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121 C CALCIFIED ALGAE SEE ALGAE, CALCIFIED CAMOUFLAGE JOHN J. STACHOWICZ University of California, Davis Camouflage is a means by which animals avoid detection by other animals by blending in with the environment. As a result, the animal may either not be perceived at all or be perceived to be something it is not, and thus ignored or avoided. Although humans most often think of camou- flage as visual, many marine organisms have poorly developed visual systems, so chemically mediated camouflage is common as well. Both chemical and visual camouflage protect animals from predators as well as facilitate predation by “sit-and-wait” predators. Camouflage can be a major reason why some organisms are able to live in areas with very high densities of predators. GENERAL CONSIDERATIONS Predators are numerous in the sea, and the intensity of their consumption of prey provides a strong selective force favoring adapations to avoid consumption. These generally fall into two categories: avoidance of detection and avoidance of consumption once detected. Camouflage deals largely with avoidance of detection and can involve general background-matching strategies or very specific matching of particular substrates or organisms. Most examples are inferred examples of camouflage because they appear dif- ficult for humans to distinguish, but in a few cases careful field experiments have demonstrated the protective value of camouflage. The following examples of camouflage are divided into two categories: those that are fixed throughout the life of an animal (innate) and those that can be changed as an organism’s surroundings change (flexible). Innate Camouflage Among organisms that are of low mobility or are very faithful to a single site or habitat type, permanent structures or coloration may be adopted in order to match these backgrounds and avoid detection. For example, numerous limpet species excavate a “home scar” to which they return after foraging, spending the bulk of their life in the immediate vicinity of the scar. Such species often have shell colors, shapes, or textures that closely match the background of the home scars: the limpet Notoacmea incessa on the kelp Egregia, Lottia digitalis on the goose barnacle Pollicipes, and Lottia scabra on high intertidal rock surfaces are all excellent examples (Fig. A, B). Many nudibranchs are specialized feeders on one or a few closely related species of sessile invertebrates. Those that sequester toxic chemicals from their prey often adopt bright coloration to warn predators of their toxicity, while less toxic species may have morphologies that camouflage them on their host. For example, the nudibranch Dendronotus frondosus has finely branched cerata that are pigmented to look like the branches of Obelia, the hydroid on which it lives; Rostanga pulchra is completely orange and flattened and nearly impossible to distinguish from its host species, the encrusting orange sponge Ophlitaspongia pennata. Other species, such as the majid crab Mimulus foliatus, do not match their background per se but possess disruptive coloration such as large pigment blotches or alternating color patterns that break up the outline of the organism and make it difficult to distinguish. Absence of color altogether can also serve as camou- flage for animals that live in the open water. Many larvae of benthic invertebrates, as well as holoplanktonic copepods, are transparent or nearly so, reducing the ability of visually oriented predators such as fishes to locate and capture them. Similarly, planktonic predatory chaetognaths may be another example of the lack of coloration enhancing the ability of a predator to capture food, because some of these “arrow worms” are known to prey on visually-oriented fish larvae. Flexible Camouflage Strategies Being well camouflaged in one environment might make an animal more conspicuous when it moves to another environment. Thus, animals that are mobile or inhabit variable environments may need to alter their camouflage depending on their current location. A variety of crustaceans, molluscs, and fishes can change color in response to new surroundings, but the mode (and speed) with which they accomplish this feat varies dramatically. Some cephalopods, such as cuttlefish and octopuses, exert neuromuscular control over their color by contracting or expanding chromatophores—cells containing pigment—in their mantle tissue. This allows these animals to change color in a matter of seconds. Among fishes, a variety of sculpins, kelpfish, and gunnels are often well camouflaged. Some can rapidly change their coloration, while others do so more gradually as a result of the slow changing of the pigments that occur...
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