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Notes Ecology, 82(10), 2001, pp. 2961–2967 q 2001 by the Ecological Society of America DOES VARIABLE COLORATION IN JUVENILE MARINE CRABS REDUCE RISK OF VISUAL PREDATION? ALVARO T. PALMA1 AND ROBERT S. STENECK University of Maine, Darling Marine Center, Walpole, Maine 04573 USA Abstract. We discovered that newly settled marine rock crabs, Cancer irroratus, exhibit a variety of non-adult colors early in life. This color polymorphism predominates in populations of minute juvenile crabs living in polychromatic habitats where it apparently renders them inconspicuous to visual predators such as fish. Experiments revealed lower frequencies of non-adult color morphs in monochromatic three-dimensional habitats with predators and polychromatic habitats from which predators were excluded. These patterns result from selective predation on visually contrasting color morphs. Adult crabs are monochromatic, conspicuous, and not associated with shelters. Both polymorphic newly settled and monochromatic large individuals occur in environments dominated by small predatory fish where larger adult crabs are at low risk of predation. Behavioral and visual crypsis may only be important early in life when post-settlement mortality is high, and survival at that stage determines recruitment and ultimately population densities. The well-known examples of camouflage among insects usually apply to adults who, unlike these marine counterparts, are small relative to their predators and thus remain vulnerable throughout their lives. Many other large marine crustaceans are cryptic only early in life, suggesting that this early developmental color polymorphism might be an important difference between marine and terrestrial arthropods. Key words: camouflage; Cancer irroratus; color polymorphism; color variants; crypsis; Gulf of Maine; predation; post-settlement; rock crabs; settlement; subtidal. INTRODUCTION The ecological and evolutionary success of many organisms depends on their ability to hide from predators. Myriad species of insects evolved remarkable ways to blend into their surroundings. For example, the peppered moth (Biston betularia) adapted chromatically to the pollution-blackened trees of England due to selective predation by birds on contrasting light moths (Kettlewell 1955, Majerus 1998). While such antipredator camouflage is well known among adult insects and small marine crustaceans (e.g., Hay et al. 1989, Hacker and Steneck 1990, Duffy and Hay 1994, Stachowicz and Hay 1999), similar patterns in large marine arthropods are rare. In marine systems, crustaceans are the most diverse group of arthropods. Among crustaceans, decapods such as crabs, lobsters, and shrimps comprise an ecologically and economically important component of Manuscript received 24 July 2000; revised 8 February 2001; accepted 2 March 2001. 1 Present address: Facultad de Ciencias, Universidad Católica de la Ssma. Concepción, Paicavi 3000, Casilla 297, Concepción, Chile. E-mail: [email protected]. many marine systems. Decapods are highly valued food for humans and other predators because of their high food value (caloric content). Prey size relative to predator size is critical to the susceptibility of prey. Since marine decapods are particularly vulnerable to predators at the time of and just after settlement, mechanisms that mediate predation then may be critically important to the demography and possibly the evolution of the species. Many studies have demonstrated strong habitat dependency among decapods that are small as adults, or are vulnerable to predators at the time of settlement. Examples include refuge dwelling decapods such as crayfish in freshwater (Stein and Magnuson 1976), stomatopods in the marine realm (Steger 1987), settling American lobsters (Wahle and Steneck 1992), stone crabs (Beck 1995), the tropical reef crabs Caphyra rotundifrons (Hay et al. 1989), mangrove crabs (Wilson 1989), and Mithrax crabs (Stachowicz and Hay 1996). Less well known than these examples of physical crypsis (the use of structural refuges) are the examples of visual crypsis or camouflage. In this study we document a previously unreported strategy of visual crypsis discovered among newly set- 2961 2962 NOTES Ecology, Vol. 82, No. 10 FIG. 1. (Right photo) Newly settled rock crabs (Cancer irroratus) on natural polychromatic shell hash substratum. (Left) Highlight of the same seven individuals. tled rock crabs (Cancer irroratus) of the western North Atlantic. We found a color polymorphic pattern (i.e., different colored individuals within a population) that may be important in reducing early post-settlement mortality for this species. We suspect that this strategy is more widespread than is currently recognized. Polymorphic juvenile rock crabs possess this trait only early in their benthic life. We speculate that this brief (weeks to months) developmental crypsis could be due to the relatively brief period of vulnerability of this species to predators. Unlike many insects, marine decapods can attain large size (e.g., over 20 kg for Homarus americanus; Wolff 1978) that renders them relatively immune to predators (e.g., Wahle 1992, Steneck 1997). Although the expression of color camouflage and mimicry is common and has been described for many small marine invertebrates (Atkinson and Warwick 1983, Hughes and Jones 1985, Mercurio et al. 1985, Cook 1986, Espoz et al. 1995) and other crustaceans in particular (Hogarth 1978, Buss and Iverson 1981, Bulnheim and Fava 1982, Main 1987, Hacker and Madin 1991, Guarino et al. 1993), few studies have considered developmental crypsis confined to juveniles undergoing a crucial ecological transition (but see Wicksten 1979, 1983, Pennings 1990, Stachowicz and Hay 1999). Cancer irroratus is a common large benthic brachyuran decapod in shallow environments of the western North Atlantic (Williams 1984). Post-larvae of this species settle indiscriminately into several types of substrata (sandy and rocky bottoms) at similar densities (Palma et al. 1999). High mortality rates at this stage result in the highest survivorship occurring in shelterproviding cobblestone habitats (Palma et al. 1998). Within this system, we discovered and quantified color polymorphism among newly settled crabs (i.e., individuals colored differently from adults) in both natural polychromatic and artificial monochromatic habitats (Fig. 1). We employed a standardized color classification scheme in which crabs colored differently than the drab brown adults were identified as white, yellow, tan, and dark brown. The color of individual crabs only changed between molts, which progressively decline in frequency after settlement (A. Palma, personal observation). The proportion of polymorphic individuals decreased with the size of individuals. If color variations among newly settled individuals confer protection through visual crypsis, we hypothesized that its frequency of occurrence would be greatest in polychromatic natural substrata. We tested this against settlement within manufactured monochromatic gray PVC settlement collectors that mimic the interstitial spatial geometry of cobblestone nursery habitats, but not their color. Adjacent controls were comprised of two natural substrata, shell hash and cobblestone. MATERIALS AND METHODS Because chromatic patterns vary with size we conducted all comparisons synchronously among recently settled cohorts. We operationally defined newly settled crabs as those with ,10-mm carapace width. Quantitative surveys of new settlers were made in eight sites along the central coast of Maine. Specific locations are given in Palma et al. (1999). At each site, two different natural substrata (cobblestone and coarse shell hash) were surveyed using scuba at depths of 10 m below MLW. Divers haphazardly tossed 0.5-m2 quadrats and all organisms and material present in each area was October 2001 NOTES 2963 FIG. 2. Frequency of the different color variants for individuals of Cancer irroratus collected in natural substrata (cobblestones and sand) in different size classes. Numbers above each graph represent the number of individuals quantified in each class. sampled using suction to a depth of about 20 cm (methods of Wahle and Steneck 1991, Palma et al. 1998). Newly settled individuals were collected during the settlement season (August–September) between 1994 and 1997. Throughout the study, parametric comparisons of abundance or proportion of individuals with color variants were analyzed, and transformations applied to ensure normality and homogeneity of variance. Experimental treatments were placed at randomly defined locations. Data of proportions or percentages, throughout this study, were subject to arcsin(square root) angular transformations (Zar 1999). Further details on study area, experimental design, and general methods are published elsewhere (Palma et al. 1998). Both abundance and the proportion of color variants among newly settled crabs were simultaneously quantified in natural substrata and in manufactured collectors that provided a monochromatic background while maintaining the structural complexity. Collectors were placed in several of the study sites throughout the settlement period. Collectors were 0.24-m2 square structures made of rows of 3-cm diameter gray PVC pipes spaced 1 cm apart and stacked three rows deep in tiers of alternating row direction. The stack was placed inside a wire basket lined with 1-mm mesh nylon screen (Palma et al. 1998). The effect of visual predators on the proportion of color variants among newly settled individuals was tested in the field. The predator-exclusion experiment was a two-way, fixed-factor design with substratum (cobblestones and sand) and 0.5-m2 cage treatment (total predator exclusion, open control, and roofed cage control) as factors, and proportion of color variants as response variable. There were five replicate plots for each of the six treatment combinations for a total of 30 plots. The experiment was surveyed twice; thus we performed a repeated-measures ANOVA. The final data matrix was not perfectly square because some data had to be excluded due to cage breakage. The effect of predators on the proportion of polychromatic newly settled individuals inside PVC collectors was also tested. Using the PVC collectors, a predator-exclusion experiment was implemented during the settlement period of 1998, between August and September. Ten collectors were covered with the same plastic 4-mm mesh screen and 10 were left uncovered. Collectors were randomly interspersed at the west side of Damariscove Island, in the same location in Maine where the previous exclusion experiment on natural substrate took place. By the end of September all collectors (with and without screen) were retrieved and all decapods quantified in the laboratory using a 2-mm mesh size sieve. RESULTS Newly settled crabs display a variety of colors that correspond with the variety found in their settlement habitat (Fig. 1). Over 70% of the newly settled crabs were non-adult colors (Fig. 2). Whereas .70% of individuals one year and older (.15 mm in carapace width) were adult brown in color (Fig. 2). The combined proportion of individuals with non-adult brown color was significantly greater in the smallest size class compared to any of the larger size classes (F5,99 5 8.542, P , 0.0001). To eliminate the potential confounding influence of body size with color change in our experiments (e.g., Fig. 2), we quantified color differentiation of only similar-sized newly settled individuals. The population density of new settlers of ;10 individuals/m2 was similar in all three substrata (cobblestone, shell hash, and PVC collectors; F41,2 5 0.141, P 5 0.869). However, the proportion of polymorphic color variants was significantly higher in the two natural polychromatic habitats compared to the artificial monochromatic substrata (F26,2 5 11.98, P , 0.001; Fig. 3). Although reduced color polymorphism occurs ontogenetically, the short 2964 NOTES Ecology, Vol. 82, No. 10 factor repeated-measures ANOVA comparing the joint effect of substratum and cage treatment. Pairwise comparisons for the different treatment and substrata combinations were performed using Tukey’s test (Fig. 4A, Table 1). A subsequent experiment using screen-covered and uncovered collectors tested the potential effect of predators on color polymorphism inside monochromatic PVC collectors. This time, polymorphism was significantly lower inside the monochromatic, predatorrich (uncovered) collectors (0.48 6 0.26 vs. 0.77 6 0.11; F1,16 5 7.87, P 5 0.013, Fig. 4B). DISCUSSION FIG. 3. Proportion of newly settled (#10 mm carapace width) individuals with non-adult color variants on natural (polychromatic cobblestones and sand) and artificial (monochromatic gray PVC collectors) substrata (61 SE). All treatments had the same post-settlement duration. Interrupted horizontal line below the figure denotes significant difference. duration deployment (,2 mo) of PVC collectors minimizes ontogenetic effects in this treatment. Since fish predators control the abundance of newly settled rock crabs (Palma et al. 1998), we used predatorexclusion cages at 10-m (MLW) depths where settlement rates were high (Palma et al. 1998). Cages were covered with plastic 4-mm mesh screen, so that only new settlers could enter. A significantly lower proportion of newly settled crabs with non-adult color were found inside the predator-exclusion cages irrespective of substrate, with no significant interactions in a two- Newly settled Cancer irroratus crabs display a spectrum of non-adult colors (Figs. 1, 2) that disappear as they grow. This transient polymorphic condition may be a bet-hedging strategy in a chromatically diverse and unpredictable world in which visual predators prowl. Since this species settles indiscriminately but suffers high rates of post-settlement mortality (Palma et al. 1998), the color pattern of the nursery habitats, if visual predators are present, can control the color morphs that survive. For example, a much lower percentage of color polymorphs survive in monochromatic habitats with predators than in those habitats where they are predator-free (Fig. 4B), presumably due to the higher predation rates on the several color morphs that contrast strongly against the monochromatic substrate. Conversely, a much higher percentage of color polymorphs survive in polychromatic, natural habitats with predators than in those habitats when they are predator free (Fig. 4A). Here local predation rates resulted in FIG. 4. (A) Proportion of newly settled (#10 mm carapace width) crabs with non-adult color variants in predator-exclusion, open control, and roofed-cage control polychromatic (natural substrate) cages (61 SE) for the two times the experiment was surveyed. Treatments had the same post-settlement duration. Given the lack of significance (Table 1) between polychromatic cobblestone and sand plots, these results were pooled. (B) Proportion of newly settled crabs with non-adult color variants in the monochromatic PVC-collector exclusion experiment under predator-exclusion and open conditions (61 SE). Interrupted horizontal lines at the top of each histogram indicate significant differences. NOTES October 2001 2965 TABLE 1. Results of the two-factor repeated-measures ANOVA for the exclusion of predators (Treatment) and sand or cobblestone plots (Substrate). The response variable is the proportion of individuals with non-adult color variants. df MS F P Between subjects Substrate Treatment Substrate 3 Treatment Error 1 2 2 16 0.008 0.502 0.262 0.121 0.062 4.159 2.169 0.806 0.035 0.147 Within subjects Trial Trial 3 Treatment Trial 3 Substrate Trial 3 Treatment 3 Substrate Error 1 2 1 2 16 0.001 0.041 0.002 0.503 0.203 0.003 0.203 0.008 2.477 0.959 0.818 0.931 0.116 Source colors that match their polychromatic habitat (Fig. 1). This newly discovered survival strategy of developmental crypsis in this species may contribute to its remarkable abundance in the Gulf of Maine (Palma et al. 1999). The mechanism by which this species undergoes changes in color morphs throughout its ontogeny is not known. However, multicolored post-settlers kept in the laboratory turned to an adult brown color after several molts over a period of several months. Marine ecology has undergone a paradigm shift in recent decades. Processes such as competition and predation among adults were once assumed to be the primary drivers of local demography and community structure (Paine 1969, Dayton 1975, Lubchenco 1978). More recently, however, ‘‘supply side’’ ecology (e.g., Underwood and Fairweather 1989) emphasizes processes affecting early settlement and post-settlement phases (Gaines and Roughgarden 1985, Doherty and Fowler 1994). If strong interactions early in life diminish ontogenetically, due to increased body size, then the specific mediating characteristics may be important only during early benthic stages. Our study suggests that developmental crypsis confers an advantage to newly settled rock crabs in environments with small visual predators. Predator–prey size scaling may be different in marine and terrestrial systems. Whereas large crabs may pass through a brief period of predator vulnerability, most insects are small and remain vulnerable throughout their life. The phenomenon of color polymorphic new settlers and monochromatic large crabs occurs in environments dominated by small predatory fish (Hacunda 1981, Malpass 1992, Wahle and Steneck 1992, Steneck 1997), where larger crabs are less threatened. Undoubtedly large predatory fish were much more abundant in historic and prehistoric times in coastal areas of the Western North Atlantic (Witman and Sebens 1992, Steneck 1997). Thus it is possible that until recently (i.e., the past century) large fish predators could have had a stronger impact on larger rock crabs than they do today. Nevertheless, small crabs have probably always been most vulnerable to the widest range of fish predators in the Gulf of Maine. It is unknown if the developmental crypsis we describe may have persisted later into a crab’s ontogeny when larger predators were more common. We do not know why color polymorphism is lost as crabs mature. It is possible that it is a ‘‘costly’’ condition to maintain. However the advantages of light color morphs (e.g., white and yellow) that mimic shell chips (Fig. 1) are lost at large sizes since most rocks of adult crab size are drab over the range of this species (A. Palma, personal observation). Crypsis is found among other decapods that are bite sized. Small crabs remain cryptic through all developmental stages. For example, the chip crab, Heterocrypta granulata, is camouflaged to resemble shellhash. It ‘‘. . . so closely resembles the bits of shell and rock fragments among which it hides that it is difficult to know how common it might be (Gosner 1978).’’ Other small decapods such as small adult shrimp mimic the brown alga Sargassum in the Sargasso Sea (Hacker and Madin 1991). However, among relatively large decapods such as lobsters, crypsis is only known early in life. The transparent phyllosoma phase may protect spiny lobster post-larvae by minimizing contrast with the pelagic realm in which they develop (Herrnkind and Butler 1986). Several species of newly settled spiny lobsters are cryptically colored to blend in with the algal habitats in which they settle. Examples include Panulirus argus (Marx and Herrnkind 1985), P. japonicus (Yoshimura and Yamakawa 1988), and P. cygnus (Pearce and Phillips 1994). The American lobster (and other clawed lobsters) are not visually cryptic but are physically cryptic living their first several benthic years within small, shelter-providing spaces where they are relatively safe from predators (Wahle and Steneck 1992). Much smaller decapods such as freshwater NOTES 2966 crayfish (Stein and Magnuson 1976) and marine stomatopods remain hidden within their shelters during their entire life (Steger 1987). Despite their staggering diversity, insects are small. Arguably, their small body size results from phyletic constraints on respiration, which is limited by trachea and an open circulatory system. More importantly, most insects are small relative to their predators and thus, as a group, they do not typically outgrow their vulnerability the way large marine decapod crustaceans can. This may be a fundamental ecological distinction between arthropods of the terrestrial realm and some marine groups. Because body-size-related niche shifts are so great among some large decapods (e.g., Wahle 1992), the rock crab–insect analog may only apply to insect-sized baby crabs. ACKNOWLEDGMENTS We are thankful for the valuable help in the field and laboratory provided by several interns between 1994 and 1998. We thank the University of Maine’s Darling Marine Center for its facilities and help from its support staff. The ideas within this manuscript were greatly improved by the helpful comments of M. Bertness, M. Fogarty, R. Wahle, L. Mayer, L. Watling, S. Zimsen, P. Marquet, M. Fernandez, and F. Labra. This research was also supported by NOAA/NURC at University of Connecticut at Avery Point and University of Maine/University of New Hampshire Sea Grant Program to R.S.S. A.T.P. also acknowledges the support of a postdoctoral grant (Fondecyt No. 3990032) while working on this manuscript. This is contribution No. 365 to the Darling Marine Center. LITERATURE CITED Atkinson, W. D., and T. Warwick. 1983. The role of selection in the colour polymorphism of Littorina rudis and Littorina arcana Hannaford-Ellis (Prosobranchia: Littorinidae). Biological Journal of the Linnean Society 20:137–151. Beck, M. W. 1995. Size-specific shelter limitation in stone crabs: a test of the demographic bottleneck hypothesis. Ecology 76:968–980. Bulnheim, H.-P., and G. Fava. 1982. Colour polymorphism and genetic variation in Idotea baltica populations from the Adriatic Sea and Baltic Sea. Genetica 59:177–190. Buss, L. W., and E. W. Iverson. 1981. A new genus and species of Sphaeromatidae (Crustacea: Isopoda) with experiments and observations on its reproductive biology, interspecific interactions and color polymorphisms. Postilla 184:1–23. Cook, L. M. 1986. Site selection in a polymorphic mangrove snail. Biological Journal of the Linnean Society 29:101– 113. Dayton, P. K. 1975. Experimental evaluation of ecological dominance in a rocky intertidal community. Ecological Monographs 45:137–159. Doherty, P., and T. Fowler. 1994. An empirical test of recruitment limitation in a coral reef fish. Science 263:935– 939. Duffy, J. E., and M. E. Hay. 1994. Herbivore resistance to seaweed chemical defense: the roles of mobility and predation risk. Ecology 75:1304–1319. Espoz, C., G. Guzmán, and J. C. Castilla. 1995. The lichen Thelidium litorale on shell of intertidal limpets: a case of Ecology, Vol. 82, No. 10 lichen-mediated cryptic mimicry. Marine Ecology Progress Series 119:191–197. Gaines, S., and J. Roughgarden. 1985. Larval settlement rate: a leading determinant of structure in an ecological community of the marine intertidal zone. Proceedings of the National Academy of Science USA 82:3707–3711. Gosner, K. L. 1978. A field guide to the Atlantic seashore. The Peterson Field Guide Series. Houghton Mifflin, Boston, Massachusetts, USA. Guarino, S. M., C. Gambardella, M. Ianniruberto, and M. De Nicola. 1993. Colour polymorphisms in Idotea baltica from the Bay of Naples and its ecological significance. Journal of Marine Biology Association UK 73:785–794. Hacker, S. D., and L. P. Madin. 1991. Why habitat architecture and color are important to shrimp living in pelagic Sargassum: use of camouflage and plant-part mimicry. Marine Ecology Progress Series 70:143–155. Hacker, S. D., and R. S. Steneck. 1990. Habitat architecture and the abundance and body-size-dependent habitat selection of a phytal amphipod. Ecology 71:2269–2285. Hacunda, J. S. 1981. Trophic relationships among demersal fishes in a coastal area of the Gulf of Maine. Fisheries Bulletin 79:775–788. Hay, M. E., J. R. Pawlik, J. E. Duffy, and W. Fenical. 1989. Seaweed–herbivore–predator interactions: host-plant specialization reduces predation on small herbivores. Oecologia 81:418–427. Herrnkind, W. F., and M. J. Butler IV. 1986. Factors regulating postlarval settlement and juvenile microhabitat use by spiny lobsters Panulirus argus. Marine Ecology Progress Series 34:23–30. Hogarth, P. J. 1978. Variation in the carapace pattern of juvenile Carcinus maenas. Marine Biology 44:337–343. Hughes, J. M., and M. P. Jones. 1985. Shell colour polymorphism in a mangrove snail Littorina sp. (Prosobranchia: Littorinidae). Biological Journal of the Linnean Society 25: 365–378. Kettlewell, H. B. D. 1955. Selection experiments on industrial melanisms in the Lepidoptera. Heredity 9:323–342. Lubchenco, J. 1978. Plant species diversity in a marine intertidal community, importance of herbivore food preference and algal competitive abilities. American Naturalist 112:23–39. Main, K. L. 1987. Predator avoidance in seagrass meadows: prey behavior, microhabitat selection, and cryptic coloration. Ecology 68:170–180. Majerus, M. E. N. 1998. Melanisms: evolution in action. Oxford University Press, New York, New York, USA. Malpass, W. J. 1992. The ecology and resource use patterns of small, benthic, predatory fishes in rocky, nearshore habitats of the Gulf of Maine, USA. Thesis. University of Maine, Orono, Maine, USA. Marx, J. M., and W. F. Herrnkind. 1985. Macroalgae (Rhodophyta: Laurencia spp) as habitat for young juvenile spiny lobsters, Panulirus argus. Bulletin of Marine Sciences 36: 423–431. Mercurio, K. S., A. R. Palmer, and R. B. Lowell. 1985. Predator-mediated microhabitat partitioning by two species of visually cryptic, intertidal limpets. Ecology 66:1417–1425. Paine, R. T. 1969. The Pisaster–Tegula interaction: prey patches, predator food preferences and intertidal community structure. Ecology 50:950–61. Palma, A. T., R. S. Steneck, and C. Wilson. 1999. Settlementdriven, multiscale demographic patterns of large benthic decapods in the Gulf of Maine. Journal of Experimental Marine Biology and Ecology 241:107–136. Palma, A. T., R. A. Wahle, and R. S. Steneck. 1998. Different October 2001 NOTES early post-settlement strategies between American lobsters Homarus americanus and rock crabs Cancer irroratus in the Gulf of Maine. Marine Ecology Progress Series 162: 215–225. Pearce, A. F., and B. F. Phillips. 1994. Oceanic processes, puerulus settlement and recruitment of the Western rock lobster Panulirus cygnus. Pages 279–303 in P. W. Sammarco and M. L. Heron, editors. Coastal and Estuarine studies; the bio-physics of marine larval dispersal. American Geophysical Union, Washington, D.C., USA. Pennings, S. C. 1990. Size-related shifts in herbivory: specialization in the sea hare Aplysia californica Cooper. Journal of Experimental Marine Biology and Ecology 142:43– 61. Stachowicz, J. J., and M. E. Hay. 1996. Facultative mutualism between an herbivorous crab and a coralline alga: advantages of eating noxious seaweeds. Oecologia 105:377–387. Stachowicz, J. J., and M. E. Hay. 1999. Reducing predation through chemically mediated camouflage: indirect effects of plant defenses on herbivores. Ecology 80:495–509. Steger, R. 1987. Effects of refuges and recruitment on gondodactylid stomatopods, a guild of mobile prey. Ecology 68:1520–1533. Stein, R. A., and J. J. Magnuson. 1976. Behavioral response of crayfish to a fish predator. Ecology 57:751–761. Steneck, R. S. 1997. Fisheries-induced biological changes to the structure and function of the Gulf of Maine Ecosystem. Plenary Paper. Pages 151–165 in G. T. Wallace and E. F. Braasch, editors. Proceedings of the Gulf of Maine Ecosystem Dynamics Scientific Symposium and Workshop. RARGOM Report, 91–1. Regional Association for Research on the Gulf of Maine. Hanover, New Hampshire, USA. Underwood, A. J., and P. G. Fairweather. 1989. Supply-side 2967 ecology and benthic marine assemblages. Trends in Ecology and Evolution 4:16–19. Wahle, R. A. 1992. Body-size dependent anti-predator mechanisms of the American lobster. Oikos 63:52–60. Wahle, R. A., and R. S. Steneck. 1991. Recruitment habitats and nursery grounds of the American lobster (Homarus americanus Milne Edwards): a demographic bottleneck? Marine Ecology Progress Series 69:231–243. Wahle, R. A., and R. S. Steneck. 1992. Habitat restrictions in early benthic life: experiments on habitat selection and in situ predation with the American lobster. Journal of Experimental Marine Biology and Ecology 157:91–114. Wicksten, M. K. 1979. Decorating behavior in Loxorhynchus crispatus Stimpson and Loxorhynchus grandis Stimpson (Brachyura, Majidae). Crustaceana 5 (Supplement):37–46. Wicksten, M. K. 1983. Camouflage in marine invertebrates. Oceanography and Marine Biology, An Annual Review 21: 177–193. Williams, A. B. 1984. Shrimps, lobsters, and crabs of the Atlantic coast of the eastern United States, Maine to Florida. Smithsonian Institution Press, Washington, D.C., USA. Wilson, K. A. 1989. Ecology of mangrove crabs, physical factors and refuges. Bulletin of Marine Sciences 44:263– 273. Witman, J. D., and K. P. Sebens. 1992. Regional variation in fish predation intensity: a historical perspective in the Gulf of Maine. Oecologia 90:305–315. Wolff, T. 1978. Maximum size of lobsters (Homarus) Decapoda, Nephropideae. Crustaceana 23:1–14. Yoshimura, T., and H. Yamakawa. 1988. Microhabitat and behavior of settled pueruli and juveniles of the Japanese spiny lobster Panulirus japonicus at Kominato, Japan. Journal of Crustacean Biology 8:524–531. Zar, J. H. 1999. Biostatistical analysis. Prentice-Hall, Upper Saddle River, New Jersey, USA.