Caribbean Journal of Science, Vol. 39, No. 1, 116-127, 2003 Copyright 2003 College of Arts and Sciences University of Puerto Rico, Mayagu¨ez Density and Gorgonian Host-occupation Patterns by Flamingo Tongue Snails (Cyphoma gibbosum) in the Florida Keys MARK CHIAPPONE1,HELGA DIENES1,DIONE W. SWANSON2 AND STEVEN L. MILLER1 1Center for Marine Science and NOAA’s National Undersea Research Center, University of North Carolina at Wilmington, 515 Caribbean Drive, Key Largo, Florida 33037. [email protected] 2Division of Marine Biology and Fisheries, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149 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. INTRODUCTION Several hypotheses have been proposed to explain the factors that control C. gibbosum Gorgonians occur at their greatest diver- populations in typically prey-rich environ- sity and density in the wider Caribbean, ments: recruitment limitation (which has often exceeding reef-building corals in spe- yet to be adequately studied), predation by cies richness and colony density (Lasker hogfish (Lachnolaimus maximus) and other and Coffroth, 1983; Yoshioka and Yoshi- predators (Randall and Warmke, 1967; oka, 1989). Most gorgonian predators, in- Shoup, 1968), gorgonian structural de- cluding ovulid gastropods such as the fla- fenses (Lewis and Von Wallis, 1991; Van mingo tongue Cyphoma gibbosum Linnaeus, Alstyne and Paul, 1992; West, 1997), and cause only partial colony mortality, rang- chemical defenses (Pawlik et al., 1987; Sam- ing from consumption of the polyps to marco and Coll, 1992; Pawlik and Fenical, rasping of the axial coenochyme, some- 1989; Van Alstyne and Paul, 1992). Al- times to the depth of the proteinaceous axis though food abundance may be expected to (Harvell and Fenical, 1989; Neudecker, lead to significant prey preference, consid- 1985). erable variability exists in observed pat- Usually found in male and female pairs, terns of gorgonian host occupancy by C. C. gibbosum is a generalist browser and has gibbosum. These patterns range from pref- been the subject of numerous studies con- erence of several species (Birkeland and cerned with distribution and gorgonian oc- Gregory, 1975; Lasker et al., 1988) to occu- cupancy patterns in the Caribbean (e.g., pancy of gorgonian species in proportion to Birkeland and Gregory, 1975; Hazlett and their availability (Kinzie, 1970; Harvell and Bach, 1982; Harvell and Suchanek, 1987). Suchanek, 1987). The variability in experi- 116 HOST OCCUPATION BY FLAMINGO TONGUE SNAILS 117 mental results may reflect temporal or geo- Keys National Marine Sanctuary (NOAA, graphic differences in preferences or vari- 1996) and encompass many of the best- ability in prey quality (Lasker et al., 1988). developed offshore bank-barrier reefs. The Gorgonian defenses such as sclerite content no-fishing zones provide an opportunity to (Harvell and Suchanek, 1987; Van Alstyne evaluate the direct and indirect effects of and Paul, 1992; West, 1997) and secondary fishing in the Florida Keys (Bohnsack and metabolites (Hazlett and Bach, 1982; Pawlik Ault, 1996). Most of the offshore no-fishing et al., 1987; Sammarco and Coll, 1992) do zones extend seaward to only 13-15 m not clearly explain prey utilization pat- depth, with the fore reef environment terns. Cyphoma gibbosum apparently toler- within the zones characterized by high- ates high levels of gorgonian terpenes relief spur and groove topography or low- (Vrolijk and Targett, 1992) and may seques- relief hard-bottom (Chiappone and Sulli- ter these compounds in its mantle, like van, 1997). Acroporid corals historically other ovulid gastropods do (Coll et al., dominated the shallower areas of the fore 1983). reef in some locations, but they no longer This paper presents a large-scale assess- form extensive thickets of live colonies ment of the density and gorgonian host- (Dustan and Halas, 1987; Porter and Meier, occupation patterns of C. gibbosum in the 1992). The upper Keys region, excluding Florida Keys. While limited in temporal Pickles Reef sampled in this study, was for- scope, the study is the first that considers merly encompassed within the Key Largo multiple spatial scales, including compari- National Marine Sanctuary (established in sons between fished and protected areas 1975) and the Pennekamp Coral Reef State established in 1997 in the Florida Keys Na- Park (established in1960), which prohibited tional Marine Sanctuary. Two general ques- spear-fishing and collecting for marine tions are addressed. First, are there signifi- aquaria. The remaining area of the Florida cant differences in the distribution and Keys, from southwest of Molasses Reef to density of C. gibbosum in the Florida Keys Key West, excluding Looe Key, has not between shallow fore reef habitats, among been protected from spear-fishing and ma- geographic regions, and between fished rine aquarium collecting except within the and protected areas? Second, are spatial Sanctuary zones established in 1997. variations in gorgonian host occupancy re- lated to which gorgonian species are pre- ferred hosts, occupied in proportion to Survey methods their availability, or under-occupied by C. gibbosum? Cyphoma gibbosum densities, gorgonian densities, and gorgonian host-occupancy patterns were assessed by habitat type, ATERIALS AND METHODS M geographic region, and between protected Study area areas and fished sites in the Florida Keys (Table 1). Surveys were undertaken as part The Florida Keys are an archipelago of of an ongoing assessment of the commu- limestone islands extending approximately nity structure and condition of coral reef 360 km from Key Biscayne to the Dry Tor- and hard-bottom benthos in relation to the tugas (Fig. 1). Along the seaward edge or zoning plan for the Sanctuary (Miller et al., platform margin of the south Florida shelf in press). Sixty-three sites were surveyed is the reef tract, a semi-continuous series of from southwest of Key West to northern offshore bank-barrier reefs. Bank-barrier Key Largo during June to September 2001, reefs are separated from the islands by spanning over 200 km of the reef tract (Fig. Hawk Channel, a V-shaped basin5mto12 1). The shallow platform margin (1-7 m m deep that is dominated by sand, seagrass depth) was stratified with respect to two beds, and patch reefs (FDEP, 1998). habitat types (high-relief spur and groove Twenty-three no-fishing zones, most 1-2 and low-relief hard-bottom), three regional km2, were established in 1997 in the Florida sectors, and 10 of the Sanctuary’s23no- 118 M. CHIAPPONE ET AL. FIG. 1. Low-relief hard-bottom and spur and groove sites sampled for Cyphoma gibbosum on the Florida Keys shallow platform margin during June-September 2001. Closed dots (●) represent individual survey sites and zone types represent different name designations for no-fishing zones in the Florida Keys National Marine Sanctuary. fishing zones (Table 1). The fore reef habitat following procedures outlined in Cochran types sampled represent considerable vari- (1977). Spatial areas comprising each of the ability in geomorphology, topographic sampling strata were constructed in a geo- complexity, benthic community structure, graphical information system (GIS) with a and gorgonian density patterns. Sites open grid of 200 × 200 m “blocks” or sites that to fishing in the spur and groove habitat served as the primary sampling units. Cal- included Western Dry Rocks, Marker 32, culations of stratum areas and random al- Middle Sambo, No Name Reef, Pelican locations of sampling stations within strata Shoal, American Shoal, Delta Shoal, Pickles were performed with the GIS. Each site that Reef, and Sand Island. Sites open to fishing contained spur and groove or low-relief in the hard-bottom habitat included hard-bottom, as determined from FDEP Marker 26, Maryland Shoal,