Prevalence of ontogenetic changes in colour brightness among benthic invertebrates and their association with microhabitat shifts

This study examined 15 species of intertidal invertebrates to determine the pre valence of ontogenetic changes in body colour brightness, the influence of diet and sunlight on body colouration, and the relationship between shifts in brightness and in microhabitat use. Most species did not undergo substantial changes in brightness or pigmentation. Some degree of change could be detected by image analysis software in 11 of the 15 species, but changes in brightness sufficient to be detected by a human observer occurred in only 6 species, and changes in pigmentation were apparent in only 3 species. In a controlled experiment, shell brightness and pigmentation of hatchings of the snail Nucella ostrina were found to be phenotypically plastic, changing in response to exposure to sunlight but not to diets of mussels or barnacles. Ontogenetic shifts in brightness were not phylogenetically constrained, occurring in the 3 phyla represented in our study (Mollusca, Annelida, Arthropoda). Shifts in brightness and pigmentation to increasingly darker shells or exoskeletons were found to occur in all species that shifted from cryptic to exposed microhabitats during ontogeny; the size at which colour brightness shift occurs is closely matched with the size at which microhabitat shift occurs in 3 species for which such information is available. However, little or no ontogenetic shift in brightness was detected in motile species with partial or no microhabitat shift. The ontogenetic timing of colour shifts may therefore serve as a marker of a transition between ecologically distinct phases of life.

Related papers:

title: A Predator’s View of Animal Color Patterns
abstract: It has long been known that the general colors and tones of animals tend to match their backgrounds (E. Darwin, 1794; Poulton, 1890). The adaptive significance of this has been borne out in numerous experimental studies (DiCesnola, 1904; Sumner, 1934, 1935; Isley, 1938; Popham, 1942; ; Turner, 1961; Kettlewell, 1956, 1973; Kaufman, 1974; Wiklund, 1975; Curio, 1976). There is also a good understanding of warning coloration (Cott, 1940; Wickler, 1968; Edmunds, 1974; Rothschild, 1975). However, the determinants of color pattern are poorly known, although it is known in a general way that the patterns and forms of animals are similar to their backgrounds (Poulton, 1890; Thayer, 1909; Cott, 1940; Wickler, 1968; Robinson, 1969; Edmunds, 1974; Fogden and Fogden, 1974). It is the purpose of this paper to explore the factors that determine color patterns under various specific conditions. The basic assumption is that a color pattern must resemble a random sample of the background seen by predators in order to be cryptic, and must deviate from the background in one or more ways in order to be conspicuous. As a result, the actual pattern evolved in a particular place represents a compromise between factors which favor crypsis and those which favor conspicuous color patterns.

title: The Adaptiveness of Animal Colors
abstract: We understand few of the principles underlying the evolution of patterns or colors of animals. Hypotheses that explain coloration fall into three major categories: (1) physiological/structural functions of biochromes (molecules that absorb light differentially across the spectrum, (2) coloration that affects the animal's own vision, and (3) coloration that affects the animal's visibility to other animals-conspecifics and nonconspecifics.

title: Evolutionary significance of ontogenetic colour change in animals
abstract: Ontogenetic colour changes are non-reversible colour changes associated with normal progressive development of an individual of a species. This paper provides the first review of the evolutionary significance of this phenomenon in animals. Proximate mechanisms and environmental cues are briefly discussed and a conceptual framework for understanding the ultimate reasons for ontogenetic colour change is established. Changes in size, vulnerability, reproductive status, habitat and metabolism are often associated with ontogenetic colour change and can aid in understanding its adaptive significance. Neutral or non-adaptive ontogenetic colour changes due to phylogenetic inertia and developmental constraints are also considered. Existing studies of ontogenetic colour changes in marine invertebrates, terrestrial invertebrates, fish, amphibians, reptiles, birds and mammals are discussed within this framework. A need is identified for more experimental tests of hypotheses for the significance of ontogenetic colour change.

title: Physiological and morphological colour change in Antarctic krill, Euphausia superba: a field study in the Lazarev Sea
abstract: Antarctic krill, Euphausia superba, is very susceptible to harmful solar radiation because of its unique genetic setup. Exposure occurs in spring to autumn during vertical diel migration and during occasional daytime surface-swarming. We have investigated colour change in Antarctic krill, Euphausia superba, during summer and winter in the Lazarev Sea in response to ultraviolet radiation (UVR) and photosynthetically active radiation (PAR). Short-term physiological colour change and long-term (seasonal) morphological colour change are present. Both are facilitated by a single type of monochromatic red chromatophore, i.e. erythrophores, of 20–450 μm diameter. Superficial erythrophores cover large dorsal areas, especially above vital organs (brain, sinus glands), additional `profound' erythrophores cover internal organs (heart, gut, nerve cords). Short-term change in light regime causes rapid physiological colour change along dense bundles of microtubules: pigment disperses into chromorhizae upon exposure to PAR and UVA and to a lesser extent to UVB. Darkness leads to aggregation of pigment in the centre and hence blanching. There is no circadian rhythm in the dispersal state of erythrophores present in winter. Physiological colour change in adult krill is two to three times more rapid in summer than in winter. Furthermore, seasonal changes in light regime also result in a profound morphological colour change: in summer animals, abdominal astaxanthin concentration is 450% and erythrophore count is 250–480% higher than in winter krill. We conclude from our results, that pigmentation of E. superba serves in the protection from harmful solar radiation and is adapted to the varying diel and seasonal light conditions.

title: Substratum heterogeneity, crypsis, and colour polymorphism in an intertidal snail (Littorina mariae)
abstract: On the British and Irish coasts, Littorina mariae showed extensive shell colour variation; the brown morph, dark reticulata, was common in exposed conditions, and the bright yellow morph, citrina, ...

title: DOES VARIABLE COLORATION IN JUVENILE MARINE CRABS REDUCE RISK OF VISUAL PREDATION
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.

title: Phenotype-environment matching in the shore crab (Carcinus maenas)
abstract: The shore crab (Carcinus maenas) exhibits a range of carapace pattern polymorphisms, but little is known regarding their function or maintenance. If patterns represent some form of crypsis, then associations between carapace colouration and substrate are expected; to determine whether such relationships exist, frequency of crab morphs and quantity of substrate type were measured from fifteen 10×40 m2 quadrats at each of three sites along the southern shore of the Firth of Forth, Scotland. Five thousand one hundred and thirty-seven crabs and 3.6 km of line intercept transect data were collected during a 9-week period. Crab abundance, relative frequency of morphs and substrate type varied significantly among the three sites. Plain crabs were strongly associated with macro-algal substrates whereas patterned crabs were associated with mussel beds. This pronounced phenotype-environment matching, as well as various characteristics of the carapace patterns themselves, suggests that patterned crabs are cryptic on polychromatic backgrounds. The frequency of patterned crabs and the percentage of white pigment on the carapace both declined significantly with carapace width. The loss of pattern coincides with an ontogenetic shift in habitat use and we present evidence to suggest that individual crabs lose their pigment, rather than larger patterned crabs being preferentially removed from the population by predators. Throughout their life history, shore crabs encounter high variation in predation, food supply, and physical habitat; to survive they have evolved a strategy that includes elements of pattern polymorphism, crypsis, ontogenetic shifts, and plastic responses.

title: Ontogenetic shifts in resource allocation: colour change and allometric growth of defensive and reproductive structures in the Caribbean spiny lobster Panulirus argus
abstract: Resource allocation theory predicts a disproportionately large allocation of resources to defensive structures during early ontogeny in organisms that are subject to more intense predation at smaller than at larger body sizes. We tested this prediction on the Caribbean spiny lobster Panulirus argus, which exhibits a negative relationship between predation risk and body size with a high natural mortality of smaller individuals. Independent allometric growth analyses demonstrated that numerous defensive structures (e.g. orbital horns, segments supporting the antenna, the tail fan) display negative allometric growth throughout ontogeny. We interpret these findings as lobsters investing disproportionately more resources to defensive structures when small to improve survivorship. Similarly, we observed an ontogenetic shift in lobster colour pattern; small individuals (< 23 mm carapace length) that inhabit nursery grounds (preferably among red algae) displayed a disruptive pattern (camouflage), whereas larger juveniles displayed a bicolour pigmentation typical of adult lobsters. This shift in colour pattern further suggests that small lobsters employ cryptic coloration throughout their asocial algal stage. However, this cryptic coloration offers no advantage when lobsters grow larger and start dwelling in crevices. Other structures linked to reproduction (e.g. female pleopods and male pereopods) experienced either isometric or positive allometric growth throughout ontogeny. Our results support one of the main predictions of resource allocation theory and demonstrate ontogenetic shifts in defensive structures and coloration concomitantly with changes in lobster mortality risk mediated by size-dependent predation risk.  2012, ●●, ●●–●●.

title: THE ONTOGENETIC NICHE AND SPECIES INTERACTIONS IN SIZE-STRUCTURED POPULATIONS
abstract: Body size is manifestly one of the most important attributes of an organism from an ecological and evolutionary point of view. Size has a predominant influence on an animal's energetic requirements, its potential for resource exploitation, and its susceptibility to natural enemies. A large literature now exists on how physiological, life history, and population parameters scale with body dimensions (24, 131). The ecological literature on species interactions and the structure of animal communities also stresses the importance of body size. Differences in body size are a major means by which species avoid direct overlap in resource use (153), and size-selective predation can be a primary organizing force in some communities (20, 70). Size thus imposes important constraints on the manner in which an organism interacts with its environment and influences the strength, type, and symmetry of interactions with other species (152, 207). Paradoxically, ecologists have virtually ignored the implications of these observations for interactions among species that exhibit size-distributed populations. For instance, it has been often suggested that competing species

title: An ecological transition during juvenile life in a marine snail
abstract: Ecological shifts occurring after metamorphosis in benthic marine invertebrates have received much less attention than the more conspicuous transition occurring at metan~orphosis and settlement. It remains unclear whether postmetamorphic shifts occur simultaneously or at different times, and whether the shifts occur over brief, discrete periods or are extended or even continuous through juvenile life. The present study of the muricid gastropod Nucella emarginata exarmnes the ontogeny of \r.ulnerabillty to desiccation, of susceptibll~ty to hatchling predators, of shell coloration, and of distribution among microhabitats as a function of snail size. All the above parameters changed substantially over approximately the same size range. Individuals acquired the ability to survive direct exposure to desiccation for the duration of a low tide over the 3.1-6.5 mm shell length (SL) size range, and also became virtually invulnerable to hatchling predators when they reached 6.5 mm SL. The shift in mortality factors was paralleled by a change in shell colour over the 3-7 mm SL size range, and in distribution over the 3-8 mm SL size range. All shifts were therefore completed by the time individuals reached 8 mm, or by the age of -4 n ~ o based on growth rates in the laboratory. The coordination of these ecological changes in N. emarglnata over the 3-8 mm SL size range constitutes an ecological transition that partitions postinetamorphic life into 2 penods, early juvenile and late juvenile/adult, each with d~stinct selective environments and corresponding adaptive traits. A similar ontogenetic transition has also been documented in juvenile lobsters, and studies of juveniles of other species reveal that comparable ecological changes are common among benthic marine invertebrates. Interspecific variation is nevertheless expected in the exact nature and timing of the transition, particularly as a result of differences in initial juvenile size, growth rate, adult size, ability to learn, and motility.

title: ONTOGENETIC SHIFTS IN CARAPACE PATTERNING AND/OR COLOURATION IN INTERTIDAL AND SUBTIDAL BRACHYURAN CRABS
abstract: Some juvenile intertidal and subtidal crabs are known to exhibit carapace polymorphism, crypsis, or disruptive colours which are lost as the crabs mature, i.e. they undergo ontogenetic shifts in patterning and/or colouration. These patterns and colours are thought to protect young crabs from visual predators. The transformation is often dramatic and most likely refl ects a critical life-stage that is possibly unique to marine arthropods. Two main hypotheses have been proposed to explain changes in colouration as crabs grow: they no longer need such a defense as they become bigger and stronger or, they migrate from nursery habitats to areas where such patterns and colours do not confer protection. To identify the extent of ontogenetic shifts in intertidal and subtidal crab patterning and/or colouration, a database was assembled from the literature (primary and grey); from expert scientifi c opinions (via personal interviews and email correspondence); and website-derived observations from non-professionals worldwide.

title: Evidence for genetic control of pigmentation of shell and mantle edge in selected families of Pacific oysters, Crassostrea gigas
abstract: Three experimental cohorts of pedigreed oysters, each having gone through one or two generations of selection, were investigated for both shell and mantle edge pigmentation. Initial investigations showed the traits to be complex and best described as continuous. Average intraclass correlations coefficients (t) for all three cohorts of 0.766 and 0.666 (n=75) were obtained for shell and mantle edge pigmentation, respectively, indicating a high degree of genetic control. Block effects (depth at planting) were also significant in some cases, though trends were less obvious, and these effects only accounted for a maximum of 7.6% of the total observed phenotypic variation. Mantle edge pigmentation and shell pigmentation were positively correlated (P 0.09, n=75) in all but two cases (P=0.0400 and P=0.0359, n=75). This is the first report of a genetic effect on shell and mantle pigmentation in Crassostrea gigas. These findings have major implications for the manipulation of pigmentation as a desired trait in an oyster breeding program.

title: Morphological colour change in the American lobster (Homarus americanus) in response to background colour and UV light
abstract: American lobster (Homarus americanus) have a thick calcified cuticle, and do not exhibit rapid colour changes characteristic of other crustaceans. Thus, the plasticity of their coloration has been largely overlooked. Colour in lobsters is determined by the amount, location, and form of the carotenoid pigment astaxanthin, and it is possible for lobsters to alter colour by changing one of these characteristics of astaxanthin deposition. Here, short‐term colour variation in American lobster in response to environmental cues (background colour and ultraviolet (UV) light) was investigated in a laboratory experiment. Lobsters were reared in conditions controlling background colour (white, black) and UV light (present, absent). Digital photographic analysis was used to determine how these conditions influenced the luminescence (light or dark) of lobster colour, as well as the ratio of red to blue hues. Of the environmental variables considered within this experiment, UV light was the predominant factor, and caused lobsters to become darker in colour. In the absence of UV light, lobsters matched background colour, and turned darker in response to the darker background. Environmental matching has practical implications both for wild lobsters as they settle to the benthic habitat, and for enhancement programmes, to grow lobsters that are best suited for local habitats.

title: Experimental manipulation of shell color and morphology of the limpets Lottia asmi (Middendorff) and Lottia digitalis (Rathke) (Mollusca: Patellogastropoda)
abstract: We experimentally show that substratum can determine an individual patellogastropod's color and morphology. Lottia asmi (Middendorff), previously considered a high-domed, black stenotopic species on trochid gastropods, is similar to other northeastern Pacific limpet species with low profile and tessellated color patterns, when it is translocated to rock substrata. Lottia digitalis (Rathke), a highly variable species with at least two ecological variants that have been considered to be genetically determined, changes between these two forms when translocated from stalked barnacles to rocks. Color changes because the ingested pigments (algal, periostracal, etc.) and other materials (e.g., calcium carbonate) vary between substrata; morphological changes occur as responses to the topographical complexity and constraints of substrata. The geographical distribution of ecological variants of polytypic limpet species, and the ability to achieve cryptic coloration, may be determined by the geographic distributions of algae on which the limpets feed rather than by intrinsic characteristics of the limpets.

title: Juvenile colour polymorphism in the red rock crab, Cancer productus: patterns, causes, and possible adaptive significance.
abstract: Juveniles of the common red rock crab of the Northeastern Pacific, Cancer productus, display a stunning diversity of colours and patterns, while adults all have the same drab colouration. Although this is widely known, key questions remain: (1) Does the frequency of different juvenile colours or patterns vary among collection sites or seasonally? (2) Does juvenile colour polymorphism reflect genetic heterogeneity or phenotypic plasticity in response to variable environmental conditions? (3) Do juveniles of different colours or patterns prefer substrata of different heterogeneity or brightness? We therefore: (i) described the variation in colour and pattern of juvenile C. productus; (ii) tested for associations between colour/pattern morphs and crab size, collection site, and season, in the field; (iii) conducted preliminary tests for habitat preferences (background colour, substratum type, light level) of different colour/pattern morphs in laboratory experiments, and (iv) tested the effect of diet (mussels versus shrimp) and feeding rate (high versus low) on juvenile colour/pattern. We describe 30 phenotypes that embrace a wide range of colour and pattern variants. The proportions of these phenotypes did not vary significantly among four collection sites, but they did vary significantly with season: over the summer and fall, juvenile colour and pattern variation was gradually replaced by the uniform adult colouration. The number of crabs displaying adult colouration also increased with crab size. Laboratory experiments suggest no significant preferences of different juvenile morphs for different backgrounds, substrata, or light levels. Diet (mussels versus shrimp) and feeding frequency had no effect on colour/pattern. Collectively, these results, although limited in scope, are not consistent with two likely hypotheses that could explain the extensive colour and pattern variation in juvenile C. productus: (i) selection for background matching by different cryptic forms and (ii) direct effects of diet or feeding rate on colour or pattern. Most probably, the large variety of different juvenile morphs is a result of frequency-dependent selection in which abundant variants are attacked disproportionately often and rarer forms are favoured. Juvenile colour polymorphism in C. productus may reduce the vulnerability to visual predators, impede the formation of a search image, and consequently decrease the risk of predation during the juvenile stages.

title: Use of digital colour analysis to assess variation within individual adult American lobsters (Homarus americanus) and the process of addition of colour in white lobsters
abstract: A relatively low‐cost method using digital macro‐photography was developed to assess in vivo colour of American lobsters (Homarus americanus). Both R*G*B and Commission Internationale de l'Eclairage (CIE) L*a*b systems of colour analysis were used to investigate animal coloration over 11 body locations within each animal. Assuming that lightness (CIE‐L) is biologically important for American lobsters, this species was counter shaded and paired comparisons showed that different colour parameters were all highly correlated among all body locations with the exception of the ventral claw. Using a multiple forward stepwise regression of the five hues on CIE‐L, the hue Green was the most significant parameter accounting for 97% of the variation of CIE‐L. This methodology was then used to assess how dietary white American lobsters add colour to their shell when switched to a diet containing carotenoid. The rate of colour addition was proportional to the amount of carotenoid in the diet, and to the body location. This digital photographic method of colour analysis was useful in that a wide size range of samples could be assessed. All body areas were suitable for colour analysis although relatively flat and smooth locations were most practical.

title: Marine invertebrates of the Pacific Northwest
abstract: Now available in a paperback edition, updated with 30 pages of additions and corrections, this work provides a systematic treatment of almost every group of marine invertebrates of the Pacific Northwest. Close to 4,000 species are covered and many are illustrated by photographs or drawings. Developed over a period of more than 30 years by zoologists associated with the Friday Harbor Laboratories of the University of Washington and several other institutions, the keys, taxonomic lists, and bibliographies are relevant tonvertebrates of intertidal and shallow subtidal habitats between southern Oregon and the Queen Charlotte Islands of British Columbia. This book is essential for students of invertebrate zoology, marine biology, marine ecology, and fisheries ecology.

title: A new hermit crab (Decapoda: Anomura: Paguroidea: Paguridae) from the eastern North Pacific
abstract: A new intertidal species of the hermit crab genus Pagurus, recently discovered on the Olympic Peninsula of Washington, is described and illustrated. This species, Pagurus holmi n. sp., is compared and contrasted to other regional shallowwater species.

title: Distribution and dispersal of early juvenile snails: effectiveness of intertidal microhabitats as refuges and food sources
abstract: In Barkley Sound, British Columbia, Canada, newly hatched Nucella emarginata, a direct developing prosobranch gastropod, are almost exclusively located within 3 structurally complex microhabitats: the filamentous algae Cladophora columbiana, clusters of mussels Mytilus spp., and dense assemblages of the barnacle Semibalanus cariosus. When exposed to desiccation or predators for 4 to 5 h, mortality of hatchlings located in these microhabitats (1.7 to 36% mortality) was considerably lower than for individuals on open surfaces (99 to 100%). Also, food (prey species) in C. columbiana, mussel clusters, and S. cariosus microhab~tats was more abundant but of similar energetic value to that on open rock surfaces. The microhabitats used by early juvenile N. emarginata thus provide the double advantage of a considerably reduced risk of mortality and abundant prey. The means by which hatchlings disperse after emerging from their egg capsules were established by laboratory observations and by deployment of collectors in the field. Hatchlings do not actively initiate dispersal by drifting in the water column. Crawling is the usual means of travelling from the capsule to protective microhabitats, with hatchling crawling speed averaging only 3.7 mm min-' on smooth rock surfaces in the laboratory. The abundance and distribution of microhabitats that protect early juveniles could therefore be important determinants of the local abundance and distribution of N. emarginata populations. The use of protective microhabitats may be the key to survival through the vulnerable early juvenile period in many benthic marine organisms.

title: Ontogenetic changes in shell preferences and resource partitioning by the hermit crabs Pagurus hirsutiusculus and P. granosimanus
abstract: Ontogenetic shifts in resource use can serve to reduce mortality and intraspecific competition, but can also increase a population's likelihood of extinction. We examined the ontogeny of shell type (i.e. snail species) preferences as well as shell type usage in the field in 2 sympatric species of intertidal hermit crabs, Pagurus hirsutiusculus and P. granosimanus, on Vancouver Island, Canada. An experiment examining shell type preferences by 4 hermit crab size classes, spanning a broad range of juvenile and adult sizes, found that both species have well-defined shell type preferences throughout benthic life; shell type occupancy at 7 field sites was largely consistent with shell type preferences. In addition, shell type preferences in both species changed during ontogeny, in terms of the preferred shell types but also in the diversity of shell types that were used, which decreased with increasing crab size. Thus, as a cohort of hermit crabs grows from newly settled juveniles to full-sized adults, the availability of suitable shells will depend on different snail species; shell availability at different stages of ontogeny would thus be controlled by independent mechanisms. In addition, similar-sized hermit crabs of the 2 species mostly ignored the shell types used by the other species, a resource partitioning that would facilitate coexistence. If shell availability limits the local abundance of these hermit crab species, as previously suggested, our findings indicate they would be limited by different resources (i.e. shells produced by different snail species). The lack of correlation between the abundance estimates of the 2 species at our 7 field sites supports the hypothesis that the local abundance of P. hirsutiusculus and P. granosimanus is controlled by independent factors.

title: Feeding habits of newly hatched juveniles of an intertidal predatory gastropod, Nucella emarginata (Deshayes)
abstract: The feeding habits of juvenile Nucella emarginata ( = Thais emarginata), a marine prosobranch gastropod with direct development, were examined to determine when predatory feeding begins, and if ontogenetic shifts in mode of feeding occur. Most hatchlings did not attack live prey during the first 3 days after emerging from their egg capsule. By day 10, however, over 80% of the hatchlings had attacked prey. The late onset of predatory feeding appears to be ontogenetic, rather than a consequence of handling or experimental conditions. Hatchlings did not use alternate food types (mussel feces, algae, biofilm, or barnacle moults), as determined indirectly by growth, survival and organic content measurements of hatchlings. Once N. emarginata started attacking prey, six species of invertebrates which co-occur with the hatchlings in the field were consumed: three bivalves (Lasaea spp., Musculus taylori and Mytilus spp.) and three barnacles (Balanus glandula, Chthamalus dalli and Pollicipes polymerus). Hatchlings did not attack limpets (Lottia pelta and Lottia digitalis), a littorine (Littorina scutulata), the bivalve Hiatella arctica, or other hatchlings. In addition, hatchlings were able to survive for up to 120 days without food. Although no ontogenetic shift in mode of feeding was observed in young N. emarginata, at least two prey species consumed by hatchlings cease to be used during ontogeny. Possible reasons for the late onset of feeding are discussed.

title: Ontogenetic shift in stress tolerance thresholds of Mytilus trossulus: effects of desiccation and heat on juvenile mortality
abstract: We examined the sensitivity of newly settled Mytilus trossulus to heat and desiccation, as well as the ontogeny of sensitivity through the early benthic phase. Laboratory experiments were conducted to determine the sensitivity of mussels to the full range of temperatures and desiccation levels experienced in the field. Mussels of 1 to 2 mm shell length (SL) experienced a threshold of heat tolerance at 34°C and a threshold of desiccation tolerance at vapour pressure deficit levels of 1.01 kPa. Extended periods of temperatures reaching or exceeding lethal levels for newly settled M. trossulus occurred relatively rarely in Barkley Sound, British Columbia, Canada, whereas lethal levels of desiccation occurred often during the recruitment season and were usually sustained for several hours. Desiccation, therefore, appears to be a substantially greater threat to recently settled M. trossulus than heat. A final laboratory experiment characterized the changes in sensitivity to desiccation that occur as mussels increase in size. Mussels became highly tolerant to desiccation when they reached a size of 2 to 3 mm SL. This size closely corresponds to the size at which juvenile M. trossulus relocate from protective filamentous algal habitat to adult habitat, suggesting ontogenetic shifts in habitat use by juvenile M. trossulus are a response to changing sensitivity to desiccation. If so, the future survival of newly settled mussels, and thus possibly the local persistence of mussel populations, may depend upon the persistence of protective algal microhabitats under changing climate conditions.

title: Variation in the carapace pattern of juvenile Carcinus maenas
abstract: Juvenile shore crabs (Carcinus meanas L.) are highly variable with respect to carapace pattern; young crabs often have conspicuous patches of white or other pigment. Adult crabs, in contrast, are drab and usually very similar in pattern. It is probable that the patterns serve to make young crabs cryptic on certain backgrounds. Juvenile crabs of carapace widths lying between 5 and 15 mm were collected from a range of British shores (totalling 48). Pattern incidence was found to relate to two factors: the percentage of weed cover (mainly of fucoids) on the shore, and the amount of mud present. Shores of high weed cover, or with much mud present, had low frequencies of conspicuously patterned crabs. The presence of patterned crabs among the juvenile population, and their absence among adults, could result from differential visual predation removing patterned crabs progressively so that only unpatterned crabs would survive to adulthood. Alternatively, individual crabs could lose their conspicuous patterns with age. Evidence is presented in support of the latter hypothesis.

title: Effects of different light sources and illumination methods on growth and body color of shrimp Litopenaeus vannamei
abstract: Shrimps Litopenaeus vannamei with initial body weight of 2.108 +/- 0.036 g were sampled for specific growth rates (SGR) and body color measurements for 50 days under different light sources (incandescent lamp, IL; cool-white fluorescent lamp, FL; metal halide lamp, MHL; and control without lamp) and different illumination methods (illumination only in day, IOD, and illumination day and night, IDN). Body color of L. vannamei was measured according to the free astaxanthin concentration (FAC) of shrimp. The SGR, food intake (FI), feed conversion efficiency (FCE) and FAC of shrimps showed significant differences among the experimental treatment groups (P < 0.05). Maximum and minimum SGR occurred under IOD by MHL and IDN by FL, respectively (difference 56.34%). The FI of shrimp for the control group did not rank lowest among treatments, confirming that shrimp primarily use scent, not vision, to search for food. FI and FCE of shrimps were both the lowest among treatment groups under IDN by FL and growth was slow, thus FL is not a preferred light source for shrimp culture. Under IOD by MHL, shrimps had the highest FCE and the third highest FI among treatment groups ensuring rapid growth. FAC of shrimp were about 3.31 +/- 0.20 mg/kg. When under IOD by MHL and IDN by FL, FAC was significantly higher than the other treatments (P < 0.05). To summarize, when illuminated by MHL, L. vannamei had not only vivid body color due to high astaxanthin concentration but also rapid growth. Therefore, MHL is an appropriate indoor light source for shrimp super-intensive culture. SGR of shrimp was in significantly negative correlation to FAC of shrimp (P < 0.05). Thus, when FAC increased, SGR did not always follow, suggesting that the purpose of astaxanthin accumulation was not for growth promotion but for protection against intense light.

title: Ontogenetic shift in susceptibility to predators in juvenile northern abalone, Haliotis kamtschatkana
abstract: Predation has been suggested as a major cause of juvenile mortality in benthic marine invertebrates. However, the extent to which juveniles are susceptible to predators is unknown for most species, and it remains unclear to what extent ontogenetic shifts in susceptibility to predators are common among marine invertebrates. This study examined the northern abalone Haliotis kamtschatkana, a species listed as threatened in British Columbia, Canada. Our goals were to characterize the diversity and abundance of species that prey on juvenile abalone and determine if abalone experience an ontogenetic shift in susceptibility to predators. Juvenile H. kamtschatkana were found to be susceptible to a broad variety of predators: 14 of the 37 potential predator species to which we offered juvenile abalone (≤ 28 mm shell length (SL)) consumed at least one juvenile abalone. Four of those species (three crabs and one seastar) consumed ≥ 10% of the juvenile abalone that were offered in the laboratory. These species were present at field sites where abalone are found, indicating that they have the potential to be significant predators of juvenile H. kamtschatkana in the wild. The most abundant predators were small crabs, especially Lophopanopeus bellus (black-clawed crabs) and Scyra acutifrons (sharp-nosed crabs). Juvenile H. kamtschatkana also experienced a pronounced ontogenetic shift in susceptibility to predators. The risk of predation for juvenile H. kamtschatkana decreased rapidly with increasing body size, especially over the 12–13 mm SL size range. Susceptibility remained low beyond 13 mm SL, indicating relatively low and unchanging levels of predation risk once the individual reaches this size. Although abalone are susceptible to several species during the first 1–2 years of life, predator effects on juvenile abalone abundance and microhabitat use may largely be attributable to the influence of only 1 or 2 predator species that can only kill abalone

title: Why habitat architecture and color are important to shrimps living in pelagic Sargassum: use of camouflage and plant-part mimicry
abstract: Camouflage and plant-part mimicry, 2 forms of resemblance of animals to their habitat, were investigated for 2 species of shrimps living in pelagic Sarqassum natans (Linnaeus) Gaillon in the Sargasso Sea. We used field collections and laboratory experiments to correlate the size, shape, color, and behavior of Latreutes fucorum (Fabricius) and Hippolyte coerulescens (Fabricius) with the architecture and color of the Sargassum habitat (i.e. the number, size, shape and arrangement of structural components of the habitat). Components of the structural architecture of Sargassum and plastic plants were measured and related to shrimp number, body size and shape. Latreutes most resembled Sargassum fronds, while Hippolyte resembled the gas-filled bladders (vesicles). Behavioral observations showed that Latreutes characteristically clings to the fronds and Hippolyte to the main stalk and vesicles of Sargassurn plants. In habitat selection experiments, the shrimps were offered Sargassum and arhficial algae with hfferent architectures and colors. Both species were found in equal densities on Sargassum and artificial algae suggesting that food value was unimportant relative to habitat architecture. When offered a modified habitat architecture of Sargassurn, Latreutes preferred a 'fronds only' to a 'vesicles only' plant while the reverse was true for Hippolyte. When plastic plants wlth small and large fronds were offered, small Latreutes showed a significant preference for small-frond plants, while large shrimp showed no preference. This was also true in the presence of a predator. Latreutes chose yellow artificial plants significantly more than brown artificial plants but Hippolyte chose both plants equally. In general, small shrimps of both species tend to be solid-colored or transparent, while large shrimps have disruptive color patterns corresponding to their habitat. It may be that there is an ontogenetic shift from use of plant-part mimicry to camouflage. As shrimps outgrow the specific plant parts they mimic, they use color patterns to camouflage themselves and generally resemble the Sargassum habitat matrix. In this system, camouflage and plant-part mimicry may depend, in large part, on the size, shape and color of the shrimps relative to elements of the Sargassum habitat, and may change in importance as the shrimps grow larger. The importance of fish predation is discussed in relation to the shrimps and fishes found in Sargassum collections from this study.

title: Importance of Behavior and Morphological Traits for Controlling Body Temperature in Littorinid Snails
abstract: For organisms living in the intertidal zone, temperature is an important selective agent that can shape species distributions and drive phenotypic variation among populations. Littorinid snails, which occupy the upper limits of rocky shores and estuaries worldwide, often experience extreme high temperatures and prolonged aerial emersion during low tides, yet their robust physiology—coupled with morphological and behavioral traits—permits these gastropods to persist and exert strong grazing control over algal communities. We use a mechanistic heat-budget model to compare the effects of behavioral and morphological traits on the body temperatures of five species of littorinid snails under natural weather conditions. Model predictions and field experiments indicate that, for all five species, the relative contribution of shell color or sculpturing to temperature regulation is small, on the order of 0.2–2 °C, while behavioral choices such as removing the foot from the substratum or reorienting the shell can lower body temperatures by 2–4 °C on average. Temperatures in central California rarely exceeded the thermal tolerance limits of the local littorinid species during the study period, but at sites where snails are regularly exposed to extreme high temperatures, the functional significance of the tested traits may be important. The mechanistic approach used here provides the ability to gauge the importance of behavioral and morphological traits for controlling body temperature as species approach their physiological thresholds.

title: Shell colour variation in Littorina saxatilis Olivi (Prosobranchia: Littorinidae): a multi‐factor approach
abstract: The marine snail Littorina saxatilis is highly polymorphic for shell colour. It lives in the heterogeneous intertidal zone, where there are sharp transitions in a number of abiotic factors that may influence the relative fitness of morphs. We investigated the hypothesis of selected variation by relating the colour distribution to five factors (wave exposure, substratum, shore level, sex, snail age), and to interactions between them. We compared patterns from geographical areas in Sweden, Iceland and Russia. Cryptic morphs (tessellated and different dark colours) generally dominated (80–98%) while conspicuous morphs (white, yellow, red and banded) were less common (2–20%). The colour frequencies were often related to wave exposure, substratum and shore level. Frequencies rarely varied with age and never with sex. In order to test the assumption that the different colours are genetically determined we cross-bred snails from Iceland in the laboratory. Both the presence of bands and the ground colours of the shell were inherited, and we have tentative support for a one-locus two-allele model for banding. Our results support a model of selected inherited colour variation, involving a number of different selective agents, the importance of which may vary between populations on local and geographical scales.

title: Astaxanthin deposition in the cuticle of juvenile American lobster (Homarus americanus): implications for phenotypic and genotypic coloration
abstract: The phenotypic brownish-green color of an American lobster (Homarus americanus Milne-Edwards, 1837) is determined by genetic and dietary mechanisms. Diet influences color through the carotenoid astaxanthin. This pigment can appear red or blue depending if it is bound to protein, and the relative amounts of each form influence lobster color. Carotenoprotein formation was examined in sibling American lobsters rendered white by a diet low in astaxanthin, by feeding a diet containing 0, 55, 110, or 220 μg astaxanthin g−1 for 110 days beginning on 7 February 2004. The relative levels of red and blue in these lobsters were assessed through the analysis of digital photographs of the lobsters, which were taken monthly. The red/blue ratio was used to assess if free (red) or protein-bound astaxanthin (blue) was the dominant form in the lobsters, or if the two forms occurred in ratios allowing for natural coloration. Naturally colored lobsters developed only in the highest astaxanthin diet group, while lobsters fed the 55-μg diet were blue. Differences were observed among different parts of the body, and were presumed to be a function of cuticle thickness. However, within each diet treatment, some lobsters initially became red, suggesting an accumulation of free astaxanthin, while other lobsters initially became blue, suggesting an accumulation of protein-bound astaxanthin. This variation may be a result of differences in the uptake of astaxanthin, the rate of carotenoid-protein complexing, or in the total amount of protein available for binding. This variability is likely to be the key to understanding the underlying basis of genetically determined color in American lobsters.