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  Predators & defenses
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  Camouflage
 

Defenses of asteroids include camouflage, considered here, and SPINES & OSSICLES, PEDICELLARIAE, ESCAPE BY CRAWLING, RIGHTING RESPONSE, DISTASTEFUL CHEMICALS, and MUCUS, considered in other sections. 

 
Research study 1
 

photographs of sea-star larvae modified from Hardy 1956 The Open Sea Its Natural History: Part I, The World of Plankton Collins, London
The transparency of larval sea stars, and of larval echinoderms in general, suggests that camouflage has been of paramount importance for survival in the plankton - a place obviously devoid of hiding places from visual predators such as fishes, zoea larvae of crustaceans, and other visual predators.  No studies appear to have been done on this subject in west-coast asteroids. Larval photographs from Hardy 1956 The Open Sea Its Natural History: Part I, The World of Plankton Collins, London.

 
Research study 2
 

table of data on substratum-colour matching in the sea star Leptasterias hexactisThe six-armed sea star Leptasterias hexactis has several different colour morphs in San Juan Islands, Washington and elsewhere.  The morphs are 1) greenish/grayish, found on rock substrata generally at high- or mid-tide levels, 2) reddish, found on coralline algae and sponge substrata at low intertidal or subtidal levels, and 3) whiteish/yellowish found on sponge, ectoproct, and tunicate substrata at subtidal levels.  The author suggests that the colour morphs may provide possible crypsis against visual predators such as birds (and fishes?).  Alternatively, or perhaps additionally, the colours may derive from the consumption by Leptasterias of prey associated with each colour patch.  A test of this, however, involving pink and white individuals kept in the laboratory and fed on the same types of prey for 6mo, results in no colour change in any individual.  This would seem to be a nice project for further research work. Menge 1972 Ecol Monogr 42: 25.

NOTE now believed to represent a complex of several different species or subspecies

 
Simulations showing the degree of effectiveness of different colorations on camouflaging Leptasterias hexactis against different backgrounds:
photo collage of different colour morphs of Leptasterias on a rock/mussel background
1) greenish/grayish morph on a rock/mussel substratum
photo collage of different colour morphs of Leptasterias on a coralline alga background
2) reddish morph on a coralline alga substratum
photo collage of different colour morphs of Leptasterias on a predominantly sponge  background
3) yellowish morph on a sponge substratum
 
Research study 3
 

photograph comparing normal and albino coloration in bat stars Patiria miniataWhite genetic “sports” occur in bat stars Patiria miniata, as evidenced in the accompanying photograph from southern California.  The same author shows examples of albinism in sea pansies Renilla keollikeri and brittle stars Ophioderma panamense, and its occurrence in sea cucumbers Parastichopus californicus is also known.  Incidences of albinism are generally rare in marine invertebrates, but whether this owes to them falling prey to predators more readily than their normally coloured conspecifics is, of course, not known.  Human 1973 Calif Fish Game 59: 89.

 

Normal coloration appears to have much greater
camouflaging potential than albino coloration

 
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