Reference: Biol. Bull. 213: 135–140. (October 2007) © 2007 Marine Biological Laboratory

Antipredator Defense and Phenotypic Plasticity of Sclerites From Renilla muelleri, a Tropical Sea Pansy ETIENE E. G. CLAVICO, ALLAN T. DE SOUZA, BERNARDO A. P. DA GAMA, AND RENATO C. PEREIRA* Po´s-Graduac¸a˜o em Biologia Marinha, Universidade Federal Fluminense, PO Box 100.644, 24001-970, Nitero´i, Rio de Janeiro, Brazil

Abstract. Calcified sclerites are common in many benthic marine invertebrates, and despite their widespread occurrence, little is known about their ecological roles. Previous studies suggested that the sclerite composition of coral colonies may be altered in response to environmental cues such as predation and water motion. Furthermore, larger sclerites are thought to be more effective than small ones in deterring predators, while small sclerites may provide greater stiffness and resistance to deformation. The present study compared the length of the sclerites of the sea pansy Renilla muelleri from three depths in Guanabara Bay in southeastern Brazil. Our results show that sclerites are larger in deep-water specimens than in those from shallow water. Field assays were conducted in which sclerites from sea pansies at three depths were incorporated into artificial foods and offered to a natural assemblage of fish. These assays demonstrate that sclerites from R. muelleri from all three depths significantly reduced consumption by generalist carnivorous fishes. We conclude that R. muelleri uses skeletal elements not only to give the body its form but also as a defense against biotic threats.

1978; Sammarco and Coll, 1988, 1992). The subclass Octocorallia is a rich source of diterpenoids, whose biological activity includes deterrence of predators (Coll et al., 1982; Van Alstyne et al., 1994; Barsby and Kubanek, 2005). Various secondary metabolites are highly potent toxins, commonly associated with specific types of cnidarian nematocysts that perform two main functions: food capture and defense against sessile neighbors in competition for space (Barnes, 1974; Lang and Chornesky, 1990). Only a few reports suggest that nematocysts offer protection against predators (e.g., Stachowicz and Lindquist, 2000), and the frequency with which this protective function occurs among the Octocorallia is not yet known (Sammarco and Coll, 1992). The presence of calcitic sclerites may also serve as an antipredator defense (Harvell and Suchaneck, 1987; Sammarco et al., 1987; Harvell et al., 1988; Harvell and Fenical, 1989). The skeleton of many benthic invertebrates, including platyhelminth worms, sponges, molluscs, echinoderms, ascidians, and cnidarians, is composed of mineral-hardened spicules (Kingsley, 1984). Depending on the taxon, these spicules are composed of different chemical constituents and, in many cases, have different ecological functions (Bayer et al., 1983; Lewis and Wallis, 1991). The skeleton of sea pansies is typically composed of calcium carbonate with the presence of small amounts of phosphates of calcium, ammonium, or magnesium (Alonso, 1979). The sclerites of soft corals are thought to function primarily in structurally supporting colonies and in enhancing their rigidity (Koehl, 1982; Lewis and Wallis, 1991). For example, the sclerites in the gorgonian coral Briareum asbestinum act as skeletal support, conferring great stiffness and providing resistance to deformation (Wainwright et al., 1976; Koehl, 1982; Palumbi, 1986). Small sclerites in high

Introduction Sessile invertebrates may evade predators through an arsenal of chemical and physical defenses. For example, the evolutionary success of one group of sessile invertebrates— soft corals (Cnidaria, Alcyonacea)—living in areas of high predation and competition, such as in tropical regions, has been attributed to their production of significant amounts of secondary metabolites, especially terpenes (Tursch et al., Received 22 February 2007; accepted 21 May 2007. * To whom correspondence should be addressed. E-mail: renato. [email protected] 135

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densities would thus increase colony stiffness when compared to large sclerites (Koehl, 1982, 1986). Sclerite composition can vary along a water-depth gradient, such that colonies contain shorter and more densely packed sclerites as water motion increases (West, 1998), probably because small sclerites at high densities provide more surface area for tissue attachment and also leave smaller spaces composed merely of deformable soft matrix (Koehl, 1982, 1986). Variation in the sclerite composition of the colonies seems to be due to environmental cues such as predator damage, water motion, and light intensity (West, 1996, 1997). Despite the widespread occurrence of sclerites in benthic marine invertebrates, how they change in response to environmental factors and what role they play in physically protecting animals from predation are still largely unanswered questions. Not all available evidence corroborates the hypothesis that sclerites serve as a physical defense against predation. Van Alstyne et al. (1994) suggested that the primary function of sclerites in three species of the soft coral Sinularia is structural colony support, adding that defense could be efficiently achieved by secondary metabolites only. Another study proposed that ascidians do not rely on sclerites as a primary means of antipredator defense (Lindquist et al., 1992), and Chanas and Pawlik (1995) found that spicules from sponges were palatable to fish in laboratory and field assays. However, some studies suggest that octocorals possess mineral-hard sclerites that might serve as an antipredator defense (Sammarco et al., 1987; Harvell et al., 1988; Harvell and Fenical, 1989). Sclerites from temperate and tropical gorgonians, as well as from other species of tropical soft corals, may significantly deter fish feeding (Harvell et al., 1988). Additionally, spicules from Red Sea sponges deter predation by fish (Burns and Ilan, 2003). Sea pansies, anthozoan octocorals belonging to the genus Renilla, are conspicuous members of sublittoral soft-bottom communities, ranging from nearshore (2 m) to deeper (128 m) waters (Morin et al., 1985). The soft-bodied sea pansy Renilla muelleri Ko¨lliker, 1872, is brightly colored. Although they are found in embayed areas, sea pansies are more characteristically members of the subtidal fauna of shorelines exposed to ocean swell (Kastendiek, 1976). At Guanabara Bay, R. muelleri represents one of the dominant sessile invertebrates (Da Gama et al., 1995), and like most marine benthic invertebrates, it is exposed to predators at the sand-water interface. Although the specialist nudibranch Armina has been documented as the primary and co-adapted predator of R. muelleri (Eyster, 1981), at Guanabara Bay, invertivore fishes such as spotted goatfish Pseudupeneus maculatus (Bloch 1793) and wrasse Halichoeres poeyi (Steindachner 1867) bite the soft bottom, making them potential predators of R. muelleri.

Despite the great importance of sea pansies in benthic communities from this region and others worldwide, ecological studies with organisms from the genus Renilla are rare. Alonso (1979) proposed that R. muelleri sclerites provide both support and help in colony movements. Using laboratory feeding assays, Barsby and Kubanek (2005) identified briarane diterpenoids from the genus Renilla that protect the sea pansy from predation by fish and crabs. On the basis of preliminary observations, the current study compared the length and density of R. muelleri sclerites from three depths at Guanabara Bay to verify whether these characteristics differ between shallow and deep-water colonies of this octocoral. In addition, since Renilla spp. are susceptible to predation and since structural components of benthic marine invertebrates can aid in their defense against generalist consumers, we attempted to determine whether sclerites from R. muelleri could act as physical defenses against generalist consumers in the field.

Materials and Methods The colonies of Renilla muelleri used in this study were collected at Guanabara Bay, a prominent coastal bay that has an international reputation due to its historical importance and its scenic beauty (Paranhos et al., 1993). Located on the southeastern coast of Brazil (22°41⬘–23°06⬘S and 43°02⬘– 43°18⬘W) and surrounded by the second largest Brazilian city (Rio de Janeiro), the bay measures 30 km from south to north, with a 131-km perimeter, a surface area of 384 km2, and a water volume of 1.87 ⫻ 109 m3 (Kjerfve et al., 1997, 2001). To determine whether the size of sclerites of R. muelleri varies with water depth, 10 colonies of this octocoral were collected from each of three depths (shallow, medium, and deep waters, corresponding to depths of 3, 12, and 22 m, respectively). All samples were kept frozen at ⫺10°C until the beginning of all analyses. The total volume of each sample from the three depths was determined by water displacement in a graduated cylinder. The sclerite content was obtained by placing the colonies in 50-ml tubes containing 0.25 N NaOH, following the work of Alonso (1979). This solution was heated to boiling. The sclerites from each sample were rinsed at least five times with distilled water to remove any traces of NaOH, dried by heating at 100 °C, and weighed to determine the dry weight. Standard methods to obtain sclerites from sponges and other octocorals (e.g., West, 1997, 1998; Puglisi et al., 2000) were tried without success. Sclerites of these samples were first used to obtain measurements of sclerite sizes within colonies. To determine the length of sclerites, digital pictures of the sclerites from each colony were taken using a light microscope and then analyzed with the ImageJ image analysis program, ver. 1.30

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(Abramoff et al., 2004). A total of 285 sclerites from 30 colonies (10 from each depth) were measured. Field experiments and preparation of artificial foods were performed according to Pawlik et al. (1995). The sclerites from 20 ml of R. muelleri from each depth were extracted using the method described above. The sclerites from each sample (depth) were added to 0.625 g of carrageenan, 5 ml of tuna fish, and 15 ml of water to yield a final volume of 20 ml to reproduce the same concentration as found in the octocoral. To prepare pellets, the mixture was vigorously stirred and then poured into a rectangular mold that produced pellets measuring 1.0 ⫻ 0.5 ⫻ 0.5 cm each. Control pellets were made in the same way except without the addition of sclerites. Field assays were performed at Cabo Frio island, Arraial do Cabo (Rio de Janeiro State, 22°59⬘S– 42o00⬘W). Each trial set consisted of 20 ropes containing a pair of pellets (one control and one treatment) that were attached to the sea bottom (ca. 10 m depth) and exposed to generalist consumers during the time necessary to obtain measurable consumption (ca. 3 h). Differential consumption of pellets (i.e., percentage of mass eaten of each) was quantified. Whenever consumption of both treatments reached 100%, data were dismissed. Analysis of variance (ANOVA) and post hoc Tukey’s honestly significant difference (HSD) tests were used to identify differences in sclerite length in samples from different depths. The data were transformed using the square root of x ⫹ 0.5 (Zar, 1999) so that they met the requirements of normality (Shapiro Wilk⬘s W test, P ⫽ 0.11) and homogeneous variance (Cochran and Levene⬘s tests, P ⬎ 0.09). Data from single, dependent-choice experiments were analyzed using Wilcoxon tests, which are nonparametric equivalents to Student’s t tests for dependent samples, since the data were not normally distributed (Zar, 1999). Significance levels were a priori set at 5%. Results Quantification and measurement of sclerites of Renilla muelleri from the three depths Sclerite length significantly increased with depth (F2,282 ⫽ 41.278; P ⬍ 0.00001) (Fig 1). Sclerites were 57.7% longer (mean of 596.1 ␮m) in deep versus shallow waters (mean of 251.9 ␮m, Tukey, P ⫽ 0.00002) and 47% larger in intermediate (mean of 475.4 ␮m) versus shallow waters (Tukey, P ⫽ 0.01). Deep-water sclerites were 20% longer than those from intermediate-depth colonies (Tukey, P ⫽ 0.00002). On the other hand, density of sclerites in colonies did not vary significantly with depth (F2,27 ⫽ 2.3021; P ⫽ 0.12), with slightly higher densities at intermediate depth (0.2989 ⫾ 0.1161 g [mean ⫾ standard deviation] of sclerite dry weight per ml of colony) when compared to shallow (0.2337 ⫾ 0.0465 g䡠ml-1) or deep-water sea pansies (0.2302 ⫾ 0.0523 g䡠ml-1).

Figure 1. Comparison of the length of sclerites of Renilla muelleri from three depths at Guanabara Bay (means ⫾ standard deviations). Sclerite length was significantly different between all depths (ANOVA followed by Tukey test, see text).

Feeding assays Results of the field assays showed that artificial food containing the sclerites of R. muelleri (treatments) from three depths was significantly less consumed than the corresponding controls (Wilcoxon test, P ⬍ 0.003) (Fig 2). This result demonstrated that sclerites of this octocoral from three depths are active in defense against a diverse array of generalist fishes, including, in order of decreasing importance, Abudefduf saxatilis (Linnaeus, 1758), Haemulon aurolineatum Cuvier, 1829, Haemulon steindacneri (Jordan and Gilbert, 1882), Halichoeres poeyi (Steindachner, 1867), and Chaetodon striatus Linnaeus, 1758 (Ferreira et al., 2001, 2004). Discussion The results of this study indicate that sclerites from colonies of Renilla muelleri living in deep water are about 58% longer than sclerites from colonies in shallow waters, and 47% larger than those from colonies from intermediate depths. Ours is the first study to identify significant phenotypic plasticity in pennatulacean octocorals such as Renilla. Although our research corroborates previous results with the gorgonian coral Briareum asbestinum, in which colonies contained shorter sclerites at shallower sites and longer sclerites at deeper sites (West et al., 1993; West, 1998), our results on sclerite density are distinct. West (1998) found that along the depth gradient, sclerite composition varied such that colonies contained shorter and more densely packed sclerites as water motion increased. The author

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Figure 2. Effect of sclerites from Renilla muelleri from three depths on the feeding of generalist fishes in field assays. The boxes represent the interquartile range, with median values indicated by a dark square within the box and maximum and minimum values represented by vertical lines.

suggests that high densities of large sclerites could not be packed together (conferring optimal support and defenses, see West, 1998) without interfering with polyp function. In contrast, we found that the sclerite density of R. muelleri did not vary with depth. Sea pansy sclerites are typically 500-␮m-long calcium carbonate spicules resembling French baguettes (see Alonso, 1979); they vary in size but not in shape (data not shown). Variation in the size of sclerites with water depth may be related in part to their providing body support (Koehl, 1982, 1996; Palumbi, 1986). The high wave energy characteristic of shallow waters may damage tissues or even alter the population structure of certain species. Abiotic environmental factors such as light penetration and water motion can generate large-scale patterns of sclerite variability with depth (West, 1997), and both factors show some degree of correlation with these sclerite variations (West, 1996). Although the physical defense theory holds that skeletal elements not only stabilize the structure of an organism but also play a role in its defense (e.g., Burns and Ilan, 2003), this second role has remained controversial, especially for some underappreciated groups. The results of our field assays demonstrate that natural concentrations of sclerites from R. muelleri collected at three depths from Guanabara Bay defend sea pansies against generalist fishes, although sclerite length did not affect predators as predicted. Several studies have shown that skeletal structures from benthic organisms, including octocorals, are deterrents against generalist fishes (e.g., Harvell et al., 1988; Van Alstyne and Paul, 1992; West, 1998; Koh et al., 2000), but O’Neal and Pawlik (2002) did not find defensive activity from sclerites of most Caribbean gorgonian species, and

they attributed the variance among results to different assay techniques. For example, use of gravimetric versus volumetric techniques to measure sclerite concentration may alter results (Chanas and Pawlik, 1996; O’Neal and Pawlik, 2002). Our results, based on volumetric concentration, corroborate many other studies on the unpalatability of sclerites from soft corals that suggest that these structures are not tasty and that they improved physical defenses against fishes in field experiments. In addition, differences in palatability among skeletal structures of different marine invertebrates can be related to differences in chemical composition. Previous investigations clearly show that the presence of calcium carbonate can affect prey susceptibility to predation (Pennings and Paul, 1992; Schupp and Paul, 1994). A defensive role for calcified elements may be based on a chemical reaction in which calcium carbonate alters the pH in the gut of a predator (Hay et al., 1994). Therefore, Schupp and Paul (1994) suggested that the term “mineral defense” be used to distinguish this chemical effect from that of calcium carbonate’s action as a hardening agent. It is unlikely that the protection provided by sclerites from R. muelleri was due to chemical reactions with calcium carbonate, since the smallest sclerites from octocorals of the same genus (R. reniformis) did not render tissues in predation field assays unpalatable (data not shown). Few studies have correlated the defensive capacity of the sclerites with sclerite length and density. Using artificial food in feeding assays, West (1998) suggested that longer sclerites from the gorgonian Briareum asbestinum make this coral less palatable to predators than do short sclerites and that, with volume fraction held constant, longer sclerites were less palatable than short sclerites (West, 1998). Koh et al. (2000) showed that both the shape and concentration of the sclerites in a gorgonian coral influence their ability to deter predation. In contrast, our findings indicate that larger sclerites did not produce tissues that were less palatable to predators in field assays and that the presence of large and small sclerites with similar densities in sea pansies at Guanabara Bay provided antipredatory defense. Previous work (e.g., West, 1998) suggests that sclerite length rather than density is more important in determining the feeding behavior of predators. However, our results indicate that, at least for sea pansies from Guanabara Bay, the deterrent nature of sclerites from specimens from different depths is not related to either sclerite length or density, despite the high level of water motion and wave stress characteristic of shallow waters that could also select these characteristics. Acknowledgments The authors thank the staff of the Instituto de Estudos do Mar Almirante Paulo Moreira (IEAPM–Brazilian Navy) for

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support during field work. Thanks are due to CEL Ferreira for fish identification. BAPG and RCP thank CNPq (Brazilian National Research Council) for Research Productivity Fellowships, and EEGC thanks FAPERJ (Rio de Janeiro State Foundation for Research Support) for a Ph.D. fellowship.

Literature Cited Abramoff, M. D., P. J. Magelhaes, and S. J. Ram. 2004. Image processing with ImageJ. Biophotonics Int. 11: 36 – 42. Alonso, C. 1979. Estudio morfologico y biometrico de las espiculas de Renilla mu¨lleri Ko¨lliker 1872 (Anthozoa, Pennatulacea). Rev. Bras. Biol. 39: 827– 834. Barnes, R. D. 1974. Invertebrate Zoology. W. B. Saunders, Philadelphia. Bayer, F. M., M. Grasshoff, and J. Verseveldt. 1983. Illustrated Trilingual Glossary of Morphological and Anatomical Terms Applied to Octocorallia. E.J. Brill, Leiden. 75 pp. Barsby, T., and J. Kubanek. 2005. Isolation and structure elucidation of feeding deterrent diterpenoids from the sea pansy, Renilla reniformis. J. Nat. Prod. 68: 511–516. Burns, E., and M. Ilan. 2003. Comparison of anti-predatory defenses of Red Sea and Caribbean sponges. II. Physical defense. Mar. Ecol. Prog. Ser. 252: 115–123. Chanas, B., and J. R. Pawlik. 1995. Defenses of Caribbean sponges against predatory reef fish. II. Spicules, tissue toughness, and nutritional quality. Mar. Ecol. Prog. Ser. 127: 195–211. Chanas, B., and J. R. Pawlik. 1996. Does the skeleton of sponge provide a defense against predatory reef fish? Oecologia 107: 225–231. Coll, J. C., S. La Barre, P. W. Sammarco, W. T. Williams, and G. J. Bakus. 1982. Chemical defenses of soft corals (Coelenterata: Octocorallia) of the Great Barrier Reef: a study of comparative toxicities. Mar. Ecol. Prog. Ser. 8: 271–278. Da Gama, B. A. P., F. Batalha, and R. C. Pereira. 1995. Estudo populacional de Renilla reniformis (Pallas 1976) e Renilla muelleri Koliker, 1872 (Anthozoa, Pennatulacea) na Baı´a de Guanabara, Rio de Janeiro, Brasil. VI Colacmar Congresso Latinoamericano de Ciencias del Mar, Argentina. 86 pp. Eyster, L. S. 1981. Observations on the growth, reproduction and feeding of the nudibranch Armina tigrina. J. Molluscan Stud. 47: 171–181. Ferreira, C. E. L., J. E. A. Gonc¸alves and R. Coutinho. 2001. Community structure of fishes and habitat complexity on a tropical rocky shore. Environ. Biol. Fishes 61: 353–369. Ferreira, C. E. L., S. R. Floeter, J. L. Gasparini, B. P. Ferreira, and J. C. Joyeux. 2004. Trophic structure patterns of Brazilian reef fishes: a latitudinal comparison. J. Biogeogr. 31: 1093–1106. Harvell, C. D., and W. Fenical. 1989. Chemical and structural defenses in Caribbean gorgonians (Pseudopterogorgia spp.): intracolony localization of defense. Limnol. Oceanogr. 34: 382–389. Harvell, C. D., and T. H. Suchanec. 1987. Partial predation on tropical gorgonians by Cyphoma gibbosum. Mar. Ecol. Prog. Ser. 38: 37– 44. Harvell, C. D., W. Fenical, and C. H. Greene. 1988. Chemical and structural defenses of Caribbean gorgonians (Pseudopterogorgia spp). I. Development of an in situ feeding assay. Mar. Ecol. Prog. Ser. 49: 287–294. Hay, M. E., Q. E. Kappel, and W. Fenical. 1994. Synergisms in plant defense against herbivores: interactions of chemistry, calcification and plant quality. Ecology 75: 1714 –1726. Kastendiek, J. 1976. Behavior of the sea pansy Renilla kollikeri Pfeffer (Coelenterata: Penatulacea) and its influence on the distribution and biological interactions of the species. Biol. Bull. 151: 518 –537. Kingsley, R. J. 1984. Spicule formation in the invertebrates with special

139

reference to the gorgonian Leptogorgia virgulata. Am. Zool. 24: 883– 891. Kjerfve, B., C. H. A. Ribeiro, G. T. M. Dias, A. M. Filippo, and V. S. Quaresma. 1997. Oceanographic characteristcs of an impacted coastal bay: Baı´a de Guanabara, Rio de Janeiro, Brazil. Cont. Shelf. Res. 17: 1609 –1643. Kjerfve, B., L. D. Lacerda, and G. T. Dias. 2001. Baı´a de Guanabara, Rio de Janeiro, Brazil. Pp. 107–117 in Coastal Marine Ecosystems of Latin America, U. Seeliger and B. Kjerfve, eds. Springer Verlag, Berlin. Koehl, M. A. R. 1982. Mechanical design of spicule-reinforced tissue: stiffness. J. Exp. Biol. 98: 239 –267. Koehl, M. A. R. 1996. Mechanical design of sclerite-reinforced skeletons. Am. Zool. 36: 55A. Koh, L. L., N. K. C. Goh, L. M. Chou, and Y. W. Tan. 2000. Chemical and physical defenses of Singapore gorgonians (Octocorallia: Gorgonacea). J. Exp. Mar. Biol. Ecol. 251: 103–115. Lang, J. C., and E. K. Chornesky. 1990. Competition between scleractinian reef corals: a review of mechanisms and effects. Pp. 209 –252 in Ecosystems of the World: Coral Reefs, Z. Zubinsky, ed. Elsevier, Amsterdam. Lewis, J. C., and E. V. Wallis. 1991. The function of surface sclerites in gorgonians (Coelenterata, Octocorallia). Biol. Bull. 181: 275–288. Lindquist, N., M. E. Hay, and W. Fenical. 1992. Defenses of ascidians and their conspicuous larvae: adult vs. larval chemical defenses. Ecol. Monogr. 62: 547–568. Morin, J. G., J. E. Kastendiek, A. Harrington, and N. Davis. 1985. Organization and patterns of interactions in a subtidal sand community on an exposed coast. Mar. Ecol. Prog. Ser. 27: 163–185. O’Neal, W., and J. R. Pawlik. 2002. A reappraisal of the chemical and physical defenses of Caribbean gorgonian corals against predatory fishes. Mar. Ecol. Prog. Ser. 240: 117–126. Palumbi, S. R. 1986. How body plans limit acclimation: responses of a demosponge to wave force. Ecology 67: 208 –214. Paranhos, R., L. M. Mayr, and H. P. Lavrado. 1993. Temperature and salinity trends in Guanabara Bay (Brazil) from 1980 to 1990. Arq. Biol. Tecnol. 36: 685– 694. Pawlik, J. R., B. Chanas, R. J. Toonen, and W. Fenical. 1995. Defenses of Caribbean sponges against predatory reef fish. I. Chemical deterrence. Mar. Ecol. Prog. Ser. 127: 183–194. Pennings, S. C., and V. J. Paul. 1992. Effect of plant toughness, calcification and chemistry on herbivory by Dolabella auricularia. Ecology 73: 1606 –1619. Puglisi, M. P., V. J. Paul, and M. Slattery. 2000. Biogeographic comparisons of chemical and structural defenses of the pacific gorgonians Annella mollis and A. reticulata. Mar. Ecol. Prog. Ser. 207: 263–272. Sammarco, P. W., and J. C. Coll. 1988. The chemical ecology of alcyonarian corals (Coelenterata: Octocorallia). Pp. 87–116 in Bioorganic Marine Chemistry, Vol. 2, P. J. Scheuer, ed. Springer-Verlag, Berlin. Sammarco, P. W., and J. C. Coll. 1992. Chemical adaptations in the Octocorallia: evolutionary considerations. Mar. Ecol. Prog. Ser. 88: 93–104. Sammarco, P. W., S. Labarre, and J. C. Coll. 1987. Defensive strategies of soft corals (Coelenterata, Octocorallia) of the great-barrierreef. III. The relationship between ichthyotoxicity and morphology. Oecologia 74: 93–101. Schupp, P. J., and V. J. Paul. 1994. Calcium carbonate and secondary metabolites in tropical seaweeds: variable effects on herbivorous fishes. Ecology 75: 1172–1185. Stachowicz, J. J., and L. Lindquist. 2000. Hydroid defenses against predators: the importance of secondary metabolites versus nematocysts. Oecologia 124: 280 –288.

140

E. E. G. CLAVICO ET AL.

Tursch, B., J. C. Breakman, D. Dalose, and M. Kaisin. 1978. Terpenoids from coelenterates. Pp. 247–296 in Marine Natural Products: Chemical and Biological Perspectives, Vol. 2, P. J. Scheuer, ed. Academic Press, New York. Van Alstyne, K. L., and V. J. Paul. 1992. Chemical and structural antipredator deterrents in the sea fan Gorgonia ventalina: effects against generalist and specialist predators. Coral Reefs 11: 155–160. Van Alstyne, K. L., C. R. Wylie, V. J. Paul, and K. Meyer. 1992. Antipredator defenses in tropical Pacific soft corals (Coelenterata: Alcyonacea). I. Sclerites as defenses against generalist carnivorous fishes. Biol. Bull. 182: 231–240. Van Alstyne, K. L., C. R. Wylie, and V. J. Paul. 1994. Antipredator defenses in tropical Pacific soft corals (Coelenterata: Alcyonacea). II. The relative importance of chemical and structural defenses in three species of Sinularia. J. Exp. Mar. Biol. Ecol. 178: 17–34.

Wainwright, S. A., W. D. Biggs, J. D. Currey, and J. M. Gosline. 1976. Mechanical Design in Organisms. Edward Arnold, London. West, J. M. 1996. Skeletal variation in the Caribbean coral Briareum asbestinum (Gorgonacea): pattern and process across environmental gradients. Ph.D. dissertation, Cornell University, Ithaca, NY. West, J. M. 1997. Plasticity in the sclerites of a gorgonian coral: tests of water motion, light level and damage cues. Biol. Bull. 192: 279 –289. West, J. M. 1998. The dual role of sclerites in a gorgonian coral: conflicting functions of support and defense. Evol. Ecol. 12: 803– 821. West, J. M., C. D. Harvell, and A. M. Walls. 1993. Morphological plasticity in a gorgonian coral (Briareum asbestinum) over a depth cline. Mar. Ecol. Prog. Ser. 94: 61– 69. Zar, J. H. 1999. Biostatistical Analysis, 4th ed. Prentice-Hall, Englewood Cliffs, NJ.