida Keys. Mean densities of C. gibbosum were not significantly different between habitat types, among geographic regions, or between fished and protected areas. Based on sample allocation analyses, spur and groove sites open to fishing in the lower Keys region yielded more C. gibbosum than expected. Most C. gibbosum occurred individually (58 %) or in pairs (31 %) on gorgonians, indicating more gregariousness than expected based on random distribution. Snails were counted on 127 gorgonians repre- senting 3 families and 12 species. Significant differences in gorgonian host-occupation were detected, with more Plexauridae and less Gorgoniidae occupied than expected. Eunicea tourneforti, Plexaura flexuosa, P. homomalla, and Pseudoplexaura porosa were occupied more than expected, while Gorgonia ventalina was occupied in proportion to its abundance. Pseudopterogorgia americana and other gorgonians were under- occupied, even when relatively abundant. Except for P. homomalla, C. gibbosum density was only weakly correlated with total gorgonian density and individual species densities. Spatial variations in C. gibbosum density are not readily explained by preferred gorgonian availability alone. While variable larval recruit- ment, post-settlement survival, and patchy gorgonian distribution may affect these patterns, differential predation pressure by fishes such as hogfish (Lachnolaimus maximus) could also partially explain the dis- tribution patterns of C. gibbosum in the Florida Keys.